Applied Science, Faculty of
Materials Engineering, Department of
DSpace
UBCV
Nikkhah Fini, Sheida
Master of Applied Science - MASc
University of British Columbia
Recently, there is an increase in demand for the usage of aluminum extrusion alloys in automotive applications to reduce the vehicle weight. Bendability (i.e. how much bending the material can sustain without cracking) is an important material property, both for the forming of components and in crash behavior. During the production of Al-Mg-Si extrusion alloys (AA6082 non- recrystallized) which was studied in this research, the properties of the surface can be substantially different from those of the interior as these alloys are prone to forming a surface layer known as the Peripheral Coarse Grain (PCG) zone. The objective of this study is to investigate the effect of the PCG layer thickness on bendability of aluminum alloys. Different PCG layers thicknesses were achieved in the range of 50 μm to 800 μm at different extrusion ram speeds by our industry partner. In this project, different mechanical tests were done to characterize the effect of PCG layer thickness, and heat treatment on the bendability of aluminum extrusion alloys. The microstructures were examined using Barker’s etch to observe the initiation of cracks in bend region. To see the effect of PCG layer on the bendability, the PCG layer was removed from one side of the sample and then the test was conducted with the PCG layer in tension and compression. The results show that the sample with a very thin PCG layer (50μm) showed similar load- displacement curves whether the PCG layer was in compression or tension. However, for the thicker PCG layers, the bend response was poorer when the PCG layer was in tension. Tests done on the samples in ED and TD direction (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) and results show that for all thicknesses of the PCG layer, tests done in TD direction showed a lower bend angle failure compared to the tests done in ED direction. Finally, to see the effect of cooling rate on bendability, cooling rate of 13-20 °C/s was chosen and after bend test the results showed that the lower cooling rate had 10-20% poorer bendability.
The Effect of PCG Layer Thickness on Bendability of Aluminum Extrusion Alloys by Sheida Nikkhah Fini BASc, The University of Tehran, 2020 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Materials Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2023 © Sheida Nikkhah Fini, 2023 ii The following individuals certify that they have read, and recommend to the Faculty of Graduate and Postdoctoral Studies for acceptance, the thesis entitled: The Effect of PCG Layer Thickness on the Bendability of Aluminum Extrusion Alloys submitted by Sheida Nikkhah Fini in partial fulfilment of the requirements for the degree of Master of Applied Science in Materials Engineering Examining Committee: Warren Poole, Professor, Materials Engineering, UBC Supervisor Ben Britton, Associate Professor, Materials Engineering, UBC Supervisory Committee Member Tom Troczynski, Professor, Materials Engineering, UBC Supervisory Committee Member iii Abstract Recently, there is an increase in demand for the usage of aluminum extrusion alloys in automotive applications to reduce the vehicle weight. Bendability (i.e. how much bending the material can sustain without cracking) is an important material property, both for the forming of components and in crash behavior. During the production of Al-Mg-Si extrusion alloys (AA6082 non- recrystallized) which was studied in this research, the properties of the surface can be substantially different from those of the interior as these alloys are prone to forming a surface layer known as the Peripheral Coarse Grain (PCG) zone. The objective of this study is to investigate the effect of the PCG layer thickness on bendability of aluminum alloys. Different PCG layers thicknesses were achieved in the range of 50 μm to 800 μm at different extrusion ram speeds by our industry partner. In this project, different mechanical tests were done to characterize the effect of PCG layer thickness, and heat treatment on the bendability of aluminum extrusion alloys. The microstructures were examined using Barker’s etch to observe the initiation of cracks in bend region. To see the effect of PCG layer on the bendability, the PCG layer was removed from one side of the sample and then the test was conducted with the PCG layer in tension and compression. The results show that the sample with a very thin PCG layer (50μm) showed similar load- displacement curves whether the PCG layer was in compression or tension. However, for the thicker PCG layers, the bend response was poorer when the PCG layer was in tension. Tests done on the samples in ED and TD direction (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) and results show that for all thicknesses of the PCG layer, tests done in TD direction showed a lower bend angle failure compared to the tests done in ED direction. Finally, to see the iv effect of cooling rate on bendability, cooling rate of 13-20 °C/s was chosen and after bend test the results showed that the lower cooling rate had 10-20% poorer bendability. v Lay Summary Aluminum alloys are increasingly being used in the automotive sector, especially for crash structures, and other body frame components. This is primarily due to the lower density of aluminum compared to steel, which can contribute to weight reduction in vehicles. Such weight reduction can enhance fuel efficiency, reduce carbon dioxide emissions, and consequently minimize environmental impact. Al-Mg-Si alloys are frequently employed in the production of structural components and external body panels. For these alloys to be suitable for automotive applications, they must be able to deform significantly without experiencing fracture. Therefore, it is valuable to understand the impact of processing parameters on the bending behavior of these materials. This study aims to examine the effect of peripheral coarse grain (PCG) layer on the bendability of aluminum extrusion alloys. The results indicate that a thicker layer of PCG on the surface of the material can negatively impact its bendability. Materials with a minimal thickness of coarse grain on the surface can withstand higher forces during car crashes or during the forming process. vi Preface The majority of this study was conducted by Sheida Nikkhah Fini at The University of British Columbia under the supervision of Dr. Warren J. Poole. The extruded materials for this project were provided by Dr. Nick Parson from Rio Tinto Aluminum, Canada. The inverted VDA bend test was conducted by Mr. Kenneth Chong and Professor Cliff Butcher at the Waterloo University. Cooling rate measurements were done by the help of Dr. Zhijun Zhang from the Materials Engineering department, The University of British. vii Table of Contents Abstract ......................................................................................................................................... iii Lay Summary .................................................................................................................................v Preface ........................................................................................................................................... vi Table of Contents ........................................................................................................................ vii List of Tables ................................................................................................................................ xi List of Figures ............................................................................................................................. xiii List of Symbols ......................................................................................................................... xviii List of Abbreviations ................................................................................................................. xix Acknowledgements ......................................................................................................................xx Dedication ................................................................................................................................... xxi Chapter 1: Introduction ................................................................................................................1 Chapter 2: Literature Review .......................................................................................................4 2.1 Review of Al-Mg-Si Aluminum Alloys ............................................................................... 4 2.2 Chemical composition of Al-Mg-Si aluminum alloys .......................................................... 4 2.2.1 Role of Mg, Si, Fe, Mn, Cr ............................................................................................ 5 2.3 Processing route of Al-Mg-Si aluminum extrusion alloys ............................................. 6 2.3.1 Direct Chill (DC) casting: ........................................................................................... 7 2.3.2 Homogenisation .......................................................................................................... 7 2.3.3 Solution treatment combined with extrusion process ................................................. 7 2.3.4 Cooling after extrusion ............................................................................................... 8 2.3.5 Age Hardening of Al-Mg-Si aluminum alloys ........................................................... 8 viii 2.3.6 Artificial ageing ........................................................................................................... 10 2.4 Quench sensitivity ............................................................................................................... 10 2.5 Formation of the peripheral coarse grain layer ............................................................. 10 2.6 Deformation of Al-Mg-Si (6xxx) aluminum alloys during extrusion .......................... 12 2.7 Effect of cooling rate (Precipitate Free Zone) .............................................................. 12 2.8 Fracture behaviour of Al-Mg-Si aluminum alloys ........................................................ 13 2.8.1 Effect of grain boundary precipitation ......................................................................... 14 2.8.2 Role of slip line formation inside grains ...................................................................... 15 2.9 Bend Test ...................................................................................................................... 15 Chapter 3: Scope and Objectives................................................................................................17 3.1 Scope: .................................................................................................................................. 17 3.2 Objectives: .......................................................................................................................... 17 Chapter 4: Methodology..............................................................................................................19 4.1 Material ............................................................................................................................... 19 4.2 Thermomechanical Process ................................................................................................ 19 4.2.1 Homogenization Treatment ......................................................................................... 20 4.2.2 Extrusion Trials ............................................................................................................ 20 4.2.3 Solution Treatment....................................................................................................... 22 4.2.4 Cooling Rate measurement .......................................................................................... 22 4.2.5 Natural Ageing (T4) ..................................................................................................... 24 4.2.6 Artificial Ageing (T6) .................................................................................................. 24 4.3 Sample Preparation ............................................................................................................. 25 4.4 Microstructure Characterization ......................................................................................... 25 ix 4.4.1 Optical Metallography (Barker’s Etching) .................................................................. 25 4.5 Removal of PCG layer from surface ................................................................................... 29 4.6 Mechanical Testing ............................................................................................................. 29 4.6.1 Hardness Test ............................................................................................................... 30 4.6.2 Tensile Test .................................................................................................................. 30 4.6.3 VDA Bend Test............................................................................................................ 32 4.6.3.1 Inverted VDA Bend test with DIC........................................................................ 36 4.6.3.2 Bending angle correction based on the thickness ................................................. 37 4.6.3.3 Repeatability of VDA Bend tests .......................................................................... 38 4.6.3.4 Comparison of VDA bend tests run at Waterloo and UBC .................................. 40 Chapter 5: Results and Discussion: ............................................................................................41 5.1 Microstructure ..................................................................................................................... 41 5.1.1 PCG layer thickness ..................................................................................................... 41 5.1.2 After solution treatment at 515, 530 and 545°C .......................................................... 45 5.2 Tensile test .......................................................................................................................... 46 5.3 Bend test results .................................................................................................................. 50 5.3.1 Inverted VDA bend tests conducted at university of Waterloo ................................... 50 5.3.2 VDA bend test conducted at UBC ............................................................................... 63 5.3.2.1 Hardness ................................................................................................................ 63 5.3.2.2 Bending angle correction based on the thickness ................................................. 68 5.3.2.3 VDA bend tests after T6 condition (6 hours at 180°C) ........................................ 68 5.3.2.4 VDA bend tests after solution treatment at 515°C for 5 mins+ cooling rate of 18-20°C/s+ T6 ........................................................................................................................ 70 x 5.3.3 Crack initiation in bend samples for the T6 condition ................................................. 71 5.3.3.1 Bend region after bending in ED direction (bend axis ⊥ to extrusion direction) 5.3.3.2 Bending region after bending in TD direction (bend axis ∥ to extrusion direction) References:....................................................................................................................................81 Appendices: ..................................................................................................................................89 Appendix A: .............................................................................................................................. 89 Appendix B: .............................................................................................................................. 92 Appendix C: .............................................................................................................................. 99 xi List of Tables Table 2.1 Overview of precipitate phases in Al-Mg-Si alloys.[28] ................................................ 9 Table 4.1 Chemical composition (in wt.%) (as measured by optical emission spectroscopy) ..... 19 Table 4.2 Parameters for the extrusion trials ................................................................................ 22 Table 4.3 Summary of cooling rate measurement (temperature between 300°C-400°C) ............ 24 Table 4.4: Summary of geometric parameters for VDA bend test ............................................... 34 Table 4.5 Summary of bend angle for 6C strip- T6 (Repeatability of VDA Bend test) ............... 39 Table 5.1 Summary of PCG layer thickness in 4 different strips ................................................. 44 Table 5.2 Summary of mechanical properties for 5C,9C,12C( PCG layer: 50 μm,100 μm, 800μm)- T6 condition (180°C for 6 hours) ................................................................................... 49 Table 5.3 Summary of mechanical parameters for inverted VDA test (average of 2 tests) ......... 57 Table 5.4 Summary of hardness results for T6 -180°C for 6 hours on 5C strip, PCG layer thickness: 50μm ............................................................................................................................ 64 Table 5.5 Summary of hardness results for solution treatment at 515°C for 5 mins + cooling rate of 18.5 °C/s + 180°C for 6 hours on 5C strip, PCG layer thickness: 50μm .................................. 64 Table 5.6 Summary of hardness results for T6 -180°C for 6 hours on 9C strip, PCG layer thickness: 100μm .......................................................................................................................... 65 Table 5.7 Summary of hardness results for solution treatment at 515°C for 5 mins + cooling rate of 18.5 °C/s + 180°C for 6 hours on 9C strip, PCG layer thickness: 100μm ................................ 65 Table 5.8Summary of hardness results for T6 -180°C for 6 hours on 12C strip, PCG layer thickness: 800μm .......................................................................................................................... 66 Table 5.9 Summary of hardness results for a) T6 b) solution treatment at 515°C for 5 mins + cooling rate of 19.7 °C/s + 180°C for 6 hours on 12C strip, PCG layer thickness: 800μm ......... 66 Table A.1: Summary of mechanical parameters- As received- ED – 3mm thickness .................. 89 Table A.2 Summary of mechanical parameters- As received- TD – 3mm thickness ................... 89 Table A.3 Summary of mechanical parameters- T6- ED – 3mm thickness ................................. 90 Table A.4 Summary of mechanical parameters- T6- TD – 3mm thickness ................................. 90 Table A.5 Summary of mechanical parameters- T6- ED –2.5mm thickness ............................... 91 xii Table A.6 Summary of mechanical parameters- T6- TD – 2.5mm thickness .............................. 91 xiii List of Figures Figure 1.1: a compressed crash tube which buckled and folded under a compressive loading parallel to the extrusion direction of the product (the inset showing the anodized micrograph of a microstructure of an extruded strip which underwent an extreme bending, where the surface was fractured [7]. ................................................................................................................................... 3 Figure 2-1 Common range of Mg and Si content in 6xxx series alloys (wt.%)[14] ....................... 5 Figure 2.2: Temperature-time history of an aluminum extrusion alloy [22] .................................. 6 Figure 2.3: Schematic diagram of a PCG structure displaying a critical strain, strain rate, and temperature of the material whereby a PCG structure forms [39] ................................................ 11 Figure 4.1 Schematic of sample reference frame .......................................................................... 21 Figure 4.2: An illustration of the geometry of the die (schematic(left) and actual die (right). ..... 21 Figure 4.3 Example of 4 temperature-time profiles measured during cooling after the solution treatment for a 3 mm thickness ..................................................................................................... 23 Figure 4.4: Summary of cooling rate measurement for 3 different thickness of material ............ 24 Figure 4.5: Setup for Barker’s etch ............................................................................................... 26 Figure 4.6 Lambda filter and how to insert into the microscope .................................................. 28 Figure 4.7 a) polarizer+ analyzer (no lambda filter), b) polarizer+ lambda filter +analyzer and c) polarizer+ lambda filter rotated by 180° +analyzer. ..................................................................... 28 Figure 4.8 coating sample with silicone sealant and removing PCG layer from one side of sample Figure 4.9 Geometry used for the tensile test samples (dimensions in mm) ................................ 30 Figure 4.10 a) Schematic of three- point bend test b) Photo of the testing ................................... 33 Figure 4.11 VDA bend test in a) ED and b) TD directions (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) ................................................................... 33 Figure 4.12 Position of Bending angle α ...................................................................................... 34 Figure 4.13 Variables from the experiment setup [1] ................................................................... 35 Figure 4.14 Load- Punch displacement illustrating the displacement used for measuring bend angle after unloading..................................................................................................................... 36 Figure 4.15 the initial speckle pattern for the DIC ....................................................................... 36 Figure 4.16 a) schematic of inverted VDA bend test setup b) schematic of progression of test .. 37 xiv Figure 4.17 Results of force vs displacement for 10 repeat tests on UBC test rig (all on ED direction) ....................................................................................................................................... 38 Figure 4.18 Comparison of VDA bend test in Waterloo and UBC- 6C- T6- without removing PCG layer =65μm- 3 mm thickness .............................................................................................. 40 Figure 5.1 Microstructure of 5C homogenized for 2 hours at 580°C and extruded with a ram speed of 5mm/s a) front and b) back ............................................................................................ 42 Figure 5.2 Microstructure of 6C homogenized for 2 hours at 580°C and extruded with a ram speed of 10mm/s a) front and b) back ......................................................................................... 42 Figure 5.3 Microstructure of 9C homogenized for 12 hours at 580°C and extruded with a ram speed of 5mm/s a) front and b) back ........................................................................................... 43 Figure 5.4 Microstructure of 12C homogenized for 12 hours at 580°C and extruded with a ram speed of 15mm/s a) front and b) back ......................................................................................... 43 Figure 5.5 microstructure of 9C after solution treatment at 545°C for 5 minutes and barker’s etch Figure 5.6 microstructure of 9C after solution treatment at 530°C for 5 minutes and barker’s etch Figure 5.7 microstructure of 9C after solution treatment at 515°C for 5 minutes and barker’s etch Figure 5.8 True stress- True strain curve for 5C- T6 condition, PCG layer = 50μm ................... 47 Figure 5.9 True stress- True strain curve for 9C- T6 condition, PCG layer = 100μm ................. 48 Figure 5.10 True stress- True strain curve for 12C- T6 condition, PCG layer = 800μm.............. 48 Figure 5.11 Load- Displacement for 3mm thickness (without removing the PCG layer (65μm)) on: a) T4- ED and TD b) T6- ED and TD. (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) ............................................................................................ 51 Figure 5.12 Load- Displacement for 2.5mm thickness (after removing PCG layer) on:.............. 52 T6- ED and TD (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) ..................................................................................................................................... 52 Figure 5.13 Strain Path for 3mm thickness (without removing the PCG layer) on: a) T4- ED ... 53 b) T4- TD c) T6- ED d) T6-TD .................................................................................................... 53 Figure 5.14 Strain Path for 2.5mm thickness (after removing PCG layer) on: a) T6- ED b) T6-TD Figure 5.15 Strain evolution for T4 and T6 condition- 3mm thickness........................................ 55 (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) ....... 55 xv Figure 5.16 Strain evolution for T6 condition- 2.5mm thickness (PCG layer removed from both side of sample) (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) ..................................................................................................................................... 56 Figure 5.17 Bend angle vs major strain for 3mm thickness (without removing the PCG layer) on: a) ED b) TD, T6 and T4 samples ................................................................................................. 58 Figure 5.18 Bend angle vs major strain for 2.5mm thickness (after removing PCG layer) on: ... 59 a) T6- ED b) T6-TD .................................................................................................................. 59 Figure 5.19 Major strain- bend angle for T6 condition in both ED and TD direction before correction for thickness ................................................................................................................. 60 Figure 5.20 Major strain- Bend angle for T6 condition in both ED and TD direction after correction for thickness of 2.5mm ................................................................................................ 61 Figure 5.21 Summary the major strain for samples in both ED and TD directions ..................... 62 (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) ....... 62 Figure 5.22 Molar fraction of Mg2Si vs temperature .................................................................... 67 Figure 5.23 Summary normalized bend angle for the tests done after heat treatment of samples at 180°C for 6 hours (T6) in both ED and TD directions (The blue and green bars are results for the sample without removing PCG layer)........................................................................................... 69 Figure 5.24 Summary normalized bend angle for the tests done after heat treatment of samples at 515°C for 5 mins+ cooling rate of 18-20°C/s + T6 in both ED and TD direction ........................ 71 Figure 5.26 5C strip with 50μm PCG layer in tension, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition.......................................................... 73 Figure 5.27 5C strip with 50μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition........................................................ 73 Figure 5.28 9C strip with 100μm PCG layer in tension, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition........................................................ 74 Figure 5.29 9C strip with 100μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition........................................................ 74 Figure 5.30 12C strip with 800μm PCG layer in tension, bending axis perpendicular to ED direction a) bottom and b) away from the bend region, T6 condition ........................................ 75 xvi Figure 5.31 12C strip with 800μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition.......................................................... 75 Figure 5.32 5C strip with 50μm PCG layer in tension, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition........................................................ 76 Figure 5.33 5C strip with 50μm PCG layer in compression, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition........................................................ 76 Figure 5.34 9C strip with 100μm PCG layer in tension, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition........................................................ 77 Figure 5.35 9C strip with 100μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition.......................................................... 77 Figure 5.36 12C strip with 800μm PCG layer in tension, bending axis perpendicular to TD direction a) bottom and b) away from the bend region, T6 condition .......................................... 78 Figure 5.37 12C strip with 800μm PCG layer in compression, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition.......................................................... 78 Figure A.1: 5C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm ......................................... 93 Figure A.2: 5C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm ......................................... 93 Figure A.3: 5C- Load- Displacement comparison when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm ......................................... 94 Figure A.4: 9C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm ....................................... 95 Figure A.5: 9C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm ....................................... 95 Figure A.6: 9C- Load- Displacement comparison when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm ....................................... 96 Figure A.7: 12C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm ..................................... 97 Figure A.8: 12C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm ..................................... 97 xvii Figure A.9:12C- Load- Displacement comparison when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm ..................................... 98 Figure A.10: 5C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm, sample thickness=2.7mm Figure A.11: 5C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm sample thickness=2.7mm Figure A.12: 5C- Load- Displacement for comparison when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm sample thickness=2.7mm..................................................................................................................................................... 101 Figure A.13: 9C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm sample thickness=2.7mm..................................................................................................................................................... 102 Figure A.14: 9C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm sample thickness=2.7mm..................................................................................................................................................... 102 Figure A.15: 9C- Load- Displacement for comparison when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm sample thickness=2.7mm..................................................................................................................................................... 103 Figure A.16: 12C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm sample thickness=2 mm .......................................................................................................................... 104 Figure A.17: 12C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm sample thickness=2mm ........................................................................................................................... 104 Figure A.18: 12C- Load- Displacement for comparison when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm sample thickness=2 mm .......................................................................................................................... 105 xviii List of Symbols A Area αc Bend angle e Engineering Strain S Engineering Stress L Length ε𝑡𝐿 Length True Strain F Load 𝜐 Poisson Ratio S Punch displacement (mm) in bend test r Punch radius of bend test D Roller diameter (mm) in bend test L Roller distance (mm) of bend test a0 Sample thickness (mm) σf True Fracture Stress 𝜀 True Strain 𝜎 True Stress W Width ε𝑡𝑊 Width True Strain xix List of Abbreviations AC Air Cooled DIC Digital Image Correlation DC Direct Chill EDM Electrical Discharge Machining EBSD Electron Backscatter Diffraction ED Extrusion Direction FCC Face Centred Cubic PFZ Particle Free Zone PCG Peripheral Coarse Grain RTA Rio Tinto Aluminum TD Transverse Direction UTS Ultimate Tensile Strength WQ Water Quench xx Acknowledgements I would like to express my sincerest gratitude to all those who have helped and supported me throughout the course of this research, leading to the completion of my master thesis. Firstly, I extend my gratitude to my supervisor, Professor Warren Poole, whose unwavering guidance, expertise, and encouragement have been indispensable to the successful completion of this project. I would like to thank Dr. Nick Parson from Arvida Research & Development Centre (ARDC) of Rio Tinto for his valuable input and collaboration in this project. His insights and contributions have been instrumental in achieving the goals of this research. I am also grateful to our academic collaborators, Dr. Cliff Butcher and Mr. Kenneth Chong from the University of Waterloo, for their invaluable support and contributions in the experimental work and analysis. I would like to thank the UBC microstructure group members for their help and ideas in the experiments and discussions. Their expertise and insight were instrumental in the progress of this research. Lastly, I am deeply grateful to my family, especially my twin sister Shima, for their unwavering love, support, and encouragement throughout my academic journey. Their constant support and motivation have been a driving force behind my success. Thank you all for your invaluable contributions and support towards the completion of my master thesis. xxi Dedication To my family 1 Chapter 1: Introduction Aluminum alloys have wide range of application due to their attractive properties such as low density, high specific stiffness in bending, corrosion resistance, ease of fabrication process and reasonable cost. These alloys are a common choice for transportation applications, whether in the air, on the water, or on land, thanks to the combination of their properties, particularly the potential for weight reduction. The application of aluminum alloys for manufacturing the body component of automobile can result 30-40% saving of vehicle weight depending on the size of the vehicle[1]. For an electric vehicle, the driving range is directly related to the vehicle weight [2] while for the conventional vehicles with the internal combustion engine, studies show that 10% reduction in the weight results in a 8-10% enhancement of fuel economy[3], [4]. In 2016, the Ford Motor Company reduced the weight of their F150 pickup trucks by 317 kg through the substitution of aluminum for steel in the body in white. From an environmental prospective, it has been demonstrated that a reduction of 100 kg in the weight of an automobile can lead to a reduction in CO2 emissions of approximately 9 g/km[1]. Furthermore, when considering the total life cycle of materials utilized in the automotive industry, it has been shown that the utilization of aluminum alloys can result in a 20% reduction in energy consumption [5]. As a result of these findings, the use of aluminum alloys, including aluminum extrusions, has become increasingly prevalent in the manufacturing of vehicles with the aim of reducing their overall weight and thus reducing their environmental impact. In the automotive industry, Al-Mg-Si alloys are frequently employed for external body panels and structural components due to their desirable properties. The strength of these alloys is predominantly derived from nanoscale metastable precipitates that are formed during their heat 2 treatment. The 6xxx series of these alloys is primarily composed of magnesium and silicon as the major alloying elements, with the precipitation of metastable Mg-Si phases serving as the dominant strengthening mechanism for these materials. The achievable range of peak strengths in Al-Mg-Si alloys is contingent upon the level of magnesium and silicon that are incorporated into the alloy. Traditionally, alloys that possess a combined weight percentage of magnesium and silicon that is less than 1% are classified as low strength, while those that exceed 1% are considered medium to high strength [6]. In addition to magnesium and silicon, Al-Mg-Si alloys frequently contain manganese (Mn) and chromium (Cr) as alloying elements which precipitate as dispersoids during homogenization. The presence of these dispersoids can indirectly enhance the strength of the alloy by delaying recrystallization during and after high temperature extrusion, thereby improving strength through dislocation substructure and grain boundary strengthening. In most commercial Al-Mg-Si extrusion alloys, the solution treatment of the alloy is combined with the high temperature extrusion process to reduce processing costs. The quench process is then incorporated by cooling of the extrudate immediately after leaving the extrusion press. The dependency of mechanical properties such as strength and fracture strain on the cooling rate is called quench sensitivity. One of the most important mechanical properties in automotive application is bendability of these alloys as this contributes the response of the alloy in a crash situation. Figure 1.1 shows an example of a compressed crash tube which underwent buckling and folding during axial compression. 3 Figure 1.1: a compressed crash tube which buckled and folded under a compressive loading parallel to the extrusion direction of the product (the inset showing the anodized micrograph of a microstructure of an extruded strip which underwent an extreme bending, where the surface was fractured [7]. The peripheral coarse grains (PCG) layer consist of a region of large recrystallized grains on the outer surface of an extrusion (see Figure 1.1). The focus of this study is on the effect of PCG layer thickness on the bendability and tensile behavior of these alloys. In this work aluminum alloys were extruded at different ram speeds of extrusion (5mm/s-15mm/s) by our industry partner, Rio Tinto Aluminium. As a result, different PCG layer thicknesses were produced. Some of these alloys were then solution treated at a temperature high enough to create a supersaturated solid solution (515°C), and were cooled at various controlled cooling rates ranging from 13 °C/s to 20 °C/s. The alloys were subsequently aged at 180°C for 6 hours (T6). After processing, VDA bend and tensile tests were used to examine bendability, yield stress, ductility, and fracture behavior for tests conducted in both the extrusion and transverse directions. 4 Chapter 2: Literature Review 2.1 Review of Al-Mg-Si Aluminum Alloys Al-Mg-Si aluminum alloys are typically classified as a medium strength with yield stresses between 200-400 MPa and are characterized as AA6xxx alloys by the Aluminum Association [6]. Al-Mg-Si alloys are one of the most important groups of aluminum alloys intended for use in the construction, shipbuilding, automotive, and aviation due to their light weight, satisfactory strength, ease of fabrication, and corrosion resistance [8]–[11]. Further, these alloys can be extruded at high speed with good surface quality. Al-Mg-Si extrusion alloys are increasingly used in automotive applications due to their combination of strength, formability, and corrosion resistance[8], [12]. 2.2 Chemical composition of Al-Mg-Si aluminum alloys It is generally accepted that mechanical and fracture properties are determined by microstructure, which is affected by changes in alloy composition and the thermomechanical processing parameters[13]. Al-Mg-Si alloys contain magnesium (Mg) and silicon (Si) as their major alloying elements, but can contain transition metals such as iron (Fe), manganese (Mn) and chromium (Cr)[9]. These elements combine to create different phases during solidification and/or heat treatments. These phases are divided into three categories: constituent particles (with sizes of 0.5–5 μm), dispersoid particles (with sizes of 20–150 nm), and Mg–Si metastable precipitates. (with sizes of 1-5 nm)[8]. The Mg content of the alloy can vary from 0.20 to 1.20 wt.% while Si ranges between 0.20 and 1.25 wt.% as shown in Figure 2-1 where the composition of some major Al-Mg-Si extrusion alloys is shown[14]. 5 Figure 2-1 Common range of Mg and Si content in 6xxx series alloys (wt.%)[14] 2.2.1 Role of Mg, Si, Fe, Mn, Cr Magnesium: plays an important role in the strengthening of aluminum alloys via the formation of metastable intermetallic precipitates containing of Mg. Silicon: adding silicon combines with magnesium to form intermetallic metastable phases which strengthen the alloys [15]. The trend for intergranular corrosion rises as Si levels rise due to grain boundary precipitation [16]. Iron: is a common impurity element which can combine with Al and other elements such as Cu, Mn and Si and form coarse constituent particles at the end of solidification. These intermetallic are typically detrimental to formability and extrudability [17]. Manganese and Chromium: Cr and Mn can be added to change the shape, size and crystal structure of the Fe-containing particles to reduce its adverse effect [18]. In addition, Mn and Cr elements 6 lead to formation of dispersoids (typical radius of 20-100nm) during homogenization and can affect the properties of these alloys by inhibiting recrystallization[19]and grain growth during heat treatment through the Zener pinning effect [19], [20]. Many studies have been conducted to examine the effect of Mn and Cr content on material microstructure and mechanical properties[18][19] [21]. 2.3 Processing route of Al-Mg-Si aluminum extrusion alloys Figure 2.2 shows a typical extrusion processing route for an Al-Mg-Si alloy [22]. Figure 2.2: Temperature-time history of an aluminum extrusion alloy [22] 7 The processing of an aluminum extrusion alloy generally involves the following stages: 2.3.1 Direct Chill (DC) casting: The majority of Al-Mg-Si aluminum alloy extrusion billets are made using the direct chill (DC) casting technique, and due to the non-equilibrium nature of solidification, they contain a variety of intermetallic phases and micro-segregation. 2.3.2 Homogenisation The non-equilibrium solidification conditions during casting cause Mg and Si to segregate. Homogenization is a heat treatment procedure used to eliminate micro-segregation and to dissolve coarse Mg2Si particles. An industrial homogenization practice for Al-Mg-Si alloys typically consists of a relatively slow heating rate (50-200°C/hr)(to prevent large thermal gradients), a hold period of 2-12 h at 500- 590°C, followed by cooling to ambient temperature. After homogenization, Mg and Si can be in the form of Mg2Si precipitates or be retained as solutes in solution. The transformation of the plate-like - β – Al5FeSi constituent particle to rounded α – Al(MnFe)Si particles can occur in Mn-containing alloys depending on the amount of Mn and soaking temperature/time [23]. This transformation is important as the plate-like β phase is believed to be responsible for poor surface finish and poor formability of Al extrusions [19][24]. 2.3.3 Solution treatment combined with extrusion process The billets are then reheated to the appropriate extrusion temperature, typically 400-500°C. During the extrusion process, greater than 95% of the work done converted to heat which results in exit extrusion temperature of 540-560°C. In addition to achieving the desired shape change, extrusion 8 can also act to dissolve Mg2Si particles provided the extrusion conditions reach sufficient high temperature and the Mg2Si precipitates are not too coarse after homogenization. The existence of coarse Mg2Si precipitates can result in reduced mechanical properties after extrusion and ageing, because some of the Mg and Si is lost to these coarse particles. 2.3.4 Cooling after extrusion The objective of cooling after extrusion is to preserve the solid solution formed at high temperatures by rapidly cooling it to room temperature. Cooling rates between 5°C/s and 100°C/s are typically used in industry. Precipitation during quenching should be reduced for the highest precipitation hardening response. However, using high quench rates can lead to undesirable distortion of extrudates. As a result, there is frequently a trade-off between the product's ultimate strength and product shape. 2.3.5 Age Hardening of Al-Mg-Si aluminum alloys In Al-Mg-Si alloys, the main strengthening mechanism is precipitation hardening. The precipitation of the metastable β'' precipitates during the artificial aging process is the primary source of strength [12]. A supersaturated solid solution (SSSS) is formed after solution treatment [14]. A complex precipitation sequence occurs during aging with the following generally recognized [12], [14], [25]: SSSS→ atomic clusters/co-clusters → GP zones → β'' →β', U1, U2, B'→β Atomic clusters of Mg and Si atom form at the initial step of decomposition of the solid solution (even at room temperature in a phenomenon known as natural ageing), followed by GP zones that are coherent with the matrix and then β''. The formation of β'' is associated with the strengthening 9 of the alloys in the underaged and peak aged conditions, while β' is usually associated with overaged conditions. The equilibrium product of decomposition is the β phase (Mg2Si)[26], [27]. Table 2-1 summarize the most frequently identified strengthening phases in Al-Mg-Si alloys. Table 0.1 Overview of precipitate phases in Al-Mg-Si alloys.[28] Precipitation Sequences Composition Morphology Crystal structure SSSS Composition of Al-Mg-Si alloy Polycrystals FCC Atomic Cluster varying Mg and Si contents Various shapes of 2-25 atoms FCC GP zone MgxAl5-xSi6 Spherical Primarily monoclinic β˝ Mg5Al2Si4 Needles Body centered monoclinic β´ Mg1.8Si Rods Hexagonal U1 MgAl2Si2 Needle trigonal U2 MgAlSi Rods orthorhombic B´ Mg48Al6Si36 laths hexagonal β Mg2Si Plates or cubes FCC 10 2.3.6 Artificial ageing The final step is aging. Typically, Al-Mg-Si alloys reach their peak strength by artificial aging at 160 - 200 °C for 1 - 10 hours (i.e. the T6 condition). These alloys can also be naturally aged by storing at room temperature (the so-called T4 condition). During natural aging, strengthening derives from atomic cluster of Mg and Si. 2.4 Quench sensitivity To evaluate the loss of properties for various quench rates after extrusion, the concept of quench sensitivity has been developed. Milkereit et al. have recently reviewed the role of cooling rate on microstructure and properties[29]. The effect of quench rate on yield strength and ultimate tensile strength was also investigated by Naveen et al [30]. Hardness, yield strength, ultimate tensile strength were found to decrease with decreasing cooling rates[30]. The reduction in strength and hardness occurs due to the loss of solute atoms to coarse precipitates on heterogeneous nucleation sites (typically grain boundaries or Mn dispersoids) [29]–[31]. Numerous studies have been done on the effect of different factors such as cooling rate, alloy additions, dispersoid density and presence of an unrecrystallized structure on ductility of aluminum extrusion alloys [29]–[34]. 2.5 Formation of the peripheral coarse grain layer The presence of a peripheral coarse grains (PCG) layer on the surfaces of extrudates is one of the common defects that appears after high temperature extrusion in alloys that are unrecrystallized [35]. The PCG layer is a region of large recrystallized grains on the outer surface of an extrusion [36] (see Figure 1.1). The PCG layer will have different mechanical properties than the rest of the extrudate [37][38][39]. 11 The PCG layer thickness depends on extrusion parameters such as the strain, strain rate, and deformation temperature of the material. These parameters vary from the centre of the extrudate to the surface, as shown schematically in Figure 2.4 [39], [40].At a critical point, conditions favor recrystallization and the formation of a PCG layer. Figure 2.3: Schematic diagram of a PCG structure displaying a critical strain, strain rate, and temperature of the material whereby a PCG structure forms [39] It has been found that there is a direct link between processing parameters (ram speed, exit temperature, extrusion ratio, and chemistry) and the PCG layer thickness [41][39]. There are two theories for the formation of the PCG layer: The first theory suggests that the PCG layer forms by abnormal grain growth of recrystallized grains [42]. The second theory is based on the formation of a fine grain structure from dynamic recrystallization (DRX) and then abnormal grain growth of dynamically formed grains leading to the PCG structure[42]. Eivani suggested that mechanism of PCG formation was a result of normal growth of dynamically recrystallized grains during extrusion, which could finish with abnormal growth at the final stage of PCG formation[42]. Mahmoodkhani proposed that given a sufficiently high stored energy and temperature, abnormal 12 grain growth can occur resulting in a PCG layer formation [41]. Careful design of the die and the extrusion process can minimize the formation of coarse, surface grains [41]. 2.6 Deformation of Al-Mg-Si (6xxx) aluminum alloys during extrusion Generally, unrecrystallized alloys have elongated grains (with sub-grains) and exhibit a crystallographic texture that is related to the deformation path during extrusion. The presence of sub-grains and highly elongated high angle grain boundaries in the unrecrystallized microstructure potentially can play a role in the nucleation and growth of strengthening precipitates[43]. Crystallographic texture also changes with extrusion while the final texture dependent upon the strain path (e.g. axisymmetric extension, plane strain deformation and etc). The current study, however, is mainly focused on nearly plane strain deformation. 2.7 Effect of cooling rate (Precipitate Free Zone) Precipitate-free zones (PFZs) near grain boundaries are another important microstructure fracture behavior. These are two mechanism to rationalize the observation of PFZ’s: i) Fast annihilation rate of vacancies near grain boundaries which impedes nucleation of metastable phases and ii) the diffusion of solute atoms to grain boundaries and formation of large grain boundary precipitates[7]. The cooling rate affects the size of the PFZ, Slow cooling typically results in a higher number of grain boundary precipitates and a wider precipitate free zone (PFZ) adjacent to the grain boundary, which increases the propensity of intergranular fracture[30][44]–[46]. Another reason is that plastic deformation can localize in these zones compared to precipitate-containing regions, thus crack initiation and growth can occur more easily in them[20][45][47]. Therefore, the presence of 13 PFZs and a lower precipitate density, can increase the propensity for intergranular fracture and reduction in ductility of the material [45]. 2.8 Fracture behaviour of Al-Mg-Si aluminum alloys Studies on the fracture behavior of Al-Mg-Si series alloys show that these alloys shows ductile fracture that initiate with the nucleation of voids on local heterogeneities such as second phase particles subsequently, growth and coalesce of voids [48]. The voids nucleation sites can be within the grains or at grain boundaries. Void Nucleation – the formation of voids in a material is related to either particle fracture or particle interface decohesion [49].For larger particles (300 - 400 nm), particle fracture is the dominant mechanism, while interface decohesion occurs in smaller, more equiaxed particles. It worth noting that if the particle is too small void nucleation is not energetically favorable [49]. Particle fracture leads to the formation of flat voids which become more rounded as they grow, whereas interface decohesion results in the formation of round voids that elongate in the direction of principal loading[49]. In the case of particle fracture, the stress and intrinsic resistance of the particles to cracking control the mechanism. Particles are usually considered brittle solids, and void nucleation occurs when the maximum principal stress in the particle reaches a critical value. Materials with higher strength exhibit lower strain to reach this critical stress, resulting in particle fracture occurring at lower strains [49].In the case of interface decohesion, during deformation of a particle-strengthened alloy, the matrix deforms plastically, while particles are considered as solid phases that only deform elastically. This results in an increase in the elastic energy of the system. Interface decohesion only occurs when the rate of elastic energy release and the rate of surface energy created by interface decohesion results in a local decrease of energy in the system [49]. 14 Void Growth –Void growth is related to the hydrostatic stress and the change in void shape is controlled by the deviatoric stress component. as the plastic strain increases after nucleation stage, the void size increases [50]. Void Coalescence – The transition from growth to coalescence is mainly controlled by the average void spacing [87]. The fracture mechanism where voids are sparse and significant growth is required before coalescence can occur is called “void controlled”, whereas the condition where voids are densely populated, and coalescence occurs rapidly following nucleation with slight growth is called “nucleation controlled”[50]. The onset of transition from transgranular to intergranular fracture is controlled by the competition between void nucleation and growth/coalescence at the grain boundary or inside grains. At least three factors have been identified for intergranular fracture i.e. i) strain localization within the PFZ, ii) number density and size of the precipitates at the grain boundary, and iii) strain localization within the grain, i.e. formation of slip lines [51] However, under certain conditions, void nucleation may proceed more quickly in the grain interior, resulting in a transgranular mode of fracture. 2.8.1 Effect of grain boundary precipitation One of the most common mechanism of fracture in medium to high strength aluminum alloys is fracture along grain boundaries i.e. intergranular fracture. Apart from the area fraction of precipitates at the grain boundary, their size and shape and spacing also can contribute to promoting stress concentrations, void nucleation and growth/coalesce of voids, thereby promoting grain boundary fracture [52]. The studies indicated that the slow quench rate to room temperature 15 after the solution heat treatment can increase grain boundary precipitation and promote the intergranular fracture mode due to change in the width of the precipitate free zones [7], [30][45]. 2.8.2 Role of slip line formation inside grains A high stress concentration can develop at grain boundary due to the intersection of slip lines. This can result in void nucleation and intergranular ductile fracture at ~1% [53]. The distribution of slip within a grain can be modified by the presence of non-shearable precipitate. For example, the presence of Mn containing dispersoids can reduce the slip band spacing during deformation by finely distributing slip at the crack tip. Further, Mn can promote of grain refinement, which can both reduce the tendency for intergranular fracture [51]. It was found by Poole et al [54] reported that addition of 0.5wt% Mn to Al-Mg-Si-Mn alloy, increased the tensile fracture stress and strain by 25% and >200%, respectively. 2.9 Bend Test A variation of a 3-point bend test known as a VDA test (VDA238-100 test standard [55]) is commonly used within the aluminum and automotive industry[56]. This test records the bending load/displacement curve failure is considered when the load drops 60 N from its peak value. Bendability is assessed by measuring the bend angle after unloading with a protractor or using the formulas provided in section 4.6.3. It has found by some researchers that the bend angle is lower for transverse tests (bend axis parallel to the extrusion direction ED) compared to longitudinal tests (bend axis perpendicular to the extrusion direction ED) [44]. Bendability is often limited by surface cracks which then penetrates into the material. The nucleation and growth of cracks on the tensile face of the bend samples is complicated [57], i.e. it was found in several studies [13] [58] [59] that 16 joining and merging of void is the most common source of failure in Al-Mg-Si alloys, however Westermann showed that the strain localization can result in the formation of shear bands which could be the controlling mechanism of failure [59]. It was also shown by Westermann that the crystallographic orientation of surface and interior grains can also be an important effect on the failure mechanism. It has been proposed that strain localization is critical for damage evolution and the formation of surface undulations. A possibility is that surface undulations act to nucleate shear bands. In total the PCG layer thickness is thought to be detrimental to bending performance but the quantification of this effect has received little attention, further the effect of cooling rate after solution treatment on bendability has received relatively little study in previous work. 17 Chapter 3: Scope and Objectives 3.1 Scope: The primary scope of this study was to examine the influence of PCG layer thickness on the bendability of aluminum extrusion alloys, and to quantify the impact of cooling rate on the bending behavior of aluminum. The PCG layer thickness can be varied by adjusting the homogenization time and temperature, as well as the extrusion ram speed. To achieve this, a set of Al-Mg-Si-Mn-Cr alloy extruded strips were provided from Rio Tinto Aluminium, Canada, which cast and homogenization at two distinct durations (2 and 8 hours) and extrusion at different ram speeds (5-15 mm/s). In order to investigate the effect of cooling rate on bendability, the samples were subjected to solution treatment, followed by cooling at a rate of 13-20°C/s or water quenching (1000°C/s) to room temperature to obtain a slow or fast cooling rate, respectively. To assess the impact of the PCG layer on the mechanical behavior of the aluminum extrusion alloy, the bendability was measured using two different test rigs (fixed punch and moving punch) via the three-point bend test, and the tensile test was conducted in both ED and TD directions. 3.2 Objectives: The objectives of this work is as following: i. To quantify the evolution of surface strain during a VDA bend test ii. To quantify the effect of PCG layer thickness on the bendability (bend angle at a load drop of 60 N) of aluminum extrusion alloys in extrusion and transverse directions. iii. To investigate the effect of PCG layer thickness on the fracture mechanism of the alloy. 18 iv. To measure the effect of different cooling rate, after solution treatment on the bend behavior of the materials. 19 Chapter 4: Methodology In this chapter, the experimental method used for this work will be described. First, the initial material and the heat-treatment path (solution treatment, cooling rate and artificial aging) will be introduced. After that, the sample preparation and removal of PCG layer will be explained. Following this, the details of the tensile tests and three-point bend tests and hardness tests will be provided. 4.1 Material The initial material was provided by the Rio Tinto Aluminum (RTA) Research and Development Centre in Jonquiere., Quebec. The composition of the aluminum alloy is given in the Table 4.1. Table 4.1 Chemical composition (in wt.%) (as measured by optical emission spectroscopy) Alloy Mg Si Mn Cr Fe Al AA6082 0.70 1.04 0.49 0.15 0.18 97.44 4.2 Thermomechanical Process This section describes the thermomechanical process conducted on the materials to obtain the initial microstructures. The objective was to have the similar core microstructure (unrecrystallised) and obtain different PCG layer thickness by controlling the extrusion ram speed and homogenization conditions. 20 4.2.1 Homogenization Treatment Billets with a diameter of 101.4 mm were direct chill cast. After casting, the billets were homogenized as follows: heating at a rate of 250°C/h to 530°C then heated at 50°C/h to 580°C, held for 2 or 12 hours and finally water quenched. 4.2.2 Extrusion Trials After the homogenization treatments, extrusions trials were conducted using a laboratory scale extrusion press at Rio Tinto Aluminum in Quebec. Figure 4.1 is schematic to define the sample reference frame extrusion. Prior to extrusion, the billets were heated to the extrusion temperature of 490 °C using an induction heater. Then, the billets were transferred to the extrusion press which had a container temperature of 480°C, and extruded with a ram speed between 5 and 15 mm/s. Figure 4.1 shows a schematic diagram of the set up for extrusion where it can be seen that the final die opening was 90mm × 3mm (i.e. an extrusion ratio of 33:1, ER = Area of billet Area of extrudate). This produced an extrusion approximately 11 m in length. The front 2 m and back 2.5 m were scrapped. The remaining 6 m was cut into 1 m lengths labelled A to F (A being at the front). The details of the extrusion trials are summarized in Table 4.2. The exit speed was calculated from ram speed (m/min) multiplied by the extrusion ratio of 33:1 and the time between the die exit and water quench was also calculated from noting that the quench tank was 2.5 m from the die exit. 21 Figure 4.1 Schematic of sample reference frame Figure 4.2: An illustration of the geometry of the die (schematic(left) and actual die (right). 22 Table 4.2 Parameters for the extrusion trials Ext Ram Speed (mm/s) Exit Speed (m/min) Measured Exit Speed (m/min) Homogenization Measured Billet Temperature Exit Temperature Time between the die exit and water quench (s) 5 5 10 9.9 2hrs/ 580°C 493°C 528°C 15 6 10 20 19.8 2hrs/ 580°C 493°C 549°C 7.6 9 5 10 9.9 12hrs/ 580°C 500°C 533°C 15 12 15 30 29.7 12hrs/ 580°C 485°C 547°C 5 4.2.3 Solution Treatment To examine the role of cooling rate after solution treatment, some extruded sample were heat treated and cooled at a lower rate than the original press quench. To choose the solution treatment temperature, temperatures 515, 530 and 545°C were examined with the goal of minimizing the change to the as extruded microstructure. After the solution treatment, samples were cooled with a hair dryer to the room temperature. The cooling rate was measurement will be discussed in the next part. 4.2.4 Cooling Rate measurement The sample temperature was recorded using a spot-welded K type thermocouple and Omega (OMB-DAQ-300) data logger during cooling with the hair dryer. The hair dryer tip was ~ 10 cm away from the sample. The cooling rate was measured for hair dryer -cooling condition in three different thickness of materials; 2mm, 2.7mm and 3 mm. Figure 4.2 shows the temperature profile for thickness of 3 mm. The average cooling rate in the temperature range of 400 to 300°C was 19.7 °C/s for the 2 mm thick sample, 18.5°C/s for the 2.7 mm sample and 13.8°C/s for 3 mm samples 23 as shown in figure 4.3, in the temperature range of 400 – 300°C. Table 4.3 shows a summary of the results for the samples with a thickness of 2.0mm, 2.7mm and 3.0mm. Figure 4.3 Example of 4 temperature-time profiles measured during cooling after the solution treatment for a 3 mm thickness 01002003004005006000 20 40 60 80 100Temperature(°C)Time (s)#1 #2 #3 #424 Figure 4.4: Summary of cooling rate measurement for 3 different thickness of material Table 4.3 Summary of cooling rate measurement (temperature between 300°C-400°C) Thickness: 2 mm Thickness: 2.7 mm Thickness: 3 mm Cooling rate 19.7° C/s 18.5° C/s 13.8° C/s 4.2.5 Natural Ageing (T4) Extrusion trial was done in Feb 3, 2022 (water quench) and VDA tests were done in the period of April 22, 2022 → Oct 13, 2022 leading to a natural ageing period of ~180 days 4.2.6 Artificial Ageing (T6) Artificial aging was conducted on the all samples at 180°C for 6 hours in silicon oil bath followed by quenching in a bucket of water at room temperature. 3003203403603804000 1 2 3 4 5Temperature (°C)Time (s)19.7° C/s18.5° C/s13.8° C/s2 mm2.7 mm3 mm25 4.3 Sample Preparation Optical microscopy was used to observe the microstructure and the PCG layer on the top and bottom of sample. Sample preparation consisted of manual hand grinding with silicon carbide papers (400, 800, 1200, 2400, and 4000 grit) for ~ 15 mins with water as lubricant until all visible scratches were removed then polishing with 1μm diamond particle suspension on Texmet cloth for 15 minutes with 1 μm diamond suspension as the polishing solution (RedLube as the lubricant) and finally polishing with 0.05μm colloidal silica suspension on Chemotexile cloth for 15 minutes. The residue of the colloidal silica on the surface was carefully removed with a cotton ball to obtain a smooth and reflective surface. 4.4 Microstructure Characterization In order to characterize the microstructural variations and their possible effect on the overall mechanical properties Barker’s etching followed by optical microscope imaging under polarized light was used to see crack initiation in the bending region and also the PCG layer thickness. 4.4.1 Optical Metallography (Barker’s Etching) The following steps were used to prepare the sample; 1. The samples were mounted in a non-conductive media (Bakelite or epoxy). Mount height ~ 1.5 cm was used to make it easier to introduce a screw through the mount to make a good electrical contact with the sample. 2. Drill the side of the mount until you reach the aluminium sample with a drill press. 3. Screw a metal screw into hole until contact with sample is achieved. 26 4. To verify the quality of the connection, use a multimeter to check the resistance. It should read near 0 ohm. 5. Polish the sample; using the standard polishing procedure with a final colloidal silica 0.05 μm polishing step 6. Sample is ready for the etching. The Barker’s solution used was made by diluting 105mL of HBF4 solution (concentration of 48-50%) in 3395mL of distilled water. Figure 4.4 shows the setup for Barker’s etch. Figure 4.5: Setup for Barker’s etch The electro-etching procedure used: A power supply (0-60V/0-2A/210W) was used. The voltage was set to 40V for etching with the etching time varying from 3 to 6 min: initially 3 min was employed and then the sample was checked to see if one can observe the microstructure under the microscope. If the grains were not clear then 2-4 minutes of additional electro etching was done. 27 Set up for Barker’s etch: 1. A magnetic stirrer was used to assure good mixing of the solution and a contact of the solution with the sample’s surface. 2. A graphite rod was used as the cathode and the sample was anode (via the metal screw in the mount). 3. The setup was employed in a lab fume hood. 4. Before putting the sample in the solution, the voltage was set. When the sample is in the solution, the current should decrease. If the current is steady, this is a sign that the electrical connection of the sample is not good. After chemical etching (at the end for cleaning the setup), a solution of water and sodium bicarbonate (as neutralizer) should be used to rinse the sample and then rinse with water and dry with compressed air. For optical observation the polarizer / analyzer filter with a lambda filter as shown in Figure 4.5 was used. The full-wave plate is also called lambda (λ) plate adds or subtracts from 530 to 560 nm wavelengths (the actual value depends on the manufacturer) when placed into the light path. The grains have different color under polarizer due to different orientations of the surface oxide. Figure 4.6 shows the same microstructure under a) polarizer+ analyzer (no lambda filter), b) polarizer+ lambda filter +analyzer and c) polarizer+ lambda filter rotated by 180° +analyzer. 28 Figure 4.6 Lambda filter and how to insert into the microscope (a) (b) (c) Figure 4.7 a) polarizer+ analyzer (no lambda filter), b) polarizer+ lambda filter +analyzer and c) polarizer+ lambda filter rotated by 180° +analyzer. 29 4.5 Removal of PCG layer from surface To study the effect of PCG layer on bend performance, the PCG layer was removed from one side of the sample (for the tests done in UBC) and from both side of the samples (for the tests done at the University of Waterloo). For the tests done at UBC, the tests could be conducted with either PCG layer on the tensile face of the sample or on the compressive face. To remove the PCG layer, the surface of sample was first cleaned, i.e.; with soap, dried it and then with ethyl alcohol to remove any contaminants. Then Silicone Sealant (Permatex black RTV silicone adhesive sealant) with the thickness of ~ 3mm was added to the cleaned side of sample. Aluminum (in this case the PCG layer) can be dissolved by chemical etching with 100 g/L NaOH solution at a temperature between 50 to 60 °C. The average removal rate for the material was determined to be ~ 50 µm/hour. Figure 4.7 shows the sample coated by silicone sealant and the ideal sample after removing one side, i.e the PCG layer. Figure 4.8 coating sample with silicone sealant and removing PCG layer from one side of sample 4.6 Mechanical Testing To see the effect of the heat treatment procedure on mechanical properties, hardness, tensile and VDA bend tests were conducted on the strips with different PCG layer thicknesses. 30 4.6.1 Hardness Test Hardness testing was done using the Buehler Micromet3 micro-hardness machine with a dwell time of 10 seconds and a load of 500 g. Vickers Hardness (HV) was measured ten times for each sample and the average was calculated. Prior to the test, the sample surfaces were manually ground with silicon carbide papers (400, 800, 1200 and 2400 grit) to provide a smoother surface for easier measurement of the indent diagonal. 4.6.2 Tensile Test Tensile tests were conducted at room temperature using the sample geometry shown in Figure 4.8 (dimensions in mm). The samples were machined (EDM) from the extruded strip parallel to the extrusion direction (ED) and perpendicular to the extrusion direction (TD). All samples were in the peak aged (T6) condition. Figure 4.9 Geometry used for the tensile test samples (dimensions in mm) 31 Tensile experiments were conducted using an Instron 8872 tensile machine with a 25kN load cell. two INSTRON extensometer with a gauge length of 12.5 mm and 5 mm was used to measure the elongation in the length and the contraction in width of samples during tests. Load-displacement data obtained from the tests were converted to engineering stress (s) and engineering strain (e) using the measured initial area of the sample, S=F/Ao and e=∆L/Lo where Ao initial area of the cross section bearing the load and L0: initial gauge length of the extensometer. Equations 4-1 and 4-2 were used to convert engineering stress-strain to true stress (σ) and true strain (ε). 𝜎 = 𝑠(1 + 𝑒) (4-1) ε = 𝑙𝑛(1 + 𝑒) (4-2) Further, true fracture stress (σf) and true fracture strain (εf) were calculated using equations 4-4 and 4-5, where CF was calculated from equation 4-3. CF is a correction for the stress triaxiality in the neck of the tensile sample was employed based on the finite element method calculations of Puydt [61]. CF = { 1 + ( ε𝑓0.9) × 0.14 for εneck < εf < 0.91.14 for εf > 0.9 (4-3) 𝜎𝑓 = 𝐹𝑓𝑟𝑎𝑐𝑡𝑢𝑟𝑒/ (𝐶𝐹 × 𝐴𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑) (4-4) 𝜀 𝑓 = 𝑙𝑛 (𝐴𝑖𝑛𝑖𝑡𝑖𝑎𝑙 /𝐴𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 ) (4-5) where Aprojected, the projected fracture area, was calculated using the ImageJ software with the fracture images taken from the SEM. 32 The plastic anisotropy was characterized by the R-value as follows, based on volume conservation principle: ε𝑡𝑊 = 𝑙𝑛 (1 +𝑊 − 𝑊0𝑊0) − 𝜐𝜎𝑡𝐸 (4-6) ε𝑡𝑇 = − [𝑙𝑛 (1 +𝑊 − 𝑊0𝑊0) − 𝜐𝜎𝑡𝐸] − ε𝑡𝐿 (4-7) 𝑅 =ε𝑡𝑊𝜀𝑡𝑇 (4-8) where ε𝑡𝑊 and ε𝑡𝑇 are the plastic true strains in the sample width and thickness direction, respectively; 𝑊0 and 𝑊are the initial and changed sample widths; 𝐸 and 𝜐 are Young’s modulus (70 GPa) and Poisson ratio (0.33) of pure aluminum at room temperature; 𝜎𝑡 and ε𝑡𝐿 are the true stress and plastic true strain in the tensile direction. 4.6.3 VDA Bend Test Bending tests using a VDA test rig were conducted on strips with different PCG layer thicknesses to see the effect of PCG layer on the bendability (bend angle at a load drop of 60 N). A three-point bend fixture (Zwick’s VDA instrument) was mounted in an Instron 8874 servo hydraulic test frame. A square bend test specimen with dimensions of 38mm × 38mm was bent between two rollers by a punch with tip radius of 0.4 mm transversing with the speed of 2mm/ min (Note: this is a deviation from the VDA 238-100 standard which specifies a punch speed of 20 mm/min). Figure 4.9 shows the schematic and actual photo of the 3-point bend test. The separation of rollers was adjusted to be 2 times the sample thickness. VDA bend tests was conducted in two direction of ED and TD which is defined in Figure 4.10. 33 a) b) Figure 4.10 a) Schematic of three- point bend test b) Photo of the testing a) b) Figure 4.11 VDA bend test in a) ED and b) TD directions (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) The load and displacement was recorded during the test and the test was manually stopped when the load dropped 60N below the peak load. The plastic bend angle (α) was measured i) manually by means of a protractor (Figure 4.11 illustrate bending angle) and ii) by calculating the bend angle from the punch tip displacement. To estimate the bend angle from tip displacement, the formulae given in VDA 238-100 were employed [55] i.e. equations 4-9 to 4-12. Table 4.4 summarizes the ED TD 34 geometric parameters. Figure 4.12 shows variables from experimental setup and Figure 4.13 shows the load- punch displacement curve where S is the displacement used to calculate the bending angle. Figure 4.12 Position of Bending angle α Table 4.4: Summary of geometric parameters for VDA bend test r Punch radius 0.4 mm D Roller diameter (mm) 30 mm a0 Sample thickness (mm) 2-3 mm S Punch displacement (mm) L Roller distance (mm) 2a0 αc Bending angle After unloading 35 𝐶 =𝐷2+ 𝑎0 + 𝑟 (4-9) 𝑃 =𝐿2+𝐷2 (4-10) 𝑊 = √𝑃2 + (𝑆 − 𝐶)2 − 𝐶22 (4-11) 𝑆𝑖𝑛𝛼𝑐2= 𝑃×𝐶+𝑊×(𝑆−𝐶)𝑃2+(𝑆−𝐶)2 (4-12) Figure 4.13 Variables from the experiment setup [1] 36 Figure 4.14 Load- Punch displacement illustrating the displacement used for measuring bend angle after unloading 4.6.3.1 Inverted VDA Bend test with DIC Some experiments were conducted at the University of Waterloo using a different test rig. In this case, punch is fixed and the rollers move down with the speed of 2mm/min and two cameras record a speckle pattern on the surface (Figure 4.14 shows an example of the speckle pattern). The punch radius is 0.4mm and the roll spacing is twice the sample thickness. Figure 4.15 shows the schematic of the setup. Figure 4.15 the initial speckle pattern for the DIC 01234560 2 4 6 8Load (KN)Punch Displacement (mm)Sunloading displacement 37 a) b) Figure 4.16 a) schematic of inverted VDA bend test setup b) schematic of progression of test 4.6.3.2 Bending angle correction based on the thickness To eliminate the effect of sample thickness on the surface strain equation 4-13 was used where we can convert the bend angle to the normalized bend angle [62]. 𝛳𝑛 = 𝛳 ×√𝑡√𝑡𝑛 (4-13) 38 4.6.3.3 Repeatability of VDA Bend tests To examine repeatability of the bend tests we choose a strip with a homogenization treatment of 2 hours at 580°C and an extrusion ram speed of 10 mm/s (sample 6), 10 samples with the same dimensions and temper condition (as-received plus 6 hours at 180°C (T6)) were tested on the UBC test rig. The force displacement data was obtained and shown on Figure 4.16. The bending angle was measured for these 10 samples with a protractor and also from the load- displacement data (see Section 4.6.3). Table 4.5 shows the summary of the results. The difference between the data obtained from protractor and formula is ~2 degree, it indicated that the data acquired from the protractor is reliable. Figure 4.17 Results of force vs displacement for 10 repeat tests on UBC test rig (all on ED direction) 01234560 2 4 6 8 10Load (KN)Punch Displacement (mm)test 1test 2test 3test 4test 5test 6test 7test 8test 9test 1039 Table 4.5 Summary of bend angle for 6C strip- T6 (Repeatability of VDA Bend test) ED direction- T6 condition Thickness Angle Measured with Protractor Angle Measured from the formula Test 1 2.92 65 63.9 Test 2 2.93 70 68.8 Test 3 2.93 65 62.7 Test 4 2.94 64 61.9 Test 5 2.92 62 61.4 Test 6 2.92 57 49.5 Test 7 2.93 70 68.3 Test 8 2.92 65 65 Test 9 2.93 67 65.6 Test 10 2.93 65 62.9 Average 2.93 65 63 Standard Deviation 0.006 3.6 5.1 Standard Error 0.002 1.1 1.6 40 4.6.3.4 Comparison of VDA bend tests run at Waterloo and UBC To see the correlation of VDA bend results with two different methods the comparison was made for the results given from Waterloo and UBC. The sample with the PCG layer thickness of around 100μm was took to T6 condition and then without removing PCG layer from any side if strip we did VDA bend tests and capture the load- displacement results. Figure 5.24 show the results comparing the two facility. It can be seen that the results are the same at the onset of plasticity. But, there is ~10% different load at 8 mm displacement. Figure 4.18 Comparison of VDA bend test in Waterloo and UBC- 6C- T6- without removing PCG layer =65μm- 3 mm thickness 01234560 2 4 6 8 10Load (KN)Displacement(mm)test 1test 2test 3test 4test 5test 6test 7test 8test 9test 10test 1- Waterlootest 2- Waterloo41 Chapter 5: Results and Discussion: In this chapter, the results of this work will be described. First, the starting microstructure and PCG layer thickness will be introduced. After that the results of tensile test, VDA bend test and hardness of the samples will be presented. Following this, the details of the VDA bend test done in UBC will be compared with the results of inverted bend test done in Waterloo. 5.1 Microstructure 5.1.1 PCG layer thickness Different PCG layer thickness were achieved by choosing different homogenization time and extrusion ram speed. In this work, samples with a PCG layer thickness of 40 μm to 800 μm were tested. PCG1 and PCG2 indicate the PCG layer thickness on the top and bottom of strip, respectively. PCG layer was measured using an optical microscope where, the depth in 10 areas was measured to get a mean value by metallography laboratory at Rio Tinto Aluminum. Figure 5.1- 5.4 shows the PCG layer on the top and bottom of strips for 4 strips with different thickness of PCG layer using Barker’s etch method and polarized light. The details of chosen parameter and PCG layer thickness are summarized in Table 5.1. 42 Front Back Figure 5.1 Microstructure of 5C homogenized for 2 hours at 580°C and extruded with a ram speed of 5mm/s a) front and b) back Front Back Figure 5.2 Microstructure of 6C homogenized for 2 hours at 580°C and extruded with a ram speed of 10mm/s a) front and b) back (a) PCG = 40 μm (b) PCG = 50 μm (a) PCG = 65 μm (b) PCG = 100 μm 43 Front Back Figure 5.3 Microstructure of 9C homogenized for 12 hours at 580°C and extruded with a ram speed of 5mm/s a) front and b) back Front Back Figure 5.4 Microstructure of 12C homogenized for 12 hours at 580°C and extruded with a ram speed of 15mm/s a) front and b) back (a) PCG = 95 μm (b) PCG = 115 μm (a) PCG = 830 μm (b) PCG = 740 μm 44 Table 5.1 Summary of PCG layer thickness in 4 different strips Front Back Extrusion # Ram Speed (mm/s) Exit Speed (m/min) Homogenization PCG 1 (μm) PCG 2 (μm) PCG 1 (μm) PCG 2 (μm) 5 5 10 2hrs/ 580°C 40 40 50 50 6 10 20 2hrs/ 580°C 60 70 110 90 9 5 10 12hrs/ 580°C 90 100 110 120 12 15 30 12hrs/ 580°C 860 800 680 800 45 5.1.2 After solution treatment at 515, 530 and 545°C Experiments were conducted to select a solution treatment temperature which was suitable to minimize microstructure changes. Figures 5.5, 5.6 and 5.7 shows the microstructure revealed after Barker’s etch after 5 mins at 545, 530 and 515°C. Figure 5.5 microstructure of 9C after solution treatment at 545°C for 5 minutes and barker’s etch Figure 5.6 microstructure of 9C after solution treatment at 530°C for 5 minutes and barker’s etch 46 Figure 5.7 microstructure of 9C after solution treatment at 515°C for 5 minutes and barker’s etch Figure 5.5 and 5.6 show that the microstructure for 530°C and 545°C has partially recrystallized during the heat treatment. However, the treatment at 515°C appears to show minimal change in the grain structure. However, it should be noted that 515°C is below the Mg2Si solvus temperature so the solution treatment may be incomplete. This will be discussed later in Section 5.3.2.1. 5.2 Tensile test In this section, the tensile stress – strain response will be presented from samples tested parallel to ED or TD direction for the T6 (6 hours at 180°C) condition. Figures 5.8-5.10 show the true stress true strain responses for the strips with different PCG layer thickness. Table 5.2 summarizes the R-value, Young’s modulus and Poisson’s ratio, yield stress, UTS, true fracture strain and true fracture stress for these tests. The results show that in the case of 5C there is a minimal different for the stress and strain curve in ED and TD direction, while the difference is obvious for the thicker PCG layer. It can be seen that 9C and 12C have lower true fracture strain in TD direction 47 compared to ED direction, however the true fracture stress is very close in both directions. The results show that thin PCG layer (5C) shows ~10% greater fracture stress and ~ 30% higher true strain to fracture. Figure 5.8 True stress- True strain curve for 5C- T6 condition, PCG layer = 50μm 01002003004005000 0.1 0.2 0.3 0.4True stressTrue Strain5C- T6- ED- test 15C- T6- ED- test 25C- T6- TD- test 15C- T6- TD- test 248 Figure 5.9 True stress- True strain curve for 9C- T6 condition, PCG layer = 100μm Figure 5.10 True stress- True strain curve for 12C- T6 condition, PCG layer = 800μm 0501001502002503003504004505000 0.1 0.2 0.3 0.4True SressTrue Strain9C -T6- ED- test 19C- T6- ED- test 29C-T6- TD- test 19C -T6- TD- test 201002003004005000 0.1 0.2 0.3 0.4True Sress True Strain12C- T6-ED- test 112C- T6- ED- test 212C- T6- TD- test 112C- T6- TD- test 249 Table 5.2 Summary of mechanical properties for 5C,9C,12C( PCG layer: 50 μm,100 μm, 800μm)- T6 condition (180°C for 6 hours) Sample Young’s Modulus, GPa Poisson’s ratio Yield stress UTS, MPa R value True Fracture Strain True Fracture Stress, MPa 5C- T6- ED- Test 1 67.4 0.32 323 364 0.39 0.38 434 5C- T6- ED- Test 2 72.2 0.32 326 364 0.41 0.39 440 5C- T6- TD- Test 1 74.3 0.31 338 370 1.17 0.39 442 5C- T6- TD- Test 2 65.9 0.35 347 372 1.11 0.39 436 9C- T6- ED- Test 1 66.7 0.24 330 363 0.45 0.33 418 9C- T6- ED- Test 2 73.0 0.34 334 361 0.46 0.36 408 9C- T6- TD- Test 1 70.7 0.30 350 363 0.98 0.30 402 9C- T6- TD- Test 2 72.5 0.32 340 365 1.32 0.31 412 12C- T6- ED- Test 1 72.4 0.30 324 349 0.30 0.37 419 12C- T6- ED- Test 2 61.9 0.28 328 347 0.21 0.37 418 12C- T6- TD- Test 1 70.8 0.27 336 354 0.42 0.29 415 12C- T6- TD- Test 2 64.2 0.26 332 355 0.43 0.27 414 50 5.3 Bend test results In this section, the results of inverted VDA bend tests performed at the University of Waterloo will be presented. Then, the results of VDA bend test done at UBC will be shown for two different cooling rates. Finally, a comparison of results of VDA bend tests UBC and Waterloo will be presented with the same condition but different test rigs. 5.3.1 Inverted VDA bend tests conducted at university of Waterloo Experiments were done at the University of Waterloo where the evolution of surface strain could be measured during bending using DIC. The samples had thickness of 3 mm and PCG layer thickness of ~ 65 μm (sample 6C, Figure 5.2) and were tested in the T4 and T6 condition in the ED and TD direction (i.e. bend axis perpendicular to the extrusion direction and bend axis perpendicular to the TD direction, respectively). Figure 5.11 show the results for the load- displacement for these samples. The point of a load drop of 60 N is shown in green solid symbol, ie. the normal definition of failure in VDA-238. 51 a) b) Figure 5.11 Load- Displacement for 3mm thickness (without removing the PCG layer (65μm)) on: a) T4- ED and TD b) T6- ED and TD. (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) 010002000300040005000600070000 2 4 6 8 10 12 14Load (N)Displacement (mm)ED-sample 1ED-sample 2TD-sample 1TD-sample 2VDA (60N)T401000200030004000500060000 2 4 6 8 10Load (N)Displacement (mm)ED-sample 1ED-sample 2TD-sample 1TD-sample 2VDA(60N)T652 Additional tests were conducted on T6 samples were the PCG layer was removed from both sides of sample. The load- displacement results are shown in Figure 5.12. Figure 5.12 Load- Displacement for 2.5mm thickness (after removing PCG layer) on: T6- ED and TD (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) The results show that for both the T4 and T6 conditions the TD has a greater load compared to the ED samples. However, load and displacement at 60 N load drop is lower for TD direction compared to ED samples. Comparing the results of T6 condition before removing PCG layer and after the removal we can see that for 3 mm thickness (before the removal of PCG layer) we have higher load rather than 2.5mm thickness of samples. The results also present that with the same thickness of PCG layer (3mm thickness of sample) in T4 condition we have greater load- displacement response. 01000200030004000500060000 2 4 6 8 10Load (N)Displacement (mm)ED-sample 1ED-sample 2TD-sample 1TD-sample 2VDA(60N)T653 Figures 5.13 and 5.14 present the results from DIC system for major strain vs minor strain for the T4 and T6 condition in both ED and TD direction. It can be seen the strain path for the samples are similar with only a minor deviation of the minor strain from zero i.e. nearly plane strain conditions. a) b) c) d) Figure 5.13 Strain Path for 3mm thickness (without removing the PCG layer) on: a) T4- ED b) T4- TD c) T6- ED d) T6-TD 00.10.20.30.40.50.60.7-0.1 -0.05 0 0.05 0.1Major true strainMinor true strainsample 1sample 200.10.20.30.40.50.60.7-0.1 -0.05 0 0.05 0.1Major true strainMinor true strainsample 1sample 200.10.20.30.40.50.60.7-0.1 -0.05 0 0.05 0.1Major true strainMinor true strainsample 1sample 200.10.20.30.40.50.60.7-0.1 -0.05 0 0.05 0.1Major true strainMinor true strainsample 1sample 254 a) b) Figure 5.14 Strain Path for 2.5mm thickness (after removing PCG layer) on: a) T6- ED b) T6-TD Figure 5.15 shows the evolution of major strain for the samples with a thickness of 3 mm in the T4 and T6 conditions while Figure 5.16 shows the results after removing the PCG layer for the T6 condition. It can be seen that for both ED and TD, the major strain increases more quickly with punch displacement for the T6 condition compared to T4 condition. This may be due to the lower work hardening rate of the T6 condition. It can be observed that for the T6 condition that there is no difference between ED and TD direction results, up to a punch displacement of ~4.5 mm but then it diverges as the strain accumulate more quickly in TD samples. The failure strain (as defined by the 60N load drop) is 0.38 and 0.6, for the T6-TD and T6-ED tests (see Table 5.3 for a summary). In the case of the T4 samples, the failure strain is 0.55 and 0.6. Turning to the samples with the PCG layer removed it can be seen that the failure strain is 0.64 and 0.42 for ED and TD test, respectively. 00.10.20.30.40.50.60.7-0.1 -0.05 0 0.05 0.1Major true strainMinor true strainsample 1sample 2sample 300.10.20.30.40.50.60.7-0.1 -0.05 0 0.05 0.1Major true strainMinor true strainsample 1sample 2sample 355 Figure 5.15 Strain evolution for T4 and T6 condition- 3mm thickness (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) 00.20.40.60.810 2.5 5 7.5 10 12.5Major StrainDisplacement(mm)T4- ED - test1T4- ED - test2T4- TD - test1T4- TD - test2T6- ED - test1T6- ED - test2T6- TD - test1T6- TD - test260N load dropT4-TD T6-TD T6-ED T4- ED 56 Figure 5.16 Strain evolution for T6 condition- 2.5mm thickness (PCG layer removed from both side of sample) (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) 00.20.40.60.810 2.5 5 7.5 10 12.5Major StrainDisplacementT6- ED- test 1T6- ED- test 2T6- TD- test 1T6- TD- test 260N load dropPCG layer removed T6- TD T6-ED 57 The major strain vs bend angle was also extracted for the T4 and T6 condition in both ED and TD direction as shown in Figure 5.17 to 5.18 (Note: the bend angle was calculated from the formulae presented in Section 4.6.3). It can be seen that for the ED direction we have higher bend angles for a specific strain in both T4 and T6 tests. The better bend results for T4 vs T6 conditions might be due to aging effects, i.e. an increase in strength and decrease in the work hardening rate for the T6 samples. Table 5.3 summarizes the major and minor strain, load, displacement and also bend angle for these experiments at the point of 60N load drop. Table 5.3 Summary of mechanical parameters for inverted VDA test (average of 2 tests) Condition Load at 60N drop (N) Displacement at 60N drop Evaluated bend angle at 60N drop Minor Strain Major Strain Von Mises Strain T4-ED(3mm) 6237 10.78 93 0.00 0.55 0.63 T4-TD(3mm) 5757 9.07 75 -0.01 0.60 0.69 T6-ED(3mm) 5075 7.96 64 0.00 0.60 0.69 T6-TD(3mm) 4932 5.42 40 0.00 0.36 0.42 T6-ED(2.5mm) 3890 8.65 73 0.00 0.64 0.74 T6-TD(2.5mm) 3871 6.57 52 0.00 0.42 0.48 58 a) b) Figure 5.17 Bend angle vs major strain for 3mm thickness (without removing the PCG layer) on: a) ED b) TD, T6 and T4 samples 0 20 40 60 80 100 12000.10.20.30.40.50.60.70.8Bend Angle (degree)Major True StrainT4- sample 1T4-sample 2T6-sample 1T6-sample 2VDA (60N)T6 T4ED0 20 40 60 80 100 12000.10.20.30.40.50.60.70.80.9Bend Angle (degree)Major True StrainT4- sample 1T4-sample 2T6-sample 1T6-sample 2VDA (60N)TD T4T659 Figure 5.18 Bend angle vs major strain for 2.5mm thickness (after removing PCG layer) on: a) T6- ED b) T6-TD 0 20 40 60 80 100 12000.10.20.30.40.50.60.70.80.9Bend Angle (degree)Major True StrainED-sample 1ED-sample 2ED-sample 3TD-sample 1TD-sample 2TD-sample 3VDA (60N)TD ED60 To see the effect of sample thickness on the major strain- bend angle curve for the T6 condition, the bend angle was converted using the correction proposed in Section 4.3.2.3, i.e. to a converted thickness of 2.5 mm. Figure 5.19 and 5.20 show the results before and after correction. The results show that the correction formula does eliminate some of the gap between the tests. Figure 5.19 Major strain- bend angle for T6 condition in both ED and TD direction before correction for thickness ED-2.5mm TD-2.5mm ED-3mm TD-3mm 61 Figure 5.20 Major strain- Bend angle for T6 condition in both ED and TD direction after correction for thickness of 2.5mm TD-converted ED TD ED- converted 62 The histogram in Figure 5.21 summarizes the major strain for different condition. Here, it can be seen that effect of orientation (ED vs TD) is relatively small for the T4 temper but in the case of the T6 temper, (with and without removal of PCG layer) the TD samples show 35-40% lower failure strains. Figure 5.21 Summary the major strain for samples in both ED and TD directions (Note: ED- bend axis ⊥ to extrusion direction, TD- bend axis ∥ to extrusion direction) 00.10.20.30.40.50.60.7T4 (3mm) T6 (3mm) T6 (2.5mm)Major Strain ED TD63 5.3.2 VDA bend test conducted at UBC In the next section, results will be presented on the samples where the PCG layer was chemically etched away so that bend tests could be conducted with the PCG layer either on the tension or compressive surface of the bend sample. However, first the hardness test results for the top and bottom surface of the sample with be presented. 5.3.2.1 Hardness The hardness of samples was measured on each bend test sample for the side of the sample with the PCG layer removed and the opposite side and the results are shown in Table 5.4. Here the results of hardness for T6 condition is presented. The hardness of samples also measured after doing VDA bend test on the samples which were solution treated at 515°C for 5 min+ hair dryer- cooling+T6. Table 5.4- 5.6 shows the summary of results. 64 Table 5.4 Summary of hardness results for T6 -180°C for 6 hours on 5C strip, PCG layer thickness: 50μm 5C -T6 Hardness of the side with PCG layer (kgf/mm2) Hardness of the side without PCG layer (kgf/mm2) 5C-T6- ED- Bend test when PCG layer is in compression 110 ± 0.8 110 ±0.8 5C-T6- ED- Bend test when PCG layer is in tension 108 ± 1.0 111 ± 1.0 5C-T6-TD- Bend test when PCG layer is in compression 114 ± 1.0 116 ±1.5 5C-T6-TD- Bend test when PCG layer is in tension 114 ± 0.9 115 ± 0.1 Average 112 Table 5.5 Summary of hardness results for solution treatment at 515°C for 5 mins + cooling rate of 18.5 °C/s + 180°C for 6 hours on 5C strip, PCG layer thickness: 50μm 5C - 5 mins at 515°C+cooling rate of 18.5 °C/s +T6 Hardness of the side with PCG layer (kgf/mm2) Hardness of the side without PCG layer (kgf/mm2) 5C-5 mins at 515°C+ cooling rate of 18.5 °C+T6- ED- Bend test when PCG layer is in compression 100 ± 0.7 101 ±0.7 5C- 5 mins at 515°C+ cooling rate of 18.5 °C+T6-ED- Bend test when PCG layer is in tension 100 ± 0.7 101 ± 0.5 5C- 5 mins at 515°C+ cooling rate of 18.5 °C+T6-TD- Bend test when PCG layer is in compression 100 ± 1.0 101 ± 0.5 5C- 5 mins at 515°C+ cooling rate of 18.5 °C+T6-TD- Bend test when PCG layer is in tension 100 ± 0.4 101 ± 0.6 Average 100 65 Table 5.6 Summary of hardness results for T6 -180°C for 6 hours on 9C strip, PCG layer thickness: 100μm 9C -T6 Hardness of the side with PCG layer (kgf/mm2) Hardness of the side without PCG layer (kgf/mm2) 9C- T6- ED- Bend test when PCG layer is in compression 115 ± 0.6 112 ± 0.6 9C -T6- ED- Bend test when PCG layer is in tension 115 ± 0.6 112 ± 0.5 9C -T6- TD- Bend test when PCG layer is in compression 116 ± 0.8 111 ± 0.9 9C -T6- TD- Bend test when PCG layer is in tension 119 ± 1.0 115 ± 1.0 Average 114 Table 5.7 Summary of hardness results for solution treatment at 515°C for 5 mins + cooling rate of 18.5 °C/s + 180°C for 6 hours on 9C strip, PCG layer thickness: 100μm 9C - 5 mins at 515°C+ cooling rate of 18.5 °C +T6 Hardness of the side with PCG layer (kgf/mm2) Hardness of the side without PCG layer (kgf/mm2) 9C -5 mins at 515°C+ cooling rate of 18.5 °C +T6-ED- Bend test when PCG layer is in compression 100 ± 0.5 101 ± 0.5 9C -5 mins at 515°C+ cooling rate of 18.5 °C +T6-ED- Bend test when PCG layer is in tension 100 ± 1.0 101 ± 0.4 9C -5 mins at 515°C+ cooling rate of 18.5 °C +T6-TD- Bend test when PCG layer is in compression 100 ± 1.0 101 ± 1.0 9C -5 mins at 515°C+ cooling rate of 18.5 °C +T6-TD- Bend test when PCG layer is in tension 100 ± 0.7 101 ± 1.0 Average 101 66 Table 5.8Summary of hardness results for T6 -180°C for 6 hours on 12C strip, PCG layer thickness: 800μm 12C -T6 Hardness of the side with PCG layer (kgf/mm2) Hardness of the side without PCG layer (kgf/mm2) 12C- T6- ED- Bend test when PCG layer is in compression 119 ± 1.5 112 ± 0.5 12C -T6- ED- Bend test when PCG layer is in tension 111 ± 0.5 115 ± 0.9 12C -T6- TD- Bend test when PCG layer is in compression 116 ± 0.8 111 ± 0.7 12C -T6- TD- Bend test when PCG layer is in tension 118 ± 1.0 110 ± 0.6 Average 114 Table 5.9 Summary of hardness results for a) T6 b) solution treatment at 515°C for 5 mins + cooling rate of 19.7 °C/s + 180°C for 6 hours on 12C strip, PCG layer thickness: 800μm 12C - 5 mins at 515°C+ cooling rate of 19.7°C +T6 Hardness of the side with PCG layer (kgf/mm2) Hardness of the side without PCG layer (kgf/mm2) 12C -5 mins at 515°C+ cooling rate of 19.7 +T6-ED- Bend test when PCG layer is in compression 106 ± 1.0 110 ± 1.0 12C -5 mins at 515°C+ cooling rate of 19.7+T6-ED- Bend test when PCG layer is in tension 106 ± 1.0 110 ± 0.5 12C -5 mins at 515°C+ cooling rate of 19.7+T6-TD- Bend test when PCG layer is in compression 102 ± 0.4 110 ± 1.0 12C -5 mins at 515°C+ cooling rate of 19.7 +T6-TD- Bend test when PCG layer is in tension 109 ± 1.5 101 ± 1.0 Average 107 67 The hardness results show that basically there is not much difference between PCG and PCG removed surfaces. It can be seen from the average hardness of T6 condition (5C average hardness: 112, 9C average hardness: 114 and 12C average hardness: 114) that the T6 sample has about 10 HV greater hardness than when the samples which were solution treated at 515°C for 5 min +cooled 18-20°C/s +T6 condition (5C average hardness: 100, 9C average hardness: 101 and 12C average hardness: 107). Figure 5.22 shows the mole fraction of Mg2Si at 515°C is ~ 0.0028 while it is 0.012 at 180°C (the graph plateau for the temperature below 400°), That suggests that 75% of the Mg2Si has been dissolved. That could be the reason that the hardness after solution treatment at 515°C is lower than T6 at 180°C. Figure 5.22 Molar fraction of Mg2Si vs temperature In this section, the VDA bend tests results from the UBC test rig are reported. Two different conditions were investigated; solution treatment at 515°C for 5 mins followed by cooling of 13-19°C/s T6 and the other one was taking samples to T6 (6 hours at 180°C-artificially aged). In both 00.0020.0040.0060.0080.01400 450 500 550 600Molar Fraction Temperature (°C)Mg2Si515°C 68 tests the PCG layer was removed from one side of the sample and then VDA bend tests were done when the PCG layer was in tension and also in compression in both ED and TD direction. 5.3.2.2 Bending angle correction based on the thickness In order to see the effect of PCG layer thickness on the bendability of aluminum alloys PCG layer has been removed from one side of the sample (resulted in the sample thickness of 2.7mm for sample 5C and 9C but 2mm for 12C) and then VDA bend test was done in both sides to see that how PCG layer effect the bendability. So, after removing PCG layer we will have 2 different thickness of materials and this results in different bending conditions. To eliminate the effect of sample thickness on the strain equation 5.1 was used to converted to the normalized bend angle as the reference (i.e. bend angle for the thickness of 2mm)[62] 𝐴𝑛𝑔𝑙𝑒 𝑓𝑜𝑟 2 𝑚𝑚 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 = 𝐴𝑛𝑔𝑙𝑒 𝑓𝑜𝑟 2.7 𝑚𝑚 𝑡ℎ𝑖𝑐𝑘𝑛𝑒𝑠𝑠 ×√2.7√2 (5-1) 5.3.2.3 VDA bend tests after T6 condition (6 hours at 180°C) To see the effect of PCG layer thickness on the bendability of the samples we first removed PCG from one side of each sample then we did VDA test on both side; the side with PCG on the compression and tension side of VDA test. We also did the tests in both extrusion direction and transverse direction. Figure 5.23 shows the summary of the results. Note: The force vs displacement plots for all the conditions are shown in Appendix B 69 Figure 5.23 Summary normalized bend angle for the tests done after heat treatment of samples at 180°C for 6 hours (T6) in both ED and TD directions (The blue and green bars are results for the sample without removing PCG layer) The histograms show that for the sample with a very thin PCG layer (50μm) the bend angle are similar when the PCG layer is in compression or tension, however by increasing the PCG layer thickness we can see the evidence of effect of PCG layer. One can also see that for all the thickness of the PCG layer, tests were done in TD direction have 30% to 40% lower bend response to the tests done is ED direction. 70 5.3.2.4 VDA bend tests after solution treatment at 515°C for 5 mins+ cooling rate of 18-20°C/s+ T6 Figure 5.24 is summarizing the results of bend angle for three different PCG layer thickness in both ED (ED direction perpendicular to bending axis) and TD (TD direction perpendicular to bending axis) direction when PCG layer was in tension and also in compression. The bar chart show that in all cases when the PCG layer is in tension the bending angle is lower than when the PCG is in compression, another result of this figure is that for all three different PCG layer thickness the bending the bending response is better in ED direction rather than TD. Note: The force vs displacement plots for all the conditions are shown in Appendix C 71 Figure 5.24 Summary normalized bend angle for the tests done after heat treatment of samples at 515°C for 5 mins+ cooling rate of 18-20°C/s + T6 in both ED and TD direction 5.3.3 Crack initiation in bend samples for the T6 condition This section shows metallographic observations on the cracks observed from the bend tests done in two orientations (Note: ED- bend axis ⊥ to extrusion direction and TD- bend axis ∥ to extrusion direction). The bend tests were conducted when the PCG layer was in tension and in compression, noting that the PCG layer was etched away from one side of the sample. The VDA bend tests were done with the PCG layer in compression and tension. After the tests, the images of microstructure were taken using optical microscopy (Barker’s Etch). 72 5.3.3.1 Bend region after bending in ED direction (bend axis ⊥ to extrusion direction) The optical images were taken from 3 strips with different PCG layer thickness: 50, 100 and 800μm. Figure 5.25-5.30 shows the optical images of these strips after bending test when PCG is in tension and compression. The figures show the bend region and the PCG layer on one side of the sample and removed from the other side. The PCG layer thickness of 50μm is not obvious while PCG layer thickness of 100μm and 800μm is clear on top and bottom of the samples. The figures indicate that, as the angle of the bend increases, the depth of the cracks increases and moves toward the core of material. Additionally, it is apparent that the grain size of the PCG layer on the material's surface is not consistent, with larger grain sizes observed as one moves deeper into the material (see Figure 5.30 b). 73 Figure 5.26 5C strip with 50μm PCG layer in tension, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition Figure 5.27 5C strip with 50μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition (a) (b) (a) (b) Bend Angle = 87° Bend Angle = 87° 74 a) b) Figure 5.28 9C strip with 100μm PCG layer in tension, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition Figure 5.29 9C strip with 100μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition a) b) Bend Angle = 75° Bend Angle = 86° 75 Figure 5.30 12C strip with 800μm PCG layer in tension, bending axis perpendicular to ED direction a) bottom and b) away from the bend region, T6 condition Figure 5.31 12C strip with 800μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition a) b) a) b) a) b) Bend Angle = 84° Bend Angle = 80° 76 5.3.3.2 Bending region after bending in TD direction (bend axis ∥ to extrusion direction) The optical images were taken from 3 strips with different PCG layer thickness. 50μm, 100μm and 800μm. Figure 5.31-5.36 shows the optical images of these strips after bending test when PCG is in tension and compression. The PCG layer thickness of 50,100 and 800μm is clear on top and bottom of the samples. Figure 5.32 5C strip with 50μm PCG layer in tension, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition Figure 5.33 5C strip with 50μm PCG layer in compression, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition a) b) a) b) Bend Angle = 52° Bend Angle = 57° 77 Figure 5.34 9C strip with 100μm PCG layer in tension, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition Figure 5.35 9C strip with 100μm PCG layer in compression, bending axis perpendicular to ED direction a) top and b) bottom of the sample, T6 condition a) b) a) b) Bend Angle = 64° Bend Angle = 72° 78 a) b) Figure 5.36 12C strip with 800μm PCG layer in tension, bending axis perpendicular to TD direction a) bottom and b) away from the bend region, T6 condition a) b) Figure 5.37 12C strip with 800μm PCG layer in compression, bending axis perpendicular to TD direction a) top and b) bottom of the sample, T6 condition Bend Angle = 30° Bend Angle = 93° 79 Chapter 6: Summary and Future Work: 6.1 Summary: The objective of this study was to quantify the effect of PCG layer thickness on the bendability and tensile behavior of an Al-Mg-Si extrusion alloy. In addition, the effect of cooling rate after the solution treatment on the bendability of aluminum alloys was also investigated. The major findings of this study can be summarized as follows: 1. A new technique was developed for the selective removal of the PCG layer from only one side of the sample, this technique involves the use of silicone sealant as a coating material and sodium hydroxide as a solution 2. Different PCG layer thicknesses can be produced by varying extrusion and homogenization condition. 3. The microstructure of samples before and after solution treatment for 5 mins at 515°C were similar with highly elongated grains observed parallel to the extrusion direction, i.e. a primarily unrecrystallized microstructure. Samples cooled with a different cooling rate of (13-20°C/s) showed reduced bendability (10-20%) compared to the water quenched extrusions. 4. It was found that the sample with the 50μm PCG layer (50μm) showed similar load- displacement curves whether the PCG layer was in compression or tension. However, for the thicker PCG layers, the bend response was poorer when the PCG layer was in tension. 5. It was seen that for all thicknesses of the PCG layer, tests done in TD direction showed a lower bend angle compered the tests done in ED direction. 80 6. The results from the tensile tests revealed a correlation between the material's tensile behavior and its response to bending. It was found that the true fracture strain in the TD samples was lower than that in the ED samples, which was also observed in the bend test where the TD direction (Note: TD- bend axis ∥ to extrusion direction) exhibited a lower bend angle and cracked under a lower punch displacement. 6.2 Future work: It is suggested that the following work could be contemplated for the future: 1. 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Göken, “The Role of Through-Thickness Variation of Texture and Grain Size on Bending Ductility of Al–Mg–Si Profiles,” pp. 568–577, 2023. 89 Appendices: Appendix A: Summary results of inverted-VDA bend test: Table A.1: Summary of mechanical parameters- As received- ED – 3mm thickness Measurement Sample Mean 1 2 Load Drop Disp. (mm) 10.26 11.31 10.78 Load Drop Load (N) 6066 6408 6237 Bend Angle (at 60N load drop) 88 99 93 Major True Strain 0.49 0.60 0.55 Minor True Strain 0.00 0.00 0.00 Von Mises Eq True Strain 0.57 0.69 0.63 Table A.2 Summary of mechanical parameters- As received- TD – 3mm thickness Measurement Sample Mean 1 2 Load Drop Disp. (mm) 8.96 9.19 9.07 Load Drop Load (N) 5721 5794 5757 Bend Angle (at 60N load drop) 74 76 75 Major True Strain 0.58 0.61 0.60 Minor True Strain -0.01 0.00 -0.01 Von Mises Eq True Strain 0.67 0.71 0.69 90 Table A.3 Summary of mechanical parameters- T6- ED – 3mm thickness Measurement Sample Mean 1 2 Load Drop Disp. (mm) 7.85 8.07 7.96 Load Drop Load (N) 5050 5100 5075 Bend Angle (at 60N load drop) 63 65 64 Major True Strain 0.61 0.59 0.60 Minor True Strain 0.00 0.00 0.00 Von Mises Eq True Strain 0.70 0.68 0.69 Table A.4 Summary of mechanical parameters- T6- TD – 3mm thickness Measurement Sample Mean 1 2 Load Drop Disp. (mm) 5.29 5.55 5.42 Load Drop Load (N) 4907 4957 4932 Bend Angle (at 60N load drop) 39 42 40 Major True Strain 0.34 0.38 0.36 Minor True Strain 0.00 0.00 0.00 von Mises Eq True Strain 0.39 0.44 0.42 91 Table A.5 Summary of mechanical parameters- T6- ED –2.5mm thickness Table A.6 Summary of mechanical parameters- T6- TD – 2.5mm thickness Measurement Sample Mean 1 2 3 Load Drop Disp. (mm) 6.69 6.46 6.56 6.57 Load Drop Load (N) 3932 3939 3742 3871 Bend Angle (at 60N load drop) 53 51 52 52 Major True Strain 0.44 0.40 0.42 0.42 Minor True Strain -0.01 0.00 0.00 0.00 Von Mises Eq True Strain 0.51 0.47 0.48 0.48 Measurement Sample Mean 1 2 3 Load Drop Disp. (mm) 8.58 8.84 8.55 8.65 Load Drop Load (N) 3736 3959 3975 3890 Bend Angle (at 60N load drop) 72 72 72 73 Major True Strain 0.61 0.68 0.64 0.64 Minor True Strain 0.00 0.00 0.00 0.00 Von Mises Eq True Strain 0.70 0.79 0.74 0.74 92 Appendix B: VDA bend tests after T6 condition (6 hours at 180°C) Figure 1-9 shows the load vs displacement results for three different PCG layer thickness in both ED (ED direction perpendicular to bending axis) and TD (TD direction perpendicular to bending axis) direction when PCG layer was in tension and also in compression for T6 condition. 93 Figure A.1: 5C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm Figure A.2: 5C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm 01234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)5C-TD- PCG side- Test 15C-TD- PCG side- Test 25C-TD- etched side- Test 15C-TD- etched side- Test 201234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)5C-ED- PCG side- Test 15C-ED- PCG side- Test 25C-ED- etched side- Test 15C-ED- etched side- Test 294 Figure A.3: 5C- Load- Displacement comparison when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm 01234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)5C-TD- PCG side5C-TD- etched side5C-ED- PCG side5C-ED- etched side95 Figure A.4: 9C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm Figure A.5: 9C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm 01234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)9C-TD- etched side- Test 19C-TD- etched side- Test 29C-TD-PCG side- Test 19C-TD- PCG side- Test 201234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)9C-ED- PCG side- Test 19C-ED- PCG side- Test 29C-ED- etched side- Test 19C-ED- etched side- Test 296 Figure A.6: 9C- Load- Displacement comparison when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm 01234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)9C-TD- etched side9C-TD- PCG side9C-ED- PCG side9C-ED- etched side97 Figure A.7: 12C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm Figure A.8: 12C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm 01234560 2 4 6 8 10 12Load (kN)Puch Displacement (mm)12C-TD- PCG side- Test 112C-TD- PCG side- Test 212C-TD- etched side- Test 112C-TD- etched side- Test 201234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)12C-ED- PCG side- Test 112C-ED- PCG side- Test 212C-ED- etched side- Test 112C-ED- etched side- Test298 Figure A.9:12C- Load- Displacement comparison when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm 01234560 2 4 6 8 10 12Force (kN)Punch Displacement (mm)12C-TD- PCG side12C-TD- etched side12C-ED- PCG side12C-ED- etched side99 Appendix C: VDA bend tests after solution treatment at 515°C for 5 mins+ hair dryer- cooling+ T6 Figure 1-9 shows the load vs displacement results for three different PCG layer thickness in both ED (ED direction perpendicular to bending axis) and TD (TD direction perpendicular to bending axis) direction when PCG layer was in tension and also in compression for hair dryer cooling condition. 100 Figure A.10: 5C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm, sample thickness=2.7mm Figure A.11: 5C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm sample thickness=2.7mm 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling- TD - PCG side- test 1hair dryer cooling- TD - PCG side- test 2hair dryer cooling- TD - PCG side- test 3hair dryer cooling- TD - etched side - test 1hair dryer cooling- TD - etched side - test 25C 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling- ED - PCG side- test 1hair dryer cooling- ED - PCG side- test 2hair dryer cooling- ED - PCG side- test 3hair dryer cooling- ED - etched side- test 1hair dryer cooling- ED - etched side- test 25C 101 Figure A.12: 5C- Load- Displacement for comparison when PCG layer was in tension and when etched side was in tension (sample 5C)- PCG layer thickness= 50μm sample thickness=2.7mm 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling- ED - PCG sidehair dryer cooling- ED - etched sidehair dryer cooling- TD - PCG sidehair dryer cooling- TD - etched side5C 102 Figure A.13: 9C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm sample thickness=2.7mm Figure A.14: 9C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm sample thickness=2.7mm 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling- TD- PCG side- test 1hair dryer cooling- TD- PCG side- test 2hair dryer cooling- TD- PCG side- test 3hair dryer cooling- TD- etched side- test 1hair dryer cooling- TD- etched side- test 2hair dryer cooling- TD- etched side- test 39C 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling- ED- PCG side- test 1hair dryer cooling- ED- PCG side- test 2hair dryer cooling- ED- PCG side- test 3hair dryer cooling- ED- etched side-test 1hair dryer cooling- ED- etched side-test 39C 103 Figure A.15: 9C- Load- Displacement for comparison when PCG layer was in tension and when etched side was in tension (sample 9C)- PCG layer thickness= 100μm sample thickness=2.7mm 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling- ED- PCG sidehair dryer cooling- ED- etched sidehair dryer cooling- TD- PCG sidehair dryer cooling- TD- etched side104 Figure A.16: 12C- Load- Displacement for ED direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm sample thickness=2 mm Figure A.17: 12C- Load- Displacement for TD direction when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm sample thickness=2mm 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling - ED- PCG side -test 1hair dryer cooling - ED- PCG side -test 2hair dryer cooling - ED- PCG side -test 3hair dryer cooling - ED- etched side -test 1hair dryer cooling - ED- etched side -test 2hair dryer cooling - ED- etched side -test 312C 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling - TD- PCG side -test 1hair dryer cooling - TD- PCG side -test 2hair dryer cooling - TD- PCG side -test 3hair dryer cooling - TD- etched side -test 1hair dryer cooling - TD- etched side -test 2hair dryer cooling - TD- etched side -test 3105 Figure A.18: 12C- Load- Displacement for comparison when PCG layer was in tension and when etched side was in tension (sample 12C)- PCG layer thickness= 800μm sample thickness=2 mm 01234560 2 4 6 8 10 12Load (KN)Punch Displacement (mm)hair dryer cooling - ED- PCG sidehair dryer cooling - ED- etched sidehair dryer cooling - TD- PCG sidehair dryer cooling - TD- etched side
Thesis/Dissertation
eng
Materials Engineering
Vancouver : University of British Columbia Library
Attribution-NonCommercial-NoDerivatives 4.0 International
Graduate
Poole, W. J. (Warren J.)
The effect of PCG layer thickness on bendability of aluminum extrusion alloys
Text