UBC Theses and Dissertations
A study on the texture and microstructure development in extruded AA3003 alloys and the relevant mechanical behaviour Chen, Jingqi
In this study, a model alloy (i.e. AA3003) was used to examine microstructure and texture development in the extrusions and the relevant mechanical response. In particular, two homogenization heat treatments were studied as the initial condition, i.e. at 375 °C for 24 h, which produces a high density of dispersoids, and at 600 °C for 24 h, which produces a condition with almost no dispersoids. Three nearly ideal deformation modes were studied, i.e. (i) axisymmetric extension (the central region of a round bar extrusion), (ii) plane strain deformation (the central region of a strip extrusion), and (iii) simple shear deformation (using torsion tests). Electron backscatter diffraction (EBSD) was the main technique to characterize the texture and microstructure of the materials. For the axisymmetric extension and plane strain deformation, it is proposed that the high density of dispersoids in the material causes a large Zener drag, which inhibits grain boundary migration and thereby maintaining the deformation texture and microstructure in the extrusions. For the materials with almost no dispersoids, it is proposed that continuous dynamic recrystallization (CDRX, which is characterized as the subgrain coarsening or the grain boundary migration) occurs during and after the extrusion, and therefore, the texture and microstructure transform from the as-deformed to the recrystallized state. In contrast, for simple shear deformation (i.e. torsion), there is little difference observed between these two materials. However, with an increase in the level of equivalent strain, the texture changes from a deformation to a recrystallized texture. Geometric dynamic recrystallization (GDRX, which is characterized as the phenomenon of the grains continuously pinched off during the deformation) is proposed as the mechanism for the case of the simple shear deformation. For the mechanical behaviour of the extruded materials, it was found that the surface layer has little effect on the measured stress-strain curves. However, the surface layer has a large effect on the R-values, i.e. a characteristic value of the material formability. It is suggested that the large R-value difference between the surface layer and the central region of the sample is attributed to the different textures.
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