UBC Theses and Dissertations
Fabrication and characterization of steel-magnesium laminated metal composites Che, Hanqing
In this study, interstitial-free steel and commercial purity magnesium sheets were used to fabricate steel-magnesium laminated metal composites by roll bonding at 300℃. It was found that the steel and magnesium can achieve reasonable bonding after a 47% rolling reduction when the volume fraction of the laminate is 10-15% magnesium. The microstructure of the laminated composites was observed with scanning electron microscope. It was found that a continuous interface between the IF steel and the magnesium was produced during the roll bonding process. There was no evidence of intermetallic formation at the interface. A seven layer steel-magnesium laminate was fabricated by accumulative roll bonding at 300℃ with an overall reduction of 77 percent. Through-width cracks were found in the surface steel layers after the one cycle accumulative roll bonding process. The longitudinal cross-sectional microstructure of the laminate revealed that multi-localizations and even fracture occurred in steel layers inside the laminate. The mechanical properties, including tensile behavior, micro-hardness and bending behavior, of the laminated composites were assessed. The tensile property of the laminated composites was compared with those of monolithic steel and magnesium with equivalent deformation amount deformed under the same conditions. It was found that the UTS of the laminated composites obeyed the simple rule of mixtures. The fracture surfaces of the laminated composites were examined with SEM and compared with those of the monolithic IF steel and magnesium rolled under the same conditions. It was found that the fracture modes of each component were different in the laminated composites compared to the monolithic materials. Three-point bending test was conducted and it was observed that no debonding at the interface occurred for moderate strains. To investigate the fracture behavior of the laminats in bending, a series of U-shape bending tests were conducted and the bend tips were observed. Localization of the outer steel layer was observed, followed by the formation of a major crack at 45 degree to the maximum tensile stress direction. Shear cracks in the magnesium core were also found in some places adjacent to the major crack, and delamination between the steel and magnesium layers occurred.
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