Abstract
Lightweight magnesium alloys are being increasingly used in automotive and other transportation industries to achieve energy efficiency. The objective of this thesis was to study the mechanical properties of two wrought alloys AZ31 and AM30. With increasing strain rate the yield strength and ultimate tensile strength increased and the strain hardening exponent decreased for AM30 and increased for AZ31. Both alloys exhibited stable cyclic characteristics at lower strain amplitudes and cyclic hardening characteristics at higher strain amplitudes. The Bauschinger effect was pronounced at higher strain amplitudes, resulting in asymmetric hysteresis loops in both alloys. The influence of strain ratio (Rs), strain rate, and initial straining direction on the cyclic deformation characteristics and fatigue life was evaluated. At low Rs, both alloys exhibited strong cyclic hardening, which decreased as Rs increased. Fatigue crack initiation was observed to occur from the specimen surface and crack propagation was basically characterized by striation-like features.
Highlights
Noster and Scholtes [5] mentioned in their work that the strain hardening effect was very small at room temperature; rather, they reported basically the temperature effect on the stress response, while the results presented in this paper showed that, at room temperature, the material could undergo cyclic strain hardening at high strain amplitudes
[5] reported in their work on AZ31 extruded alloy that strain hardening effect was very small at room temperature; rather, they reported basically the effect of temperature on the stress amplitude response, while the results presented in this investigation and by some others [6-9, 11, 13] showed that at room temperature, the material could undergo cyclic strain hardening at high strain amplitudes
Microstructural examination revealed that both AZ31 and AM30 showed a non uniform grain distribution along the plate thickness
Summary
Except for the fact that magnesium alloys have limited formability due to the hexagonal close-packed (HCP) crystal structure, their light weight trait (density: 1.7 gm/cc versus 2.7 gm/cc for aluminum and 7.8 gm/cc for steel), high strength-to-weight ratio and good damping capacity have made these alloys more desirable than conventional structural materials - steels and aluminum alloys [1-4]. The objective of this study is to evaluate the mechanical properties of two wrought Mg alloys, namely, AZ31 and AM30 Both of these alloys were provided by General Motors Research and Development Center. This investigation compares the microstructure, micro-hardness, tensile properties, low cycle fatigue properties, monotonic and cyclic strain hardening exponent and cyclic deformation characteristics of AZ31 and AM30 alloys at different test conditions. Unless the automobile industry embraces its use, magnesium would not become economically viable in other fields [2]
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