Tensile, compression and fatigue tests were carried out on a commercially extruded Mg-Al-Zn alloy having an average grain size of about 15 μm. The tensile and compression tests at room temperature showed that the yield strength in tension was much higher than that in compression. The lower yield strength in compression resulted from its texture. The effects of the mechanical anisotropy on the fatigue behavior and its deformed microstructure were also investigated under a stress ratio of R = 0.1 and - 1. The fatigue strength, stress amplitude, at N = 107 cycles under R = -1 and 0.1 was about 120 and 90MPa, respectively. The mechanical properties and the deformed microstructure observations indicated that the formation of deformation twins was related to the between maximum stress and the yield strength in tension and compression: the deformation twins were formed in the sample (maximum stress is higher than the yield strength) and showed no deformation twins in the sample (maximum stress is lower than the yield strength).
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