Study of fatigue failure mechanisms and establishment of fatigue reliability for extruded magnesium alloys to develop light weight mechanical components

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Low-cycle and high-cycle fatigue performance and fatigue failure mechanism have been discussed for extruded magnesium alloys which showed a strong mechanical anisotropy and texture with extruding. Due to the action of mechanical twinning in compressive phase, asymmetrical shape of hysteresis loop was observed in total strain-controlled and stress-controlled low-cycle fatigue process. An energy-based model taken into account of plastic and elastic energy density was proposed to predict the fatigue lives. From the very high cycle fatigue experiments, specimens showed a stepwise S-N curve on which two knees existed. This characteristic appearance was depended on applied stress ratio, that is mean stress effect, and loading mode, such as axial loading and rotating bending fatigue, and also induced by crack initiation mechanism changing from the twin deformation in high-stress amplitude level to slip deformation in low-stress amplitude level. In this study, effect of notch on fatigue strength and improvement of fatigue strength by fine particle shot peening treatment were discussed.