Low-Cycle Fatigue Deformation Behavior and Evaluation of Fatigue Life on Extruded Magnesium Alloys

Extruded magnesium alloy shows a strong anisotropy of mechanical properties, which is caused by both of a crystallographic nature in hexagonal close packed lattice structure and a fiber texture with basal plane aligned parallel to the extruded direction by mechanical processing. To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloys, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during the total strain-controlled fatigue process and mean compressive strain during the stress-controlled fatigue process appeared due to the difference between tensile yield stress and compressive one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from the total strain- and the stress-controlled fatigue experiments.