Fatigue behavior of variable-plane-rolled AZ31 magnesium alloy

The fatigue properties of variable-plane-rolled (VPRed) and conventional extruded AZ31 magnesium alloy were investigated using total strain-controlled fatigue tests with various applied strain amplitudes. The results indicated that both the strength and elongation of the VPRed samples were higher than those of the conventional extruded samples because of their refined grain size and weak texture. Consequently, the fatigue lives of the VPRed samples were longer than those of the conventional extruded samples under strain-controlled cyclic loadings. The Manson-Coffin and Basquin approaches were used to describe the fatigue lifetime of this wrought AZ31 alloy. Finally, the microscopic and macroscopic fracture features were examined. The conventional extruded sample contained more extensive and well-developed twins than the VPRed sample in the stable propagation area of the cracks. The appearance of residual twins in the fracture surface resulted from the competition between the reverse plastic zone size ahead of the crack tip and the cyclic hardening-softening characteristic.