Analysis of fatigue damage process in magnesium alloy AZ31

We investigated in detail the process of fatigue damage, as represented by cyclic stress response and stress–strain hysteresis loop shape, in extruded magnesium alloy AZ31 by performing a controlled plastic strain amplitude test. Additionally, we compared the cyclic behavior of annealed AZ31 with that of the as-received extruded AZ31. An analysis of the experimental results showed that the characteristic loop shape and the variation in mean stress depended greatly upon the amplitude of the plastic strain applied. The twinning–untwinning process was dominant at plastic strains of greater amplitude, whereas dislocation slips were dominant at lower plastic strains, which would appear as a bi-linear tendency in the Manson–Coffin curve.