Strain Rate Dependence of Twinning Behavior in AZ31 Mg Alloys

This study investigates the impact of strain rate on the twinning process (i.e., twin nucleation, twin propagation, and twin growth) and associated mechanical behavior during compression along the normal direction (ND) and transverse direction (TD) of a rolled AZ31 Mg plate at a range of strain rates from 0.00005 s-1 to 2500 s-1. The findings reveal that the yield strength is insensitive to strain rates below 0.05 s-1 during both ND and TD compression tests, while at higher strain rates of 2500 s-1, the yield strength increases under both loading conditions. Interestingly, the TD-compressed sample exhibits a larger yield plateau at a strain rate of 2500 s-1, attributed to an increased activation of {101 over bar 2} twins. Further examination of the microstructure reveals that the twinning process is highly dependent on the strain rate. As the strain rate increases, twin nucleation is promoted, leading to a higher twin boundary density. In contrast, at lower strain rates, twin nucleation is restrained, and the external strain is mainly accommodated by twin growth, which results in higher area fractions of twinned regions.