Influence of pre-twinning on high strain rate compressive behavior of AZ31 Mg-alloys

This study aims to investigate the effect of pre-twinning on high strain rate deformation behavior of AZ31 Mg-alloy sheet. The high strain rate compressive behavior of AZ31 magnesium alloy sheet was measured in rolling direction (RD), transverse direction (TD) and normal direction (ND) by using a Split Hopkinson Pressure Bar (SHPB). The microstructural evolution and texture during pre-compression along RD and TD have been analyzed by electron back-scatter diffraction (EBSD). The results demonstrate that pre-compression along RD and TD can promote the activation of multiple twin variants in AZ31 alloys, which can significantly improve the yield strength due to grain refinement induced by {101¯2} twinning lamellas. However, the high strain rate yield strength along ND drastically decreased after pre-twinning, which is mainly attributed to the occurrence of de-twinning. The formation of {101¯2}-{101¯2} double twins and a large number of cross-twinning lamellas, after pre-twinning of TD+RD, can effectively inhibit de-twinning behavior and increase the yield strength, when high strain rate compression is applied along ND.