Twinning

detwinning and their effects on mechanical properties of commercial hot-rolled AZ31 Mg alloy were investigated under three compression along rolling direction（RD）

normal direction（ND）and RD-ND at room temperature

respectively.The results show that the grain orientation is changed and there exists many distinctly parallel and lenticular twinning bands in microstructure after compression along RD.While compression along ND

no matter how much the specimens was compressed

the absence of{1012}extension twinning and any twinning microstructure can be observed

which reveals that plastic deformation is mainly dependent on slips under compression along ND.The yield stress is decreased significantly during detwinning process

and the strain needed by complete detwinning is smaller than that of twinning.