Twinning characteristic and variant selection in compression of a pre-side-rolled Mg alloy sheet

{10−12} Twinning is one of the most important strain accommodation mechanisms for Mg alloy especially at room temperature deformation. Accompanying with twining, the lattice of matrix is rotated by large angles, and hence pre-twinning can be utilized to tailor texture of wrought Mg alloy. To better utilize this method, the present study aims to understand the twinning characteristic and variant selection in compression of a pre-side-rolled Mg alloy sheet. It confirms that the pre-generated twin lamellae can significantly enhance the yield strength for subsequent in-plane compression. But the amount of pre-side-rolling has different effect on the strain hardening rate between the two subsequent compression directions (transverse direction and rolling direction, designated as TD and RD, respectively). Moreover, the {10−12} twins in the two samples exhibit different morphology although the area fraction is nearly the same. Crystallographic analysis indicates that the variant selection in most twinned grains is consistent with Schmid law i.e., the twins are activated from the variant pair with the highest Schmid factor. In the cases of twin-twin transfer at grain boundaries, local strain accommodation is also important for variant selection. It reveals that a modified Schmid factor for rolling is effective in prediction of twin variants in pre-side-rolling. Further analysis on ideal texture indicates that the preference order of the six possible variants in side-rolling is the same with that in the subsequent TD compression, but varies from that in RD compression. This is consistent with the experimental observation that twin growth and coalescence is dominant in the former, whereas new twin variant is formed in the latter.