Microstructure evolution of twinning-induced shear bands and correlation with ‘RD-split’ texture during hot rolling in a Mg-1.1Zn-0.76Y-0.56Zr alloy

Abstract

Unlike the recrystallization-induced shear band mechanism which has been well accepted for the RE-free Mg alloys during rolling, an understanding of deformed microstructure evolution (twin mode/variant selection and dislocations) at different strains is crucial for interpreting the shear band mechanism in the RE-containing Mg alloys upon hot rolling. In this study, a Mg-1.1Zn-0.76Y-0.56Zr alloy ingot was subjected to hot rolling at 440 °C with single-pass reductions of 10–50%, and the microstructure evolution and texture development of this hot-rolled plates at different reductions were investigated, with aim to disclose the roles of different types of twins/variants and dislocation mechanisms in the shear band (SB) formation and their correlation with the macro-texture characteristics. As the dominate twinning mode for most parent grains at lower reductions, and the primary {10−12} extension twins/variants together with basal <a > slip activated in twins contribute to formation of basal texture in the twinned grains, thus subsequently facilitating the operation of secondary {10−11} and {10−13} compression twins and following {10–12} twins. Afterwards cross-grain boundary (GB) paired twins for compression twin and their double twins were frequently observed at the nearby basal-oriented parent grains with low misorientation (≤34.5°), which should correspond to the predecessor of SBs. Further EBSD observation at higher reductions (R0.4 and R0.5) reveals that most of the banding structures are distributed homogenously and are likely transformed from the {10–11}-{10–12} twins, which are the predominant twin types under such state. The ‘RD-split’ textures start to be formed at lower reductions (R0.3) and keeps stable at higher reductions (R0.4-R0.5), which were explained by the correlations with some variant pairs of {10–12} twins and/or {10–11}-{10–12} twins predicted by Schimid factor analysis as well as shear bands. Nevertheless, the contributions of <c + a > slip to the ‘RD-split’ texture could be ignored on basis of corresponding EBSD analysis and reappearance of such texture after rolling at a low temperature (170 °C). • Primary {10-12} twins/variates and basal slip activated in twins contribute to basal texture formation in twinned grains. • Secondary compression twins and ternary {10-12} twins were mainly activated after basal orientation formation. • Paired twins for double twins at the nearby basal-oriented grains are likely the predecessor of shear bands. • The ‘RD-split’ texture was mainly correlated with {10-12} twins, double twins and shear bands with different activity.