The effect of grain size on deformation modes and deformation heterogeneity in a rolled Mg–Zn–Ca alloy

Grain refinement could promote the activation of non-basal slip and enhance the strength and ductility of Mg alloy simultaneously. In this work, the grain size effect on deformation modes and deformation heterogeneity and its relations to crystallographic orientation in a rolled Mg–1.58Zn–0.1Ca alloy sheet with a weakened transverse direction (TD) spread texture were investigated via intragranular misorientation axis (IGMA) and high resolution-digital image correlation (HR-DIC) measurement. The results indicate that a decrease of the grain size from 55 to 13 μm increased the yield strength (YS) by 56.9%, from 72 MPa to 113 MPa, for the TD samples, but only by 8% for the rolling direction (RD) samples, from 125.7 to 135.7 MPa. Moreover, grain refinement enhanced the elongation by 76.4% for the TD samples, from 11% to 19.1%, and merely by 26.5% for the RD samples, from 16.6% to 21%. The transition in dominant deformation modes due to grain size decreasing can be summarized as: for the RD samples: basal slip → prismatic slip; for the TD samples: basal slip + tension twinning → prismatic slip. The enhanced activity of prismatic slip in the fine-grained (FG)-TD and FG-RD samples can be ascribed to the reduced ratio of critical resolved shear stress (CRSS)prismatic/CRSSbasal. For both the RD and TD samples, grain refinement facilitated deformation homogeneity, which could be related to the enhanced activity of basal slip and non-basal slip, as well as the resulting improved deformation compatibility across grain boundary.