Improving ductility of a Mg alloy via non-basal slip induced by Ca addition

Abstract

Addition of a small amount of Ca improves the ductility of Mg alloys. However, the mechanism underlying this effect is not well understood. In this work, tensile testing of an extruded Mg−0.47 wt% Ca alloy was conducted inside a scanning electron microscope. Electron backscattered diffraction-based slip trace analysis was performed to study in-grain slip activities at 1%, 2%, 4%, 8%, and 16% tensile strain. While the majority of the grains were deformed by {0001}<112_0> basal slip, slip lines from {11_00} prismatic planes and {11_01} pyramidal I planes were also frequently observed, and their fractions increased with strain. Ex situ transmission electron microscopy indicated that the pyramidal I slip lines were associated with <a> dislocations instead of <c+a> dislocations. From Schmid factor analysis, the critical resolved shear stresses of prismatic slip and pyramidal <a> slip are approximately twice that of basal slip in this Mg–Ca alloy. The enhanced activity of non-basal <a> slip improved the material's ductility. Our first-principles calculations found that solute Ca atoms would reduce the unstable stacking fault energy for all slip modes.