Towards high ductility in magnesium alloys - The role of intergranular deformation

This paper investigates the intergranular deformation behavior and its effect on the overall ductility of a Mg-Gd-Y alloy, using in-situ tension in scanning electron microscopy (SEM) combined with electron backscattered diffraction (EBSD) and digital image correlation (DIC) techniques. At regions surrounding grain boundaries, the majority of activated dislocation slip traces were found to form in pairs across grain boundary, and the basal-to-basal (B-B) slip pair is the dominant type. Strain accommodation around the grain boundary interfaces is affected by both Schmid factor in the adjacent grains and the m(k) value between these main slip systems. A m(k) value was proposed in this paper as the maximum value of the product of the Schmid factor and the m(k) value of the adjacent grains to measure strain accommodation around the grain boundary interface, where a higher m(k) value would mean a larger local strain. It is suggested that the overall ductility of a Mg alloy could be evaluated by measuring its average m(k) value. As an evidence, the Mg-Gd-Y alloy tubes with higher m(k) value generally show higher elongations during tensile tests in this study.