Yttrium improves Mg ductility by enhancing grain-boundary strain compatibility: Mesoscopic deformation analysis

Magnesium (Mg) alloys are attractive lightweight structural materials owing to their low density and high specific strength. However, their widespread application is limited by inherently low tensile ductility at room temperature, which is closely related to limited formability. This limitation is primarily attributed to the insufficient activation of non-basal slip systems at room temperature. The addition of Yttrium (Y) has been reported to promote non-basal slip activity, leading to improved mechanical performance. In this study, the mechanisms of ductility enhancement in Mg–Y alloys are investigated from the perspective of mesoscopic deformation behavior using digital image correlation (DIC) combined with careful identical-area observations during tensile deformation. Pure Mg and Mg–1.3Y (at.%) were systematically examined. DIC strain mapping demonstrated that both materials exhibited pronounced deformation heterogeneity, characterized by strain localization in specific grains with relatively high Schmid factor. Notably, the two materials exhibited markedly different grain-boundary deformation behaviors. In pure Mg, severe surface steps and early formation of microcrack-like features were observed at grain boundaries, whereas such damage was significantly suppressed in the Mg–1.3Y alloy. These results indicate that improved strain compatibility and mitigation of grain-boundary surface steps play a critical role in enhancing the tensile ductility of Mg–Y alloys.