Formation of basal slip-induced cleavage microcracks in a peak-aged cast Mg–Gd–Y alloy deformed in tension

In this study, the room temperature microscopic fracture behavior in a peak-aged cast Mg–Gd–Y alloy deformed in tension was investigated. Interrupted tensile tests were performed up to different stress/strain levels; the microcracks were observed and counted in differently deformed samples by optical and scanning electron microscopy; the nature and preferential sites of the microcracks were studied by electron backscattered diffraction (EBSD) analysis. The results suggest that cleavage microcracks act as the dominant cracking mode in the studied alloy. These microcracks occur preferentially in grains with favorable orientations for basal slip and large grain sizes, and are independent of the normal stress across the basal plane. The correlations of microcrack formation with stresses and microstructure are well explained by a basal slip-induced crack initiation model. Based on the revealed fracture mechanism, better understanding of the relationship between mechanical properties and microstructure of Mg-RE alloys is obtained.