Unveiling the underlying mechanism of forming edge cracks upon high strain-rate rolling of magnesium alloy

Abstract In the current study, high strain-rate rolling (≥10 s-1) has been successfully employed to produce Mg-3Al-1Zn alloy sheets to a high reduction of 82% with a fine grain structure in a single pass. The underlying mechanism of forming primary and secondary edge cracks has been investigated. It is found that dynamic recrystallization (DRX) induced by subgrains tends to blunt cracks, while twinning-induced DRX is mainly observed around sharp crack tips. The motion of emitted dislocations from blunted cracks is inhibited by the DRX grain boundaries. This, on one hand, increases local work hardening, and on the other hand, causes stress concentration along grain boundaries especially in the triple junctions leading to the formation of secondary cracks.