Analysis of strain hardening behavior in a ductile Mg–Yb based alloy

A ductile Mg–Yb based alloy shows a larger strain hardening exponent of 0.45 than those of high-formable Mg alloys, suggesting better strain hardening ability and formability at room temperature. Hence we investigated the strain hardening behavior of the studied alloy under tensile mode. The studied alloy exhibits four strain hardening stages labeled as stage I, II, III, and IV from small to large strain, different from the majority of Mg alloys. Specifically, stage II is characterized by an increased strain hardening rate rather than plateau or decrease, which is principally attributed to the combined results of reducing effective slip length by twin boundaries, increasing the hardness of twinned regions by Basinski mechanism, and the interactions of dislocation-stacking faults. Moreover, the dropping strain hardening rate suddenly slows in a strain of ~15% in stage III, which associates with basal-dissociated sessile dislocation structures that can hinder mobile dislocation so as to enhance hardening rate. Finally, we concluded that strong strain hardening ability in studied alloy essentially ascribes the alloying effect of Yb, which decreases stacking fault energy so that facilitate the formation of twins and stacking faults.