Achieving Superior Superplasticity in a Mg–6Al–Zn Plate via Multi-pass Submerged Friction Stir Processing

A large-scale Mg–6Al–Zn plate was prepared by multi-pass submerged friction stir processing (M-SFSP) and its superplastic deformation behavior was investigated. The maximum elongation of 467%, 332% and 421% was attained for the samples oriented in the processing direction (PD), 45° tilted toward the PD, and transverse direction (TD), respectively, when deformed at 623 K and a strain rate of 1 × 10 −3 s −1 . This was attributed to the homogeneous and fine-grained structure with mostly high-angle grain boundaries facilitating the prevalent deformation mechanism of grain boundary sliding, along with the weakened texture and dynamic recrystallization during hot deformation.