Superplastic behavior and microstructure evolution of a fine-grained Mg-Y-Nd alloy processed by submerged friction stir processing

In this study, a fine-grained Mg-Y-Nd alloy with an average grain size of ~1.3 μm and small second phases of ~280 nm was prepared by submerged friction stir processing (SFSP). Microstructure evolution and superplastic behavior of Mg-Y-Nd alloy processed by SFSP was investigated in the temperature ranges of 683-758 K and the strain rate ranges from 2×10−2 to 4×10−4 s−1. Due to the fine-grained and stable microstructure, excellent high strain rate superplasticity (HSRS) of 900% was achieved at 758 K and 2×10−2 s−1, and the maximum elongation of 967% was obtained at 733 K and 3×10−3 s−1. Because of the good deformation compatibility, cavities were easily formed at the grain boundaries instead of the interface between particles and matrix. Grain boundary sliding accommodated by lattice diffusion was the dominated deformation mechanism during superplastic deformation.