FINE-GRAINED Mg-Y-Nd ALLOY WITH HIGH-STRAIN-RATE SUPERPLASTICITY PRODUCED BY SUBMERGED FRICTION STIR PROCESSING

摘要

Grain refinement is an important method to improve the ductility and formability of magnesium alloys. Submerged friction stir processing (SFSP), which is carried out under water to enhance the cooling rate of FSP, has a significant effect on microstructure refinement. In this study, microstructure and superplasticity of a Mg-Y-Nd alloy prepared by SFSP are investigated. The as-cast base material mainly consists of coarse a-Mg and net-shaped eutectic phases located at grain boundaries. After SFSP, microstructure of the alloy is mainly composed of fine-grained magnesium grains (~1.3 μm) and homogeneously distributed second phase particles. The SFSP Mg-Y-Nd alloy shows relatively good high-strain-rate superplasticity, and its elongations are all above 500% within a temperature range of 708-758 K strained at 0.1 per second. The high-strain-rate superplasticity is attributed to the fine-grained microstructure and high thermal stability during superplastic deformation.