Superplasticity of multi-directional impact forged Mg-Gd-Y-Zr alloy

A novel multi-directional impact forging (MDIF) process was successfully applied to a Mg-Gd-Y-Zr alloy and the superplasticity of the MDIFed alloy was investigated. It was shown that the initial microstructure after MDIF had a unique characteristic of coarse grains decorated by profuse tension twins. Tensile tests at various temperatures and initial strain rates displayed that the MDIFed alloy exhibited superplasticity at temperatures higher than 400 °C, especially the maximum elongation of about 300% was achieved at 450 °C and 5 × 10−4 s−1. It was observed that the initial twin lamellas diminished and even vanished with the occurrence of static recrystallization (SRX) during preheating. The detailed microstructural analysis revealed that SRX during preheating and dynamic recrystallization (DRX) during tensile testing conduced to the superplasticity. With strain rate sensitivity exponent m-value of about 0.32, the superplastic deformation mechanism was supposed to be predominated by glide-controlled dislocation creep assisted by grain boundaries sliding.