Enhanced superplasticity of ultrafine-grained WEQ612 magnesium alloy via the coupling effect of grain boundary segregation and dense precipitation

Abstract

Achieving low-temperature, high-strain-rate (LTHSR) superplasticity is important for preparing rare-earth (RE)–Mg alloy products with complex shapes. Herein, an ultrafine-grained Mg–6.22Y–0.98Er–2.11Ag (wt%, WEQ612) alloy was prepared via equal-channel angular pressing (ECAP). After 16 passes of ECAP and aging at 473 K for 58 h, an average grain size of 600 nm was achieved, and there was a high density of intergranular precipitates with an average size of approximately 180 nm. The WEQ612 alloy exhibited excellent superplasticity during superplastic deformation, with elongations of 451% at 523 K and 1 × 10−4 s−1, and 834% at 573 K and 1 × 10−2 s−1. The high density of intergranular precipitates, which were uniformly distributed at the grain boundaries, promoted dynamic recrystallization (DRX) during superplastic deformation and inhibited grain growth. The grain boundary co-segregation of Y and Ag further improved the grain boundary stability of the alloy. Despite the general consensus that grain boundary sliding (GBS) is the main mechanism of superplasticity, a more complex role of GBS and DRX was identified in this study. The identified mechanism provides a reference for GBS and grain boundary rotation as well as dislocation motion during superplastic deformation, and helps to describe the intermediate processes that occur during superplastic deformation. Thus, this study provides insights into the development of LTHSR superplastic RE–Mg alloys.