Superplasticity at Elevated Temperature of a Coarse‐Grained Mg–Li Alloy

Abstract

Tensile tests on Mg–10.73Li–4.49Al–0.52Y alloy processed by equal channel angular pressing (ECAP) are conducted at 473–623 K with initial strain rates of 5 × 10−4–1 × 10−2 s−1 and the microstructures and the deformation mechanism are investigated. Homogeneous microstructure with an average coarse grain size of 154.6 µm is obtained after ECAP process. The results indicate that the alloy exhibits significant superplasticity with a maximum elongation of 512% at 523 K with initial strain rate of 5 × 10−4 s−1. Even with strain rate of 1 × 10−2 s−1, the elongations exceed 150% at all temperatures, which suggests that the alloy exhibits notable high strain rate quasi‐superplasticity. Under the optimum superplastic condition, the value of the strain rate sensitivity is 0.53 and the activation energy is 89.7 kJ mol−1, indicating that the dominant deformation mechanism in this alloy is grain boundary sliding (GBS) controlled by a combination of grain boundary diffusion and lattice diffusion. Grain refinement occurs during pre‐heating and deformation, which is favor for GBS. The nucleation, growth, and coalescence of cavities are the main failure mechanism during superplastic deformation.