Deformation behavior and phase transformation of a dual-phase Mg−8.9Li−2.7Al-0.85Si alloy under compression test at elevated temperatures

Abstract

The hot deformation behaviors of a dual-phase Mg− 8.9Li− 2.7Al-0.85Si alloy were investigated via hot compression tests conducted at temperatures ranging from 423 K to 573 K and strain rates varying from 0.001 s⁻¹ to 1 s⁻¹. Processing maps were established based on dynamic material modeling (DMM) at true strains of 0.4 and 0.6. The optimized parameters for hot working are 523–573 K with strain rates of 0.001–0.05 s⁻¹ at a strain of 0.6. The flow instability domains are primarily distributed in the superposition area with low temperatures and high strain rates. While the Mg− 8.9Li− 2.7Al-0.85Si alloy deformed at 423 K with a strain rate of 1 s⁻¹, considerable deformation twinning formed in the α-Mg phases, and the β-Li phases were severely deformed and broken. The proportion of dynamic recrystallization in the β-Li phases was markedly higher than that in the α-Mg phases. When the temperature increased to 573 K at a lower strain rate, the coordination deformation ability between the α-Mg and β-Li phases was improved by more active slip systems, but the proportion of dynamic recrystallization was relatively low at a strain rate of 0.01 s⁻¹. The secondary α-Mg precipitated in the β-Li grain boundary when the alloy deformed at 573 K and a strain rate of 0.001 s⁻¹, which is described as deformation-induced phase transformation. The α-Mg phases with micron scales and massive α/β interfaces can hinder dislocation movement, leading to grain refinement and strength enhancement.