Modeling of flow behavior and microstructure evolution of a dual-phase Mg-Li alloy during hot deformation

Dual-phase (DP) Mg-Li alloys have attracted increasing interest in advanced structural applications owing to their extremely low density and favourable strength-ductility synergy. In this study, the flow behavior and microstructure evolution of an LA91 DP Mg-Li alloy during hot deformation were systematically investigated by hot compression tests over a wide range of deformation parameters. The results reveal that the hot deformation behavior is governed by the coupled effects of β-phase transformation, dynamic precipitation of secondary α-phase, and dynamic recrystallisation (DRX). The β → α transformation increases the volume fraction of primary α-phase after deformation, which is significantly suppressed at elevated temperatures but only weakly influenced by strain rate. At high temperatures, the secondary α-phase exhibits diverse morphologies, including grain-boundary, acicular, short rod-like, and spherical forms, with a strain-rate-induced transition from spherical to acicular morphology, while its volume fraction is predominantly controlled by temperature. DRX is markedly inhibited at high strain rates and low temperatures, whereas complete DRX with pronounced grain growth occurs at 300°C. Based on these microstructural interaction mechanisms, a physically-based constitutive model was developed to describe the flow behavior and microstructural evolution during hot deformation. The model demonstrates excellent agreement with experimental results, achieving a correlation coefficient of 0.992 and an average prediction error of 5.875%, and accurately captures the evolution of phase fractions, grain size, and DRX fraction. These results confirm the capability of the model to reliably predict the hot deformation behavior of DP Mg-Li alloys.