Study on Microstructure Evolution and Continuous Dynamic Recrystallization Constitutive Model of Dual-Phase Mg-Li Alloy LA103Z during Hot Deformation

Hot compression tests of a dual-phase Mg-Li alloy (LA103Z) were carried out at the temperatures of 250, 300, 350, 400 °C and the strain rates of 0.001, 0.01, 0.1 and 1 s – 1 on a Gleeble-3500. The effects of deformation temperature, strain rate and strain on the microstructure evolution of LA103Z were analyzed. As temperature increases and strain rate decreases, the flow stress of LA103Z decreases and the grains of β-Li phase gradually grow up and tend to be equiaxed. With the increase in deformation temperature, part of α-Mg phases inside the grains of β-Li phase dissolve and precipitate along the grain boundaries of the β-Li phase, and strain rate has little effect on α-Mg phase. The dynamic recrystallization mechanism of the β-Li phase is continuous dynamic recrystallization, while dynamic recrystallization process in the α-Mg phase is retarded. Then based on the explored continuous dynamic recrystallization mechanism and Internal State Variable method, a continuous dynamic recrystallization constitutive equation for LA103Z under hot deformation conditions was established. The correlation coefficient R between the calculated and experimental stresses of this constitutive model is 0.9961, and the average relative error of grain size prediction is 3.75%, indicating this model can accurately predict the flow behavior and microstructure evolution of LA103Z during hot deformation.