Deformation behavior, microstructure evolution and phase transformation of dual-phase Mg-Li-Zn-Sr-Ca alloy under isothermal compression

Abstract

The deformation behavior, phase transformation and microstructure evolution of dual-phase Mg-Li-Zn-Sr-Ca alloy under different deformation parameters were investigated through isothermal compression experiments. Serrated flow behavior was observed in the flow curves, indicating a strain aging behavior. R=0.9971 and AARE=3.88 % demonstrate the reliable predictive capability of established constitutive model. Hot processing maps indicate that instability region is only at T=423–490 K, $\dot{\epsilon }$ =0.007 s^–1-1 s^–1. As the temperature exceeds 523 K, needle-shaped phases precipitated from the β-Li phase, which was confirmed to be α-Mg phase. With increasing temperature and reducing strain rate, the quantity and size of them increased. Furthermore, its precipitation may be due to the high lattice diffusion coefficient of the β-Li phase. The degree of dynamic recrystallization (DRX) increased, the proportion of low-angle grain boundaries (LAGBs) and kernel average misorientation (KAM) decreased, these phenomena primarily associated with the dynamic recovery (DRV) and DRX processes. In addition, under the same processing parameters, the degree of DRX in the α-Mg phase is higher than that of the β-Li phase, the density of geometrically necessary dislocations (GND) of the α-Mg phase is higher than that of the β-Li phase. The β-Li phase can be activated more slip system and it can reduce the accumulation of dislocations. Meanwhile, the high density of GND of the α-Mg phase also predicts a higher strain energy and a greater drive force for recrystallisation. As the temperature rises, the intensity of the (0002) basal texture of the α-Mg phase increased, which is attributed to the selective growth of DRXed grains.