Hot Deformation Behavior and Microstructural Evolution Based on the Processing Map of Dual-Phase Mg-Li Based Alloy

The deformation behavior of the as-extruded Mg-Li-Al-Zn-Si alloy was studied by conducting a hot compression test, with a temperature range of 180-330 degrees C and a strain rate range of 0.01-10 s(-1). The constitutive relationship of flow stress, temperature, and strain rate was expressed by the Zener-Hollomon parameter and included the Arrhenius term. By considering the effect of strain on the material constants, the flow stress at 240-330 degrees C could be precisely predicted with the constitutive equation (incorporating the influence of strain). A processing map was established at the strain of 0.7. The unsafe domains that are characterized by uneven microstructures were detected at low temperatures (<230 degrees C) or high temperatures (>280 degrees C), with high strain rates (>1 s(-1)). The optimum hot deformation region was obtained at a medium temperature (270-300 degrees C), with a peak power dissipation efficiency of 0.44. The microstructural evolution in different domains is investigated. The unstable domains are characterized by a non-uniform flow behavior and uneven microstructure. The observation showed that the dynamic recrystallization (DRX) process could easily occur at the safe domain with high power dissipation efficiency. For the alpha-phase, some features of continuous dynamic recrystallization can be found. The triple points serve as prominent nucleation sites for the beta-phase DRX grains and the growth in the grains was carried out by subgrain boundary migration. The microstructure exhibits characteristics of discontinuous dynamic recrystallization.