Hot deformation behavior of AZ80 magnesium alloy towards optimization of its hot workability

The flow stress curves of AZ80 magnesium alloy were obtained by isothermal compression experiment conducted at 275-400 °C and 0.001-1 s− 1. Work-hardening behavior and dynamic recrystallization leading softening behavior in hot deformation process were described by Z parameter. Deformation activation energy at different strains was calculated by constitutive equation and power dissipation map at different strains was constructed. Combining the Z parameter and the power dissipation efficiency, the effect of different deformation temperatures and strain rates on deformation mechanism and microstructure were investigated, especially the effect of dynamic recrystallization on grain refinement was analyzed in detail. The results showed that with increasing deformation temperature and decreasing strain rate, the Z parameters decreased and the power dissipation efficiency increased, which was contributed to the occurrence of dynamic recrystallization softening. A decreasing tendency of deformation activation energy with increasing strains was observed. Furthermore, the optimum hot processing domain for fine grain microstructure was determined as 283-310 °C and 0.001-0.0017 s− 1 corresponding to a power dissipation value of 0.41, where the fine grain structure with average grain size of 8 μm could be generated. The results were applied to the workability optimization of typical component in isothermal forging experiment, which could obtain fine grain structure with average grain size of 5 μm and significantly improve strength of the component.