A physical-based constitutive model was developed to model the viscoplastic flow behavior and microstructure evolution of AZ80 magnesium alloy during the hot working process.The competing deformation mechanisms,including work hardening,dynamic recovery,and dynamic recrystallization,in an isothermal compression environment were considered in the model.The inteal state variables,including the normalized dislocation density and recrystallized volume fraction,were incorporated into the model to articulate the microstructure evolution during hot deformation.The kinetic condition critical for dynamic recrystallization,considering the effects of the deformation temperature and strain rate,was obtained by employing both the Poliak-Jonas criterion and Zener-Hollomon parameter.Microstructure observations indicate that the recrystallized volume fraction increases with decreasing Z parameter at constant strain,which is consistent with the predicted kinetics model.Based on the developed model,a good correlation was also obtained between the predicted and experimental flow stress.The results indicate a good predictability of the model in describing the hot deformation behavior and microstructure evolution of AZ80 magnesium alloy.