Field fluctuations viscoplastic self-consistent crystal plasticity extended for modeling of hexagonal metals: Applications to deformation and recrystallization of alloy AZ31

Abstract

In this paper, a recently developed field-fluctuations viscoplastic self-consistent (FF-VPSC) polycrystal plasticity formulation for cubic metals incorporating grain fragmentation and recrystallization models is extended to the modeling of hexagonal metals. The extended FF-VPSC model calculates the second moments of lattice rotation rates based on the second moments of stress fields and resulting intragranular misorientation distributions not only inside grains but also inside twins. The novel model retains a temperature-sensitive dislocation density-based hardening law along with an advanced composite grain model for handling primary and secondary twinning at the grain level. The model is used to interpret and predict the mechanical response and texture evolution during deformation and dynamic recrystallization of magnesium alloy AZ31 in simple tension at temperatures ranging from room temperature to 200°C at a quasi-static strain rate. To study the role of deformation mechanisms on recrystallization kinetics, the alloy was pulled along the normal direction (ND), transverse direction (TD), and 45° direction between ND and the rolling direction (RD). Taking the experimentally measured initial texture and grain size as inputs, the model was successfully calibrated and validated to capture the evolution of thermo-mechanical response, texture, and twin volume fraction from room temperature to the dynamic recrystallization regime at 200°C. The differences in the response amongst the loading directions were successfully predicted owing to the extent of dynamic recrystallization and varying relative activities of slip and twinning modes, which the model internally adjusts based on slip and twin resistances evolving with the imposed loading conditions and temperature.