Kinetics Model for Dynamic Recrystallization of 7075 Aluminum Alloy in Thermoplastic Deformation

The true stress-true strain curves of as-cast 7075 aluminum alloy were achieved through a series of isothermal upsetting experiments in the temperature range of 573-723 K, and the strain rate range of 0.01-10 s-1. Based on the analysis of hardened rate curves, it was uncovered that the flow stress curves of the alloy had three characteristic points including the critical strain for dynamic recrystallization, the strain for peak stress and the strain for maximum softening rate. Some main parameters such as the activation energy of dynamic recrystallization, were obtained by solving hyperbolic sine equation. The evolution of dynamic recrystallization amount during thermoplastic deformation was described. And a dimensionless intermediate variable Z/A was designed to build a dynamic coupled model between deformation temperature, strain rate, strain and dynamic recrystallization volume fraction. The results show that as the strain increased, the dynamic recrystallization volume fraction increased gradually until to 100%, in addition, with the increase of the strain rate or decreased of deformation temperature, the dynamic recrystallization would be restrained.