Flow softening behavior during high temperature deformation of AZ31Mg alloy

In the present study, the flow softening behavior occurring during high temperature deformation of AZ31 Mg alloy was investigated. Flow softening of AZ31 Mg alloy was considered to arise mainly due to thermal softening by deformation heating and microstructural softening by dynamic recrystallization (DRX). Artificial neural networks method was used to derive the accurate amounts of thermal softening by deformation heating. To quantify the microstructural softening, a series of mechanical tests (high temperature compressions and load relaxation tests) were conducted at various temperatures (250–500 °C) and strain rates (10−4–102/s). To verify the proposed formulations, the hot-forging of AZ31 Mg alloy was conducted at the condition of 250 °C, 0.5/s (optimum DRX condition) with the 970 tonnes press. The Finite Element Method (FEM) was also used to simulate the hot-forging of AZ31 Mg alloy using identical conditions as experimental ones. The effect of DRX kinetics on microstructure evolution (fraction of recrystallization and recrystallized grain sizes) was implemented in a commercial FEM code followed by remapping of the state variables of temperatures, strain rates and strains. The predicted grain sizes and fractions of DRX showed good agreement with experimental results.