Modeling of Flow Stress and Grain Size Based on Z Parameter and Material Constants of Al-5.2Mg-0.6Mn Alloy during Hot Deformation

Abstract

The flow stress curves of Al-5.2Mg-0.6Mn alloy were tested by isothermal compression method with Gleeble-1500 thermal simulator at the temperatures of 300, 350, 400, 450 and 500°C with strain rate of 0.001, 0.01, 0.1 and 1s-1, respectively. The morphologies of grains deformed were analyzed by TEM. Four material constants including structural factor (A), stress exponential (n), stress multiplier (α) and average activation energy (Q) of the alloy were calculated by linear regression processing. The models of flow stress (σ) and grain size (d) based on Zener-Hollomon parameter (Z) and the constants were established. The results show that the values of A, n, α, Q of the alloy were equal to 3.058×109s-1, 3.314, 0.0184 mm2N-1, 160.94 kJmol-1 respectively, and the models of flow stress and average sub-grains size can be described as σ=54.31ln {(0.327×10-9Z)0.302 +[(0.327×10-9Z)0.604+1]0.5} and d=(0.045lnZ-0.675)-1, respectively. The flow stress appreciably reduced but average grain size increased with decreasing Z value. The conditions of dynamic recrystallization occurring for the alloy were the temperature above or equal to 350°C and lnZ below or equal to 24.47.