Effect of thermo-mechanical processing parameters on the dynamic restoration mechanism in an Mg-4Y-2Nd-1Sm-0.5Zr alloy during hot compression

Abstract

Microstructure evolution and dynamic restoration mechanism of solution-treated Mg-4Y-2Nd-1Sm-0.5Zr alloy have been studied under three TMP parameters consisting of deformation temperatures (350–500 °C), strain rates (0.01–5 s−1), and strains (0.2, 0.4, and 0.8). A strong dynamic softening is observed in all stress-strain curves, even at higher strain rates (1 and 5 s−1) due to an adiabatic heating effect. Various stress-strain curves are applied to construct a processing map and develop an Arrhenius-type constitutive equation. With the prediction of the processing map, an optimal processing domain has been determined to be the temperature range 450–500 °C and strain rate range 0.01–0.1 s−1 at a strain of 0.8. The volume fraction of DRX grains is the largest in the corresponding domain of high temperature and low strain rate. For the effect of TMP parameters on the dynamic restoration, the discontinuous dynamic recrystallization (DDRX) and continuous DRX (CDRX) synergistic effect occur throughout the whole process at high temperature and high strain rate. In terms of high temperature and low strain rate, DDRX characteristics at a low strain and then the DDRX + CDRX synergistic effect is observed at a higher strain. Although the DRX process is weak at low temperature and low strain rate, deformation twins have occurred and provided nucleation sites for DRX grains.