Study on the effect of solution treatment on hot deformation behavior and workability of Mg-7Gd-5Y-0.6Zn-0.8Zr magnesium alloy

The effect of solution treatment on hot deformation behavior and workability of Mg-7Gd-5Y-0.6Zn-0.8Zr alloy has been studied by isothermal compression test in the temperature range from 350 °C to 500 °C and the strain rate range from 0.001s−1 to 1s−1. The precipitation of LPSO phases inside the deformation grains of solution treated alloy increased when the strain rate reduced (≤0.01s−1 in particular), and decreased when the deformation temperature rose beyond 475 °C. The precipitation of LPSO phases and existence of stacking faults hindered the growth of dynamically recrystallized grains and caused insufficient DRX. After solution treatment, the deformation activation energy increased by 34.65KJ/mol compared to the as-cast alloy due to increased solute amount of REs in the Mg matrix. Besides, solution treatment narrowed the flow instability region of Mg-7Gd-5Y-0.6Zn-0.8Zr alloy at low temperature and high strain rate due to more homogenous deformation, but weakened the hot working ability at high temperature due to higher sensitivity of deformation microstructure to temperature. The processing maps of as-cast and solution treated alloy exhibited two similar dynamic recrystallization (DRX) regions, i.e. Region I (390-440 °C, 0.001-0.01s−1) and Region II (440-465 °C, 0.01-0.1s−1). Besides, the as-cast alloy possessed a wider workability region (Region III: 465-500 °C and 0.03-1s−1) than the solution treated alloy (Region III: 465-490 °C and 0.3-1s−1) at high temperature.