High temperature mechanical properties and strain hardening mechanism of directionally solidified Mg-Gd-Y alloy

The Mg-6.0Gd-0.5Y alloy, with straight grain boundaries and preferred growth orientation [22$4(\_)$3], was prepared by directional solidification. The microstructure evolution during tensile tests at 150–350 °C was investigated using Electron Back-Scattered Diffraction (EBSD) and High-Resolution Transmission Electron Microscopy (HRTEM). Subsequently, the relationship between the deformation mechanism and mechanical properties was discussed. The results show that there are obvious uniform plastic deformation stage and work hardening stage after yield for the tensile stress-strain curves of the Mg-6.0Gd-0.5Y samples tested at 150°C–250 °C, while evident dynamic recrystallization characteristic can be observed for the curve of the sample tested at 350 °C. It is found that the stable high-temperature strength of the Mg-6.0Gd-0.5Y alloy can be attributed to the delayed dynamic recrystallization, the formation of compression twins and I1-type stacking faults. In addition, the superior plasticity of the alloy is related to the high concentration of crystal orientation, the activation of tensile twins, and non-basal slip which can provide more than 5 independent systems.