Microstructure, Texture, and Superplasticity of a Fine-Grained Mg-Gd-Zr Alloy Processed by Equal-Channel Angular Pressing

There are limited reports to date on the microstructure and superplasticity of the Mg-Gd alloys after processing by equal-channel angular pressing (ECAP). Accordingly, the effects of ECAP temperature from 473 K to 723 K (200 °C to 450 °C) and number of passes (2, 4, and 8) on the microstructure and texture of an extruded Mg-5Gd-0.4Zr (GW50) alloy were investigated by scanning electron microscope, transmission electron microscope, and electron backscattered diffraction. The results show that the optimum ECAP temperature is 623 K (350 °C). Higher temperatures give extensive grain growth and the material has insufficient formability at lower temperatures. The results show also that the alloy exhibits no further grain refinement after four ECAP passes and there is slight grain growth at 8 ECAP passes. Samples were processed by four passes at 623 K (350 °C) and then subjected to shear punch testing. The results confirm the occurrence of superplastic behavior at 723 K (450 °C) with a maximum strain rate sensitivity index of ~0.47 and an activation energy of ~110 kJ mol⁻¹. The results are consistent with the occurrence of flow by grain boundary sliding in the superplastic region.