Enhanced superplasticity in friction stir processed Mg–Gd–Y–Zr alloy

Fine-grained supersaturated Mg–10Gd–3Y–0.5Zr (GW103) alloy with predominant high-angle grain boundaries (HAGB) was prepared by friction stir processing (FSP). The FSP GW103 alloy was subjected to superplastic investigation at a small temperature range of 400–425 °C. Fine β-Mg5(Gd,Y) particles precipitated at the grain boundaries during heating before superplastic deformation, and their volume fraction decreased significantly with increasing the temperature from 400 to 425 °C. Superplasticity of the FSP GW103 alloy was sensitive to the testing temperature, and a maximum superplasticity of 1110% was achieved at 1 × 10−3 s−1 and a medium temperature of 415 °C. Grain boundary sliding was identified as the main deformation mechanism in FSP GW103 alloy. The high superplasticity is attributed to the fine grains, high percentage of HAGBs, and a moderate volume fraction of β particles that precipitated at 415 °C.

► Fine-grained supersaturated Mg–Gd–Y–Zr alloy was prepared by friction stir processing. ► Fine Mg5(Gd,Y) particles precipitated during heating before superplastic deformation. ► Particle number decreased significantly with increasing temperature from 400 to 425 oC. ► Superplasticity was highly sensitive to temperature. ► Maximum superplasticity of 1110% was achieved at 415 oC and 1 × 10−3 s−1.