Modification of long period stacking ordered phase and improvement of mechanical properties of Mg–Gd–Zn–Zr alloy by friction stir processing

•The coarse LPSO phase at grain boundary is modified to smaller size less than 5 μm during FSP.•FSP causes remarkable grain refinement (1.6±0.3 µm).•The β-phases are formed during friction stir processing (FSP).•Enhanced mechanical properties, especially yield strength are obtained after FSP.

The effect of friction stir processing (FSP) on the modification of microstructure and mechanical properties of Mg–14Gd–2.3Zn–0.6Zr (wt%) alloy has been investigated. The coarse long period stacking ordered (LPSO) phase at grain boundary in the alloy was successfully broken into fine particles (~1 µm) due to the complicated deformation beneath the shoulder and around the pin. The grain size was also significantly refined from 23±4 μm to 1.6±0.3 µm through dynamic recrystallization (DRX) during FSP. Yield strength of the FSP sample was increased by ~30% probably due to the grain size and LPSO phase refinement as well as fine precipitation around the LPSO phase while the elongation decreased by ~39% maybe because of the heterogeneous microstructure.