Effect of extrusion deformation on microstructural evolution and stability of high-temperature mechanical properties of Mg-Gd-Y-Zn-Zr alloy containing SFs

This study systematically investigates the evolution behavior and strengthening mechanisms of stacking fault (SFs) in the Mg-7Gd-3Y-1Zn-0.5Zr (VW73B) alloy during hot deformation and aging. It further examines the relationship between these structures and the alloy’s high-temperature stability, under the condition that no block-shaped Long-Period Stacking Ordered (LPSO) phase is present. The results show that after hot extrusion, two typical types of SFs form within the grains. These include SFs in fine dynamically recrystallized grains and kinked SFs in deformed grains. The kinking of SFs occurs mainly during the second stage of extrusion deformation. The yield strength(YS), ultimate tensile strength(UTS), and elongation of the as-extruded alloy are 275.5MPa, 365MPa, and 14%, respectively. Calculations of strengthening contributions reveal that grain boundary strengthening and solid solution strengthening play the most significant roles in enhancing the alloy strength. The peak-aged VW73B alloy exhibits excellent high-temperature mechanical properties. After tensile testing at 250°C under different holding times, the mechanical properties show no significant fluctuation, which is mainly attributed to the mutual constraint between the SFs and the β' phase in the alloy, jointly hindering each other’s growth. Furthermore, this study elucidates the underlying mechanism by which the β' phase impedes the growth of SFs from a stress-field perspective.