Microstructural and mechanical properties of friction-stir-welded and post-heat-treated Inconel 718 alloy

This study was performed to investigate the microstructural and mechanical properties of friction-stir-welded and post-heat-treated Inconel 718 alloy. Friction stir welding (FSW) was performed at a rotation speed of 200 rpm and welding speed of 150 mm/min; heat treatment was performed after welding at 720 °C for 8 h in vacuum. As a result, the grain size due to FSW was significantly refined from 5 to 20 μm in the base material to 1–3 μm in the stir zone; this was accompanied by dynamic recrystallization, which resulted in enhancements in the mechanical properties as compared to the base material. In particular, applying heat treatment after FSW led to improvements in the mechanical properties of the welds—the microhardness and tensile strength increased by more than 50% and 40%, respectively, as compared to FSW alone.