Microstructural and mechanical evolution of a high-entropy superalloy during friction stir welding and post-weld heat treatment

• Pre-weld solution heat treatment suppressed welding defects and improved weldability. • Grain structure evolution was independent of pre-/post-weld heat treatment. • Post-weld heat treatment restored γ′ precipitates uniformly across the weld. • Stir zone exhibited an excellent strength–ductility balance. The effects of pre-weld and post-weld heat treatment on the microstructure and mechanical properties of friction stir welded Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.3 high-entropy superalloy were investigated. Welds were produced using base metals in two pre-weld conditions: artificially aged (AA) and solution heat treated (SHT). Pre-weld AA resulted in tunnel-like defects at the root of the stir zone, whereas pre-weld SHT improved material flow and suppressed defect formation. Electron backscatter diffraction indicated that grain structure evolution during welding was governed by discontinuous recrystallization and was largely independent of the pre-weld condition. During welding, most strengthening precipitates dissolved, leading to local softening in some welds. Subsequent post-weld heat treatment re-precipitated the strengthening phases throughout the welds, resulting in a substantial increase in hardness and tensile strength. After post-weld heat treatment, the welds exhibited nearly identical microstructures and mechanical properties irrespective of the pre-weld condition. These findings demonstrated that SHT was the preferred pre-weld condition, as it improved weldability and process efficiency without compromising the final mechanical performance of the welds.