Microstructures and mechanical properties of friction stir welded and processed high entropy alloys

High entropy alloys (HEAs) have recently attracted significant attention due to their exceptional mechanical properties and potential applications across various fields. Friction stir welding and processing (FSW/P), as notable solid-state welding and processing techniques, have been proved effectiveness in enhancing microstructures and mechanical properties of HEAs. This review article summarizes the current status of FSW/P of HEAs. The welding materials and conditions used for FSW/P in HEAs are reviewed and discussed. The effects of FSW/P on the evolutions of grain structure, texture, dislocation, and secondary phase for different HEAs are highlighted. Furthermore, the influences of FSW/P on the mechanical properties of various HEAs are analyzed. Finally, potential applications, challenges, and future directions of FSW/P in HEAs are forecasted. Overall, FSW/P enable to refine grains of HEAs through dynamic recrystallization and to activate diverse deformation mechanisms of HEAs through tailoring phase structures, thereby significantly improving the strength, hardness, and ductility of both single- and dual-phase HEAs. Future progress in this field will rely on comprehensive optimization of processing parameters and alloy composition, integration of multi-scale modeling with advanced characterization for in-depth exploration of microstructural mechanisms, systematic evaluation of functional properties, and effective bridging of the gap between laboratory research and industrial application. The review aims to provide an overview of recent advancements in the FSW/P of HEAs and encourage further research in this area.