Review of tool geometry in the processing of aluminum alloys by FSW

The tool pin design of the Friction Stir Welding (FSW) tool is important for the generation of heat, plasticization and flow of material. The stirring of the tool pin between the tool-workpiece material has a considerable impact on the evolution of grain size, the formation of weld defects and the overall strength of the weld joint. This study presents a detailed examination of various tool pin geometries such as cylindrical, cylindrical threaded, tapered cylindrical, taper threaded cylindrical, tri-flute and polygonal tools and their implications on mechanical properties and microstructural evolution for producing defect-free joints. The rationale behind this study is to consolidate scattered research for AA6061-T651 materials and to identify the impact of different tool pin geometries in relation with process variables. Also, need for optimization and standardization of various process variables relative to the tool pin geometry to achieve a high-strength joint is discussed to address various industrial applications. Various research gaps specifically in numerical modeling, process control optimization, effect of pulsating action in polygonal tools, plunge force monitoring, heat input characterization, etc are identified that will further promote FSW developments, ensuring their increased usage with enhanced efficiency, reliability and sustainability.