Refilling Probe Hole of Friction Spot Joints by Friction Forming

Friction stir spot welding (FSSpW) is a variant of friction stir welding (FSW) that has wider industrial application. However, Probe hole left after the welding is the main limitation of their process. In this present study, modified FSSpW has been developed and the refilling is achieved by friction forming process. This process has been called Friction Stir Spot Welding with refilling by Friction Forming Process (FSSpW-FFP). The Aluminum alloy (AA 6061-T6) plates are welded in two stages. Welding and refilling are achieved in first and second stages, respectively. Mechanical and metallurgical properties of the joints are studied and compared with welds made by FSSpW. The mechanical properties studied in the present work are tensile shear strength and microhardness. Macro-and microstructures of weld joints are compared and analyzed. The mechanical and metallurgical properties of the joints made by FSSpW-FFP are found to be better than the joints made by FSSpW. The tensile shear strength of the joint with refilled hole is higher than that of the joint with probe hole. The refilling process increases effective cross-sectional area of the nugget, resulting in higher tensile shear strength and joint efficiency at medium and high tool rotational speeds. After experiment, fracture surfaces are analyzed in detail using scanning electron microscope (SEM). The pull out of the nugget, i. e., plug type fracture, occurs in the joint with refilled probe hole, while shear fracture through the nugget is observed in the joint with probe hole.