Exploring a novel chamfered tool design for short duration refill friction stir spot welds of high strength aluminium

This work investigates refll friction stir spot welded joints of AA2024-T3 aluminium alloy, produced with short welding times
between 3 s and 0.75 s. A novel tool geometry that incorporates a chamfer on the inner edge of the shoulder tip is investigated
as a means of improving joint quality at short welding times by easing material fow during the refll stage. The infuence of shoulder design on weld microstructure, defect formation, material fow, and mechanical properties was assessed. When compared with a standard shoulder geometry, it was found that the introduction of a chamfer on the inner tip edge improved material fow during the refll stage and led to improved material mixing at the weld periphery. The formation of voids in the region of the weld periphery was eliminated and tensile lap-shear strength of the welded joints was increased by 19% to 7.2 kN, and 27% to 8.16 kN, for 0.75 s and 1.5 s duration welds, respectively.