Effect of the shoulder size and dwell time on the static Strength and fracture mode of projection friction stir spot welded 2024 aluminum alloy

Automotive industry has developed a variant of the Friction Stir Welding named Friction Stir Spot Welding (FSSW), to replace resistance spot welding (RSW) for aluminum sheets. It is claimed that the use of energy and the investment cost are decreased with using of friction stir spot welding in comparison with resistance spot welding. However, one of the disadvantages of FSSW technique is that a keyhole generally remains at the center of the stir zone. Keyhole defect can reduce the mechanical properties of FSSW joints. A novel friction stir spot welding technique was developed with the purpose to improve the mechanical property of the joints by removing the keyhole. This novel FSSW method was applied to 2024 Al alloy sheets, 1 mm in thickness, under different shoulder size and dwell times. The effect of shoulder size and dwell time on the mechanical properties of the spot joints has been studied. Studies show that this new spot welding technique can produce a defect-free metallurgical bond with a homogenous fine grain microstructure. The welding parameters variations change the bonding area, depth stir zone, upper sheet thickness, grain size and mechanical properties of the welds.