Parametric study of FSSW of aluminium alloy 5754 using a pinless tool

A parametric study of friction stir spot welding (FSSW) of lap joints in aluminium alloy 5754 using a pinless tool with scrolled shoulder is presented. Experimental plan was done according to the response surface methodology (RSM), where tool rotation speed varied between 988 and 3511 rev/min, plunge rate between 24.4 and 150 mm/min and dwell time between 1 and 3.5 s. The plunge depth was held constant at 0.4 mm. During welding, the axial force and torque were monitored using a dynamometer. The welds were tensile shear tested, and the broken samples were visually examined. The weld bond line and microstructure were analysed using light optic microscope under polarised light, and SEM was used for examination of fractured surface. Mathematical models describing the relationship between welding parameters and joint strength, axial force and torque were developed. FSSW parameters, at which maximal joint strength was obtained, were considered as optimal. At these welding parameters, the axial force and torque were in the lower range among tested parameters. Material flow and joint formation are experimentally presented and schematically illustrated.