Investigation on interface morphology and joint configuration of dissimilar sheet thickness FSSW of marine grade Al alloy

Abstract

Aim of this study is to investigate the interface morphology and joint configuration of dissimilar thickness aluminium alloy 5052-H32 sheets during friction stir spot welding. The investigation begins with the optimization of two important process parameters, viz. tool rpm and dwell time, from welding of similar thickness sheets. Further, different combinations of sheet thicknesses were welded using the optimized parameters. Effect of altering sheet thickness on the mechanical and structural properties were compared with welds of similar sheet thickness. For similar thickness welds, maximum failure load of 4020 N was noted at minimum tool rotational speed of 450 rpm and maximum dwell time of 8 s. The obtained weld zones revealed the presence of hook which was found to vary in its pattern and location for different combinations of sheet thicknesses. Minimum hardness of 63 HV was obtained in the periphery of the thermo-mechanically affected zone and heat-affected zone. In addition, welds with thinner top sheets showed higher load-bearing capacity and wider bonded area as compared to thicker and equal thickness top sheet welds. The maximum failure load of 7160 N was obtained for 1.5 and 2.5-mm-thick top and bottom sheets, respectively. Moreover, three fracture modes were observed in tensile/shear tests, namely interfacial, circumferential and nugget pullout fracture mode. Samples which failed in circumferential and nugget pullout fracture mode showed better joint strength.