Characterization and Optimization of Flat Friction Stir Spot Welding of Triple Sheet Dissimilar Aluminium Alloy Joints

The method of flat friction stir spot welding (FFSSW) was used to investigate the tensile behavior of three thin dissimilar aluminium alloys (Two sheets of AA6082-T6 and one sheet of AA6061-T6). Tool with probe and a probe less tool is used in this two-step process of joining. Experiments were conducted at various tool tilt angles (TTA), tool rotational speeds (TRS), dwell time (DT) and Tool plunge depths (TPD). The quality welds were produced at optimized process parameters (TTA 2(0), TRS 2125 rpm, DT 15 s and TPD 0.1 mm). Elimination of protuberance and reduction of keyhole in the joint is achieved for improving bonding length. Micrographs of joints were examined using optical microscopy and scanning electron microscopy (SEM). The complete bonding with finer grains at stir zone (SZ) improved the strength of FFSSW joint. Energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis of specimen indicates the presence of Mg2Si precipitates in SZ. The fracture behavior of upper and lower interfaces was examined. The finer dimples are observed in fractograph, which confirm the ductile behaviour of fracture. The morphology at tool surfaces was also studied. The mechanical properties of three-sheet FFSSW joints were compared with other similar techniques of joining. Better understanding of mechanical properties and weld behavior of three sheets FFSSW is done with the help of fractography and SEM.