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Friction stir spot welding (FSSW) is a spot-like solid-state joining process suitable for welding structural components in overlap configuration. In the past few years, the use of conventional spot welding in automotive applications has become more complex due to the extensive use of lightweight alloys. FSSW has a potential to replace these conventional methods as well as to reduce manufacturing steps and lower overall costs. In FSSW the tool is not traversed and instead creates the joint by plunging into and retracting out a rotating tool of the overlapping sheets. FSSW has been performed in two different aluminium alloys - AA5754-H22 and AA6082-T6 in similar and dissimilar combination using different joining parameters (e.g. plunge rate, rotational speed and plunge depth). FSSW connections have been accomplished using same tool geometry - cylindrical 3 flute pin and flat shoulder. Mechanical behaviour has been investigated in terms of hardness, cross-tension and tensile shear.

Friction Spot Welding – FSpW, also known, as Refill Friction Spot Welding is a new solid-state spot process developed by GKSS, exhibiting as one of the main advantages, no key-hole on the surface of the material after the completion of the process. In the present work FSpW has been performed in 2 mm-thick Alclad AA2024-T3 varying tool rotational speeds, sleeve plunge depths in lower sheet and plunge rates. Mechanical properties of the connections have been investigated in terms of hardness and shear testing. The fracture mechanisms were observed by SEM and the microstructural features by OM. The results have demonstrated that the optimum tool rotational speed is dependent on the other welding parameters as plunge rate and plunge depth. Plunge depths of around 25% (0.5 mm) of bottom plate thickness have proved to be adequate to reach a good mechanical performance of the connections.