Tool geometry optimization in friction stir spot welding of Al-steel joints

The necessity to reduce the weight of transport structures, such as cars and airplanes, has become more important due to gas emission regulations. In this regard, the use of hybrid structures made of steel and aluminum is a way to achieve this goal. Joining aluminum to steel is a great challenge and Friction Stir Spot Welding (FSSW) has become as a new potential welding technique to produce dissimilar joints. Despite Friction Stir Welding has been studied on different similar joints, the information related to the influence of FSSW parameters on the evolution of aluminum-steel joints is scarce. So, the effect of the tool geometry and its penetration depth during FSSW of AA5052-LCS (Low Carbon Steel) joints, has been studied. During FSSW, axial load and consumed electrical current were recorded in order to improve the understanding of the welding process. Macro and microstructural characterization was done on the cross section of the welded spots. The mechanical properties of the joints were determined by microhardness profiles and by Peel and Cross Tension tests. The fracture loads increased when the tool penetration depth goes up. The tool geometry optimization also increased the fracture loads.