Influence of Copper-Sided Tin Coating on the Weldability and Formation of Friction Stir Welded Aluminum-Copper-Joints

Although the joining of aluminum and copper is a difficult task, several studies have shown that friction stir welding (FSW) is capable of producing aluminum-copper-joints with excellent performance. Therefore, it is desirable to use this joining technique for the production of cost- and weight-reduced conductors for the automotive sector. The exposed copper contact spots in automobiles are usually coated with tin for design reasons and in order to improve their corrosion resistance. In this context, it is possible to perform the weld at first and to coat afterwards, or to weld already coated copper workpieces. Taking this into account, this paper presents results on the influence of copper-sided tinning on the joint formation as well as the achievable mechanical and electrical properties of friction stir butt welded aluminum-copper joints. Two variants were considered. The first variant included copper blanks with a tinned surface. For the second variant the surface and the abutting edge of the copper were coated. The best welds achieved excellent electrical properties and their tensile strength was only slightly reduced compared to the aluminum base material. Thus, it was shown that if these tensile strength losses are acceptable, FSW of aluminum to tin coated copper is applicable.