The objective is to firmly join aluminum and copper parts, which cannot be welded with conventional techniques. The welds need to be mechanically strong and simultaneously have a high electrical conductivity. The welding process needs to be robust. A particular project calls for joining sheet metal like materials.
Friction stir welding (FSW) is a mechanical joining process bonding materials in their solid phases. IWS engineers expanded the method with respect to process control and tool geometry to enable the joining of dissimilar metals. The process does not melt the materials and thus mostly avoids the formation of undesired intermetallic phases.
The rotating FSW tool applies pressure onto the material surface in the welding region via a so-called shoulder. The material is plastified due to friction-induced heat. A pin is immersed into the material to regulate the material flow. The process forms a fine-grained and thermo-mechanically solidified high strength seam structure. Sheet and strip shaped parts can be connected forming butt and overlap joints.
Internal tests showed the possibilities of joining of aluminum and copper parts of various alloys and geometries. Tensile tests of optimized welds demonstrated that breakage generally occurred within the mechanically weaker aluminum.
The welding zone is completely different compared other joining processes for dissimilar metals. All melt and solder based processes show a very typical continuous transition zone between the two materials. Friction stir welding does not create such a zone since both materials are simultaneously deformed and kneaded. This is advantageous for properties such as electrical conductivity, which suffers in other processes as a consequence of a low conductive intermetallic interface region.
Fraunhofer Institute for Material and Beam Technology IWS