Effects of Heat Input on the Intermetallic Compounds and Mechanical Properties of Al/Cu Joints Fabricated by Micro Friction Stir Welding

The 0.5 mm thickness ultra-thin sheets of 6061-T4 Al and T2 Cu were butt joined by micro friction stir welding under different ω/ν. When the ω/ν was 36, the welding process resulted in a defect-free joint. This joint exhibited the highest tensile strength (222 Mpa), which was similar to the Al BM. This joint failed in the heat-affected zone on the Al side, where the hardness was lowest, leading to a ductile fracture. When the ω/ν was 9, the welding process led to the formation of agglomerated intermetallic compounds (IMCs) in upper nugget zone (NZ), and the IMCs layer of Al2Cu and Al4Cu9 developed in lower NZ. Therefore, the joint strength was greatly weakened, resulting in failure at the Al/Cu interface. The fracture mode of the joint exhibited a mixture of ductile and brittle behaviors.