Effects of heat input on the intermetallic compounds and mechanical properties of Al/Cu joints fabricated by micro friction stir welding

Abstract

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.