High-power ultrasonic spot welding of copper to type 304L austenitic stainless steel

The demand for a robust welding technique capable of joining copper and steel is driven by their extensive application across various industrial sectors. Addressing the limitations of current welding methods, this study explores the effectiveness of ultrasonic welding in joining commercially pure copper to type 304L stainless steel. The effects of different welding parameters on the characteristics of the welded joints were investigated. The results demonstrate the successful welding of the two metals without inserting an interlayer despite the metallurgical immiscibility of copper and iron. The interfacial bond density and the joint strength were found to increase with the applied welding energy. A joint strength of approximately 80% of the base copper strength was obtained. Transmission electron microscopy (TEM) analysis unveiled a well-bonded interface with excellent continuity between the two metals. A diffusion layer containing nano-sized chromium-rich oxide or intermetallic compound particles was observed. It was noticed that copper penetrated the partially disrupted chromium-rich oxide layer reaching and developing intimate contact with the newly uncoated stainless steel surface. A synergy of mechanical interlocking and solid-state metallurgical adhesion was revealed for the bonding mechanism in addition to potential metallurgical interactions at the interface.