Effect of storage parameters and surface state on the ultrasonic welding behavior and mechanical properties of aluminum stranded wires

Abstract Ultrasonic metal welding is a solid-state joining technique widely used in electrical and electronics manufacturing, including aluminum wire connections for modern vehicles. Throughout production, transport, and storage, aluminum stranded wires are exposed to possible contamination and progressive surface oxidation, both of which can adversely affect the wire quality and, consequently, the quality of the welds. This study focuses on the influence of surface impurities and oxide-layer characteristics on the USMW performance of aluminum stranded wires. To isolate key variables, the wires were subjected to controlled storage environments with varying temperature, relative humidity, and storage duration. Despite differences in these storage parameters, all joints after USMW met the mechanical performance requirements specified in the relevant DIN standard. However, weldability and the magnitude of property degradation still varied markedly depending on the storage environment. The results of welding combined with advanced XPS surface analysis and laser vibrometry investigations show that storage humidity is the primary factor governing the surface state of the wires as well as post-weld properties, underscoring the need for strict environmental control prior to welding. A further key parameter is the condition of the native oxide film on each strand’s surface immediately after wire production.