Laser-based surface pretreatment for ultrasonic metal welding of copper and dissimilar aluminium-copper joints

Abstract Ultrasonic metal welding (USMW) is a widely used solid-state welding process for electrical components. Despite careful dimensioning, defective welds occur due to the large number of influencing variables, which sometimes remain undetected by existing monitoring strategies. One known major influencing factor is the surface condition of the components to be welded, which is controlled in industrial applications using mostly chemical or mechanical cleaning methods. Existing surface-based mechanisms in USMW are insufficiently described in the literature or contradict each other, so that corresponding cleaning methods are usually developed on an application-specific basis. To further complicate efforts to define an optimal process, the surfaces of the materials used are usually only standardized in general terms, but not for USMW. This work, therefore, investigates the suitability of the surfaces of commonly used copper and aluminium materials for USMW and then defines an optimal state. Based on this, a nanosecond-pulsed laser process is developed that best meets these requirements. In addition, the potential of optimizing the welding process of copper joints to the laser-treated surface condition to achieve a robust overall process chain and transfer the results to the specific requirements of aluminum-copper joints is demonstrated. The welded joints are characterized in detail mechanically, electrically and metallographically in order to quantify the surface influence on the welding result.