Shunt current-assisted one-step resistance element welding of vibration-damping aluminum to ultra-high-strength hot-press-formed steel

Abstract

To satisfy recent demands for reducing NVH (noise, vibration, harshness), vehicle weight, and improving collision safety, the development of reliable processes for dissimilar joining of lightweight vibration-damping aluminum to ultra-high strength steels is required. The resistance element welding (REW) process to join the dissimilar material involves a two-step process of pre-drilling a hole in the aluminum to insert the element and then welding to join the element to steel. Consequently, this increases cycle time and makes it challenging to ensure joint quality due to potential robot teaching errors. To overcome these limitations, an innovative one-step REW process was proposed to shorten the two-step REW process into a single process. However, the thermoplastic resin layer at the interface of the vibration-damping aluminum limits current conduction, posing challenges for REW. The current study introduces stainless-steel clips to bypass the thermoplastic resin layer between the vibration-damping aluminum, which limits the current conduction during the one-step REW process. The adjacent REW joint ensures further bypass of the current and acts as an initial weld point (shunt weld) for continuous one-step REW. Optimization of the welding variables was carried out to achieve excellent joint performance in terms of joint formation. Subsequently, the quality evaluation of the joint was done based on the evaluation of microstructure and mechanical properties. This process significantly enhances productivity with one-step REW instead of the traditional two-step welding. It surpasses the difficulty of welding the vibration-damping aluminum to HPF (hot press forming) steel.