Investigation of jet and micro-gap discharge in Cu-Al plates EMPW process

•The complete process of the jet and micro-gap discharge have been captured for the first time.•The cause of the micro-gap discharge has been analyzed numerically.•The formation of the potholes on the metal surface can be explained by the micro-discharge. Electromagnetic pulse welding (EMPW) is an environmentally-friendly, fast, and efficient welding technology for dissimilar metals. In this study, a 28 kJ/20 kV EMPW system is designed and developed to carry out the EMPW experiment of welding 1060 aluminum plate and T2 copper plate. The complete process of the jet has been captured during the welding process through an integrated observation system. And a micro-gap discharge is also first discovered during the transient physical process. The results of the scanning electron microscopy (SEM) and the energy dispersive spectrometry (EDS) analysis show that the interface morphologies of the ablation caused by the micro-gap discharge and the EMPW seam are different. A 3D finite element simulation model is established to investigate the cause of the micro-gap discharge in COMSOL Multiphysics. Based on the analysis of the motion behavior of the plate and the distribution of electromagnetic parameters, the simulation results show that the micro-gap discharge may be the result of the fact that the electric field strength is higher than the breakdown strength of air. Thus, the micro-gap discharge can release the energy of the plate. And the site where the micro-gap discharge is released is related to the induced potential difference and the contact pressure. This paper explains the formation of potholes on the welding surface, trying to enrich the study on the transient physical process of the EMPW.