Orthogonal experiments and bonding analysis of ultrasonic welded multi-strand single core copper cables

The join demand for multi-strand single core copper cables in battery packs is increasing vigorously for new energy vehicles. In this paper, the influences of ultrasonic welding parameters on the microstructure, gap fraction and T-peel strength of the copper cable joints were studied systematically by orthogonal experiments. Under the optimum combination of parameters (welding time = 0.8 s, pressure = 4 bar, amplitude = 62.4 mu m), a contact joint with low gap fraction of 2.07% was obtained and the maximum T-peel force reached 432.9 N. The T-peel fracture characterized by dimples indicates that metallurgical bonding was formed between copper wires, rather than simple mechanical interlock. Furthermore, the electron backscattered diffraction (EBSD) technology was used to analyze grain boundary types and texture evolution during ultrasonic welding. After ultrasonic welding, continuous 111 texture and lots of large angle grain boundaries (LAGBs) that composed of high-density dislocations and substructure were found in bonding interfaces of copper wires, which indicates that serious plastic deformation has occurred in bonding region. When interfacial temperature of cables joints provides enough energy for dislocations motion and rearrangement, the dislocations and substructure nucleate and grow into equiaxed grains through the process of copper recrystallization under high interfacial temperature, which promotes the formation of new interfaces between the copper wires.