Molecular dynamics simulation of interface atomic diffusion in ultrasonic metal welding

Abstract The formation of a reliable joint between a large number of aluminum strands for battery applications is crucial in automotive industry, especially in the technology of autonomous vehicles. Therefore, in this study, mechanical deformations and diffusion patterns of the mating interface in ultrasonic welding of aluminum were investigated using molecular dynamics simulations. Furthermore, microscopic observations of the joints between aluminum strands from ultrasonic welding illustrating the influence of two process parameters were done. To study the nanomechanics of the joint formation, two aluminum crystallites of different orientations were built. The impact of the sliding velocity and the compression rate of the upper crystal block on the diffusion pattern at the interface of the two crystallites were quantified via the diffusion coefficient. Tensile deformations of several joint configurations were performed to investigate the load-bearing capacity of the solid state bond, taking into account the compression rate, the sliding velocity and the crystallite orientation. The atomic scale simulations revealed that the orientations of the crystallites govern the interface diffusion and the tensile strength of the joint significantly. Furthermore, interface atom diffusion increased with increasing the sliding velocity. Additionally, it was observed that a higher sliding velocity enhances the friction heat generation between the crystallites and significantly increases the interface temperature.