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.

Nonuniform-to-uniform structural transitions induced by ultrasonic vibrations

“…On the atomic scale, molecular dynamics (MD) simulations have exerted attention on the atomic and strain-energy distributions at Al/Al, Cu/Al, Cu/Cu and Ti/Al interfaces joined via an UV-assisted method, 27–35 giving insights into the effect of UVs on the structural evolution of joints. However, there are still no direct images capturing atomic-scale motions of dislocations which, together with atomic diffusion, are involved and essential in material flow and plastic deformation in Mg/Al UVeFSW processes.…”

“…Computer simulations can therefore be an effective tool for probing relative problems. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Wu's group [20][21][22][23][24] employed the computational fluid dynamics method and proposed novel constitutive models to investigate the action of UVs on material flow. Their models are based on the Eulerian formulation where materials are treated as non-Newtonian fluids with high viscosity, together with the consideration of the acoustic softening effect.…”

“…However, their numerical investigations focused on the dynamic processes occurring at a large scale (a few millimeters), and lack of motion profiles of dislocations on an atomic scale, even though their measurement of flow stress consists of the plastic-deformation term which is established based on the motions of dislocations. 25,26 On the atomic scale, molecular dynamics (MD) simulations have exerted attention on the atomic and strain-energy distributions at Al/Al, Cu/Al, Cu/Cu and Ti/Al interfaces joined via an UV-assisted method, [27][28][29][30][31][32][33][34][35] giving insights into the effect of UVs on the structural evolution of joints. However, there are still no direct images capturing atomic-scale motions of dislocations which, together with atomic diffusion, are involved and essential in material flow and plastic deformation in Mg/ Al UVeFSW processes.…”

Molecular dynamics simulations of TC4 titanium alloy with mechanical property calculations after various heat treatments

“…10 Mostafavi et al studied interface atomic diffusion in ultrasonic metal welding using MD simulations. 11 Regarding defects, the crack growth in pure titanium under uniaxial tension 12 was studied, along with fatigue crack propagation in hexagonal close packed (HCP) titanium crystals. 13 Wang et al reported the important impact of temperature on intergranular crack propagation in pure a-Ti.…”

“…10 Mostafavi et al studied interface atomic diffusion in ultrasonic metal welding using MD simulations. 11…”