Molecular dynamics simulation of atomic diffusion in friction stir spot welded Al to Cu joints

Dissimilar metals joining, especially Aluminum (Al) to copper (Cu), have gained importance in batteries for electric vehicles. Although friction stir spot welding (FSSW) has recently been used for welding dissimilar materials, progress has been very slow toward understanding the effect of temperature on diffusion condition between the two materials with the same FCC crystal structure. The thermo-mechanical modeling has been used to define the trajectory of Al and Cu particles at the weld interface, but it had a limitation to quantified the diffusion coefficient. Hence, the molecular dynamics (MD) study has been used to investigate the atomic interdiffusion of Al and Cu. The transmission electron microscopy results are used to validate the MD simulation outcome to understand the formation of dislocations and intermetallic compounds. The MD results implicated the formation of γ-phase (BCC), i.e., Al4Cu9 IMC toward the Cu side. Further, the In-situ investigation of non-FCC phase formation at FSSW condition has also been studied.