Numerical simulations on the interfacial diffusion behaviors of friction stir welding Al/Cu laminated composite plate

A 6.5 mm thick aluminum(base) / copper(clad) laminated composite joint was successfully fabricated via friction stir welding (FSW), with the material mixing behavior at the aluminum(Al) / copper(Cu) interface systematically investigated using the Coupled Euler-Lagrange (CEL) method. Molecular dynamics (MD) simulations were employed to elucidate the diffusion mechanisms of intermetallic compounds (IMCs) on the retreating side (RS). Results show that, at a constant welding speed of 150 mm/min, increasing rotational speed enhances Cu concentration near the weld center with pronounced dissimilar metal migration. The RS exhibits less variation in volume fraction profile compared to the advancing side (AS), accompanied by expansion of the Al/Cu stir zone. Maintaining rotational speed at 900 rpm, elevated welding speeds reduce heat generation, leading to insufficient metal plasticization and void formation in the stir zone. Insufficient heat input at 300 mm/min causes severe interface damage, as evidenced by significant fluctuations in the volume fraction curve. MD analysis reveals that elevated temperature at RS promotes atomic interdiffusion at the Al/Cu interface, where Cu demonstrates higher diffusivity in Al lattice than vice versa, attributed to lattice constant mismatch and dissolution enthalpy difference. First-neighbor hopping is identified as the predominant diffusion mechanism for Cu atoms, with shear rate increase further accelerating interfacial diffusion. Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS)-assisted X-ray diffraction (XRD) analysis confirms that excessive IMC growth (primarily Al₂Cu and Al4Cu9 phases) under high heat input induces a heterogeneous thickness distribution and reduces joint integrity.