The effect of FeCoNiCrTi on intermetallic compounds at the aluminum/copper dissimilar metal laser welded interface

The laser welding technology of aluminum and copper directly impacts the reliability of electric vehicles. In this study, lap laser welding experiments were conducted on 1 mm-thick 6061 aluminum alloy and T2 copper. The effects of adding the FeCoNiCrTi high-entropy alloy on the fracture morphology, intermetallic compounds (IMCs), and mechanical properties of the weld joints were investigated using field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS). Furthermore, the elastic moduli of the phases formed before and after the addition of FeCoNiCrTi were calculated through first-principles calculations based on density functional theory (DFT). The results show that the tensile strength of the joints with the addition of FeCoNiCrTi was improved, while the microhardness slightly decreased. Additionally, the thickness of the IMC layer reduced from 2.199 μm to 1.027 μm. The newly formed phases exhibit superior shear modulus, Young’s modulus, and bulk modulus compared to those of the joint without FeCoNiCrTi addition, and all were identified as ductile phases. The addition of FeCoNiCrTi also enhances the material strength and crack propagation resistance in the joint region, leading to a transition in the fracture mode of the joint from brittleness to ductility. These findings provide a reliable explanation of the effect of FeCoNiCrTi on the mechanical properties of aluminum/copper welded joints.