Intermediate layer characterization and fracture behavior of laser-welded copper/aluminum metal joints

• Laser welding of Cu to Al alloy in the overlap form was performed.
• Heterogeneous interfacial zones formed in the intermediate layer of the joint.
• Intermetallic compounds and phase distribution in the different zones were characterized.
• Relationship between the thickness of zones and mechanical properties was defined with the gray theory.
• γ2-Cu9Al4 and θ-CuAl2 exerted a great influence on the mechanical properties.

Copper and aluminum were welded using a continuous Nd:YAG laser, and the influence of the processing parameters on the intermediate layer was investigated. The intermediate layer along the interface was characterized, and the failure mechanism was identified. Four distinct zones with various intermetallic compounds and structures formed in the intermediate layer and determined the corresponding joint strength. Utilizing gradually increasing heat input produced different thicknesses for these four zones. A laser beam power of 1650 W and a welding speed of 95 mm/s were the optimized parameters. The thickness of the intermetallic compound γ2-Cu9Al4 and the shear–tensile strength of the joint decreased with the increase of welding speed in the weld. The shear–tensile load of the dissimilar metal joint reached 539.52 N with the optimized parameters. Fracture during shear–tensile testing occurred in the zone with 20.08–54.65% Cu. It was concluded that eutectic and hypoeutectic structures containing a significant amount of θ-CuAl2 led to a weak joint. The relationship between the mechanical properties and thickness of the different intermediate zones is thoroughly illustrated.