Effect of zinc interlayer on ultrasonic spot welded aluminum-to-copper joints

Dissimilar aluminum (Al) and copper (Cu) metals were joined together using ultrasonic spot welding (USW), a solid state welding technology. The welds were made with and without a zinc (Zn) interlayer to study the microstructural and mechanical properties of weld joints to analyze the effect of the Zn interlayer. USWed Al-to-Cu joints did not produce any intermetallic compounds (IMCs), and only swirls and voids were observed. It was determined through energy dispersive X-ray spectroscopy and X-ray diffraction scans that welds with a Zn interlayer placed in-between the faying surfaces of the base metals formed a composite-like eutectic structure of Al and Al₂Cu at the center and Al–Zn and CuZn₅ at the edges of the welded joint. Al–Cu joints welded with a Zn interlayer in-between displayed lap shear tensile strengths 25–170% greater than those of the welds without any interlayer