Microstructure and properties of resistance spot welded Al/Cu joint with an interlayer of zinc

Aluminum and copper plates were joined using resistance spot welding with a zinc interlayer. The interfacial microstructure of the weld joint was examined, and the electrical resistance and tensile shear strength of the joints were evaluated. At the welding interface zone of the joint, an Al₂Cu layer was formed adjacent to the copper side, while a eutectic structure layer composed of Al₂Cu and α-Al was observed near the nugget on the aluminum side. The electrical resistance value of the joints remained relatively stable with variations in welding current and welding time, maintaining an approximate value of 112 µΩ. As the welding current increased or the welding time was extended, the tensile shear load of the joint exhibited a trend of initial increase followed by a subsequent decrease. The maximum tensile shear load, approximately 4.23 kN, was achieved when the welding current was set to 28 kA and the welding time was maintained at 400 ms. The results indicate that the application of a zinc interlayer in the resistance spot welding of aluminum and copper facilitates the formation of larger nuggets through low-temperature eutectic liquefaction within the zinc-aluminum system, consequently improving the joint performance.