Microstructure characterization and mechanical properties of laser-welded copper and aluminum lap joint

The microstructure in the intermediate layer of a laser-welded Cu–Al lap joint was examined metallographically. Tensile shear test was performed, and fracture surface analysis was also performed using scanning electron microscopy with energy dispersive spectroscopy. Results showed that there were several different zones with diverse characteristics of morphology and composition in the intermediate layer of the weld joint. Banded and cellular structures were observed in the hypereutectic zone; a lamellar structure was found in the eutectic zone which was the narrowest zone with the finest microstructure; a dendritic structure was obtained in the hypoeutectic zone with the coarsest microstructure and widest zone. The joint faulted in the dendritic hypoeutectic zone, under a combination of brittle and shear mode in the fracture surface. The maximum shear load of the Cu–Al joint decreased with increasing primary dendrite arm spacing and the growth of secondary dendrite in the hypoeutectic zone, which was induced by increasing laser power.