Effects of Lap Configuration on Mechanical Properties and Composition Distribution of Three-layer Overlapped Laser Weldments on Al/Cu Dissimilar Materials

Abstract

Battery cells are connected via bus-bars to meet performance requirements, such as power and capacity, and multiple layers of dissimilar materials functioning as anodes, cathodes, or bus-bars are overlapped and welded together. In laser welding, the formation of brittle intermetallic phases in the weld joint is inevitable and, in turn, deteriorates the mechanical properties. To obtain the desirable joint performance, appropriate welding parameters to avoid intermetallic phase formations and joint designs to release stress concentrations must be obtained. This study investigates the effects of lap configurations and process parameters on the tensile-shear load, T-peel load, and composition distribution when multi-layered joints of dissimilar materials are produced by laser welding. Two layers of 0.4 mm Al sheets were welded with a single 0.2 mm Cu sheet, which was emulated using electric vehicle battery interconnects. The results show that the penetration depth varied in accordance with the lap configuration even under the same heat input condition. The lap configuration and welding parameters influenced the composition distribution of the welds, as they altered the solidification rate, number of Cu/Al contact interfaces, and location of the high-density material. The failure load of the T-peel specimens was always lower than that of the tensile-shear specimens except for the Cu−Al−Al lap configuration. The T-peel load of the Cu−Al−Al lap configuration was similar to that of the tensile-shear load. When the stress-concentrated joint was homogeneous, it was more robust.