Parameter Optimization and Characterization of Aluminum-Copper Laser Welded Joints

Battery packs of electric vehicles are typically composed of lithium-ion batteries with aluminum and copper acting as cell terminals. These terminals are joined together in series by means of connector tabs to produce sufficient power and energy output. Such critical electrical and structural cell terminal connections involve several challenges when joining thin, highly reflective and dissimilar materials with widely differing thermo-mechanical properties. This may involve potential deformation during the joining process and the formation of brittle intermetallic compounds that reduce conductivity and deteriorate mechanical properties. Among various joining techniques, laser welding has demonstrated significant advantages, including the capability to produce joints with low electrical contact resistance and high mechanical strength, along with high precision required for delicate materials like aluminum and copper. The primary objective of this study was to join 0.8 mm thick aluminum and copper tabs through the laser welding methodology, with a particular emphasis on optimizing welding parameters including laser output power and welding speed to achieve robust and reliable connections. Through systematic experimentation, the influence of these parameters on weld strength and joint properties was explored. Utilizing a normalized laser power of 0.87 and a normalized welding speed of 0.75, a normalized lap weld strength of 39.62 was achieved for 25.4 mm wide thin sheets. Furthermore, formation and characterization of intermetallic compounds (IMC) along with microhardness distribution within the weld zone were examined. This investigation provides valuable insights into mechanical properties of the cell connections and their potential influence on overall joint durability.