The impact of ring-shaped laser beam on dissimilar welding of Al-Cu thin sheets for battery tab-to-busbar connection: Microstructural, mechanical and electrical characteristics

Abstract

Al-Cu dissimilar laser welding has gained substantial attention in the electric vehicle battery manufacturing, while challenged by the formation of brittle Al-Cu intermetallic compounds (IMCs). This study investigated the impact of beam shaping technology on the characteristics of Al-Cu dissimilar laser welds by using a coaxial core and ring dual beam laser system. The investigation assessed multi-level weld characteristics including weld geometry, IMC formation, mechanical and electrical properties. Results showed that the dual laser beam can effectively avoid imperfections observed with single beam, such as full penetration related to core-only beam and surface discontinuity defects associated with ring-only beam, respectively. For the core-only weld, extensive upward migration of Cu promoted the formation of brittle CuAl2 and Cu9Al4/Cu3Al2, leading to a considerable reduction in joint strength and a sharp increase in the electrical resistance. For the ring-only weld, the insufficient bonding area between Al and Cu sheet, leads to a significant degradation of joint strength, although a minimal electrical resistance was identified. An optimized power splitting was determined at 40% for the core beam and 60% for the ring beam, which allows the minimal formation of Al-Cu IMCs and consequently, the improved mechanical strength and reduced electrical resistance.