Controlled mixing of Al and Cu in laser welded joints with combined use of core/ring beams and oscillation for EV battery pack applications

Abstract

Laser welding is an industrially accepted method to join highly reflective and conductive materials such as aluminum and copper for EV battery pack applications. Joining dissimilar materials, such as Al to Cu, is particularly challenging with laser welding because of the non-homogenous mixing of Al and Cu, resulting in the formation of imperfections such as porosities, cracks, and hard and brittle intermetallic compounds (IMCs) in the weld zone. Alongside the aforementioned defects, weld morphology also plays a major role in determining the electromechanical properties of the welded joint. This work investigates the use of novel in-source beam-shaping consisting of a core and ring provided by a high power fiber laser to weld 0.5 mm – 0.5 mm Al to Cu in a lap joint configuration. The central core provides the necessary keyhole formation, enhancing the penetration depth. In contrast, the ring helps enlarge the melt pool and improve material mixing. Industrial laser systems also provide flexibility to dynamically oscillate the laser beam to improve the melt pool mixing. An ideal selection of the beam shaping strategy composed of core and ring beams with oscillations strategies can provide an optimum material mixing and a more distributed IMC formation in the weld zone and, therefore, help mitigate the detrimental effect of IMCs. Accordingly, this work proposes a systematic analysis of the use of core and ring beam shaping along with circular oscillation to assess their influence on mechanical and electrical properties of a partial penetration Al to Cu lap joint. An experimental plan is devised to investigate the effect of core and ring beam shape in tandem with beam oscillation. The welded joints were characterized for the weld seam chemistry, tensile strength, and electrical contact resistance. The results confirmed combining core and ring beams with beam oscillation helps in improved material mixing, maximizing the joint surface area and elevating electromechanical properties of the welded joint.