Investigation on indirect laser welding of copper to aluminum

Abstract

Laser beam welding of aluminum (Al) to copper (Cu) is challenging due to the formation of intermetallic compounds that are brittle and have high resistivities. However, the Cu/Al phase diagram shows a region were solubility of Cu in Al is present and, on the other hand, a region with the formation of a eutectic phase between α-Al and Al2Cu is present as well. Targeting this area turned to be advantageous for solid state welding, as shown for probeless Friction-Stir-Spot-Welding realizing ductile joints between Al and Cu.In this paper an approach based on indirect laser welding of Cu with Al will be presented and discussed. A green laser was used in order to join Cu to Al in lap joint configuration. The laser beam irradiates the Cu surface, whereby the formation of a common melt pool between Cu and Al is avoided. The heat input and the temperature gradient are assumed to support diffusion at the interface between Cu and Al forming a near eutectic layer. Indeed, a melting layer is formed at the interface between Cu and Al supporting joint formation based on a firmly bonding between both materials. The solidified layer presents a copper rich area towards the copper sheet with plate-like structures of Al2Cu, a region with α-Al crystals on the aluminum side and a eutectic layer of lamellar Al2Cu and α-Al in between. The described morphology is very similar to investigations on probeless Friction-Stir-Spot-Welding, whereas a very low pressure is adopted in indirect laser welding and Al-oxide layer seems not to act as a barrier for joint formation.