Remote laser welding of zinc coated steels in a zero-gap lap joint configuration

Zinc coated steels have been increasingly used in the automotive industry due to their excellent corrosion resistance. However, the presence of zinc coating on the steel sheet poses significant challenges in the laser welding process. Zinc has a lower boiling point (906 °C) than the melting point of steel (>1300 °C). When zinc coated steels are laser welded in a zero-gap lap joint configuration, a highly pressurized zinc vapor is readily produced at the faying interface. Without special precaution, a large amount of spatter and blowholes can be produced, which can degrade the weld quality and mechanical performance of the welds. The state-of-the art approach to mitigate the negative impact of zinc vapor is to employ a series of dimples having an approximate height of 0.1–0.2 mm to provide a channel along the faying interface for the resulting zinc vapor to escape. In this study, an innovative remote laser welding process has been developed to directly weld zinc coated steels in a zero-gap lap joint configuration without the use of dimples. Experimental results show that high-integrity welds can be achieved with excellent mechanical performance. The new process can dramatically reduce the cycle time and manufacturing cost by eliminating the dimpling process.