Investigating impact of zinc vapor jet on keyhole dynamics and liquid ejection from molten pool during remote laser welding of zinc-coated steel in zero-gap lap joint configuration

When Zn-coated steels are laser welded in a zero part-to-part gap lap joint configuration, highly pressurised Zn vapors are readily produced, generating spatters in the weld. The best practice is to set a non-zero gap to facilitate vapor degassing; however, this necessitates additional operations, escalating production costs. This paper aims to investigate the keyhole dynamics and the ejections from the molten pool due to the interaction between high-pressure Zn vapors and the liquid metal, during remote laser welding of Zn-coated DX57D+Z steel sheets at zero nominal part-to-part gap in lap joint configuration. This is achieved by complementing experimental trials with multi-physics Computational Fluid Dynamics (CFD) simulations. The findings showed that the interplay between heat-affected zone, Zn evaporation zone, size/shape of the laser beam are critical factors for controlling the effect of Zn vapors jet on keyhole stability and liquid ejections. Opportunities for laser beam shaping are discussed throughout the paper.