Laser-Mig Hybrid Welding of aluminium to steel — A straightforward analytical model for wetting length

Abstract

Laser-MIG hybrid welding was recently suggested as a feasible process for joining of aluminium to steel for both structural as well as tailored blank applications. In this process, the aluminium is molten to create a brazed bond to the zinc-coated steel sheet, which remains solid. Using thin-sheet materials in a thickness range of approximately 1 mm in butt joint configuration, this process allows a joining speed of more than 100 mm/s at a laser power of 4 kW whilst retaining some gap bridging ability. In such a case, the wetting length of the aluminium melt on the top and bottom sides of the zinc-coated steel sheet is of significance for the properties of the joint. Therefore, an understanding of the parameters governing wetting length is required. To promote this understanding, a model to calculate wetting length in dependence of processing conditions is suggested. Based on the assumption that there is a correlation between the temperature field on the steel sheet and wetting length, an analytical model for the temperature field is developed and correlated with experimental results on the material combination AA6016 T4 (thickness 1.15 mm) and DC05+ZE (1 mm). Both model and experiments show that the wetting length is correlated to the melting isotherm of the zinc coating (provided a sufficient amount of melt is created). These results shall contribute to an improved understanding of the process.