On the meaning of zinc coatings in hybrid welding of aluminium to steel

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. For the case of butt joints, the wetting length of the aluminium melt on the top and bottom side 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, two models to calculate wetting length in dependence of processing conditions are suggested. Based on the assumption that there is a correlation between either the filler wire supply and wetting length or the temperature field on the steel sheet and wetting length, two analytical models are developed and correlated with experimental results. As a result, it is demonstrated that the wetting length should be 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.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. For the case of butt joints, the wetting length of the aluminium melt on the top and bottom side 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, two models to calculate wetting length in dependence of processing conditions are suggested. Based on the assumption that there is a correlation between either the filler wire supply and wetting length or the temperature field on the steel sheet and wetting length, two analytical models are developed and correlated with experimental results. As a result, it is demonstrated that the wetting length should be correlated to the melting isother...