A laser welding-brazing (LWB) process to join zinc coated steel and aluminium sheets in two different flange geometries is reported. The deep drawing steel sheets are covered by a zinc layer of maximum thickness 10 mm, and a zinc based filler wire was used in the welding experiments with a Nd-YAG laser. Because of the differences in melting temperatures between iron (1808 K), aluminium (933 K), and zinc (693 K), it is possible to weld the aluminium alloy only. Owing to the zinc coating on the steel side, a Zn-Al alloy can be brazed onto the steel without any flux agent. The inevitable formation of a Fe-Al intermetallic phase at the bondline of the weld seam and the steel can be limited to a thickness of less than 5 mm and to a proportion of the contact area only. Mechanical as well as dynamic tests show results comparable to those obtained via other joining techniques. Salt chamber corrosion tests of varnished specimens display minor damage and no decline in tensile strength.

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Joining of iron with aluminium in the liquid phase is complicated due to the formation of brittle intermetallics within Fe-Al melts. In this work we present the technology of a laser weldingbrazing (LWB) process to join zinc-coated steel and aluminium sheets in an overlap geometry. The process is divided into welding of the aluminium sheet and brazing of filler material and molten aluminium sheet onto the zinc-covered steel sheet to avoid the liquid stage of iron. It is possible to join those materials with a single laser beam. However, with a second laser beam, the melt flow can be controlled more effectively and the wetting behaviour can be improved by preheating the zinc-covered steel sheet surface. This is beneficial since the process works without any flux agent. Wetting lengths increase by using this technique and generate a joint that exceeds the tensile strength of the base material. Due to the zinc cover on the steel sheet there are two possible filler materials that have miscibility with zinc as well as aluminium. Zinc based filler materials have the advantage of a lower melting point and thus lower process temperatures. And aluminium based filler wires result in more ductile brazed seams, making it possible to deform such joints in a later application as tailored blanks.

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