Fluxless laser beam joining of aluminium with zinc coated steel

Abstract

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 μm, 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 μm 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.