Corrosion behaviour of laser beam welded aluminium and magnesium alloys inthe automotive industry

The pitting behaviour of unwelded and laser beam welded AlMgSi alloys and a n AlMgMn alloy was investigated. Electrochemical investigations and the met allographic determination of the pit volume were used to characterize the s usceptibility to pitting corrosion. Both investigation methods showed that, in the unwelded condition, the material AlMgMn was the most resistant. In the case of laser beam welded materials, the resistance to pitting corrosio n is lower or also higher than that of the non-affected materials depending on the material combination selected. The material combination AlMgSi0.5/A lMgSi1 F21 proved to be the most suitable. Magnesium extruded alloys with approx. 3 to 8% Al and 0.5 to 0.8% Zn are su sceptible to filiform corrosion and pitting corrosion in aqueous chloride s olutions depending on chloride concentration. The resistance of unwelded al loys increases with Al content. On welding of the alloys, the corrosion res istance is determined by the Al/Mg proportion at the surface of the non-aff ected material and the laser welding seam. The pits occur mainly in the hea t affected zone of the welding seam. The laser beam welded material AZ61 HP was found to have the highest resistance.