Corrosion Protection of Joining Areas in Magnesium Die-Cast and Sheet Products

The common joining techniques for Mg sheet and die cast alloys such as riveting, friction-stir welding and adhesive bonding all introduce additional challenges for protection in the joining areas. First of all, the sheet products are prone to high rate of corrosion due to surface contamination. Introduction of iron-rich contaminants can be encountered from the friction-stir welding process. Although powder coating on top of conversion pre-treatments is practical for mitigating corrosion, the lap-shear adhesion of such surfaces can be negatively impacted when the adhesively bonded joints are exposed to a corrosion environment. Anodized surfaces are better in terms of their ability to retain adhesion strength, but their resistance to galvanic corrosion is an issue. Development of galvanically compatible coatings for steel rivets will benefit the adaptation of riveting as a joining technology for magnesium.