Functional Coating Systems on Magnesium Diecastings for Corrosion Protection and Tribological Applications

The use of magnesium diecastings for many automotive applications is mainly hindered by the lack of cost effective functional coating systems. For car body applications, e.g. no satisfying coating system is currently available matching Class A surface requirements for exterior car body components. In the first part of this paper a novel multilayer coating system is introduced containing one layer based on silicone-modified organic resins which provides excellent corrosion resistance and an improved leveling behavior. Thus the coverage of different surface defects originating from diecasting is possible without or with only minimum posttreatment like sanding and grinding. Results showing the performance of the novel coating systems in salt spray testing and VDA cyclic testing are presented. The second part of the paper focuses on the application of thermally sprayed ceramic and metallurgical coatings on magnesium substrates to provide wear resistant surfaces for tribological application. The surfaces are coated with a secondary polymer layer or thin film in order to obtain in addition a low friction coefficient under dry lubrication conditions. Experimental results of the tribological performance of these combined coating systems on different magnesium alloys are presented.