PVD coating and substrate pretreatment concepts for magnesium alloys by multinary coatings based on Ti(X)N

Due to their low density and high specific strength, magnesium alloys exhibit high economic and ecological potential to save weight and fuel. Nevertheless magnesium alloys are known for their high susceptibility to corrosion attack and their low wear resistance. So the surface has to be protected. PVD coatings are known for their good wear resistance and decorative properties. Nevertheless, common PVD coatings cannot be applied to magnesium due to the risk of severe galvanic corrosion between substrate and coating. Therefore, coating concepts have been tailor-made for magnesium alloys which ensure both good corrosion resistance and high hardness. The coatings are based on TiMgAlN. Besides this, the coating color can be varied in a wide range by adjusting the magnesium content to meet decorative demands. TiMgAlN coatings were deposited by a commercial PVD deposition unit type CemeCon CC800/9 using both DC and HiPIMS technology. The coatings were examined concerning their chemical, structural and electrochemical properties. TiMgAlN coatings were able to withstand a 48 h salt spray test without corrosion attack. Additionally electrical impedance spectroscopy was carried out to examine electrochemical properties more closely. It was shown that XRD phase structure is crucially influenced by the substrate material (HSS and AZ31) although coatings were deposited in the same batch and chemical composition is identical. (C) 2012 Elsevier B.V. All rights reserved.