Environmentally friendly corrosion resistant coatings as alternatives for cadmium and chromium in the aerospace industry

Abstract

European REACh regulations are aimed at the complete removal of the toxic and carcinogenic cadmium and hexavalent chromium coatings currently being employed for corrosion protection of ultra-high strength steel and other aviation components. A powdered aluminium alloy containing 12 mass % manganese, applied with atmospheric plasma spraying, were tested as a possible alternative to cadmium electroplating. Complemented with the development of a permanganate-vanadate based conversion coating as an alternative to the Cr(VI) based treatment. The plasma sprayed AlMn12 alloy had very good electrochemical properties and medium term corrosion resistance, but did not pass the bend adhesion test. The Mn-V conversion coating showed much promise, as it performed similar/better than a commercial Cr(III)-Zr coating in short and medium term corrosion tests. Further additional tests and process refinement are still required, but the Mn-V coating clearly has significant potential as a possible future alternative to chromate conversion coating.