Alternative to cadmium coatings: AlMn based coatings by magnetron sputtering

摘要

Due to the European directive on chemicals, cadmium coatings produced from highly toxic and carcinogenic baths must be replaced by "green" solutions. The development of alternative coating processes with at least equal or even better performances is far to be completed. Thanks to its advantageous physical properties, aluminum is one of the most produced metals. Despite its good resistance to overall corrosion, pitting corrosion is still problematic for aluminum in contact with water and in the presence of chloride ions for example. Incorporation of alloying elements was reported as a possible method to improve the corrosion resistance of aluminum coatings, essentially limiting the sensitivity to localized corrosion in saline environments. Especially aluminum manganese alloys have corrosion potential close to the cadmium potential so they have been chosen as candidate for the cadmium substitution. PVD technique such as magnetron sputtering is a non-polluting deposition process giving dense deposits with high purity, well-defined stoichiometry and controlled thickness. This technique was used to deposit AlxMny and Al/AbcMny on steel with thicknesses between 1 and 2 μm. Chemical and structural characterizations have been performed. Corrosion performance was evaluated by salt spray test and electrochemical techniques (polarization curves).