Aluminium alloys surface preparation for new Chromate-Free Conversion Coatings

High strength aluminium alloys are widely used in the aircraft industry as structural materials. To enhance their corrosion resistance, a chemical conversion treatment is usually used. It also allows paint deposition. Conversion coatings rely on hexavalent chromium compounds although they will be prohibited by the Registration, Authorization and Restriction of Chemicals (REACh) Regulation in 2024 [1]. Nowadays various chromate-free coatings are under investigation to replace Chromate Conversion Coating (CCC). Permanganate Conversion Coatings (PCC) seem promising to replace CCC [2]. Although corrosion resistance can be improved by the PCC [3], there is still a lack of understanding concerning the deposition mechanisms and the role of surface pretreatments in providing good deposition and corrosion performance.