High strength aluminium alloys are widely used in the aircraft industry as structural materials. Toenhance their corrosion resistance, a chemical conversion treatment is usually used. It also allowspaint deposition. Conversion coatings rely on hexavalent chromium compounds although they willbe prohibited by the Registration, Authorization and Restriction of Chemicals (REACh) Regulationin 2024 [1]. Nowadays various chromate-free coatings are under investigation to replace ChromateConversion Coating (CCC). Permanganate Conversion Coatings (PCC) seem promising to replaceCCC [2]. Although corrosion resistance can be improved by the PCC [3], there is still a lack ofunderstanding concerning the deposition mechanisms and the role of surface pretreatments inproviding good deposition and corrosion performance.The aim of this work was to investigate the influence of surface pretreatments on the surfacechemistry and on the subsequent deposition of the PCC, especially the role of iron in sulphate,nitrate and ferrous ion based deoxidation baths. Different baths with various formulations andtreatment conditions have been studied. After deoxidation, substrates were converted in acid bathscontaining among other, potassium permanganate and corrosion inhibitor of aluminium. A purealuminium sample (99.999 % at. purity) as reference and an AA2024-T3 aluminium alloy weretested. The surfaces were analyzed by means of highly sensitive surface techniques, which are XrayPhotoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry(ToF-SIMS). Moreover, the dissolved species in the bath during immersion treatments werestudied by Inductively coupled plasma - Optical Emission Spectrometry (ICP-OES).During pretreatment, the aluminium dissolution rate was mainly influenced by temperature, whereasoxide thickness after deoxidation depends on nitric and sulfuric acid concentrations, andtemperature. After conversion, the coating was composed of manganese and the corrosion inhibitoroxide/hydroxide in the outer part and aluminium oxide/hydroxide in the inner part. For the alloy, thecoating was thicker and the inner part is enriched in copper. The coating thickness and copperenrichment were influenced by the deoxidation conditions.
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