Chromate conversion coatings based on hexavalent chromium will be prohibited in the following years in reply to the REACH regulation. In substitution of hexavalent chromium, manufacturers in the aeronautics sector have developed new formulations for conversion coatings based on trivalent chromium In this study, neutral salt spray tests were performed for different batches of 2024 aluminium alloy coated by trivalent chromium-based conversion coatings named SOCOSURF TCS-PACS. Results have shown a heterogeneity in anti-corrosion performance for the different batches. In order to explain such differences and to make the process more robust, a better understanding of the formation mechanism of conversion coatings based on 2024 aluminium alloy is required. The study thus involves the comparison of two distinct batches of 2024-T3 alloy. Both morphological and chemical characterization of the surfaces and study of their reactivity were carried out, at each step of the surface preparation and conversion treatments, using microscopic observations and electrochemical measurements. The study also focused on the mechanism of nucleation and growth of trivalent chromium coating at various stages of coating growth. Results were analysed in order to identify the critical alloy surface properties and treatment process parameters regarding the nucleation and growth of trivalent chromium coating.
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