In situ incorporation of corrosion inhibitors into Plasma electrolytic oxidation coatings on 2024-T3 alloy

Plasma Electrolytic Oxidation (PEO) has been targeted as an eco-friendly alternative to Chromic acid anodizing (CAA) as it results in the formation of multifunctional ceramic-like coatings with similar corrosion resistance to CAA. Nevertheless, the PEO process usually produces thick coatings (50-100) µm, thus limiting their use in fatigue-sensitive applications in the aircraft industry. A possible way to overcome this limitation is the “flash” PEO process, producing thin coatings (≤ 8 μm) in treatment times as short as 1–3 min.

The present work studies the in situ incorporation of corrosion inhibitors (V-, Mo-, La-, Sn-, W-, and Ce-salts with and without EDTA in thin (< 8 µm) PEO coatings.

The screening process to select the best flash-PEO coating was according to the higher corrosion resistance (EIS, 1h)-thickness ratio. The coatings generated in W- and Ce/EDTA-containing electrolytes were selected for further analysis. The morphology, composition, corrosion resistance and paint adhesion (ISO 2409) were evaluated using conventional characterization techniques (SEM, XRD, WCA, salt spray, etc). The most promising results were obtained for the coating formed in Ce-Na2EDTA electrolyte since it showed an optimum paint adhesion capacity and no signs of corrosion in painted condition after 1000 h of exposure in a salt spray chamber.