Tartaric-sulphuric acid anodized clad AA2024-T3 post-treated in Ce-containing solutions at different temperatures: Corrosion behaviour and Ce ions distribution

The effect of temperature of a Ce-H2O2 post-treatment on the corrosion resistance of clad AA2024-T3 anodized in tartaric-sulfuric acid as well as the distribution of Ce oxyhydroxides in the anodized layer was investigated. Electrochemical impedance spectroscopy tests showed that samples post-treated at moderate temperatures (up to 50 °C) presented more stable and slightly higher impedance modulus than untreated ones. Increasing the post-treatment temperature to 75 °C decreased the corrosion resistance, likely due to damaging of the porous and barrier layer protective properties, as indicated by electric equivalent circuit fitting. Scanning electron microscopy characterization showed that Ce oxyhydroxides deposition (3+ and 4+ oxidation states as determined by X-ray photoelectron spectroscopy) was enhanced with increasing post-treatment temperature, and that pores were not blocked. Glow Discharge Optical Emission Spectrometry and Rutherford Backscattering Spectrometry analyses indicated local enrichment of Ce species at the bottom of the pores, whereas scanning transmission electron microscopy confirmed the presence of Ce-containing nanoparticles stuck to the pore's walls. Analyses of corroded samples showed increased amounts of Ce oxyhydroxides on the surface and that Ce species remained inside the pores, indicating that the post-treatment protocol successfully and durably incorporated Ce ions within the structure of the anodized layer.