Abstract: Many cerium compounds are promising corrosion inhibitors for aluminum alloy. However, the formation mechanism of Ce conversion films is not clear yet. Scanning microreference electrode technique (SMRE) was used to probe the potential imaging of 2024-T3 Al alloy in CeCl3 solution. The pitting corrosion of Al alloy in CeCl3 decreased with immersion time and disappeared finally. Additionally, the competition of inhibition and corrosion between Ce3＋ and Cl－ on Al alloy was in situ monitored in CeCl3 by SMRE. The results of X-ray photoelectron spectroscopy (XPS) showed that the Ce conversion films consisted of Al2O3, CeO2 and Ce2O3 (Ce(OH)3), and CeO2/Ce2O3 mass ratio decreased with immersion time. It is concluded that when the critical pH for Ce(OH)3 formation is reached, Ce(OH)3 will precipitate at micro cathodic area of the Al alloy surface. Consequently, H2O2, the product of the catholic reaction will oxidize part of Ce(OH)3 to CeO2.

Key words: Ce conversion films, 2024-T3 Al alloy, Localized corrosion, Scanning microreference electrode technique