Corrosion behaviour of sol–gel coatings doped with cerium salts on 2024-T3 aluminum alloy

The corrosion behaviour of the sol–gel coatings doped with cerium chloride or cerium nitrate on 2024-T3 aluminum alloy was investigated by using electrochemical impedance spectroscopy (EIS) and immersion tests. The sol–gel matrix was obtained through hydrolysis, condensation of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetramethoxysilane (TMOS), using diethylentriamine as curing agent. The results indicated that cerium nitrate with concentration of 1 × 10−3 mol L−1 in the silane solution was excellent on self-healing for the sol–gel coating, while cerium chloride had no obvious effect. This result suggested that the introduction of Cl− promoted the under-film pitting of 2024-T3 substrate. It was found that Ce(OH)3 and Ce(OH)22+ simultaneously existed in the silane solution by X-ray diffraction (XRD) analysis. Ce(OH)22+ transformed to CeO2 due to high-temperature curing of sol–gel matrix demonstrated by X-ray photoelectron spectroscopy (XPS) analysis. Therefore, it can be considered that Ce(OH)3 and CeO2 played inhibition roles in the corrosion process of the sol–gel coatings.