Microstructural characteristics of cerium oxide conversion coatings obtained by various aqueous deposition methods

Microstructural characteristics of cerium oxide conversion coatings obtained by electrolytic, dip-immersion and spray deposition methods from aqueous solutions were studied by transmission electron microscopy and electron diffraction analysis. The coatings were applied to aluminum alloy 7075-T6 panels and the pretreatment conditions were the same for all coating methods. The results indicated that the as-deposited coatings were all composed of nanocrystalline particles with narrow size distributions. Electron diffraction analysis revealed that the electrolytic and the spray coatings developed the same crystal structure, possibly Ce7O12, while the dip-immersion coating had a different structure that has not been reported in the literature. After post-treatment in phosphate solution, all three as-deposited coatings were converted to hydrated cerium phosphate.