<p>Al₂O₃/CeO₂ composite coatings were prepared on AlSi10Mg substrates, laying the foundation for their application in the shipbuilding and aerospace sectors. Using Ce(NO₃)₃ to prepare rare earth conversion coatings on PEO coatings improves the morphology of the coatings, decreasing porosity to 6.1%. The RECC film is preferentially deposited in the depressed regions of the PEO coating, reducing the number of protrusions in the 3D surface topography. The Ce content increased to 5.62%, which was present on both the surface and the depth of the coatings. The composite coatings were mainly composed of γ-Al₂O₃, α-Al₂O₃, CeO₂, and Ce₂O₃, with Ce valences of Ce³⁺ and Ce⁴⁺. The average roughness was reduced to 2.055&#xa0;µm. The corrosion current density was reduced from 1.92 × 10⁻⁵ to 1.52 × 10⁻⁷&#xa0;A/cm². The PEO/RECC composite coating obtained the optimal corrosion resistance at the processing conditions of 30&#xa0;min and a Ce(NO₃)₃ concentration of 0.03&#xa0;mol/L. Compared to the processing time and Ce³⁺ concentration, the concentration has a significant influence on the RECC treatment parameters. The self-healing capability of the RECC conversion film effectively resists Cl⁻ attack, and the CeO₂/Al₂O₃ composite coating demonstrates an excellent protective effect for the substrate.</p>