<p>Using plasma electrolytic oxidation, various additives were doped into a silicate-based electrolyte to regulate the pore size of the resulting coatings. We successfully prepared Al₂O₃-based ternary composite coatings on 17% SiCp/2009 aluminum matrix composites, and systematically investigated the effects of metal soluble salts and rare earth soluble salts (Y(NO₃)₃·6H₂O, Eu(NO₃)₃·6H₂O, Ce(NO₃)₃·6H₂O, and K₂ZrF₆) on the phase structure and surface morphology of the PEO coatings. Their corrosion resistance was also evaluated via electrochemical workstation tests and ultrasonic cavitation corrosion tests. Among the ternary composite coatings obtained, those with K₂ZrF₆ added showed a significant reduction in pore size—from 2.49 ± 0.06 to 1.50 ± 0.01 μm—and in porosity, from 7.10 ± 0.47 to 2.93 ± 0.36%—more notable than with the other three rare earth additives. Electrochemical tests revealed that coatings with K₂ZrF₆ and Ce(NO₃)₃·6H₂O had corrosion current densities an order of magnitude lower than other groups; the K₂ZrF₆-added coating had a density of 2.38 × 10⁻⁷ and a 0.2 V positive shift in corrosion potential. ZrO₂–SiO₂–Al₂O₃ coatings exhibited the best corrosion resistance, with CeO₂–SiO₂–Al₂O₃ performed best among rare earth-based coatings. In summary, regulating pore size and porosity positively enhances PEO coating corrosion resistance.</p> Graphical Abstract <p></p>