Multifunctional Epoxy Coatings Containing Flake-like CeO2–Melamine Composite Fillers for Enhanced Corrosion Protection

Metal corrosion shortens the service life of engineering materials and can cause structural failure and serious safety hazards. Conventional polymer coatings rely mainly on passive barrier protection and often provide limited protection after mechanical damage. Here, we developed a smart epoxy coating containing flake-like CeO2–melamine (CeO2-MA) composite fillers and systematically evaluated the effect of filler content on corrosion protection. Among the tested formulations, the 0.5 wt.% CeO2-MA/epoxy coating exhibited the best overall corrosion protection. Following 72 h of immersion under artificial-defect conditions, its low-frequency impedance modulus (|Z|0.01Hz) was approximately 3.3 times that of the epoxy control. This improved protection may be associated with the complementary effects of melamine adsorption and the formation of cerium-containing deposits in damaged regions. After thermal treatment at 60 °C for 10 min, the coating exhibited pronounced scratch narrowing with only minor residual grooves, along with partial recovery of electrochemical barrier performance. These findings support a multifunctional coating strategy, although direct validation of the inhibition mechanism and longer-term evaluation of the recovered barrier performance remains necessary.