Dual functional salt-responsive and self-healing composite coating for enhanced corrosion resistance of AZ31B Mg alloy

Conventional self-healing anti-corrosion coatings face limitations in corrosion inhibitor release kinetics, triggering conditions, and inhibition efficiency, which compromise their protective effectiveness for magnesium alloys. In this study, we developed a novel dual-functional PEO/EP@PIN composite coating with salt-responsive self-healing properties. The coating system innovatively combines a plasma electrolytic oxidation (PEO) interlayer with an epoxy (EP) topcoat embedded with polyaniline (PANI) microcapsules containing 1-decyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IN) ionic liquid corrosion inhibitor. The PANI microcapsules enable rapid Na + -triggered inhibitor release in high-salinity environments, while the PEO layer ensures robust interfacial adhesion to the Mg substrate. Electrochemical tests demonstrated that the coating achieves an ultralow corrosion current density of 6.26 × 10 −11 A·cm −2 , representing a 7-order-of-magnitude reduction compared to bare Mg alloy, while maintaining a high impedance modulus of 8.97 Ω·cm 2 after 30 days of immersion in 5.0 wt% NaCl solution. Scratch-healing experiments and XPS analysis revealed that the released IN inhibitor forms Mg-N/S chemical bonds with the substrate and generates hydrolyzed Mg(OH)₂ barrier phases, effectively blocking corrosive media penetration. This work elucidates the salt-responsive and self-healing mechanisms of the coating, providing new insights for developing smart anti-corrosion coatings for magnesium alloys.