Corrosion Resistance and Functional Properties of Particle-Modified Plasma Electrolytic Oxidation Coatings on Metals

Plasma Electrolytic Oxidation (PEO), also known as Micro Arc Oxidation (MAO), has recently attracted significant interest due to its ability to produce thick, well-adherent coatings with excellent corrosion and wear resistance. Key features of PEO coatings include the high porosity of the outer layer and the capability to incorporate particles dispersed in the electrolyte directly into the growing oxide layer. This latter feature enables functionalization of the coated surface and improves its corrosion properties.

In this study, PEO coatings were produced and characterized on aluminum and magnesium alloys by incorporating metallic and non-metallic particles. The coatings were synthesized using different current modes, namely direct current and pulsed unipolar current, with particle incorporation achieved by simple dispersion of the particles in the PEO electrolyte. Various types of particles were embedded in the coatings, including graphite nanoparticles to enhance wear resistance; metallic particles (copper or silver) to impart bactericidal, fungicidal, or antifouling properties; glass particles to improve wear and corrosion resistance; and titanium dioxide particles to generate photocatalytic surfaces. In all cases, the impact of particle incorporation on corrosion properties was also evaluated.

The resulting coatings were characterized on both the surface and cross-section using scanning electron microscopy (SEM) and X-ray diffraction (XRD) to confirm particle incorporation and to analyze the microstructure and morphology. Functional performance was further evaluated through corrosion, wear, biological, and photocatalytic tests, depending on the incorporated particles. In particular, corrosion properties were evaluated through electrochemical tests. In all cases, significant particle incorporation was achieved, resulting in coatings with enhanced, well-defined functional properties. In most cases, particle incorporation also leads to an improvement in corrosion properties.