A new nanoparticle penetrant used for plasma electrolytic oxidation film coated on AZ31 Mg alloy in service environment

A new penetrant of improved self-assembled nanophase particle (SANP) solution was used to protect AZ31 Mg alloy with plasma electrolytic oxidation (PEO) film in the service environment. The improved SANP technique was carried out by increasing water concentration, prolonging hydrolytic time, reducing solution acidity and adding phytic acid (PAH) inhibitor. Properties of the improved SANP solution and the PEO + SANP film were evaluated by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and potentiodynamic polarization. Service performance of the PEO + fluorocarbon (FC) paint treated by the improved SANP technique was estimated by thermal shock method (TSM) and neutral salt spray test (NSST). Experiment results indicated that permeability of the improved SANP solution was increased obviously due to the formation of smaller nanoparticles. Uniformity and corrosion protection of the PEO + improved SANP film were further enhanced attributed to the restriction in the formation of bigger inorganic particles and the stability of the PAH inhibitor, respectively. For the composite film of PEO film + improved SANP + FC, it still had strong adhesion and good corrosion protection after the service environment tests of TSM and NSST due to the chemical combinations of SANP/PEO and SANP/FC.