Plasma electrolytic oxidation (PEO) coatings were developed on magnesium alloy AZ91 under AC conditions in alkaline silicate electrolytes with and without fluoride ions. After PEO, sealing processes based on boiling water, cerium salts and phosphonic acid were applied and characterized by SEM, EDS, XRD and contact angle measurements. The corrosion performance and effectiveness of the sealing processes were investigated on the basis of electrochemical tests in 0.5% NaCl solution and continuous exposure to salt fog per ASTM B117 standard up to 7 days. Post-treatments improved the hydrophobic properties and impedance of the coatings, thus reducing the susceptibility to corrosion.
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