High-corrosion resistance of the microarc oxidation coatings on magnesium alloy obtained in potassium fluotitanate electrolytes

• MAO coatings are formed in electrolytes containing K2TiF6, (NaPO3)6, NaOH and TEA.
• The optimal concentration of K2TiF6, (NaPO3)6 and NaOH are 8.0, 8.0 and 3.0 g/L.
• MAO coatings are mainly composed of MgO, Mg3(PO4)2, and Mg2TiO4.
• The coatings can show good corrosion properties in a 240-h salt spray test.

Microarc oxidation (MAO) coatings were prepared on AZ91D magnesium alloys in the electrolytes containing 10 ml/L triethanolamine and various concentrations of potassium fluotitanate, sodium hexametaphosphate, and sodium hydroxide. The corrosion resistances of the MAO coatings were evaluated using electrochemical impedance spectroscopy (EIS). Based upon corrosion the resistance of the coatings, an optimized electrolyte that was composed of 8.0 g/L K2TiF6, 8.0 g/L (NaPO3)6, 3.0 g/L NaOH and 10.0 ml/L TEA was obtained. The coating that was formed at 6 A/dm2 was mainly composed from MgO, Mg3(PO4)2, Mg2TiO4, and amorphous phases. The coating exhibited excellent corrosion resistance due to its larger coating thickness, smaller amount of micropores and cracks, and the existence of more stable compositions.