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

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/LK2TiF6, 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/dm(2) was mainly composed from MgO, Mg-3(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. (C) 2015 Elsevier B.V. All rights reserved.