Fabrication and characterization of micro‐arc oxidation (MAO) coatings on Mg‐Li alloy in alkaline polyphosphate electrolytes without and with the addition of K₂TiF₆

Abstract

Abstract Micro‐arc oxidation (MAO) has been accomplished on Mg‐Li alloy in alkaline polyphosphate electrolytes without and with the addition of 10 g/L K 2 TiF 6 . The surface/cross‐section microstructures of the fabricated coatings were analyzed by scanning electron microscope (SEM); the compositions of the fabricated MAO coatings were analyzed by X‐ray diffraction (XRD) and energy dispersive X‐ray analysis (EDAX); the corrosion behaviors of bare and MAO coated Mg‐Li alloys were evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) in 3.5 wt% NaCl solution. Novel hybrid MAO coatings which showed hybrid composition of MgF 2 /Ti 2 O 5 /Ti 6 O 11 /MgO, as well as hybrid structure of a dense inner layer, a dense outer layer and an intermediate layer with some sealed/semi‐sealed pores, had been fabricated on Mg‐Li alloy in alkaline polyphosphate electrolytes with the addition of K 2 TiF 6 . Meanwhile, the corrosion resistance of the fabricated MAO coatings was improved obviously as the result of the addition of K 2 TiF 6 in the electrolytes. Moreover, the multiple roles of ${\rm TiF}_{{\rm 6}}^{{\rm 2}{-} } $ on the MAO process accounted for the fabrication of the corrosion‐resistant hybrid MAO coatings.