Deposition of duplex MAO layer/nanostructured titanium dioxide composite coatings on Mg–1%Ca alloy using a combined technique of air plasma spraying and micro arc oxidation

Micro arc oxidation (MAO) layer (as bond coat) was successfully deposited on Mg–1%Ca alloy in KF + NaAlO2 electrolyte. In order to improve the corrosion resistance of the conventional MAO coated Mg–1%Ca alloy, air plasma sprayed (APS) nanostructure TiO2 coating (as top coat with bimodal structure) was successfully applied on the aforementioned bond coat. The results indicated that the porous MAO layer was effectively sealed by the (APS) nanostructure TiO2 top coat which showed compact and dense structure along with nano regions. In fact, MAO coating acted as interlayer to provide inert rough surface and necessary hardness for the Mg alloy to bond with air plasma sprayed TiO2 top layer. The positive effect of the air plasma sprayed nanostructure TiO2 coating was attributed to its mechanical isolation against aggressive medium to the MAO coating and Mg matrix. So, novel duplex ceramic composite coating (MAO/nanoAPSTiO2) could significantly improve the corrosion resistance of the Mg–1%Ca alloy in the chloride solutions. [Display omitted] •MAO/APS nano TiO2 composite coating was successfully applied on Mg–1%Ca alloy.•MAO layer was well sealed by air plasma sprayed nanostructure TiO2 coating.•Composite coating remarkably reduced anodic current density of the Mg alloy.•Highest impedance values were observed for the composite coated Mg alloy.•MAO as inert bond coat prevented galvanic cell formation at the interface.