Brown ceramic oxide coatings were prepared on AZ91D magnesium alloys by micro-arc oxidation

and effects of different NaVO3 concentration on the color

microstructure and properties of the coatings were investigated. The results reveal that with increasing in NaVO3 concentration

growth rate of the oxidation coatings is increased

and corrosion resistance of the coating exhibits firstly increase and then decrease

meanwhile

the color of the coatings becomes dark brown gradually. However

excessive NaVO3 concentration is harmful for the micro-oxidation process. EPMA analysis shows that the coating is mainly contained Mg

Al

V

O and little P element

and absence of the phase containing P element can be observed in the XRD

which is attributed to little P content in the coating and thin coatings resulting in the little deposition containing P phase.