Preparation And Characterization Of Black Ceramic Coating On AZ91D Magnesium Alloy By Micro Arc Oxidation With Low Energy Consumption

Magnesium and its alloy have many excellent physical and mechanical properties，whichmake them are widely applied to the field of fireworks, lighting, metallurgy, chemicalindustry, transportation, aerospace, and3C electronics. However，its lower surface hardnessand poor corrosion resistance limits its further application. The micro-arc oxidationtechnology is a kind of surface treatment technology and has broad application prospects, itcan convert to the ceramic-type coating in situ under the conditions of Plasma chemical，electrochemical and thermal-chemical effects and improved their anti-corrosion,wear-resisting and electrical-insulating. Micro-arc oxidation black ceramic coating have awide range of application prospect in protection of material，decoration and optical propertiesdue to ceramic properties and special optical properties. But the high energy consumption ofthe micro-arc oxidation coloring technique is expensive. This reason limits the micro-arcoxidation coloring technique widely used in industrial production. Therefore, the study ofmicro-arc oxidation of low-power coloring technology is very meaningful.Low energy black ceramic coating process has been developed by micro-arc oxidationon AZ91D magnesium alloy in an electrolyte system containing Na2SiO3,（Na2PO3）6,KF,NH4VO3,EDTA and additives. Through the single factor experiment and orthogonaltests optimization electrolyte and electric parameters, finally obtained optimal technologyparameters of Low energy black ceramic coating.The influences of technology parameters onmicro-arc oxidation process and performance of Low energy black ceramic coatings wereinvestigated, such as consumption of energy, color value and chromatic aberration. By thisMAO technique, the MAO black coating is color uniformity and shiny, have good bindingcapacity. At the same time the consumption of energy of the low energy coloring technologyis0.602kw h/(m2.μm), is30%of the general micro-arc oxidation coloring technology. BySEM, EDS, XPS, and XRD analysis the surface morphology, material composition, structureand phase composition of the low energy black ceramic coating. Using Electrochemicalmeasurement system measure the corrosion resistance of MAO coating. The results shownthat the low energy black ceramic coating have a few discharge pores，is dense,and noobvious hierarchical structure, the coating main mainly composed of MgO,VO2and amorphous or microcrystal oxides. The V2O5and another Vanadium oxide result in the blackcolor of ceramic layer. The hardness of Low energy black micro-arc oxidation film is up toabout316HV. The polarization curve shown that corrosion current density of black ceramiccoating was0.00023μA/cm2, four orders of magnitude lower than that of the bared alloy(3.664μA/cm2), which reveal that corrosion resistance of low energy black ceramic coatingformed on AZ91D magnesium alloys by MAO is significantly improved.