| This work using micro-arc oxidation (MAO) technology deposited ceramic coatings on AZ31and Mg-10Gd-2Y-0.4Zr substrate. The effects of power parameters and reaction time on both coatings were investigated in Na2SiO3-NaOH-NaF electrolyte environment. Coating thickness, microstructure of surface and cross section, elements compositions of both coatings were analyzed by X-ray diffraction (XRD), eddy current thickness meter, X-ray spectrometer (EDS) and scanning electron microscope (SEM). The corrosion resistance of ceramic was investigated by the electrochemical methods and salt spray test. And the sealing technology of ceramic coatings on rare earth magnesium alloy substrate were investigated.In Na2SiO3-NaOH-NaF electrolyte system, both MAO ceramic coatings on magnesium substrate were porous. Thickness of the coating, diameter of pore and surface roughness will increase as power frequency decreases, voltage, duty ratio and reaction time increase. Metallographical composition of AZ31magnesium ceramic coatings is primarily Mg2SiO4and MgO. And the proportion of both coatings changes with various deposition parameters. Mg-10Gd-2Y-0.4Zr ceramic coating mainly contains MgO, whose proportion will increase as power frequency decreases, and voltage, duty ratio and reaction time increase.Both magnesium based ceramic coatings will have a best corrosion resistance performance when they were deposited in300Hz frequency, under same voltage, duty ratio and reaction time, because the coating was very dense inside. The proportion of Mg2SiO4was greater than MgO in AZ31magnesium ceramic coatings, when it reacted for20minutes. As result of that, this coating has a better corrosion resistance. When the duty ratio was10%, MgO proportion was much less in rare earth magnesium based ceramic coating, so the corrosion resistance performance was better.AZ31magnesium ceramic coating has a better corrosion resistance performance than rare earth magnesium ceramic coating under same parameters. Electrochemical tests show that corrosion resistance of AZ31magnesium coating is1-2order higher than rare earth magnesium ceramic coating. Salt spray tests show that AZ31magnesium ceramic coating can hold for300hours in salt environments, meanwhile corrosion pit was shown on surface of rare earth magnesium ceramic coating after50hours salt spray.The ant-corrosion ability of Mg-10Gd-2Y-0.4Zr MAO coating can be enhanced by organic resin sealing. But the anti-corrosion ability varies with different type of resin. The anti-salt spray performance ability lies from high to low is ceramic coating+three proof anti-corrosion primer> ceramic coating+four proof anti-corrosion primer> ceramic coating+chlorinated polyvinyl chloride based zinc chromate primer> ceramic coating+epoxy zinc chromate primer> ceramic coating+silane coupling agent.The corrosion resistance performance of rare earth magnesium MAO coating can be enhanced by sealing Mg-10Gd-2Y-0.4Zr coating with high temperature melting paraffin. Electrochemical tests show that magnitude of anti-corrosion ability increased for one order after sealing process. Salt spray tests show that this coating can sustain for more than100hours in salt environment after paraffin sealing process. |
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