Effect Of Electrical Parameters Interaction Of Microarc Oxidation Coatings On Magnesium Alloys Under Two Power Supply.

The micro arc oxidation coating on AZ91D magnesium alloy was prepared undertwo modes of the power by using orthogonal experiment design. The thickness,corrosion resistance, component, surface morphology and cross-section morphology ofthe coating were studied to analyze the influence of electric parameters of the power andtheir interaction on the coating. Moreover, the influence of the electric parametershaving the same frequency in numerical value and practical effectiveness on MAOcoating was also studied under two modes of the power.Under Mode Two of the power, electric parameters and their interaction have thesame influence on the thickness of the coating and corrosion resistance in drop test.Among which a voltage has a significant influence but duty ratio almost has noinfluence. So the thickness of the coating became bigger and corrosion resistance indrop test was improved when the voltage was increased. When the final voltage,frequency and duty ratio were chose450V,900HZ and40%respectively, there was abest combination for improving the thickness of the coating and corrosion resistance indrop test. In particular, the value of duty ratio can be chose in different level accordingto the actual situation.Similarly, the influence of electric parameters and their interaction on the corrosioncurrent is not far from that on the polarization resistance. However, the interaction ofthe electric parameters has a great influence on the best combination for reducing thecorrosion current and improving the polarization resistance. The best combination of thethree electric parameters for improving corrosion resistance in electrochemistry test isA₄B₃C₂, i.e.450V,700HZ and20%.Under Mode One of the power, there is the same influence of electric parametersand their interaction on the thickness of the coating and corrosion resistance in drop testas that under Mode Two. And a voltage has a more significant influence than otherelectric parameters and their interaction. The best combination of the three electricparameters for improving the thickness of the coating is A₃B₂C₁, i.e.400V,1400HZ,20%and that for improving corrosion resistance in drop test is A₃B₂C₂, i.e.400V,1400HZ and30%.Compared with that under Mode Two, the influence of electric parameters and theirinteraction on the corrosion current is also not far from that on the polarizationresistance and the interaction of the electric parameters has a great influence on the best combination which is A₃B₂C₃, i.e.400V,1400HZ and40%for improving corrosionresistance in electrochemistry test.Under two modes of the power, the thickness and corrosion resistance in drop testof the coating prepared under the electric parameters having the same frequency innumerical value and in practical effectiveness are all slightly different. However, thecorrosion resistance in electrochemistry test has a big difference and the biggest ofwhich reaches three orders of magnitude because duty ratio and the interaction have agreat influence on it.