Study On Preparation And Properties Of Micro Arc Oxidation Black Ceramic Coating On Magnesium Alloy

Micro-arc oxidation(MAO)is an effective surface technology which can merge protection and decoration with coloring into one.We could get a colored and corrosion resistances excellent ceramic layer can protect the substrate on surface of magnesium alloy only by once treatment with MAO.It is significant to broaden the field of application of magnesium alloy by preparing black ceramic coating on magnesium alloy.The study is based on a copper colored metal salt and select the corresponding complexing agent,then join the basis of electrolysis of electrolysis of Na2SiO3,KF and NaOH in which the magnesium alloy has under micro-arc oxidation treatment.The influence of coloring salt,magnesium alloy substrate and and basic electrolyte on prepareing black ceramic layer growth by MAO in this study,analysis the component and phase and distribution of ceramic layer,evaluate the corrosion resistance of the film and the spectral reflectance by the electrochemical method and spectrophotometer.Research showed that:Under the best conditions of electrolyte formulation and process parameters prepared the black ceramic coating has smooth surface and uniform color.Black ceramic coating is dense,a few discharge pores were found on the coating surface.coloring salt significant changes the color of the films,When copper ions and complexation reaction,Cu2+ and complexant together to create metal complexing compound with negative electricity.the film color from white to black with the increase of the concentration of coloring salt which due to lots of metal complexing compound in electrolytic solution.Further,the increase of the salt content so that the colored surface of the film decreased size and number of micro-cracks and improve the compactness of the film.The main composition of the black film is periclase and forsterite,The film shows black is due to copper elements into the film form a compound with very low content,but greatly affected the appearance.Content in the matrix component Al,Zn and Zr elements has no effect on color film processing on different grades of magnesium alloys.The main basis of the electrolyte layer thickness to promote growth and to maintain a stable layer color.The test results of the spectrophotometer show that the spectrophotometer show that The film on the UV Vis optical reflectivity decreases with film color deepens,The visible optical reflectance reduce to 10%(from 55%).Corrosion resistance of colored film was evaluated by polarization curve in 3.5%wt NaCl solution show that corrosion resistance as a darker color improve,the Ecorr of film change from-1.512 V to-1.322 V.