Research On Preparation And Corrosion Resistance Of Mg-Mn-MM Micro-arc Oxidation Ceramic Coatings

Micro-arc oxidation（MAO）technology was used to prepare ceramic coating on the magnesium alloy surface.There are very few studies on magnesium alloy micro arc oxidation to date.In this paper,the chemical composition of the electrolyte solution and electrical parameters were studied to optimize the experimental conditions and get better ceramic coating.Diiferent types of adents were used as source of titanium to form TiO₂ phase.The micro-structure,phase composition as well as corrosion mechanism of the composite ceramic coating were analysed.Use corrosion resistances of ceramic coatings as evaluation index,the ceramic coatings were prepared in aluminate,phosphate and silicate electrolyte system and the basic electrolyte solution were obtained.The properties of the ceramic coating which was prepared by single electrolyte system were poor,thus the single factor of concentration ecperimental method was carried out to optimize experiment in this paper.Furthermore,the orthogonal experiments were done under fixed concentration of electrolyte concentration and the optimize electrolyte cocentration were obtained as following:15g/L NaAlO₂,9g/L Na3PO4,3g/L NaF and 4g/L NaOH.The optimum electrical parameters were: direct voltage: 300 V,the frequency: 600 Hz,duty ratio: 15%and the electrolysis time: 15 min.Two additives（K₂TiF₆,TiO₂）were served as titanium sources and added to the electrolyte solution to form TiO₂.The micro-structure,phase composition as well as corrosion mechanism of the composite ceramic coatings which were perpared by different types of titanium source were analysed.The experimental results indicated that TiO₂ can improve the quality of composite ceramic coatings effectively.The film thickness is 24μm when 8g/L K₂TiF₆ solution were added and the conrresbonding thickness is 22μm when 5g/L TiO₂ were added.The density and flatness of composite ceramic films were significantly improved.TiO₂ phase generated which was mainly composed by anatase and brookite.Moreover,the corrosion resistances of the oatings were effectively improved after titanium adgents were added.The corrosion current density of composite ceramic coating with 8g/L K₂TiF₆ was the minimum and the AC impedance value significantly increased with the minimum corrosion rate.The study analysis results showed that the TiO₂ phase on the film can not only promote the performance of film ceramic coating,can also play a plugged role,which made the etching solution cannot pass the loose layer,its special microstructure was the main reason for improving corrosion resistance of the coatings.