Study On Dual Electrolyte Optimization And Coating Properties Of Micro-arc Oxidation Based On Mixture Experiment Design

AZ91D magnesium alloy and pure magnesium used widely in industrial appliction were chosen as substrate to be processed by micro-arc oxidation(MAO)in silicate-aluminate dual electrolyte.The optimization and coating properties of MAO were both researched by mixture experiment design.The ternary quadratic regression equation and quaternary regression equation were established about the film thickness(μm),drip liquid whiten time(s),and the corrosion current density(A/cm2)and concentrations of Na2SiO3(x1),NaAlO2(x2),NaOH(x3)and KF(x4).On the other hand,the significance of the regression equation was examined and the best theoretical values was solved by programming solution.In addition,intuitive analysis and comprehensive analysis of different processes were studied.For the regression analysis of micro-arc oxidation coating on AZ91 D magnesium alloy,it was found that the sodium silicate and potassium fluoride exist in solution,while the ratio of sodium silicate was 0.334 and the ratio of potassium fluoride was about 0.666,the thickness of the AZ91 D magnesium alloy could reach the maximum value of 28.3 μm.According to the regression equation of AZ91 D magnesium alloy by drip liquid whiten time and electrolytes,It was found that the sodium silicate and potassium fluoride exist in solution,while The ratio of sodium silicate was 0.39 and the ratio of potassium fluoride was about 0.61,AZ91 D magnesium alloy drip corrosion resistance was better,the time reacheed about 132 s.Although the regression equations of the corrosion current density of the two groups were significant,the results were not consistent,they could not be used as analytical standards.According to intuitive analysis,potassium fluoride could promote the growth of the micro-arc oxidation coating and increase film thickness which was an important factor improving the drip corrosion resistance;for corrosion current density,AZ91 D magnesium alloy after micro-arc oxidation treatment were lower 1~2 order of magnitude than substrate.For the regression analysis of micro-arc oxidation coating on pure magnesium,it was found that only potassium fluoride exists in solution,the thickness and drip liquid whiten time of pure magnesium could reach the maximum value of about 85 μm and 73 s.the regression equations of the corrosion current density of the two groups were not significant,so they could not be used as the analytical standards.According to intuitive analysis,potassium fluoride could promote the growth of the micro-arc oxidation coating,but wrecked the flatness of surface.For corrosion current density,pure magnesium after micro-arc oxidation treatment were lower 2~4 order of magnitude than substrate.Therefore,According to the corrosion resistance,the coating properties of the 3# test scheme were the best of all schemes for AZ91 D magnesium alloy and pure magnesium.The proportion of 3# scheme was sodium silicate in 0.450,sodium aluminate in 0.009,sodium hydroxide in 0.307 and potassium fluoride in 0.234.And the specific concentration of composite electrolyte were sodium silicate 20.25 g/L,sodium aluminate 0.11 g/L,sodium hydroxide 4.61 g/L and potassium fluoride 10.53 g/L.