Study On The Effect Of Electrolyte On AM60B Micro-arc Oxidation Coatings Based On Regression Orthogonal Experimental Design

In this paper,the regression orthogonal test method was applied to change the concentration proportion of three components,Na₂SiO₃,NaOH and KF,and micro-arc oxidation?MAO?coatings were prepared on AM60B magnesium alloy.Furthermore,regression models were established based on the results of corrosion current density(J_corr)and dripping time(Y_?Time?)of coatings.The influence of changing the electrolyte concentration on corrosion resistance of coatings was analyzed by means of analysis of variance and response surface methodology,and then determined the optimal electrolyte components proportion.Moreover,further study the effect of concentration content of various components on forming process,microstructure and property of MAO coatings.The results show that the regression models about corrosion current density and dripping time of coatings based on the regression orthogonal test method are significant,and the lack fit of models are not significant.The regression models have high fitting degree and high prediction accuracy for coating response values.The optimization analysis predicted that the optimal concentration of each component is15g/L Na₂SiO₃+7.5g/L NaOH+3.5g/L KF.In this electrolyte,the coatings'anti-corrosion ability was best,the lowest corrosion current density can reach1.66×10^-9A/cm².In the basic alkaline electrolyte composed of Na₂SiO₃,NaOH and KF,the different concentration of the three components has a great influence on the microstructure and corrosion resistance of the coating.Experimental analysis shows that when in the electrolyte the total concentration of each component is high and appropriate,the coating has smaller surface porosity,more uniform micropore size,larger thickness,less microcrack,higher density and better corrosion resistance.The estimated optimal concentration shows that the concentration of Na₂SiO₃,the main salt in the electrolyte,should be on high side,the concentration of NaOH,the pH regulator,should be on middle side,and the concentration of KF,the additive,should be on low side,which is conducive to micro-arc oxidation into coatings.The effect of silicon-fluorine ratio in electrolyte has great influence on the microstructure and corrosion resistance of MAO coatings.When the silicon-fluorine ratio is greater than zero,the coating formation reaction is more intense,the coating thickness is larger,and the MgF₂ phase is generated in the inner layer,which is conducive to improving the corrosion resistance of the coatings.In addition,with the increase of silicon-fluorine ratio in the electrolyte,the competition and synergism between anion F^-and SiO₃^2-are changed,which cause worse microstructure and corrosion resistance of the coating.When the silicon-fluorine ratio is 0.5,the better synergistic action between F^-and SiO₃^2-forms a film-layer with larger thickness,dense structure and fewer defects.That is to say,both large thickness and excellent corrosion resistance has been obtained at this point.The various of the total concentration of different components in the electrolyte mainly affects the thickness and density of the film-layer by affecting the coating forming reaction rate,so as to change the drop corrosion resistance?drop time?of the film-layer and make the drop corrosion resistance increase with the increase of the total concentration of each component.However,the change of the total concentration of each component has little influence on the inner layer,so it has little influence on the electrochemical corrosion resistance?corrosion current density?of the coating.On the contrary,the long-term corrosion resistance of the coating is changed due to the difference in the structure of the coating.