Effect Of Electrolyte On Micro-arc Oxidation Coatings On Aluminum Based On Regression Orthogonal Experimental Design

Micro-arc oxidation?MAO?is a surface coating technology which can effectively enhance the corrosion resistance,wear resistance and insulation of magnesium,aluminum and titanium metals.The chemical composition of electrolyte and the setting of electrical parameters will have a direct impact on the structure of the film.Therefore,a comprehensive and systematic study of the effect of electrolyte on the micro-arc oxidation film of A356 aluminum alloy is great value and significance for improving the structure of the films,and further enhancing the corrosion resistance of the films.Based on this,the regression model of four response values of films thickness,drip time,corrosion potential and corrosion current density about the concentration of Na₂SiO₃,NaOH and KF was established by using regression orthogonal rotational combination design.The significance of regression models and model coefficients was tested by ANOVA.The influence of electrolyte on the response values of micro-arc oxidation film was further analyzed by response surface graph,and the response values of micro-arc oxidation film was optimized.The influence of Na₂SiO₃,NaOH and KF on micro-arc oxidation process,phase composition,surface and cross-section morphology,drip time and electrochemical corrosion resistance of aluminium alloy were studied based on the asterisk arm test and zero level test in the experimental project.The results show that the regression models of film thickness?T?,drip time?D?,corrosion potential?E?and corrosion current density?J?are significant,and the lack fit of models are not significant.The regression models have high fitting degree and high prediction accuracy for film response values.The significant effects of NaOH,Na₂SiO₃,KF and interaction among electrolyte components on the response values of films were as follows:Na₂SiO₃,Na₂SiO₃×KF,NaOH×KF,Na₂SiO₃×NaOH have very significant influence on the film thickness,KF,Na₂SiO₃×NaOH×KF have significant influence on he film thickness;Na₂SiO₃,KF,Na₂SiO₃×KF,Na₂SiO₃×NaOH have very significant influence on the dropping time;KF,Na₂SiO₃,NaOH×KF,Na₂SiO₃×NaOH×KF,Na₂SiO₃×KF have very significant influence on corrosion potential,NaOH have significant influence on corrosion potential;NaOH,Na₂SiO₃,Na₂SiO₃×NaOH,NaOH×KF,Na₂SiO₃×KF have very significant influence on the corrosion current density.The optimization results show that the maximum film thickness can reach 14?m when the concentration of Na₂SiO₃,NaOH and KF are 14.5g/L,8.9g/L and 15.0g/L respectively;the dropping time can reach 56.7 minutes when the concentration of Na₂SiO₃,NaOH and KF in the electrolyte is 12.9g/L,7.1g/L and 14.7g/L,respectively;the maximum corrosion potential can reach-0.88V when the concentration of Na₂SiO₃,NaOH and KF in the electrolyte is 5.0g/L,3.2g/L and 10.5g/L,respectively;the lowest corrosion current density can reach 4.34*10^-8A/cm² when the concentration of Na₂SiO₃,NaOH and KF in electrolyte are 12.5g/L,5.0g/L and 11.64g/L,respectively.It is beneficial for micro-arc oxidation ceramic coatings to grow when adding Na₂SiO₃,NaOH and KF in the electrolyte of NaOH-KF,Na₂SiO₃-KF and Na₂SiO₃-NaOH systems.The main constituent phase of the films are?-Al₂O₃.The porosity of the film decreases,the compactness increases,the corrosion resistance of droplets decreases slightly,and the electrochemical corrosion resistance increases with the concentration of Na₂SiO₃ increasing from 7.5g/L to 15g/L.The density of film decreases,the corrosion resistance of dropping time and the electrochemistry decreases with the increase of NaOH concentration from 7.5g/L to15g/L.The film thickness decreased slightly,the film compactness increased,the corrosion resistance of dropping time changed little,and the electrochemical corrosion resistance increased with the concentration of KF from 7.5g/L to 15g/L.