Effect Of The Electrolyte With Different Main Salt On The Microstructure And Properties Of Micro Arc Oxidation Coatings On TC4 Titanium Alloys

In this paper,Based on the uniform mixture design,the comparison of the effect of electrolyte on the structure and properties of micro arc oxidation coating on TC4titanium alloy under different electrolyte systems(one of Na₂Si O₃,Na₃PO₄,NaAlO₂,KF and Na OH)was studied,and the optimal scheme of each performance was obtained.The results show that the conductivity has the greatest influence on the feasibility of the reaction and the formability of the coating,and Na OH has the largest impact on the conductivity and pH value of the solution,followed by KF and the least main salt.The trend of the temperature change value(?t)of the electrolyte is completely consistent with the conductivity and pH value,and the breakdown voltage is inversely proportional to the conductivity.For the feasibility and formability under the same scheme,the phosphate system is the best overall,the reaction of micro arc oxidation is the most mild among the three electrolyte systems,and the surface of the coating is the smoothest.The silicate system is the most rough and loose.The reaction under the aluminate system is the most intense,and the feasibility and formability is the worst.Under the same scheme,the phosphate system is the best,the reaction is the mildest,and the surface of the film is the smoothest,the silicate system is the roughest,the aluminate system is the most violent,and the feasibility and film-forming performance are the worst.Rutile type TiO₂ and anatase type TiO₂ are found in the three electrolyte systems.The difference is that there is only a small amount of Al₂Si O₅ in silicate film,amorphous phosphate in phosphate system and a large amount of Al₂TiO₅ in aluminate system.In silicate and phosphate systems,increasing the concentration of main salt can improve the thickness and pitting corrosion resistance of the coating,but it will make the coating more rough and porous.Increasing the concentration of Na OH is conducive to the transformation of metastable anatase TiO₂ into more stable rutile TiO₂,but it will reduce the density and electrochemical corrosion resistance of the coating.In aluminate system,increasing the concentration of NaAlO₂ can increase the content of Al₂Si O₅which can significantly improve the wear resistance of the coating,although it can not significantly improve the film thickness.Increasing the concentration of KF can improve the conductivity,but the overall effect on the structure and properties of the coating is the least.The wear resistance of the coating can be improved by increasing the concentration of main salt and decreasing the concentration of Na OH.The best corrosion resistance in H⁺and Cl^-environment of the coating prepared in silicate system is 7#scheme;The best corrosion resistance in H⁺environment of the phosphate and aluminate coatings is 7#,and that in Cl^-environment is 10#.Under the same friction test conditions of the three salt systems,the best wear resistance of the film is 7#.The components of the 7#scheme are:main salt:5.82 g/L,KF:3.54 g/L,Na OH:2.18 g/L.The components of the 10#scheme are:main salt:0.75 g/L,KF:5.07 g/L,Na OH:2.05 g/L.Under the same scheme,the coating thickness under silicate system is the largest,and the corrosion resistance is the best.The coating of phosphate system is the most compact and smooth,and the electrochemical corrosion resistance is the best.Under the same friction test conditions,the coating obtained under aluminate system has the best wear resistance.