The Research On Influence Of Different Mian Salt Electrolytes On The Properties Of TA2 Pure Titanium Micro-arc Oxidation Coatings

In this paper,TA2 pure titanium as the research object,using the formula uniform design method in phosphate,silicate,aluminate three kinds of salt system for micro-arc oxidation,to study the different salt system of different electrolyte components on the feasibility of micro-arc oxidation test,film-forming property,film thickness,microstructure and corrosion resistance.In addition,the phase composition and composition of the film in each salt system were analyzed and studied.Firstly,to study the relationship between the electrolyte components in different salt systems and the thickness of the film（μm）,the completely whitening time of the drip（min）,the corrosion current density（A/cm²）and to obtain the best value of each index.Finally,the best solution in each salt system can be obtained through comprehensive analysis based on the microstructure of the film,the principle of corrosion resistance of the film layer and considering the thickness of the film layer.It was found that the influence of NaOH on the film thickness is the most significant,followed by Na₂SiO_3,and KF is the least.When the proportion of NaOH in the electrolyte reaches 0.691,the film thickness reaches the maximum of 14.67μm.The surface morphology of the films shows that the high proportion of Na₂SiO₃ in the electrolyte is easy to form the surface morphology of granular accumulation.High proportion of NaOH tends to make the film produe large pores,cracks and other defects.In the drop test,it was found that the film thickness is not the main factor affecting the drop corrosion resistance of the film,and the drip corrosion resistance of the film is closely related to its microstructure morphology.In the electrochemical test,it was found that the surface porosity,micropore size and microcrack of the film greatly affect the electrochemical corrosion resistance of the film.It was also found that the ratio of Na₂SiO₃ and NaOH in the electrolyte has a significant effect on the drip corrosion resistance and electrochemical corrosion resistance of the film.Through the comprehensive analysis of the film thickness and corrosion resistance of each electrolyte scheme,it was determined that 2#is the best scheme,and the ratio of electrolyte is Na₂SiO₃0.613,KF0.290 and NaOH0.097.In addition,according to XRD analysis,the main phase composition of the film is rutile TiO₂,anatase TiO₂,and a small amount of amorphous compounds;According to EDS analysis,Ti,O and Siare the main elements of the film,and the content of F element is very small.The distribution of Siand Tielements in the film shows an alternating complementary trend,and the content of Sielement on the outside of the membrane layer is greater than the internal membrane layer.It was found that Na₃PO₄ has the greatest influence on the film thickness,followed by NaOH,and KF is the least.The higher the proportion of Na₃PO₄in the electrolyte,the more substances involved in the film formation reaction will be increased,which can significantly increase the thickness of the film.By analyzing the surface morphology of the films,it can be seen that Na₃PO₄ is easy to form a typical"honeycomb"morphology,and NaOH has a significant effect on the surface porosity,micropore morphology and pore size distribution of the film.In addition to the film thickness,the drip corrosion resistance of the film is also related to the microstructure morphology,phase composition and content of the film,the effect of Na₃PO₄ and NaOH on the drip corrosion resistane of the coating is more significant.In the electrochemical test,it was found that the electrochemical corrosion of the film is mainly characterized by permeability,and NaOH has a great influence on the electrochemical corrosion resistance of the film.Finally,according to the principle of focusing on the corrosion resistance of the film and considering the thickness of the film,the performance of the film obtained by 1#scheme is the best,and the ratio of the electrolyte is Na₃PO₄0.776,KF0.078 and NaOH0.145.In addition,according to XRD analysis,the film is mainly composed of anatase type TiO₂or rutile type TiO₂.According to EDS analysis,Ti,O and P are the main components of the film.The results show that the thickness of the microarc oxidation films in the aluminate system is generally thin,and NaOH has the greatest effect on the thickness of the film.followed by KF and NaAlO₂ is the least.When the proportion of NaOH in the electrolyte reaches 0.691,the thickness of the micro-arc oxidation films reaches the maximum of10.77μm.The surface morphology analysis shows that NaAlO₂is conducive to the formation of a typical"crater"like surface morphology,When the NaOH component is too high,it is easy to produce surface defects such as microcracks and large pores on the surface of the film.In the drop test,it was found that the drip corrosion resistance of the film is mainly related to the surface porosity,micropore morphology,surface defects and other microstructure characteristic parameters of the film,NaOH has the greatest influence on the drop corrosion resistance of the film.In the electrochemical test,it was found that the there is little difference in electrochemical corrosion resistance under different schemes,and the films prepared in scheme 2#showed better electrochemical corrosion resistance.Considering the corrosion resistance and thickness of the film,among all the electrolyte schemes,the film prepared by the 2#scheme has the best performance,with the electrolyte ratio of NaAlO₂0.613,KF0.290 and NaOH0.097.In addition,according to the XRD analysis shows that the main composition of membrane layer of high melting point of Al₂TiO₅ and rutile TiO₂;According to EDS analysis,the film contains Ti、O、Al and F elements,and the content of F element is the least.Tiand O elements are uniformly distributed in the film,and Al element decreases gradually from the outside to the inside of the film.