Studies On The Processes Of Sulfuric-tartaric Anodizing And Sealing For Aluminium Alloy

Aluminum alloy has the superior proprieties such as light weight,high specific strength,and good processability.It can be widely used in various fields,especially for the aeronautical and space industry.However,we still need to consider its corrosion performance during the course of service environment.Anodizing can provide an effective way to improve its corrosion resistance,just like the several choromate-containing processes.Nowdays the related environment protection laws require the alternate processes because of their poisonous properties.At present,the chromium-free tartaric-sulfuric anodizing(TSA)and its post-sealing process have gradually been applied in the aviation,aerospace and defense industries abroad.But the related domestic applications mostly remain in the chromic acid anodizing(CAA).And the awareness of the environmental protection and the country’s environmental governance have been rising this years,so the development of viable hexavalent chromium substitution technology in China has become more urgent.Therefore,this thesis explores the TSA anodizing process and its sealing process to provide theoretical and experimental basis for its application in China.In this thesis,LY12 aluminum alloy is used as the base material and the pre-treatment that had existed in our laboratory was prescribed.Next,through the two homogenization designs which used corrosion resistance as indicators,the optimal parameters of the TSA process: tartaric acid and sulfuric acid concentration ratio and anodizing voltage,anodizing temperature,anodizing time were obtained sequentially: sulfuric acid 55g/L,tartaric acid 88g/L;anodizing voltage,time,and temperature were 14 V,23min,and 37°C.In addition,the dispersibility of the TSA anodizing process,the contact angle,roughness,and additives were also studied.It was found that the dispersibility of the TSA anodizing process meets the production requirements,and the contact angle of the sample surface after treatment becomes smaller,but roughness does not change much.Additives such as sodium tungstate and sodium molybdate can reduce the anodic oxidation film formation rate and improve the corrosion resistance of the anodic oxidation film.The thinning effect of sodium molybdate is obviously greater than sodium tungstate,but the corrosion resistance is less effective than that of sodium tungstate.About sealing process,three types sealing were investigated: sealing with potassium permanganate,zirconium-titanium and trivalent chromium.The results show that the samples have excellent corrosion resistance after sealing with potassium permanganate,which is comparable to traditional potassium dichromate sealing and nickel fluoride sealing,and better than boiling water;zirconium-titanium sealing can also improve the corrosion resistance of the samples,but the effect is poor than that with the traditional sealing;samples with trivalent chromium sealing show poor appearance and uneven film.At last,the test aluminum alloy specimens obtained from the part of given missile rudder bearing,were anodized and sealed,and it was found that TSA process and potassium dichromate sealing significantly improve the corrosion resistance of the sample.This suggests that the TSA and subsequent sealing processes investigated in this thesis preliminary meet the conditions of production applications.