The Corrosion Resistangt Performance Reaserch Of Ceramic Coatings On LY12 Aluminum Alloy

Aluminum alloy is the most widely used nonferrous metal materials in industry. The surface treatment and protection work has always been one of common concerns for the material researchers both at home and abroad.And anodized aluminum oxide coating, silicon oxide coating as common inorganic protective coatings on the surface of the aluminum alloy with high mechanical strength, excellent corrosion resistance performance were researched and used widely. But the study of inorganic coating corrosion resistance hardly researched, even less use of electrochemical methods evaluation research . The Sol gel method is widely used as the coating preparation method now, it has advantages on simple technological process, the material shape etc. So, Finding better preparation of inorganic coating performanc and preparation technology and using electric chemistry method to explore its anticorrosion mechanism to improve its protection performance on aluminum alloy is needful.Alumina coatings was prepared on aluminum alloy surface by the sol gel method. Additionally, the influence of the different times of coating on coating surface morphology and corrosion resistance was studied.Researches show that at 500℃ heat treatment , the main content of alumina coating is y- Al2O3; With the increase of number of sol coating,each of the sol coating seals holes on the last coating, holes on the surface of the coating reduce with crack increased gradually. Coating coated 6 times has the best corrosion resistant, By EIS testing found that coating resistance Rcand charge transfer resistance values Rct increases first then decreases,accompanied by the formation of corrosion products and dissolve corrosion process.The anodic oxidation film-alumina coating double coating was prepared by coated 6 times on the surface of anodic oxidation film, And corrosion resistance of double coating was studied. Researches show that alumina coating seals holes on anodic oxide film, Anodic oxidation film samples Rp value reached 105Ω·cm , and double coat’s Rp value reach 10 Ω·nm , promoted four orders of magnitude more matrix; Corrosion current density of the oxide film sample reduces the three orders of magnitude relative to matrix; double coating corrosion current density decreased two orders of magnitude relative to the oxide film sample to 4.772×10-9A/cm~2, double coat can significantly improve the corrosion resistance performance of anodic oxide film. Anodic oxidation film immersing in 3.5% Nacl solution exists self-sealing effect,coating resistance Rc increased with coating capacitance QCPE decreases.Additionally, after 157 days the corrosion resistant performance of oxidation film receded.At the same time,double coat dipped to 330 days still has good corrosion resistance.Silicon oxide coating was prepared by sol gel method on aluminum alloy surface,the influence of the different volume of addition of PVA on coating surface morphology and corrosion resistance was studied.Researches show that at 500℃ heat treatment , the main content of alumina coating is noncrystalline Si02. With the increase of PVA content in the coating performance is more dense,continuous, and surface crack is gradually reduce, but when the amounts of PVA exceed,the flocculation exsit in sol; Add 7% PVA coating samples of corrosion current density is lower than that of the matrix of two to three orders of magnitude,since corrosion potential is moved about 100 mv positively. Coating surface isevenly without crack, coating resistance value Rc reach 106Ω·cm,and has good shielding performance and corrosion resistance.