| Cast aluminum is a traditional metal material,which has the advantages of low density and high specific strength.With the development of modern industry and new casting technology,cast aluminum alloy has been widely used in automobile manufacturing,spacecraft development,mechanical processing and other industrial fields.However,due to the poor corrosion resistance of cast aluminum in the industrial and atmospheric environment,more and more attention has been paid to its anticorrosion.In this paper,silane composite passivation film was prepared on the surface of cast aluminum alloy to improve the corrosion resistance of metal materials,Scanning electron microscope(SEM),energy spectrum analyzer(EDS),Fourier infrared spectroscopy analyzer(FT-IR)and electrochemical workstation were used to characterize and test the performance and structure of the membrane,in order to determine the optimal formulation and technological process of passivation film preparation,as well as to study the film formation mechanism and corrosion behavior of passivation film.By single factor experiment and orthogonal experiment,explored the passivation membrane,the optimal formula and the optimum technological conditions:mass ratio for 2:1:17 KH560 silane coupling agent,anhydrous ethanol and deionized water,3 g/L isopropanol aluminum,hydrolyzing together for 10 h.A thin layer of uniform liquid film was coated on the surface of the cast aluminum matrix by dipping pulling method and the film was placed in a box furnace with programmable atmosphere protection and dried at 100?for 20min.The test results showed that the corrosion current of the passivation film is 3.78×10-7A/cm2,and the polarization resistance is 869.38 k?·cm-2.A colorless transparent film was prepared,which was continuously dense and uniformly covered the surface of the matrix.Ce(NO3)3and La(NO3)3were used as additives to further improve the corrosion resistance of the film layer.The optimal addition amount of rare earth salt is 0.5g/L Ce(NO3)3or 0.3g/L La(NO3)3by single factor experiment.The results obtained by electrochemical test and scanning electron microscope show that the addition of rare earth salt can effectively improve the corrosion resistance of the film layer.The corrosion current of cerium doped passivation film is 1.35×10-7A/cm2,and the polarization resistance is 5712.61 k?·cm-2;the corrosion current of lanthanum doped passivation film is 3.16×10-7A/cm2,and the polarization resistance is 3446.91 k?·cm-2,and the impedance is an order of magnitude higher than that of the base film layer.After adding rare earth salt,the flatness of film layer decreases.The film forming mechanism of KH560-isopropanol aluminum passivation film and the corrosion behavior of cerium nitrate doped passivation film in 5wt%Na Cl solution were analyzed.After the hydrolysis reaction of KH560 and aluminum isopropanol in aqueous solution,it was dehydrated,condensed and crosslinked to form a network structure and adsorbed on the metal surface.It was condensed with the hydroxyl group on the metal surface to form a compact organic composite film.The corrosion behavior of cerium nitrate doped passivation film in 5wt%Na Cl solution can be divided into three stages:The first stage is the rupture of the outer silane film,and the corrosion potential and membrane layer impedance decrease rapidly;The second stage is the release of Ce3+and the repair of the membrane layer.The corrosion potential and impedance of the membrane layer rise rapidly to close to the initial value within a short period of time,and the value fluctuates up and down in a small range.The third stage is the corrosion damage of the membrane structure.When Ce3+is completely released and the membrane cannot be repaired,the passivation film gradually loses its blocking effect on the electrolyte solution after a long time of immersion.It shows that the doping of cerium nitrate not only improves the corrosion resistance of the film layer,but also endowing the film layer with the function of"self-healing". |
PDF Full Text Request