Study On The Preparation Of Silyl-based Chromium-free Passivation Solution And Its Corrosion Resistance Mechanism

Due to its large output,relatively low price and excellent performance,steel is widely used in various fields,but its corrosion resistance is relatively poor.Hot dip galvanizing is a common steel anticorrosion method.Passivation treatment can further strengthen the protection of galvanized steel.Corrosion ability to extend its service life.The passivation process uses a conventional chromate passivation solution with excellent protection properties,whereas chromium ions are inherently toxic and pollute the environment.There are still some gaps in performance and stability between the existing chromium-free passivation solution and the chromate passivation solution.The development of silane-based organic/inorganic compounded chromium-free passivation solution was carried out,and the influence of passivation parameters on the protection performance of chromium-free passivation solution was studied.The main research contents and conclusions are as follows:（1）Process research on the composition of chromium-free passivation solution.The addition of the main components in the silane-based organic/inorganic composite chromium-free passivation solution was optimized by orthogonal experiments,mainly include:8%silane coupling agent（KH-792）,2%elastic emulsion,3.6%ammonium fluorotitanate,0.7%coconut oil fatty acid monoethanolamide.（2）Study on the influence of passivation process parameters on passivation performance.The corrosion resistance of chromium-free passivation films was investigated under different passivation conditions.The experimental results show that the corrosion rate is 0.031 g×m^-2/h at the condition of pH 2,the passivation temperature is55°C,and the passivation time is 60 s,which is basically equivalent to the corrosion resistance of low valent chromate.（3）Microstructure and mechanism analysis of chromium-free passivation film.The SEM and AFM were used to find that the coating was uniform and dense,and the pitting corrosion was minimal.Zn₅（OH）₈Cl₂×H₂O with strong compactness in the film layer was found by EDS and XRD.XPS and infrared spectroscopy were used to detect the bonding of the film mainly including O-Si,Si-O-Si,Si-O-Zn and finally form a dense network structure in the form of siloxane on the surface of the galvanized steel sheet.The film strengthens the corrosion resistance of the film.（4）Electrochemical performance of chromium-free passivation film.Under the optimized passivation process,the corrosion current of the chromium-free passivation film was studied by polarization curve,which was 2.49×10^-6A/cm².The AC impedance shows that the diameter of the capacitive arc is slightly larger than the chromate passivation film,which can hinder the corrosion of the coating.The prepared silane-based organic/inorganic composite chromium-free passivation solution has the same protective performance as the low-cost chromate,and has the advantages of low cost,simple preparation process and stable use performance,and has potential industrial application value.In the preparation process of chromium-free passivation solution,the relationship between passivation process parameters and passivation performance,and the protection mechanism of passivati on solution are useful for the research and development of chromium-free passivation.