Study On The Preparation And Corrosion Resistance Of Chromium Trivalent Chromium Composite Passivation Film

Galvanized sheet due to its low cost,good corrosion resistance and can be used as a sacrifice anode cathodic protection,gradually favored by more and more people in the iron and steel protective measures,because itself is lively,but zinc layer in the environment of easy corrosion was going to be easy corrosion generated white material,thus seriously affect the appearance quality of the products and its service life.Based on the situation,galvanization passivation and therefore is more important,hexavalent chromium because its toxicity is bigger,and bigger environmental hazards to human body,at home and abroad,various legal doctrine under the limit,its used for passivation treatment is limited.In contrast,trivalent chromium due to its low toxicity,carcinogenicity,passivation film properties and hexavalent chromium passivation film close to nature,therefore,trivalent chromium passivation technology has gradually replaced hexavalent chromium passivation technology trends.This experiment by orthogonal test and extreme difference analysis method,respectively,to determine the color trivalent chromium passivation solution,the composition of trivalent chromium passivation liquid blue and white,was studied by single factor experiment passivation passivation temperature and time,stop time,the influence of the passivation solution pH for passivation membrane performance,and the optimum passivation conditions were determined.By copper sulfate spot corrosion test,salt spray test,salt water soak,electrochemical analysis and other methods,respectively,the color of trivalent chromium passivation film with trivalent chromium passivation film blue and white had been used to characterize the corrosion resistant properties,scanning electron microscopy(SEM),EDS energy spectrum instrument by means of passivation film microstructure and composition was analyzed,and through adhesion test on the passivation film adhesion test.According to the analysis results,the trivalent chromium passivation mechanism is discussed.The optimal formula of trivalent chromium blue and white passivation for galvanized layer was determined by orthogonal experiment.Cobalt nitrate 2 g/L,Silicone resin1.4 g/L,Polyurethane resin 0.8g/L,Benzotriazole 0.05 g/L,Glycol butyl ether0.3 g/L.The optimum process parameter is: passivation temperature 30?C,=1.8,The passivation time of 30 s,10s for empty stop time,65?C oven drying.The blue and white passivation film obtained through the test can reach 126 h.At the same time,the optimal composition of chromium-colored passivation liquid with zinc coating was determined: chromium sulfate 10g/L,Nitric acid nickel 1.5g/L,Polyurethane resin 10 g/L,Sodium chloride 2.0g/L,Sodium nitrate 4.3g/L.The optimum process parameter is: passivation temperature 30?C,Passivation pH=2.0,The passivation time of 120 s,The null time is 10 s,65?C oven drying.The colored passivation film obtained through the test can reach 142 h.The comparison of the microscopic appearance before and after passivation in the SEM image can be seen that the galvanized layer surface after color trivalent chromium passivation and trivalent chromium passivation,blue and white micro crack,groove surface used to be a good filling and package,the galvanized layer formed on the surface of a layer of dense,uniform passivation membrane,so as to improve the corrosion resistance of zinc coating.According to the analysis of EDS composition,the main components of the trivalent chromium passivation film are: Zn?Cr?Si?O,indicating that the passivation liquid forms an inorganic organic hybridized film on the surface of the zinc coating.