Hot Dip Galvanizing And Silicate/molybdate Passivation Process Research

Iron and steel is an important strategic resource.Iron and steel in the economic development cannot be ignored status,due to corrosion caused by a huge loss of steel.It is of great economic significance and far-reaching tactical significance to realize corrosion control and reduce the loss caused by corrosion of steel.Hot-dip galvanizing technology is the most commonly used in the world and the operation is very simple and convenient steel surface corrosion treatment.However,galvanized steel sheet in the air,especially in humid environments prone to corrosion,the surface of the formation of"white rust." Therefore,in order to extend the corrosion time of galvanized steel parts,in the galvanized surface passivation of a layer of conversion film is very necessary.In order to improve the corrosion resistance of galvanized steel sheet,the influence of other elements on the quality of the coating was studied.0.2%Al-0.2%RE-Zn was chosen as the main element of the alloy coating.Based on the silicate passivation process,the selective silicate/molybdate compound passivation process was chosen as the main research object.The sole component test and orthogonal test were used to screen and optimize the various components in the silicon/molybdenum complex passivation solution.The composition and technological conditions of the mixture were as follows:Na2SiO3·9H2O 35g/L,Na2Mo04·2H2O 25 g/L,NaF 18 g/L,HEDP 14 mL/L,H2O28 mL/L,passivation liquid pH of 2.5,immersion temperature of 25?,immersion treatment time of 40s,dry way for the natural dry.The corrosion resistance of the passivation film was tested by the experiment of copper sulfate,neutral salt spray test,salt water immersion experiment,scratch test,polarization curve and AC impedance spectroscopy.The results showed that silicate/molybdic acid Salt chrome-free passivation process can effectively improve the corrosion resistance of galvanized matrix.Through SEM test,it can be observed that the microstructure of the silicon-free chromium-free passivation film is more uniform,dense and smooth than the silicate passivation film.The chemotaxis of diverse elements in the passivation film was analyzed by XPS.After comparison,the main components were Zn4Si2O7(OH)2·2H2O?Zn(OH)2?ZnO?SiO2?ZnMoO4?Na2SiF6.The resistance of the passivation film was tested by the experiment of copper sulfate,neutral salt spray test,salt water immersion experiment,scratch test,polarization curve and AC impedance spectroscopy.The results showed that the silicate/molybdate The corrosion resistance of the conversion film obtained by the chrome-free passivation process is lower than that of the chromate passivation film,but the corrosion rate of the galvanized matrix can be greatly retarded compared with the untreated galvanized sheet.The passivation process is characterized by no pollution,low cost in the passivation process,simple process,and good application prospect in the field of chrome-free passivation technology.