Composite Passivation Technology for Galvanized Steel

In order to replace the toxic chromate passivation,a composite passivation film was prepared on the galvanized steel by tracking the hydrolysis process of vinyl triethoxy silane(A-151) via conductivity tests and then adding the hydrolysis solution into the basic passivation bath.The corrosion resistance and mechanism of the composite passivation film were studied by neutral salt spray tests (NSS),polarization curve tests and electrochemical impedance spectroscopy (EIS).SEM/EDS were used to analyze the appearance and elements of passivated galvanized steel.The NSS results show that the corrosion area percentage of treated samples was only 4% after 72 h NSS.The SEM/EDS results indicate that a film about 8μm was formed on the galvanized steel,and the constitutes were Si,Mo,P and O.The composite passivation film blocks the anodic reaction of corrosion process.EIS results show that the total impedance of the composite film at the lowest frequency increased by more than one order of magnitude compared with the galvanized steel.