The Research On Testing For Corrosion Behavior And Passivation Of Hot-dip Galvanized Steel

Hot-dip galvanized steel widely apply for domestic construction. The study of corrosion behaviour of hot-dip galvanized steel can deduce the mechanism of corrosion, and optimize the method of corrosion control. Corrosion behaviour of hot-dip galvanized steel in 5% NaCl aqueous solution was studied by electrochemical impedance spectrum techniques, and scanning electron microscope was used to observe the morphology of the hot-dip galvanized steel. The results revealed that Corrosion behaviour of hot-dip galvanized steel has a great relationship with corrosion produts. With the increase of immersion time, corrosion products are constantly changing, and the impedance of corrosion products are different. Parameters fitted by equivalent circuit show that the impedance of corrosion products increased at first, then decreased.A new technological design of free-chromated passivation has been studied. A series of tests was been taken to select the best experimental procedure parameter, such as bath temperature, dipping time, solution's pH and solution's concentration.Electrochemical behavior of the molybdate and acrylic composite passivation film in 3.5%NaCl solution was studied by polarization curve and electrochemical impedance spectrum( EIS) techniques. Anti-corrosion performance was tested by 48 hours salt spray test and salt water immersion method. Scanning electron microscope( SEM) was used to observe the morphology of the original film. Compared with unpassivated hot-dip galvanized steel and chromate passivated hot-dip galvanized steel, it was found that anti-corrosion performance of the molybdate and acrylic composite passivation film is better.