Study on lanthanum salt conversion coating modified with citric acid on hot dip galvanized steel

Modified lanthanum salt conversion coatings prepared by rare earth salt route based on lanthanum nitrate solution were proposed as alternatives to the process involving toxic hexavalent chromate. The structure and composition of the coating were determined with X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy. The surface morphologies of the treated samples were observed with scanning electron microscopy. The natural salt spray and electrochemical impendence spectra tests were carried out to evaluate the coating performance. The results showed that the corrosion resistance of the lanthanum salt conversion coating modified with citric acid on hot dip galvanized steel was superior to that of common lanthanum salt conversion coating.