Study of Corrosion Behavior of Molybdating Films on the Galva-nized Steel

Molybdating for galvanized steel can improve the corrosion resistance of the zinc deposit on the steel. The corrosion resistance of molybdating coatings formed in certain technical treatments is almost as the same as that of chromating coatings on the zinc deposit in Neutral NaCl Salt Spray(NSS) tests and NaCl solution immersion tests, and even better than that of chromating coatings in Acid NaCl Salt Spray (ASS) test. If cracking occurs in the molybdating coatings, it will lower the corrosion resistance of the coatings in NSS tests and NaCl solution immersion tests. However, the corrosion resistance mainly depends on the thickness of the coatings. The molybdating coatings can retard the cathodic reaction during the corrosion, and the corrosion current will be thus decrease.