Corrosion Resistance of Steel Sheets with Zn Protective Coatings

Abstract

Zinc coatings are commonly used to protect the surface of flat steel products against the aggressive influence of the environment and to delay the corrosion process. These materials are used among others in the automotive industry, aviation and aviation infrastructure, residential construction, power engineering and household appliances industry. These coatings are also an alternative to cadmium coatings. In order to ensure greater effectiveness of protection of galvanized steel products, it is possible to apply additional protection in the form of a conversion coating produced in a process which uses, among others, chromates as a passivator. The resulting passive layer additionally protects the zinc coating against aggressive environmental influences and thus extends the service life of the products. Both trivalent and hexavalent chromium is used in the chromating process. However, according to the Directive of the European Parliament and of the Council of Europe, the toxic and carcinogenic Cr (VI) must be eliminated and replaced by Cr (III) in the chromating process. The study included the evaluation of the corrosion resistance of the samples using the comparative method in an accelerated laboratory test in a neutral salt spray (NSS) test. Zinc coatings with varied thickness without passivation and a Cr (III) passivated zinc coating were tested.