Effect of the method of removing zinc coatings defects produced by the hot-dip galvanizing on their corrosion resistance

The primary purpose of the galvanized coating is to protect the iron or steelwork against corrosion, while considerations related to aesthetics or decorative features should be secondary. Zinc coatings manufactured in industrial conditions may have many potential appearance defects, which, do not have a decisive impact on the protection of the substrate against corrosion. The post-galvanizing defects are usually the result of improper surface preparation of steel products before HDG (hot dip galvanizing). However, this has some influence on their corrosion resistance. The aim of the work was was to determine the effect of removing zinc coatings defects on their corrosion resistance. The tests were carried out on hot-dip galvanized samples of S235 steel with zinc coating defects, i.e. with non-galvanized places as a result of using an anti-weld, an oil marker or traces of stickers. Zinc paint and a corrector commonly used in Galvanizing Plants: "zinc spray" were used to repair the zinc coating. Metallographic analysis was performed to assess the microstructure of the zinc coatings. The coating thickness was measured in acc. with PN-EN ISO 1463. Corrosion resistance of the zinc coatings after repair was assessed on the basis of NSS test results acc. to PN-EN ISO 9227. This work is practical. The presented test results clearly indicate that the use of the "zinc spray" corrector does not provide good corrosion resistance in accordance with PN-EN ISO 1461