Effect of chromium on anticorrosive performance of zinc hot dip galvanised coatings

Abstract

Low carbon steel substrates were galvanised in molten zinc containing 0·5 and 1 wt-% chromium. The as cast coatings were exposed in a salt spray chamber for 2, 6, 10 and 14 days. The corroded samples were examined with optical microscopy, scanning electron microscopy and X-ray diffraction. From the above investigation it was deduced that chromium is beneficial with regard to the corrosion performance of the coating, as was shown by comparison with pure zinc galvanised samples exposed in the salt spray chamber under the same conditions. The action of chromium could be attributed to the fact that it is more anodic than zinc or to the fact that a Cr rich surface layer (η phase) which acts as a corrosion barrier is formed.