The effect of bismuth on the structure of zinc hot-dip galvanized coatings

Low carbon steel substrates were galvanized in molten zinc containing 0.0, 0.5, 1.0 and 2.0 wt.% bismuth. The as-cast coatings were examined with optical microscopy, scanning electron microscopy and X-ray diffraction. From the above investigation it was deduced that Bi addition does not affect the morphology of the galvanized coatings with regard to the “traditional” galvanized coatings, although it is mainly accumulated in the eta phase and in the upper part of the zeta phase in the form of inclusions. However these inclusions could accelerate the coating corrosion because Bi is cathodic to Zn. Furthermore the thickness of the galvanized coatings is reduced when Bi is added.