The effect of preflux bath additives on the morphology and structure of the hot‐dip galvanized coatings

The effect of CdCl₂, NiCl₂ and SnCl₂ on the morphology and on the structure of hot‐dip galvanized coatings was examined with optical microscopy, scanning electron microscopy and X‐ray diffraction, when these salts are added in the preflux bath. From this investigation it turned out, that the morphology of the coatings formed after fluxing in a preflux bath containing CdCl₂ is very similar to the morphology of the coatings formed in the usual flux, regardless of the concentration of the Cd salt and the solvent used (water or aqueous solution containing 50% ZnCl₂^.NH₄Cl) in the preflux bath. By contrast, Ni enhances the growth of small‐sized crystallites of the zeta‐phase instead of the columnar growth, and finally it results in reduction of the coating thickness. This phenomenon is likely to be affected by the NiCl₂ concentration but not by the solvent used (pure water or aqueous solution containing 50% ZnCl₂^.NH₄Cl). Finally, Sn addition seems to be inert with regard to the coating structure. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)