A morphological and microstructural study of flame-sprayed zinc coatings on low-alloyed steels as a contribution to explaining their corrosion resistance

Zinc is an ideal coating material for steels because it offers simultaneously cathodic and barrier protection. Several processes have been developed to provide zinc coatings. Thermal spraying is widely used due to the fact that it is simple, quick and effective. The present work deals with the morphology, the structure and the corrosion performance of zinc coatings deposited with thermal spraying. The study was performed with scanning electron microscopy and X-ray diffraction, while microstructural characterization was accomplished transmission electron microscopy. Finally, corrosion tests were performed with exposure of the coated samples in a salt-spray chamber. From the microstructural investigation it was deduced that before corrosion the as-produced coatings are mainly composed of zinc, while zinc oxide nanoparticles are dispersed in their mass. After corrosion tests it was found that zinc flame-sprayed coatings provide adequate corrosion protection because the corrosive elements did not penetrate the coating or reach the substrate. (c) 2008 WILEY-VCH Verfag GmbH & Co. KGaA, Weinheim.