INFLUENCE OF COPPER, CADMIUM AND TIN ADDITIONS IN THE GALVANIZING BATH ON THE STRUCTURE, THICKNESS AND CRACKING BEHAVIOR OF THE GALVANIZED COATINGS

The influence of copper, cadmium and tin additions in the galvanizing bath on the morphology and thickness of galvanized coatings has been s tudied using X-ray diffraction and optical and scanning electron micro scopy associated with energy-dispersive spectroscopy microanalysis. Co pper promotes the delta(1) phase and hinders the zeta phase growth. In the opposite, cadmium promotes the zeta and Gamma phase formation and hinders the growth of the delta(1) phase. No change in the morphology of galvanized coatings has been observed with the addition of tin. Me chanisms have been proposed in order to explain the effect of the abov e elements on the formation of intermetallics. The cracking of the coa tings after tensile testing in the plastic region of the specimens has been examined. The delta(1) phase is responsible for the nucleation a nd propagation of transverse cracks parallel to the steel substrate. C admium hinders the nucleation and propagation of the transverse cracks during loading up to the yield point of the steel; however, the colum nar growth of the zeta phase results in the complete flaking of the co ating during loading up to the ultimate tensile strength of steel. The Gamma phase remains always adhered to the steel substrate.