Study of zinc coatings on steel substrate attained by two different techniques

The purpose of this work was to identify the influence of different process variables, such as bath temperature, cooling rate, air knives wiping, immersion time and bath alloy additions, on the morphology and coating thickness attained using two different galvanizing processes: Cook Norteman and Sendzimir. The data of these operational variables were reported for each process. Scanning electron microscopy was used to characterize the microstructure of the metallic samples. Also, impact and bending tests were performed, in order to evaluate the adhesion of the coatings. The most influential step found in coating thickness was immersion time. In contrast, aluminum concentration was the most important factor determining coating morphology, since it controls the formation of Fe-Zn intermetallic phases. For Al concentration lower than 0.09 wt.%, the layer formed on the steel consisted of eta, zeta, delta and Gamma phases. Higher concentration of Al (more than 0.16 wt.%) produced a thicker layer of eta phase, that is richer in Zn than in the former case. Also, lamellae rich in Fe, Al and Zn were formed close to the substrate-coating interphase. Both coatings showed good adhesive strenght, under the same testing conditions. (C) 1999 Elsevier Science S.A. All rights reserved.