Microstructure, Growth Kinetics, and Corrosion Resistance of Hot-Dip Galvanized Zn–5% Al Coatings

Several characteristics of Zn—5% Al coatings—namely microstructure, growth kinetics, and electrochemical behavior—have been studied. A ZnCl₂-based flux for the production of Zn–5% Al coatings by a dry hot-dip galvanizing process, developed in this work, produced coatings with good adhesion and without bare spots. The coating thickness is practically independent of the immersion time (between 1 and 600 seconds). The formation of an intermetallic compound on the surface of the steel during the first moments of contact with the molten bath is responsible for this behavior. Electrochemical tests in a 0.1 M NaCl deaerated solution have shown that the corrosion potential is ca. 400 mV anodic in relation to the corrosion potential of the steel and that preferential dissolution of zinc occurs during anodic polarization, resulting in a surface enrichment of aluminum.