CORRELATION OF MICROSTRUCTURE WITH CORROSION AND ELECTROCHEMICAL BEHAVIORS OF THE BATCH-TYPE HOT-DIP AL-ZN COATINGS .2. 55-PERCENT AL-ZN COATING

A batch-type hot-dip 55%Al-Zn coating has been successfully prepared in the laboratory. The attempt was made to investigate the corrosion behavior of the coatings in terms of galvanic coupling and open-circuit potential measurements. The electrochemical property of the coatings was studied with polarization curve techniques. The cooling speed of the coatings, either with furnace, air or water cooling, significantly affects the coating structure and corrosion behavior. A broad passivation region, further studied with electrochemical, x-ray diffraction (XRD), and scanning electron microscopy-energy-dispersive spectrography (SEM-EDS) techniques, was found for both air-cooled and water-quenched coatings. The intermetallic layer, identified to be FeAl3, Fe2Al5 and Fe4Al13, was found to be responsible for the passivation behavior.