CORRELATION OF MICROSTRUCTURE WITH CORROSION AND ELECTROCHEMICAL-BEHAVIOR OF THE BATCH-TYPE HOT-DIP AL-ZN COATINGS .1. ZN AND 5-PERCENT AL-ZN COATINGS

The batch-type hot-dip Zn and 5%Al-Zn coatings were investigated in the present work for correlations between their corrosion resistance, electrochemical behaviors, and microstructures. The microstructures of the coatings were altered with air cooling and water quenching for studying the corrosion resistance mechanism. Polarization curves can distinguish the layering character of the Zn coating. The 5%Al-Zn coatings possess prominent electrochemical passivation behavior. Intermetallic layers formed mainly between Fe and Al, adhering to substrate, were identified with energy-dispersive x-ray analysis and were believed to be responsible for the passivation phenomena observed in polarization curves. Faster cooling speed tends to lower the corrosion potential, E(com) on the basis of polarization measurement of the zinc but not the 5%Al-Zn coating and significantly affects the corrosion resistance of both coatings. The open-circuit potential as well as the galvanic coupling currents were also investigated for the coatings.