Effect of aluminium on the passivation of zinc-aluminium alloys in artificial seawater at 80 °C

The effect of Al (0.15, 0.3 and 1.0 wt.%) on the passivation of Zn-Al alloys in artificial seawater at 80 degrees C is investigated by electrochemical measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is found that the presence of Al in Zn-Al alloys can retard passivation. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements show that Al increases the current density but decreases the corrosion resistance of passive films, respectively. Mott-Schottky analysis reveals that Al increases the electrical conductivity and the capacitance of the films. Passivation of Zn-Al alloys occurs in artificial seawater when the immersion time is between 120 and 288 h, due to the presence of various Zn and Al protective compounds at the surfaces. Depassivation occurs when the immersion time is between 288 and 720 h, probably due to the decrease of solution pH and the Cl penetration mechanism. (c) 2012 Elsevier Ltd. All rights reserved.