Effect of immersion time on the electrochemical behaviour of AZ31B alloy

Effect of immersion time on the electrochemical behaviour of AZ31B alloy in 0.01 M KOH solution under open circuit potential (OCP) conditions was studied by various electrochemical methods. Polarization results revealed that increasing immersion time leads to decrease the corrosion rate of this alloy. Also, electrochemical impedance spectroscopy (EIS) results showed that the reciprocal capacitance of the passive film is proportional to its thickness which increases with increasing immersion time. In Mott-Schottky analysis, no evidence of p-type semiconducting behaviour was found, indicating that the oxygen vacancies preponderated over the cation vacancies. Moreover, the Mott-Schottky results showed that the donor density increases by increasing the immersion time from 1 to 6 h, while it decreases when the immersion time reaches 9 and 24 h. Therefore, it is clear that higher immersion time offers better conditions for forming the passive films with higher protection behaviour, due to the growth of a much thicker and less defective films. (C) 2015 Elsevier B.V. All rights reserved.