The role of chloride in the electrochemical behaviour of AZ31B Mg alloy in 0.05 M NaOH was investigated by means of potentiodynamic polarization, Mott–Schottky analysis, electrochemical impedance spectroscopy and scanning electron microscopy. Potentiodynamic polarization curves indicated that chloride concentration increase leads to a narrower passivation region of AZ31B Mg alloy. Also, the polarization curves revealed that increasing chloride concentration leads to higher corrosion current density in AZ31B Mg alloy. The micrographs clearly showed that the number and depth of pits increased with increasing chloride concentration. The Mott–Schottky analysis showed that the passive films have n-type semiconductive characteristics, where the number of oxygen vacancies and interstitials predominate over the cation vacancies. Moreover, Mott–Schottky results showed that the donor densities are in the range of 1021 cm–3 and increase with increasing chloride concentration.
