The effect of chloride ions concentration on the semiconducting behaviors of 1050 and 6061 Al alloys in 0.003 M NaOH has been investigated by using potentiodynamic polarization, cyclic potentiodynamic polarization and Mott-Schottky analysis. Potentiodynamic and cyclic potentiodynamic polarization curves indicate that chloride ions concentration narrowed passivation region for both Al alloys. Also, these polarization curves revealed that increasing chloride ions concentration leads to decrease the pitting potential of both Al alloys. Mott–Schottky analysis demonstrated that the passive films formed on both Al alloys in 0.003 M NaOH with and without NaCl addition show n-type semiconducting behaviors in nature. For both alloys, the passive films formed in chloride-free solution are most stable, and that formed in chloride-containing solution are unstable. Also, the Mott– Schottky results showed that the donor density evaluated from the Mott–Schottky plots increases with increasing chloride ions concentration.
