The electrochemical behaviour of aluminium and Al-silicon alloys in aqueous solutions containing different concentrations of chloride ions was investigated. Electrochemical impedance spectroscopy (EIS) and polarization techniques were used. The electrodes were anodically passivated under galvanostatic control. The effect of formation voltage on the stability of the passive film was studied. The open-circuit impedance measurements have shown that the dissolution of the anodic oxide formed on aluminium or aluminium alloys follows the empirical relation : C-1 = C-0(-1) - Bt(1/2) C-1 is proportional to the oxide film thickness. B represents the rate coefficient of the oxide film dissolution. The results revealed that the presence of chloride ions even in the oxidizing medium (1 M HNO3) delays the passivation of the material. Complex plane analysis of the formed oxide film indicates that the corrosion resistance increases as the concentration of chloride ions increases. For naturally passivated electrodes, the corrosion resistance decreases as the concentration of chloride ions increases. This behaviour was explained by film repair-film removal equilibria.