The role of chloride ions in the pitting corrosion of some Al-Si alloys was investigated by chemical, polarization and EIS measurements, as well as SEM studies. Differences in corrosion rates of pure aluminium and the alloys are discussed. The capacitive behaviour of the oxide covered surface is replaced by resistive behaviour as immersion time increases in HCl solutions. At neutral pH corrosion currents increase then decrease with chloride ion concentrations. Pitting by chloride ions initiates more readily in acidic media.