It is well known that iron and silicon are major elements in industrial pure aluminum alloy 1100. These elements form Al‐Fe‐Si ternary intermetallic compounds such as FeAl3, Fe3SiAl12, Fe3Si2Al9, Fe2Si2Al9 etc. The corrosion characteristics of the 1100 specimen and the Al‐Fe‐Si intermetallic compound specimens are experimentally investigated in NaCl and AlCl3 solutions. The electrochemical measurements, SEM surface observation and EPMA analysis reveal that (1) the iron content of the compounds influences the initiation of pitting attacks: the higher content of iron in the compound is, the more easily occurs the initiation of pitting attack, and (2) an existence of the compound in the bottom of the active pitting cavity, whether the iron content of the compound is higher or not, contributes to the further propagation of pitting attack as a cathodic site.

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The electrochemical experiments and metallurgical observations have been made to estimate the chloride ion concentration in the pitting cavity on the aluminum 1100 specimens which are corroded in 0.1 kmol/m 3 NaCl solution for 3.9 Ms. The estimation is based on the experimental fact that the corrosion potential (open circuit potential) of the 1100 specimens coincided with the pitting potential for all period of immersion. It is indicated that the value of the chloride ion concentration in pitting cavity is equivalent to that of 0.46～0.61 kmol/m 3 AlCl 3 solution as a substitutive solution of the pit solution.

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