The effect of anodic oxide film structure, barrier type and porous type on galvanic corrosion resistance of aluminum in 0.5 kmol/m 3 H 3 BO 3 / 0.05 kmol/m 3 Na 2 B 4 O 7 with NaCl was examined by electrochemical random signal (electrochemical noise) analysis technique. When pitting corrosion occurs, rest potential suddenly decreases and current increases rapidly, and rest potential and current change with fluctuation during galvanic corrosion. The galvanic current change correlates closely with corrosion potential change. As the thickness of both types of anodic oxide films and decreasing of chloride ion concentration, the incubation time of pitting corrosion became longer, and incubation time of pitting corrosion of specimen formed porous type anodic oxide film is longer than that of specimen formed barrier type anodic oxide film. The inverse of incubation time increase with chloride ion concentration to the power of n, Cl n . The value of n is between 1.2 and 2.5 in both oxide films.

A new type of electrochemical noise analysis technique with First Fourier Transformation, FFT, was applied to galvanic corrosion of barrier and porous type anodic oxide films formed on aluminum in 0.5 kmol/m 3 H 3 BO 4 / 0.05 kmol/m 3 Na 2 B 4 O 7 solutions with 0.01 kmol/m 3 NaCl. During localized corrosion, the current and potential were changed, with fluctuations and the potential and the current fluctuations show good correlation. The slope of the PSD spectra of both types of anodized specimens are about minus one (-1), just after localized corrosion started. This technique allows observation of electrochemical impedance changes during localized corrosion. The impedance spectra are independent of signal frequency and the impedance of porous types anodic oxide film specimens decrease with immersion time and increases with anodizing time.

Four different types of anodic films, barrier type, porous type anodized in (COOH) 2 solution, porous type anodized in H 2 SO 4 solution and composite type, were formed on pure aluminum and aluminum alloy specimens. The effect of anodic oxide film structure on galvanic corrosion of aluminum and its alloys was measured by electrochemical noise technique. During incubation period (before localized corrosion started), both current and potential slightly changed with time. After localized corrosion started, those changed suddenly with time with fluctuation. The composite type anodic oxide film formed on pure aluminum and 6061 alloys showed the longest incubation period than other types of anodic oxide films formed on these specimens. However, anodic oxide treatment did not increase corrosion resistance of 2017 alloy.