ELECTROCHEMICAL NOISE STUDY ON GALVANIC CORROSION OF ALUMINUM ALLOY IN CHLORIDE ENVIRONMENTS - EFFECT OF OXIDE FILM STRUCTURE

摘要

Four different types of anodic films, barrier type, porous type anodized in (COOH){sub}2 solution, porous type anodized in H{sub}2SO{sub}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.