Pit Growth Study in Al Alloys by the Foil Penetration Technique

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Abstract

The foil penetration technique was used to study pit growth in AA1100-O and AA2024-T3. Preliminary work on AA1100-O foils of different thicknesses indicated that the pit growth rate increased with increasing applied potential, suggesting that pit growth was not under transport control. Foil penetration experiments were also carried out on AA2024-T3 foils of a given thickness, at open circuit as well as anodic potentials. Dichromate ions and other oxidizing agents were added to some test solutions. Dichromate ions were shown to have little influence on the pit growth rate at controlled anodic potentials, even when added in large concentrations. However, dichromate ions effectively inhibited pitting at open circuit when present in very small amounts. Polarization curves of AA2024-T3 in 1 M NaCl with various additives show a large effect of dichromate ions in the cathodic region and no effect in the anodic region. These observations suggest that chromate (or its reduction product) acts as a cathodic inhibitor. Examination of penetrated samples was performed by optical and scanning electron microscopies, as well as by microradiography.

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Keywords

foil penetration technique, AA2024-T3, dichromate ions

Citation

Sehgal, A.; Frankel, G. S.; Zoofan, B.; Rokhlin, S. "Pit Growth Study in Al Alloys by the Foil Penetration Technique," Journal of the Electrochemical Society, v. 147, no. 1, 2000, pp. 140-148.