Pit growth study in Al alloys by the foil penetration technique

The foil penetration technique was used to study pit growth in AA1100-O and AA2024-T3. Preliminary work, on AA1100-0 foils of different thicknesses in dicated that the pit growth rate increased with increasing applied potentia l, suggesting that pit growth was not under transport control. Foil penetra tion experiments were also carried out on AA2024-T3 fails of a given thickn ess, at open circuit as well as anodic potentials. Dichromate ions and othe r oxidizing agents a ere added to some rest 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 i ons effectively inhibited pitting at open circuit when present in very smal l amounts. Polarization curves of AA2024-T3 in M NaCl with various additive s show a large effect of dichromate ions in the cathodic region and no effe ct 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 anti scanning electron microscopies, as we ll as by microradiography. (C) 2000 The Electrochemical Society. S0013-4651 (99)03-050-5. All rights reserved.