Inhibition of pitting corrosion on aluminum alloy 2024-T3: Effect of soluble chromate additions vs. chromate conversion coating
Pitting potentials (E{sub pit}) of aluminum alloy (AA) 2024-T3 (UNS A92024) were improved with additions of 0.01 M sodium chromate (Na{sub 2}CrO{sub 4}, pH 8) and 0.0062 M Na{sub 2}Cro{sub 4} + 0.0038 M chromic acid (H{sub 2}CrO{sub 4}, pH 6) additions to 0.1 M sodium sulfate (Na{sub 2}SO{sub 4}) + 0.005 M sodium chloride (NaCl, pH 6) after 2-h periods at open-circuit potential (OCP). Chromate conversion coatings (CCC) on AA 2024-T3 also improved E{sub pit} determined in fast potentiodynamic scans without periods at OCP. These tests were designed to minimize chromate leaching and long-range transport of chromate. The OCP of CCC AA 2024-T3, Al{sub 2}Cu, Al{sub 2}CuMg, 99.999% Cu, and 99.998% Al were not changed significantly in 0.1 M Na{sub 2}SO{sub 4} + 0.005 M NaCl. Moreover, the OCP of AA 2024-T3, Al{sub 2}Cu, Al{sub 2}CuMg, and 99.999% Cu were not changed significantly in 0.1 M Na{sub 2}SO{sub 4} + 0.005 M NaCl with the addition of 0.01 M soluble chromate at pH 6 and pH 8. The mass transport limiting current density for O{sub 2} reduction also was not altered significantly by CCC or soluble chromate additions. Consequently, if the AA 2024-T3 matrix were polarized locally to the measured OCP of the intermetallics or replaced copper, inhibition of stable pitting on AA 2024-T3 is more likely to result form suppressed pit stabilization (in 0.1 M Na{sub 2}SO{sub 4} + 0.005 M NaCl with the addition of chromate at pH 6 or pH 8, or with CCC) than from eliminating two aspects associated with the potency of local galvanic couples (e.g., OCP of cathode sites and their oxygen reduction reaction kinetics [ORR]).
- Research Organization:
- Univ. of Virginia, Charlottesville, VA (US)
- OSTI ID:
- 20034194
- Journal Information:
- Corrosion (Houston), Vol. 56, Issue 3; Other Information: PBD: Mar 2000; ISSN 0010-9312
- Country of Publication:
- United States
- Language:
- English
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