Mechanism of activation of aluminum by low-melting point elements. Part 2: Effect of zinc on activation of aluminum in pitting corrosion
- Kobe Steel, Ltd. (Japan)
- UMIST, Manchester (United Kingdom). Corrosion and Protection Centre
To clarify the mechanism of pitting corrosion of Al, the effect of a large amount of Zn (up to 2%) on Al pitting was studied in terms of pitting potential (E{sub pit}), repassivation potential (E{sub pit}), and pit nucleation transients. E{sub pit} in 0.5 M sodium chloride (NaCl) decreased with increased Zn content, and E{sub rep} was 50 mV to 60 mV below E{sub pit}, independent of Zn content. The shift of the anodic polarization curve in 6 M hydrochloric acid ([HCl] pit-like solution) was consistent with the change of E{sub pit} with Zn content. Analysis of passive current noise at the pA level in buffered solutions, with or without chloride (Cl{sup {minus}}), showed noise caused by Cl{sup {minus}} started at roughly the lowest potential where pitting occurred and had a similar potential dependence, irrespective of Zn content. Therefore, it was considered that pit nucleation had the same potential dependence, and possibly the same frequency, in Al-Zn alloys and pure Al and that the effect of Zn simply was to enhance dissolution kinetics in the local environment, facilitating the transition to stable pitting. A previously proposed model for the atomistics of activation was detailed.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 305357
- Journal Information:
- Corrosion, Journal Name: Corrosion Journal Issue: 1 Vol. 55; ISSN 0010-9312; ISSN CORRAK
- Country of Publication:
- United States
- Language:
- English
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