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    Sealing of Anodised Aluminium Alloys with Rare Earth Metal Salt Solutions


    Mansfield, C. and Chen, F. and Breslin, Carmel B. and Dull, D. (1998) Sealing of Anodised Aluminium Alloys with Rare Earth Metal Salt Solutions. Journal of the Electrochemical Society, 145 (8). pp. 2792-2798. ISSN 0013-4651

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    Abstract

    Boric‐sulfuric acid anodized (BSAA) aluminum alloys have been sealed in hot solutions of cerium or yttrium salts. For comparison, sealing has also been performed in the presently used dilute chromate solution, boiling water, and a cold nickel fluoride solution. The corrosion resistance of the sealed BSAA Al alloys Al 2024, Al 6061, and Al 7075 has been evaluated by recording impedance spectra during exposure in 0.5 N NaCl for 7 days. Shorter or longer exposure times have also been used depending on the corrosion resistance obtained by different sealing processes. From the impedance spectra the time dependence of the pore resistance, R po, and the specific admittance, A s, has been determined. At the end of the exposure the pitted area, A pit, was calculated. The relationship between A s and R po has been evaluated. Two different sealing mechanisms were detected. For sealing in dilute chromate the pores in the outer oxide layer stayed open, while for hot water sealing or sealing in cold nickel fluoride the pores were closed by an oxide/hydroxide. Sealing of BSAA Al alloys in cerium or yttrium salt solutions occurred according to one of these two mechanisms depending on alloy type and solution composition. Based on the experimental values of R po, A s, and A pit it was concluded that sealing in cerium nitrate and yttrium sulfate solutions provided corrosion resistance similar to that of chromate‐sealed BSAA Al alloys.

    Item Type: Article
    Keywords: aluminium alloys; anodised layers; surface treatment; corrosion resistance; electric impedance;
    Academic Unit: Faculty of Science and Engineering > Chemistry
    Item ID: 7949
    Identification Number: https://doi.org/10.1149/1.1838716
    Depositing User: Dr. Carmel Breslin
    Date Deposited: 21 Feb 2017 16:16
    Journal or Publication Title: Journal of the Electrochemical Society
    Publisher: Electrochemical Society
    Refereed: Yes
    Funders: Boeing Information, Space and Defence Systems
    URI:

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