STP1134

    Examination of the Influence of Lithium on the Repassivation Rate of Aluminum Alloys

    Published: Jan 1992


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    Abstract

    The influence of lithium on the rate of repassivation of aluminum alloys was studied by conducting scratch-repassivation experiments on samples with differing lithium and copper contents and with differing heat treatments in a buffer solution containing either 0.5M sodium sulfate or 0.5M sodium chloride. The experiments were conducted under either open circuit conditions, with the resulting potential transient recorded, or under potentiostatic conditions, with the resulting current transient recorded. Due to the rapid repassivation rate of aluminum alloys, unique experimental and analytical procedures had to be developed. In particular, the experiments were designed to minimize the time between initiation and completion of the scratch and to generate the bare surface at a constant rate. A constant bare surface generation rate allowed for determination of the bare surface current density from the slope of the rise transient rather than from the maximum current observed as done by previous investigators. The bare surface current density determined in this manner was always greater than that calculated from the maximum current. Lithium in solid solution was found to slightly increase the bare surface current density but it did not significantly alter the rate of repassivation over the range of lithium concentrations studied. The precipitation of lithium phases altered the repassivation behavior but, the nature of the observed changes depended on the type of precipitate.

    Keywords:

    aluminum alloys, corrosion, aluminum-lithium alloys, film rupture, passivity, pitting, repassivation, stress corrosion cracking (SCC), scratch test


    Author Information:

    Stoudt, MR
    Materials research engineer, and group leader, Corrosion Group, National Institute of Standards and Technology, Gaithersburg, MD

    Vasudevan, AK
    Program manager, Office of Naval Research, Arlington, VA

    Ricker, RE
    Materials research engineer, and group leader, Corrosion Group, National Institute of Standards and Technology, Gaithersburg, MD


    Paper ID: STP19590S

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP19590S


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