STP1134: Time-Lapse Video Techniques in the Corrosion Testing of Aluminum Alloys

    Newton, CJ
    Research metallurgist and senior consulting scientist, Alcan International Ltd., Banbury Laboratories, Banbury, Oxfordshire

    Holroyd, NJH
    Research metallurgist and senior consulting scientist, Alcan International Ltd., Banbury Laboratories, Banbury, Oxfordshire

    Pages: 27    Published: Jan 1992


    Abstract

    This paper describes the use of time-lapse video techniques for in situ observation during controlled and free corrosion of high-strength Al-Zn-Mg-Cu alloys 7075 and 7150 and two Al-Zn binary alloys. Direct observation of corroding 7075 in various tempers shows that, as a precursor to stable pit formation, a deformable gelatinous layer of corrosion product develops. Gas is evolved at the metal/hydrated oxide interface, which distorts the gel layer at potentials below those expected for pitting. During stress corrosion cracking of 7150 T6, time-lapse video images confirm that initial drying after total immersion of 0.6M NaCl solution leads to an acceleration in the apparent rate of crack growth from 5 × 10-7 m/s to 9 × 10-6 m/s. This rate is sustained for only a few minutes but could help explain the aggressive nature of alternate immersion testing.

    Keywords:

    aluminum alloys, corrosion, time-lapse video, stress corrosion cracking, alternate immersion


    Paper ID: STP19588S

    Committee/Subcommittee: G01.11

    DOI: 10.1520/STP19588S


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