STP425: Influence of Stress and Temperature on Short-Transverse Stress Corrosion Cracking of an Al-4.2Zn-2.5Mg Alloy

    Helfrich, W. J.
    Research engineer, Kaiser Aluminum & Chemical Corp., Spokane, Wash.

    Pages: 10    Published: Jan 1967


    Abstract

    Stress corrosion cracking of an age-hardened Al-Zn-Mg alloy (7039) subject to continuous immersion in a 1 N NaCl solution was studied at stresses of 5 to 55 ksi and temperatures of 30 to 100 C and found to be an activated process. The rate, r, of stress corrosion (proportional to the inverse failure time) can be expressed as: r=r0exp{[Q*(O)sV*]/RT} where Q* (O) is the activation energy in the absence of stress, s, and V* is the activation volume. Q* (O) has a value of 20 ± 0.8 kg∙cal/mole, and V* is approximately 28 to 34 cm3/mole for applied stresses of 25 ksi or higher. It is suggested that the rate-determining step in the stress corrosion of 7039 involves anodic dissolution of MgZn2 at grain boundaries. The mechanism of stress corrosion cracking is discussed with reference to previously derived models.

    Keywords:

    aluminum alloy, stress corrosion, cracking, activation, electrochemical dissolution, pitting (corrosion), corrosion


    Paper ID: STP46449S

    Committee/Subcommittee: G01.05

    DOI: 10.1520/STP46449S


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