SEDL / STP / STP425-EB / STP46449S

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

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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.