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Pre-exposure embrittlement of an Al-Cu-Mg alloy, AA2024-T351

Lookup NU author(s): Emeritus Professor Terry Evans


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When Al-Cu-Mg (AA2024-T351) alloy plate is immersed in 0.53 M NaCl solution, intergranular corrosion occurs, which initially takes the form of narrow fissures at the surface. Although growth of these fissures is initially rapid, it soon slows and the penetration depth is limited. However, these intergranular fissures can give rise to intergranular subcritical crack growth and eventual catastrophic fracture if specimens are strained slowly in laboratory air after pre-exposure to the NaCl solution. In our experiments, tensile specimens of the alloy were strained at strain rates in the range 10(-7)-10(-) (4)/s, and the cracking propensity was found to increase with pre-exposure times up to around 300 h. However, cracking was much reduced with longer pre-exposure times and became negligible after 500 h. This rather unexpected result can be explained by the observation that the intergranular corrosion fissure becomes increasingly broad and un-crack-like with extended pre-exposure times, failing to meet the prerequisite initiation conditions required for intergranular stress corrosion cracking. A further unexpected result was that straining specimens in the same 0.53 m NaCl solution after pre-exposure produced no intergranular crack growth. To investigate this further, tensile tests were conducted under electrochemical control, and this showed that the free corrosion potential in the test solution was too low in 0.53 m NaCl to allow cracking to proceed.

Publication metadata

Author(s): Holroyd NJH, Evans JT, Scamans GM

Publication type: Article

Publication status: Published

Journal: Corrosion Reviews

Year: 2015

Volume: 33

Issue: 6

Pages: 361-372

Print publication date: 01/11/2015

Online publication date: 17/09/2015

Acceptance date: 26/07/2015

ISSN (print): 0334-6005

ISSN (electronic): 2191-0316

Publisher: Walter De Gruyter, Inc

DOI: 10.1515/corrrev-2015-0037


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