Localized corrosion susceptibility of Al-Li-Cu-Mg-Zn alloy AF/C458 due to interrupted quenching from solutionizing temperatures

J. E. Kertz, P. I. Gouma, R. G. Buchheit

Research output: Contribution to journalArticlepeer-review

79 Scopus citations

Abstract

Isothermal time-temperature-localized corrosion-behavior curves were determined for the Al-1.8Li-2.70Cu-0.6Mg-0.3Zn alloy AF/C458, to understand the effect of slow or delayed quenching on localized corrosion susceptibility. Alloy samples were subject to a series of systematic interrupted quenching experiments conducted at temperatures ranging from 480°C to 230°C for times ranging from 5 to 1000 seconds. Individual samples were then exposed to an oxidizing aqueous chloride solution consisting of 57 g/L NaCl plus 10 mL/L H2O2 to induce localized attack. The localized corrosion mode was characterized by optical microscopy. Additionally, the microstructure of selected samples was characterized by transmission electron microscopy (TEM) to relate the corrosion mode and morphology to microstructural features. Results showed that only pitting attack was exhibited by samples subjected to isothermal treatment at temperatures greater than 430°C. At temperatures ranging from 280°C to 430°C, isothermal treatment tended to induce susceptibility to intergranular attack (IGA) and intersubgranular attack (ISGA) for all treatment times investigated. For isothermal treatments at temperatures lower than 280°C, only pitting was observed for treatment times less than about 30 seconds, while IGA and ISGA were observed for longer treatment times. Comparisons showed that the time-temperature domains for IGA and ISGA were virtually coincident. Based on this finding and the results from TEM characterization, IGA and ISGA appear to be related to the precipitation of a Zn-modified T1 (Al2(Cu, Zn)Li) precipitate, which can occur both on low-angle and high-angle grain boundaries in this alloy. When the alloy is resistant to IGA and ISGA, the grain boundaries are decorated by θ′ (Al2Cu), and TB (Al7Cu4Li) phase particles, or subgrain boundaries are populated by a comparatively low density of T1 precipitates. It is, therefore, speculated that θ′ and TB are more corrosion-resistant precipitate phases than T1, and that a critical concentration of boundary T1 must exist for IGA or ISGA to occur.

Original languageEnglish
Pages (from-to)2561-2573
Number of pages13
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume32
Issue number10
DOIs
StatePublished - Oct 2001

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

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