Exfoliation corrosion test procedures

Although the size and shape of the specimen will depend on the purpose of the test, rectangular specimens of the dimensions 2.5 cm by 5 cm by 0.3 cm thick are common. A typical variation is found when a corrosion test requires the specimen to be mechanically stressed as part of the evaluation procedure. It would be normal in this case to use a standard tensile test specimen for the corrosion test. Other examples are the use of disk-shaped specimens for rotational erosion tests, or special configurations for stress corrosion, exfoliation, or crevice tests. 

Historically, exfoliation corrosion problems have been associated principally with high-strength aluminum alloys used in aircraft construction and by the U.S. Department of Defense. This chapter, therefore, will deal mainly with test procedures developed for alloys of aluminum. 

Standardised testing procedures should be used for assessing the susceptibility to exfoliation corrosion [18]. The selection of the test solution and the duration of immersion depend on the alloy series ... 

For some materials, the processing procedures that develop the desired high resistance to corrosion affect other characteristics, which can be tested by methods that do produce numoical data. If a correlation can be established between these other data and the corrosion results desired, then measurement of these other characteristics provides a quick lot-release tool provid-itig high statistical confidence. The most notable examples are the tensile strength plus electrical conductivity criteria used for some of the 7xvc alloys in T7 type tempers that provide high resistance to stress corrosion or exfoliation (Tables 2a and 2b). Examples of alloys for which such relationships have been developed are 7075-T73,7075-T76,7050-T74, and 7150-T77. 

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