Exfoliation corrosion (EFC) of AA7178 (UNS A97178) has been quantitatively studied using the exfoliation of slices in humidity (ESH) test, which measures exfoliation layer thickness of the specimens as a function of time in a humid environment after an electrochemical pretreatment. The effects of relative humidity (RH), temper, and applied stress on EFC kinetics of AA7178 were investigated using ESH tests. The critical RH for EFC propagation in AA7178 was found to be about 56% RH and the EFC kinetics increased with RH. The ESH results on the effect of temper were consistent with published results from EXCO tests, but they provide a quantitative description of the temper effect. The effects of applied compressive and tensile stress on EFC kinetics were studied using a four-point bending jig. Compression accelerated EFC significantly and tension reduced kinetics. An equation describing the effects of RH, stress, and time on EFC kinetics was developed based on the ESH results.

Subject
Scanning electron microscopy, Humidity, Corrosion kinetics, Skin, Exfoliation, Thermal stress, Corrosion products, Stress, Constants, Pretreatment, Bending, Tensile stress, Samples
Keywords:
aluminum, exfoliation corrosion, relative humidity, stress effects, temper effects
NACE International
2006
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