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RESEARCH PRODUCT

Measurement of the intergranular corrosion growth kinetics on a 2024 aluminium alloy : new experimental approaches of damage as function of the environmental conditions

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Costs of aeronautical maintenance can be reduced by implementation of “smart” inspection strategies integrating predictive data on the evolution of defects such as the propagation rate of intergranular corrosion.In this work, intergranular corrosion damage on 2024 aluminium alloy was characterized by two modes : the “perforating” damage (dissolution of the grain boundary tips) and the “blunting” damage (dissolution of the grain walls in the intergranular cavities). To evaluate the “perforating” damage, a new version of the TFP method (OTFP method) which is more complete, was designed. The OTFP method allows to detect all the intergranular corrosion defects and not only the fastest full penetrating grain boundary thanks to the optical nature of the detection. In this method the detection backside of the thin foil is free, which makes possible the collection of the trapped electrolyte in the intergranular cavities to carry out its chemical analysis. This not well-known data, was used to validate “mass-transport” models which could be implemented in predictive simulations considering the effect of the environmental conditions. The porosity inside the foil induced by the intergranular corrosion and enhanced by the “blunting” dissolution was followed in real-time by measuring the electrical conductivity using an eddy current probe.These methods were first calibrated in potentiostatic tests and then successfully applied to evaluate the intergranular corrosion damage in atmospheric corrosion conditions.