Real-Time Monitoring of Intergranular Corrosion Damage on AA2024

The total porosity induced by the intergranular corrosion was selected as a monitoring parameter to follow in real-time the defect propagation of AA2024. The pertinence of eddy current (EC) probing has been tested on very thin foils of AA2024 (30 μm in thickness) in immersion conditions under potentiostatic control and in atmospheric conditions simulated by controlled salt spray experiments. Combining this nondestructive evaluation technique with a direct optical interrogation of the backside of the test specimen (derived from the foil penetration technique) allows one to discuss the contribution of both the dissolution in the depth and along the grain boundaries to the total porosity. In immersion conditions, it was demonstrated that the intergranular corrosion propagation on the selected thin foils is characterized by a continuous increase in porosity during a potentiostatic corrosion test. In salt spray experiments, even if the repeatability is affected by the lack of control of defect initiation, the transition in the defect propagation regimes can be followed. The possible limitation of the detection of defects resulting from the low sensitivity of the EC method is discussed.