Noise resistance and shot noise parameters on the study of IGC of aluminium alloys with different heat treatments

In the present paper, the effect of heat treatment on the susceptibility to intergranular corrosion (IGC) of aluminium alloys is analysed. Samples of aluminium alloys AA2024 and AA7075 were first subjected to different heat treatments. Then the susceptibility of these samples to IGC was determined by means of normalized tests, based on the immersion of the samples in an aggressive medium and the subsequent evaluation of the attack, using metallographic analysis. In order to quantity the IGC suffered by the samples, both the degree and the depth of the attacks were measured. In addition, electrochemical noise (EN) signals were recorded during the normalized tests. This technique is especially interesting for the study of corrosion processes of systems with low impedance, such as those faced in this paper, since it does not modify the corrosion potential of the system. Three parameters were used to analyse the EN signals: noise resistance (Rn) and two shot noise parameters, the characteristic charge (q) and the characteristic frequency (fn). Finally, the relationship between the results of the metallographic analysis and those obtained from the analysis of EN signals was established. Unfortunately, a poor correlation between the shot noise parameters and the degree of IGC was found, due to both the high localization and high activities of all systems.