Impedance analysis of Portevin-Le Chatelier effect on aluminium alloy

The paper presents the results of an electrochemical investigation of the surface PLC effect connected with a non-uniform process of plastic flow of aluminium alloys containing magnesium. The PLC effect exemplified as a serration results in a non-homogenous change of an external surface of a stressed sample. The dynamic electrochemical impedance spectroscopy investigations were carried out in dynamic conditions during tensile tests. The surface PLC effect resulted in cyclic changes of dc current values and of instantaneous impedance spectra, which were correlated with the oscillatory character of measured mechanical parameters. An analysis with the electrical equivalent circuit revealed that the process discussed was a multistage one, depended on polarization and was directly connected with mechanical factors of the PLC effect. The most distinct surface PLC effect was found for the low levels of anodic polarization, where a tendency to repassivation is low. For high polarization a number of phenomena occur simultaneously, such as the repassivation processes and the initiation of local corrosion, which cause significant problems in an analysis of these studies.