Local electrochemical impedance spectroscopy study of the influence of ageing in air and laser shock processing on the micro-electrochemical behaviour of AA2050-T8 aluminium alloy

Abstract

In the present paper, the micro-electrochemical behaviour of AA2050-T8 in 0.1 M NaCl was first studied after polishing by means of local electrochemical impedance spectroscopy and field-emission scanning electron microscopy/electron dispersive spectroscopy (FE-SEM/EDS). The influence of ageing in air and LSP was then investigated. Ageing in air for three months led to an increase in the charge transfer resistance. This was clearly observed in sites surrounding constituent particles where the charge transfer resistance was in the order of 1 MΩ cm 2 (instead of 10 −3 MΩ cm 2 after polishing). Increased passivity around particles was confirmed from FE-SEM/EDS analysis. On the other hand, the effect of LSP on the behaviour of the matrix was found to be extremely beneficial. Both charge transfer and oxide film resistances were sharply increased to approximately 0.35 MΩ cm 2 and 1 MΩ cm 2, respectively, as opposed to approximately 1.9 × 10 −3 MΩ cm 2 and 4.2 × 10 −3 MΩ cm 2, respectively, after ageing in air. This was attributed to the presence of compressive stresses at the specimen surface after LSP treatment. Stress values were determined from XRD measurements.