Electrochemical impedance spectroscopic study on cathodic polarisation of 5083 Al alloy under stagnant and dynamic flow conditions in 3·5% NaCl solution

Abstract

This research was conducted to compare the cathodic polarisation behaviour of 5083 Al–Mg alloy under stagnant and dynamic flow conditions in 3·5% NaCl solution. The effect of flow velocity upon corrosion processes under cathodic polarisation was studied by electrochemical impedance spectroscopy (EIS) using rotating cylinder electrode. Cathodic behaviour of the specimens was determined by potentiodynamic tests. Specimens were cathodically polarised to –0·8, –0·9 and –1 V_SCE for 20 h, EIS data were obtained at intervals of 0, 2·5, 5, 10, 15 and 20 h after the exposure without interrupting the polarisation. The EIS data analysis shows that the existence of fluid flow increases pit initiation level. It seems that under stagnant condition cathodic polarisation has an adverse effect on corrosion resistance; however, under dynamic flow condition it may have a positive and favourable effect on corrosion resistance. The removal of intermetallic particles may lead to gradual improvement of corrosion resistance and a decrease in pit surface growth rate. The applied cathodic polarisation and the hydrodynamic forces at the walls of specimens are two possible major factors in particles removal processes; furthermore, it seems that these two factors complement each other.