Investigation of the cathodic process influence on the electrochemical noise signals arising from pitting corrosion of Al alloys using wavelet analysis

Abstract

The standard deviation of partial signal (SDPS) plot is obtained from wavelet analysis of electrochemical noise (EN) data. This paper employs the SDPS plots of EN current signals arising from pitting corrosion on the symmetrical and asymmetrical cells of AA6061 and AA2024 alloys in 3.5% NaCl solution with different O2 concentrations (3–25ppm) to obtain a better understanding of the influence of the cathodic reaction on the EN current signals. EIS measurements reveal that an increase of O2 concentration from 3 to 5ppm leads to the stronger passive oxide layer on the Al alloys. The time records and corresponding SDPS plots arising from symmetrical cells show an increase in the amplitude and the time width of EN current transients with increasing O2 concentration from 3 to 5ppm. According to an earlier modeling of EN transients this can be attributed to the enhancement of current noise detection. The EIS shows that the thickness of the passive oxide layer decreases with increasing O2 concentration from 5 to 25ppm. Thus, an increase in the time width of EN current transients with increasing O2 concentration from 5 to 25ppm can be assigned to an increase in the corrosion activity. The optimal O2 concentration for EN current measurements is 5ppm (i.e. naturally aerated solutions).