Abstract
The current fluctuations between nominally identical pairs of aluminum or SiC-reinforced aluminum alloys in neutral chloride electrolytes were analyzed with respect to the time dependence, and frequency dependence of the power spectral density of the fluctuations. The results were compared to the pitting related parameters of critical potential, EC, and protection potential, Ep, obtained from potentiodynamic tests and microscopic observations. The materials examined included Al 7075-T73, Al 3003, Al 2024, Al 8090, SiC -reinforced 2124 and 2219 and a fine grain superplastic 7064 material with and without 10% SiCp. The results of this work show: 1) the intensity of electrochemical noise for Al 7075-T73 correlates with pit depth in the case of cupric ion-accelerated pitting in neutral, aerated 0.5 M NaCl; 2) a SiC phase in 2000 series composites produces an increased intensity of electrochemical noise most likely associated with an elevated pit initiation rate; and 3) solution-annealed Al-Li 8090 shows a long time for repassivation in refreshed neutral, aerated 0.5 M NaCl relative to the other materials examined. However, the Al 8090 remains more or less inert to pitting as the solution pH rises as would occur in occluded regions.
