Localized corrosion of aluminum alloy 6061 in the presence of Aspergillus niger

Figure shows impedance plots of non-anodized aluminum alloy AA 6061 in the presence of Aspergillus niger at 2, 6, 8 and 15 days, and electrical equivalent circuit model used to fit impedance data (upper part), where Rs corresponds to the solution resistance, CPE is a constant phase element, R1 is the charge transfer resistance, R2 and C correspond to adsorption-desorption and surface coverage processes, respectively. The shape of the impedance diagrams is similar for the four experimental times, a capacitive behavior showing a depressed semicircle at high frequency (from 10 kHz to ∼0.1 Hz), with the center lying below the real axis, and an inductive behavior showing a loop below the real axis at low frequencies (from ∼0.1 Hz to 0.05 Hz), which is a typical loop shape of an adsorption process and may be associated with the adherence of spores to the metallic surface, originating differential aeration cells which may produce localized corrosion.164