On exfoliation corrosion of alloy 2060 T8E30 in an aggressive acid environment
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abstract
2015 Elsevier B.V. All rights reserved. In this study, we investigated exfoliation corrosion (EFC) of the alloy 2060 T3E80 in an aggressive solution, namely EXCO. The pH value increased from 0.25 at the initial time point to 3.45 after 96 h of testing. In Stage 1 (0.25 < pH < 3.00), the pH value increased significantly and the aluminum surface experienced anodic dissolution. During this step, a massive hydrogen evolution reaction was observed, and pits formed due to the galvanic effect between the anodic and cathodic sites. The electrochemical impedance spectroscopy (EIS) test and equivalent analogs suggest that the inductive loop at low Nyquist frequencies and phase angle plots correspond to the adsorbed intermediates in the reduction reaction. In Stage 2 (3.00 < pH < 3.45), the pH value slowly increased. The continuous pits along the grain boundaries produced intergranular corrosion (IGC) during this stage. A small amount of delamination occurred at this stage. In Stage 3, pH remains constant and IGC extensively propagate, allowing the accumulation of white gelatinous corrosion products under the grains. These, along with hydrogen bubbles underneath the grain, exerted pressure to the grain that was attacked by IGC, resulting in a lifting of the grain. The grain lifting at this stage was abundant. It is clear from the cyclic potentiodynamic polarization and scanning electron microscopy images that the pits formed on this alloy surface in the EXCO solution can be attributed to fall-out of particles instead of passive film breakdown.
