Pitting corrosion of Al2024-T3 in sodium chloride solution

Pitting corrosion behavior of Al2024-T3 in sodium chloride solution was investigated by using potentiodynamic scanning (PDS) measurements and electrochemical impedance spectroscopy (EIS) technique. When pitting corrosion Of the alloy occurs, there exists a passive region in the anodic branch of PDS polarization curve, which is enlarged with the increasing of immersion time due to the competition of the halide ions with OH- ions to adsorb on the oxide film to form the corrosion products film and the increase of pitting corrosion area. Two capacitive semicircles were observed in complex plane plot. For more extensive pitting and general corrosion of Al2024-T3, the passive region in PDS disappeared, while another depressed semicircle was observed in Nyquist plot because of the formation of corrosion products film. On the other hand, the low frequency inductive loop, which had often been regarded as a manifestation of pitting or formation and precipitation of a salt film, was not observed, which indicates that the low frequency inductive loop can not be the characteristic of pitting corrosion or the formation of salt film. The results also show that higher reactant CPE exponent values will correspond to more extensive transformation of a metal surface by very localized corrosion, while general corrosion can result in a smaller CPE exponent value.