Study of electrochemical behavior and morphology of pitting on anodized 2024 aluminum alloy

Pitting behavior of anodized 2024 aluminum alloy in NaCl solution was studied using electrochemical methods and SEM. Three stages were observed during potentiostatic polarization of the anodized alloy. In the first stage, current decreases with time, following the relation log i=−n log t, where parameter n indicates the passivation tendency of the alloy. The stage corresponds to the induction time for pitting and increased chloride concentration will shorten the stage. After the induction time, pitting happens and the current begins to increase continuously. In the third stage, the current reaches a stable value, and the growth of pits is controlled by ohmic drop. The relationship between pitting potential of the anodized alloy and chloride concentration in the solution follows the expression Ep=A−B log[Cl−]. On anodized 2024 aluminum alloy pits develop preferentially along the interface between the anodic film and the substrate. Large, shallow pits were formed.