Mechanism of Activation of Aluminum by Low Melting Point Elements: Part 1 — Effect of Zinc on Activation of Aluminum in Metastable Pitting

The effect of a small amount of alloyed Zn (up to 0.13%) on metastable pitting of Al was studied in terms of pit nucleation, propagation, and repassivation in an effort to clarify the mechanism of pitting corrosion of Al. The passive current in 0.5 M sodium chloride (NaCl) was increased by alloyed Zn, but there was no effect of Zn content on pitting potential (E_pit) at the 0.02% or 0.13% levels. In studies of current transients below E_pit, the frequency of the current spikes showed little or no dependence on Zn content. However, in the propagation stage of metastable pitting, the presence of Zn made the growth rate faster, the growth time prolonged, and the final size larger. Therefore, it could be concluded that alloyed Zn has an effect only on propagation and repassivation of metastable pits and not their nucleation frequency.