Pitting behavior of the AA6061 alloy and Al5N in a diluted chloride solution

The effect of aeration on the pitting potential (Ep) of the AA6061 alloy and high‐purity aluminum (Al5N) is studied in diluted chloride solutions. The Ep values are determined by a potentiodynamic scan in aerated and de‐aerated solutions of 10−3 M NaCl and 10−3 M NaCl + 0.05 M KH2PO4/K2HPO4 buffer. Applying the hypothesis testing procedure, it is concluded that the presence of oxygen in a 10−3 M NaCl solution decreases the Ep for AA6061 by 100 mV and does not affect the Ep for Al5N. This decrease is related to the alloy dissolution around the iron‐rich particles and is analyzed in terms of the model of localized acidification. For the AA6061 alloy tested in an aerated 10−3 M NaCl solution, it has been demonstrated by statistical analysis that the alkaline attack due to the oxygen reduction on the iron‐rich particles present in the alloy promotes the initiation of pitting at a potential 100 mV lower than that reported for de‐aerated 10−3 M NaCl. On the other hand, the pitting potential of high‐purity aluminum is not affected by the aeration or de‐aeration conditions of the solution.