Evaluation of sealing methods for anodized aluminum alloys with electrochemical impedance spectroscopy (EIS)

Abstract

Al alloys 2024, 6061 and 7075 have been anodized in H 2 SO 4 solutions of two different concentrations and sealed in either boiling water or solutions of nickel acetate, cerium acetate or yttrium acetate at two different temperatures. The same aluminum alloys were anodized in Boeing's Boric-Sulfuric Acid Anodizing (BSAA) process and sealed in a dilute chromate solution or boiling water. The properties of the sealed oxide layers and their changes during exposure to 0.5 N NaCl were monitored using EIS. From the impedance spectra, the pore resistance, R po , and the specific admittance, As, were determined as a function of exDosure time extending up to 14 days. At the end of exposure, the anodized surfaces were examined by visual observation to determine the total pitted area, A pit . Sealing in cerium acetate solutions produced samples with a corrosion resistance comparable to that determined for sealing in nickel acetate.