Electrochemical Quartz Crystal Microbalance Study of Corrosion of Phases in AA2024
Journal of the Electrochemical Society
The electrochemical quartz crystal microbalance ͑EQCM͒ was used to directly measure the dissolution rate at cathodic potentials, and thus the cathodic corrosion rate, of thin-film analogs of phases in AA2024. Thin films of pure Al, Al-4% Cu, and Al 2 Cu were studied in 0.1 M NaCl containing 0, 10 Ϫ4 , or 10 Ϫ2 M Cr 2 O 7 Ϫ2 . A range of cathodic potentials was studied for each material. The true cathodic current density was calculated from the difference of the net current density and the
... nsity and the dissolution rate, which was determined by the EQCM. For pure Al and Al-4Cu, the cathodic corrosion rate was large relative to the net current density, so the true cathodic current density was considerably larger than the measured net current density. The cathodic current density was almost identical to the net current density for Al 2 Cu because the dissolution rate was very small compared to the cathodic reaction rate. Various potentials in the limiting oxygen reduction reaction region were examined, but the effect of the applied potential was small. The presence of dichromate in solution decreased both the cathodic corrosion rate and the cathodic current density on these thin-film analogs. In particular, it decreased more effectively the cathodic reaction rate on Al 2 Cu, which can support faster cathodic reaction rates.