Electrochemical impedance spectroscopy was used to study the corrosion resistance of Al 7075-T6 after degreasing and one of three different alkaline activations. Electrochemical tests were conducted using an aqueous solution containing 0.35 w/v% NaCl and 0.70 w/v% (NH(4))(2)SO(4) at its natural pH of similar to 5.5 or with its pH adjusted to similar to 9.0. These tests showed increasing the electrolyte pH to 9.0 made the electrolyte less corrosive, which allowed impedance characterization at low frequency (1.00-0.01 Hz) after only 1500 s of stabilization prior to testing. The total impedance of the native oxide was similar to 5.9 k Omega cm(2) and degreasing did not alter this value. Degreasing followed by activation in 5 wt % Na(2)CO(3) or 1 wt % NaOH decreased the total impedance by similar to 20% to 4.8 k Omega cm(2), whereas activation in 2 wt % NaOH decreased impedance by similar to 30% to 4.2 k Omega cm(2). The decreased impedance after activation allowed a cerium-containing solution to penetrate the surface oxide and react with the substrate to form a conversion coating. Thus, increasing the electrolyte pH made the electrolyte less corrosive, which enabled characterization of the decrease in surface oxide impedance after alkaline treatments using electrochemical impedance spectroscopy. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3610404] All rights reserved.