Anodizing of 2024-T3 Aluminum Alloy in Mixed- Electrolyte of Sulfuric, Boric and Phosphoric Acids and Determination of the Oxide Layer Thickness and Investigation of Corrosion Behavior by Using Electrochemical Impedance Spectroscopy Technique

In order to improve corrosion resistance of 2024-T3 aluminum alloy، anodizing process was performed in different concentrations of mixed-electrolyte of sulfuric، boric and phosphoric acids for 10 and 20 minutes under the current density of 1 and 2 mA/cm2 at room temperature. Corrosion behavior of the anodized alloy in aqueous media containing 3. 5 wt% of NaCl was studied by using electrochemical impedance spectroscopy technique and the corrosion parameters were determined by using of an appropriate equivalent circuit. Thickness of the oxide layer was determined by a simple method using electrochemical impedance spectroscopy technique. Finally، in order to compare the corrosion rates of the anodized samples، Tafel extrapolation technique was used. The results revealed good corrosion resistance of the alloy which was anodized in mixed-electrolyte. This electrolyte is a suitable replacement for chromate baths which are generally used in anodizing of 2024-T3 aluminum alloy.