Optimizing corrosion resistance and hardness of alumina coatings by ethanol

Hard anodization of aluminum alloys typically requires sub-zero temperatures. This study evaluates the feasibility of hard anodization of AA7075-T735 at a near-ambient temperature (20 °C) using an ethanol-modified sulfuric acid electrolyte, with results compared to those obtained at 0 °C. Corrosion behavior was assessed by potentiodynamic polarization and electrochemical impedance spectroscopy, while hardness was measured by Vickers microhardness. The results revealed that the addition of 10 vol% ethanol produced a superior corrosion resistance at both temperatures, with passive current densities in the order of 10⁻⁸ A/cm² and high polarization resistance (>1 kΩ.cm²). At 20°C, 20 vol% further improved hardness and efficiency, whereas 30 vol% ethanol degraded performance. Controlled ethanol addition enables high-quality hard anodization at ambient temperatures, which is advantageous for industrial-scale applications due to lower costs.