Effects of Additive for Anodizing Electrolyte on Anodic Film of High Silicon Aluminum Alloy

High silicon aluminum alloy, Al-12.7Si-0.7Mg, is newly developed and in urgent need of surface treatment techniques. Sulfuric acid concentration, anodization temperature, anodization time and current density being fixed, three kinds of organic acids were investigated as additives of electrolytes for anodic oxidation of high silicon aluminum alloy. Optimal concentrations of organic acids were worked out by inspecting their effect on film weight and corrosion time, respectively. The study showed that citric acid was the best additive. Voltage-time curves of anodic oxidation for high silicon aluminum alloy in different electrolytes conformed to the typical characteristic curve of aluminum anodic oxidation. Oxide films obtained from sulfuric-citric mixed acid electrolyte were smooth, well- distributed, compact, and exhibited exceedingly low corrosion rate and excellent corrosion resistance.