The Influence of the Electrolyte Composition for Hard Anodizing of Aluminum on Corrosion Resistance of Synthesized Coatings

Abstract

The effect of the electrolyte composition for hard anodizing of aluminum on the corrosion resistance of the synthesized anodic coatings was studied. The hard anodizing was carried out at temperatures of –4–0°C for 60 min at a current density of 5 A/ dm² . The basic electrolyte was a 20% aqueous solution of H₂SO₄ . Hydrogen peroxide (H₂O₂) was added to the electrolyte in concentrations of 30; 50; 70 and 100 g/L to determine strong oxidants influence on the characteristics of the anode layers. The concentration of 70 g/L H₂O₂ in the electrolyte, which ensures the synthesis of the thickest and least porous coating, was optimal. At the initial moment of immersion of anodic coatings synthesized in hydrogen peroxide electrolyte, their corrosion resistance decreases. When peroxide electrolyte concentration increases from 30 to 100 g/L, corrosion currents increase by 30 and 90%, respectively. However, with increasing exposure of coatings in the environment, their corrosion current density decreases more intensively with a decrease in their porosity. After 14 days, no dependence of the coatings corrosion durability on the composition of the electrolyte observed, what indicated a complete closure of the pores.