The influence of the electrolyte composition for hard anodizing of aluminium on corrosion resistance of synthesized coatings

The effect of the composition of the electrolyte for hard anodizing of aluminum on the corrosion resistance of the synthesized anodic coatings is studied. The hard anodizing process is carried out at a temperature of –4–0°C for 60 min at a current density of 5 A/dm2. The basic electrolyte is a 20% aqueous solution of H2SO4. To determine the effect of strong oxidants on the characteristics of the anode layers, hydrogen peroxide (H2O2) is added to the electrolyte in concentrations of 30; 50; 70 and 100 g/l. It is found that the concentration of 70 g/l H2O2 in the electrolyte, which ensures the synthesis of the thickest and least porous coating, is optimal. It was established that at the initial moment of im­mersion of anodic coatings synthesized in hydrogen peroxide electrolyte, their corrosion resistance decreases. When its 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 corrosion durability of the coatings on the composition of the electrolyte observed, which may indicate a complete closure of the pores.