Formation of ceramic alumina nanocomposite coatings on aluminium for enhanced corrosion resistance

Plasma electrolytic oxidation (PEO) has been considered as a novel technique to form ceramic nanocomposite coatings on aluminium and magnesium alloys for corrosion protection. However, a systematic study of the effect of process parameters on the properties of the coatings has not been well demonstrated. In the present study, aluminium was treated by PEO at various treatment time, current density, temperature and concentration of NaOH and Na2SiO3 and their effect on the surface properties of the coatings has been investigated systematically. It was found that the temperature and treatment time were the major factors affecting the thickness and growth. The coatings mainly consisted of α-alumina, γ-alumina and Al2(SiO3)3. The ceramic composite coatings with best corrosion resistance were obtained at higher current density, lower temperature, moderate treatment time and optimum concentration of NaOH and Na2SiO3. The crystallite size of the composite coating was found to be in nanometer scale (9–131 nm).