Corrosion-Resistance of MAO-Coatings on Al-Si Alloys

Abstract

The results of the experimental study of the influence of micro-arc oxidation (MAO) on the corrosion resistance of aluminum alloy samples AK12D are presented in this paper. The description of the research methodology, including the formation of the hardened layer on the surface of laboratory samples by MAO under various process conditions and the study of their corrosion resistance are given. The studies were conducted in accordance with the experimental design theory for fractional factorial experiment 23-1. The MAO process was carried out using an alkaline electrolyte. MDO process factors were chosen according to an electrolyte concentration of the components (caustic potash - KOH and water glass - Na2SiO3) and electrical parameters of the process determined by the capacitors capacitance. In addition to corrosion resistance of the samples, the thickness, porosity, and microhardness of MAO layer were determined. Regression equations and conclusions about the degree of influence of modes of micro-arc oxidation on the corrosion resistance of the samples were compiled on the basis of the data obtained. The results showed that the MAO process regimes have a significant effect on the corrosion resistance of the samples. Regression equations describing the effect of the thickness and porosity of the surface on the corrosion rate are derived. It has been found that the greatest influence on the corrosion resistance renders the mean value of porosity. With an increase of this parameter there is an increase in the corrosion resistance of the coating. To account for this effect, it has been suggested that the corrosion resistance of the MAO layer should not correlate with the porosity but with the absolute volume occupied by the pores in the coating. The study was conducted to investigate the prospects for the use of the MAO method for improving the corrosion properties of parts and details made of Al-Si aluminum alloys.