Binary Additives Enhance Micro Arc Oxidation Coating on 6061Al Alloy with Improved Anti-Corrosion Property

Abstract

Given the corrosion tendency of the natural oxide film of aluminum alloys, micro arc oxidation (MAO) treatment is used as an efficient and economic method to enhance the corrosion resistance. However, irregular voids, pores, and micro cracks are easily formed during the MAO process, which are harmful to the anti-corrosion property of MAO coatings. In this paper, binary additives of electrolytes, including (NaPO3)6 and H3BO3, were used to obtain MAO coatings with improved thickness and compact microstructures on 6061 aluminum alloys. The as-prepared coatings were investigated using a thickness meter, scanning electron microscope (SEM), X-ray diffractometer (XRD), and electrochemical impedance spectroscope (EIS). The results showed that the coordinated influence of the binary additives could change the discharge behaviors and micro morphologies of the MAO coatings compared to the base silicate electrolyte. A thicker and stronger MAO coating could be achieved, which was mainly composed of Al2O3 phases. The EIS tests revealed that the corrosion current density of the obtained optimal MAO coating decreased by three orders of magnitude from 1.209 × 10−6 A·cm−2 to 2.981 × 10−9 A·cm−2. We believe that the binary additive-enhanced MAO coatings could provide a promising anti-corrosion solution in various applications.