Effect of Al₂O₃ Doping and Ultrasonic Assisting on Structure and Properties of Micro-arc Oxidation Coating on Surface of Pure Aluminum

Pure aluminum substrate was treated by micro-arc oxidation with the assistance of ultrasonic in a composite electrolyte added with Al₂O₃ powder. The effects of Al₂O₃ doping and ultrasonic assisting on the microstructure, phase composition, corrosion resistance and friction and wear performance of micro-arc oxidation coating were investigated. The results show that the ultrasonic assisting promoted more Al₂O₃ particles to participate in the micro-arc oxidation process. The micro-arc oxidation coating was more smooth and compact with uniformly distributed small pores, and had lower porosity. Comparing with micro-arc oxidation coatings without Al₂O₃ doping or ultrasonic assisting, the free corrosion current density of the micro-arc oxidation coating with Al₂O₃ doping and ultrasonic assisting was obviously reduced; the polarization resistance increased significantly; the friction coefficient and specific wear rate both decreased. Therefore the corrosion resistance and the friction and wear properties were greatly improved.