Microstructure and wear resistance of micro-arc oxidation ceramic coatings prepared on 2A50 aluminum alloys

Abstract

With a bipolar pulse power, wear-resistant ceramic coatings with high micro-hardness were in-situ fabricated on 2A50 aluminum alloy using micro-arc oxidation method in silicate electrolyte. The effect of cathodic voltage on microstructure, phase structure, micro-hardness and wear properties was investigated by changing cathodic voltage from 0 to −200 V. The phase structure, microstructure, micro-hardness and wear resistance were determined by XRD, SEM, HVS-1000 Vicker's micro-hardness tester and tribology tester. The results show that the phase of the obtained coatings is mainly composed of γ-Al2O3. The coating consists of the inner dense layer and the outer loose layer. As the cathodic voltage increases, the quantity and size of the micro-pores in the coatings first decrease and then increase. Micro-arc oxidation can greatly strengthen 2A50 aluminum alloy, the micro-hardness increases from 75 HV0.5 to 1321 HV0.5 after a micro-arc oxidation under a cathodic voltage of −100 V. The friction coefficient of the ceramic coatings are in the range of 0.35–0.55, and the coating obtained under −100 V exhibits the best wear resistance. The wear mechanism is deduced to be the combination of abrasive and adhesive wear.