Improve the tribological performance of anodic coating by plasma discharge treatment

Abstract

Anodizing and plasma discharge technology had been combined to improve the tribological performance of Al-alloys. Based on the calculation of plasma discharge radius and the analysis on coating pore parameters obtained in different electrolytes, the sulfuric-phosphoric acid electrolyte had been selected to prepare anodic coating with the pore size of about 40 nm. The effect of plasma discharge on the crystallinity of the anodic coating had been simulated by COMSOL Multiphysics software and verified by XRD respectively. The compactness of the coating had been characterized by SEM and Image J software. Then, results proved that amorphous alumina could be transformed into crystalline alumina, and form a thick compact alumina ceramic coating on the surface of Al-alloys. The influence of plasma discharge time on the adhesion, roughness and hardness of the coating had also been studied, with the results that demonstrated when plasma discharge time was 15 min, the adhesion, roughness and hardness of the coating were 63.5 N, 1.56 μm and 175 HV, respectively. Of course, the tribological performance of the coating had been tested, and it was shown that the friction coefficient of the coating was about 0.45, and the mass wear loss rate was 1.68 × 10−5 mm3/N · m. Due to the low hardness of Al substrates, in the process of the friction test, the effect of load stress on the mass wear rate of the coating was greater than that of sliding velocity.