Anti-Wear Ceramic Coating Prepared On The Surface Of AZ31 Magnesium Alloy

Magnesium alloy is the lightest metal of the structural material, but its lower hardness and plastic shear resistance result in less friction and wear properties, which greatly restricts its application field of aerospace and other application area. So it is necessary to modify magnesium Alloy to improve its friction and wear properties. In this paper, the wear resistance of the alloy is improved by using micro-arc oxidation in situ growth of AZ31 magnesium alloy wear-resistant oxide ceramic coatings. The oxide ceramic film structure, friction and wear properties of the composition and its relationship with the electrolyte system, process parameters, and the relationship between doping agents are systematically analyzed, providing theoretical basis for the promotion of AZ31 magnesium alloy.XRD, EDS, SEM and other testing methods are used to analyze the phase composition, element composition and distribution in the thickness of the oxide film, then the morphology of the film and wear scar are observed. The worn surface roughness and contour of oxide film are characterized by Surface Roughness Profilometer. The hardness of the surface of the film is analyzed by Nano-indentation. The friction coefficient of the oxide film is analyzed by Ball-disc Tribometer. Finally the coating wear life and wear rate are measured by friction and wear testing machine.Study results show that the optimum electrolyte system are: Sodium 10g/L, sodium hydroxide 5.5g/L, sodium tungstate 1.5g/L, sodium citrate 1g/L; the best electrical parameters are current density 7A/dm², frequency 500Hz, 10% duty cycle, the reaction time 300s; film thickness is 14μm; phase composition are MgO and Mg2SiO4; nano-hardness is 2.56GPa; friction coefficient is 0.2329 and the volume wear rate is 9.098×10^-6mm³/Nm.To further improve the friction and wear properties of oxide film, the effects of doping K₂Cr₂O₇ and Na₂B₄O₇ on friction and wear properties of the film are studied respectively. The results display that doping K₂Cr₂O₇ film shows the best wear resistance when doping concentration reaches 0.5g/L. The bottom friction coefficient of the prepared coating under load is 0.2111. The volume wear rate under high load is 6.746×10^-6mm³/Nm. Nano-hardness is 3.47GPa and the film wear mechanism is adhesive wear.