| The poor anti-wear property of Mg alloys limits their application in engineering. So improving the wear resistance of Mg alloys has become an urgent problem. In this dissertation, the ceramic coating was in situ formed on the surface of ZK60 Mg alloy by micro-arc oxidation (MAO) in order to enhance the wear resistance. Moreover, the friction mechanism of the coatings was studied to provide a technical foundation for its engineering application.The effect of electrolyte, current density, frequency, duty ratio and reaction time on hardness and friction performance of the MAO coating formed on the Mg alloy substrate was studied. The ideal MAO coating has been obtained by optimizing process parameters. For example, in a system with Na3PO4 as the electrolyte, the MAO coating had optimum anti-wear performance when the coating was prepared under the current density of 12 A/dm2, frequency of 500 Hz, duty ratio of 15% and reaction time of 5 min. The nanohardness, friction coefficient and wear rate were 4.99 GPa, 0.3 or so and 1.27×10-5 mm3/Nm, respectively.The effect of NaAlO2 or graphite doping and co-doping on the hardness and friction property of the MAO ceramic coating was studied. The results showed that all the dopings could increase the hardness and reduce the friction coefficient to improve the friction performance of the coatings. Among these dopings, NaAlO2-doped coating showed the best friction performance. When the doping concentration of NaAlO2 was 4 g/L, the nanohardness, friction coefficient and wear rate were 6.302GPa, 0.25 and 0.75×10-5mm3/Nm, respectively. Additionally, the tests showed that the NaAlO2-doped coating had better adhension and anti-thermocycling performance.The morphology, phase composition, element component and valence of the coatings before and after the doping were characterized by SEM, XRD, XPS, and EDS. The results showed that the formed coating was composed of periclase MgO and there were a lot of micropores with uniform pore distribution on the surface of the coating. There was the phase of spinel MgAl2O4 in the coating when NaAlO2 was doped into the electrolyte and the graphite element when graphite was doped into the electrolyte. The wear mechanism of the graphite and NaAlO2 doped coatings was discussed under different mechanical parameters and environments. The results showed that the friction coefficient of the graphite-doped coating was increased with the load, and decreased with the increase of the sliding velocity and friction time in the normal environment, and the adhesion wear of the coating was changed into fatigue wear. The friction coefficient of the NaAlO2-doped coating was increased with the load and friction time, and decreased with the increase of the sliding velocity in the ambient atmosphere, and this kind of wear was mainly adhesive. The friction coefficient in vacuum was lower than that in air, even the wear got worse. The wear type of the graphite-doped coating was mainly abrasive and fatigue, while the type of the NaAlO2-doped coating was abrasive and adhesive in vacuum. The friction coefficient at low temperature was higher than that at room temperature. The wear type of the graphite-doped coating was adhesive and fatigue, while the type of the NaAlO2-doped coating was abrasive and adhesive at low temperature and in vacuum. The anti-fatigue and anti-wear properties of NaAlO2-doped coating were better than those of graphite-doped coating whether in air or vacuum.
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