Fabrication Of Self-lubricating Compound Coatings On Magnesium Alloy And The Research On Tribological Performance Of The Coating

For the question on that the development of magnesium alloy faced in the slider guide rail pair, this paper studies the fabrication of the self-lubricating compound coatings on magnesium alloy combining micro-arc oxidatfon (MAO) technology and magnetron sputtering technology, and the effect of electrical parameters on compound coatings through the characterization of morphology, crystal phase composition, chemical composition and tribological performance of the coating.The study shows the typical MAO coating surface is characterized with volcano heaps which are not in the same shape, and the crater of the volcano is the channel after the pulse discharge. The surface is a porous structure and consist of Mg, O, Si, F and other elements. The section of the MAO coating is composed of dense layers and loose layers, and the dense layer combined to the magnesium alloy closely. The section of the MAO coating also consist of Mg, O, Si, F and other elements. The XRD results show MAO coating consists of spinel, Mg2SiO4, MgF2 and periclase. The nanohardness of MAO coating is far greater than that of magnesium alloy, as well as the abrasion resistance of the coatings.This thesis also studies the effect of electrolyte, current density, frequency, duty ratio and reaction time on characterization of morphology, crystal phase composition, chemical composition and tribological performance of the MAO coating. The optimized process parameters system are current density of 7A/dm2, frequency of 800 Hz, duty ratio of 15% and reaction time of 5 min. Under this process parameters system, the abrasion weight loss is about 0.002g and the friction coefficient is about 0.4.This thesis studies that the characterization of morphology, chemical composition, chemical distribution and tribological performance of the typical MAO-Magnetron sputtering compound coating:the results shows surface of the compound coating deposit a layer of graphite-like coating, which partly cover the microporous of the MAO coating, and it is made up mainly by C, Mg, Si, O and other elements. The layer of graphite-like coating is about 400 nm thick, and evenly covers the MAO coating. The nanohardness and the tribological performance of the compound coating has improved, and friction coefficient of the compound coating is about 0.1.This thesis also studies the effect of deposition power, target-substrate distance, deposition pressure and negative bias voltage on characterization of morphology, chemical composition and tribological performance of the compound coating. The optimized process parameters system are deposition power of 25W, target-substrate distance of 50mm, deposition pressure of 0.5Pa and negative bias voltage of -60V.Under this process parameters system, the compound coating has excellent friction properties and the friction coefficient is about 0.1.This thesis analyzes the wear mechanism of both MAO coating and the compound coating by observing the wear morphology of different stages of wear. The wear type of the MAO coating is mainly abrasive and adhesive, while the type of the compound coating is adhesive and fatigue.