Study On Fretting Tribological Behavior Of Mg-Sn-Y Alloy Under Lubrication

Mg alloys have attracted tremendous attention due to their low density,high strength/weight ratio and specific strength,excellent castability,good vibration damping characteristics.However,its high temperature mechanical properties and wear resistance are not ideal,which can be effectively improved by adding tin,lithium and rare earth elements.Considering the failure caused by fretting wear in the practical application of magnesium alloys,there are few systematic studies on the fretting performance and mechanism of magnesium alloys under lubrication conditions.In this paper,Mg-Sn-Y alloys are investigated with ionic liquids,synthetic lubricants and synthetic greases selected as lubricants,and systematic fretting wear tests are carried out on tangential fretting wear devices.The mechanism of fretting wear is analyzed in detail by means of scanning electron microscopy,energy spectrum analyzer,white light interferometer,X-ray photoelectron spectrometer and so on.The following conclusions are drawn:（1）The introduction of high-performance lubricants transforms the fretting running state into slip regime in which oil-film provides good friction reduction and wear resistance.And lubrication function of synthetic oils（PAO and MACs）are superior to that of ionic liquids（[BMIM][BF₄]and[BMIM][PF₆]）.（2）The wear mechanism of Mg-Sn-Y alloy under PAO and MACs lubrication is dominated by abrasive wear and delamination,while that under ionic liquids is abrasive wear,corrosion wear and delamination.Adhesive wear,oxidation wear and delamination are the predominant wear mechanism without lubrication.Wear debris and transfer layer adhered to the friction interface originate from Mg-Sn-Y sunbstrate,which are mainly composed of magnesium and its compounds.Wear debris and transfer layer can enhance the mechanical properties of mating interfaces for reducing friction and wear,thereby changing the fretting regime.（3）The lubrication film formed by grease at the friction interface not only reduces friction,but also promotes the transition of fretting operation zone from partial slip regime to mixed fretting regime and slip regime.The lithium-based grease with 85 wt.%PAO is superior to that with 85 wt.%mineral oil in anti-wear abilities.There is little difference in friction reduction between the two greases.The anti-wear performance of grease is mainly embodied in that the lubricating film prevents the direct contact of the contact surface and reduces the plastic deformation friction layer on the surface.（4）Without lubrication,serious adhesive wear occurs at the the center of wear tracks,oxidation wear occurs at the edge of wear tracks in direct contact with air,and the discharged wear debris cause abrasive wear,accompanied by severe delamination.The lubrication film formed by lithium base grease of 85 wt.%PAO prevents the direct contact between the two contact surfaces,thus greatly reducing the adhesive wear of the contact center.The wear mechanism is dominated by abrasive wear,oxidation wear and severe delamination.The lithium grease with 85 wt.%mineral oil can prevent air from entering the contact surface better.The wear mechanism is dominated by abrasive wear and slight delamination.