Study On Tribological Properties Of Mixed Micro-textured Aluminum Substrates Under Different Lubrication Conditions

Aluminum alloy is widely used in machinery industry and other fields due to its advantages such as low density,but its surface hardness and poor wear resistance seriously limit its performance.Therefore,it is of great significance to improve the tribological properties of aluminum alloy surface.In this paper,the influence of micro-texture and graphite coating on the tribological properties of aluminum alloy surface was studied by simulation and experiment.The main research works are as follows:The microtextures with three single morphologies of square pits,circular pits and strip grooves,as well as the microtextures with three combined morphologies of square and circular mixed pits,square and strip grooves mixed pits and circular and strip grooves mixed pits were used as simulation objects.Based on the Hertz contact theory,the geometry of the micro-texture was determined,and the lubrication model was established based on the Reynolds equation.The numerical analysis of the lubrication model was carried out by the computational fluid dynamics method.The influence of the micro-texture morphology and geometric parameters on the bearing capacity of the lubricating oil film between friction pairs was studied.The results show that the bearing capacity of the lubricating oil film between the mixed micro-texture of circular pits and strip grooves and that of the mixed micro-texture of square pits and strip grooves is better at the same depth.Therefore,these two mixed micro-textures were selected as experimental research objects.Using the laser processing technology in internal combustion engine piston,each in aluminum alloy surface processing of a series of different sizes of circular pit-bar groove mixed pits of micro texture and square-bar groove mixed micro texture,uses the friction and wear testing machine to explore without texture surface and different size mixture of micro texture surface in dry friction and tribological properties of boundary lubrication.The results show that,with the increase of grinding time,the wear-mark widths of non-textured and mixed micro-textured substrates also increase,and the difference of wear-mark widths between them gradually decreases with the increase of grinding time.The friction coefficient of the non-textured matrix surface gradually increases with the increase of grinding time,but the friction coefficient of the mixed micro-textured matrix surface gradually decreases with the increase of grinding time.In boundary lubrication,the two mixed micro texture on the surface of the average friction coefficient are presented first rising trend,after falling for circular depressions-bar groove mixed micro texture,when the texture size is 70 ?m on the surface of the average minimum friction coefficient,square pit-bar groove for mixed micro texture,when the texture size is 80?m on the surface of the average friction coefficient is minimal.Compared with the non-textured surface,the average friction coefficient of the mixed micro-textured surface is reduced to a certain extent.Solid graphite coating was sprayed on the surface of non-textured and mixed micro-textured substrates by thermal spraying technology.The effects of mixed micro-textured and graphite coating on the interaction of aluminum alloy substrates were analyzed by friction experiments.The results show that the average friction coefficient of mixed micro-textured specimens is lower than that of non-textured specimens under solid lubrication of graphite coating.Under the coexistence of boundary lubrication and graphite coating solid lubricant,the synergistic effect of mixed micro-texture and graphite coating not only improves the anti-wear property of aluminum alloy,but also reduces the wear degree of the friction ball,and plays a good surface protection role.