Research On The Wear Resistance Coating On Cast Aluminum Alloy By HVOF And Fretting Wear Resistance

Fretting wear is a common form of damage in engineering applications.There are many key inner hole aluminum alloy parts serving in special or extreme conditions.During the service,the inner surface will be damaged,which will affect the safety,reliability and service life of components.In this paper,High Velocity Oxygen Fuel spraying was used to prepare aluminum bronze,Cu Ni In and Ni Co Cr Al YTa wear-resistant protective coatings on the surface of aluminum alloy substrates.The cross-sectional morphology,microhardness and bonding strength of the coatings were compared.The fretting wear resistance of the coatings were tested at 25?,200?and 300?to explore the fretting wear mechanism.The results show that the three coatings are dense and uniform,with high hardness and good bonding strength between coating and the aluminum alloy substrate,which improve the fretting wear resistance of the substrate to different extent.Under the condition of fretting wear at different temperatures,the coatings exhibit different wear mechanisms.Among them,the average fretting friction coefficient of aluminum bronze coating is the lowest,which is selected as the coating material with the best anti-friction wear performance for further investigation.In order to deposit high quality aluminum bronze coating on cast aluminum alloy surface,four factors and three levels orthogonal experiments were designed with kerosene flow rate,oxygen flow rate,powder feeding rate and spraying distance as the main process parameters to study the effects of the above process parameters on porosity,thickness,microhardness and bonding strength of the coating,so as to obtain the best process conditions.According to the results of orthogonal experiment,the range analysis method was used to determine the optimal process parameters.The optimal process parameters are kerosene flow rate of 22 L/h,oxygen flow rate of 900 L/min,powder feeding rate of 80 g/min,spraying distance of 200 mm.The porosity,the bonding strength and the microhardness of the aluminum bronze prepared with the optimal process parameters are 0.10%,61.63 MPa and 330.33 HV_0.3respectively.The results of fretting wear test at different frequencies at 200?show that with the increase of frequency,the average friction coefficient of the aluminum bronze coating first increases and then decreases,the wear rate decreases.The wear mechanism changes from abrasive wear to adhesive wear.The Inclined High Velocity Oxygen Fuel spraying was used to prepare the aluminum bronze coating on the inner surface of the small-size inner bore parts.The inclined angle of the spray gun is calculated according to the flame width and the diameter of the bore,and the spraying position is determined by laser positioning.For the inner bores of(?)28 mm and(?)42 mm,the inclination angle of the spray gun is 35°and 25°respectively.The prepared aluminum bronze coating is dense,and the thickness and microhardness are uniform along the pore depth.