| Magnesium alloy materials are increasingly used in lightweight fields such as automobiles,medical equipment,and space vehicles.However,the wear resistance and corrosion resistance of magnesium alloys are relatively low,which makes its application limited.In this paper,the authors studied the microstructure and properties of plasma sprayed nickel graphite coating on the surface of AZ31 magnesium alloy,thereby improving the wear resistance and corrosion resistance of the magnesium alloy surface.The topic has important engineering practical significance for promoting the wider application of magnesium alloys.This paper has studied the orthogonal design of plasma spraying process parameter design L9?34?such as spraying distance,power supply,powder feed rate and gas flow.Based on this,a plasma spray nickel graphite process test on the surface of AZ31 magnesium alloy was performed,the plasma spraying process parameters were optimized,and a Ni Al/Ni-C coating was prepared on the surface of AZ31 magnesium alloy;Advanced materials analysis methods such as X-ray diffraction?XRD?,scanning electron microscope?SEM?and super depth of field microscope were used to analyze the chemical composition and microstructure of the Ni Al/nickel graphite coating on the surface of AZ31magnesium alloy;The tensile strength test method was used to test the Ni Al/nickel graphite coating-substrate bonding strength on the surface of AZ31magnesium alloy.The effects of plasma spraying process parameters such as spraying distance,power supply,powder feed and gas flow on the bonding strength of Ni-C coating to AZ31 magnesium alloy and the internal porosity of Ni-C coating were analyzed.The micro-hardness tester and friction and wear tester were used to test the friction and wear performance of the Ni-C working layer;3.5%Na Cl total dipping corrosion test and electrochemical test were used to test the corrosion resistance of Ni Al/nickel graphite coatings with different thickness.The influence of coating thickness on the corrosion resistance of Ni Al/nickel graphite coating was analyzed.The research results show that the specific parameters of the optimized AZ31 magnesium alloy surface plasma sprayed Ni-C are 110 mm from the substrate of the spray gun,20 k W of power,55 g/min-1of powder supply,and 30L·min-1of APS working gas flow.The Ni-C coating prepared by this process consists of Ni,graphite phase and a small amount of Ni O;Ni Al/nickel graphite coating-substrate bonding strength is about 31.26 Mpa;main gas flow rate of spraying is 25 L·min-1.When other process parameters remain unchanged,the internal porosity of the nickel graphite coating is 2.25%,and the hardness value reaches 351.38 HV,which is much higher than that of the magnesium alloy substrate;Under Ni-C coating wear test conditions of 120 r/min,the load pressure has little effect on the friction and wear performance of the coating surface.At friction speeds of 240 r/min and 360 r/min,as the load on the Ni-C coating of the grinding balls increases,the wear of the coating surface changes from abrasive wear to oxidative wear and strong adhesive wear;Under the friction and wear test conditions of 120 r/min and friction load of 60 N,the wear depth of plasma sprayed Ni-C coating is about 2/5 of the AZ31 magnesium alloy matrix;The weight loss rate of Ni Al/Ni-graphite composite coating in 3.5%Na Cl corrosion solution is much lower than that of AZ31 magnesium alloy.As the coating thickness increases,the corrosion rate decreases further.Especially when the coating thickness is 316?m,the average corrosion rate is only 0.0031g/?m2·h?,and the corrosion current density of the composite material is 2.125E-5A/cm2,which is about two orders of magnitude lower than that of the untreated AZ31 magnesium alloy substrate. |
PDF Full Text Request