Study On Laser Cladding Coating On Automobile Engine Valve Surface

The valve is an important part to ensure the reliability and durability of engine performance.The damage rate of the valve is quite high due to the high speed invasion and corrosion of the high temperature gas,mechanical wear and various complex stresses.Either corrosion or wear will destroy the original mechanical properties of the material and lead to valve failure,which seriously shortens the working cycle of the valve.In order to prolong the service life of the valve and reduce the loss,the development of the engine valve with excellent corrosion resistance and wear resistance has a great development prospect and practical value.The main research contents of this paper: Ti-48Al-2Cr-2Nb /Ti C/ Hb N coating was prepared on the matrix surface of 21-4N austenitic heat resistant alloy steel.The influence of laser cladding process parameters on the surface forming quality,microhardness,residual stress and other properties of the coating was studied,and the influence of different Hb N content on the friction and wear properties of the coating was also discussed.First of all,before preparing the laser cladding coating,the substrate material is pretreated,including ultrasonic cleaning,sandpaper grinding,laser preheating and so on.The powder materials were weighed by electronic balance,and then put into the cleaned ball mill tank for ball mill to achieve the purpose of mixing evenly.Then laser cladding synchronous powder feeding technology was used to prepare the coating.Through the use of energy spectrometer,dimensional microhardness tester,scanning electron microscope,X-ray diffraction analyzer,high temperature friction and wear testing machine,electrochemical workstation and other instruments,the laser cladding technology prepared by the coating morphology,microhardness,phase composition,as well as different HBN content coating wear resistance,corrosion resistance,etc.Based on the theoretical analysis of the static characteristics of engine valves,it is found that the stress on the valves is mainly related to the material properties,load and temperature of the valves and the working conditions of the valves.Abaqus was used to simulate the residual stress of the coating,and Workbench was used to conduct the static analysis and modal analysis of the engine coated valve model.It was found that the application of Ti-48Al-2Cr-2Nb/Ti C/ Hb N coating could effectively improve the performance of the engine valve.The results show that when the laser power is 1000 W,the coating does not form,mainly because the laser power is too small or the scanning speed is too fast,and the coating does not form a good metallurgical bond with the substrate.When the laser power is 1100 W and 1200 W and the scanning speed is constant,the crack number of the coating decreases gradually.When the laser power is 1200 W and the scanning speed is 400mm/min,the coating has no obvious microstructure defects,and the maximum microhardness is 925 HV,which is about 2.5 times that of the substrate.The above technological parameters are the best technological parameters of laser cladding.Friction and wear tests were carried out on h BN coatings with different contents.With the increase of h BN content from 1% to 6%,the friction and wear properties of the matrix are significantly improved.With the increase of h BN content,the friction coefficient and wear amount both decrease first and then increase.When the h BN content is 4%,the wear resistance of the coating is the best.Electrochemical corrosion tests were carried out on different content of h BN coatings.It was found that the corrosion resistance increased first and then decreased with the increase of h BN content.The corrosion resistance of the coating is the best when the h BN content is 4%.The simulation results show that the maximum deformation of the bottom surface of the coated valve is 0.007 mm,while that of the ordinary valve is 0.008 mm.The maximum stress of the coated valve differs by 2MPa from that of the ordinary valve,which effectively reduces the stress phenomenon at the constraint place.Analysis of the six order modal analysis of coated valves and ordinary valves shows that the engine vibration frequency is far less than the first order frequency,that is,the valve will not resonance with the automobile engine.The maximum residual stress of the coating appeared in the core and gradually decreased to the outside of the coating.The residual stress of the coating with different h BN content decreases first and then increases with the increase of h BN content.Under the optimal laser cladding parameters,when the h BN content is 4%,the residual stress of the coating is the smallest,which is 36.80 MPa.