Study On Post-treatment Technology And Properties Of High-speed Laser Cladding Coating

With the rapid enchancment of science and technology,people have higher requirements for the performance of equipment.People pay more and more attention to the service life of key components of mechanical equipment.The hydraulic support column is an important part of coal mining equipment.In longterm use,due to the harsh working environment,it is easy to damage the surface of the parts due to corrosion,which seriously affects the work efficiency and safety,so it needs to be surface modified.High-speed laser cladding technology can quickly produce a high-performance coating on the surface of hydraulic support column,thus improving the service life of parts.However,there are a lot of unmelted particles on the surface of the coating,which leads to the defects of insufficient surface accuracy,excessive roughness and thermal stress.Because of these practical problems,this paper explores the feasibility of surfacestrengthening technology(powerful spinning and ultrasonic high-frequency percussion)as a post-treatment method of coating and the influence of different stress-relieving annealing parameters on the surface properties of the coating.In this paper,iron-based alloy coating was prepared on the surface of27 Si Mn steel,a common material of hydraulic support column,by high-speed laser cladding technology,and then the surface was strengthened by different posttreatment processes.The microstructure and phase of the coating were characterized by a scanning electron microscope(SEM+EDS),backscattering diffractometer(EBSD),and X-ray diffractometer(XRD).The roughness,hardness,residual stress,and corrosion resistance of the coating surface were tested by roughness tester,hardness tester,residual stress tester,and electrochemical workstation.The main results are as follows:(1)turning to remove unmelted particles on the surface of the coating,and then carrying out a powerful spinning treatment.After the coating is extruded by rotating wheels,the microstructure of the surface layer is denser,some austenite is transformed into martensite,and the grain refinement degree gradually decreases along the radial direction;The roughness decreased by 36.5%,the microhardness of the section increased by 32.9%,the residual stress of the surface layer changed from 306.92 MPa to-583.24 MPa,and the corrosion resistance was improved.(2)turning to remove unmelted particles on the surface of the coating,followed by ultrasonic high-frequency percussion.After the coating was struck by the tool head at high frequency,the surface crystal plane changed from austenite(111)to(200).Roughness decreased by 65.5%,reaching mirror effect,hardness increased by 15.0%,surface residual stress changed from 306.92 MPa to-92.18 MPa,and the corrosion resistance was improved.(3)Sandpaper polishing to remove unmelted particles on the surface of the coating,followed by stress relief annealing.The sample is heated to the specified temperature with the furnace,kept for two hours,and cooled with the furnace.In the range of stress relief annealing temperature from 200℃ to 400℃,the residual stress on the coating surface decreases with the increase of holding temperature,and the residual stress of the sample after stress-relieving annealing at 400℃decreases by-110.5MPa,which is 49.9%.After stress relief annealing at 500℃,the coating undergoes phase transformation,and the residual compressive stress is transformed into residual tensile stress.Stress relief annealing at different temperatures has little effect on corrosion resistance,and the coating treated by stress relief annealing at 400℃ has the best corrosion resistance.The above results show that powerful spinning and ultrasonic highfrequency percussion can effectively improve the surface quality and mechanical properties of Fe-based alloy coatings by high-speed laser cladding.Stress relief annealing at 400℃ has the lowest residual compressive stress and the best corrosion resistance.