Study On Surface Integrity Of HT200 Cast Iron After Laser-induced Cavitation Strengthening

Cast iron is widely used in fluid machinery,automotive parts,machine tool industry and other important fields because of its low melting point,good casting performance,excellent machinability,deformation resistance and wear resistance.Cast iron is often used to manufacture wear-resistant parts,so higher requirements are put forward for the surface integrity of cast iron.Laser-induced cavitation strengthening technology is a new surface strengthening technology,which uses the jet induced by laser-induced cavitation to impact the material surface,causing plastic deformation and residual compressive stress,so as to improve the surface integrity of the material.In this paper,HT200 cast iron is taken as the research object,the micro-jet caused by cavitation bubble collapse and material plastic deformation are simulated;the effect of cavitation bubble on surface morphology and residual stress of cast iron under circumstances of different laser parameters is analyzed;the effect of copper cladding process on the surface properties of cast iron is studied.The main contents and results of this paper are as follows:(1)The mechanism of laser-induced cavitation bubble impact on the surface of cast iron was analyzed theoretically.The parameters of jet produced by near-wall cavitation bubble collapse were obtained by analysis and calculation,and the effect of relative distance parameter on micro-jet was explored.The strengthening mechanism of cast iron was studied from the point of view of material plastic deformation.The results show that micro-jet strengthening is an important factor in laser-induced cavitation strengthening of cast iron.(2)The growth of cavitation bubble near the wall and the phenomenon of microjet caused by bubble are simulated and analyzed in the Fluent module of ANSYS software,and the variation rules of jet velocity,time and other parameters are obtained.The surface morphology and residual stress distribution of materials are simulated by using the smooth particle dynamics solver and Lagrange solver in Autodyn module.The simulation results show that when the relative distance parameter ? equals 0.1,a jet with a velocity of 490m/s and a duration of 8us will appear on the surface of the material;local erosion will occur on the surface of cast iron,and the maximum deformation will occur in the center of the impact area,while the residual stress distribution center will be located in the sub-surface of the material.(3)Laser-induced cavitation strengthening platform was built,and the technology of copper cladding bonding on cast iron was put forward.The surface morphology and residual compressive stress of materials under circumstances of different laser energy,defocusing amount and cladding were measured and analyzed by laser confocal microscope and X-ray diffractometer.The experimental results show that the surface roughness of the copper cladding area is 57.8% lower than that of the non-cladding area,and the residual stress of cast iron surface in the copper cladding area after the impact with laser energy of 400 mJ is equal to that in the non-cladding area after the impact with laser energy of 200 mJ.(4)The strengthening mechanism of laser-induced cavitation on the surface of HT200 cast iron was analyzed and summarized.The micro-jet generated by laserinduced cavitation impacts on the surface of cast iron,plastic deformation occurs on the surface of the material,resulting in the increase of residual stress,and the surface of the material was strengthened.Copper cladding process could maintain or even improve the surface integrity of the material to a higher degree while strengthening its surface.Copper cladding process is more advantageous in strengthening parts requiring high surface integrity.