| The continuous improvement of the level of industrialization and science has prompted the rapid development of industrial equipment.At the same time,a large number of mechanical equipment and other products enter the scrap period every year,resulting in a waste of resources.The rise of green remanufacturing engineering not only alleviates the contradiction between resource waste and resource shortage,but also conforms to the current development strategy of our country.As one of the main means of remanufacturing engineering,laser cladding rapidly melts,expands and solidifies the cladding material using a high-heat laser source.The formed functional coating is metallurgically bonded to the surface of the substrate.The surface properties of waste parts such as wear resistance,corrosion resistance and high temperature resistance are effectively strengthened.Their service life can be extended by laser cladding.However,with the continuous expansion of the application range of laser cladding,defects such as low cladding efficiency and poor forming surface flatness have become increasingly prominent,which need to be solved urgently.The development of high-speed laser cladding can improve work efficiency and surface quality.However,subsequent reprocessing is still required to make the surface meet the application requirements such as roughness and geometric accuracy.At present,the research on subsequent reprocessing at home and abroad mostly focuses on the turning and milling characteristics of the coating,resulting in a waste of resources to a certain extent.As a nearly equal-material processing technology,power spinning is one of the important means of plastic forming of cylindrical parts.It has high process efficiency and is suitable for processing highstrength,difficult-to-deform materials.While improving the surface quality,the shape of the coating can be controlled.It provides new possibilities for post-treatment of coatings.The relatively flat surface of the high-speed laser cladding coating also provides a good foundation for the microstructure and properties of the coating after power spinning.In this paper,the Fe-based composite coating was prepared on the substrate of 27 Si Mn cylindrical parts,which are commonly used in hydraulic support columns.The surface strengthening of high-speed laser cladding and power spinning were studied.Based on studying the influence of process parameters on the properties of high-speed laser cladding coatings,the feasibility of post-processing by power spinning was further explored.The purpose was to improve the mechanical properties of the coating while improving the surface morphology of the coating.The influence of spinning process parameters on the coating morphology was compared and analyzed.The stress state during the power spinning process of the coating was discussed,and the evolution mechanism of the coating structure was revealed.Meanwhile,the wear resistance,corrosion resistance,and tensile properties of the coating after spinning were investigated experimentally.To prepare high-speed laser cladding coatings with good performance,the method of combining numerical simulation and process experiment was used to carry out related research.On the theory of the thermal-mechanical coupling and stress-strain equations,the effects of laser power and coating thickness on the temperature field distribution characteristics during the cladding process were analyzed using ANSYS.The microstructure and mechanical properties of the cladding coatings with different process parameters were compared.Within the experimental parameters,the surface of the coating was smooth and free of defects such as pits and cracks.The high-speed laser cladding coating had an obvious multilayer overlapping phenomenon,and its structure was mainly composed of network-like dendrites and equiaxed crystals.Through the comparison of wear amount and wear scar geometry,the influence of process parameters on the wear resistance of coatings was analyzed.From the perspective of electrochemical curves and corrosion morphology,the corrosion resistance of coatings under different process parameters was researched.Compared with the substrate,the self-corrosion potential Ecorr of the Fe-based coating prepared by the optimal process parameters was increased by 94.7m V,and the self-corrosion current density Icorr was only one-tenth of the substrate.At the same time,the phase and wear properties of coatings with different thicknesses under the same process parameters were compared and analyzed.Through the above analysis,the combination of process parameters for preparing coatings with excellent performances through high-speed laser cladding was obtained.Subsequently,theoretical analysis and experimental research on the rework process of power spinning were carried out on the optimal cladding layer.Using the 3D numerical simulation software,the equivalent stress,axial and radial stress distributions of the coating during the spinning process were calculated.The effects of process parameters on spinning force and stress were analyzed in detail.The results show that the spinning force was decreased with the increase of the spindle speed,and increased with the improvement of the feed speed and the thinning amount of a single pass.Combined with the experimental analysis,it was concluded that the slowest feed rate would cause the surface of the molded part to burst due to repeated rolling,while the feed rate that was too fast would lead to uneven deformation.Within the range of experimental parameters,the surface quality after power spinning was improved with an increase in spindle speed.While the slower spindle speed could cause diameter expansion and ellipse phenomenon easily.Based on process experiments,the macroscopic morphology and microstructure of the coating after spinning were characterized and analyzed.The stress strain of the microstructure during spinning was explained.Calculated by the Williamson-Hall formula,the average grain size before and after spinning was 46.34 nm and 35.25 nm.The evolution mechanism of the microstructure was revealed.The power spinning effectively promoted the grain refinement of the surface layer.Under the action of the rotating wheel,the crystals were sheared and slipped.The grains were flattened and elongated,and the surface grains were partially broken and regularly arranged along the feeding direction.Larger strains could lead to a high density of dislocations.The surface hardening effect of the coating was evident.Finally,the relevant experimental research on the cladding coating after power spinning was made,mainly including the phase composition and mechanical properties.The coating surface after spinning was smooth,and the surface roughness Ra was decreased to 2.4 μm.The coating structure was denser and the volume ratio of ferrite was increased.More Mo and Cr are beneficial to the formation and stability of the passive film,so it had better corrosion resistance.Compared with non-spinning,the Rockwell hardness of the surface layer after spinning was increased by 5.5%.Under the same test conditions,the wear resistance was doubled,and the wear mechanism was mainly abrasive wear.Tensile experiments showed that the plasticity of the coating was decreased and the elongation was reduced.The coating area was a brittle fracture,and cleavage steps of different heights were visible.To reduce the large residual stress of the coating after power spinning,the coating was subjected to stress relief annealing.Contrasting with before annealing,the residual stress in the cladding layer was only 36.91%,and its wear resistance was significantly improved by 47.44%,but the hardness was reduced by approximately 5.8%.In conclusion,the effect of process parameters on the properties of high-speed laser cladding Fe-based coatings was studied detailedly in this study.The post-treatment process of the cladding layer after power spinning was systematically analyzed.The microstructure evolution mechanism of the coating during the spinning process was systematically clarified.The macroscopic mechanical properties of the coating after spinning were investigated.The new process is provided for the remanufacturing of cylindrical parts such as hydraulic supports. |
PDF Full Text Request