| Laser cladding technology,as a frontier technology in the field of material surface engineering,has been paid attention to and applied by research institutions and industrial fields.However,the compositional segregation and uneven structure of the cladding layer limit the large-scale application of laser cladding.How to solve this problem has become the focus of laser cladding technology research.In this paper,42 Cr Mo steel is used as the matrix,Ni Cr BSi alloy powder is used as the cladding layer material,and the laser cladding experiment is assisted by a selfdeveloped DC electric field,alternating magnetic field and ultrasonic field compound device.The workpiece is placed in an alternating magnetic field,and a direct current is passed into both ends of the workpiece.At the same time,no-load ultrasonic is applied above the substrate to be cladding,so that the direct current field,alternating magnetic field and ultrasonic field act on the workpiece together.Through the compound action of the three fields,the heat and mass transfer process inside the molten pool is accelerated,the composition segregation of the cladding layer and the uneven structure of the structure are improved,and the mechanical properties of the cladding layer are improved.The experiment uses a self-built electro-magnetic-ultrasonic composite device to make the three fields controllable at the same time,and conducts a non-assisted field,a single physical field and a compound field assisted laser cladding control experiment,and analyzes and compares the performance of the cladding layer.Furthermore,the parameters of the composite field-assisted laser cladding are optimized.At the same time,the finite element simulation method is used to study the influence of different auxiliary fields on the molten pool flow in the process of assisted laser cladding.Firstly,the laser cladding experiment without auxiliary field was carried out,and 9sets of orthogonal experiments were designed to study the influence of laser power,spot diameter and scanning speed on the properties of the cladding layer without auxiliary field.The results show that the laser power is the main influencing factor for the height of the cladding layer,the diameter of the spot has the greatest influence on the width of the cladding layer,and the scanning speed has a significant effect on the depth of the cladding layer.The laser power has the greatest influence on the microhardness and wear resistance of the cladding layer.When the laser power increases,the microhardness of the cladding layer decreases.Then,on the basis of the previous experiments,the process parameters with better experimental effect were selected,and the control experiments of laser cladding assisted by no auxiliary field,electro-magnetic field,ultrasonic field and compound field were carried out.The influence of the external physical field on the flow of the laser cladding molten pool was studied by the finite element simulation method.By observing the microstructure,it is found that applying a physical field has a refinement effect on the structure of the cladding layer.However,the stirring effect of the electromagnetic force of the electric-magnetic field on the molten pool,the acoustic flow effect of the ultrasonic field and the cavitation effect on the dendrite breaking and the stirring effect on the molten pool make the microstructure of the compound field cladding layer more refined.The diffusion is more uniform and the degree of component segregation is smaller.Through finite element simulation,it is found that the compound field has the most obvious effect on the increase of the velocity of the molten pool and the greatest impact.The hardness test and wear resistance test results show that the compound field cladding layer has the highest hardness and the smallest wear volume,indicating that the application of electromagnetic and ultrasonic compound fields during the laser cladding process can help increase the hardness of the cladding layer and improve the wear resistance.Furthermore,the parameters of compound field assisted laser cladding were optimized.Through the response surface parameter optimization experiment,the influence of the three factors of the intensity of direct current electric field,the intensity of alternating magnetic field and the ultrasonic power on the quality of cladding layer was analyzed,and then the factor parameter combination to obtain the better quality of cladding layer was selected.Through the perturbation diagram analysis of the single influence between the variable and the response,as the ultrasonic power increases,the microhardness of the cladding layer decreases;with the increase of the DC electric field intensity,the microhardness of the cladding layer increases.The microhardness of the cladding layer increases first and then decreases with the increase of the alternating magnetic field.Through the response surface optimization parameter analysis,the best physical field parameter combination is obtained: ultrasonic power 150 W,alternating magnetic field strength 40 m T,DC current strength 10 A,and experiments verify that it can obtain a cladding layer of ideal quality.In this paper,the laser cladding technology assisted by DC electric field,alternating magnetic field and ultrasonic field is studied experimentally and its parameters are optimized.This study is a technical exploration of compound physical field to effectively solve the problems of component segregation and uneven structure in existing laser cladding process,which provides reference and reference for the research of multiphysical field assisted laser cladding. |
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