| In the process of high speed friction stir welding(HR-FSW)welding the Al alloy ultrathin plate(≤1mm),due to the insufficient stirring of the micro welding tool,the joint often appears insufficient flow of plastic metal material on the Advancing Side(AS),obvious“S” line in the weld center,holes and tunnels at the root and other defects,which have a great influence on the improvement of joint quality.To solve this problem,a new “magneticcontrolled” friction stir welding technology is proposed in this study.A coaxial rotating magnetic field assisted HR-FSW welding device is designed.Aluminum alloy sheet with thickness of 1mm6061-T6 is taken as the test object,and simulation and experimental verification are combined.The effect of coaxial rotating magnetic field on the quality of HRFSW butt joint was investigated,and the feasibility and reliability of “magnetic controlled”friction stir welding technology in the Al alloy ultrathin plate welding were verified.In this study,based on the basic theory of electromagnetism,through in-depth analysis of the principle of magnetic eddy current action,and through continuous improvement,a coaxial rotating magnetic field assisted HR-FSW welding device was designed.The magnetic field assisted HR-FSW welding model was established by deducing the mathematical model of electromagnetic force in the welding process.The magnetic field force was preliminally verified by the designed magnetic aggregation verification device.The results show that when the magnetic gap is less than 1mm,the vortex magnetic field with the maximum intensity can be formed in the center of the weld,and the magnetic field intensity is 5500 GS.The magnetic transient model was established by Max-well magnetic field analysis module in ANSYS simulation software,and the distribution characteristics of magnetic field intensity in the center of Al alloy weld were analyzed.The results showed that the magnetic field intensity decreased along with the center of weld to both sides with iron as the plate,and the magnetic field simulation results were consistent with the actual verification results.Based on the analysis of the electromagnetic force data of the plate,it is found that the electromagnetic force of the plate fluctuates up and down along the X and Y directions,with periodic characteristics.Driven by the motorized spindle,a rotating magnetic field with spatial high frequency variation is formed inside the weld,and the vibration frequency is200 Hz.It is preliminarily verified that the electromagnetic force can be generated when the coaxial rotating magnetic field is applied to the moving the Al alloy ultrathin plate.Based on the simulation results,a three-way force detection device was added,and the axial force and forward resistance in the welding process were collected by the method of experimental verification.After the data was collected,the waveform of axial force and forward resistance was drawn by filtering the data line with MATLAB software.Compared with the conventional HR-FSW experimental results,the addition of magnetic field reduces the welding load of HR-FSW,and the fluctuation range of axial force is small in the welding stability stage,and the axial force decreases.The periodic electromagnetic force along the X and Y directions increases the forward resistance,and the difference between them is close to10 N,which is consistent with the simulation results.The coaxial rotating magnetic field auxiliary heat source model was established by Maxwell magnetic field control equation,and the temperature field was simulated by ANSYS software.The measured results of temperature field under different welding methods were compared.It is found that the average temperature in the weld zone increases by about 40℃after the magnetic field is applied,and the simulation results of magnetic field and temperature field are consistent with the measured results with an error of less than 8%,which preliminatively indicates that the magnetic eddy current generated in the weld has a local thermal effect on the weld metal.The magnetic field assisted HR-FSW welding process test was designed by single factor variable method.The joint performance analysis and weld microstructure observation were combined,and the influence of spindle speed and welding speed on joint quality under the action of magnetic field was studied by EBSD technology,so as to verify the effect of magnetic field.The results show that,under the action of magnetic field,the roughness and smoothness of weld surface are higher,the texture of fish scale is more delicate and uniform,the boundary line of each area of joint section is blurred,the streamline layer of metal accumulation and “S” defect disappear on the Advancing Side,and the grain size in weld core zone is smaller and compact.The tensile strength of the joint is not significantly increased,and the fluctuation range of hardness value is more stable,which is increased by 8.7%.It fully shows that the “magnetic control” HR-FSW welding method effectively strengthens the mixing of the plastic metal in the weld zone,refines the grain size in the weld core zone,promotes the flow of the plastic metal in the weld,effectively improves the internal forming of the weld,and plays a certain positive role in improving the welding quality of the joint. |
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