Simulation And Experimental Study On Temperature Field Of Fsw Assisted By Magnetic Field

For high speed friction stir welding is used to weld aluminum alloy sheet,due to small size and fast heat dissipation,greater heat input power is required,otherwise welding defects are easy to occur,so additional energy auxiliary welding can be applied.According to the principle of electromagnetic induction,no matter whether it is a magnetic conductive metal or not,as long as the closed conductive body will produce electromagnetic induction eddy current in the changing magnetic field,which will produce thermal and mechanical effects on the welding of aluminum alloy sheet.The introduction of magnetic field in the welding process,in addition to increasing the welding temperature,the magnetic field will also affect the microstructure and composition distribution of the metal in the weld zone,thus enhancing the comprehensive performance of the welded joint.Therefore,the research on the mechanism and method of magnetic field assisted welding has important engineering application significance.Taking 1.5mm thick 6061 aluminum alloy sheet as the research object,a magnetic field assisted friction stir welding equipment was designed.Based on electromagnetic principle and eddy current field effect,theoretical analysis and simulation were carried out to demonstrate the feasibility of magnetic field assisted welding.The MAXWELL software is used to numerically simulate the magnetic field and obtain the magnetic field strength and distribution.Then,the distribution of the induced magnetic field generated by rotation is simulated and analyzed to analyze the effects of induced magnetic field parameters such as the magnetic field strength,electromagnetic force,and eddy current loss on the welding quality.The results show that the magnetic field strength of iron is the highest at the weld center,which is about 5000 GS.The magnetic field intensity decreases with the weld center to both sides,and the direction is in the shape of double vortex.When the rotational speed increased from 8000 rpm to 12000 rpm,the magnetic flux change rate accelerated,and the magnetic induction intensity increased more significantly.The heat source model was established,and the welding temperature change under the action of magnetic field was simulated numerically by ANSYS software,and the change of temperature field with or without the assistance of magnetic field was compared and analyzed.The temperature changes in the welding process under different welding speed and rotation speed were compared and analyzed,and the temperature changes were measured by experiments.The results show that the welding temperature increases in all welding stages and regions with magnetic field assisted welding,and the temperature increases most obviously in the lower pressure stage.In the acceleration stage,the temperature increase of the forward side,the welding core area and the backward side is 8℃,65℃ and 57℃ respectively.The temperature increase of the advancing side,the welding core area and the receding side in the stability stage is 55℃,20℃ and 22℃ respectively,and the magnetic field has a more significant influence on the receding side of the weld.The forming of weld surface,tensile fracture morphology,microstructure characteristics of weld area,tensile strength and hardness of joint in different areas were studied by magnetic field assisted welding test under different welding process parameters.The results show that the additional heat input of eddy current field can make up for part of the heat input lost due to the increase of welding speed,enhance the metal fluidity of weld tissue,avoid the occurrence of welding defects,and effectively improve the quality of weld,but it is easy to overburn when the welding speed is low.From the perspective of microstructure,the electromagnetic force effect of metal particles inside the welding core area is obvious,dispersing metal impurity particles,making the plastic flow sufficient and the organization more uniform.From the point of view of tensile properties,the tensile strength of the joint assisted by the magnetic field is increased by about 3%.From the point of view of microhardness,the hardness increased by about 7.4% when the magnetic field was assisted.It shows that the flow of plastic metal in the weld zone is enhanced under the action of magnetic field,which makes up for the shortage of mechanical agitation,breaks the grain structure and plays a role of fine grain strengthening.