Caculation Simulation And Stress Control Of Local Induction Heat Treatment Of TC4 Titanium Alloy Thin-wall Weldments

TC4 titanium alloy is widely used in many fields due to its advantages of low density,high specific strength and good corrosion resistance.However,due to the low thermal conductivity,high melting point,and low modulus of elasticity of titanium alloy itself,and the huge temperature difference between the molten pool and the base metal during the welding process of titanium alloy,it is inevitable that titanium alloy welded parts have large residual stress and certain overall deformation.In view of the above problems,this paper takes TC4 titanium alloy thin-walled parts as the research object,and uses finite element simulation combined with experimental research methods to explore the influence of local induction heat treatment process on the residual stress and deformation of titanium alloy weldments,so as to realize the residual stress and deformation of titanium alloy weldments.The control of stress reduces the deformation of thin-walled parts.A finite element model of the titanium alloy thin plate was established,and the mobile heat source was programmed through the ANSYS classic interface to simulate the distribution and change of the temperature field,stress field and deformation field during laser welding.The simulation results show that the heat source temperature field in the laser welding process is distributed in an ellipsoid shape.The center temperature of the heat source can be as high as 2800℃,the diameter of the molten pool is about1 mm,and the maximum longitudinal stress after welding can reach 780 MPa.After welding,the deformation of the sheet in the vertical direction of the weld is about0.2mm,and the degree of deformation is 0.67%.Along the direction of the weld,the sheet after welding shows a U-shaped warping deformation facing the heat source.The warping deformation is about 0.12 mm,and the degree of deformation is about 0.12 mm.0.12%.A finite element mathematical model of electromagnetic induction local heat treatment was created.The finite element model of TC4 titanium alloy thin-walled parts,coils,magnets and air was created by COMSOL finite element simulation software.The electromagnetic-thermal coupling calculation method was used to calculate the temperature field of the titanium alloy thin-walled parts after heating,and the mathematical function was used to simulate the heat source.The model replaces the three-dimensional coil movement,and the fitted heat source temperature distribution curve is basically consistent with the electromagnetic heating temperature distribution curve of the coil induction heating within 0.02 m from the center of the heat source.Then use the fitting heat source model to simulate the temperature field,stress field and deformation field distribution and changes of 650℃,750℃ and 850℃ one,three,six,nine,twelve local reciprocating heat treatments after welding by ANSYS software.The simulation results show that 850℃ three times or more local reciprocating heat treatment has the best stress relief effect,which can eliminate 36% of the residual stress after welding.During the cooling process after local heat treatment,because the base material hinders the cooling and shrinkage of the heated area,stress rebound in the weld area will occur,resulting in higher tensile stress.The optimal temperature for heat treatment control deformation is 750°C,and the number of reciprocations is nine reciprocations.After the heat treatment of this process,the warping deformation of the sheet perpendicular to the weld direction is basically zero,and the warping deformation along the weld direction is about 0.2mm,the degree of deformation is 0.2%.The longitudinal stress measured results and the simulation results were compared and analyzed,and it was found that the simulation results and the measured results are basically consistent in the weld zone.The experimental results showed that the residual stress in the center of the weld of the workpiece after partial heat treatment has nothing to do with the initial stress,but is related to the heat treatment temperature;the higher the heat treatment temperature,the more complete the residual stress is released.At the same temperature,increasing the number of heat treatment reciprocations can further release the stress.After the number of heating reaches three times,the stress will not continue to decrease if the number of reciprocating is increased;the metallographic observation results show that the local induction heat treatment of the weldment below850℃ hardly changes the microstructure of the weld zone of the titanium alloy weldment;Corrosion behavior test results show that as the heat treatment temperature increases,the stress corrosion sensitivity index of welded parts gradually decreases,and the stress corrosion resistance performance gradually improves.