Investigations On Residual Stresses In Laser Welding Of Ti6Al4V Titanium Alloy Thin Plate And Its Simulation

Ti6Al4V titanium alloy is widely used in the manufacturing of aerospace structural components due to its excellent mechanical properties.Residual stresses and deformations are generated due to inhomogeneous heating and welding of complex structural components during welding.Therefore,it is important to explore the residual stress distribution of complex structural members after welding.This article combines finite element simulation technology study the laser welding of Ti6Al4 V titanium alloy.The 4 mm Ti6Al4 V titanium alloy plates as the research object,three different welding speeds(11 mm/s,16 mm/s,and 23mm/s)were used to study the microstructure and mechanical properties of titanium alloy laser welded joints.Obtained the optimal welding process parameters through comparing finite element analysis,metallographic observation,and mechanical property tests.Firstly,titanium alloy laser welding was carried out at three different speeds.After welding,the macroscopic morphology of the weld joints was evaluated and the microstructure of the joint was analyzed at different welding speeds.It was found that the base material(BM)is mainly composed of α phase and β phase.The microstructure of the weld metal(WM)is α′phase,the Heat-affected zone(HAZ)is primary α and small amount α′ phase.The drill-hole method was used to test the residual stress of welded plates in three different welding speeds.The results show that the longitudinal residual stress in the heat-affected zone was the largest,the residual stress in the weld metal was next to that in the heat-affected zone.The transverse residual stress is less than 80 MPa for all three samples.The peak value of longitudinal residual stress exceeds 600 MPa at 11 mm/s and 23 mm/s welding speeds,while the peak value of residual stress is 589 MPa at 16 mm/s welding speed.The results shows that the residual stress of 16 mm/s plate welding is the smallest.The microhardness distribution of weld joints is: WM > HAZ > BM.The maximum shear force of welded joints is: WM >HAZ > BM.The maximum microhardness at the center of the weld metal of a 16 mm/s welding specimen is 385 HV,which is larger than the 11 mm/s and 23 mm/s welding speed.The maximum microhardness in the weld center of the 16 mm/s welding specimen is 385 HV,which is larger than the welding speed of 11 mm/s and 23 mm/s.The results of the shear punch test indicate that the maximum shear force in the center of the weld metal at welding speed of 16 mm/s is 2851 N,which is greater than 2693 N at welding speed of 23 mm/s and2292 N at welding speed of 11 mm/s.The comparison indicates that 16 mm/s is the optimal welding process parameter.Secondly,finite element simulation of titanium alloy plate laser welding was conducted in the optimal welding parameters of 16 mm/s.The cone heat source model was chosen and the indirect thermal coupling algorithm was used to simulate the temperature and stress fields of butt welding under experimental conditions.Adjust the heat source model parameters to compare the temperature field distribution based on the actual weld morphology.The temperature field results are in good agreement with the actual weld morphology.The residual stress simulation results showed a consistent trend with the drill-hole method residual stress tests.Conduct residual stress and deformation analysis during the welding process of titanium alloy plates.The temperature field results indicate that the peak temperature at the center of the weld metal is 4784 ℃.Conduct residual stress and deformation analysis during the flat plate welding process.The longitudinal residual stress value during the flat plate welding process is relatively large,with a peak stress of 720 MPa.The butt welding deformation in all directions is less than 0.3 mm.The optimal cone heat source model parameters obtained from the finite element simulation of titanium alloy plates was applied to the finite element simulation of titanium alloy thin-walled structure.Finally,the welding finite element simulation of the titanium alloy thin-walled structure of the aviation engine casing structure was carried out.A 1/5 model was established using rotational symmetric constraints during the welding simulation process to reduce the number of grids and save computational time.The temperature field results indicate that the highest temperature at the center of the weld metal is 4857 ℃.The stress field shows that the maximum axial stress after welding is 1050 MPa.The radial stress concentration occurs in the weld area of the inner ring rib plate,with peak residual tensile stress of 366 MPa.The circumferential maximum residual tensile stress was 933 MPa in the circumferential weld of the outer ring end face welding.According to the welded deformation mapping,the overall deformation of the weld structure is less than 0.6 mm,with a maximum deformation of 0.56 mm along the x-axis,0.53 mm along the y-axis,and 0.46 mm along the z-axis.Obtained deformation curve from the outer ring,and the curve shows that the circumferential deformation in the center area of the weld metal is the largest,with a maximum value of 0.52 mm.The axial deformation curve changes relatively stably,and the axial deformation on the three paths is about 0.1 mm.The radial deformation in the center of the weld is smaller than the axial deformation in the path around the weld metal,and the maximum radial deformation in the path around the weld is 0.35 mm.