Numerical Analysis Of Residual Stress In Laser+GMAW Hybrid Welding For T-joint Of Aluminum Alloy

Aluminum alloy material has been widely used in aerospace,ship,high-speed rail and automobile manufacturing because of its low density,high strength,good corrosion resistance and good formability,etc.,while aluminum alloy welding joints are prone to crack,porosity,edge bite and joint deformation and other welding defects,which limit the application of aluminum alloy.Aluminum alloy welding needs to adopt welding methods characterized by small heat input,high energy density and fast welding speed,while laser+GMAW hybrid welding can meet the welding requirements.The mechanical properties of welded joints are reduced due to the unavoidable residual stress caused by the non-uniform heating during welding.The distribution of heat flux and molten pool stress in t-joint of aluminum alloy are more complex.Therefore,this paper adopts the method of numerical simulation and experimental detection to study the residual stress of aluminum alloy T-joint laser +GMAW hybrid welding,which has important academic significance and engineering application value.In this paper,4mm and 12 mm thick 6061 aluminum alloy plates were used for t-joint hybrid heat source welding experiment,and the residual stress distribution of the workpiece was measured by X-ray diffraction method.Based on the macroscopic heat transfer,a geometric model was established according to the size of the joint and the morphology of the cross section molten pool,and a suitable hybrid welding heat source was selected.The arc heat flux and heat content of overheated droplet are described using an double ellipsoid body heat source model,and the laser power is regarded as conic body distribution.Based on the thermal-elastic-plastic theory,a three-dimensional finite element model of residual stress was established for aluminum alloy T-joint laser +GMAW hybrid welding.The temperature field and stress field were calculated by ANSYS finite element analysis software to study the evolution process of residual stress and analyze the distribution characteristics of residual stress under different process parameters.The results show that the longitudinal residual stress measured by X-ray diffraction is in good agreement with that calculated by hybrid welding,which proves the accuracy and reliability of the numerical model.Before the weld pool passes through each joint position,the transverse and longitudinal stresses gradually show a larger compressive stress.The stress in the thickness direction first shows a tensile stress of 80 MPa and then changes to a larger compressive stress,while the equivalent stress first increases and then decreases.In the cooling process of the 50 s,the transverse compressive stress gradually decreases,the longitudinal stress changes from compressive stress to larger tensile stress,the compressive stress in the thickness direction decreases,and the equivalent stress gradually increases.Under the heating action of the heat source of weld A,the transverse stress and the thickness stress have A small range of change,while the longitudinal stress has a large reduction,but the longitudinal stress at the starting and stopping arc points has a small change.For 4mm thick aluminum alloy T-joint,when the laser power increases from0.2k W to 3k W,the tensile stress peak value in the weld and near joint area decreases gradually,which is 296 MPa,286MPa,260 MPa and 251 MPa respectively,while the width of high stress area increases.Compared with 0.2Kw and 1k W,the longitudinal tensile stress peaks of 2k W and 3k W are smaller and lower than the material yield strength,while the width of high stress region of 2k W is smaller than 3k W.Therefore,a better longitudinal stress distribution can be obtained under the condition of 2k W laser power.Different welding speed under the condition of the longitudinal tensile stress peak value is less than the yield strength of material,welding speed from 20 mm/s reduced to 8 mm/s,The peak of the longitudinal tensile stress of welding seam decreases gradually,while the high stress area width of 12mm/s and 8mm/s basic same,so under the welding speed of 8 mm/s good residual stress distribution can be obtained.The 12 mm thick aluminum alloy T-joint is thicker than 4mm,and the longitudinal stress and equivalent stress have a stress trough between the weld on both sides.The increase of laser power from 2k W to 5k W has little influence on the distribution of transverse stress and thickness stress,and the width of high longitudinal stress area is basically the same,while the peak value of longitudinal tensile stress at both sides of welding seams with laser power of 5k W is smaller than that of other parameters.Therefore,the residual stress distribution can be obtained at 5k W laser power.