Research On Quality Defect Repairing Technology Of Aluminum Alloy Laser-arc Hybrid Welding Joint

6082 aluminum alloy is widely used in high-speed train body due to its advantages of low density,high specific strength and good corrosion resistance.Laser-MIG hybrid welding has the advantages of large welding depth-to-width ratio,high welding efficiency,small welding deformation,and high process stability.It is very suitable for welding aluminum alloys.However,due to the large number of laser-MIG hybrid welding process parameters,and the total length of a single car body weld exceeds 1 km,excessive welding defects will inevitably occur during the welding process,which will reduce the service safety of high-speed trains.Therefore,welding repair technology is indispensable in practical application.This paper uses different welding methods to repair the defects of 6082 aluminum alloy composite welding joints.Through experiments and finite element analysis,the mechanical properties of the welded joints before and after repairing and the evolution of residual stress and deformation law in the repairing process are studied.The specific work and research and the achievements mainly include:Firstly,the effect of laser-MIG hybrid welding parameters on the joint quality of 6082 aluminum alloy was studied.Ten groups of different laser-MIG hybrid welding parameters were selected to study the effects of welding speed,laser power,welding current and spot diameter on joint formability and micropores.The results show that the influence of welding heat input on joint forming is obvious.The welding parameters such as laser power,welding current and welding speed change the shape of the weld section by affecting the total welding heat input.There is a peak 5.4k J/m in the welding heat input.Before reaching the peak value,increasing the welding heat input is beneficial to the joint formation.After reaching 5.45 k J/m,with the increase of heat input,the porosity increases and the welding defects increase.Secondly,laser-MIG welding and MIG welding are used to discuss the effects of different repair methods on welded joints from the aspects of metallographic structure,tensile properties,micro-zone mechanical properties,hardness and deformation of welding test plate.It was found that the tensile strength of the test plate was 229 MPa before repair,and decreased to 210 MPa after three times of composite welding and then to 200 MPa after three times of repair.Compared with laser-MIG hybrid welding repair,the MIG welding repair caused a significant increase in grain size in the heat-affected zone after three repairs,leading to a decrease in joint plasticity.The hardness of the joint after MIG welding repair was lower,and the softened area of the joint was larger.The results of welding deformation show that the overall deformation angle of MIG welding repair is larger,and the transverse angle of MIG repair is 4.014°higher than that of the original welding test plate after three times.The above results show that the effect of laser-MIG hybrid welding repair is better.Finally,the effect of repair times on the residual stress field was studied,and the numerical model of laser-MIG hybrid welding repair of 6082 aluminum alloy was established by using ABAQU software.The residual stress predicted by the model is in good agreement with the experimental results.It is found that the change of constraints is the main reason for the increase of residual stress in repaired joints.As the number of repairs increased from 0 to 3,the maximum longitudinal and transverse residual stresses increased from 146.8MPa and30 MPa to 170 MPa and 40.8MPa,respectively.And the maximum longitudinal residual stress area appears in the depth direction of the plate center close to the weld metal,and the maximum transverse residual stress area is located on the top surface.