Research On Laser Welding Process And Mechanism Of 6082 Aluminum Alloy

Lightweight high-speed train has become a problem urgently to be solved in the current rail transit industry and future development trend.The density of aluminum alloy because of smaller and higher specific strength are widely used in rail transit industry.Laser welding of aluminum alloy compared to the traditional arc welding with high efficiency and better welding joint quality.In this dissertation,the welding process and mechanism of plate butt joint of 6082-T6 aluminum alloy were studied by means of laser wire filling welding and laser-MIG composite welding aiming at many welding requirements of 6082-T6 aluminum alloy for high-speed train.The effects of technological parameters such as defocusing amount,optical wire spacing,laser power,welding speed and wire feeding speed on weld forming,joint microstructure,joint mechanical properties and welding defects of laser fillet filling welding and laser-MIG composite welding were analyzed by means of control variables.The optimum welding parameters of the two laser welding methods were determined.The test results show that the optimal welding parameters for laser fillet welding are defocusing capacity-4mm,laser power 1900 W,welding speed 0.9m/min,and protective gas flow rate 20L/min.And the optimum technological parameters of laser-MIG composite welding are the optical wire spacing of 3mm,the laser power of 1900 W,the wire feeding speed of 4m/min,and the protective gas flow rate of 20L/min.The well-formed welded joints were evaluated by means of microstructure analysis and mechanical property test.It was found that the weld zone of the joint was mainly composed of dendritic ?-Zn solid solution and reticular ?-Al solid solution,and the heat-affected zone was mainly composed of columnar crystals in the form of bars and blocks.Under the optimal process parameters,the minimum hardness is 80 HV,the tensile strength is 300 MPa and the elongation is 3.60%.The grain size of welded joint increases gradually and the mechanical properties of welded joint decrease with the decrease of welding speed or the increase of laser power.The microstructure of the weld center of laser-MIG composite welding joint is mainly fine equiaxed crystal,and the transition zone is columnar crystal growing in the direction of vertical fusion line.The grain size and the width of transition zone in the upper part of arc zone are larger than that in the lower part of laser zone.Under the optimal process parameters,the minimum hardness is 95 HV,the tensile strength is 313 MPa and the elongation is 6.149%.Due to its composition and weld ability,the 6082-T6 aluminum alloy is prone to thermal crack and porosity during laser welding.The weld defects of well-formed laser fillet weld and laser-MIG composite weld were tested.The experimental results show that the thermal crack tendency and porosity of the welded joint of laser-MIG composite welding are smaller than that of laser-filled wire welding.Due to the addition of Mg and Si alloy elements in ER4047 wire added in the laser-MIG composite welding process,the content of alloy elements in the weld is regulated to reduce the tendency of weld heat crack.At the same time,MIG heat source in composite welding can increase the laser keyhole radius,enhance the radiation capacity of the plasma,dilute the plasma,and enhance the flow of the weld pool,accelerate the bubble overflow of the weld,and reduce the porosity.