Study On The Laser Beam Wobbling Welding Process Of 6061 Aluminum Sheet Lap

Aluminum alloy has the advantages of low density,high specific strength,large specific modulus,good formability,excellent corrosion resistance and so on.It is an ideal lightweight material for automobile body.Wobbling welding is a new kind of laser welding technology,compared with the traditional laser welding,the process through regulating light scanning path,increasing the keyhole stability,promoting the molten pool flow,expand the pool area,effectively reduce the workpiece positioning accuracy requirements of assembly accuracy and beams,and greatly relieves the problem of aluminum alloy laser welding blowhole defect multiple,has extensive application prospect in car body.In this paper,the laser wobbling welding process of 6061 aluminum alloy sheet lap joint for automobile body is studied,and the influence of laser wobbling trajectory,wobbling amplitude and wobbling frequency on weld formation,joint microstructure,pore defects and mechanical properties are analyzed.The welding process window of the lap joint with good performance has important guiding significance for the application of the laser wobbling welding process for the lap joint of the aluminum alloy sheet of the automobile body.The main conclusions of this paper are as follows:(1)The influence of wobbling process parameters on the macroscopic forming of laser wobbling welding seam in lapped aluminum alloy sheet was studied.By calculating the spatial distribution of the input energy in the welding process and analyzing the flow behavior on the surface of the weld pool,the influence of the wobbling trajectory on the weld formation was revealed.The study found that compared with the linear,circular and8-shaped laser wobbling trajectory,the infinity laser wobbling trajectory showed uneven spatial distribution of energy in the weld and the highest peak energy,significant periodic surge flow behavior on the surface of the weld pool,better surface forming,and the best bond surface fusion.Based on the infinity laser wobbling trajectory,the influence of wobbling amplitude and wobbling frequency on weld forming were analyzed,and it was found that too large or too small wobbling amplitude and wobbling frequency would make weld deformation difference.For the 1mm(upper plate)and 2mm(lower plate)thick aluminum alloy overlap laser wobbling welding process,the best process parameters obtained are:?-shaped laser wobbling trajectory,4000W laser power,45mm/s welding speed,zero defocus,25L/min shielding gas(argon gas),wobbling amplitude of 2mm,wobbling frequency of 100Hz,and its weld formation is as follows:the weld surface is regular and regularly distributed,and the weld surface is flat and evenly wide,without hump,macroscopically visible welding defects such as undercuts,surface voids,landings,spatters,cracks,etc.;the lap surface melting width and weld penetration depth are the largest,the weld width ratio is small,the weld lap surface fusion is the best,and the penetration depth ratio is small,the weld seam penetration is remarkable.(2)The effect of wobbling process parameters on the microstructure and mechanical properties of laser wobbling welding welds of aluminum alloy sheets was studied.The results show that compared with traditional laser welding,the equiaxed grains in the weld center of laser wobbling welding are smaller,which is mainly due to the increase of subcooling and the intensification of melt convection caused by laser wobbling.The periodic variation of keyhole fluctuation and flow in molten pool during welding process inhibited the occurrence of porosity defects after aluminum alloy welding.The microhardness of the joint weld center is the lowest,and there is a relatively obvious softening phenomenon,which is mainly due to the burning loss of Mg element and the relatively less strengthening of The precipitated Mg₂Si.There are two fracture modes in lap laser wobbling welding joints,the tensile fracture of the joint bears a greater maximum load force than the shear fracture.The fracture morphology shows that the tensile fracture belongs to the mixed fracture including the micro ductile fracture and the micro brittle fracture,and the shear fracture belongs to the ductile fracture.