Magnetic Field-assisted Welding Process Ofcmt Welding Aluminum Alloy And Analysis Of Microstructure And Properties Of Joints

With the introduction of the policy of banning the sale of fuel vehicles in various countries,the development of new energy vehicles has become the general trend.The problem of battery life of new energy vehicles still needs to be solved.It is one of the solutions to use light metal aluminum alloy instead of the traditional ferrous metal structure to reduce the weight of the vehicle body and realize the weight reduction of the car,so as to reduce the energy consumption of the car and improve the endurance of the car.For aluminum alloy structural parts at different positions of the vehicle body,the connection of dissimilar aluminum alloys is unavoidable.The application of Cold Metal Transfer(CMT)is a simple and efficient process.However,for the fusion welding of dissimilar aluminum alloys,the problem of porosity in the joints,the coarsening of grains and the reduction of performance are still urgent problems to be solved.Using magnetic field-assisted welding process,it is believed that it can regulate the welding process,improve weld formation,reduce welding defects and refine grain structure to improve joint mechanical properties.In this paper,2 mm 5083 aluminum and 6061 aluminum were used as research objects,and 1.2 mm ER 4043 was used as the filling material.A longitudinal magnetic field plus CMT welding processing system was used for the butt test of dissimilar aluminum alloys.And use the high-speed photography system to collect data of the welding process.The results show that when the excitation current increases from 0A to 6A,the shape of the welding arc gradually changes from a semi-sphere to a cone.The welding arc expanded and the arc duration was extended.Under the action of magnetic field,the transition frequency of the droplet is reduced,the volume of the droplet is increased,and the droplet is deflected around the welding wire.Due to the influence of the magnetic field,obvious fluctuations appear on the surface of the molten pool,and a significant rotating eddy current appears on the surface.Next,the formation and microstructure of welded joints under magnetic field were studied.With the increase of the excitation current,the penetration depth of the welded joint gradually decreases,until the current is 6A,the welded joint is not welded through.When the exciting current changes from 0-6A,the weld width of the welded joint and the remaining height on the front gradually increase,and the remaining height on the back gradually decreases.The magnetic field can reduce the porosity inside the joint.The magnetic field can reduce the porosity inside the joint.In the test,the porosity inside the joint is the lowest when the excitation current is 3A.Due to the magnetic field used to stir the molten pool,the microstructure inside the joint gradually developed from columnar crystals to equiaxed crystals,and grains larger than 200 ?m almost disappeared.The eutectic study between dendrites found that the magnetic field increased the relative area of the eutectic from 8.9% to 30.5%,the eutectic structure was also refined,and the elongated primary silicon phase was transformed into particles.Finally,the tensile strength and mechanical properties of the joint under different excitation parameters are analyzed.Under the action of a magnetic field,the change in tensile strength of the joint first increases and then decreases rapidly.When the excitation current is 3A,the fracture position of the joint is 6061 side base metal,and the remaining fracture positions are welds.Fracture characteristics analysis found that the joint fracture was related to the pore content in the joint.The stress concentration caused by a large number of pores caused brittle fracture characteristics of the joint.The micro hardness test found that the hardness of the heat affected zone and the weld zone of the joint was increased under the magnetic field.Under the action of magnetic field,more strengthened phases are generated in the welded joint.The strengthened phase prevents dislocation movement and increases the hardness of the joint.