The Researchs On Laser Welding Of Seam Formation And Microstructure Properties For New Energy Vehicle Battery Lug

The power battery of new energy vehicles,as the driving energy of new energy vehicles,its quality directly affects the service life of new energy vehicles.The electrode lug part of power battery(TU1 copper nickel plating sheet and 1050 aluminum alloy sheet with thickness of 0.3mm)shall be welded with busbar(Busbar,6061 aluminum alloy)on both sides of module.When this kind of material uses the traditional welding method,it is easy to produce cracks and deformation in the welding process,which affects the quality of the battery.Laser welding has higher energy density,faster welding speed and smaller heating area,which is suitable for the production of new energy vehicle power battery module with higher welding deformation and accuracy requirements.In this paper,IPG fiber laser is used as welding heat source to stack the electrode lug material and bus bar of new energy vehicle power battery.The influence of laser welding power and welding speed on weld forming and mechanical properties of electrode lug material of power battery is studied.Firstly,the mechanism of laser and welding materials in welding process is studied,and the formula of laser power density of two critical points in laser welding process is derived.Secondly,using the single variable method,the effects of laser power and welding speed on the forming characteristics and variation of the welding seam of battery electrode lug material and bus bar were explored.For Al-Al and Cu-Al welded joints,maintain a constant welding speed,with the increase of power,the degree of burning on the weld surface will increase,and the fish scale shape on the weld surface will become more and more irregular or even disappear;while keep the laser power unchanged,when the welding speed increases,the welding quality of the weld surface and section of Al-Al and Cu-Al welded joints can be effectively improved.Thirdly,SEM was used to observe the microstructure of the weld area under specific welding parameters.It is found that the transition zone and weld zone can be observed in both Al-Al and Cu-Al joints.The results show that the grains in the weld zone of Al-Al welded joint are equiaxed grains with uniform size,while the grains in the transition zone are dendritic,the transition zone of Cu-Al welded joint is mainly composed of massive grains and dendritic grains.Finally,the mechanical properties of Al-Al and Cu-Al welded joints were tested to observe the fracture position and determine the fracture form.The curve of hardness with welded joint welded by Al-Al is shaped like a"U",and the highest hardness area is base metal area.With the increase of laser power,the hardness of the Al-Al weld zone decreased gradually,but with the increase of welding speed,it was opposite.The hardness curve of Cu-Al welded joint is an inverted“U”shape,and the hardness of base metal is the lowest.With the increase of laser power,the hardness of the Cu-Al weld zone increased first and then decreased,and with the increase of welding speed,it decreased.For Al-Al and Cu-Al welded joints,the shear strength increased first and then decreased with the increase of laser power and welding speed.Some necking phenomenon can be observed on the fracture surface of Al-Al welded joint,and its fracture type is pure shear fracture;there is no obvious necking phenomenon on the fracture surface of Cu-Al welded joint,and its fracture type is brittle fracture;through energy spectrum analysis,the formation of Al₂Cu and Al₃Cu₄metal compounds on the fracture surface,and the brittle compound is the main reason for the fracture.