Study On Laser-MIG Hybrid Welding Process For Medium Thickness Plate Of Commercial Pure Titanium TA2

In order to meet the requirements of light weight of materials and environmental corrosion resistance of materials in industrial production,the application of titanium alloys has become more and more extensive,and higher requirements have been placed on their connections.In this paper,the laser-MIG hybrid welding butt joint test of 6 mm,8 mm and10 mm thickness TA2 test plates are carried out by IPG fiber laser to determine the feasibility of double-sided forming of medium thickness TA2 laser-MIG hybrid welding single-sided welding.At the same time,the mechanical properties of the composite joints of three thicknesses were tested to meet the basic performance requirements of the production.The laser-MIG hybrid welding process are studied on 8 mm TA2,and the influence of process parameters on the weld morphology of the composite joint are studied.At the same time,the microstructure of each region in the composite joint are observed and analyzed.For different defocusing amount of 6 mm TA2 by the laser-MIG hybrid welding,the pores in the composite welded joint are analyzed,and the pore flow mechanism of the molten pool in the joint was numerically calculated by FLUENT software.The results of three thicknesses of TA2 laser-MIG hybrid butt welding show that the surface of the three composite welded joints is better formed in the best parameters,continuous and uniform,no defects such as splashing and undercutting,and silver on the front and back.The tensile strength of the composite welded joints of three thicknesses is greater than the tensile strength of the base metal,the elongation is less than the elongation of the base metal,and the fracture morphology is a microporous dense dimple;The microhardness of the weld zone of the composite welded joints of three thicknesses is greater than the microhardness of the base metal zone,followed by the heat affected zone.The results of docking test of 8 mm TA2 by laser-MIG hybrid welding show that when the residence time of the protective cover is 150 s,the front side of the weld has a metallic luster of silver white,and the welding protection effect is guaranteed;as the defocusing amount increases,The weld width is increased,the residual height is slightly increased,and the penetration depth is basically unchanged.As the laser power increases,the weld width and penetration depth increase,and the weld height is slightly reduced,which is basically linear.Relationship;as the arc current increases,the melt width increases,the penetration depth increases first and then decreases,and the weld residual height remains substantiallyunchanged.The microstructure observation of the composite welded joint shows that the base material area is composed of uniform isometric ? grains,the grain size of the weld zone and the heat affected zone is coarse,and the size of the grain size is related to the distance from the center of the weld.Both the slit and the heat-affected zone have columnar ? crystal grains,irregular zigzag ? crystal grains,and a small amount of needle-like ? crystal grains,? twin crystals and the like.The results of laser-MIG hybrid welding process with different defocusing amount on6 mmTA2 show that the amount of defocus increases and the pores in the joint become smaller and less.The numerical simulation of the fluid flow state of the molten pool in the composite welded joint under different defocusing conditions shows that as the defocusing amount increases,the depth of the small hole of the laser acting on the molten pool becomes smaller,and the melting width of the weld surface becomes larger.When the defocusing amount is +6,the laser small hole in the molten pool has a large depth in the molten pool,and the small hole is closed after the liquid metal bridge is formed,so that the closed small hole in the closed lower part forms a larger hole to the molten pool.Moving backwards,it flows clockwise from the tail of the molten pool,preventing the holes from moving upwards.When the amount of defocus is +8,the weld width of the weld increases,and the working area of the laser in the weld becomes smaller,and the relative arc area becomes larger.When the defocusing amount is +12,the laser action and the spot diameter on the surface of the molten pool are further increased,but the energy density of the laser is decreased,so that the melt width of the weld increased,and the depth of the small holes in the molten pool becomes smaller.When the small hole is formed by the surface tension to form a liquid metal bridge,the bottom of the small hole is closed,which reduces the possibility that the small hole collapses to form a hole in the molten pool,and the obtained simulation result is consistent with the X-ray inspection result.