Study On Laser-arc Hybrid High-speed Welding Process Of TA2 Pure Titanium Sheet

With the development of modern industry and the improvement of energy-saving and environmental protection requirements,the manufacturing industry is increasingly demanding to reduce the structural weight of products,especially in the fields of aerospace,petroleum,electric power and chemical industry,which puts forward higher requirements for improving the quality and reliability of transmission pipelines.Titanium and its alloys have good corrosion resistance,excellent plastic toughness and high specific strength,and are ideal materials for manufacturing welded pipes.At present,most of the thin-walled welded pipes produced in industry use the traditional TIG welding method,but their production efficiency is not high.Laser welding has the advantages of high energy density and fast welding speed.Compared with TIG welding,it can greatly improve the welding speed and improve the production efficiency.However,laser welding at high speed also has edge bite defects.In this paper,the 1.2mm thick TA2 sheet is taken as the research object,and TIG arc is added as the auxiliary heat source to improve the weld seam forming of laser high-speed welding.The forming law,welding characteristics and microstructure and properties of butt joint of laser and laser-TIG hybrid high-speed welding are studied.Firstly,the laser high-speed welding process test was carried out,and the effects of laser power,defocus,incident angle and welding speed on weld formation and welding characteristics were studied,and the formation mechanism of undercut during high-speed welding was analyzed.The influence of welding process parameters on weld width and undercut was studied.It was found that the weld was well formed and the undercut depth was small at high power,laser focus position and incident angle of +3.Plasma morphology was significantly affected by process parameters,and the length of molten pool increases with the increase of incident angle and welding speed With the increase of welding speed,the solidification rate at the tail of the molten pool became faster,and undercut defects were formed in the weld.Then,the laser-TIG composite welding process test was carried out to study the effects of heat source sequence,welding current and tungsten electrode height on weld formation and welding characteristics,and the mechanism of inhibiting undercut in high-speed welding was analyzed.The influence of welding process parameters on weld width,penetration depth and residual height was studied,and it was found that the addition of TIG arc improved weld formation During hybrid welding,the plasma morphology was stable,the energy input and residence time of the molten pool were increased,the action area of the heat source was expanded,and the molten pool spread and wetted to both sides,thus eliminating the undercut defect.Finally,the effects of three welding methods and welding speed on the microstructure and mechanical properties of butt joint of 1.2mm pure titanium sheet were studied.It was found that all weld joints were composed of ? grains with different shapes,which were mainly divided into blocky,columnar and irregularly shaped ?grains.Aciform ? grains appeared in the center of laser welding bead,and disappeared after TIG arc is added,and the width of heat affected zone increased.The hardness distribution of the joint was W-shaped as a whole,with the highest hardness in the weld zone and the lowest hardness in the heat affected zone.Tensile specimens of welded joints were all broken at the base metal,and the tensile strength was higher than that of the base metal,but the elongation decreased.The plasticity of the joint can be improved by adding TIG arc.