Research On The Equipment And Welding Technology Of Controlling Magnetic Arc TIG In Narrow-gap Welding

Titanium alloy is called―Marine Metal‖and has bright prospect in the field of shipmanufacture because of its excellent corrosion resistance and non magnetic feature.Narrow-gap TIG welding method is especially suitable for thick plates owing to itsability to easily get high quality seams and economical efficiency. However, the mostdifficult technical problem is poor sidewall fusion.To enhance the navy military forces, speed up the application of titanium alloy inthe naval equipment and solve the welding problem of deep submergence vehicle inmarine engineering, we analysis the mechanism of controlling magnetic arc TIGwelding system in narrow gap and develop the magnetron arc TIG welding platformwhich can be applied in laboratory conditions based on the introduction of technology.This equipment could be successfully applied to the automatic welding of thick-platetitanium alloy in narrow-gap. The problem of sidewall fusion could be solved bycontrolling welding arc periodically oscillating in the transverse alternating magneticfield.(1) We study the influence of tungsten electrode tips on the quality of weldingseams. The results show that the tungsten electrode with terrace of2mm*0.8mm tipwould obtain ideal welding qualities including the largest sidewall and well-fusedbottom.(2) We study the influence of welding parameters during welding formationprocedure. The problem of sidewall fusion is improved when the current increases.Besides, the arc impact depth, penetration, and fusion width all increase at the sametime. With the increasing of the arc length, the seams’ non-uniformity is deteriorated.The surface pits are obviously increased. As magnetic field intensity increases, theproblem of sidewall fusion is gradually solved. When the magnetic field frequencyincreases, the arc impact depth and penetration grow, but fusion width and sidewallfusion drop.(3) The influences of the magnetic field intensity on the microstructure of titaniumalloys are deeply researched. The change rules of titanium alloy histomorphology areassociated with the variation of magnetic field intensity. The macrostructure ofcolumnar crystals transforme to flat crystals and equiaxial grains appearing in the frontof bonding line. In the center of the weld columnar grains grow perpendicularly to weldsurface. The microstructure generally become uniform lamellar structure and equiaxedalpha phase as magnetic field intensity increases.(4)56mm Ti-6Al-4V titanium alloy is welded using this controlling magnetic arcTIG welding equipment. The microstructure of intraformation and interlamination are analyzed. Tensile properties, impaction toughness and hardness of the welding seamsare tested along the thickness direction. The change rules of thoese properties areanalyzed and explained.