Mass Transfer And Spiking Research In Deep Penetration Electron Beam Welding Of Titanium Alloy

The ANSYS software was employed to simulate the flow field of molten poolof titanium-alloy electron-beam deep-penetration welding, and the tracer was usedto explore the mass transfer of molten pool. The non-destructive testing of X-ray,optical microscope and energy-spectrum analysis were used to research theformation mechanism of spiking defect, and its influencing factors and controlmethod.The results of ANSYS numerical simulation show that there is a circulation inthe surface of molten pool under the action of surface tension, the maximumvelocity of the fluid was0.295m/s.The liquid metal flowed from the bottom to thetop under the action of recoil pressure of metal vapor and surface tension after thekeyhole formed, the rate of liquid metal gradually decreased as the increasing ofpenetration. During the phase of liquid metal backfilling keyhole, two pairs ofvortex that flowed in the opposite direction were formed in the molten pool, the rateof liquid metal gradually decreased. There was a vortex in the surface of moltenpool when the backfilling of keyhole was completed.The tracer test of tungsten element had shown that the tungsten element existedin the entire cross section of weld, that the content of tungsten element decreasedfrom the position of presetting layer to the two sides, The "layering" occurred in thedirection of molten width. The process of mass transfer of molten pool inelectron-beam deep-penetration welding can be divided into five stages. a) Theprimary stage of formation of keyhole; b) The middle stage of formation ofkeyhole;c) The late stage of formation of keyhole;d) Backfilling the keyhole; e) Theclosing of keyhole.The formation mechanism of spiking defect of TA15titanium alloy is asfollows: there was a lot of high-temperature Al steam in the keyhole, the Al steamgenerated greater impediment to the filling of the keyhole tip, the keyhole closedbefore the filling metal arrived at the keyhole tip because the rate of filling metal istoo small or the root of the keyhole is too thin, plus the fluctuations of electron gunresulted in the fluctuations of penetration in the direction of welding, a closedcavity was formed in the root of molten pool, thus the metal vapor of molten poolcan’t escape the molten pool, the rapid solidification of the root of molten poolformed the spiking defect. The welding parameters of lower focus, small currentand high welding speed, the complex waveform of scan and the preheating caneffectively avoid the emergence of spiking defect or reduce the number of spiking defect.