Research On Melting Technology Of Electron Beam Cold Hearth Melting Of TC4 Titanium Alloy

TC4 (Ti-6A1-4V) alloy was developed by the United States in 1954. This alloy is a two-phaseα+βtype titanium alloy, which has a series of advantages such as high strength, high ductility, favorable plastic property, high temperature resistance and corrosion resistance. It is the most widely used and the largest output of titanium alloy. The alloy is mainly used under the annealed state, and solution and aging treatment can also be enhanced, mainly finished and semi-finished bars, sheets, plates, profiles and forgings and castings.TC4 titanium alloy is mainly used by the aerospace industry in the manufacture of aircraft structural parts and a variety of bearing types of fasteners, so using it has very strict performance requirements. In recent years there are many researches about this alloy ingot. In order to obtain uniform composition and quality qualified TC4 titanium alloy ingots, the paper carried out electron beam cold hearth melting experiments to study the melting process of different parameters, different raw materials components, and other factors on the impact of melting. The paper also carried out comparative study through mathematical models and computer simulation compared with experimental results.We found that saturated vapor pressure of the elements had a great influence of the elements evaporation during melting. In the TC4 titanium alloy, the aluminum vapor pressure ratio is about eight hundred times than matrix elements and more than two thousand times as to V element, which resulting that in melting Al has a large area of the evaporation loss, and with the melt temperature, Al element evaporation loss has increased significantly, but V element evaporation is very little, the relative content after melting has increased slightly.In the melting process, adding raw materials has a great impact on the Al element evaporation. When the molten alloy material is with a higher alloying degree of VAR ingot, A1 element evaporation loss is very little. It mainly in the cooling bed refining stage has certain extent evaporation, in the material melting and crucible solidification stage the volatilization is very little. When the raw material is added the simple substance Al, the element evaporation loss increased in the melting stage, and as the Al content more in raw materials increasing. Research of the skull found that, from raw materials melting side to the titanium liquid outflow side, Al element content was decreased, the final A1 element of the mass fraction reduced and stabilized to the average level of the ingot.In the electron beam cold hearth melting process of TC4 titanium alloy, the melting speed with 100kg/h was the best, and the ingots melt out fully complied with national standards, and ingotd had good quality, distribution of various elements,100kg/h is an ideal melting speed. TC4 titanium alloy ingot melt out was in the axial direction, the mass fraction of the alloying elements was accordance with the national standard. Al element distribution from the upper to the lower part of the ingot was decreased, and with the melting rate decreasing, the decrease was more obvious, mainly due to the beginning of melting, TC4 titanium alloy melt keep high temperature for a long time, so Al element evaporation loss seriously, contents were low. In the radial direction, the alloy element distribution was very uniform and melting effect was good.From ANSYS simulation we found that the melt trickled from cooling bed down the crucible, mainly through the melt temperature, a stable pool formed, and melt solidification, melt temperature decreased and the solidification end,5 main melting stages. Melt from the melting point beginning cooling were two main stages. In the stage of rapid solidification, melt cooling quickly, in a very short time, rapidly beginning cooling. In the cooling equilibrium stage, the temperature difference between melt and crucible wall smaller, cooling was gradually smooth. When the cooling time is reach 500s, the inside and outside temperature of crucible basically balance. ANSYS simulation software accurately reflects the distribution of melting temperature field, and the result is in good agreement with experiment.