Numerical Simulation Of Solidification Process During Electron Beam Cold Hearth Melting For TC4 Alloy Ingot

TC4(Ti-6Al-4V)alloy as the earliest two-phase titanium alloys,has been widely used in aerospace and ocean ships because of its outstanding performance.Until now,TC4 alloy is still the most productive and widely used of all kinds of titanium and titanium alloys.Electron Beam Cold Heart Melting(EBCHM)has become an indispensable advanced technology in the smelting of clean titanium and titanium alloys due to its excellent impurity removal ability.Qualified titanium and titanium alloy ingot can be directly rolled into metal without forging during single EBCHM,which can greatly reduce the production cost and its great significance to promote the application of titanium and titanium alloy.However,at present,TC4 alloy ingot has some problems such as poor surface quality(cracks),uneven structure and internal holes during single EBCHM.The process parameters directly affect the quality of the final TC4 alloy ingot during EBCHM.In this thesis,Based on the finite element simulation method,the influencing of main technological parameters on the temperature field,solidification structure,flow field and stress field of TC4 alloy during EBCHM are research and discussed,which aims to provide scientific theoretical basis for setting technological parameters in practical production.The thesis firstly aimed at the actual production of TC4 alloy round ingot for a factory,simulated the round ingot solidification process,and analyzed the influence of different process parameters on the temperature field and solidification structure,and provide scientific basis for production.Next,on the base of the previous research of the team:The morphology of the molten of large-scale TC4 alloy slab ingot was considered under the influence of convection;and the stress field of the large-scale TC4 alloy slab was studied.The temperature field of TC4 alloy round ingot shows that the amplitude of solid-mushy interface and mushy-liquid interface increases with the pouring temperature and pulling speed increase.The influence of pulling speed on the shape of molten is greater than the pouring temperature.From the calculated results of grians structure found the experimental micrographs coincide with the simulation results.The number of grains decreases and the average grain radius increases with the pouring temperature increase.The number of grains increases first and then decreases and the average grain radius decreases first and then increases with the prulling speed increase.In this simulation,the pulling speed should be controlled within 5.4×10-4 m/s in order to prevent leakage.From the coupling simulation of temperature field and flow field for the large-scale TC4 alloy slab ingot shows that the shape of molten after coupling flow field has a great change compared with single temperature field,specifically,the liquid phase area becomes narrower,the volume of the paste area increases,the paste area becomes irregular and forming a "contact angle" deep into the solid phase area,the solidified shell becomes thinner.Reducing the pouring temperature,pulling speed and increasing the area of overflow area can effectively reduce the macro-segregation and quality defects of the slab ingot,and help to improve the quality of the shab ingot.When the overflow area is set in the center of the wide surface of the crystallizer,the same curvature of the solid-liquid interface can be obtained at both ends of the crystallizer.Finally,the calculated results of stress field shows that the surface effective stress of the slab ingot is basically formed in the crystallizer,and the inner effective stress is mainly formed outside the crystizer.The position of the maximum surface effective stress appears below the meniscus in the crystallizer.The center area 92 mm away from the narrow surface appears at the maximum position of inner effective stress.In this simulation condition,the change of pouring temperature has little effect on the distribution of stress field.The effective stress on the surface and inner of the ingot decreases with the pulling speed increase.According to the prediction of hot tearing indicator,the most likely position of cracks on the surface of slab ingot is the corner,narrow surface,and wide surface.The most likely location of inner crack is in the center area 92 mm away from the narrow surface.