Numerical Simulation Of Solidification Process In Welded Molten Pool Of Ti-45%Al Alloy

With the rapid development of computer technology and the continuous improvement of solidification theory, numerical simulation technology has been able to reproduce clearly the physical process of molten pool solidification. Based on the previous development, the welding temperature field of Ti-45%Al alloy under TIG welding and the dendrite growth during the solidification process of molten pool were numerically simulated.The welding temperature field of Ti-45%Al alloy was firstly simulated by finite difference method. The accuracy of the temperature field model is verified through comparing the thermal cycling curves obtained by the simulation results and the experimental results. Secondly,considering the solidification characteristics of the weld pool, a dendritic growth model based on the cellular automata method was established. The growth morphology of equiaxial and cylindrical crystal of Ti-45%Al alloy was simulated in the isothermal field, and the distribution of solute concentration was analyzed, and the growth regularity of dendrites under different coagulation parameters was discussed. The results show as follow: The larger subcooling will promote the rapid growth of dendrites and accompany complex dendritic morphology. A sufficiently low anisotropy can cause unstable growth of dendrites, resulting in high dendrite branching morphogenesis and slow growth of dendrites. Given a different preferred orientation angle, the dendrites have a good symmetry at 0° and 45° and a poor symmetry at 30° and 60°.The increase of nucleation number restrains the growth of high-order dendrites, the spacing of columnar grains is reduced and the phenomenon of a mixture of cell and dendrite crystal appears. The cooling rate affects the growth velocity of dendrite and the size of the dendrite arm spacing, it also leads to the serious solute segregation. Gradually the temperature gradient increases, the solid/liquid interface will form the dendrites-crystal-plane crystal in three forms,while the growth rate of dendrites gradually decreases, and the distance between the primary arms becomes smaller.Based on the model of dendritic growth, the welding temperature field and the arc-shaped pool model in the process of welding solidification were coupled by the interpolation method,followed by the simulation of the microstructural growth and the distribution of solute concentration during the solidification of the molten pool. At same time, discussed the effect of different welding process factors on the morphological changes. The results show as follow:The morphology of molten pool are composed of columnar crystals and dendrite crystals. The higher heat input leads to the more developed columnar crystals. The larger the internal nucleation density, the more developed the dendrite crystals. The smaller the surface coefficient of heat transfer, the slower the cooling rate, which will increase the growth of columnar crystals.For simulation results, the metallographic test and hardness test were carried out. The results show as follow: The morphology of Ti-45%Al alloy in the molten pool are composed of columnar crystals and dendrite crystals, the larger welding heat will promote the growth of columnar crystals. That is consistent with the above simulation results. Compared with the base metal, the hardness of weld joint will be significantly increased, while the low heat input will bring a higher hardness of the welded joint.