Dendrite Phase Field Model Based On LBM Algorithm Coupled With Flow Field

Microstructure is the main factor to determine the casting performance, master and control the formation of casting microstructure will be able to control the mechanical properties and service life of casts, therefore, the microstructure simulation has become a new way for the development of alloy material. Numerical simulation can reduce the development cost and period, but also can provide a basis for the optimization of the casting performance. The phase field method can couple with other fields, such as temperature field, concentration field and flow field, and capture the real dendrite growth during the solidification process.In the course of solidification, temperature, mass and momentum transfer and other factors influence the dendrite growth, but the convection in supercooled melt directly restricted the above factors, consequently, study the dendrite growth under the forced and natural convection will have important scientific and engineering significance for the deep understanding of the influence mechanism during solidification process.In this paper, the dendrite growth pure diffusion phase field is coupled with the LBM (Lattice Boltzmann Method) model that can compute solute transport efficiently, and the phase field-Lattice Boltzmann tow dimensional transport model (PF-LBM) is constructed. The model described the influence of supercooled melt on the microstructure evolution during isothermal solidification under forced convection. On the base of the new constructed PF-LBM model, take Al-4.5%Cu (mass fraction) for simulation example, the influence of different flow conditions, anisotropy and initial composition on the single dendrite growth of the binary alloy in the isothermal condition under the action of forced and natural convection. The results showed that: in the pure solute diffusion, the dendrite growth morphology is symmetry; but in the case of forced convection, the melt flow disturbed the solute distribution, the dendrite tip growth rate in the incident flow regions is greater than that of pure diffusion, but the dendrite growth is inhibited in the downstream, and the asymmetric dendrite growth morphology formed that is different from pure diffusion. The dendrites growth changes the pressure direction between liquid metal flows? and the eddy currents appears when the flow rate increased which speed up the dendrite growth in downstream. Anisotropy has a significant impact on the dendrite growth during solidification. When anisotropic coefficient increases, the main branches and lateral branches become thinner, when the anisotropy coefficient increases to0.08, the dendrite growth become abnormal and dendrite morphology is aberrant and distorted. The forced convection will enhance the impact of anisotropy on dendrite growth during the solidification process. The natural convection in the liquid phase can significantly alter the concentration and temperature distribution, which made the dendrite growth asymmetrical along flow direction. The increases of temperature gradient will enhance the intensity of natural convection flow field, which accelerated the development of dendrite morphology asymmetry and alloy solidification rate. The increases alloy initial composition will make dendrite arm thinner and slow down the solidification rate.