Phase-field Simulation Of Solidification Process For Multi-component Alloys Coupled With Multi-field

The formation process of alloy microstructure during solidification can be simulated through computer simulation software, which can predict the casting performance and service life, and also provide a reasonable production process to improve the casting quality. In this paper, the LBM-PF model is established on the basis of KKS phase-field model, by coupling with the flow field and solving the discrete equations solved with LBM algorithm. Al-Cu series alloy is taken as examples for the simulation.(1)The Al-Cu binary alloy dendrite growth process of monocrystal and polycrystal is simulated by the LBM-PF model during isothermal and non-isothermal solidification under the effect of the force laminar flow. The results showed that: compared with the pure diffusion, the fluid flow changes the distribution of the solute and heat, which makes the dendrite grow asymmetrically; with the increase of the flow velocity, the asymmetry of dendrite becomes more obvious, and the eddy current in the downstream regions get greater, which promote the dendrite growth in downstream. The increase of the flow velocity also increase the migration velocity of the solid-liquid interface oriented to the supercooled melt field and the dendrite tip curvature radius, reduce the distance between the dendrite arms and make the interface uneven, the morphology in various sizes and shapes, the above experimental phenomena are consistent with the M-S instability criterion. The secondary dendrite in non-isothermal solidification is bigger than that in the isothermal solidification process, the release of the solidification latent heat reduces the heat supercooling degree, increases the dendrite tip curvature radius and inhibits the major dendrite growth. In the multigrain solidification process, at the beginning of the dendrite growth, because of the far distance between grains, the dendrite grows independently; with the dendrite growth, the distance between grains become narrow, the solute diffusion layer and the temperature diffusion layer contact and influence with each other, and the dendrite growth is inhibited.(2)The Al-Cu-Mg ternary alloy dendrite growth process of monocrystal and polycrystal is simulated during isothermal and non-isothermal solidification under the effect of flow field. The result showed that:During isothermal dendrite growth process, since the diffusion coefficient of Mg is larger than that of Cu, Mg distributes more uniformly. In downstream, with the dendrite growth, the vortex becomes bigger and the accumulated solute is taken away from the dendrite area, which accelerated the dendrite growth even exceeded the upstream dendrite growth rate; in the non-isothermal solidification, the presence of the released latent heat and temperature gradients influenced the thermal motion of atoms, which affected the solute redistribution; the simulation results of polycrystal is similar to that of the Al-Cu binary alloy polycrystal.