Three-dimensional Phase Field Simulation Of Dendritic Morphology Of Al-Si Alloy

As the typical structure in metal solidification microstructure,dendritic interface morphology and steady-state selection directly determine the solidified structure characteristics and the final properties of the material research.With the development of computational materials science,numerical simulation combined with experimental research has become the frontier field of current materials research.The phase field method,as a powerful tool for describing the evolution of complex phase interface,has been widely used in simulating the dendritic morphology evolution during solidification of metal.In this paper,the three-dimensional phase field model including solid phase diffusion coefficient is used to study the dendritic growth process of Al-Si alloy.1.Phase field method is used to simulate the growth process of dendrite under different phase field model parameters and then the appropriate phase field model parameters are determined.The results show that the interface width changes the steady-state behavior of the dendritic tip,the relaxation time has an important influence on the preferred orientation of dendrites and the growth of secondary branches.2.The evolution of equiaxed dendrites under different interface width,undercooling,supersaturation and thermal noise amplitude are simulated.The results show that the interface width affects the complexity of dendritic morphology and the concentration of solute at the dendritic tip;the undercooling has an important influence on the growth rate of dendrite and the degree of development of secondary branches;the supersaturation will change the degree of microsegregation and the speed of the dendritic tip;the thermal noise amplitude will induce the asymmetric growth of the secondary branches on both sides of the dendritic trunk,while the tip morphology of the dendrite changes little.3.The evolution process of dendritic sidebranching under different primary dendritic spacing,pulling velocity,temperature gradient and thermal noise amplitude during directional solidification are simulated.It is found that the primary dendritic spacing affects the number and development of secondary branches and the growth of tertiary branches;the pulling velocity changes the stability of the primary dendritic interface,the degree of enrichment of solute in secondary branches and the degree of development of secondary branches in the root of the primary dendrite;the temperature gradient will affect the early dendritic profile and the morphology and growth direction of the secondary branches.The enrichment of solute in secondary branches will cause coarsening and remelting of secondary branches;the thermal noise amplitude not only changes the asymmetry of the secondary branches on both sides of the dendritic trunk,the irregularity of the morphology and the heterogeneity of the solute inside the dendrite,but also changes the steady-state behavior and morphology of the dendritic tip;dendritic tip morphology,tip steady-state behavior and solute concentration affect the secondary branches formation.