Abstract: Based on the phase field model of binary alloy dendrite growth, a multifaceted alloy phase field model with the external fields such as coupling flow field,temperature field and concentration field is established.Under the natural convection,the single dendrite and multi dendrite are simulated to observe the changes of dendrite morphology,flow field and concentration field during the solidification of the dendrite.It was found that the natural convection iscaused by the change of temperature gradient and concentration gradient,and the symmetry of the dendrite as a whole is broken, the upstream tip growth is promoted and its speed is larger than that of the downstream tip,and the horizontal tip growth speed locate between those of the upstream and downstream tips. The growth speed and concentration of the secondary dendrite arm are basically the same as that of primary dendrite arm,the fluctuation of energy and structure on dendrites is more obvious. In addition,with the increase of anisotropy intensity,the dendrite size becomes larger,the growth rate is accelerated,the main dendrite arm becomes thinner,the internal depression becomes obvious,the tip becomes sharp,the spacing between secondary dendrite arms increases and when the anisotropy intensity of single dendrite is 0.05,there is an obvious “necking” phenomenon,when anisotropy intensity of multi dendrite is 0.03,there is an obvious “necking” phenomenon.

Key words: dendrite growth, phase field simulation, lattice Bltzmann method, natural convection