A macro-micro coupled model combined with the finite differential method and the modified cellular automaton model is used to simulate the solidification of Al-2.5Si alloy in metallic mold

considering the temperature field

solute field and the growth of dendrite. Compared with the classic cellular automaton

the modified cellular automaton model considered not only the temperature field diffusion

but also effects of the diffusion of solute in liquid and interface curvature as well as the enrichment of solute on supercooling of dendrite tip. Large-grid and small-grid were respectively used to simulate the macro-temperature field and micro\|structure evolution in the coupled model. Three typical images of columnar-to-equiaxed grain transition were obtained at three pouring temperatures. Considering boundary condition

it was showed that the simulated results differed from theoretical analysis in nucleation of equaixed grain