A three-dimensional （3-D） modified cellular automaton （MCA） method was developed for simulating the dendrite morphology of cubic system alloys. Two-dimensional （2-D） equations of growth velocities of the dendrite tip, interface curvature and anisotropy of the surface energy were extended to 3-D system in the model. Therefore, the model was able to describe the morphology evolution of 3-D dendrites. Then, the model was applied to simulate the mechanism of spacing adjustment for 3-D columnar dendrite growth, and the competitive growth of columnar dendrites with different preferred growth orientations under constant temperature gradient and pulling velocity. Directional solidification experiments of NH4Cl-H2O transparent alloy were performed. It was found that the simulated results compared well with the experimental results. Therefore, the model was reliable for simulating the 3-D dendrite growth of cubic system alloys.
The effects of cooling rate on the solidification parameters and microstructure of Al-7Si-0.3Mg-0.15 Fe alloy during solidification process were studied.To obtain different cooling rates,the step casting with five different thicknesses was used and the cooling rates and solidification parameters were determined by computer-aided thermal analysis method.The results show that at higher cooling rates,the primary α（Al） dendrite nucleation temperature,eutectic reaction temperature and solidus temperature shift to lower temperatures.Besides,with increasing cooling rate from 0.19 ℃/s up to 6.25 ℃/s,the secondary dendritic arm spacing decreases from 68 μm to 20 μm,and the primary dendritic volume fraction declines by approximately 5%.In addition,it reduces the length of Fe-bearing phase from 28 μm to 18 μm with a better uniform distribution.It is also found that high cooling rates make for modifying eutectic silicon into fibrous branched morphology,and decreasing block or lamella shape eutectic silicon.
