| The paper simulated the microstructure evolution of Al-Si alloy during near-liquidus casting by means of phase-field method, and studied the relationship between the microstructure of semi-solid metal and composition, technology. Then the optimum composition and technical condition for semi-solid metal was obtained. It is important for designing Al-Si semi-solid alloys.This paper calculated the microstructure evolution of Al-Si alloy during near-liquidus casting with the continuous nucleation model and narrow band solid-liquid interface method, and obtained how technical condition influence on microstructure of different parts of the billets. The optimum semi-solid metal composition.and technical parameters were obtained by simulating the microstructure evolution of Al-Si alloy (Al-5.0%Si, Al-7.0%Si and Al-9.0%Si), the results showed that:(1) When the billet was cast from the normal casting temperature (950.0K), the center microstructure was coarse and asymmetric greatly; When the billet was cast upper the liquidus temperature about 10.0K (900.0K), the microstructure was uniform and there was little difference between the border and the center; When the billet was cast from the temperature (888.OK) which close to the liquidus, the grains were uniform, fine and globular, and the average grain diameter was 25.0μm～32.0μm. (2) The grains were coarse and long strip at high casting velocity 4.0×10-3m/s; The grains were finer, more uniform and more global with reducing of casting velocity. The growth of grains was ball-like growth, and the grains were fine, uniform and global at 1.5×10-3m/s. (3) The microstructure of Al-7.0%Si was the best among Al-5.0%Si, Al-7.0%Si and Al-9.0%Si at 2.0 X 10"3 m/s during near-liquidus casting of heat preservation.By means of stimulating, the optimum condition of Al-Si alloy was that the composition was Al-7.0%Si and the casting velocity was 2.0×10-3m/s at 888.0K during near-liquidus casting. |
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