For predicting hot tearing during casting process, viscosity properties and constitutive equations in the semi-solid region are required. In this research, viscosity properties of two alloys, which are Al5 mass%Mg alloy with TiB grain-refiner and Al2 mass%Cu alloy with TiB grain-refiner, are estimated using the image-based modelling method as suggested by Matsushita et al. As to the mechanical properties of the solid phase in semi-solid region, it is found that by using the temperature dependent value rather than the value just below the solidus temperature, the prediction accuracy of the viscosity value in semi-solid region has increased. By comparing the obtained numerical properties with the experimental properties, it is found that the method can predict the viscosity properties of Al5 mass%Mg alloy and Al2 mass%Cu alloy in the semi-solid region at the solid fraction where hot tears are likely to occur.

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