The microstructural evolution of Al-Cu alloy in semi-continuous castings was simulated by using multi-scale calculation method. A new method for semisolid alloy design is proposed on the basis of microstructural simulation. The theoretical models of temperature field and phase transformation were established with respect to the continuous casting process. The solid fraction was used to couple the models for macro-scale and mesoscale calculations. A method of treating the non-physical boundary was proposed for the castings at the outlet side of the tools

witch is effective and of high precision for the steady casting process. The influence of concentration

pouring temperature and casting velocity on the microstructures of Al-Cu alloy was simulated using multi-scale simulation technique. It is shown that grains grow dendritically and meet with their neighbours to form high concentration boundaries. The influence of pouring temperature and the casting velocity on the microstructures become small when the concentration of Cu reaches 8wt%

which favors the formation of desired structure in semisolid alloys. The simulated result for ZL201 alloy is well consistent with the experimental. This work demonstrates that the multi-scale simulation is an effective method to the semisolid alloy design and the prediction of the processing parameters.