Thixocasting or semi-solid casting is an alternative to the traditional casting processes. A numerical simulation of these methods is useful to define the real process. A new test concept will be presented to determine parameters, such as temperature and rates, as well as the die filling and solidification processes. The simulation tools permit us to understand better the processes, to predict and to eliminate potential defects before they take place. The studied component is a steering knuckle made of an A357 aluminium alloy. The microstructure is characterized by optical microscopy. It has been preceded to the development of a model based on the experimental data, it has been defined to the semi-solid as an homogeneous material with thixotropic properties, and the microstructure is a structural parameter. The results are compared with real tests.