Aluminium-Silicon alloys are widely used in the automotive industry. The existence of a small amount of iron in the AlSi7Fe1 alloy would lead to the formation of β-Al5FeSi intermetallic, which is acted as the potential nucleation position of the cracks. Typically, the solidification of the AlSi7Fe1 alloy starts with the development of the primary α-Al dendrites, followed by the precipitation of the plate-shaped β-Al5FeSi, and ended with the ternary eutectic reaction. However, the local thermodynamic conditions will be strongly updated by the advection of the solute element over a long distance under the forced flow conditions, and thereby its influence on the amount and distribution of the formed β-Al5FeSi. In turn, the uneven distribution of participated β-Al5FeSi will block the liquid flow. In this study, the interaction between the forced liquid flow and the precipita-tion kinetics of β-Al5FeSi in AlSi7Fe1 alloy is numerically studied using a three-phase volume-average-based solidification model. The three phases are the melt, the primary solid phase of co-lumnar dendrites, and the second solid phase of intermetallic precipitates. The dynamic precipita-tion of the intermetallic phase is modelled, and its blocking effect on the flow is considered by a modified permeability. According to the current simulation results, the RMF (rotating magnetic field) induces a strong azimuthal flow and a secondary meridional flow (Ekman effect) at the front of the mushy zone during unidirectional solidification. This forced flow reduces the mushy zone thick-ness, induces the central segregation channel, and affects the distribution of the intermetallic pre-cipitates, which in turn modifies the interdendritic flow. The distribution of β-Al5FeSi is dominant-ly influenced by the flow-induced macrosegregation. Both interdendritic flow and the microstruc-ture formation are strongly coupled. A satisfactory simulation–experiment agreement has been ob-tained for Si and Fe distribution across the sample section.