Abstract: The influence of low-frequency electromagnetic field on microstructure and morphology of primary Si particles of Al-19.2%Si alloy ingot specimens prepared by semicontinuous casting process was investigated with electronic optical microscopy, where the specimens were taken from different parts of the cast to which different electromagnetic fields are applied. The results showed that when applying the low-frequency electromagnetic field to the casting process the microstructure can be improved obviously with the sump in melt decreased due to more uniform temperature distribution in comparison with DC casting, especially efficient refinement of primary Si particles along with the increasing magnetic field intensity is shown. However, the increasing frequency of electromagnetic field will result in bigger primary Si particle size. In this experiment, the finest size of primary Si particles is found at 15 Hz under 12000 At.