Abstract:Solidification microstructure evolution of as-cast Al-8.8Mg-9.2Si, Al-12.6Mg-7.4Si and Al-15.4Mg-9.8Si with different calculated Mg₂Si content in the ferrous mold were studied by optical microscope(OM) and scanning electron microscope (SEM).The results show that the solidification path of the three alloys are . The solidification microstructure at room temperature is composed of a certain amount of primary Mg₂Si phase, binary eutectic and ternary eutectic clusters. With the increase of Si content and Mg content, the number of primary Mg₂Si phase increases, its growth morphology changes from octahedral polygon to dendritic with more developed secondary dendritic walls, but the morphology of the eutectic Mg₂Si phase did not change significantly. The solidification microstructure morphology of Al-12.6Mg-7.4Si and Al-15.4Mg-9.8Si alloys was compared, it was found that the cumulative value of the aspect ratio of eutectic cells decreased with the increase of Mg₂Si content.