The behavior of hot-tearing and solidification structures in Al-2～6mass%Mg-0～3mass%Si alloys cast in I-beam shaped mold was investigated by XRD, DSC measurements and OM, SEM-EDS observations. In the as-cast state of all alloys, solidification structures mainly consisted of primary crystallized α-Al and secondary crystallized eutectics, such as Al8Mg5, Mg2Si, and Si phases. The shape of α-Al phase changed from celler to dendritic when Mg and Si contents increased. The area fraction of the hot-tearing region decreased with increasing amount of crystallized eutectic phases with increasing Mg and Si contents, due to the healing effects on cracks at the hot-tearing regions. The temperature range between the liqidus and solidus phases and the cell size of the α-Al phase had more or less no influence on the hot-tearing.
