The phenomenon of formation of special surface riched in silicon has been studied when Al-18%Si alloy solidified unidirectionally under the condition of the primary single field-direct magnetic field. Direct magnetic field force has not provided stirring in this melt. Silicon has been found macrosegregation as intensity of magnetization is about 2400Gs, and the thickness of the segregation layer grows with the increase of the magnetic induction intensity. The effect of direct magnetic field on the solidification behavior and the law of structure formation has been discussed.