By imposing a high frequency magnetic field, the surface quality and macro/micro structure of the direct chill cast billets are improved. The casting speed can also be improved by simultaneous applying mold and electromagnetic coil, especially for the alloys with a wide freezing range such as Al-Cu-Mg alloy. The extent of macrosegregation in the Al-Cu-Mg alloy is reduced by application of the magnetic field. Moreover, the inverse segregation layer usually observed in the direct chill cast billet is eliminated by the effect of the electromagnetic field. The microstructure of the hot-rolled and heat treated billets cast under the high frequency field also show better characteristics.