CONTROL OF PRIMARY SILICON CRYSTAL SIZE O F SEMISOLID HYPEREUTECTIC AL-SI ALLOY BY SLURRY-MELT MIXING PROCESS

The hypereutectic Al-Si alloy slurries with various mean sizes of prim ary silicon crystals were produced by the slurry-melt mixing process, in which the hypoeutectic alloy slurry and the hypereutectic alloy mel t with various silicon contents were mixed and cooled under different environmental conditions. Two kinds of parameters were examined to eva luate the effect of the combination of the alloy composition on the pr imary silicon crystal size: one is related to the stability of the pri mary silicon crystals in the mixed alloy, and the other to the number of them which are to nucleate in the second alloy. It was elucidated t hat both of them provide a good guide on controlling the primary silic on crystal size. And it was also observed that the heat absorptivity o f the mixing vessel plays a more important role in the refinement of t he primary silicon crystals than the thermal condition of the atmosphe re.