Al-7%Si合金における初晶α-Al相の粒状化機構

抄録

  In recent years, semi-solid casting technologies are becoming increasingly practical. In the semi-solid casting process, the granulation of the primary α-Al phase is carried out to improve fluidity. However, the mechanism of the granulation has not been fully clarified so far. Therefore, this paper aimed to clarify the mechanism by pouring molten Al-7%Si alloy just above the liquidus temperature and then super-heating it at 100℃. The molten Al-7%Si alloy was also poured from a high position. The granulation mechanism of the primary α-Al phase was then discussed based on the results obtained.

  By pouring the molten Al-7%Si alloy just above the liquidus temperature, large amounts of the granulated primary α-Al phase were obtained. The reason for this may be because the growth velocity of each crystal decreased as the nucleation number density increased, causing the interfacial stability to increase because of the decrease of the solute quantity which accumulated on the solid/liquid interface. In addition, the results were related more to the enforced diffusion of the solute accumulated on the solid/liquid interface by the molten metal flow at the time of crystal growth, than to the pouring of the molten alloy at the super heat of 100℃.