一方向凝固を行ったAl-7%Si合金のポロシティ生成に及ぼすPの影響

抄録

  The fatigue strength of aluminum alloy casting is influenced by shrinkage porosity. However, the effect of impurity elements on the formation behavior of shrinkage porosity is not necessarily known. In this paper, investigations were conducted on the effects of phosphorus, an impurity element, on the formation behavior of shrinkage porosity in Al-7%Si alloys, using an uncontrolled unidirectional solidification method. The results are as follows.

  Shrinkage porosity is unlikely to form in alloys not containing phosphorus, and likely to form in those that do, due to the following reasons : First, it is thought that the interface of the solid AlP in molten metal and molten metal acts as the site of porosity generation. The second reason is because protuberance was observed at the surface of the primary α-Al dendrite in the porosity of an alloy not containing phosphorus. This protuberance is thought to be a divorced eutectic α-Al phase whose growth precedes the eutectic silicon phase during the cooling process of eutectic solidification. In the case of alloys containing phosphorus, eutectic cells are unlikely to generate because there are no primary α-Al dendrites at the boundary of the crystal grains. Therefore, the liquidus phase of the boundary of the crystal grains is moved to compensate for the solidification shrinkage of eutectic cells. As a result, it naturally follows that, shrinkage porosity is formed at the boundary of the crystal grains.