Srを添加したAl-7%Si 合金における過改良組織の検討

抄録

  In recent years, hypo-eutectic Al-Si alloys are generally modified by adding Sr. Excessive Sr addition is known to cause crystallization of blocky Al₂Si₂Sr phase called over-modified structure, the formation mechanism of which has not yet been clarified. In this study, ingots with different Sr contents were produced from Al-7%Si alloys without phosphorus. The causes of the crystallization of the Al₂Si₂Sr phase were then studied by means of observing the microstructure. The reason why the phase was mainly formed at the base of the branches of the primary α-Al phase was also considered.

  In conclusion, limited Sr content taken into the eutectic Si phase is likely to have caused the crystallization of blocky Al₂Si₂Sr phase. The reason why the Al₂Si₂Sr phase was observed at the base of the branches of the primary dendritic α-Al phase may be due to the accumulation and concentration of solute atoms, ejected from adjacent second branches, at the base of the branches.