鋳造工程における溶融Al-Si-Fe-Mn合金からの FeおよびMnを含む金属間化合物の晶出に関する熱力学的検討

抄録

Al-Si-based cast alloys are commonly used for engines and automobile transmissions. When Al-Si alloy is contaminated with Fe, Fe reacts with Al and Si during solidification, forming solid intermetallic compounds such as Al₁₅Fe₄Si₂ and Al₅FeSi. It is reported that Al₅FeSi, which forms at high Fe content, significantly deteriorates the strength and elongation of Al-Si alloy. On the other hand, when Mn is added to an Al-Si alloy containing Fe, Al₁₅(Fe,Mn)₄Si₂ precipitates instead of Al₅FeSi. Therefore, the addition of Mn can suppress the harmful effect of Al₅FeSi precipitation on the Al-Si alloy. In this study, to understand the forming conditions of Al₁₅(Fe,Mn)₄Si₂ and Al₅FeSi, molten Al-Si-Fe-Mn alloy was equilibrated with Al₁₅(Fe,Mn)₄Si₂ and Al₅FeSi, and the Fe and Mn contents of the alloy was investigated. Based on the experimental results, the forming conditions of Al₁₅(Fe,Mn)₄Si₂ and Al₅FeSi in molten Al-Si-Fe-Mn alloy during solidification were thermodynamically discussed. It was found that molten Al-12mass%Si alloy is saturated with both Al₁₅(Fe,Mn)₄Si₂ and Al₅FeSi at 850 K. The forming condition of β-Al₅FeSi and the condition required to change Al₅FeSi into Al₁₅(Fe,Mn)₄Si₂ at 850 K were obtained as follows; [mass%Fe] > – 0.018 [mass%Mn] + 0.7 [mass%Mn] > 0.1 [mass%Fe] + 0.13