The Effect of Fe Content on the Solidification Pathway, Microstructure and Thermal Conductivity of Hypoeutectic Al–Si Alloys

In the present study, the solidification pathway, microstructure and thermal conductivity of Fe-rich Al–x Si (x = 5, 7, 9, wt%, the same below) alloys were systematically investigated. The results showed that the thermal conductivity was firstly improved and then decreased with Fe content increasing. The improvement and decreasing rate of thermal conductivity was related to the Si content. The change of thermal conductivity was closely related to the change of microstructure and solidification pathway. The addition of Fe element resulted to the precipitation of ternary β (Al5SiFe) phase (βT) and binary β phase (βB). The precipitation of βT was benefited to improve the thermal conductivity. On the contrast, the precipitation of βB was prone to deteriorate the thermal conductivity. The precipitation amount of βT phase and βB phase was related to the critical value of Fe content (Fecrit). The calculation results showed that the Fecrit of Al–x Si alloys was about 0.20% (5% Si), 0.29% (7% Si) and 0.38% (9% Si), respectively. When the Fe content was less critical value (Fecrit), the precipitation amount of βT phase was increased by Fe increasing. Furthermore, when the Fe content was more than Fecrit, the precipitation amount of βT phase was changed slightly, and the precipitation amount of βB phase continued to increase with Fe content increasing.