Unveiling the Refinement Effect of the Coarse Fe-Rich Phase in Al-Si-Fe Alloy under Controlled Diffusion Solidification Treatments

In this paper, the controlled diffusion solidification (CDS) technology is utilized to enhance the mechanical properties of alloys with high Fe content (≥ 2 wt.%). The study systematically investigates the impact of different casting temperatures (T2) on the microstructure, mechanical properties, and solidification process of the target alloys under the CDS technology. The results indicate that the CDS technology can hinder the formation of primary Fe-rich phases in Al-Si-Fe alloys with high Fe content (≥ 2 wt.%) compared to conventional casting (CC). However, it cannot entirely prevent the formation of these needle primary Fe-rich phases. When the two melts are mixed instantaneously, there is a certain temperature difference. The alloy exhibits a corresponding degree of subcooling, which increases the number of nuclei of the primary phase. According to the solidification sequence analysis, the alloy will form a large number of α-Al and Al₃Fe nuclei. The greater the number of nuclei, the finer the grain size. After mixing, the high-temperature melt is exposed to the cooling effect of the low-temperature melt. This results in a shorter time for the homogenization of temperature and concentration fields in the melt. Consequently, the reaction time for the formation of the primary Fe-rich phase is insufficient, hindering a portion of the primary β-Fe phase formation. During the CDS technology, when the casting temperature (T2) reaches 870 °C, most of the α-Al grains and needle Fe-rich phases exhibit smaller shapes and sizes compared to the other specimens, resulting in the best mechanical properties