Simultaneous refinement and modification of the eutectic Si in hypoeutectic Al–Si alloys achieved via the addition of SiC nanoparticles

This paper reports that the addition of SiCnps is demonstrated to induce the simultaneous modification and refinement of the eutectic Si in the SiCnps/A356 samples, which becomes increasingly significant with increasing SiCnps addition. The effect of SiCnps addition is primarily investigated via the results obtained from differential scanning calorimetry and high resolution transmission electron microscopy. The modification and refinement of the eutectic Si are closely related to the interaction between the SiCnps and the solidification front (SF). When the particle size of the SiCnps is greater than the critical size, the SiCnps tend to move ahead of the SF, while smaller SiCnps tend to be engulfed. Here, SiCnps distributed at the interface between the eutectic Si/Al phase hinder the growth of the eutectic Si. Meanwhile, SiCnps are observed to act as heterogeneous nucleation sites for the eutectic Si. Hence, the simultaneous modification and refinement of the eutectic Si is mainly facilitated by a combination of the above two individual effects of SiCnps addition. Furthermore, SiCnps distributed in the eutectic Si leads to the formation of multiple Si crystal twin variants.