| Summary: | The effect of the distribution of the primary phase Si and TiB<sub>2</sub> particles in the hypereutectic Al-Si alloy was studied and found to be influenced by the cooling rate. Therefore, this article studies the effect of the cooling rate on the multi-phase structure of TiB<sub>2</sub> particles in Al-20Si using a wedge-shaped mold. The sizes, shapes, and distribution of primary phase Si and TiB<sub>2</sub> particles inside primary phase Si were observed through SEM. The effect of TiB<sub>2</sub> particles on cracks in primary phase Si was studied using nanoindentation technology, and the interface relationship between primary Si and TiB<sub>2</sub> was studied using TEM. Finally, based on the experimental results, the trapping mechanism of primary Si for TiB<sub>2</sub> particles is discussed. The results indicate that the faster the cooling rate, the finer and more uniform the size distribution of the primary Si phase in the structure. TiB<sub>2</sub> mostly exists as individual particles. Moreover, the pushing rate of the solid–liquid interface during solidification is faster, resulting in more TiB<sub>2</sub> particles being engulfed by the primary Si phase.
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