The formation of coarse primary Si is the main scientific challenge faced in the preparation of high-Si Al matrix composites. The SiC/Al-50Si composites are prepared by high pressure solidification, which allows the primary Si to form a SiC–Si spherical microstructure with SiC, while the solubility of Si in Al is increased by high pressure to reduce the proportion of primary Si, thus enhancing the strength of the composites. The results show that the high melt viscosity under high pressure makes the SiC particles almost “fixed” in situ. The SEM analysis shows that the presence of SiC in the growth front of the primary Si will hinder its continued growth and eventually form SiC–Si spherical microstructure. Through aging treatment, a large number of dispersed nanoscale Si phases are precipitated in the α-Al supersaturated solid solution. The TEM analysis shows that a semi-coherent interface is formed between the α-Al matrix and the nanoscale Si precipitates. The three-point bending tests shows that the bending strength of the aged SiC/Al-50Si composites prepared at 3 GPa is 387.6 MPa, which is 18.6% higher than that of the unaged composites.