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In this study, Al–Si matrix composites containing different contents of in situ TiB2 particles and (Ce+Yb) were fabricated via a mixed salt–metal reaction of KBF4 and K2TiF6 and the effects of the reinforcement particles on the microstructure and mechanical properties of the composites were investigated. Results revealed that the addition of TiB2 particles and (Ce+Yb) further refined the α-Al grains and modified the eutectic Si phase of the composite. Moreover, the combined addition of (Ce+Yb) resulted in the suppression of TiB2 agglomeration, causing a notable modification in the distribution and morphology of TiB2 particles as well as a significant reduction in their size compared with the condition without the addition of (Ce+Yb). The mechanical properties of 3 wt.% TiB2/Al–Si matrix composites with the combined addition of 0.4 wt.% (Ce+Yb) reached the maximum values with the ultimate tensile strength, yield strength, and elongation of 372.4 MPa, 268.7 MPa, and 4.5%, respectively, which increased by 30.1%, 40.1%, and 9.8%, respectively, compared with those of Al–Si matrix alloy. Optical microscopy, scanning electron microscopy with energy-dispersive spectroscopy, and X-ray diffraction were used to demonstrate the presence of (Ce+Yb)-containing precipitates, other precipitates, and in situ TiB2 particles. [ABSTRACT FROM AUTHOR]