Aiming at the bottleneck in in-situ synthesized Ti₅Si₃ reinforced aluminum matrix composites (AMCs), where the complex constitution of reinforcements and poor controllability of formation process make it difficult to stably regulate the microstructure and properties of composites, Al-5Si-xTi₅Si₃ composites (x=0.8, 2.0, 3.2 (mass fraction/%)) are fabricated by designing raw material proportions and powder metallurgy process parameters in this work. The effects of reinforcement content on the microstructure and mechanical properties of the composites are systematically investigated. The results show that Si segregates around Ti particles via diffusion and solid-solution precipitation, and interdiffusion reaction occurs between Si and Ti to form Ti₅Si₃ particles. With the formation of a nanoscale TiSi interfacial transition layer, the incoherent Ti₅Si₃/Al interface transforms into a semi-coherent/coherent composite Ti₅Si₃/TiSi/Al interface, which effectively improves the interfacial bonding between reinforcement particles and the Al matrix. As the reinforcement content increases, the microstructure of reinforcements gradually evolves from blocky morphology to nanoparticle clusters and further grows into nanorods, and the grain size of the composites is significantly refined. Sound interfacial bonding enables efficient load transfer across the interface and promotes the load-bearing capacity of reinforcements. Under the synergistic effect of dislocation strengthening, grain refinement strengthening and load transfer strengthening, the yield strength and tensile strength of the Al-5Si-3.2Ti₅Si₃ composite reach 318 MPa and 377 MPa, which are 51.4% and 42.8% higher than those of the matrix, respectively, while maintaining favorable ductility. These findings provide a new strategy for the microstructure design of high-strength and high-toughness AMCs, and offer an experimental foundation for the application of such materials in critical engineering fields such as aerospace.