The Al/TiB₂ interface is of significant importance in controlling the mechanical properties of Al-B₄C composites and tuning the heterogeneous nucleation of Al/Si alloys in industry. Its stability and bonding conditions are critical for both purposes. In this paper, the interfacial energies were investigated by first-principles calculations, and the results support the reported grain refinement mechanisms in Al/Si alloys. Moreover, to improve the mechanical properties of the interface, Mg and Si were doped at the interface, and our simulations show that the two interfaces will both weaken after doping Mg/Si, thus the formation of TiB₂ is inhibited. As a result, the processability of the Al-B₄C composites may be improved. Our results provide a theoretical basis and guidance for practical applications.