B4C plates were immersed in liquid aluminum alloyed with Sc, Zr, and Ti to investigate the interfacial reactions between B4C and liquid aluminum at 730 degrees C. The influences of alloying elements on the interfacial microstructure and reaction products in terms of individual and combined additions were examined using a scanning electron microscopy (SEM) and a transmission electron microscopy (TEM). Results reveal that all three elements react with B4C and form interfacial layers that act as a diffusion barrier to limit the decomposition of B4C in liquid aluminum. The interfacial reactions and the reaction products in each system are outlined. Moreover, by the combined addition of Sc, Zr, and Ti, most of the Ti is enriched at the interface, which not only offers appropriate protection of the B4C but also reduces the consumption of Sc and Zr at the interface.