B₄C/Al MMC is one of the most potential neutron-shielding materials. The poor wettability of B₄C/Al interface damages the mechanical properties. To understand the alloying (or doping) effects in improving the wettability of Al/B₄C interfaces, we investigated the Al(111)/AlB₂(0001) and Al(111)/TiB₂(0001) interfacial structures via a combined approach of experiment and DFT calculations. We find a larger work of adhesion (W_ad) on the Al(111)/TiB₂(0001) than the Al(111)/AlB₂(0001) interfaces. The subsequently calculated partial density of states (PDOS) of doped-diborides shew fewer anti-bonding states in Al(111)/TiB₂(0001) than in Al(111)/AlB₂(0001), which contribute to a stronger bonding between Ti-3d and B-2p states and lead to a higher W_ad and better wetting. Furthermore, we predict improved wettability of Al/B₄C by a V-doping, because of the fewer anti-bonding states in vanadium-boron molecular orbitals. The same approach developed in this study may be applied for general design of alloy elements to improve the interfacial wetting of alloy-semiconductor systems.