Effect of Nb, Ti introduction sequence on adsorption of Nb on TiB2 surface and grain refinement performance of Al-4Ti-1Nb-1B

• Introducing Ti before Nb during synthesis of Al-4Ti-1Nb-1B grain refiner yields superior grain refinement and anti-Si poisoning in Al-Si alloys, especially at high Si contents. • The Ti-first sequence reduces the ground-state energy variation (ΔE), facilitating Nb adsorption on TiB2 surfaces, as confirmed by TEM showing highest average Nb content (3.80 at.%). • First-principles calculations reveal that Nb adsorption enhances TiB2/Al interfacial adhesion (Wad) and suppresses Si segregation (κSi), thereby mitigating Si poisoning. • This study provides a novel strategy for designing advanced grain refiners for Al-Si alloys, with potential industrial applications in aerospace and automotive sectors.