A novel Al–5Ti–0.25C–4Sr master alloy was synthesized sustainably from Al/Ti machining chips to overcome Si poisoning in A356 alloys. The master alloy exhibited synergistic α-Al grain refinement and eutectic Si modification in A356 alloy. The optimal addition (1.2 wt%) effectively reduced the average α-Al grain size and eutectic Si were reduced by 46.5% and 69.3%, leading to a 53.1% enhancement in ultimate tensile strength (150 MPa) compared to the unmodified alloy. Microstructural analysis revealed that the refinement stems from heterogeneous nucleation on TiAl3, TiC, and Ti2Al20Sr particles. The modification was attributed to Sr-induced twinning, which was further elucidated by first-principles calculations showing strong Sr adsorption on the Si (100) surface. This work provides a cost-effective and eco-friendly strategy for high-performance Al-Si alloy production.
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