Recycling of Al/Ti machining chips into a novel Al–5Ti–0.25C–4Sr master alloy for synergistic refinement and modification of A356 alloy

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 TiAl 3 , TiC, and Ti 2 Al 20 Sr 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.