Synergistic effects of silicon alloying and plastic deformation on thermal expansion behavior and mechanical performance of dual-phase Mg-Li alloys

Mg‑Li alloys face limitations in certain practical applications due to their high coefficient of thermal expansion (CTE) and relatively low absolute strength. In this study, an ultra‑light (1.587 g·cm −3 ) Mg‑Li alloy with low thermal expansion and enhanced mechanical properties was developed through Si alloying and plastic deformation. Density functional theory (DFT) calculations indicate that Mg 2 Si inherently exhibits low positive thermal expansion, contributing to the reduction of the overall CTE of the alloy. Additionally, grain refinement and the thermal mismatch stress (TMS) at phase interfaces also influence the thermal expansion behavior of the material. After rolling, the synergistic effects of residual compressive stress, grain refinement, and finely dispersed second‑phase particles with strong interfacial bonding to the matrix enable the LZ85‑2Si alloy to achieve an optimal combination of low CTE, high strength, and high ductility. The rolled LZ85‑2Si alloy exhibits a CTE of 23.2 × 10 –6 K −1 , which is lower than that of conventional Mg alloys. Meanwhile, its ultimate tensile strength (UTS) and elongation are increased by 72.7% and 45.9%, respectively, compared with the as‑cast state, demonstrating an excellent strength‑ductility synergy. Grain refinement, precipitation strengthening, and dislocation strengthening are identified as the dominant strengthening mechanisms. This study provides valuable insights for optimizing the performance of Mg-Li alloys, thereby contributing to the expansion of their application scope in various industrial fields.