在传统铸造 Al-Si 合金中存在的粗大树枝晶 α-Al 相以及针状共晶 Si 严重割裂基体，显著降低合金的力学性能。 为细化 Al-Si 合金的组织，提升其力学性能，本文使用扫描电镜 (SEM) 、电子探针 (EPMA) 、 X 射线衍射仪 (XRD) 以及万能材料试验机， 研究了不同添加量 Y/Al-5Ti-1B 变质剂 (Al-5Ti-1B 均为 2% ， 稀土 Y 分别为 0.05% 、 0.1% 、 0.2% 、0.3% 、 0.4% 、 0.5% ，质量分数 ) 对 Al-7Si 合金微观组织和力学性能的影响，并探究了其对 Al-7Si 合金的变质机理。 实验 结 果 表 明 ，当 Al-5Ti-1B 含量为 2% 、稀土 Y 含量为 0.4% 时，变质效果最佳，共晶 Si 由粗大针状变为细小颗粒状，长和宽分别减小至 2.7 和 0.8 μm ，相较于未经变质处理的 Al-7Si 合金，减小了 90.6% 和 4.7% 。 合金抗拉强度由原来的 168.1 MPa 提升至 209.1 MPa ，增加了 24.4% 。 同时伸长率从 6.23% 提升至 9.62% ，增长了 54.4% 。 此外，合金的断裂方式也从脆性断裂转变为韧 - 脆混合断裂。

In traditional casting of Al-Si alloys, the coarse dendritic α-Al phase and acicular eutectic Si strongly split the matrix, significantly compromising the mechanical properties. To refine the microstructure of Al-Si alloys and enhance their mechanical performance, the investigation focused on the influence of different additions of Y/Al-5Ti-1B modifiers (with Al-5Ti-1B held constant at 2 wt. %, and rare earth element Y varied at 0.05 wt. %, 0.1 wt. %, 0.2 wt. %, 0.3 wt. %, 0.4 wt. %, 0.5 wt. %) on the microstructure and mechanical properties of Al-7Si alloy was conducted by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and a universal materials testing machine. Furthermore, the modification mechanisms of Y/Al-5Ti-1B on an Al-7Si alloy were also explored. The results demonstrate that the optimal modification effect is achieved with 2 wt. % Al-5Ti-1B and 0.4 wt. % rare earth Y. The coarse needle-like eutectic Si transforms into fine granular structures, with lengths and widths reduced to 2.7 and 0.8 μm, respectively. This represents significant decreases of 90.6% and 4.7%, respectively, compared to those of the unmodified alloy. The ultimate tensile strength (UTS) increases by 24.4% from 168.1 MPa to 209.1 MPa, while the elongation (EL) increases by 54.4% from 6.23% to 9.62%. The fracture mode of the alloy transforms from a typical brittle fracture to a ductile-brittle mixed fracture.