利用DTA、OM、SEM、TEM、EPMA以及拉伸实验等方法研究了在添加α-Al晶粒细化剂Al-Ti-B中间合金和共晶Si变质剂Sr条件下，微合金化元素La对亚共晶Al-Si合金凝固组织与力学性能的影响。结果表明：添加微量稀土La能进一步细化α-Al，变质共晶Si，显著提高合金的塑性。分析表明：微量La能降低α-Al晶核与TiB₂的润湿角，减小α-Al的形核过冷度，促进α-Al的进一步细化；La能诱发交错孪晶的形成，增大共晶Si的孪晶密度，改变Si相的长大行为，进一步改变共晶Si的形貌。当La的添加量达到0.10%时，LaAlSi金属间化合物在凝固过程的共晶反应阶段形成，该化合物的形成将降低合金的塑性。

Hypoeutectic Al-Si alloys are extensively used in the welding industry owing to their excellent cast-ability, low coefficient of thermal expansion, and good weldability. Unfortunately, Al-Si alloys solidify under conventional cooling conditions, forming coarse dendritic α-Al grains with an eutectic structure and a flake-like morphology that has poor mechanical properties. Chemical inoculations are often used to control the size of α-Al grains and the morphology of the eutectic Si particles. The grain refiner Al-Ti-B master alloy and eutectic Si modifier Sr are commonly used in industry. In recent years, great attention has been paid to controlling the microstructure and mechanical properties of hypoeutectic Al-Si alloys through the use of the cost-effective rare earth element La. Previous studies have mainly focused on the effects of La addition on the microstructural evolution and improvements of the mechanical properties. However, to date there have been no studies on the effects of combined addition of La, Al-Ti-B master alloy and Sr on the microstructure and mechanical properties of Al-Si alloys. In this work, solidification experiments were performed to investigate the effects of the micro-alloying element La, Al-Ti-B master alloy, and Sr on the solidification microstructure and mechanical properties of hypoeutectic Al-Si alloys. These results show that synergistic effects are achieved by combinations of La, Al-Ti-B master alloy, and Sr. An addition of 0.06%La was sufficient for effective α-Al grain refinement, eutectic Si particle modification, and improved the ductility of the alloys. Excess La addition formed a coarse LaAlSi intermetallic compound, which deteriorated the ductility of the alloy. The micro-alloying element La refined the α-Al grains by acting as a surfactant that decreased the wetting angle between the TiB₂ nucleation substrate and the α-Al nucleus. It modified the eutectic Si particles by promoting the formation of the multiple Si twins and changing the growth behaviors of the Si particles.