Al-Cu-Mn-Mg 合金因其优异的综合性能，被广泛应用于航空航天和轨道交通等领域。 然而，该合金在铸造 过程中容易出现热裂缺陷，严重影响铸件的质量和可靠性。 因此，提高合金的晶粒细化效果，对于改善合金的铸造性能 具有重要意义。Al-Ti-B细化剂是铝合金铸造中最常用的晶粒细化剂，但不同Ti/B质量比的Al-Ti-B细化剂对晶粒细化 效果及热裂机制尚未系统研究。 采用X射线衍射仪(XRD)、光学显微镜(OM)、扫描电镜(SEM)和CRC(constrainedrod cast)金属型约束热裂棒模具等，分析了不同Ti/B质量比的Al-Ti-B细化剂对铸造 Al-Cu-Mn-Mg合金微观组织和热裂 倾向性的影响。 实验结果表明，4种Ti/B比的Al-Ti-B细化剂中Al3 Ti和TiB2相的含量存在显著差异。 在B含量均为 0.3%(质量分数)的条件下，添加 Al-3Ti-1B、Al-4Ti-1B、Al-5Ti-1B 和 Al-5Ti-2B 的 Al-5Cu-0.7Mn-0.55Mg 合金的平均晶 粒尺寸分别为162.07、113.73、107.81 和 88.00 μm，对应的热裂纹倾向性指数依次为 112、136、96 和 24。微观机制分析表 明，TiB2 相的含量对晶粒细化效果和热裂倾向性具有显著影响。 特别是Al-5Ti-2B细化剂，在晶粒细化的同时，显著降 低了合金的热裂倾向性，展现出优异的性能。

Al-Cu-Mn-Mg alloys are widely used in aerospace, rail transportation, and other fields because of their excellent comprehensive properties. However, this alloy is prone to hot cracking defects during the casting process, which severely affects the quality and reliability of castings. Therefore, improving the grain refinement effect of an alloy is highly important for enhancing its casting performance. The Al-Ti-B refiner is the most commonly used grain refiner in aluminium alloy casting, but the effects of Al-Ti-B refiners with different Ti-B mass ratios on grain refinement and hot cracking mechanisms have not yet been systematically studied. The influence of Al-Ti-B refiners with different Ti/B mass ratios on the microstructure and hot cracking susceptibility (HCS) of cast Al-Cu-Mn-Mg alloys was investigated via X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and constrained rod casting (CRC) metal molds restrained by hot cracking rod molds. The experimental results reveal that the contents of the Al3 Ti and TiB2 phases in the four Al-Ti-B refiners (Al-3Ti-1B, Al-4Ti-1B, Al-5Ti-1B, and Al-5Ti-2B) significantly differ. At a constant B content of 0.3 wt.%, the average grain sizes of the Al-5Cu-0.7Mn-0.55Mg alloy refined by these four refiners are 162.07, 113.73, 107.81 and 88.00 μm, respectively. The corresponding HRC indices are 112, 136, 96 and 24. Microstructural mechanism  analysis reveals that the content of the TiB2 phase significantly influences both the grain refinement efficiency and hot cracking susceptibility. Notably, the Al-5Ti-2B refiner demonstrates superior performance by simultaneously achieving effective grain refinement and substantially reducing the hot cracking tendency of the alloy.