Hot cracking has been a long-term challenge for the solidification processing of many high-performance aluminum alloys, such as 7075, 6061, and 2024 alloys. Nano-treating, by adding a low loading of ceramic nanoparticles into a metal matrix, can effectively reduce the hot cracking susceptibility of aluminum alloys during solidification processes such as casting, welding, and additive manufacturing. While previous studies have shown that ceramic nanoparticles enhance heterogeneous nucleation, inhibit grain growth, and modify secondary phases during solidification of various alloys, no systematic study has been conducted to investigate the underlying mechanisms of hot cracking elimination by different nanoparticles on different alloy systems. In this work, TiC and TiB₂ nanoparticles have been incorporated into hot crack susceptible aluminum alloys 7075, 6061, and 2024, and a detailed thermal analysis and microstructure study were carried out to investigate the nanoparticle-enabled principal mechanisms of hot cracking elimination. It is discovered that the underlying mechanism is attributed to the unusual modification of both grains and intermetallic phases as well as a much higher liquid fraction at the final stage of solidification. More specifically, nanoparticles enable faster nucleation with a gradual latent heat release, an effective growth restriction of spherical aluminum α-grains (especially by TiC nanoparticles), a significant modification of the intermetallic phases, and a higher liquid fraction of non-equilibrium eutectic due to nanoparticle-induced diffusion blockage at the terminal stages of solidification.

热裂纹一直是许多高性能铝合金（如 7075、6061 和 2024 合金）凝固加工的长期挑战。纳米处理通过在金属基体中添加低负载量的陶瓷纳米颗粒，可以有效降低铝合金在铸造、焊接和增材制造等凝固过程中的热裂敏感性。虽然之前的研究表明陶瓷纳米粒子在各种合金的凝固过程中增强了异质成核、抑制晶粒生长和改变二次相，但尚未进行系统研究来研究不同纳米粒子在不同合金系统上消除热裂纹的潜在机制。在这项工作中，TiC 和 TiB ₂纳米粒子已被纳入热裂纹敏感铝合金 7075、6061 和 2024，并进行了详细的热分析和微观结构研究，以研究纳米粒子激活消除热裂纹的主要机制。发现潜在机制归因于晶粒和金属间相的不寻常改性以及在凝固的最后阶段更高的液体分数。更具体地说，纳米粒子能够通过逐渐释放潜热实现更快的成核，这是球形铝α的有效生长限制- 晶粒（尤其是 TiC 纳米颗粒），金属间相的显着改性，以及由于纳米颗粒在凝固的最后阶段引起的扩散阻塞，非平衡共晶的液体比例更高。