Al-5Ti-1B is the most widely used grain refiner for Al alloys. However, it is not effective for grain refining Al alloys containing more than 3 wt pct Si. This adverse effect of Si is referred to as Si poisoning. In spite of extensive experimental and theoretical investigations in the past decades, the exact mechanism for Si poisoning is still not clear. In this work, the state-of-the-art electron microscopy was performed to investigate the mechanism for Si poisoning. Our experimental results suggest that Si segregates preferably to the TiB₂/Al-Si melt interface and the pre-existing Al₃Ti 2-dimensional compound (2DC) layer on TiB₂ surface dissolves into the Al-Si melt. Based on the experimental results, we have postulated a new mechanism for Si poisoning: interfacial segregation of Si leads to enrichment of Si at the TiB₂/Al-Si melt interface, and this in turn makes the pre-existing Al₃Ti 2DC on the TiB₂ surface unstable and dissolve gradually in the melt, resulting in a loss of TiB₂ nucleation potency and hence a decreased total number of potent TiB₂ particles available for heterogeneous nucleation and grain initiation and consequently an increased grain size. This mechanism for Si poisoning can explain consistently the experimentally observed phenomenon reported in the literature.

Al-5Ti-1B是铝合金中使用最广泛的晶粒细化剂。然而，它对于包含大于3wt％的硅的晶粒细化铝合金是无效的。Si的这种不利影响被称为Si中毒。尽管在过去几十年中进行了广泛的实验和理论研究，但Si中毒的确切机理仍不清楚。在这项工作中，进行了最先进的电子显微镜研究，以研究Si中毒的机理。我们的实验结果表明，优选的Si偏析到的TiB ₂ / Al-Si系熔体界面和预先存在的Al ₃上的Ti的TiB 2维化合物（2DC）层₂表面溶解在Al-Si熔体中。根据实验结果，我们推测出了一种新的Si中毒机理：Si的界面偏析导致TiB ₂ / Al-Si熔体界面处的Si富集，进而使预先存在的Al ₃ Ti 2DC析出。 TiB ₂表面不稳定并逐渐溶解在熔体中，导致TiB ₂成核能力下降，因此可用于异相成核和晶粒萌生的有效TiB ₂颗粒总数减少，因此晶粒尺寸增大。硅中毒的这种机制可以一致地解释文献中报道的实验观察到的现象。