铝铁硅中间合金中富铁相液固结构演变及其促进铝硅合金中硅相形核机制的研究

As reported early, one Fe-rich phase can enhance nucleation of eutectic silicon in Al-Si alloy. According to this phenomenon, we prepared a kind of Al-Fe-Si master alloy. With the addition of the master alloy, the silicon phases (both eutectic and primary silicon) in Al-Si alloy are refined. Unfortunately, the mechanism of this is unknown. So this project proposes to start with the investigation of liquid structure in Al-Fe-Si master alloy. High temperature liquid XRD, first principle calculation and other possible methods will be used to investigate the behavior of Fe in liquid state and solidification in Al-Fe-Si master alloy. Structure evolution of Fe-rich phase will be discussed subsequently. HRTEM and other possible methods will be used to characterize the Fe-rich phase surrounded by silicon in Al-Si alloy which has been refined by the Al-Fe-Si master alloy. The structure at the temperature where silicon nucleation takes place in Al-Si alloy of the characterized Fe-rich phase will be determined, with the help of structure evolution of Fe-rich phase in Al-Fe-Si master alloy. By first principle calculation method, the mechanism of the enhanced nucleation of silicon in Al-Si alloy will be studied. In the end, the pattern for the formation and structure evolution of Fe-rich phase will be determined. The mechanism that Fe-rich phase enhances the nucleation of silicon in Al-Si alloy will also be interpreted, which will promote further refinement of silicon phase in Al-Si alloy. And this will benefit industry production of Al-Si alloy.

有报道称，某种AlFeSi相存在着促进铝硅合金中共晶硅形核现象。根据这一现象，利用我们制备的Al-Fe-Si中间合金，对铝硅合金进行处理，得到的凝固组织中硅相（包括初生硅和共晶硅）的晶粒更加细小。但是，这种促进硅相形核的机制还尚不清楚。因此，本项目从Al-Fe-Si中间合金的熔体结构入手，利用高温液态XRD实验、第一性原理等方法，研究不同条件下Al-Fe-Si中间合金中Fe元素在熔体和凝固两个阶段的行为，探索不同富铁相的结构演变规律。利用HRTEM等手段，表征处理后铝硅合金中硅相包裹的富铁相，结合富铁相的结构演变规律，确定被包裹的富铁相在铝硅合金硅相形核温度区间的结构。借助第一性原理计算手段，探索富铁相促进硅相形核的规律和机制。在此基础上，建立富铁相的形成、结构演变和促进硅相形核的规律和机制，为实际生产中进一步细化铝硅合金中的硅相提供理论依据。

为探索金属液态中金属间化合物结构对形核的影响，制备了含有富铁相的Al-10Si-2Fe中间合金，利用第一性原理分子动力学计算分析，结合液态X射线衍射仪和固态X射线衍射分析，发现其中富铁相主要是alpha-Al8Si2Fe2、beta-Al5FeSi和delta-Al3SiFe2，计算了键对的结合力，分析了它们的存在条件和相互之间转变的条件。通过实验研究，发现在Al-Si合金熔体中的AlFeSi原子团簇能够引发Si相中弥散分布的纳米颗粒（5纳米左右），同时对Si相有促进形核的作用。由此促进了Sr变质条件下的亚共晶Al-Si合金共晶团的细化，对过共晶Al-Si合金中的初生硅同样有细化作用。对亚共晶Al-Si合金共晶团的细化，大幅度的提高了其延伸率，降低了缩松和热裂倾向。.探索了Ni-Si中间合金对Al-Si合金的作用，发现Ni-Si中间合金与Al-Si-Fe中间合金有相似的效果。