晶种合金的结构演变对Al–Si合金组织与性能的影响及作用机制

Al–Si based alloys are the most common aluminum alloys. Nowadays, during the melt treatment process for these alloys, there is a mutual inhibition and neutralization effect between the chemical modifiers and refiners of Si phases. Furthermore, the modification and the refinement treatments have been conventionally performed separately, which cause the complicated process and non-stable treatment effects. The mechanism of the modification and refinement of microstructure needs to be further studied. Based on the significant double modification effect, the improvement of the mechanical properties and the service security, a novel method to carry out the double modification simultaneously with the addition of Al–Hf–P seed crystal alloy is proposed in this project. The in-situ reaction synthesis and structural evolution rule of the hafnium-rich phases in aluminum melt are the main research objects, and the influence mechanism of this novel master alloy for the solidification structure and mechanical properties will be systematically studied using a series of analysis means, such as the liquid structure simulation and so on. The characteristic cluster structure of liquid Al–(Si)–Hf–P alloy will be investigated by the simulation technique, the phase compositions and structural characteristics of Hf–P phases will be analyzed and then the critical condition of phase transition of AlP induced by Hf and the corresponding controlled mechanism for Hf–P compounds will be determined. The evolution process of this seed crystal alloy in Al–Si melt, the double nucleation behavior of Hf–P/AlP for primary Si phase and the formation and structural evolution rule of the heat-resistant phase as (HfAlSi) will be revealed. Finally, a novel method to synthesize the Al–Hf–P seed crystal alloy with a large number of Hf–P particles and a new technology of melt treatment of Al–Si alloys will be proposed. This project would be very instructive to further the multiphase melt reaction theory and the mechanism of modification and refinement of Si phases, and to promote the development of melt treatment techniques with great theoretical and practical significance.

Al–Si合金是最通用的铝合金材料，而现有变质和晶粒细化处理中存在硅相作用元素间相互毒害、工序繁琐等问题，影响了其熔体处理效果，作用机理有待深入探索。本项目提出了一种利用Al–Hf–P晶种合金实现对其同步双重变质、提升性能及工件安全性的新技术，并以富铪相在铝熔体内的原位反应合成与结构演变规律为研究对象，借助液态结构模拟等分析手段深入系统研究其对Al–Si合金组织及性能的影响。模拟构建Al–(Si)–Hf–P熔体团簇结构，实验确定Hf–P相的组成、结构特性、临界形成条件及调控机制，研究该晶种合金在Al–Si熔体内的演变历程，阐述Hf–P协同AlP对硅相的双效形核行为，明确（HfAlSi）耐热相的形成及演变规律，揭示该晶种合金对Al–Si合金强韧化机制，获得其制备方法及铝合金熔体处理新技术。本项目的开展有助于完善同步双重变质与多相熔体反应理论，对推动熔体处理技术的发展具有重要的理论和实际意义。

Al–Si合金是最通用的铝合金材料，而现有变质和晶粒细化处理中存在硅相作用元素间相互毒害、工序繁琐等问题，影响了其熔体处理效果，降低了工件工作可靠性、制约服役寿命。.本项目针对Al–Hf–P晶种合金的结构演变对Al–Si合金组织与性能的影响及作用机制展开研究。首先，采用第一性原理分子动力学模拟详细研究了Al90Hf5P5体系液态结构，构建其偏偶相关函数，分析Hf、P原子偏配位数及特征化学短程序，由此推演出熔体内Al5HfP结构单元的存在，P原子第一配位处Hf原子所占比例高达14.72%，此结构单元的存在将促进HfP团簇的形成。基于液态结构模拟，通过熔体原位反应成功地制备出富含HfP相的Al–Hf–P系中间合金，详细研究了Hf/P比、熔体原位反应温度对其物相组成及组织的影响，明确了不同凝固速度下合金的组织特征。为揭示该晶种合金对Al–Si合金的作用过程，结合Al75Si15Hf5P5体系液态结构模拟进行统计分析。基于不同热状态下偏偶相关函数及偏配位数等信息，探究了Hf、Si、P原子周围配位层原子分布情况，发现Hf–P原子对的结合力稍高于Si–Hf原子对，上述两种原子间的结合力远高于体系内其它原子对。.采用该晶种合金对Al–Si合金进行熔体处理，设计并优化了熔体处理参数，合金内初晶Si相细化至18.43μm，布氏硬度、抗拉强度分别增长了17.2%、34.8%。基于硅相组织形态分析，结合化学动力学理论，推演出晶种合金在熔体内的结构演变过程，提出初晶Si内存在HfP/AlP双效形核的细化机制。向Al–12Si合金内引入Hf元素，合金内共晶Si相变质显著，含1.2%Hf合金布氏硬度、抗拉强度分别达到了67.4HB、224.7MPa。继续增加合金内Hf含量，共晶Si相形貌趋向性增强，析出片状、颗粒状脆生HfSi2相。热处理后，Al–12Si–1.2Hf合金仍是性能最优。拓展晶种合金在Al–Mg2Si复合材料内的应用，确立最优熔体处理参数，探明Hf元素可同步实现对初晶及共晶Mg2Si的细化、变质处理。结合FESEM分析，揭示HfP作为Mg2Si异质形核核心的细化机制。本项目的开展有助于完善同步双重变质与多相熔体反应理论，对推动熔体处理技术的发展具有重要的理论和实际意义。