变形态Al-Cu-Mg-Ag合金中Mg-Ag原子团簇竞争生长机理与控制方法研究

Quenching after solid solution usually leads to the obvious warping distortion of aluminum alloy sheets. The subsequent straightening process is inevitably required to control and improve the sheet flatness. However, the straightening noticeably suppresses the precipitation of high density Ω phase, thereby significantly degrading the heat-resistant properties of Al-Cu-Mg-Ag alloy sheets and restricting its wide applications on high speed aircrafts. This has been the major issue of the preparation of Al-Cu-Mg-Ag alloy sheets all over the world. In order to overcome the serious heat-resistance shortage of deformed Al-Cu-Mg-Ag alloy sheets, this research focuses on the effective control of the competitive growth of Mg-Ag co-clusters, which act as the Ω precursors. After revealing the intrinsic mechanism how straightening affects the formation of Mg-Ag co-clusters by quantitative atom probe tomography and transmission electron microscope analysis, a new idea involving the combination of pre-aging and suitable bulk Ag content is proposed to accelerate the formation of high density Mg-Ag co-clusters and to enable the dense Ω precipitation, ultimately improving the mechanical properties of Al-Cu-Mg-Ag alloy sheets at elevated temperatures. The success of our research will break through the conventional microstructure controlling method of heat-resistant Al-Cu-Mg-Ag alloys and help to develop new technical prototype for sheet preparation. Our results will also establish a solid foundation for the applications of excellent heat-resistant Al-Cu-Mg-Ag alloy sheets in China.

铝合金薄板固溶淬火后常常发生翘曲变形，必须引入矫直变形处理来平整板型。但矫直变形显著抑制Al-Cu-Mg-Ag合金中耐热Ω相的大量析出，大幅度降低薄板的耐热性能，严重制约其在高速飞行器上的大规模应用。这是目前该合金薄板制备所遇到的世界性难题。本项目旨在解决变形态Al-Cu-Mg-Ag合金薄板耐热性能严重不足的问题，以有效控制Ω相先驱体Mg-Ag原子团簇的竞争生长为切入点，借助三维原子探针及透射电镜定量分析技术，在全面理解矫直变形抑制Mg-Ag原子团簇形成机制的基础上，提出将预时效及Ag含量调控相结合来促进预析出Mg-Ag原子团簇大量形成、保证后续Ω相充分析出的新思路，以达到显著提高变形态Al-Cu-Mg-Ag合金薄板耐热性能的目标。本课题的成功实施将打破该合金耐热微结构的传统调控模式，发展相应的新型制备技术原型，为我国高耐热Al-Cu-Mg-Ag合金薄板的应用奠定坚实基础。

固溶时效后析出的高热稳定性Ω相赋予Al-Cu-Mg-Ag合金优异的高温力学性能，在高速飞行器结构件上极具应用前景。实际生产中，该合金板材固溶淬火后经常发生翘曲变形，必须引入矫直处理来平整板型。但矫直变形显著抑制耐热Ω相的大量析出，大幅度降低合金板材的高温力学性能。这已成为该系合金工程应用所面临的世界性难题。本项目针对变形态Al-Cu-Mg-Ag合金板材耐热性能差的问题，围绕时效初期Ω相及其先驱体Mg-Ag原子团簇的形成与调控，通过研究预变形影响Mg-Ag原子团簇竞争形成的微观机制、变形前的预时效处理提高Ω相析出数量的基本规律以及Ag含量与Ω相形核率之间的紧密关联这三个方面的内容，发现预变形处理直接干扰Mg、Ag原子的强烈偏聚，抑制Mg-Ag原子团簇形成，降低Ω相形核数量的基本原理，并对比证实变形前的短时间预时效处理可以有效提高变形态合金中Mg-Ag原子团簇的数量，确保Ω相的后续析出。同时，Ag元素的合金化研究进一步表明提高Ag含量可以降低Mg-Ag原子团簇的形核能垒，大幅度提高时效初期Mg-Ag原子团簇的数量，从而显著提高Ω相的形核率，促进变形态合金中形成高密度Ω相。基于以上研究成果，本项目建立了可获得高耐热变形态Al-Cu-Mg-Ag合金板材典型组织结构的协同调控思路和方法，即通过预时效制度与高Ag成分设计的有效结合，确保时效初期的变形态合金中形成足够多的可作为Ω相稳定形核核心的Mg-Ag原子团簇。本项目的研究成果将有助于打破变形态Al-Cu-Mg-Ag合金板材耐热性能不足的现状，为其在高速飞行器上的大规模应用奠定基础。