形变和时效协同作用下6xxx系铝合金的精细组织演变与性能调控

There is rising application of Al-Mg-Si-(Cu) (6xxx series) Al alloys in light-weight transportation vehicles as well as electrical conductors and thermal conductors. Synergistic treatment incorporating both cold-deformation and ageing could evidently improve the mechanical, physical and chemical properties, such as strength, electrical conductivity and corrosion resistance, of these alloys. Two key interaction processes are responsible for the property that can be achieved by this method. The first one is the simultaneous defects generation and solutes diffusion during cold-deformation, while the second one is the concurrent defects annihilation and precipitation during the post-ageing. Understandings on these two issues are still limited, especially when compared with the clear picture to describe the precipitation hardening in conventional T6 treatment, due to the complexities. The present project aims to reveal the nano-scale and even atomic-scale structural and chemical evolution of the crystal defects and hardening precipitates in Al-Mg-Si-(Cu) alloys processed by combined deformation and ageing, using the state-of-the-art transmission electron microscopy (TEM) including quantitative high-resolution TEM, high-angle angular dark-field scanning TEM, three-dimensional tomographic reconstruction and in-situ heating TEM. Based on experimental observations and theoretical calculations, this study will provide deep insights into the mechanism governing the interplay between solutes segregation and annihilation/rearrangement of structural defects. The systematic and detailed analysis will finally be conducted to build quantitative relationship among processing parameters, microstructure and performance. This project can not only enrich knowledge regarding physical metallurgy of Al alloys but also give new thermo-mechanical routes and new strategies to design Al alloys with optimized properties.

Al-Mg-Si-(Cu) (6xxx系)铝合金在轻量化交通工具和导电导热材料领域应用广泛。对此类合金进行冷变形和时效协同处理可以改善其强度、导电性及抗腐蚀性等。该制备方法中有两个关键的科学问题尚未解决：1. 冷变形时缺陷形成与溶质原子迁移的关系；2. 后续时效时缺陷退化与溶质析出交互作用的机制。相对描述传统时效工艺析出硬化的图像，对上述工艺中微观结构演变及其对性能影响的认识尚不完善。本项目拟采用定量高分辨电子显微术、高角度环形暗场成像、透射电镜三维重构技术和原位加热电镜技术并结合理论计算和性能测试，从纳米尺度乃至原子尺度揭示形变和时效协同作用下铝合金中晶体缺陷和析出相的结构及其演变规律，阐释晶体缺陷和析出相的相互影响机制，建立形变和时效结合制备的6xxx系铝合金工艺条件、微观结构及性能间的量化关系。本项目既可以丰富铝合金物理冶金学知识，也有助于探寻铝合金改性的新思路和新工艺路径。

6xxx系铝合金应用广泛，本课题开展形变和时效协同作用下6xxx系铝合金的精细组织演变与性能调控的研究，为提升该类铝合金的性能提供新的工艺路径。本课题系统研究后续时效工艺对冷变形Al-Mg-Si-(Cu)合金微观结构演变和性能的影响以及Al-Mg-Si-(Cu)合金内部溶质原子集聚状态（如溶质偏聚物的化学成分、尺寸和界面）对冷变形后微观组织及后续时效及性能的影响，深化了对形变时效工艺相关机制的认识，优化了形变和时效组合工艺，提出了新颖的热加工路线图。本课题探明了冷变形量对Al-Mg-Si-(Cu)合金微观组织和内部缺陷的演变及后续时效过程析出的影响规律，阐释了位错和析出相的演化机制，揭示了不同变形量和预时效制度下铝合金的力学性能，进一步优化了形变和时效协同工艺。本课题也研究了蠕变变形和时效协同作用下目标合金微观组织和性能演变规律，为设计高热稳定性铝合金和高效率蠕变时效成形工艺提供指导。本课题开展了透射电镜微柱原位压缩实验，实验探究了晶体缺陷退化和溶质析出的相互影响，发现变形和时效结合制备的Al-Mg-Si-(Cu)合金强度和塑性结合好的主要原因是良好的位错容纳能力。本课题利用高角度环形暗场像和近原子分辨率能谱分析技术精确分析了Al-Mg-Si-(Cu)合金中纳米析出相的结构演变特性，深化了对析出相形核和长大机制的认识，按计划实验测量了形变铝合金中纳米析出相原子结构及界面特征，利用第一性原理计算研究了缺陷引起的原子占位的改变，形成了缺陷对析出相结构稳定性的认识。综合微观结构测量及其演变规律的认识，课题揭示了变形铝合金时效时溶质原子扩散和缺陷退化交互作用的物理图像，提出了变形前预时效和变形后处理温度对形变和时效组合制备铝合金组织及性能调控的机制。本课题的成果具有普适性，为铝合金改性提供了新工艺路径和新思路，深化了位错和析出交互作用及其对性能影响规律的认识，有助于优化热加工工艺和开发高性能铝材进而增强我国高性能铝材研制的自主创新能力。