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

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。

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.