Abstract This study concerns the effect of low Cu additions ( ≲ 0.1 at.%) on the precipitate crystal structure evolution in three Al-Mg-Si(-Cu) alloys during overageing. The evolution was assessed through a combination of atomic resolution scanning transmission electron microscopy, scanning electron diffraction, and differential scanning calorimetry. It was found that relatively small changes in the Cu level and the Si:Mg ratio had significant effects on the resulting distribution of precipitate phases, their structural evolution, and their thermal stability. Two Si-rich alloys formed hybrid β′ phase and Q′ phase precipitates on overageing. A third Mg-rich alloy primarily formed L phase precipitates, which exhibited superior thermal stability. Three distinct Cu-containing sub-units that form the basis for all Al-Mg-Si-Cu precipitate phases were identified: the three-fold symmetric Q′/C and the βCu′ sub-units, in addition to a newly discovered C sub-unit. The formation of each sub-unit was discussed, and the atomic structures and connections to other precipitate phases in the Al-Mg-Si(-Cu) system were elaborated. The work presented provides new insights into the complex precipitation of Cu-added Al-Mg-Si alloys, with implications for material properties. The results obtained will be of importance in future alloy and process development, and are thought to be of high value in modelling work on the quaternary Al-Mg-Si-Cu system.

中文翻译：

---

低Cu添加量对过时效Al-Mg-Si(-Cu)合金析出晶体结构的影响

摘要 本研究涉及在过时效期间低 Cu 添加量 (≲ 0.1 at.%) 对三种 Al-Mg-Si(-Cu) 合金中析出晶体结构演变的影响。通过原子分辨率扫描透射电子显微镜、扫描电子衍射和差示扫描量热法的组合评估演变。结果表明，Cu 含量和 Si:Mg 比例相对较小的变化对析出相的分布、结构演变和热稳定性有显着影响。两种富硅合金在过时效时形成混合β'相和Q'相析出物。第三种富镁合金主要形成 L 相沉淀物，其表现出优异的热稳定性。确定了构成所有 Al-Mg-Si-Cu 沉淀相基础的三个不同的含 Cu 亚单元：三重对称 Q'/C 和 βCu' 亚单元，以及新发现的 C亚基。讨论了每个亚单元的形成，并详细阐述了 Al-Mg-Si(-Cu) 系统中原子结构和与其他沉淀相的联系。所呈现的工作提供了对添加铜的 Al-Mg-Si 合金的复杂沉淀的新见解，对材料性能有影响。获得的结果对于未来的合金和工艺开发具有重要意义，并且被认为在四元 Al-Mg-Si-Cu 系统的建模工作中具有很高的价值。并详细阐述了 Al-Mg-Si(-Cu) 系统中的原子结构和与其他沉淀相的联系。所呈现的工作提供了对添加铜的 Al-Mg-Si 合金的复杂沉淀的新见解，对材料性能有影响。获得的结果对于未来的合金和工艺开发具有重要意义，并且被认为在四元 Al-Mg-Si-Cu 系统的建模工作中具有很高的价值。并详细阐述了 Al-Mg-Si(-Cu) 系统中的原子结构和与其他沉淀相的联系。所呈现的工作提供了对添加铜的 Al-Mg-Si 合金的复杂沉淀的新见解，对材料性能有影响。获得的结果对于未来的合金和工艺开发具有重要意义，并且被认为在四元 Al-Mg-Si-Cu 系统的建模工作中具有很高的价值。