The strength improvement in the heat-treatable Al-Zn-Mg-Cu alloys is generally achieved by increasing the volume fraction of nanoprecipitates and reducing the grain size. However, utilizing one of them usually leads to a drastic decrease in ductility. Herein, we architect a hierarchical microstructure integrating bimodal grain structures, nanoprecipitates, and hard-brittle coarse particles wrapped by ductility coarse grain (CG) bands via conventional cold rolling (CR) deformation and heat treatment methods to break the strength-ductility dilemma in the Al-8.89Zn-1.98Mg-2.06Cu-0.12Zr-0.05Sc-0.05Hf (wt.%) alloy. The results reveal that the coupling of high-volume fraction (∼1.2%) nanoprecipitates, ∼52% narrow CG bands, and most coarse particles encapsulated by CG bands contribute to the 45% CR sample with outstanding overall mechanical properties (a tensile strength of 655 MPa, a yield strength of 620 MPa, and an elongation of 15.5%). Microstructure-based strength analysis confirms that the high strength relates to a trade-off between the hierarchical features, namely high-volume fraction nanoprecipitates to counterbalance the strength loss caused by grain coarsening. The excellent ductility is due to the introduction of medium CG content with a narrow width that can trigger a cross-scale strain distribution during plastic deformation, suppressing the catastrophic failure in the fine grain (FG) regions and facilitating the dimple fracture along the CG bands. This study proposes a feasible approach for tailoring hierarchical microstructures in Al-Zn-Mg-Cu alloys to achieve a superior strength-ductility combination.

中文翻译：

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通过优化分级微观结构，新型 Al-Zn-Mg-Cu-Zr-Sc-Hf 合金的强度-延展性协同作用


可热处理Al-Zn-Mg-Cu合金的强度提高通常是通过增加纳米沉淀物的体积分数和减小晶粒尺寸来实现的。然而，使用其中一种通常会导致延展性急剧下降。在此，我们通过传统的冷轧（CR）变形和热处理方法构建了一种集成双峰晶粒结构、纳米沉淀物和延展性粗晶（CG）带包裹的硬脆粗颗粒的分级微观结构，以打破强度-延展性困境Al-8.89Zn-1.98Mg-2.06Cu-0.12Zr-0.05Sc-0.05Hf（重量％）合金。结果表明，高体积分数 (∼1.2%) 纳米沉淀物、∼52% 窄 CG 带和 CG 带封装的大多数粗颗粒的耦合有助于使 45% CR 样品具有出色的整体机械性能（拉伸强度为655 MPa，屈服强度 620 MPa，伸长率 15.5%）。基于微观结构的强度分析证实，高强度与分级特征之间的权衡有关，即高体积分数纳米沉淀物以抵消晶粒粗化引起的强度损失。优异的延展性是由于引入了宽度较窄的中等 CG 含量，可以在塑性变形过程中触发跨尺度应变分布，抑制细晶 (FG) 区域的灾难性失效，并促进沿 CG 带的韧窝断裂。这项研究提出了一种可行的方法，用于定制 Al-Zn-Mg-Cu 合金的分级微观结构，以实现优异的强度-延展性组合。