The natural aging (NA) response of a commercial Al–Zn–Mg alloy has been tracked to investigate the effects of solute clusters on its mechanical properties. It has been observed that the increase of yield strength during NA is not accompanied by the degradation of uniform elongation due to the simultaneously enhanced strain hardening ability. As a consequence, the Al–Zn–Mg alloy with dense solute clusters shows a comparable yield strength, better strain hardening ability and uniform tensile strain relative to its artificially aged counterparts containing precipitates. This positive effect of solute clusters on strain hardening has been systematically studied by tracing the microstructure evolution during deformation through synchrotron X-ray diffraction and atom probe tomography. We found that the dislocation multiplication dominates over the entire deformation process until failure in NA alloys; however, no effect of solute clusters on the dislocation density evolution can be identified. On the other hand, solute clusters themselves dramatically evolve, showing a dissolution-to-coarsening transition during deformation, which can be understood on the basis of a kinetic model. The experimental evidence strongly suggest that the dislocation storage and strain-induced evolution of solute clusters are insufficient to account for the observed high strain hardening rate, and the contribution from other possible mechanisms are estimated in a semi-quantitative manner.

已经跟踪了商用Al-Zn-Mg合金的自然时效（NA）反应，以研究溶质团簇对其机械性能的影响。已经观察到，由于同时增强了应变硬化能力，因此在NA期间屈服强度的增加并没有伴随均匀伸长率的降低。结果，相对于含有沉淀物的人工时效合金，具有密集溶质簇的Al-Zn-Mg合金具有可比的屈服强度，更好的应变硬化能力和均匀的拉伸应变。通过同步加速器X射线衍射和原子探针断层成像追踪变形过程中的微观结构演变，已系统地研究了溶质团簇对应变硬化的积极影响。我们发现，位错倍数在整个变形过程中占主导地位，直到NA合金失效为止。然而，无法确定溶质团簇对位错密度演化的影响。另一方面，溶质团簇本身会急剧演化，表现出在变形过程中从溶解到粗化的转变，这可以从动力学模型的基础上理解。实验证据强烈表明，位错存储和应变诱导的溶质团簇演化不足以说明所观察到的高应变硬化速率，并且以半定量方式估计了其他可能机理的贡献。溶质团簇本身会急剧演化，表现出在变形过程中从溶解到粗化的转变，这可以从动力学模型的基础上理解。实验证据强烈表明，位错存储和应变诱导的溶质团簇演化不足以说明所观察到的高应变硬化速率，并且以半定量方式估计了其他可能机理的贡献。溶质团簇本身会急剧演化，表现出在变形过程中从溶解到粗化的转变，这可以从动力学模型的基础上理解。实验证据强烈表明，位错存储和应变诱导的溶质团簇演化不足以说明所观察到的高应变硬化速率，并且以半定量方式估计了其他可能机理的贡献。