The increase in zinc content in Al–Zn–Mg–Cu alloys provides an effective method to enhance the strength. Transmission electron microscopy (TEM) and tensile test were employed to analyze the microstructure and tensile properties, respectively, of Al–9.3Zn–2.0Mg–1.8Cu alloy (9.3Zn alloy) and Al–9.8Zn–2.0Mg–1.8Cu alloy (9.8Zn alloy) with single- and double-stage aging states. The results showed that the two alloys possessed a closed strength under single-stage peak-aging treatment. As for double-stage aging treatment, 9.8Zn alloy had a higher strength values than 9.3Zn alloy under the same aging regimes. With the second step aging time prolonging, the strength gap was extended. The main precipitates for the two alloys with single-stage peak-aging state were GP zones and η′ phase, while there were a majority of η′ phases and η phases for the two alloys under typical double-stage over-aging state. Under double-stage over-aging state, the proportion of precipitate with large size for 9.3Zn alloy was larger than that for 9.8Zn alloy. Besides, a more obvious trend was revealed for the double-stage over-aging state. The gap of strength between the two alloys was explained by the difference of precipitation characteristics via interaction mechanism between precipitates and dislocations.

中文翻译：

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不同添加Zn含量的Al-Zn-Mg-Cu合金时效析出特征及拉伸性能

Al-Zn-Mg-Cu合金中锌含量的增加提供了一种提高强度的有效方法。采用透射电子显微镜（TEM）和拉伸试验分别分析了Al-9.3Zn-2.0Mg-1.8Cu合金（9.3Zn合金）和Al-9.8Zn-2.0Mg-1.8Cu合金的显微组织和拉伸性能（9.8Zn 合金）具有单级和双级时效状态。结果表明，两种合金在单级峰时效处理下均具有封闭强度。对于双阶段时效处理，在相同时效条件下，9.8Zn 合金的强度值高于 9.3Zn 合金。随着第二步时效时间的延长，强度差距扩大。两种单阶段峰时效态合金的主要析出物为 GP 区和 η' 相，而在典型的双阶段过时效状态下，两种合金均以η'相和η相为主。在双阶段过时效状态下，9.3Zn合金的大尺寸析出物比例大于9.8Zn合金。此外，双阶段过老化状态显示出更明显的趋势。两种合金之间的强度差距可以通过析出物和位错之间的相互作用机制通过析出特征的差异来解释。