铝合金是特种车辆轻量化的最佳选择之一。传统高强7×××系合金耐蚀及可焊接性较差，而5×××系合金强度低。申请人前期已开发出了耐蚀可焊Zn/Mg<1.0的Al-Mg-Zn系列合金，但合金的强度与高强7×××系合金相比仍有100MPa的差距。究其原因主要在于和其他相对发展成熟的铝合金相比，新合金中主要强化相T-Mg32(AlX)49相的析出行为及强化机制仍不明确，阻碍了针对合金微观结构的精细调控。本项目拟针对不同Zn/Mg比以及Cu和Ag微合金化合金，采用三维原子探针与扫描透射原子成像相结合的方法，从原子尺度上揭示Cu和Ag与Zn/Mg的竞争析出机理，确定时效初期不同种类原子团簇的成分结构、热稳定性、向强化相转化过程中的长大机制，以及强化相与位错之间的交互作用规律。通过对不同阶段时效产物成分分布、形状、尺寸等微观组织精细调控实现合金强度的显著提高，为新合金的开发提供理论依据和指导作用。

Lightweight Al alloy is extensively used in large vehicle industry. 5××× series Al alloy exhibits good corrosion resistance and good weldability compared with traditional high strength 7××× series Al alloy, although the strength of 5××× series Al alloy is not enough for the use on advanced vehicles. The applicant has developed corrosion resistant and weldable Al-Mg-Zn alloy with Mg/Zn<1.0. But the strength is still 100MPa lower than those high strength 7××× series Al alloys. This is mainly because of the ambiguity of the precipitation sequence and precipitation hardening behavior of T-Mg32(AlX)49 phase, and it has been an obstacle for microstructural control of the alloy. Therefore this proposal focuses on the Al-Mg-Zn alloy with different Zn/Mg ratios and the additions of Cu and Ag micro-alloying elements in the alloy. A combination of APT and HAADF-STEM is used to systematically characterize the competition precipitation between Cu and Ag elements and Mg/Zn at an atomic level during artificial aging treatment. We also concentrate on the composition, structure and thermal stability of good clusters and their transformation to the subsequent precipitation of key strengthening phases. Subsequently the interaction between dislocations and different strengthening precipitates are investigated. The carefully control of atom segregation, size and aspect ratio of the precipitates is an effective method to improve the strength of the developed alloy. The successful completion of the proposal will be a strong theoretical guidance for the optimization of alloy design and heat treatment process.