| Summary: | A quantitative relationship between microstructure and tensile properties of Al–Zn–Mg–Cu alloys with various alloying degrees was investigated in this study. Three kinds of high strength Al–Zn–Mg–Cu alloys with little strength difference were used for the microstructural characteristic and statistical analysis. A strength model with high accuracy was established through the systematical calculation of strengthening theories, which was validated by the microstructure and ultimate tensile strength of a testing sample. The model gives the precise ratio of the contribution of precipitation hardening and even the component achieved from the bypass mechanism. Moreover, guidance on the regulation of precipitation phases was proposed from the strength model. It can be disclosed that the alloys will show the best strength when the precipitates of 7xxx series Al alloy are distributed near the right of critical radius, which is identified as 2.5 nm in this model.
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