Beihang Univ, Sch Mat Sci & Engn, Beijing 100083, Peoples R China
; Chinese Acad Sci, Inst High Energy Phys, Beijing Synchrotron Radiat Facil Div, Beijing 100039, Peoples R China
The evolution of microstructure parameters (precipitate size and volume fraction) for two types of Al-Zn-Mg-Cu alloys (7075 and 7055) during aging has been studied by synchrotron-radiation small angle X-ray scattering (SAXS). The results show that the precipitates are only a few nanometers for both alloys ageing even at higher temperature of 160 degrees C for 72 h (4.44 and 5.82 nm, respectively). The maximum of the precipitate volume fraction increases with in creasing Zn content and is about 0.023 similar to 0.028 and 0.052 similar to 0.054, respectively. The coarsening of precipitate is consistent with LSW (Lifshitz-Slyozov-Wagner) model even at the initial stage where volume fraction is still varying. The activation energy of coarsening regime has been determined to be about 1.22 +/- 0.02 eV and 1.25 +/- 0.02 eV for alloys 7075 and 7055, respectively.