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采用高分辨透射电子显微镜和高角环形暗场扫描透射电子显微镜结合X射线能谱仪,研究Al-Zn-Mg-Cu合金η相沿小角晶界的析出序列。试样在135°C分别时效5 min到6 h。结果表明,η相在小角晶界的析出序列是:SSS→VRC→GP II区→η′→η。基于非平衡晶界偏析和非平衡晶界共偏析理论,在Al-Zn-Mg-Cu合金时效过程中,通过溶质-空位对的扩散,大量的沉淀形成元素偏析到晶界。这种晶界偏析在VRC、GP II区、η′相和η相的形核和生长中起重要作用。
High-resolution transmission electron microscopy and high-angle circular dark-field scanning transmission electron microscopy coupled with X-ray spectrometer were used to study the eutectic phases of η phase of Al-Zn-Mg-Cu alloy. Samples were aged at 135 ° C for 5 min to 6 h. The results show that the precipitating sequence of η phase at small-angle grain boundaries is: SSS → VRC → GP II → η ’→ η. Based on the non-equilibrium grain boundary segregation and the non-equilibrium grain boundary co-segregation theory, a large number of precipitates form elemental segregation to the grain boundaries during the aging of the Al-Zn-Mg-Cu alloy through the solute-vacancy pair diffusion. This grain boundary segregation plays an important role in the nucleation and growth of VRC, GP II zones, η ’and η phases.