Heterogeneous Precipitation Mechanism of η Phase at E/Al Interface in 7475 Aluminum Alloy

The heterogeneous precipitation behavior and nucleation and growth mechanisms of η phase at E/Al interfaces in 7475 aluminum alloy were studied using high resolution transmission electron microscopy (HRTEM) and 3D reconstruction technique in high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). It is found that the nucleation location, nucleation rate, growth rate and morphology of η phase are greatly different when η phase are formed at E particles with different morphology and volume or the same E particle. The decisive factors that affect the nucleation, growth and coarsening of η phase are the interface energy and elastic strain energy of E phase. The growth of η phase belongs to the diffusion-controlled transformation. Solute atoms are transferred by the interphase interface diffusion at a high speed.