Atomic structure of GPB-II zone and its evolution in an Al-Zn-Mg-Cu-Si crossover alloy during aging

• Published in: Materials characterization 2024-09, Vol.215, p.114151, Article 114151
• Main Authors: Guo, Kehong, Liang, Shangshang, Wen, Shengping, Wei, Wu, Wu, Xiaolan, Gao, Kunyuan, Huang, Hui, Nie, Zuoren
• Format: Article
• Language: English
• Subjects: Al-Zn-Mg-Cu-Si alloys; Atomic structure; Crossover alloy; HAADF-STEM; Hybrid precipitate
• ISSN: 1044-5803
• DOI: 10.1016/j.matchar.2024.114151

The GPB-II zone is the main strengthening precipitate in the Al-4.5Zn-1.5Mg-1.0Cu-0.35Si (wt.%) crossover alloy, resulting in increased alloy strength and ductility. The atomic structure of the GPB-II zone and its evolution process during aging have been studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in the present work. It is shown that the GPB-II zone is a hybrid precipitate consisting of the L phase (a disordered phase with a QP lattice and is normally present in Al-Mg-Si-Cu alloy) on the inner part and Guinier-Preston-Bagaryatsky (GPB) zones (an important strengthening phase in Al-Cu-Mg alloy) on the outer part. The GPB-II zone is formed by the GPB zone nucleating at the Cu site (in-between and on the Si-network) of the L phase. The unique combination of the GPB zone and L phase was investigated, and the “Si parallelogram embedding with Cu” was proposed. The GPB zone provides the atoms for the L phase’s growth and results in the coarsening of the L phase with few GPB zones after a long aging time. The role of the Zn element in the formation of the GPB-II zone was discussed. It is thought to have a similar effect as Cu and can also promote the formation of GPB zones on the L phase. •The atomic structure of GPB-II zone in a crossover alloy was studied by HAADF-STEM.•The GPB-II zone is a hybrid precipitate that consists of the GPB zone and L phase.•The unique combination of the L phase and GPB zone was investigated.•The GPB zone can provide atoms for the L phase’s growth during aging.•The role of Zn in the formation of the GPB-II zone was revealed.