Formation of a new intermediate phase and its evolution toward θ’ during aging of pre-deformed Al-Cu alloys

Peipei Ma¹，Chunhui Liu^1,2，Ziyao Ma²，Lihua Zhan^1,2，Minghui Huang^1,2

1. Light Alloy Research Institute of Central South University, State Key Laboratory of High-Performance Complex Manufacturing, Central South University2. School of Mechanical and Electrical Engineering, Central South University

摘 要：The frequent occurrence of hitherto unknown phase Pre-θ’-2 and unusual 1.5 _cθ’ thick θ’ precipitate was observed by atomic-resolution scanning transmission electron microscopy in the well-studied Al-Cu alloys. This phenomenon is associated with heterogeneous precipitate nucleation and growth on preexisting dislocations introduced by slight deformation prior to aging. In this study, the precise structure details of Pre-θ’-2 was determined by atomic scale imaging, image simulation based on image forming theories and first principle calculations. Pre-θ’-2 has a well-defined ordered structure sandwiched between two 2 aAl(～1.5 _cθ’) spaced Cu layers on {200}Alplanes. The strong structural similarities between Pre-θ’-2 and 1.5 _cθ’ thick θ’ in terms of interfacial structure and thickness, coupled with energetic calculations and preliminary in-situ observations, lead us to propose a new precipitation path toward key strengthening phase θ’.

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