Inclined θ′ precipitates with terraced Cu/Mn-rich multilayers in Al–Cu alloys

Abstract

In this work, an inclined θ′ morphology with terraced Cu/Mn-rich multilayers is observed in Al–Cu based alloys. The GPA (geometric phase analysis) results indicate that the inclined (∼3.1°) θ′ precipitates could induce significant lattice distortion at the interface. The chemical analysis results demonstrate that Mn atoms could get into the coherent (001)θ′//(001)Al interface with large misfit strains, which may contribute to maintaining the coherent relationship of the (001)θ'//(001)Al interface. Additionally, the interfacial energy between coherent Cu/Mn-rich (001)θ'//(001)Al interface and semi-coherent (010)θ′//(010)Al interface is more closer than that of the normal (001)θ'//(001)Al interface, suggesting a weakness of the anisotropic interfacial energy of θ′ with Cu/Mn-rich layers. The phase field simulation results suggest the formation of inclined θ′ precipitates when elastic strain energy dominates the θ′ morphology. Therefore, the inclined morphology of θ′ precipitates with terraced Cu/Mn-rich multilayers is a plausible outcome in Al–Cu alloys.

Keywords

• Electron microscopy
• Aluminum alloys
• θ′ precipitate
• Geometric phase analysis