Microstructure evolution and shearing behaviour of delta '/theta '/delta ' precipitates in an aged Al-Cu-Li-Mg aluminium alloy

We report here on the microstructure evolution and the strengthening behaviour of the delta'/theta'/delta' precipitates in the aged Al-Cu-Li-Mg aluminium alloy by atomic high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and in-situ TEM compression straining. On the chosen zone axis, atomic HAADF-STEM images reveal the in-situ microstructure evolution of the delta'/theta'/delta' precipitates. A monolayer GP(theta') zone, grown on the (001)(Al) plane, evolves from the Cu-rich region. After the transformation of the GP(theta') zone to theta' phase, the boundaries of the theta' phase are coated with the theta' phases, forming a matured delta'/theta'/delta' precipitate. Additionally, the growth of delta ' phases on the two sides of theta' is not affected by the inclined boundaries of theta' and the hard impingement of the thin T-1 precipitate. During the in-situ TEM compression straining on the peak-aged nanopillar, the deviated slip band structures and the large displacement bursts are presumably associated with the dislocation-precipitate interaction of the T-1 and delta'/theta'/delta' precipitates. Furthermore, evidence from atomic HAADF-STEM images shows that dislocations can cut the delta'/theta'/delta' precipitate, producing the stacking fault layers within the theta' phase of the sheared delta'/theta'/delta' precipitate. (c) 2023 Elsevier B.V. All rights reserved.