Microstructure evolution and shearing behaviour of δꞌ/θꞌ/δꞌ precipitates in an aged Al-Cu-Li-Mg aluminium alloy

We report here on the microstructure evolution and the strengthening behaviour of the δꞌ/θꞌ/δꞌ 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 δꞌ/θꞌ/δꞌ precipitates. A monolayer GP(θꞌ) zone, grown on the (001)Al plane, evolves from the Cu-rich region. After the transformation of the GP(θꞌ) zone to θꞌ phase, the boundaries of the θꞌ phase are coated with the δꞌ phases, forming a matured δꞌ/θꞌ/δꞌ precipitate. Additionally, the growth of δꞌ phases on the two sides of θꞌ is not affected by the inclined boundaries of θꞌ and the hard impingement of the thin T1 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 T1 and δꞌ/θꞌ/δꞌ precipitates. Furthermore, evidence from atomic HAADF-STEM images shows that dislocations can cut the δꞌ/θꞌ/δꞌ precipitate, producing the stacking fault layers within the θꞌ phase of the sheared δꞌ/θꞌ/δꞌ precipitate.