Fig. 1. Effect of heat treatments on yield strength (YS) and tensile strength (TS) before and after aging.

Fig. 2. Selective engineering stress-strain curves of different heat treatments.

Fig. 3. IPF superimposed by grain boundary map of different heat treatments: (a) HR, (b) HR + age, (c) WQ, (d) WQ + age, (e) 0.1 ℃/s, (f) 0.1 ℃/s + age.

Fig. 4. TEM micrographs of different heat treatments: (a) HR, (b) HR with higher magnification, (c) WQ, (d) 0.1 ℃/s. The inset is the SAED pattern of the arrowed precipitates.

Fig. 5. EDS analysis of (a) arrowed nanoprecipitates in Fig. 4(b), (b) arrowed nanoprecipitates in Fig. 4(c), (c) nanoprecipitates in Fig. 4(d).

Fig. 6. TEM micrographs of the aged samples: (a) HR + age, (b) CR + age, (c) WQ + age, (d) 0.1 ℃/s + age.

Fig. 7. Size distribution of Cu-rich nanoprecipitates in different heat treatments: (a) HR + age, (b) CR + age, (c) WQ + age, (d) 0.1 ℃/s + age.

Fig. 8. IFFT images of Cu-rich precipitates with different diameters.

Fig. 9. Number fractions of Cu-rich nanoprecipitates with bcc (red), 9R (green), 3R (blue) and fcc (black) structures in different heat treatments.

Fig. 10. Calculated number of nuclei as a function of dislocation density: the blue, black and red lines are the number by homogeneous nucleation, heterogeneous nucleation and a sum of the two, respectively. The effect of dislocation density on precipitation can be roughly divided into three zones, where purple, red and green zones represent the no effect zone, negative effect zone, and positive effect zone, respectively. The theoretical numbers of nuclei of different heat treatments are shown by dashed lines.

Fig. 11. Schematic diagram showing the nucleation, growth and coarsening process of the Cu-rich precipitates: the black dots represent Cu in solution, green dots represent Cu nuclei, blue circles represent coherent bcc-Cu nanoprecipitates, red circles represent incoherent Cu nanoprecipitates.