## 2 Materials and Methods
### Methods  
Samples (40 mm \(\times\) 20 mm \(\times\) 5 mm) were taken from the raw materials and quenched immediately to room temperature after solution treatment at 803 K for 840 min. Such samples are referred to as the solution treated (ST) samples hereafter. A few of the ST samples were then aged at 433 K for up to 1500 min and reached the peak aging (PA) state at 600 min. The other ST samples were cold rolled (CR) with good lubrication conditions at room temperature from 5 mm to 0.5 mm by multiple passes to an accumulated true strain of \(\varepsilon=2.3\) with \(<\)5% for each rolling pass. The rolled sheet was water cooled after a few passes to avoid deformation heating. The rolled samples were then aged at 373 K, 403 K and 433 K for up to 1500 min. CR-373K (420 min) represented the CR sample aged at 373 K for 420 min and CR-373K (1200 min) represented the CR sample aged at 373 K for 1200 min. An FM800 microhardness tester was used to measure the Vickers microhardness of the samples on the rolling direction (RD)-transverse direction (TD) plane to track the evolution of aging hardening. A load of 200 gram force (gf) with a dwell time of 10 s was used. Ten points were tested for each sample and the average value was obtained. Room temperature tensile tests were carried out on an MTS810 universal testing machine along the RD with a tensile rate of 1 mm/min. The room temperature tensile samples were processed into a dog-bone shape with a gage length of 15 mm and a width of 5 mm. At least three specimens for each condition were tested to ensure the accuracy of the experimental results. Subsequently, the fracture behavior of the alloy in different states was observed by SEM. The samples for optical microscopy were prepared by standard metallographic techniques and the results were analyzed on a LEXT OLS5000 laser confocal microscope. To reveal the microstructural evolution of the alloy under different conditions, an FEI G2 F20 TEM instrument operating at 200 kV was used. The (111), (200) and (220) incomplete pole figures (\(\chi\) = 0-80\({}^{\circ}\) and \(\Phi\) = 0-360\({}^{\circ}\)) were obtained by a Bruker D8 Discover X-ray diffractometer. The orientation distribution functions (ODFs) were then calculated by the series expansion method based on these three-incomplete-pole data [13]. The volume fractions of the texture components were then calculated by the decomposition method [14]. To estimate the dislocation densities of the as-deformed samples and subsequent aging samples, the microcrystallite sizes and the lattice microstrain of the samples were measured by the Williamson-Hall method [15]. Through the equation \(\mathrm{Bcos}\theta=\frac{K\lambda}{d}+\varepsilon\sin\theta\) (where \(\lambda\) is the wavelength of Cu K\({}_{\alpha}\) radiation (0.154 nm), K is a constant of approximately 0.9 and \(\theta\) is the Bragg angle), \(\mathrm{Bcos}\theta\) and the \(\mathrm{sin}\theta\) were fitted linearly. The microstrains and microcrystallite size were calculated from the slopes and intercepts of the fitted curve and then used to calculate the dislocation densities of the CR and CR-373K samples according to the equation of \(\rho=2\sqrt{3}\varepsilon/(\mathrm{db})\)[16] (where \(\rho\) is the dislocation density and b is Burgers vector, which has a magnitude of 0.286 nm for aluminum alloys [17]).