## 3 Results and Discussion
### Microstructural Observation
When the alloys were subjected to the two-stage homogenization heat treatment (410 \({}^{\circ}\)C for 3 h and 470 \({}^{\circ}\)C for 20 h), 410 \({}^{\circ}\)C was a relatively low temperature for the precipitation of Al\({}_{3}\)Zr. Therefore, when alloy A(0.1 Zr) went through the two-stage homogenization heat treatment, the Al\({}_{3}\)Zr grains obtained were significantly smaller and denser than those through the one-stage homogenization heat treatment. However, 410 \({}^{\circ}\)C was a relatively high temperature for the precipitation of Al\({}_{3}\)Sc, so the precipitated grains were slightly thicker than the Al\({}_{3}\)Zr grains precipitated from alloy A(0.1 Zr). Although the Al\({}_{3}\)Sc grains of alloy B(0.05 Sc) through the two-stage homogenization heat treatment were slightly smaller than those through the one-stage homogenization heat treatment, both types of homogenization were high-temperature heat treatments for the Al\({}_{3}\)Sc grains. Consequently, the changing range (\(\sim\)10%) of the Al\({}_{3}\)Sc grain sizes of alloy B(0.05 Sc) after the two types of homogenization treatments was much lower than that (\(\sim\)40%) of the Al\({}_{3}\)Zr grains of alloy A(0.1 Zr). The microstructures of the hot-rolled alloy A(0.1 Zr) containing trace Zr and alloy B(0.05 Sc) containing trace Sc that were subjected to the 420 \({}^{\circ}\)C annealing heat treatment for 2.5 h and the 30% cold working process are shown in Figure 4. Regardless of the one-stage or two-stage homogenization heat treatment, all showed linear net textures. From the analysis of Figure 3, the precipitated Al\({}_{3}\)Zr grains of the Zr-containing alloy A(0.1 Zr) through the two-stage homogenization heat treatment were finer and denser than those through the one-stage homogenization heat treatment. The fine grains restrained dislocations better than the coarse grains [18]. Therefore, the net textures through the  
Figure 3: Microstructures observation showing Al\({}_{3}\)Zr (Spherical-like) and Al\({}_{3}\)Sc (Spherical-like) by transmission electron microscope (TEM) analysis of (**a**) 1-Hom. alloy A(0.1 Zr); (**b**) 1-Hom. alloy B(0.05 Sc); (**c**) 2-Hom. alloy A(0.1 Zr); (**d**) 2-Hom. alloy B(0.05 Sc); (**e**) EDS analysis of spherical-like particle in alloy A(0.1 Zr); (**f**) EDS analysis of spherical-like particle in alloy B(0.05 Sc) (asterisks indicate that peaks are possibly omitted). two-stage homogenization heat treatment in Figure 4c were finer than those through the one-stage homogenization heat treatment in Figure 4a; the Sc-containing alloy B(0.05 Sc) also had a similar phenomenon as shown in Figure 4b,d. Regardless of the one-stage or two-stage homogenization heat treatment, the net textures of the B(0.05 Sc) alloys in Figure 4b,d were denser than those of the A(0.1 Zr) alloy in Figure 4a,c. Although the Al\({}_{3}\)Sc grains were slightly coarser and contained less content than the Al\({}_{3}\)Zr grains, the Al\({}_{3}\)Sc grains could restrain the dislocation movement more obviously [12]. From the microstructures of alloy A(0.1 Zr) after T6 treatment (470 \({}^{\circ}\)C solution water quenching for 1 h and 120 \({}^{\circ}\)C artificial aging for 24 h) as shown in Figure 5a,c, a considerable amount of recrystallization and remaining textures along the rolling direction (RD) were observed. The microstructures of alloy B(0.05 Sc) was also measured as shown in Figure 5b,d. Electron backscatter diffraction software (EBSD, Oxford AZtec) was used to perform quantitative analysis of the grain boundary angle distribution ratio and to calculate the degree of the recrystallization of the T6 alloys. It was found that the degree of the recrystallization of alloy B(0.05 Sc) was far lower than that of alloy A(0.1 Zr). After the one-stage and the two-stage homogenization heat treatments, the recrystallization ratios were about 66% and 59%, respectively.