## 3 Results and Discussions
### The Results of the Stress-Strain Curves
#### 3.2.2 The Influence of Different Forming Directions on Dynamic Impact Shear Properties
It was also found that some small new grains with large angle grain boundaries were formed along the grain boundary of long axial grain, as shown in the C region of Figure 10b,c. This phenomenon was similar to the results of [PERSON] et al. [26]. On the one hand, because of the deformation, the small angle dislocation interface was transformed into the large angle dislocation interface to form some new crystals; on the other hand, because of the stress annealing, the larger storage can promote the nucleation in the place where the deformation was especially serious, and the independent and fine recrystallized grain can be formed. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Shear Modulus/(GPa)** & \(2.5\times 10^{4}\) s\({}^{-1}\) & \(3.5\times 10^{4}\) s\({}^{-1}\) & \(4.5\times 10^{4}\) s\({}^{-1}\) \\ \hline
**ND** & **18** & **20** & **11** \\
**TD** & **17** & **16** & **14** \\
**RD** & **18** & **19** & **13** \\ \hline \hline \end{tabular}
\end{table} 
Table 4: The shear modulus of aluminum alloy 7050-T7451 at different directions. In Figure 11a, the microstructure of RD can be seen. The deformation of grain structure was inhomogeneity, and each grain was coarse which showed flat and non equiaxed shape from Figure 11b. The direction of grain deformation was also the same as the rolling direction, and there was a certain amount of fine recrystallized grains existed in the gap between large grains. In Figure 12a, the microstructure of TD can be seen; it can be seen that there were obvious coarse grains, and a large number of approximately equiaxed grains were distributed symmetrically on both sides of the coarse grains, and the size of the equiaxed grains was as not equal. From Figure 12b, it can be seen that a certain little grains were embedded in the interior of large grains. Figure 11: Microstructure of aluminum alloy 7050-T7451 in RD: (**a**) EBSD 500\(\times\); (**b**) EBSD 1000\(\times\). Figure 10: Microstructure of aluminum alloy 7050-T7451 in ND: (**a**) electron backscattered diffraction (EBSD) 500\(\times\); (**b**) EBSD 1000\(\times\); (**c**) SEM 4000\(\times\). BC: band contrast; GB: grain boundary. From Figures 10 and 11, it can be seen that the grain structure had a certain preferential orientation along the direction of plate rolling (i.e., RD); this was due to the slip system which was easy to move inside was the first deformation during the rolling process of aluminum alloy 7050-T7451. And at the same time, the surrounding grains acted as coordinative deformation under the action of external force and gradually moved towards the direction of easy sliding of the slipping system, which led to preferential distribution of grain orientation [27]. Then, the direction of the two most significant differences on dynamic shear mechanical properties of the specimens, that is, ND and TD, the microstructures of the specimens in the two directions at different strain rates after impact shear are shown in Figures 13 and 14. In Figures 13 and 14 it can be seen that with the increase of strain rate, the deformation extent of grains was both aggravated in ND and TD. The proportion of large angle grain boundary was  
Figure 14: Microstructure of aluminum alloy 7050-T7451 in TD at different strain rates after impact shear: (**a**) \(2.5\times 10^{4}\) s\({}^{-1}\); (**b**) \(3.5\times 10^{4}\) s\({}^{-1}\); (**c**) \(4.5\times 10^{4}\) s\({}^{-1}\). Figure 12: Microstructure of aluminum alloy 7050-T7451 in TD: (**a**) EBSD 500\(\times\); (**b**) EBSD 1000\(\times\). Figure 13: Microstructure of aluminum alloy 7050-T7451 in ND at different strain rates after impact shear: (**a**) \(2.5\times 10^{4}\)s\({}^{-1}\); (**b**) \(3.5\times 10^{4}\) s\({}^{-1}\); (**c**) \(4.5\times 10^{4}\) s\({}^{-1}\). decreased, and the proportion of small angle grain boundary was increased, which was due to the shear deformation leading to the grains division.