# Role of Multi-Scale Microstructure in the Degradation of AI Wire for Power Transmission
## 3 Results
### Microstructure Characterization
#### 3.3.2 Electron Backscatter Diffraction (EBSD) Observations  
Previous studies have shown that texture is a common microstructure of clod-drawn face-centered cubic metals, which could influence the mechanical properties [21; 22; 23]. Figure 5 gives the radial orientation distribution maps of the CPAWs and the AFWs. It can be seen that the orientations of the radial grains in the Al wires are \(<\)001\(>\) orientation and \(<\)111\(>\) orientation. Besides, the number of \(<\)111\(>\) oriented grains is more than that of \(<\)001\(>\) oriented grains. Therefore, both the cold-drawn Al wire and the annealed Al wire have a strong \(<\)111\(>\) texture and a relatively weak \(<\)001\(>\) texture. The texture component in this work is the same as that reported by others. Figure 4: The axial microstructures observed by TEM of (**a**) the cold-drawn CPAW, (**b**) the CPAW annealed at 90 \({}^{\circ}\)C for 8 h, (**c**) the CPAW annealed at 250 \({}^{\circ}\)C for 8 h, (**d**) the cold-drawn AFW, (**e**) the AFW annealed at 200 \({}^{\circ}\)C for 8 h, (**f**) the AFW annealed at 250 \({}^{\circ}\)C for 8 h.  
Figure 5: The radial orientation distribution maps of (**a**) the cold-drawn CPAW, (**b**) the CPAW annealed at 90 \({}^{\circ}\)C for 8 h, (**c**) the CPAW annealed at 250 \({}^{\circ}\)C for 8 h, (**d**) the cold-drawn AFW, (**e**) the AFW annealed at 200 \({}^{\circ}\)C for 8 h, (**f**) the AFW annealed at 250 \({}^{\circ}\)C for 8 h.  
Equation (3) was used to calculate the volume fraction of texture to quantitatively display the texture distribution:  
\[f_{<111>}=\frac{S_{<111>}}{S_{0}}, \tag{3}\]  
where \(f_{<111>}\) is the volume fraction of the \(<\)111> texture; \(S_{<111>}\) is the area of the \(<\)111> orientated grains and \(S_{0}\) is the area fo the maps. Figure 6 shows the calculated results. The volume fraction of \(<\)111> texture in the CPAWs ranges from \(\sim\)0.6 to \(\sim\)0.9, which is the same as that in the AFWs. As a result, the annealing treatment has little effect on the volume fraction of \(<\)111> texture. Figure 7 shows the axial orientation distribution maps of the CPAWs and the AFWs. The axial orientation presents a random distribution without texture. Thus, the texture in the CPAWs and AFWs is fiber texture along the drawing direction. As shown in Figure 7, the grain is elongated along the axial direction, which is consistent with that observed by TEM (Figure 4). Therefore, the grain size should be characterized by radial grain size and axial grain size, which can be defined as grain width and grain length, respectively. Figure 6: The volume fraction of \(<\)111> texture and \(<\)001> texture in the cold-drawn CPAW, the annealed CPAWs, the cold-drawn AFW and the annealed AFWs. Figure 7: The axial orientation distribution maps of (**a**) the cold-drawn CPAW, (**b**) the CPAW annealed at 90 \({}^{\circ}\)C for 8 h, (**c**) the CPAW annealed at 250 \({}^{\circ}\)C for 8 h, (**d**) the cold-drawn AFW, (**e**) the AFW annealed at 200 \({}^{\circ}\)C for 8 h, (**f**) the AFW annealed at 250 \({}^{\circ}\)C for 8 h.  
The grain width and the grain length of the CPAWs and the AFWs were measured on the basis of the radial TEM images and the axial orientation distribution maps, respectively. In this paper, all grain boundaries with the misorientation angle of more than 2\({}^{\circ}\) were used for statistics. As shown in Figure 8a, the grain width of the cold-drawn AFWs (0.31 \(\upmu\)m) is smaller than that of the cold-drawn CPAWs (0.42 \(\upmu\)m). With further annealing, the grain widths of the CPAWs annealed at 90 \({}^{\circ}\)C and 250 \({}^{\circ}\)C were respectively measured to be 0.43 \(\upmu\)m and 1.07 \(\upmu\)m. While, the grain width of the AFWs annealed at 200 \({}^{\circ}\)C and 250 \({}^{\circ}\)C gradually increased to 0.39 \(\upmu\)m and 1.02 \(\upmu\)m. Obviously, with the increase of annealing temperature, the difference of grain width between the CPAWs and AFWs decreases gradually.