*3.2. Spatial Distribution of the Textures*

It is generally reported that the rolling texture of fcc symmetries mainly contains the Goss ({011} <100>), brass ({011} <211>), S ({123} <634>), and copper components ({112} <111>). To quantitatively determine the volume fractions of the typical texture components and to analyze the spatial distribution of the rolling textures, the crystal orientation maps of the four samples showing the spatial distribution of fcc rolling components are illustrated in Figure 3 (in which each grain color specifies a texture component), and the corresponding volume fractions of the rolling components are listed in Table 2. Together with the brass, copper, and Goss, the S1 ({241} <112>), S2 ({231} <124>), S3 ({231} <346>) component and Taylor component ({4411} <11118>) are also presented in the base metal and weld metal of the joints. As shown in Figure 3, the colors are orange for copper, green for S1, purple for S2, blue for S3, cyan for Taylor, yellow for brass, and red for Goss.

**Figure 3.** Spatial distributions of typical fcc rolling components of base metal and weld metal in 5A90 Al–Li alloys along different sample directions, with orange for copper, green for S1, purple for S2, blue for S3, cyan for Taylor, yellow for Brass, and red for Goss: (**a**) sample HBM; (**b**) sample HWM; (**c**) sample TBM; and (**d**) sample TWM.


**Table 2.** Volume fraction of the typical fcc rolling components (%).

It can be seen that the sample HBM (Figure 3a) exhibits significant Brass components and the overall intensity of the components is approximately 69.4%. This is obviously a consequence of the higher deformation degree during the rolling processing subjected to 5A90 Al–Li alloys [18]. In sample TBM, the rolling components show weak distribution intensities with a sum percentage about 38.3%, with the S components including S1, S2, and S3 as the predominate ingredients.

For the weld metal, the overall texture intensity of the sample HWM and the sample TWM is 12.3% and 9.4%, exhibiting a relatively weak texture in the weld metal (see Figure 3b,d and Table 1). In general, the overall texture of the weld metal is basically decided by the orientations of the grains [25] in the columnar zone [19] and the weld metal zone having the equiaxed grains is likely to have an almost random texture, while brass, copper and S components are normally encountered in the deformation texture of fcc materials [20,26]. The present work conforms this and the brass, copper, S and Goss components are in presence in the weld metal, which suggests some similar texture components in the weld metal were formed as base metal during the laser welding.

Previous reports [19,27] have suggested that the welded joint could develop several major textures and strong texture might exist at the base metal, HAZ and columnar grain zone of the weld metal, whereas the grain orientation at equiaxed grain zone in the center of weld metal was relatively random. The present work also confirms that the original base metal structure has been eliminated and replaced by a very fine equiaxed grain structure in the weld metal. All these phenomena remind us that during the solidification of aluminum alloys, the equiaxed grains formed in the weld metal are more prone to have random distributions with weaker intensities.

Generally speaking, the equiaxed grains are more likely be generated by the continuous dynamic recrystallization [26]. However, during the solidification of the welding pool, almost all equiaxed grains are those newly-nucleated and grown, hence the grain orientation is random [17]. Therefore, the equiaxed grain cannot be generated by the dynamic recrystallization occurred during laser welding. The formation of equiaxed grains in the weld metal could be ascribed to the heterogeneous nucleation mechanism aided by equilibrium Al3Zr phase as well as the growth of pre-existing nuclei created by dendrite fragmentation, or by grain detachment resulted from Nd:YAG laser welding processes [16]. Hence, the random texture developed in the weld metal can be quite different from the normal random texture generated by the continuous dynamic recrystallization.

### *3.3. Texture Fiber Analysis*

It is generally known that the rolling texture of fcc symmetries is near the location of so-called α-fiber and β-fiber textures in the Euler space [18,20]. The α-fiber mainly contains the Goss and the Brass orientations, while the β-fiber mainly contains brass, S and copper components.

Figure 4 shows the α-fiber and β-fiber texture analysis of the four samples (in reduced Euler spaces). It can be directly observed that both α-fiber and β-fiber textures are much stronger in base metal (sample HBM and sample TBM) than those of the weld metal (sample HWM and sample TWM). This is not surprising since the higher degree of deformation preferentially developed textures in base metal. Moreover, both α-fiber and β-fiber textures could be modified by different rolling rates, during which the major crystallographic features could be involved. Figure 4 clearly shows the difference in the fiber texture between sample HBM and TBM. On the α-fiber (Figure 4a), the intensity of sample HBM is obviously stronger than that in sample TBM when the *φ*<sup>1</sup> angel ranges from 20◦ to 40◦ (meaning that the brass texture is more prevalent), while on the β-fiber (Figure 4b), the intensity of sample TBM is stronger than that of sample HBM when the *φ*<sup>2</sup> angel ranges from 50◦ to 70◦ (meaning that the S texture is more prevalent). The outcome is consistent with the results in Table 1, and might indicate that S and Brass textures are preferentially developed with referring to the rolling direction in the base metal.

**Figure 4.** Texture fiber analysis of base metal and weld metal in 5A90 Al–Li alloys along the different sample directions: (**a**) α-fiber; and (**b**) β-fiber.
