*3.1. Microstructure of ECAPed and ECAP-Rolled Alloys*

The optical microstructure of the cast alloy and ECAPed alloys with different processing passes are shown in Figure 2. As seen in Figure 2a, the grey phase of the cast alloy is indicative of the α-rich Mg phase and the darker phase is β-rich Li phase. Clearly, the α-Mg phase is large and irregularly distributed in the β-Li matrix. After ECAP processing, the microstructure of α-Mg phase is continuously deformed with increase in number of passes and the reduction in grain size accordingly. As shown in Figure 2b, after four passes, the α-Mg phase shows elongated phases distributed in a particular angle showing a distinct plastic flow pattern. In addition, compared with the as-cast microstructure, the β-Li phase also decreased after 4 passes ECAP. After ECAP for 8 passes, the α-Mg phase grains are further lengthened with both phases oriented in the direction of the extrusion flow lines, as shown in Figure 2c. After 16-passes ECAP, as shown in Figure 2d, the α-Mg phase is further refined, presenting the typical plastic-deformation flows.

Figure 3a shows the optical microstructure of cast-rolled Mg-9Li alloy in the rolling direction. Clearly, the α-Mg phase is elongated and arranged in order along the rolling direction. Figure 3b,c is the optical microstructure of the ECAP-rolled alloy observed from the rolling direction (RD) and normal to the rolling direction (ND) respectively. Note that, this alloy was firstly ECAP processed for 8 passes, and then subjected to rolling until a 50% reduction in thickness. Thus, the samples of Figure 3b,c are named as E8R-RD and E8R-ND, respectively. Compared to the ECAPed alloys, the duplex phases of the alloy was further elongated and arranged in order along the rolling direction, presenting the typical plastic deformation flow. Meanwhile, the alloy has a more severe plastic-deformation flow in the direction normal to the rolling direction, presenting the typical fibrous microstructure.

**Figure 2.** Optical Micrographs of as-cast and equal-channel-angular-pressing (ECAP)ed Mg-9Li alloys: (**a**) cast; (**b**) E4; (**c**) E8; (**d**) E16.

**Figure 3.** Optical Micrographs of Rolled Mg-9Li alloys: (**a**) CR along the rolling direction (CR-RD); (**b**) E8R along the rolling direction (E8R-RD); (**c**) E8R normal to the rolling direction ND (E8R-ND).

Figure 4 presents the XRD spectra of the Mg-9Li alloys after ECAP and post rolling. As shown in Figure 4a with the cast and ECAPed alloys with different passes, it is clear that the peaks, as well as their intensities, of the two-phase structure changes with the number of ECAP passes in the alloy. Compared with the as-cast alloy, the peaks of the α-Mg and β-Li phases have many different crystal faces. For example, (200), (220), (310) peaks are formed in the Li-rich phase whiles (1012), (1120) peaks

are formed in the α-Mg phase. Comparatively, after 8 passes, the α-Mg shows peaks of (1010), (1011), (1120) whereas the peak increased obviously and the diffraction peaks of (200) and (211) crystal planes are enhanced in the β-Li phase. The XRD spectra of the ECAP-rolled alloys are shown in Figure 4b. The diffraction peaks of the β-Li phase (110) crystal plane are weakened after rolling whereas the diffraction peaks are stronger on the basal (200) and cone (310) planes after rolling. Among all the diffraction peaks of the α-Mg phase, the diffraction peak of the basal plane (0002) is the strongest, which indicates the existence of strong basal texture in the ECAP-rolled alloys [32–34]. Meanwhile, the peaks of (200) crystal planes of the ECAPed alloys were further strengthened after rolling, and this phenomenon was more obvious in the alloys with larger ECAP passes.

**Figure 4.** X-ray diffraction patterns of Mg-9Li alloys: (**a**) as-cast and ECAPed alloys; (**b**) rolled alloys.
