2.1 Materials
The material utilized in the present work is an as-extruded dual-phase magnesium-lithium alloy LZ91. The material was prepared by melting high purity element magnesium, lithium, and zinc in a vacuum induction melting furnace under a protective gas of high purity argon gas, followed by stirring and a setting of 3 min, then they were poured into the cylindrical billets with a temperature of 730 ℃. Then it was held at 250 ℃ for 1 h and to obtain an as-cast ingot. After that, the obtained as-cast ingot was extruded at the temperature of 200 ℃ with an extruding speed of 2 m/min. Finally, an extruded rod with dimensions of Φ110 mm × 400 mm was obtained. The chemical compositions of the LZ91 alloy are displayed in Table 1 , and the mechanical properties are listed in Table 2 , respectively.
In order to observe the microstructure of the LZ91 alloy, the specimen surface was ground with 800, 1200, 2000 grits silicon carbide paper, respectively, then it was an electrolytic etched perchloric acid-ethanol solution (perchlorate acid: ethanol = 1: 9) for 90 seconds. The metallography of the cross-section and side surface of the specimen was presented in Figure 1 , which was characterized by an optical microscope (OM, OLYMPUS GX53). It can be seen clearly that the microstructure of LZ91 alloy mainly consists of a brighter α-Mg phase and a relatively darker β-Li phase. Moreover, it should be noted that there is a significant difference between the microstructure of the cross-section and the side surface of the specimen. The α-Mg phase inFigure 1a distributes in β-Li phases with irregular shapes, while Figure 1b shows that the α-Mg and β-Li phases were both elongated along axial direction due to the radial extrusion.