Effect of Mischmetal on Microstructure and Mechanical Properties of Superlight Mg-Li Alloys

The influence of mischmetal (lanthanum and cerium) on the microstructure and mechanical properties of Mg-9Li-3Al-xRE (x=0, 0.5, 1, 1.5, 2, wt%) alloys was investigated by optical microscope, scanning electron microscope (SEM) with an energy dispersive spectroscope (EDS), and X-ray diffraction (XRD). In as-cast alloys, Al4RE phase is formed, the content of Mg17Al12 phase and the volume fraction of α-Mg phase decrease. In addition, α-Mg phase is refined and the mechanical properties of Mg-9Li-3Al-xRE alloys are improved. However, with increasing mischmetal content, the size of Al4RE phase increases and the mechanical properties decrease. In extruded alloys, Al4RE phase is broken into the particles of 1∼3 μm in the β-Li matrix phase and α/β interphase. And the best mechanical properties are obtained for Mg-9Li-3Al-1.5RE alloy with a tensile strength of 228.3MPa and elongation of 20.8%, increased by 88.6% and 197.4%, respectively, compared with as-cast Mg-9Li-3Al alloy.