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.

As-cast Mg-9Li-3Al-xSi(x=0, 0.1, 0.5, 1.0, wt%)alloys were prepared and then investigated by optical microscope (OM), scanning electron microscope (SEM) and X-ray diffractometer (XRD) and mechanical properties test. Results show that the as-cast Mg-9Li-3Al alloy consists of α-Mg, β-Li and Mg17Al12 phases. The addition of Si leads to the formation of new phase (Mg2Si) and the refinement of the grain size. Moreover, Si addition can restrain the formation of Mg17Al12. However, when the content of Si is excessive, α-Mg phase will be coarsened and Chinese script Mg2Si phase is formed in the phase boundary. The tensile strength of alloys initially increases and then decreases while the elongation decreases monotonically with the increase of Si content. Specifically, as-cast Mg-9Li-3Al-0.1Si shows a favorable combination of ductility and strength with an ultimate tensile strength of 182.5 MPa, yield strength of 136.8 MPa, and an elongation of 12.1%.