Microstructure and Mechanical Properties of as-Cast Mg-Li-Al-xSi Alloys

As-cast Mg-9Li-3A1-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 alpha-Mg, beta-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, alpha-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-3A1-0.1Si 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%.