The effects of Sn addition on the microstructure of as-cast and as-extruded Mg-9Li alloys were investigated. The results show that α-Mg, β-Li, Li2MgSn, and Mg2Sn are primary phases in the microstructures of the as-cast and as-extruded Mg-9Li-xSn （x=0, 5; in mass fraction, %） alloys. Li2MgSn phase evolves from continuously net-like structure in the as-cast state to fine granular in the as-extruded state. After the extrusion, Mg-9Li-5Sn alloy has finer microstructures. Li2MgSn or Mg2Sn compound can act as the heterogeneous nucleation sites for dynamic recrystallization during the extrusion due to the crystallography matching relationship Extrusion deformation leads to dynamic recrystallization, which results in the grain refinement and uniform distribution. The as-extruded Mg-9Li-5Sn alloy possesses the lowest grain size of 45.9 μm.
Mg-14Li-1Al （LA141）, LA141-0.3Y, LA141-0.3Sr, and LA141-0.3Y-0.3Sr alloys were prepared in an induction furnace in the argon atmosphere. The microstructures of these alloys were investigated through scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results show that yttrium and/or strontium additions produce a strong grain refining effect in LA141 alloy. The mean grain sizes of the alloys with addition of Y and/or Sr are reduced remarkably from 600 to 500, 260, 230 μm, respectively. Al 2 Y, Al 4 Sr and Mg 17 Sr 2 phases with different morphologies are verified and exist inside the grain or at the grain boundaries, thus possibly act as heterogeneous nucleation sites and pin up grain boundaries, which restrain the grain growth.
Mg-5Li-xSn （x=0.15, 0.25 and 0.65, mass fraction） alloys were prepared. The microstructures of these alloys were investigated through optical microscope （OM）, scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results indicate that Sn additions produce a strong grain refinement effect on Mg-5Li alloy. The mean grain size of as-cast Mg-Li alloys with Sn is reduced remarkably from 556 μm to 345 μm, and that of the as-extruded alloys is reduced from 33 μm to 23 μm when the Sn content increases from 0.15% to 0.65%. The near net-like Mg2Sn phase in the as-cast alloys is verified at the grain boundaries. After extrusion, the granular Mg2Sn phase mainly exists inside the grains and thus can act as nucleation sites of α-Mg grains during the dynamic recrystallization and make the microstructure finer.
The as-cast and as-extruded Mg-9Li, Mg-9Li-0.3Ce alloys were respectively prepared through a simple alloying process and hot extrusion. The microstructures of these alloys were investigated by optical microscope （OM）, scanning electron microscope （SEM）, X-ray diffractometer （XRD） and energy dispersive spectrometer （EDS）. The results indicate that Ce addition produces a strong grain refining effect in Mg-9Li alloy. The grain size of the as-extruded alloy reduces abruptly from 88.2 μm to 10.5 μm when the addition of Ce is 0.36%. Mg12Ce is verified and exists inside the grains or at the grain boundaries, thus possibly pins up grain boundaries and restrains the grain growth.
