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In this study, the tensile and high-cycle fatigue properties of as-cast, solid solution treated and as-extruded Mg-8Li-3Al-2Zn-0.5Y alloy are investigated. The results show that the yield strength and ultimate tensile strength of as-cast alloy is 198.1 MPa and 222.5 MPa, which are improved to 274.7 MPa and 321.7 MPa, 282.4 MPa and 319.3 MPa after solid solution and extrusion treatment, respectively. The high-cycle fatigue strength (at 107 cycles, R = -1) of as-cast studied alloy is 65 MPa, which is improved to 90 MPa and 105 MPa after solid solution and extrusion treatment, respectively. The improvement of fatigue property of the solid solution treated alloy is mainly due to the lattice distortion caused by solid solution hindering the crack propagation. However, the improvement of fatigue property of the as-extruded alloy is mainly due to that the refined grains, stacked dislocations and dispersed secondary particles impede the crack propagation.

The effects of Al/Zn ratio (mass ratio) on microstructure and mechanical properties of the Mg−8Li alloy were investigated. The results indicate that in the as-cast Mg−8Li−xAl−yZn (x+y=5) alloys (LAZ alloys), when the Al/Zn ratio is 1:4 and 2:3, the secondary phases are mainly AlLi and MgLiZn phases; when the Al/Zn ratio is 3:2 and 4:1, the secondary phases are mainly AlLi and MgLi2Al phases. The decomposition temperature of MgLiZn phase is about 300 °C and the decomposition temperatures of AlLi phase and MgLi2Al phase are higher (∼350 °C). Solid solution strengthening is the main factor for the improvement of strength of Mg−8Li−xAl−yZn alloys. The Mg−8Li−3Al−2Zn alloy after solution treatment at 350 °C for 4 h has the best comprehensive mechanical properties (yield strength of 272.5 MPa, ultimate tensile strength of 315.0 MPa and elongation of 3.4%) among the studied as-cast and solid solution treated Mg−8Li−xAl−yZn alloys.

In this work, the microstructure characterization and mechanical properties of the as-cast and as-extruded Mg-xLi-5Zn-0.5Er (x = 8, 10 and 12 wt%) alloys are investigated. The as-cast Mg-xLi-5Zn-0.5Er alloys contain α-Mg, β-Li, Mg–Zn–Er and Mg–Li–Zn phases. Besides the matrix phase change (α-Mg + β-Li phases or only β-Li phase), the quantity and size of the Mg–Li–Zn phase decrease and the Mg–Zn–Er phase is from discontinuous clubbed dispersion to discrete distribution of irregular masses with the increasing Li content from 8 wt% to 12 wt%. The grains of Mg-xLi-5Zn-0.5Er alloys are all refined after extrusion. A part of the Mg–Zn–Er phase is crushed along the extrusion direction and the Mg–Li–Zn phase which is solid dissolved into matrix during homogenization separates out. The fiber texture of β-Li becomes weaker and the fiber texture appears with the Li addition from 8 wt% to 10 wt%. The strength difference of the as-extruded alloys is primarily attributed to the different precipitated Mg–Li–Zn phase evolution. The highest strength (ultimate tensile strength = 252 MPa) among three as-extruded alloys is obtained in the as-extruded Mg–10Li–5Zn-0.5Er alloy with the most dispersed and fine Mg–Li–Zn particles.