Comparative study regarding the effect of Al, Zn, and Gd on the microstructure and mechanical properties of Mg alloy Mg-Sn-Li

•No new phase is formed in Mg-5Sn-0.3Li alloy with addition of Al or Zn.•With Gd addition, needle-like or particle-like GdMgSn phase forms.•Extruded Mg-Sn-Li alloy has a low tension-compression yield asymmetry (about 1.00).•Addition of Al or Zn except Gd benefits to mechanical properties.

The effect of Al, Zn, and Gd respectively on the microstructure and mechanical properties of Mg alloy Mg-Sn-Li (the base alloy) is performed. Our results reveal that with Al addition (Al-modified alloy) or Zn addition (Zn-modified alloy), the secondary dendrite arm spacing of the primary α-Mg phase is refined and no new phase is formed. Gd addition (Gd-modified alloy) results in the formation of needle-like or particle-like GdMgSn phase. The extruded base alloy has a low tension-compression yield asymmetry (about 1.00). Addition of Al or Gd yields a slight increase in value of tension-compression yield asymmetry, while Zn a notable reduce. Under tension along the extrusion direction, the yield strength and ultimate tensile strength of Al-modified and Zn-modified alloy other than Gd-modified alloy are enhanced when compared with the base alloy. This is attributed to solute strengthening, the reduced volume fraction of tin-containing metallic compounds and the existence of many needle-like GdMgSn phases in α-Mg matrix. The yield strength of the Gd-modified alloy under tension is the lowest whereas not under compression. This associates with the fact that GdMgSn phases distributed mainly in the interior of grains would offer resistance to twin propagation and growth.

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