The Effect of Y/Er and Zn Addition on the Microstructure and Mechanical Properties of Mg-11Li Alloy

Abstract

Although body-centered cubic (BCC) structural magnesium–lithium (Mg-Li) alloys have lower density and better formability than common hexagonal close-packed (HCP) Mg alloys, their applications remain limited due to their low strength. The purpose of this study is to investigate the effect of Y/Er and Zn addition on the microstructure and tensile properties of Mg-11Li alloy with a BCC structural matrix by comparing Mg-11Li, Mg-11Li-4Y-2Er-2Zn, and Mg-11Li-8Y-4Er-4Zn (wt %) alloys. The results indicate that the addition of Y/Er and Zn at a ratio of 3:1 cannot promote the formation of long-period stacking ordered structure in Mg-11Li alloy such as that in Mg-Y-Er-Zn alloys and the dominant intermetallic phases formed are BCC Mg24RE5 and face-centered cubic (FCC) Mg3RE2Zn3 phases. With an increase of the content of Y/Er and Zn in an as-cast alloy, the fraction of intermetallic particles increases and the grain size decreases. The addition of Y/Er, as well as Zn, dramatically promotes the refinement of dynamic recrystallization (DRX) during extrusion. The initial intermetallic phases induced by Y/Er and Zn addition are broken into relatively fine particles during extrusion, and this contributes to refining the dynamic recrystallized (DRXed) grains mainly by the particle stimulated nucleation mechanism. The as-extruded Mg-11Li-4Y-2Er-2Zn and Mg-11Li-8Y-4Er-4Zn alloys exhibit much higher tensile strength as compared with as-extruded Mg-11Li alloy, which is mainly ascribed to the refined DRXed grains and numerous dispersed intermetallic phase particles. It is suggested that further refinement of intermetallic particles in these extruded Mg-11Li-based alloys may lead to higher quality alloy materials with low density and excellent mechanical properties.

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“…When the dye concentration increases, more reactants and reaction intermediates react with the hydroxyl radicals, leading to an insufficient number of hydroxyl radicals. 35 Therefore, the degradation rate decreased with increasing dye concentration.…”

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“…Alloys with other solute elements such as Zn, Al, Mn, Gd and Sn have also exhibited significant effects on grain refinement and mechanical properties [20], features that can be achieved by alloying and post processing. For example, a remarkable grain size reduction from 300 m to 33 m was achieved via extrusion [21].…”

“…The increase in strength was attributed to precipitation strengthening, and formation of twins and stacking faults whereas the increase in ductility was ascribed to the gradual dissolution of Mg25(Gd, Y)5 at grain boundaries. M Zhang et al [20] reported that addition of Y/Er and Zn to Mg-11Li, did not lead to the formation of the LPSO phase of the extruded alloys but increased the formation of intermetallic phases and a decrease in grain size. Improved strength was ascribed to refined dynamic crystallized grains and numerous intermetallic dispersions.…”