Evolution of microstructure and mechanical properties of a duplex Mg–Li alloy under extrusion with an increasing ratio

• Deformation of duplex Mg–Li alloy is mainly contributed by Li-based β phase.
• Duplex Mg–5Li–2Zn with a medium extrusion ratio has the best compression ductility.
• Duplex Mg–Li alloy with a little β phase deforms like Mg alloys of single α phase.

Mg–5Li–2Zn dual phase alloy was prepared and extruded with ratios of 10, 25 and 79. Microstructures were acquired, and Vickers hardness was examined as well as tensile and compressive properties. The results showed that the alloy possessed a low fraction of β-Li phase besides α-Mg phase. The increase of the extrusion ratio decreased the widths of both phases and also the grain size of α-Mg phase, while increased the homogeneity of the extruded alloys. The strengths were almost the same after the alloy was extruded with ratios of 10 and 25, and the alloy extruded with the ratio of 79 presented a higher strength and a lower ductility. Serrated flow appeared during the tension of the alloy extruded with the ratio of 10. In both tensile and compressive strain–stress curves, yield plateaus were more and more invisible with the increase of the extrusion ratio. It seemed that the deforming behavior of the duplex Mg–5Li–2Zn alloy is still of the pattern of hexagonal Mg alloy with little effect of β-Li phase because of its low fraction.