Microstructures and mechanical properties of as-cast mg-xyb and mg-xyb-0.4zr alloys

As-cast Mg-xYb and Mg-xYb-0.4Zr magnesium alloys (x=l, 2, 4, 8; mass fraction, %) were prepared using flux protection method. Microstructures of the alloys were analyzed by using of OM, XRD, DSC, SEM and EDS, and mechanical properties were measured by tensile and hardness tests. It was found that adding Yb in Mg could refine grain size remarkably but not change the primary columnar morphology when x <= 4. But all the Mg-xYb-0.4Zr alloys have fine equiaxed grains, while the tensile strength and hardness increase with the increments of Yb content. As x=8, the strength and elongation dropped sharply due to the formation of continuous network Mg2Yb intermetallics and eutectics on grain boundaries. The results show that Yb has refining effect on Mg grains, and Zr is an effective modificator for Mg-xYb binary alloys.