Abstract To understand the alloying effects of a heavy rare earth metal, ytterbium, in magnesium, two series of Mg-Yb and Mg-Yb-0.5Zr magnesium alloys were prepared using flux protection with Yb additions of 0.5, 1, 2, 3, 4 and 8 % (mass fraction), respectively. Microstructure analyses and mechanical properties tests of the alloys were performed by use of optical microscope, X-ray diffraction, differential scanning calorimeter, Scanning electric microscope and electro-probe, et al. It is found that adding ytterbium in pure Mg can refine grain sizes remarkably but not change the primary columnar morphology below 4% Yb contents. All Mg-Yb binary alloys obtained fine equiaxed grains with the addition of 0.5% (mass fraction) zirconium. The tensile strengths and hardness of the alloys increase with the increase of Yb contents. In the case of high Yb content, 8%, the strength and elongation drops sharply due to the formation of continuous network Mg2Yb intermetallics and eutectic structures on grain boundaries. The results show that ytterbium has refining and alloying effects on magnesium and zirconium was an effective grain refiner in Mg-Yb binary alloys.
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