Three different levels of zirconium – 0.25 wt%, 0.5 wt% and 1 wt% were added to the melt in the form of Magnesium-15 wt% Zirconium master alloy. Samples were cast at 0 and 30 minutes after grain refiner addition. Two pouring tempera- tures, 705o
C (1300o F) and 815o mold was preheated to 350o C (1500o C (660o samples were produced. A protective (SF6
was used. The experimental setup is shown in Figure 3. Results
F), and hockey puck sized + CO2
F), were used. The ) cover gas
Acknowledgements
This work was sponsored by the United States Automotive Materials Partnership (USAMP) and the US Department of Energy, EERE, Vehicle Technologies Program.
BIBLIOGRAPHY
Figures 4 through 7 show the optical micrographs from hock- ey puck samples for pure magnesium and additions of 0.25, 0.5, and 1 wt% zirconium in the form of magnesium-15 wt% zirconium master alloy. As shown in Figure 5, substantial grain refinement occurs even at an addition of 0.25 wt% zir- conium, which is less than that needed for the peritectic reac- tion to occur. This suggests that the peritectic reaction is not needed for grain refinement. This provides an opportunity to engineer an efficient zirconium-based grain refiner similar to TiBor, e.g. use 0.05% zirconium instead of the current 1%.
1. Saha, P., Viswanathan, S., “AFS/FEF Student Technology Competition - Microstructural Characterization of Magnesium-Zirconium Alloys,” International Journal of Metalcasting, Vol. 2, Issue 4, pp 91-92 (2008).
2. Qian, M., StJohn, D.H., Frost, M.T., “Heterogeneous Nuclei Size in Magnesium-Zirconium Alloys”, Scripta Materialia, Vol. 50, pp 1115-1119 (2004).
3. Qian, M., Zheng, L., Graham, D., Frost, M.T., StJohn, D.H., “Settling of Undissolved Zirconium Particles in Pure Magnesium Melts”, Journal of Light Metals, Vol. 1, Issue 3, pp 157-165 (2001).
Figure 4. Optical micrograph of pure Mg hockey puck sample (25 X, grain size 900 µm).
Figure 5. Optical micrograph of Mg + 0.25% Zr hockey puck sample (50 X, grain size 246 µm).
Figure 6. Optical micrograph of Mg + 0.5% Zr hockey puck sample (50 X, grain size 84 µm).
International Journal of Metalcasting/Winter 10
Figure 7. Optical micrograph of Mg + 1% Zr hockey puck sample (50 X, grain size 58 µm).
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