The Loss of Dissolved Zirconium in Zirconium-Refined Magnesium Alloys after Remelting
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Magnesium–rare earth–zirconium (Mg-RE-Zr) materials are a high value-added class of speciality alloys used chiefly for aerospace applications, where the use of zirconium ensures the critically needed structural uniformity and consistency in performance through potent grain refinement. However, the manufacture of these alloy components has proved to be problematic and volatile. A viable approach preferred by manufacturers is to simply remelt fully grain-refined prealloyed ingot materials and cast. Unfortunately, the dissolved Zr content in these alloys decreases appreciably after remelting, leading to significantly increased grain sizes and inhomogeneity. This work investigates the mechanisms responsible for the loss of dissolved Zr in Zr-refined magnesium alloys after remelting. It was revealed that the phenomenon stems from the unique Zr-rich cores existing in these alloys. Precipitation of zirconium from these supersaturated cores during heating reduces the dissolved Zr content in the α-Mg phase. On the other hand, once precipitated out, the zirconium precipitates show very limited dissolution in molten magnesium due to their discontinuous dissolution behavior in the absence of agitation. The loss of dissolved Zr was found to be reversible by agitation when remelted in an iron-free environment while irreversible in steel crucibles due to the interference from iron.
KeywordsMagnesium Alloy Master Alloy Conical Sample Pure Magnesium Peritectic Temperature
This work was funded by the Australian Magnesium Corporation (now Advanced Magnesium Technologies) under a CAST-AMC alliance project. The CAST Cooperative Research Centre was established under and is supported, in part, by the Australian Government’s Cooperative Research Centres Scheme. The authors thank Xuewen Yuan, Daniel Graham, and Lihui Zheng, UQ, and Craig Korn and Steve Peck, CSIRO Manufacturing and Infrastructure Technology (Brisbane), for their valuable help with the experimental work on casting and metallography. The authors also thank Professor Jin Zou, The Centre for Microscopy and Microanalysis (CMM), UQ, for attaining the micrographs presented in Figure 7. ZH was funded by the Australian Research Council (ARC) under ARC LP 0347773. Valuable comments and suggestions from the reviewers are acknowledged.
- 2.M. Qian, D.H. StJohn, and M.T. Frost: in Magnesium Alloys and Their Applications, K.U. Kainer, ed., Wiley-VCH, Weinheim, 2003, pp. 706–12.Google Scholar
- 6.E.F. Emley: Principles of Magnesium Technology, Pergamon Press, Oxford, United Kingdom, 1966, pp. 127–55.Google Scholar
- 12.N.J. Ricketts and S.P. Cashion: in Magnesium Technology 2001, J. Hyrn, ed., TMS, Warrendale, PA, 2001, pp. 31–36.Google Scholar
- 15.C.J. Bettles, C.T. Forwood, D.S. Jones, J.R. Griffiths, M.T. Frost, D.H. StJohn, M. Qian, G.-L. Song, and J.F. Nie: SAE 2003 Trans. J. Mater. Manufact., 2003, vol. 112, pp. 726–32.Google Scholar
- 16.M. Qian, D.H. StJohn, and M.T. Frost: in Magnesium Technology 2003, H. Kaplan, ed., TMS, Warrendale, PA, 2003, pp. 209–15.Google Scholar