Creation of fine and spherical magnesium crystals via control of nucleation and growth instabilities

Qian, Ma (2006). Creation of fine and spherical magnesium crystals via control of nucleation and growth instabilities. In: K. U. Kainer, Magnesium: Proceedings of the 7th International Conference Magnesium Alloys and Their Applications. Magnesium 2006: 7th International Conference on Magnesium Alloys and Their Applications, Dresden, Germany, (200-206). 6-9 November 2006.


Author Qian, Ma
Title of paper Creation of fine and spherical magnesium crystals via control of nucleation and growth instabilities
Conference name Magnesium 2006: 7th International Conference on Magnesium Alloys and Their Applications
Conference location Dresden, Germany
Conference dates 6-9 November 2006
Proceedings title Magnesium: Proceedings of the 7th International Conference Magnesium Alloys and Their Applications
Place of Publication Weinheim, Germany
Publisher Karger
Publication Year 2006
Sub-type Fully published paper
ISBN 9783527317646
3527317643
Editor K. U. Kainer
Start page 200
End page 206
Total pages 7
Language eng
Formatted Abstract/Summary
Achievement of a fine and uniform spherical grain microstructure in a casting is desirable because of the many benefits it brings in the solidification process itself and the properties of the casting. This work demonstrates, both theoretically and experimentally, how to produce fine and spherical magnesium crystals in magnesium alloys via control of nucleation and growth instabilities by grain refinement. The theoretical basis adopted is the Mullins-Sekerka (M-S) stability criterion for spherical growth in a supercooled melt and recent advances in grain refinement of magnesium. The applicability of the M-S stability criterion to the growth of magnesium crystals in a magnesium alloy melt is discussed in detail. It is shown that fine and spherical magnesium crystals are achievable by grain refinement in a magnesium alloy cast either from a normal superheat or the semisolid region of the alloy. Three different magnesium alloys have been demonstrated. The mechanism for the formation of spherical magnesium crystals is discussed in terms of the nucleation rate, which determines the grain density; (ii) the growth anisotropy, which affects the selection of crystal morphology; (iii) the degree of constitutional supercooling, which determines the transition from spherical to dendritic growth; (iv) the growth velocity, which influences the size distribution of the resultant spherical magnesium crystals. The approach demonstrated offers an alternative for semisolid metal processing, where spherical crystals can be produced directly from the liquid state without agitation.
Subjects 09 Engineering
Q-Index Code EX
Additional Notes Presented during Symposium G: "Casting, Recycling, Melting".

 
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Created: Fri, 27 Nov 2009, 14:48:30 EST by Ms Lynette Adams on behalf of School of Engineering