Semi-Solid Casting of Metal Matrix Nanocomposites |
| Journal |
Solid State Phenomena (Volumes 116 - 117) |
| Volume |
Semi-Solid Processing of Alloys and Composites |
| Edited by |
C.G. Kang, S.K. Kim and S.Y. Lee |
| Pages |
478-483 |
| DOI |
10.4028/www.scientific.net/SSP.116-117.478 |
| Online since |
October, 2006 |
| Authors |
Michael De Cicco,
Lih Sheng Turng,
Xiao Chun Li,
John H. Perepezko
|
| Keywords |
Nanocomposite, Nucleation, Semi-Solid Casting, Ultrasonic Dispersion |
| Abstract |
Semi-solid casting (SSC) techniques have proven useful in the mass production of high integrity
castings for the automotive and other industries. Recent research has shown metal matrix
nanocomposite (MMNC) materials to have greatly improved properties in comparison to their base
metals. However, current methods of MMNC production are costly and time consuming. Thus
development of a process that combines the integrity and cost effectiveness of semi-solid casting
with the property improvement of MMNCs would have the potential to greatly improve cast part
quality available to engineers in a wide variety of industries. This paper presents a method of
combining SSC with MMNC in a way that benefits from MMNCs’ tendency to naturally form the
globular microstructure necessary for SSC. This method uses ultrasonically dispersed nanoparticles
as nucleating agents to achieve globular primary grains such that fluidity is maintained even at high
solid fractions. Once particle dispersion is achieved, the material needs no further processing to
become a semi-solid slurry of globular primary grains as it cools. This quiescent method of slurry
production, while still imposing some constraints on cooling rates, has a large process window
making this process capable of industrial rates of throughput. It was found that the key factor to
achieving globular microstructure is a sufficiently slow cooling rate at the onset of solidification
such that particle-induced nucleation can occur. Once nucleation occurs, continued cooling is
virtually unconstrained, with globular microstructure evident in quenched samples as well as
samples cooled at rates as slow as 1 °C/min. This method was demonstrated in several material
systems using zinc (Zn), aluminum (Al), and magnesium (Mg) alloys and nanoparticles of
aluminum oxide (Al2O3), silicon carbide (SiC), and titanium oxide (TiO2). Additionally, several
nucleation models are examined for applicability to nanoscale composites. |
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