Production of A356–SiC
P
composite by an innovative casting
process
S. M. H. Mirbagheri Æ S. Sookhtehsaraee
Received: 23 June 2007 / Accepted: 26 August 2008 / Published online: 23 September 2008
Ó Springer Science+Business Media, LLC 2008
Abstract In the present study, a novel procedure was
introduced for casting of metal matrix composites by
adding a mortar consisting expandable polystyrene beads,
carboxy methyl cellulose paste, SiC particles and water as
a mould pattern. This process was applied for A356 Alu-
minium alloy/SiC
P
composite. Technology of this method
is based on a balance between the solidification rate and the
buoyancy of the reinforcement particles. The experimental
results show that effective parameters in fabrication of a
sound part are density and size of pre-puff polystyrene
beads, percentage of the reinforcement particles, mould
material, thickness of mould cavity, casting temperature
and cooling rate. However, the innovative method will only
be successful for the thin-wall parts, which their solidifi-
cation times become shorter than the floatation time of the
reinforcement particles.
Introduction
The A356/SiC composite has shown a significant
improvement in mechanical properties. The improvement
is due to the transfer of shear tension at the matrix–
reinforcement interface. Totally, an important consider-
ation in the production of metal matrix composites
(MMC) is interfacial characteristics between matrix and
reinforcement. For ceramic-reinforced MMC, it is gen-
erally desirable to obtain a strong interface, which leads
to high load transfer capabilities and hence high modulus
and strength of the composite. On the contrary, poor
interfacial bonding has shown to result in a reduced
elastic modulus and work hardening rate, which is an
indicative of reduced load transfer capabilities. However,
within the A356/SiC
p
composite many variables such as
volume fraction, size, distribution and surface morphol-
ogy of reinforcement particles can affect mechanical
properties [1–4]. According to many theoretical and
experimental studies carried out on the Al/SiC
p
com-
posite, SiC
p
reacts with Al to form Al
4
C
3
and Si [4]. The
Al
4
C
3
phase tends to form discreet hexagonal-shaped
precipitates at the interface between the Al SiC particles.
Therefore the brittle Al
4
C
3
and insoluble in the Al liquid
has undesirable effects on the mechanical properties of
the composite. On the other hand, this interfacial reac-
tion is the function of the temperature and holding time
(DG
0
=-88.5 kJ/mol) [5–10]. Therefore, the use of
adequate combinations of processing parameters, such as
temperature, holding time, etc., can be the alternative
solution to suppress the interfacial reaction. Although
there are various methods employed in fabricating MMC
using different processing parameters, melt process,
squeeze casting, powder metallurgy (PM), hot pressing,
thixo-forming and spray forming, are gaining commercial
importance in recent year [6–8]. Melt processing meth-
ods, such as compo-casting and rheo-casting, have been
the simplest and cost–effective methods for fabricating
SiC
p
/Al alloy composites. However, the process can only
be applied to certain matrix alloys where prolonged
contact time at elevated temperatures will not degrade
SiC
p
. For example, Al alloy have to contain high Si
contents, such as 8 wt.% when fabricating at 700 °C, to
S. M. H. Mirbagheri (&) Á S. Sookhtehsaraee
Department of Mining and Metallurgical Engineering,
Amirkabir University of Technology, P.O. Box 15875-4413,
Tehran, Iran
e-mail: smhmirbagheri@cic.aut.ac.ir; mirbagherii@gmail.com
123
J Mater Sci (2008) 43:6944–6951
DOI 10.1007/s10853-008-2973-7