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|Title: ||The production and evaluation of squeeze cast A1-alloy matrix-short ceramic fibre composites|
|Authors: ||Zantout, B.|
|Issue Date: ||1986|
|Publisher: ||© B. Zantout|
|Abstract: ||Research work on metal matrix-fibre composites has concentrated in
the past on aligned fibre composites. The poor transverse strength
of these composites is seen as a major hindrance to their practical
use in the majority of engineering applications because stresses exist
in more than one direction. Materials with isotropic properties are
preferred and consequently reinforcement of composites in three dimensions
will be necessary.
With this objective, an investigation was conducted to assess the method
of fabrication and properties of A1-a110y reinforced with short fibres
(SiC and A1 203) randomly oriented in three dimensions. Two composite
systems were examined: Al-4.S Cu alloy reinforced with SiC fibre;
and Al-3.7S Mg alloy reinforced with A1 203 fibre.
The general approach was to establish a satisfactory manufacturing
method for the composites before evaluating their mechanical properties.
The vortex technique was used to introduce the fibres into the molten
alloy. Pre-treatment of the fibres, to induce wetting, and the use of
a specially designed device for fibre separation and introduction to
the molten A1-ai10ys was found to be necessary so that a uniform distribution
of fibres oriented in three dimensions could be achieved.
The composites were squeeze cast, under conditions which were experimentally
determined, to ensure the production of pore-free castings
with fine equiaxed structures. The improvement in tensile strength and
ductility of the cast metal, provided by squeeze casting, would be
beneficial to composite properties.
Composite castings, with up to 10% volume fibre, were produced with a
sound structure and with fibres that were uniformly distributed and
randomly oriented in three dimensions.
It was found that the reaction between the fibres and the respective
molten alloy must be closely controlled so that fibre reinforcement
can be realised. In this respect the optimum time of contact between
the fibres and the molten alloy was experimentally defined for both
The tensile properties (UTS, 0.1% proof stress, and ductility) of the
fibre-free alloys were substantially improved by squeeze casting. The
addition of fibre produced further substantial improvement in the tensile
properties of the squeeze cast composites, in particular elastic
modulus and 0.1% proof stress. Furthermore, composite properties were
isotropic. The improvement in the tensile properties of composite
castings (as a result of the addition of fibre) was maintained at elevated
temperatures. At 250oC, castings of both composite systems with
10% (volume) fibre had 0.1% proof stress and elastic modulus values
similar to those for the fibre-free castings at room temperature ..
The tensile properties of the composite castings were not affected by
thermal cycling (at experimental conditions). The fatigue life of the
squeeze cast composite was substantially improved over and above the
initial improvement in fatigue life of the fibre-free castings produced
by squeeze casting. Wear of cutting tools was adversely affected by the
presence of fibres.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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