Metal Matrix Composites
The property benefits of MMCs allow engineers to replace heavy cast iron parts
with fibre reinforced light alloys without sacrificing performance. The methods
used to achieve the gains cost-effectively involve a combination of pressure
casting and fibre preform shapes to selectively reinforce the engine components.
Application successes include reinforced pistons, engine blocks and cylinder
heads Saffil alumina fibres are used to reinforce aluminum alloys and result in
greatly enhanced modulus and high temperature tensile and fatigue strength,
lower thermal conductivity and thermal expansion, and superior wear
resistance.
Preforms for Cast Metal Composites
Preforms based on
performance-proven Saffil Alumina Fibre are used as reinforcement materials for
cast aluminium and magnesium automotive components.
The preform is a rigid
and porous shape containing discontinuous Saffil Alumina Fibre, and possibly one
or more additional reinforcement materials. These additional materials include
particles of aluminium oxide, silicon carbide, and titanium dioxide, or other
fibre reinforcements such as graphite. A large selection of standard preform
compositions are available from Saffil’s perform partners, as well as customized
compositions and shapes.
Preforms can be used in precision casting processes
such as squeeze casting and high-pressure die casting. The preform is preheated
and then placed in the casting die. When the molten metal is forced into the die
cavity under pressure, it infiltrates the porous preform and thereby
incorporates the reinforcement material as an integral part of the cast
component’s microstructure. This type of material is known as a Metal Matrix
Composite (MMC) or Fibre Reinforced Metal (FRM).
The result is a high
performance cast component with material properties which are tailored to a
specific application. Using preform technology, many material characteristics
features properties can be modified, including mechanical, vibration and thermal
properties. Because the density of Saffil Alumina Fibre is only slightly higher
than that of aluminium (3.3 g/cc vs. 2.7 g/cc), these material properties can be
modified with adding little or no additional mass, and in many cases the
superior mechanical properties of the composite material enable vital weight
reductions to be achieved.
Engineered Microstructures Deliver
Performance
Preform technology disconnects the intrinsic link between
component geometry and engineering mechanics. This is accomplished by providing
a product that enables the local modification of the components microstructure,
and thereby freeing the automotive engineer from a predefined set of monolithic
material properties. This new found freedom can result in a large variety of
performance enhancements:
| • | Locally increase strength and
stiffness |
| • | Tune the component's natural
frequencies |
| • | Decrease the natural frequency
density |
| • | Increase the alloy's vibration damping
capacity |
| • | Improve mechanical properties at elevated
temperatures |
| • | Prevent creep and fatigue failure in
thermally stressed components |
| • | Control thermal
expansion |
These examples are just some of the
creative and cost-effective ways in which automotive engineers have used Saffil
fibre-based preforms to improve the performance of cast aluminium and magnesium
parts.
Ultimately, increased performance must translate to an improvement in
the bottom-line via increased competitiveness (cost or market share) and fibre
preforms help MMCs accomplish this in terms of :
| • | Improved power and handling for performance
vehicles |
| • | Reduction in vehicle noise, vibration, and
harshness (NVH) |
| • | Cross-platform commonization of
components |
| • | Lighter and more fuel efficient engines and
vehicles |
| • | Reduced warranty costs due to quieter and
more durable parts |
Over the last two decades,
Saffil fibre preform technology has made a significant impact on the mechanical
systems of many production vehicles, and the list of applications continues to
expand:
| • | Engine blocks (cylinder liners and bearing
caps) |
| • | Cylinder heads (valve seats and
guides) |
| • | Pistons (ring grooves and combustion
bowls) |
| • | Brakes (calipers and rotors) |