The document discusses applications of aluminum metal matrix composites for the Department of Defense, including their use in lightweight track shoes for the Bradley Fighting Vehicle, seeker support structures for missiles, and pistons for military vehicles. It also outlines the manufacturing process of squeeze casting used to produce metal matrix composites and its advantages over other methods in achieving close tolerances, superior mechanical properties, and internal integrity. Current and potential applications within the DOD are highlighted along with the properties and benefits of silicon carbide whiskers as a reinforcement.

1. DoD Applications
of Aluminum Metal
Matrix Composites
DoD Applications
of Aluminum Metal
Matrix Composites
May 27, 1999
Charles R. Hargreaves, P.E.
Engineering Site Manager
Advanced Refractory Technologies

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AcknowledgmentsAcknowledgments
U.S. Army Tank Automotive and
Armaments Command
Donald Ostberg – COTR
Luis Hinojosa
National Automotive Center – TARDEC
North American Technology and Industrial
Base Organization
U.S. Air Force – Wright Laboratories
U.S. Office of the Secretary of Defense
Canadian Department of National Defense

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Automotive
Application
Military
Application
MFG. PART APPLICATION REINFORCEMENT
GM
Toyota
John Deere
Mahle
Mazda
Saab
Gas Diesel
Pistons
2L Turbo Diesel
Kaowool®
Saffil®
+
Ni Powder
SiC(w)
Honda Prelude
Honda Acura NSX
Porsche Boxter
GM-EV1
Toyota
GM-EV1
Chrysler Prowler
Lotus Elise
Block – 2.2L Cylinder Bores
3.2L Engine Cylinder Bores
2.5L Engine Cylinder Bores
Engine Cradle
Engine Pully
Brake Drum
Brake Rotor
Brake Rotor
Saffil®
+ Graphite
Fibers + SiC(p)
ALYN B4C(p)
Kaowool®
SiC(p)
SiC(p)
SiC(p)
ART
ART
ART
BFV-Track Shoe
AMRAAM–Seeker Support Structure
HMMWV-Diesel Pistons (6.5L)
SiC(w)
SiC(w)
SiC(w)
Pistons
Application
Current (Al MMC) ApplicationsCurrent (Al MMC) Applications

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Current ApplicationsCurrent Applications
Lightweight Track for Bradley Fighting
Vehicle (replacing heavy forged steel
components)
Single-Pin and Double-Pin Track Shoe
Lightweight Seeker Support for
AMRAAM Missile (replacing expensive
Titanium component)
High Performance Diesel Pistons for
HMMWV (replacing cast iron crown
with MMC)

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Double-Pin ShoeDouble-Pin Shoe

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Single-pin Shoe With PreformsSingle-pin Shoe With Preforms
Centerguide
SiCw preform
Sprocket window
SiCw preforms

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Seeker Support RingSeeker Support Ring
MMC ring
Pure Al ears

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Design of Seeker SupportDesign of Seeker Support
CTE testing defines SiCw loading in
MMC ring mating with Titanium missile
hull (mating surface o-ring must maintain
gas-tight seal to prevent air infiltration)
Upright ears are pure Al that is E-Beam
welded to MMC ring

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MMC Crown area
Diesel PistonDiesel Piston

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SiCw MaterialsSiCw Materials
CHARACTERISTIC WX-50 WX-70
Mean Whisker Length (microns) 6 – 10 6 – 10
Mean Whisker Diameter (microns) 0.7 – 1.1 0.7 – 1.1
Mean Whisker Aspect Ratio 7 – 15 7 – 15
Particulate Content 50 vol. % 30 vol. %
Particulate Size (microns) 30 30
Surface Area 2 – 4 m2
/g 2 – 4 m2
/g
Free Carbon 0.2 wt. % 0.2 wt %
Free Silica 6.0 wt. % 6.0 wt. %

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SiCw SEMsSiCw SEMs
Old SiCw Technology New Synthesis Technology

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Full Production Level ReadinessFull Production Level Readiness
Time: Capacity: Cost:
1/97 1000 Kg/Yr. $1,000/Kg Before program started
2/99 2500 Kg/Yr. $330/Kg Current capabilities in Pilot Plan
11/99 5000 Kg/Yr. $200/Kg Using existing workforce and
Harper furnace
1/00 10000 Kg/Yr. $100/Kg Expanded workforce to utilize
Harper furnace at full capacity

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Relationship of Capacity to CostRelationship of Capacity to Cost
0
200
400
600
800
1000
1200
SiCw Timeline
CostperKg
0
2000
4000
6000
8000
10000
12000
AnnualCapacity
COST ($/Kg)
CAPACITY (Kg/Yr)
1/97 2/99 11/99 1/00

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Squeeze CastingSqueeze Casting
ART has decided to manufacture its
AlMMCs via Squeeze Casting due to three
characteristics inherent in the process:
Achieve a near net shape with very
close tolerance
Achieve superior mechanical properties
Improve internal integrity
These qualities are obtained by
maintaining high cavity pressure
throughout the solidification process.

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Squeeze CastorSqueeze Castor
At GM’s AMDC

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Squeeze Casting cont.Squeeze Casting cont.
In addition, Squeeze Casting (SC) lends itself
well to the manufacture of metal matrix
composites by allowing for:
The insertion of preforms into the Die
Low pressure infiltrations of the preforms
High pressure to completely fill and feed the preform
These characteristics allow designers to tailor
material properties to the component
requirements; selectively stiffening,
strengthening and/or imparting wear resistance
where needed.

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Complex Shape PreformsComplex Shape Preforms

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Infiltration ModelingInfiltration Modeling
Flow of fluid can be modeled using d’Arcy’s law
∆P = ∆Pγ + ∆Pν = Sfγ SL COSθ + VLµ
∆∆∆∆P = Pressure required to drive fluid through body
Sf = Fiber surface area
γγγγSL = Solid-liquid surface energy
θθθθ = Wetting angle
V = Velocity of fluid
L = Depth of infiltration
µµµµ = Viscosity of fluid
K = Permeability of body
The permeability of body can be modeled using
rf = Fiber radius
Vf = Fiber volume fraction
Κ
5
2

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Improved Mechanical PropertiesImproved Mechanical Properties
Are a direct result of the Microstructures
obtained via the rapid, high pressure,
solidification inherent in Squeeze casting.
These microstructures consist of:
A freedom from porosity and solidification shrinkage
A very fine grain size
Fine silicon morphology
A small Dendrite Arm Spacing (DAS)

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DAS
Grain
Size
Al-Si Eutectic
Basic Microstructure ElementsBasic Microstructure Elements

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Source:MetalHandbookVol.2,10thEdition
Mechanical Properties As a
Function of Dendrite Cell Size
Mechanical Properties As a
Function of Dendrite Cell Size

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As SiCw loading↑:Yield Strength ↑
Tensile Strength ↔
Elongation (ductility) ↓
SiCw Loading Tensile Strength Yield Strength Elongation
(vol. %) (ksi) (ksi) (%)
19.8 56.4 28.8 1.01
29.9 55.7 49.9 0.27
33.3 56.0 55.0 0.21
Tensile Test ResultsTensile Test Results

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Data obtained from KRC’s Centerguide Wear Tester
As SiCw loading↑: Wear ↓ (4x better then current
forged steel)
As SiCw/SiCp ↑: Wear ↓
WEAR DEPTH
SiCw
Loading
(vol. %)
Forged
Steel
(in)
ADI
(in)
MMC
WX-50
(in)
MMC
WX-70
(in)
0 0.025 0.075
19.8 0.10 – 0.20 0.10 – 0.20
29.9
33.3 0.012 0.005
Wear Test ResultsWear Test Results

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Centerguide Wear TesterCenterguide Wear Tester

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Thermal PropertiesThermal Properties
CTE Test Results
X 10E – 6 / °C
SiCw Loading
(vol. %) Axis As Cast T5 T6
0 X 23.26 21.96 20.01
Z 23.77 22.21 23.42
24 X 14.04 13.91 14.88
Z 17.97 18.13 14.39
40 X 12.14 10.68 10.94
Z 15.83 16.40 15.41

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Thermal PropertiesThermal Properties
SiCw Test
Conductivity
(W / mK)
Loading
(vol. %)
Temperature
(°F)
As Cast T5 T6
0 70 168.0 187.1 152.8
24 70 118.5 121.0 104.2
40 70 102.4 95.9 77.4

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ConclusionConclusion
For high fatigue, structural applications, such
as these in this Army Program, where fatigue
and wear resistance are of primary
importance, Squeeze Casting with preforms
is the process of choice.

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ConclusionsConclusions
IPPD environment worked well
Computer models an essential tool
Cost must be a design parameter