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stiffness, electromagnetic shielding,
thermal conductivity, and vibration
damping virtues. Magnesium
compares favorably to aluminum
and steel not only for strength and
density, but also with regard to
bending, torsion, and denting.
Simple part-for-part replacement
of die castings offers improved
material properties. However, the full
benefit of net shape Thixomolding
comes from significantly less
machining involved and the
ability to replace many parts of an
assembly with just one Thixomolded
component. For example, a 50:1
reduction in subassemblies was
accomplished in an electronic check-
sorting part application
[4]
.
OTHER PROCESSINGAND
ALLOY DEVELOPMENTS
In 2007, research efforts
began to address value-added
products under National Science
Foundation sponsorship
[6]
. The
fine grain size and eutectic
microstructure of Thixomolded
Mg alloys were found to be
ideal precursors for applying
thermomechanical processing
to generate micron-sized grains
dispersed with nanometer-
sized phases. Thus, strength
can be increased by 100 MPa in
sheet product, while doubling
elongation and fatigue strength
and increasing fracture toughness
(Fig. 3). In a heat treatment study
conducted with researchers at
the University of Michigan, low
textures were found to improve
cold formability
[7]
.
The new technology discovered
through this study was adopted
in the biomedical market. As one
example, the DonJoy “OA nano”
Mighty Light orthopedic knee brace
was developed, claimed to be the
world’s lightestOAkneebrace (Fig. 4).
Other applications for biomedical
instruments and aircraft container
brackets are being explored.
During an extension of this
NSF project, Thixomat’s subsidiary
nanoMAG invented a new
alloy, BioMg 250 bioabsorbable
magnesium alloy. It is based on
microalloying essential nutrients
and bone growth agents for the
body and has twice the strength of
traditional bioabsorbable polymer
implants. The alloy is expected
to achieve new bone generation
and load-bearing fracture fixing
followed by bioabsorption.
Company sources say it could
eliminate expensive, painful,
and infection-prone secondary
operations often required to
remove titanium or stainless steel
implants, for example. Exposure for
52 weeks in vivo (in rabbit knees) at
the NSF ERC at the North Carolina
Agricultural and Technical State
University shows bioabsorption
and new bone growth around the
BioMg 250 implants (Figs. 5 and 6).
LOOKINGAHEAD
Commercial use of Thixomolded
Mg is expected to continue
to expand in the E/C market,
especially in complex shapes at
thinner wall sections down to
0.5 mm where its superior bend/
dent resistance over aluminum
is beneficial. Use in automobiles
and the aerospace industry, for
lightweighting, can be enhanced by
higher temperature Mg alloys such
Fig. 4 —
DonJoy “OA nano” orthopedic
knee brace.
THIXOMOLDINGAPPLICATIONS
Automobiles
Electronic/Communication
Sporting goods
Handheld tools
Seat backs
Laptop computers
Sunglasses
Drills
Steering column brackets
Cell phones
Gun scopes
Saws
Mirror parts and brackets
Digital projectors
Fishing reels
Chainsaws
Lazy Susan bins
Digital cameras
Snowboard clamps
Nailers
Foldable car tops
Camcorders
Motorcycle wheels
Windshield wiper boxes
TV surrounds
Go-cycle bicycle
Lift gate mechanisms
Walkmans
LED maglite
Cup holders
MP3 players
Brackets for trucks
Defense detectors
LED light fixtures
Radar detectors
Electronic boxes
Check sorters
E-book readers
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