A new lightweight, high-strength magnesium sheet technology targets
applications in military vehicle armor, resorbable biomedical implants and
structural aerospace applications.
The new sheet is said to provide 200 percent higher strength
and improved toughness compared to conventional magnesium, while also providing
the strength of carbon steel sheet at one-fourth the weight.
The new sheet technology has been developed by a company called
nanoMAG, a subsidiary of Thixomat, Ann
Arbor, MI. The approach is related to the thixomolding injection molding
process which converts magnesium alloys into complex parts.
"This is a significant advancement in magnesium that brings
unprecedented performance in terms of strength and light weight, meeting the
challenging demands of the automotive, military, biomedical and aerospace
markets," says Stephen LeBeau, president of nanoMAG. The company received a two-year $730,000 contract
from the U.S. Dept. of Defense to develop lightweight composite military
vehicle armor using nanoMAG sheet as the base structural carrier for vehicle
platforms.
The patent-pending process features isotropic fine-grained
strengthening that permits low-volume manufacturing for specialty applications
at a competitive cost.
According to nanoMAG, magnesium alloy
sheet traditionally has been cost prohibitive, difficult to form and limited in
availability.
Developed with the University of Michigan, the Thixomolding
Thermal Mechanical Process (TTMP) produces ultra-fine-grain "nanocrystalline"
magnesium sheet with properties superior to conventional metals. The nano
structure is produced in-situ in a bulk form, avoiding the manufacturing issues
associated with the handling of fine powders.
The process uses
thixomolding to
produce a sheet bar which is put through secondary thermomechanical heat
processing. A key factor is the precise control of the microstructure which
increases the yield strength of the original stock by more than 200 percent to
more than 250 MPa along with 10 percent elongation. The result is an advanced
magnesium sheet/plate with a superior strength-to-weight ratio than competitive
materials.
nanoMAG describes its manufacturing plant as a "mini-mill,"
a term that usually refers to production of steel shapes through remelting of
scrap.
The operation consists of discrete manufacturing cells
capable of producing 500 tons per year with a relatively small initial capital
investment compared to construction of a greenfield metals plant that performs
casting and rolling.
nanoMAG says the fine-grain sheet material also forms easily,
allowing fabrication of net-shape finished components currently not available.
nanoMAG estimates that the global market for magnesium sheet
is 1,250 tons a year, with revenues totaling $50 million. The global market for
medical implants is estimated to exceed $4 billion with roughly 50 percent tied
to ligament repairs that could benefit from improved fastening systems using
magnesium resorbable implants. This approach to temporary metallic implants is
one of the latest developments in biomaterials. Scientists have reported that
side effects of special degradation products are unlikely since magnesium is an
important micronutrient, and its role in biological systems has been
investigated extensively.
For structural applications, laminated composites of
magnesium sheet with carbon fiber have been successfully fabricated.
New aircraft designs will make greater use of lightweight
materials, such as carbon composites, titanium, aluminum-lithium alloys and
magnesium.
nanoMAG and the University of Michigan received a National
Science Foundation (NSF) grant to demonstrate the commercial feasibility of the
material. Another NSF grant for $500,000 has been awarded for scale-up work. nanoMAG
has a pilot/pre-production plant in operation in Ann Arbor, MI. The company is
actively seeking development partners to test and validate early pre-production
samples tailored to end-use markets.
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