Scientific & Industrial Research Organisation
(CSIRO) scientists have discovered a new process which
could soon lead to the production of aluminium cars
and planes that get stronger the longer they are left
to 'bake' in the sun.Dr Roger Lumley of CSIRO Elaborately
Transformed Metals (CETM) says the new process involves
curing, or age-hardening, aluminium to a point where
the curing process can be completed by exposure to
sunlight rather than in a furnace.The discovery arises
from CSIRO's work in light alloys and advanced metals.
found in the course of this work that if the high-temperature
aging process used to strengthen aluminium components,
such as castings or motor vehicle body panels, is
interrupted, and the material is allowed to undergo
secondary aging at ambient temperature, the material
became 20 per cent tougher," Dr Lumley says.
At the same time, the 'total-energy-to-rupture' point
can also be extended dramatically (by up to 800 per
cent) resulting in safer cars with crumple zones able
to absorb much more energy as they deform or rupture
on impact. "We have developed two heat treatments
using our new knowledge both of which overcome the
age-old problem of either increasing the strength
of aluminium, and reducing its fracture toughness,
or vice versa,'' Dr Lumley says. "Aluminium alloys
used in the automotive, building and aerospace industries
are typically age-hardened, that is they are strengthened
after their initial formation by a curing process,
or aged at high temperatures in a large furnace."
This method produces a range of curing times for aluminium
alloys. For example the most common treatment, which
gives the strongest alloys, is called T6. To generate
the tensile properties required for structural applications
T6-treated aluminium alloy is typically aged for 6-8
hours at 150-170ºC.
"CSIRO's T6i4 heat treatment significantly reduces
the time of high temperature aging to about an hour,
and uses Australia's warm climate to complete the
process," Dr Lumley says. "Significantly
it means aluminium car body panels, for example, can
be assembled and painted, (the baking cycle used to
harden the paint adds to the process) and they will
continue to strengthen in the sun. The process would
continue, albeit at a slower rate, for the life of
the vehicle," he says.
According to CETM's Industry Manager, Barrie Finnin,
even better results can be achieved using CSIRO's
T6i6 process, where, after several hours of secondary
aging at ambient temperature, the material is again
subjected to high temperature aging. "This can
provide significant improvements to mechanical properties
over the T6i4 treatment," Mr Finnin says. "A
likely application for our T6i6 process would be for
aircraft skins and other aerospace applications, or
any application where weight reduction and high strength
Both T6i4 and T6i6 offer considerable savings in time
and energy over conventional techniques, and in most
cases requires no additional equipment.
Dr Lumley says the secret of the CSIRO discovery is
all to do with the microstructure of aluminium alloys.
"What you end up with in the new process is a
finer structure, engineered at the nano-scale, in
a way that translates into mechanical property improvements,"
CSIRO says the potential spin-offs of the new processes
for industry are enormous. Not only can aluminium
alloy producers boost the strength of their product
while making considerable energy cost savings, but
the processes also allow a faster turnaround time
in producing finished components and may even ead
to reduced furnace sizes.
The technology, which is protected by a series of
international patent applications, is now in the proving-out
stage and is being evaluated by Forgecast Australia
Pty Ltd - a manufacturer of non-ferrous metal components
for global markets with facilities in Mitcham, Victoria
and Tijuana, Mexico.
"Commercial applications are starting to build
industry confidence in our innovation, which should
encourage further use of aluminium alloys," Mr
Forgecast's General Manager, Jim Kealy, says the T6i6
technology could provide a competitive advantage,
particularly where the improvement in properties fulfil
a specific customer need.