Aerospace & Defense Technology - December 2021 - 15

Lightweight Alloys
lead in development of aluminum for
3D printing. Some of the original success
in printing aluminum came with
AlSi12, an alloy that is 12% silicon.
This is a fairly significant amount of Si
for an aluminum alloy, but the Si serves
to increase the flowability of the meltpool,
and also to decrease the amount
of contraction as the meltpool solidifies.
In this sense, the more silicon the
better! But in the sense of mechanical
properties, a high silicon content is not
a good thing.
The next step was a logical one: reduce
the proportion of silicon in the
alloy from 12 to 10% and add magnesium
to increase the strength. The resulting
was AlSi10Mg, affectionately
known by insiders as " alsitenmag. "
Even with the additional magnesium,
however, AlSi10Mg wasn't an ideal stopping
point; parts printed with it still
didn't meet many of the mechanical requirements
of the final applications. This
printed alloy tends to have low elongation,
which is pretty significant: the
higher the elongation, the tougher the
material. Even with this deficiency, many
people stopped here and settled for " alsitenmag "
as acceptable, even though it
wasn't what they were really looking for.
The Safety Factor
A large proportion of the applications
that were good candidates for
printing were originally castings in
A356, one of the most widely used
cast-aluminum alloys. It is lightweight
and extremely corrosion resistant. To
push the mechanical properties a bit
further, one can add more magnesium,
which leads to A357, a
stronger alloy that can be heat
treated to better properties but is
a bit harder to cast. This could be
an ideal candidate for LPBF, but
there's a catch: A357 also contains
0.04 to 0.07% beryllium-and beryllium
is one of the most toxic metals
to humans there is. Especially if it is
inhaled, which can happen during
powder-handling and post-processing.
Not an ideal fit for AM.
Fortunately, the beryllium can be
eliminated from the alloy, with the result
being F357 (think F for Free of
beryllium). F357 is lightweight, offers
Metal powder for additive manufacturing.
great weldability, can be anodized, has
high corrosion-resistance and is tolerant
of a wide range of temperatures. It's an
excellent candidate for those AM parts
with thin walled, complex structures
that you see in a number of aerospace
and high-end motorsports applications.
While a number of leading AM equipment
makers are exploring F357 now, if
you have a need for this aluminum
alloy there are several things to consider
as you decide on which LPBF 3D
printing system to use to deliver
your parts at the highest levels of
quality.
Making Aluminum F357 Work for You
* Surface finish is important, especially
at those increasingly low angles
that AM machines can print
these days, sometimes completely
support-free. Not to mention those
Two views of
3D-printed Aluminum
F357 heat exchangers;
note the ultra-thin features
in the core (cross-section
image at left). The AM process
for using Aluminum F357 in
VELO3D's Sapphire 3D printing
system was developed jointly
with PWR, a global supplier of
advanced cooling solutions to
Formula 1, NASCAR, other racing
series, and the automotive, military,
and aerospace industries.
Aerospace & Defense Technology, December 2021 www.aerodefensetech.com
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Aerospace & Defense Technology - December 2021

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