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Review FOI(A) February 2010
Furukawa Review, No. 26 2004 60 2. SUPERPLASTIC FORMING
2.1 Superplastic Phenomenon
While ordinary aluminum alloys elongate by less than
about 100 % even when deformed at high temperatures,
some materials with suitable microstructure exhibit
high elongation strain ranging from several hundreds
to one thousand percent when deformed under
specified conditions. Such a phenomenon is called
“superplasticity”.
Superplastic aluminum alloys generally have very
fine grain structure of about 10 μm in diameter, where
the grain refinement is achieved by optimizing the
kind and amount of additional elements suppressing
grain growth and by controlling the thermo-mechanical
process. Superplastic behavior occurs when these
alloys are deformed at high temperatures of 400~550
˚C with a relative strain rate of 10–4~10–3/s. Because
grain boundary sliding during deformation becomes
significantly activated under these conditions, these
alloys exhibit an extremely large degree of ductility.
In addition, since the flow stress at high temperatures
is very low due to fine grain structure, superplastic
aluminum alloys can be blown-formed just like plastics
with a low pressure of several atmospheres.
2.2 Features of Superplastic Forming
1) Even products which are usually formed in several
parts separately can be integrally formed as a single
part through superplastic forming. The single-piece
forming minimizes the number of parts and joints,
and thus leads to weight and cost savings.
2) Since the forming needs only the female die,
investment cost for dies is reduced.
3) The high formability expands the possibility of
product design.
4) Because of high temperature forming, excellent
form-frozenness is given. But, it is necessary to take
into account thermal contraction.
5) Superior transferability of the die surface to the metal
sheet is provided.
6) Surface defects accompanied by cold press-forming
such as Lüders line and surface roughening do not
arise.
7) Superplastic forming takes longer time than cold
press-forming. It is suitable, accordingly, not for
1. INTRODUCTION
Weight saving is the most important requirement in
the area of aircraft industry. High-strength superplastic
aluminum alloys such as 2004-alloy (Al-Cu system) and
7475-alloys (Al-Zn-Mg-Cu system) have long been used
for aircraft components. However, following points are
the shortcomings of these alloys; 1) it is very expensive
to manufacture the alloy sheets, 2) solution treating and
subsequent aging are indispensable for strengthening
the formed products and 3) corrosion resistance and
weldability are insufficient.
On the other hand, 5000-series alloys (Al-Mg system)
are widely used in various applications because they
have moderate strength, good corrosion resistance,
favorable weldability and ease of surface treatment. The
Research Laboratory in Furukawa-Sky Aluminum Co.
developed “ALNOVI-1” with excellent superplasticity
t h r o u g h o p t i m i z i n g t h e a l l o y c o m p o s i t i o n a n d
manufacturing processes of 5083-alloy, which has
been widely used for structural materials with medium
strength. Being somewhat inferior in superplasticity to
conventional high-strength superplastic aluminum alloys,
the “ALNOVI-1” is more advantageous in manufacturing
cost and exhibits about 300 MPa in strength without heat
treatment after superplastic forming. Typical applications
of the “ALNOVI-1” had been automotive and building
parts rather than aircraft components.
In 2001, Superform Aluminum in UK, a leading
company in superplastic forming, made a prototype
of landing lamp drum assembly for aircraft from the
“ALNOVI-1” sheet by high-temperature blow forming.
Airbus S.A.S., which has a 50 % share of the aircraft
manufacturing market in the world, was very interested in
the alloy sheet and appointed it as a candidate material.
Then the Fukaya Works and the “ALNOVI-1” acquired the
manufacturing factory and product approvals from Airbus
S.A.S.
Superplastic 5083 Aluminum Alloy Sheet “ALNOVI†-1”
　
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