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AA CRYO Document Information:
Title
Aluminum Alloys for Cryogenic Applications
The Aluminum Association Inc.
Publication Date:
Jan 1, 1999
Scope:
INTRODUCTION
Cryogenics is the science of cold. Its name, appropriately, is derived
from the Greek word kryos,
which means "icy cold." A cryogenic process, therefore, utilizes low
temperatures to produce a
physical change in a liquid, gas or solid.
Except in research laboratories, cryogenics was a little used science
until about 35 years ago.
Processes utilizing extremely low temperatures, however, date back to
1908 when attempts to liquefy
helium gas first proved successful (1). Since then cryogenic processes
have been used to liquefy
other gases, notably nitrogen and oxygen, and to make certain
materials superconductive (2).
Cryogenic temperatures are also used to achieve super-conducting
capabilities and to achieve
specialized surgical techniques.
The means of achieving cryogenic conditions have been adequately
described in various technical
references (1,3) and lie beyond the scope of this work. This
publication deals principally with the
advantages of utilizing aluminum and aluminum alloys for cryogenic
equipment for the process
industries. Its purpose is to convey useful ideas to the designer and
user of cryogenic equipment
in this field, through illustration of typical successful equipment,
and to share the technical
data compiled from tests conducted by the aluminum industry to help
further the state of the art.
The field of cryogenics may be assumed to deal with temperatures below
about −100°C
(− 190°F). At these temperatures, many materials undergo
changes in their physical
structure which severely limit their usefulness in cryogenic
applications. Some metals, like many
steels for example, become extremely brittle.
Aluminum alloys, however, have been demonstrated (4) to have an
unusual ability to maintain their
ductility and resistance to shock loading at extremely low
temperatures down nearly to absolute
zero (−273°C, −459°F). As temperature decreases
below room temperature, their
tensile and yield strengths actually improve as the temperature
decreases, and ductility as
toughness of most alloys increase as well, as we will demonstrate in
this publication. Even at the
lowest test temperatures available, in liquid helium at
−273°C (−452°F),
strengths remain high and ductility and toughness remain well above
room temperature for most
classes of alloys. Consequently aluminum alloys offer distinct
advantages when used as materials of
construction for cryogenic equipment or for structures that will
experience cryogenic cold.
While the focus of this publication is on these relatively low
temperatures (−100°C to
−273°C), the data herein also serve to illustrate well why
aluminum and its alloys are
ideal candidates for structural applications in arctic environments,
and other situations where
temperatures ranging from below room temperature to −100°C
govern design conditions(5).
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