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General
Aluminum Information
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To
Aluminum Alloys
information
Go
To
Aluminum Temper
information
What is an alloy?
An alloy is simply a mixture of metals melted together to form a new
metal with characteristics distinct from those metals from which it is
made.
What
is
an Aluminum
Alloy?
An Aluminum alloy is an alloy primarily of pure aluminum, mixed with
different alloying elements that give rise to an entire range of
materials, each of which is designed to maximize a particular
characteristic such as strength, ductility, formability, machinability,
or electrical conductivity.
Do
the
different alloys
have a different color or aspect?
No, they are aesthetically interchageable.
Is
it
necessary to
specify the alloy?
Only if there is some physical characteristic of the alloy that will
have some bearing on the success of the project (such as corrosion
resistence) is it necessary to specify the actual alloy. Generally, the
fabricator will purchase the material on the basis of shape or form,
and it will arrive with the most commonly available and least expensive
alloy present locally.
If there is any question of the integrity of the material in any way,
the designs must be approved by an engineer, but you will be able to
accept substitutions of alloys with confidence that the resulting
product will be aesthetically acceptable.
What
is
Temper?
This
is the
quality of metal that describes it’s ability to spring back after it is
flexed - in effect, the stiffness. It doesn’t have anything to do with
how hard the metal is. Soft temper means that when it is bent, it stays
bent, and it doesn’t take much force to do it. Hard temper means that
when it is bent, it springs back flat, and it takes a lot of force to
put a kink into it. There are several degrees of temper; Soft, 1/4
Hard, 1/2 Hard, 3/4 Hard, and Hard. All metals are subject to temper,
and it is a quality of the product that is imparted at the mill. It has
no impact on hardness, color, machinability or weldability. However,
bending (kinking) and heating to a high temperature can remove the
temper and soften the metal at that point. This is called annealing.
What
about Finishing?
Finishing aluminum is a little more complex than it
seems at first.
Polishing
It can be polished, with an abrasive finish like #4 satin
finish, or even a high polish, but the metal itself is comparatively
soft, so these finishes mar easily and they are not recommended without
applying a clear organic coating to protect them.
Lacquering
Aluminum is an extremely reactive metal. It combines
instantly on contact with air to form a thin film of aluminum oxide
which in turn is extremely un-reactive and protects the surface from
further corrosion. This film is not really visible, but it if the metal
is touched, it comes off on your hands as a black smudge. The metal
does not stain or visibly corrode (except in extreme chemical
envrionments like salt spray from winter street salt or exposure to
seawater) but this smudging is undesirable in most environments. Having
said that, there are many architectural environments in which bare
aluminum extruded shapes are used with acceptable results.
The best way for a fabricator keep the silvery look of the
parent metal is to abrade the surface with the abrasive finish you
require, then lacquer the piece with a clear organic finish. Be sure to
use an organic finish that is specifically designed for use with
aluminum - conventional finishes will either react with the metal, or
will not adhere correctly.
Anodizing
This was invented for aluminum (it also works with
titanium). It is a process of dipping the aluminum into a liquid
solution that contains chemicals that clear the metal surface of its
coating of aluminum oxide whereupon a dye is introduced into the
solution which can now penetrate the surface of the metal to some
depth. The process requires a high current to pass through the metal
during the process in order to fix the dye and seal the aluminum with a
hard surface, so it must be done in anodizing shops and cannot be
touched up on site. It produces an extremely durable tint to the metal,
the color of which can be specified (and there are scores available).
However, be aware that most of the anodizing colors available are meant
to be used in interiors and will fade in the sunlight. There is a broad
range of exterior colors available, but you must specify them as such.
Clear Anodizing
This is the finish that is most common on natural-colored
pre-finished aluminum sheet, available from many architectural metal
suppliers. It is simply a non-dyed version of the anodizing process
described above, and one of the most common methods to render large
aluminum surfaces wear-resistant and corrosion resistant.
Bronze Anodizing
This is the extremely common method for producing the
extremely durable dark “bronze” finish on architectural aluminum
extrusions used in window frames. The process is identical to
those above, and the color is light fast for exterior purposes. The
shade of bronze can be specified from extremely light to almost black.
Hard
Anodizing
The
same process, but not for color - it is a method for
creating an extremely hard surface to any aluminum material. This is
used for example for bolts, sheets that need abrasion resistance etc.,
or to minimize galvanic reaction between aluminum surfaces and other
metals. It is not really architecturally interesting, and somewhat
expensive, but has many uses in Industry. It is used in very expensive
cookware to impart a hard non-stick surface to pots and pans.
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Aluminum Temper
information
The
Alloys
Even
with
casual contact with Aluminum you will encounter alot of
aluminum alloys.They
are
described below.
Many
of the forms in which aluminum is regularly produced are available in
not just a single alloy, but a number of alloys. It is not always
necessary to specify the alloy in
specifying the material - the fabricator will acquire the appropriate
material by simply requesting from the supplier whatever form and
dimensions are required and the supplier will ship the most common
alloy in stock, unless directed to a particular alloy. But it is of
interest that the stock finish (or "mill finish", which is the surface
finish of the material as it comes from the manufacturer) of different
alloys is
sometimes different
between alloys (as seen
in the difference in mill finish between tread
plate, and brite
tread plate),
and the length in which the same product is available
will be different for different alloys (for example, the forms of
aluminum produced in the 6063 alloys
are generally available in 16 to 24 foot lengths, whereas the same
forms of aluminum produced in the 6061
alloys of generally in 12 foot lengths, and so on).
Alloy
Numbers
These numbers refer to a
specific chemical composition of the aluminum alloy - the "recipe" of
the metal. Pure aluminum is not a very useful product in any structural
work - aluminum products almost without exception are produced from
batches of pure aluminum mixed with a number of alloying elements that
have been carefully specified by metallurgists in order to maximize
particular characteristics of the finished metal. For example, an
aluminum alloy that is easily extruded, may be difficult to machine, or
an alloy that machines well, may be difficult to weld, etc. This is why
there are so may different products in so many different alloys.
The Alloys
Alloy 1100
A low
strength but very workable alloy with excellent
corrosion resistance. It is not heat treatable. It is easily welded,
however it is soft, and spalls when machined.
1100-O:
Annealed
(or "soft", bendable condition)
1100-H14:
Strain
hardened
Alloy 2011
A free
machining, heat treatable alloy, with fair corrosion resistance, but
not very easily welded.
2011-T3: Heat treated, cold worked and naturally aged
Alloy 2024
Heat treatable
with high strength, good machinability and fair corrosion resistance.
It welds very poorly.
2024-O: Annealed (or "soft",
bendable condition)
2024-T3: Heat treated, cold worked
and naturally aged
2024-T351: Heat treated, cold worked
and naturally aged
Alloy 3003
This alloy
is not heat treatable but welds very well and has
very good workability. Like alloy 1100 it is somewhat soft and
difficult to machine.
3003-H14: Strain hardened
3003-H22: Strain hardened,
partially annealed
Alloy 5005
Poor
machinability, good workability and welds very well.
It finishes very well, and offers excellent corrosion resistance.
5005-H34: Strain-hardened and
stabilized
Alloy 5052
Strong,
not heat treatable, easily welded, with excellent corrosion
characteristics.
5052-O: Annealed (or "soft",
bendable condition)
5052-H32: Strain-hardened and
stabilized
Alloy 5086
Very
strong, not heat treatable, with excellent corrosion resistance and
good weldability.
5086-H116: Strain-hardened only
5086-H32: Strain-hardened and
stabilized
5086-H34: Strain-hardened and
stabilized
Alloy 6061
Heat
treatable, easily welded, with very good corrosion
resistance and finishing characteristics. Very commonly used for
architectural products
6061-O: Annealed (or "soft",
bendable condition)
6061-T4: Heat treated and naturally
aged
6061-T6: Heat treated and
artificially aged
6061-T65: Heat treated and
artificially aged
6061-T6511: Heat treated and
artificially aged
Alloy 6063
This heat
treatable is specifically designed for extrusions, very popular for
architectural shapes.
6063-T52: Cooled from an elevated
temperature shaping process and artificially aged
Alloy 7050
High
strength, excellent corrosion resistence, heat treatable, and weldable,
but has poor workability.
7050-T7451: Heat treated, overaged
and strengthened
Alloy 7075
Heat
treatable, this alloy is the strongest and hardest
aluminum alloy. It has good machining characteristics but is not very
easliy welded nor is it very workable.
7075-O:
Annealed (or "soft",
bendable condition)
7075-T6: Heat treated and
artificially aged
7075-T651: Heat treated and
artificially aged
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information
Temper
TEMPER
Temper is a measure of a metal's
resistence to bending or kinking. It does not refer to how hard the
metal is. Low temper, such as H-1 (also referred to as "1/8 Hard"),
indicates a tendency to
bend or kink permanently when subjected to very little force. High
temper,such as H-8 or "Full Hard", indicates a tendency to spring back
upon bending.
TEMPER
LETTERS
The
letters that appear after each
alloy number refer to the "temper" of the alloy itself and are
independent of the alloy. This means that a single alloy can be
available in a variety of tempers and a variety of alloys can be
available in the same temper.
F temper (as fabricated tempers)
This letter indicates that there has been no effort to control the
temper of the material - you receive it "as is".
O
temper (annealed temper)
Annealing is a process of heating
up metal past a critical tempurature whereby the material is relieved
of the internal stresses from production or fabrication. It is the
lowest temper available (the most easily bent).
W
temper (solution heat treated temper)
This letter refers to metal that
has undergone a specific procedure to produce a temper for a particular
batch of metal in order to comply with some specific need of the
customer.
H
tempers (strain-hardened tempers)
This letter designates a process of stretching or compressing in order
to impart a particular temper.
H_1
1/8
hard
H_2
1/4
hard
H_3
3/8
hard
H_4
1/2
hard
H_5 5/8 hard
H_6
3/4
hard
H_7
7/8
hard
H_8
Full
hard
T
tempers (thermally treated tempers)
These tempers are imparted by heating, quenching, or cooling in a
controlled way.
T1
Cooled after being shaped to its final dimensions during a process
involving a lot of heat (such as extrusion), then naturally aged to a
stable condition.
T2
Cooled
after being shaped to its final dimensions during a process
involving a lot of heat (such as extrusion), then cold worked.
T3 Solution heat
treated, cold worked and naturally aged to a stable condition.
T4
Solution
heat treated and naturally aged to a stable condition
T5
Cooled after being shaped to its final dimensions during a process
involving a lot of heat (such as extrusion), then artificially aged. T5
is T1 that has been artificially aged.
T6
Solution
heat treated and artificially aged to a stable condition. T6
is T4 that has been artificially aged.
T7
Solution
heat treated and naturally aged past the point of a stable
condition. This process provides control of some special
characteristics.
T8
Solution
heat treated, cold worked and artificially aged. T8 is T3 that
has been artificially aged.
T9
Solution
heat treated, artificially aged and cold worked A stable
temper T9 is T6 that has been cold worked.
T10
Cooled
after being shaped to its final dimensions during a process
involving a lot of heat (such as extrusion), then cold worked and
artificially aged. T10 is T2 that has been artificially aged.
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