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variety of applications including pump housings,
transmission cases, cylinder blocks.
As previously mentioned, heat-treating improves the
strength of aluminum alloys through a process known as
"precipitation hardening." In simple terms, precipitation
hardening is a process that occurs during the heating and
cooling of an aluminum alloy in which minute particles or
"precipitates" are formed in the aluminum matrix. These
particles reduce slippage between "grains" which in turns
increases material hardness and strength.
The chemistry involved varies with each particular alloy.
However, in basic
terms, when an
aluminum alloy is
heated for a
certain amount of
time above its
" s o l u t i o n
temperature," the
alloying elements
dissolve uniformly
into the aluminum
matrix. Following a
quench (or rapid
cooling), the
alloying elements
will slowly fall out
of solution and
combine with each
other to form
evenly distributed
precipitates. This
step, known as
aging, occurs at room temperature, however, and alloy can
be artificially aged at an elevated temperature in order to
speed up the process.
Another method for increasing the strength of aluminum
alloys is by work hardening. Work hardening occurs during
forming processes including forging, stamping and tube
bending. During these forming processes, the alloy
undergoes plastic deformation and the metallic grains are
broken and become smaller. The tighter grain structure
prevents inter-granular slippage thereby increasing the
strength of the alloy.
Annealing is a process that imparts the "softest" or most
ductile condition to a heat-treatable aluminum alloy. For
annealing, the alloy is heated to above its solution
temperature and then slowly cooled to room temperature.
During the cooling processes, the alloying elements fall out
of solution and form large unevenly distributed crystals,
which do not effectively prevent granular slippage. The
result is a soft, low strength alloy condition. Burns
Stainless anneals all aluminum tubing prior to bending.
The temper designation system is used to specify the
condition, or temper, of a heat treatable alloy. The most
common designations include O (sometimes erroneously
referred to as TO), F, T4 and T6. O refers to soft or
annealed condition and is the preferred temper for forming
processes such as tube bending. F refers to the condition
of the material following a forming process during which
work hardening occurs, and is the official designation of
tubing bends. T4 designates that the alloy was solution
heat treated and
naturally aged. T6
is sometimes
referred to as fully
"heat treated" and
is the result of
solution heat
treating and
artificial aging.
Burns Stainless
carries only drawn
seamless 6061
aluminum tubing
for straight tubing
and bends. The
tubing specification
is ASTM B-210
and/or Federal
G e n e r a l
Specification WW-
T-700/6. This
tubing is manufactured by cold drawing a true seamless
extruded tube made from hollow extrusion ingot processed
by die and mandrel extrusion process. Straight 6061
aluminum tubing available from Burns Stainless is sold in
the T6 condition. It is important to note that welding will
effect the temper of a tube since it locally heats up the
metal. If the strength of a T6 temper is necessary for your
welded assembly, it is important that the assembly be heat
treated. It is also important to note that the aluminum
bends are annealed and through the bending process
achieve a certain level of work hardening. Again, if heat
treated properties are required, the assembly must be heat
treated.
Burns Stainless LLC 949.631.5120 Monday - Friday 7:30 am to 4:30 pm fax 949.631.3184 burnsstainless.com
Aluminum
Burns Stainless recommends extra care when polishing
aluminum in the O condition, because the softness of the
material tends to make it pick up and gouge if the polishing
medium is not kept extremely clean.
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