When castings have been treated, the heat
more strength is required than that obtainable from
treatment and the composition of the casting are
2017 or 2024.
indicated by the letter T and an alloying number. An
Alloy 7178 is used where highest strength is
example of this is the sand casting alloy 355, which has
necessary. Alloy 7178 contains a small amount of
several different compositions and tempers and is
chromium as a stabilizing agent, as does alloy 7075.
designated by 355-T6, 355-T51, and A355-T51.
Nonheat-treatable alloys used in aircraft
Aluminum alloy castings are produced by one of
construction are 1100, 3003, and 5052. These alloys do
three basic methods--sand mold, permanent mold, and
not respond to any heat treatment other than a
die cast. In casting aluminum, in most cases, different
softening, annealing effect. They may be hardened only
types of alloys must be used for different types of
by cold-working.
castings. Sand castings and die castings require
Alloy 1100 is used where strength is not an
different types of alloys than those used in permanent
important factor, but where weight, economy, and
molds.
corrosion resistance are desirable. This alloy is used for
SHOP CHARACTERISTICS OF ALUMINUM
fuel tanks, fairings, oil tanks, and for the repair of wing
ALLOYS.--Aluminum is one of the most readily
tips and tanks.
workable of all the common commercial metals. It can
Alloy 3003 is similar to 1100 and is generally used
be fabricated readily into a variety of shapes by any
for the same purposes. It contains a small percentage of
conventional method; however, formability varies a
manganese and is stronger and harder than 1100, but
great deal with the alloy and temper.
retains enough work ability that it is usually preferred
In general, the aircraft manufacturers form the
over 1100 in most applications.
heat-treatable alloys in the -0 or -T4 condition before
Alloy 5052 is used for fuel lines, hydraulic lines,
they have reached their full strength. They are
fuel tanks, and wing tips. Substantially higher strength
subsequently heat-treated or aged to the maximum
without too much sacrifice of workability can be
strength (-T6) condition before installation in aircraft.
obtained in 5052. It is preferred over 1100 and 3003 in
By this combination of processes, the advantage of
many applications.
forming in a soft condition is obtained without
sacrificing the maximum obtainable strength/weight
Alclad is the name given to standard aluminum
ratio.
alloys that have been coated on both sides with a thin
layer of pure aluminum. Alclad has very good
Aluminum is one of the most readily weldable of
corrosion-resisting qualities and is used exclusively for
all metals. The nonheat-treatable alloys can be welded
exterior surfaces of aircraft. Alclad sheets are available
by all methods, and the heat-treatable alloys can be
in all tempers of 2014, 2017, 7075, and 7178.
successfully spot welded. The melting point for pure
aluminum is 1,216F, while various aluminum alloys
CASTING
ALLOYS.--Aluminum
casting
melt at slightly lower temperatures. Aluminum
alloys, like wrought alloys, are divided into two groups.
products do not show any color changes when heated,
In one group, the physical properties of the alloys are
even up to the melting point. Riveting is the most
determined by the elements added and cannot be
reliable method of joining stress-carrying parts of
changed after the metal is cast. In the other group, the
heat-treated aluminum alloy structures.
elements added make it possible to heat-treat the
casting to produce desired physical properties.
Titanium and Titanium Alloys
The casting alloys are identified by a letter
preceding the alloy number. This is exactly opposite
Titanium and titanium alloys are used chiefly for
from the case of wrought alloys, in which the letters
parts that require good corrosion resistance, moderate
follow the number. When a letter precedes a number, it
strength up to 600F, and lightweight.
indicates a slight variation in the composition of the
TYPES, CHARACTERISTICS, AND USES.--
original alloy. This variation in composition is made
Titanium alloys are being used in quantity for jet engine
simply to impart some desirable quality. In casting
compressor wheels, compressor blades, spacer rings,
alloy 214, for example, the addition of zinc, to increase
housing compartments, and airframe parts such as
its pouring qualities, is designated by the letter A in
engine pads, ducting, wing surfaces, fire walls, fuselage
front of the number, thus creating the designation
skin adjacent to the engine outlet, and armor plate.
A214.
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