fuel tanks, fairings, oil tanks, and for the repair of wing
tips and tanks.
Alloy 3003 is similar to 1100 and is generally used
for the same purposes. It contains a small percentage of
manganese and is stronger and harder than 1100, but
retains enough work ability that it is usually preferred
over 1100 in most applications.
Alloy 5052 is used for fuel lines, hydraulic lines,
fuel tanks, and wing tips. Substantially higher strength
without too much sacrifice of workability can be
obtained in 5052. It is preferred over 1100 and 3003 in
Alclad is the name given to standard aluminum
alloys that have been coated on both sides with a thin
layer of pure aluminum. Alclad has very good
corrosion-resisting qualities and is used exclusively for
exterior surfaces of aircraft. Alclad sheets are available
in all tempers of 2014, 2017, 7075, and 7178.
CASTING ALLOYS.Aluminum casting alloys,
like wrought alloys, are divided into two groups. In one
group, the physical properties of the alloys are
determined by the elements added and cannot be
changed after the metal is cast. In the other group, the
elements added make it possible to heat-treat the casting
to produce desired physical properties.
The casting alloys are identified by a letter pre-
ceding the alloy number. This is exactly opposite from
the case of wrought alloys, in which the letters follow
the number. When a letter precedes a number, it
indicates a slight variation in the composition of the
original alloy. This variation in composition is made
simply to impart some desirable quality. In casting alloy
214, for example, the addition of zinc, to increase its
pouring qualities, is designated by the letter A in front
of the number, thus creating the designation A214.
When castings have been treated, the heat treatment
and the composition of the casting are indicated by the
letter T and an alloying number. An example of this is
the sand casting alloy 355, which has several different
compositions and tempers and is designated by 355-T6,
355-T51, and A355-T51.
Aluminum alloy castings are produced by one of
three basic methods-sand mold, permanent mold, and
die cast. In casting aluminum, in most cases, different
types of alloys must be used for different types of
castings. Sand castings and die castings require different
types of alloys than those used in permanent molds.
SHOP CHARACTERISTICS OF ALUMINUM
ALLOYS.Aluminum is one of the most readily
workable of all the common commercial metals. It can
be fabricated readily into a variety of shapes by any
conventional method; however, formability varies a
great deal with the alloy and temper.
In general, the aircraft manufacturers form the
heat-treatable alloys in the -0 or -T4 condition before
they have reached their full strength. They are
subsequently heat-treated or aged to the maximum
strength (-T6) condition before installation in aircraft.
By this combination of processes, the advantage of
forming in a soft condition is obtained without
sacrificing the maximum obtainable strength/weight
Aluminum is one of the most readily weldable of all
metals. The nonheat-treatable alloys can be welded by
all methods, and the heat-treatable alloys can be
successfully spot welded. The melting point for pure
aluminum is 1,216°F, while various aluminum alloys
melt at slightly lower temperatures. Aluminum products
do not show any color changes when heated, even up to
the melting point. Riveting is the most reliable method
of joining stress-carrying parts of heat-treated
aluminum alloy structures.
Titanium and Titanium Alloys
Titanium and titanium alloys are used chiefly for
parts that require good corrosion resistance, moderate
strength up to 600°F, and lightweight.
TYPES, CHARACTERISTICS, AND USES.
Titanium alloys are being used in quantity for jet engine
compressor wheels, compressor blades, spacer rings,
housing compartments, and airframe parts such as
engine pads, ducting, wing surfaces, fire walls, fuselage
skin adjacent to the engine outlet, and armor plate.
In view of titaniums high melting temperature,
approximately 3,300°F, its high-temperature properties
are disappointing. The ultimate and yield strengths of
titanium drop fast above 800°F. In applications where
the declines might be tolerated, the absorption of oxygen
and nitrogen from the air at temperatures above 1,000°F
makes the metal so brittle on long exposure that it soon
becomes worthless. Titanium has some merit for
short-time exposure up to 2,000°F where strength is not
important, as in aircraft fire walls.
Sharp tools are essential in machining techniques
because titanium has a tendency to resist or back away
from the cutting edge of tools. It is readily welded, but
the tendency of the metal to absorb oxygen, nitrogen,
and hydrogen must never be ignored. Machine welding