melts at the comparatively low temperature of 1,216F.
being used in the chrome-molybdenum steels; the
chromium content varies from 0.80 to 1.10 percent.
It is nonmagnetic, and is an excellent conductor of
Molybdenum raises the ultimate strength of steel
without affecting ductility or workability. Molybdenum
Commercially pure aluminum has a tensile
steels are tough, wear resistant, and harden throughout
strength of about 13,000 psi, but by rolling or other
from heat treatment. They are especially adaptable for
cold-working processes, its strength may be
welding, and for this reason are used principally for
approximately doubled. By alloying with other metals,
welded structural parts and assemblies. SAE 4130 is
together with the use of heat-treating processes, the
used for parts such as engine mounts, nuts, bolts, gear
tensile strength may be raised to as high as 96,000 psi,
structures, support brackets for accessories, and other
or to well within the strength range of structural steel.
structural parts.
Aluminum alloy material, although strong, is easily
The progress of jet propulsion in the field of naval
worked, for it is very malleable and ductile. It may be
aviation has been aided by the continuous research in
rolled into sheets as thin as 0.0017 inch or drawn into
high-temperature metallurgy. This research has brought
wire 0.004 inch in diameter. Most aluminum alloy sheet
forth alloys to withstand the high temperatures and
stock used in aircraft construction ranges from 0.016 to
velocities encountered in jet power units. These alloys
0.096 inch in thickness; however, some of the larger
are chemically similar to the previously mentioned
aircraft use sheet stock that may be as thick as 0.0356
steels, but may also contain cobalt, copper, and
inch.
columbium in varied amounts as alloying elements.
One disadvantage of aluminum alloy is the
NONFERROUS AIRCRAFT METALS
difficulty of making reliable soldered joints. Oxidation
of the surface of the heated metal prevents soft solder
The term nonferrous refers to all metals that have
from adhering to the material; therefore, to produce
elements other than iron as their principal constituent.
good joints of aluminum alloy, a riveting process is
This group includes aluminum, titanium, copper,
used. Some aluminum alloys are also successfully
magnesium, and their alloys; and in addition, such alloy
welded.
metals as Monel and Babbitt.
The various types of aluminum may be divided into
two classescasing alloys (those suitable for casting in
Aluminum and Aluminum Alloys
sand, permanent mold, and die castings) and the
wrought alloys (those that may be shaped by rolling,
Commercially pure aluminum is a white, lustrous
drawing, or forging). Of the two, the wrought alloys are
metal, light in weight and corrosion resistant.
the most widely used in aircraft construction, being
Aluminum combined with various percentages of other
used for stringers, bulkheads, skin, rivets, and extruded
metals (generally copper, manganese, magnesium, and
sections. Casting alloys are not extensively used in
chromium) form the alloys that are used in aircraft
aircraft.
construction. Aluminum alloys in which the principal
alloying ingredients are either manganese, magnesium,
WROUGHT ALLOYS.--Wrought alloys are
or chromium, or magnesium and silicon, show little
divided into two classes-nonheat treatable and heat
attack in corrosive environments. On the other hand,
treatable. In the nonheat-treatable class, strain
those alloys in which substantial percentages of copper
hardening (cold-working) is the only means of
are used are more susceptible to corrosive action. The
increasing the tensile strength. Heat-treatable alloys
total percentage of alloying elements is seldom more
may be hardened by heat treatment, by cold-working,
than 6 or 7 percent in the wrought aluminum alloys.
or by the application of both processes.
TYPES, CHARACTERISTICS, AND USES.--
Aluminum products are identified by a universally
Aluminum is one of the most widely used metals in
used designation system. Under this arrangement,
modern aircraft construction. It is vital to the aviation
wrought aluminum and wrought aluminum alloys are
industry because of its high strength/weight ratio, its
designated by a four-digit index system.
corrosion-resisting qualities, and its comparative ease
The first digit of the designation indicates the major
of fabrication. The outstanding characteristic of
alloying element or alloy group, as shown in table 2-2.
aluminum is its light weight. In color, aluminum
The 1xxx indicates aluminum of 99.0 percent or
resembles silver, although it possesses a characteristic
greater; 2xxx indicates an aluminum alloy in which
bluish tinge of its own. Commercially pure aluminum
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