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During the
twentieth century aluminum became an essential metal in the aircraft
industry. Beginning with the cylinder block of the engine that
powered the Wright brother's plane at Kitty Hawk in 1903, which
was a one-piece casting in an aluminum alloy containing 8% copper,
the use of aluminum has grown.
In 1907 aluminum was used in propeller blades. In 1908 aluminum
parts were used in control mechanisms of aircraft. Aluminum covers,
seats, cowlings, cast brackets and similar parts were common by
the beginning of the World War I. In 1916 a reconnaissance bomber
was developed that used aluminum in the working structure of the
airplane for the first time. The aircraft airframe is one of the
most demanding applications of aluminum and its alloys. The first
high-strength, heat treatable aluminum alloy, Duralumin, was employed
initially for the framework of rigid airships by Germany and the
Allies during World War I. Duralumin was an aluminum-copper-magnesium
alloy; it was originated in Germany and developed in the United
States as alloy 17S-T (2017-T4) and was utilized initially as
sheet and plate. Later, in 1931, its 40,000-psi yield strength
was surpassed by alloy 2024-T3 with yield strength of 50,000-psi.
Alloy 2024-T6, with 60,000-psi yield strength, was the predominant
alloy in aircraft forgings from 1928 to 1945. Alloy 2024-T4 with
anodic coating is standard for aluminum screws, bolts, and nuts
made to military specifications. Alloy 2020-T6 was introduced
in 1957 as an aluminum structural alloy with good strength properties
up to 350 ºF; it has a modulus of elasticity 8% higher, and a
density 3% lower, than 7075-T6. Alloy 2020-T6 has been employed
as the major structural material in the aircraft industry, and
is even being used in the structure of the Saturn S-II, which
is the second stage of the Saturn V. Supersonic aircraft, designed
to withstand aerodynamic heating to 250ºF for over 100 hr, generally
utilize the 2xxx series alloys in artificially aged tempers for
skin sheet. Table 5 contains the nominal
composition of common wrought aluminum 2xxx series alloys and
their product forms. Table 6 contains
the physical properties of wrought 2xxx series alloys. A comparison
of the corrosion and fabrication characteristics and typical applications
is contained in Table 7. Table
8 contains the mechanical properties of wrought 2xxx alloys
and Table 9 contains the chemical composition
limits of the 2xxx alloys.
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