NON-FERROUS
METALS AND THEIR ALLOYS
The term "nonferrous" refers to all
metals which have elements other than iron as their base or principal
constituent. This group includes such metals as aluminum, titanium, copper, and
magnesium, as well as such alloyed metals as Monel
In structural as well as other use, non-ferrous
metal have some specific applications including in aircraft applications.
Copper: Copper is one of the thirty-eight `non-ferrous'
metals which are known to man. For engineering purposes, copper is one of the
most important of these. It is used as the basis for a wide range of brass and bronze
alloys. It is widely used for electrical conductors and for heat-exchangers
such as motor car radiators. Its main properties can be listed as:
Density 8900
kg/m3;
Melting point 1083 °C;
Tensile strength 232 MPa
Soft, very ductile,
relatively low tensile strength, second only to silver in conductivity, it is
easy to join by soldering and brazing, it is highly corrosion resistant.
The
properties of `pure' copper depend upon the degree of purity and the method of
refinement. Often traces of impurities are retained deliberately to enhance the
properties of copper for a particular application .
Four groups of copper alloys are: (a) the brass
alloys; (b) the tin bronze alloys; (c) the aluminium bronze alloys; (d) the
cupro-nickel alloys.
Monel: Monel,
the leading high-nickel alloy, combines the properties of high strength and
excellent corrosion resistance. This metal consists of 68 percent nickel, 29
percent copper, 0.2 percent iron, 1 percent manganese, and 1.8 percent of other
elements. It cannot be hardened by heat treatment. Monel, adaptable to casting
and hot- or cold-working, can be successfully welded. It has working properties
similar to those of steel. When forged and annealed, it has a tensile strength
of 80,000 p.s.i. This can be increased by cold-working to 125,000 p.s.i.,
sufficient for classification among the tough alloys. Monel has been
successfully used for gears and chains to operate retractable landing gears,
and for structural parts subject to corrosion. In aircraft, Monel is used for
parts demanding both strength and high resistance to corrosion (such as exhaust
manifolds and carburetor needle valves and sleeves).
K-Monel:
K-Monel is a nonferrous alloy containing mainly nickel, copper, and
aluminum. It is produced by adding a small amount of aluminum to the Monel
formula. It is corrosion resistant and capable of bed hardened by heat
treatment. K-Monel has been successfully used for gears, and structural members
in aircraft which are subjected to corrosive attacks. This alloy is nonmagnetic
at all temperatures. K-Monel sheet has been successfully welded by both
oxyacetylene and electric-arc welding.
Aluminium
and its alloys:
Aluminum
is one of the most widely used metals in modern aircraft construction. It is
vital to the aviation industry because of its high strength-to weight ratio and
its comparative ease of fabrication, The outstanding
characteristic of aluminum is its light weight. Aluminum melts at the comparatively
low temperature of 1,250° F. It is nonmagnetic. When pure in form, aluminum has
a tensile strength of about 13,000 p.s.i., but by rolling or after cold-working
processes its strength may be approximately doubled. By alloying with other
metals, or by using heat-treating processes, the tensile strength may be raised
to as high as 65,000 p.s.i. or to within the strength range of structural
steel.
The
various types of aluminum may be divided into two general classes: (1) The
casting alloys (those suitable for casting in sand, permanent mold, or die
castings), and (2) the wrought alloys (those which may be shaped by rolling,
drawing, or forging). Of these two, the wrought alloys are the most widely used
in aircraft construction, being used for stringers, bulkheads, skin, rivets,
and extruded sections.
Aluminum
casting alloys are divided into two basic groups. In one, the physical
properties of the alloys are determined by the alloying elements and cannot be
changed after the metal is cast. In the other, the alloying elements make it
possible to heat treat the casting to produce the desired physical properties.
Wrought aluminum and wrought aluminum alloys are divided
into two general classes, nonheat-treatable alloys and heat-treatable alloys.
Nonheat-treatable alloys are those in which the
mechanical properties are determined by the amount of cold-work introduced
after the final annealing operation. The mechanical properties obtained by cold
working are destroyed by any subsequent heating and cannot be restored except
by additional cold working, which is not always possible. The "full
hard" temper is produced by the maximum amount of cold-work that is
commercially practicable. Metal in the "as fabricated" condition is
produced from the ingot without any subsequent controlled amount of cold
working or thermal treatment. There is, consequently, a variable amount of
strain hardening, depending upon the thickness of the section.
For heat-treatable aluminum alloys the mechanical
properties are obtained by heat treating to a suitable temperature, holding at
that temperature long enough to allow the alloying constituent to enter into
solid solution, and then quenching to hold the constituent in solution. The
metal is left in a supersaturated, unstable state and is then age hardened
either by natural aging at room temperature or by artificial aging at some
elevated temperature.
Alclad Aluminum: The
terms "Alclad and Pureclad" are used to designate sheets that consist
of an aluminum alloy core coated with a layer of pure aluminum to a depth of
approximately 53/2 percent on each side. The pure aluminum coating affords a
dual protection for the core, preventing contact with any corrosive agents,
and protecting the core electrolytically by preventing any attack caused by
scratching or from other abrasions.
Titanium and Titanium Alloys
Titanium was discovered by an English priest named
Gregot. A crude separation of titanium ore was accomplished in 1825. In 1906 a
sufficient amount of pure titanium was isolated in metallic form to permit a
study. Following this study, in 1932, an extraction process was developed which
became the first commercial method for producing titanium. The United States
Bureau of Mines began making titanium sponge in 1946, and 4 years later the
melting process began.
The use
of titanium is widespread. It is used in many commercial enterprises and is in
constant demand for such items as pumps, screens, and other tools and fixtures
where corrosion attack is prevalent. In aircraft construction and repair,
titanium is used for fuselage skins, engine shrouds, firewalls, longerons,
frames, fittings, air ducts, and fasteners.
Titanium
is used for making compressor disks, spacer rings, compressor blades and vanes,
through bolts, turbine housings and liners, and miscellaneous hardward for
turbine engines.
Titanium
falls between aluminum and stainless steel in terms of elasticity, density, and
elevated temperature strength. It has a melting point of from 2,730° F. to
3,155° F., low thermal conductivity, and a low coefficient of expansion. It is
light, strong, and resistant to stress-corrosion cracking. Titanium is
approximately 60 percent heavier than aluminum and about 50 percent lighter
than stainless steel.
Because
of the high melting point of titanium, high-temperature properties are
disappointing. The ultimate yield strength of titanium drops rapidly above 800°
F. 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. However, titanium does have some merit for short-time exposure up to
3,000° F. where strength is not important. Aircraft firewalls. demand this
requirement.
Magnesium
and Magnesium Alloys
Magnesium, the world's lightest structural metal, is
a silvery-white material weighing only two-thirds as much as aluminum.
Magnesium does not possess sufficient strength in its pure state for structural
uses, but when alloyed with zinc, aluminum, and manganese it produces an alloy
having the highest strength-to-weight ratio of any of the commonly used metals.
Some of
today's aircraft require in excess of one-half ton of this metal for use in
hundreds of vital spots. Some wing panels are fabricated entirely from
magnesium alloys, weigh 18 percent less than standard aluminum panels, and have
flown hundreds of satisfactory hours. Among the aircraft parts that have been
made from magnesium with a substantial savings in weight are nosewheel doors,
flap cover skin, aileron cover skin, oil tanks, floorings, fuselage parts,
wingtips, engine nacelles, instrument panels, radio masts, hydraulic fluid
tanks, oxygen bottle cases, ducts, and seats.
Magnesium
alloys possess good casting characteristics. Their properties compare
favorably with those of cast aluminum. In forging, hydraulic presses are
ordinarily used, although, under certain conditions, forging can be
accomplished in mechanical presses or with drop hammers.
