COPPER AND COPPER ALLOYS
The properties of copper that are most important are high electrical and thermal
conductivity, good corrosion resistance, machinability, strength, and ease of fabrication.
In addition, copper is nonmagnetic, has a pleasing color, can be welded, brazed, and
soldered, and is easily finished by plating or lacquering. Certain of these basic properties
may be improved by suitable alloying. Most of the copper that is used for electrical
conductors contains over 99.9 percent copper and is identified as electrolytic tough-pitch
copper (ETP) or oxygen-free high-conductivity copper (OFHC). Electrolytic tough-pitch
copper is also used for roofing, gutters, downspouts, automobile radiators and gaskets,
kettles, vats, pressure vessels, and distillery and other process equipment. Electrolytic
tough-pitch copper contains from 0.02 to 0.05 percent oxygen, which is combined with
copper as the compound cuprous oxide (Cu2O). As cast, copper oxide and copper form
an inter dendritic eutectic mixture. After working and annealing, the inter dendritic
network is destroyed, and the strength is improved. Oxygen-free copper is used in
electronic tubes or similar applications because it makes a perfect seal to glass.
The most important commercial copper alloys may be classified as follows:
I .Brasses-alloys of copper and zinc
a. Alpha brasses-alloys containing up to 36 percent zinc
1. Yellow alpha brasses 20 to 36 percent zinc
2. Red brasses 5 to 20 percent zinc
b. Alpha plus beta brasses 54 to 62 percent copper
II .Bronzes-up to 12 percent of alloying element
a. Tin bronzes .
b. Silicon bronzes
c. Aluminium bronzes
d. Beryllium bronzes
III. Cupronickels-alloys of copper and nickel
IV. Nickel silvers-alloys of copper, [nickel, and zinc]
General Brasses are essentially alloys of copper and zinc. Some of these alloys have
small amounts of other elements such as lead, tin or aluminum. Variations in composition
will result in desired color, strength, ductility, machinability, corrosion resistance, or a
combination of such properties. The solubility of zinc in the alpha () solid solution
increases from 32.5 percent at 1657°F to about 39 percent at 850°F. Since copper is. f.c.c.
(face-centered cubic), the solid solution is f.c.c. The beta () phase is a b.c.c. (bodycentered
cubic) electron compound and undergoes ordering, indicated by a dot-dash line,
in the region of 850 to 875°F. On cooling in this temperature range the b.c.c. ( phase,
with copper and zinc atoms randomly dispersed at lattice points, changes continuously to
the ordered structure which is still b.c.c. but with the copper atoms at the corners and
zinc atoms at the centers of the unit cubes. The ordering reaction is so rapid that it cannot
be retarded or prevented by quenching.
Alpha Brasses Alpha brasses containing up to 36 percent zinc possess relatively good
corrosion resistance and good working properties. The color of brasses varies according
to percentage of copper content from red for high-copper alloys to yellow at about 62
Yellow Alpha Brasses These contain 20 to 36 percent zinc, combine good strength with high
ductility and are therefore suited for drastic cold-working operations. It is common
practice to stress-relief anneal these brasses after severe cold working to prevent season
cracking. Season cracking or Stress corrosion cracking is due to the high residual
stresses left in the brass as a result of cold working.
These contain between 5 and 20 percent zinc. They generally have better corrosion
resistance than yellow brasses and are not susceptib1e to season cracking or
dezincification. The most common low zinc brasses are gilding metal (95Cu-5Zn).
Gilding metal (95Cu-5Zn) has higher strength than copper and is used for coins,
medals, tokens, fuse caps, primers, emblems, plaques, and as a base for articles to be
gold-plated or highly polished
Alpha Plus Beta Brasses
These contain from 54 to 62 percent copper. phase is more brittle than the
phase. Therefore, these alloys are more difficult to cold-work. At elevated
temperatures the phase becomes very plastic, and since most of these alloys may be
heated into the single-phase region, they have excellent hot-working properties.
In general, the term bronze was originally applied to the copper tin alloys. However, the
term is now used for any copper alloy, with the exception of copper-zinc alloy, that
contains up to approximately 12 percent of the principal alloying element.
Tin Bronzes: These are generally referred to as phosphor bronzes. Since phosphorus is
always present as a deoxidizer in casting. .The usual range of phosphorus content is in
between 0.01 and 0.5 percent, and of tin between 1 and 11 percent. The phosphor bronzes
are characterized by high strength, toughness, high corrosion resistance, low coefficient
of friction and freedom from season cracking. They are used extensively for diaphragms,
bellows, lock washers, cotter pins, bushings, clutch disks, and springs.
Zinc is sometimes used to replace part of the tin; the result is an improvement in
the casting properties and toughness with little effect on Wear resistance. Lead is often
added to tin bronze to improve machinability and. wear resistance. High-lead tin bronze
may contain as much as 25 percent lead. The leaded alloys are used for bushing and
bearings under moderate or light loads.
The solubility of beryllium in the a solid solution decreases from 2.1 percent at 1590°F
to less than 0.25 percent at room temperature. This change in solubility is always
indicative of age hardening possibilities. The optimum mechanical properties are
obtained in an alloy containing approximately 2percent beryllium. A typical heattreating
cycle for this alloy would be; solution-anneal at 1450°F, water-quench, coldwork,
and finally age at 600°F.
The maximum solubility of aluminum in the a solid solution is approximately 9.5 percent
at 1050°F. The phase undergoes a eutectoid reaction at 1050°F to form the ( + F2)
mixture. Most commercial aluminum bronzes contain between 4 and 11 percent
These are essentially terinary alloys of copper, nickel and zinc. The addition of nickel to
the copper- zinc alloy gives it a pleasing silver- blue white colour and good corrosion
resistance to food chemicals, water, and atmosphere. These alloys make excellent base
metals for plating with chromium, nickel, or silver. They are used for rivets, screws,table
flatware, Zippers, Costume jewelry, name plates and radio dails.
Aluminum and its alloys
The best-known characteristic of aluminum is its light weight, the density being about
one-third that of steel or copper alloys. Certain aluminum alloys have a better strength-toweight
ratio than that of high strength steels.
1. Aluminum has good malleability and formability, high corrosion resistance, and high
electrical and thermal conductivity. An ultra pure form of aluminum is used for
photographic reflectors to take advantage of its high light reflectivity and nontarnishing
2. Aluminum is nontoxic, nonmagnetic, and non-sparking. The nonmagnetic
characteristic makes aluminum useful for electrical shielding purposes such as bus-bar
housings or enclosures for other electrical equipment.
3. Although the electrical conductivity of electric-conductor (EC) grade aluminum is
about 62 percent that of copper, its light weight makes it more suitable as an electrical
conductor for many industrial applications.
4. Pure aluminum has a tensile strength of about 13,000 psi. However, substantial
increases in strength are obtained by cold working or alloying. Some alloys, properly
heat-treated, approach tensile strengths of 100,000 psi.
5. One of the most important characteristics of aluminum is its machinability and
workability. It can be cast by any known method, rolled to any desired thickness,
stamped, drawn, spun, hammered, forged, and extruded to almost any conceivable shape.
6.Commercially pure aluminum, 1100 alloy (99.0+ percent AI), is suitable for
applications where good formability or very good resistance to corrosion (or both) are
required and where high strength is. not necessary. It has been used extensively for
cooking utensils, various architectural components, food and chemical handling and
storage equipment; and welded assemblies.
Aluminum-Copper Alloys (2xxx Series):
The maximum solubility of Copper in aluminum is 5.65 percent at 1018°F, and the
solubility decreases to 0.45 percent at 5720 F. Therefore, alloys containing between 2:5
and 5 percent copper will respond to heat treatment by age hardening.
Types of Aluminium Alloys
• Aluminum-Manganese Alloy
• Aluminum-Silicon Alloys
• Aluminum-Magnesium Alloys
TITANIUM AND TITANIUM ALLOYS
Titanium metal has a close-packed hexagonal crystal structure, called alpha, at room
temperature. This structure transforms to body centered cubic beta at 16250F.
Commercially pure titanium is lower in strength, more corrosion-resistant, and less
expensive than titanium alloys. It is used for applications requiring high ductility for
fabrication but little strength, such as chemical process piping, valves and tanks, aircraft
firewalls, tailpipes, and compressor cases.
The addition of alloying elements to titanium will influence the alpha to beta
transformation temperature. It is common practice to refer to alloying elements as alpha
or beta stabilizers. An alpha stabilizer means that as solute is added, the alpha to beta
transformation temperature is raised.
Most of the alpha alloys contain some beta-stabilizing alloying elements. The
compositions of these alloys are balanced by high aluminum content so that the alloys
are essentially one-phase alpha. Coarse, plate like alpha in a Ti-5At-2.5Sn alloy after
hot working and annealing. The alpha alloys have two main attributes, weld ability and
retention of strength at high temperatures. The first results from the one phase
microstructure, the second from the presence of aluminum. Alloying elements in
solution strengthen the alpha-phase alloys, and aluminum is the most effective
strengthener of alpha alloys..
Alloys These contain enough beta-stabilizing elements to cause the beta
phase to persist down to room temperature and they are stronger than alpha alloys. beta-
:phase as strengthened by beta alloying additions in solution. is stronger than the alpha
phase. Aging at elevated temperature causes precipitation offline particles of alpha in
the volumes that were beta grains prior to quenching. This fine structure is stronger than
the coarse, annealed alpha-beta structure. In some cases, quenched titanium alloy
structures may be of an unstable form of alpha designated alpha prime and called