Bronze refers to a broad range of copper alloys,
usually with tin as the main additive, but sometimes with other
elements such as phosphorus, manganese, aluminum, or silicon. (See
table below.) It is strong and tough, and has myriad uses in industry.
It was particularly significant in antiquity, giving its name to
the Bronze Age.
The introduction of bronze was significant to
any civilization that encountered it. Tools, weapons, armor, and
various building materials like decorative tiles made of bronze
were harder and more durable than their stone and copper ("Chalcolithic")
predecessors. In early use, the natural impurity arsenic sometimes
created a superior natural alloy; this is termed arsenical bronze.
While copper and tin can naturally co-occur, the two ores are rarely
found together (although one ancient site in Thailand provides a
counterexample). Serious bronze work has therefore always involved
trade. (In fact, archaeologists suspect that a serious disruption
of the tin trade precipitated the transition to the Iron Age.) For
Europe, the major source for tin was Great Britain.
The earliest tin-alloy bronzes date to the late 4th millennium
BC in Susa (Iran) and some ancient sites in Luristan (Iran) and
Bronze was stronger than the era's iron; quality steels were not
available until thousands of years later. But the Bronze Age gave
way to the Iron Age, perhaps because the shipping of tin around
the Mediterranean (or from Great Britain) became more limited during
the major population migrations around 1200 – 1100 BC, which
dramatically limited supplies and raised prices. Bronze was still
used during the Iron Age, but for many purposes the weaker iron
was found to be sufficiently strong. As ironworking improved, iron
became both cheaper and stronger, eclipsing bronze in Europe by
the early to mid-Middle Ages.
When steel is excluded from the discussion, bronze is superior
to iron in nearly every application. While it develops a patina,
it does not oxidize. It is considerably less brittle than iron and
has a lower casting temperature. (Steel, of course, has properties
that bronze cannot compete with.)
Copper-based alloys have lower melting points than steel and are
more readily produced from their constituent metals. They are generally
about 10 percent heavier than steel, although alloys using aluminium
or silicon may be slightly less dense. Bronzes are softer and weaker
than steel, and more elastic, though bronze springs are less stiff
(and so store less energy) for the same bulk. Bronzes resist corrosion
(especially seawater corrosion) and metal fatigue better than steel.
Bronzes also conduct heat and electricity better than most steels.
The cost of copper-base alloys is generally higher than that of
steels but lower than that of nickel-base alloys.
Copper and its alloys have a huge variety of uses that reflect
their versatile physical, mechanical, and chemical properties. Some
common examples are the high electrical conductivity of pure copper,
the excellent deep-drawing qualities of cartridge case brass, the
low-friction properties of bearing bronze, the resonant qualities
of bell bronze, and the resistance to corrosion by sea water of
several bronze alloys.
In the twentieth century, silicon was introduced as the primary
alloying element, creating an alloy with wide application in industry
and the major form used in contemporary statuary. Aluminium is also
used for the structural metal Aluminium bronze.
Bronze is the most popular metal for top-quality bells and cymbals,
and, more recently, saxophones. Bronze is also widely used for cast
metal sculpture (see bronze sculpture). Common bronze alloys often
have the unusual and very desirable property of expanding slightly
just before they set, thus filling in the finest details of a mould.
Bronze also has very little metal-on-metal friction, which made
it invaluable for the building of cannon where iron cannonballs
would otherwise stick in the barrel. Bronze is still widely used
today for springs, bearings, bushings and similar fittings, and
is particularly common in the bearings of small electric motors.
Phosphor bronze is particularly suited to precision-grade bearings
and springs. Bronze can be found in the deep crevices of porcelain
Bronze is typically 60% copper and 40% tin. Alpha bronze consists
of the alpha solid solution of tin in copper. Alpha bronze alloys
of 4-5% tin are used to make coins, springs, turbines and blades.
Commercial bronze (otherwise known as brass) is 90% copper and
10% zinc, and contains no tin. It is stronger than copper and it
has equivalent ductility. It is used for screws and wires.
Classification of copper and its alloys
Classification of Copper and Its Alloys - Wrought / Extruded
Principal alloying element
Copper alloys, Brass
Copper nickel, Nickel silvers