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Bronze


Roman statuette of bronze
from Swedish Iron Age,
found at Íland
()

Bronze is the traditional name for a broad range of alloys of copper, usually with zinc and tin but not limited to just those metal. First utilized during the Bronze Age, to which it gave its name, bronze was used to produce tools, weapons and armor which proved either more durable or harder than their stone and copper predecessors. During the bronze age, arsenic was often included in the bronze (mostly as an impurity), which made the alloy harder still.

Bronze was still used to a considerable extent during the iron age but for many purposes the weaker iron was sufficently strong to serve. The abundance of iron allowed it to usurp the title as reigning metal. As an example, Roman officers were equipped with bronze swords while foot soldiers had to make due with iron blades.

Bronze is the most popular metal for top quality bells and cymbals, and also for cast metal sculpturess. Common bronze alloys often have the unusual and very desirable property of expanding slightly just before it sets, thus filling the finest details of a mould.

Copper-based alloys have lower melting points than steels and are more readily produced from their constituent metals. They are comparable to steel in density, most copper alloys being only about 10% heavier, while those with a lot of aluminium or silicon may be slightly less dense than steel. Bronzes are softer and weaker than steel, and more elastic, though bronze springs are less stiff (lower 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 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 by several bronze alloys.

See also brass, a subset of the bronze alloys in which zinc is the principal additive, and cupronickel, an alloy used on ships.