Page 18 - Curriculum Visions Dynamic Book

Copper alloys: brass
An alloy is a mixture of metals. Copper forms alloys more easily than most other metals. Each of the alloying metals gives the alloy its own special properties. Some metals make the alloy stronger, others change its colour, make it easier to machine or make it even more resistant to corrosion or wear. The metals most often alloyed with copper are shown on the next few pages.
Brass
Brass is one of the most widely used alloys. It is mainly copper, alloyed with between 5 and 40% zinc. Brass is often used for corrosion-resistant decorative purposes such as door furniture. It is much harder and stronger than copper and it will machine well.
The most common mixture of brass contains 36% zinc and is known as common brass. The properties of brass can be altered significantly by adding small quantities of other elements. Those most commonly used are lead, tin, aluminium, manganese, iron, nickel, arsenic and silicon. For example, by adding up to
3% lead the machinability of brass can be improved significantly.
Copper-rich brasses have special uses, such as making the percussion caps of ammunition; those with between 10 and 20% zinc are called gilding metals and are used for decorative brasswork and jewellery. This form of brass will take an enamel well and is easy to braze.
As the amount of zinc is increased still further, the brass develops the property of being easily shaped when hot. This material is used to make inexpensive,
but complex engineering shapes that are easy to machine.
However, even higher proportions of zinc make the alloy more susceptible to corrosion when the brass is placed in water. To counteract this problem, arsenic is added to the alloy.
Tin can also be added to brass to improve its corrosion resistance, and tin-zinc-copper brasses, in which there is 1% tin, are known as admiralty brass because of their suitability for use on ships.
 Brass is usually made from about 64% copper and 36% zinc. Adjusting
the proportions produces very different properties; for example, the alloy becomes harder as more zinc is added. Other metals can be added to give additional qualities, as the diagram on the right illustrates.
Copper
Zinc
 A jug made of brass and copper.
Brass top and handle.
The tarnished surface has been cleaned using a solvent.
This part of the jug is made of copper.
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