Page 24 - Curriculum Visions Dynamic Book

Copper
Zinc
(Above) Brass is one of the most widely used alloys. Brass is usually made from 64% copper and 36% zinc. The more zinc, the harder the alloy. Brass
is often used for corrosion-resistant decorative purposes such as door hardware. It is much
harder and stronger than copper and zinc, and it machines 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 takes an enamel well and is easy to glaze.
As the amount of zinc is increased even 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 amounts of zinc make the alloy more likely to corrode when the brass is put in water. To counteract this problem, arsenic is added to the alloy.
Tin can also be added to brass to improve its corrosion resistance. Tin-zinc-copper brasses in which there is 1% tin are known as admiralty brass because of their suitability for use on ships.
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be taken to keep oxygen away from the molten alloy. This has traditionally been done by allowing a slag of waste to float on the surface, although modern processes often do away with slag and mix the metals in a vacuum.
A base metal can be made stronger by alloying it with other metals. Indeed, the vast majority of metals used today are alloys of a number of metals. Stainless steel is a common example of a metal alloy