Some of the more common metals met in engineering will now be briefly described. Most metals are alloyed to combine the better qualities of the constituents and sometimes to obtain properties that none of them alone possesses. The various properties, composition and uses of some common engineering materials.
Material properties and uses as shown in the table.
Steel
Steel is an alloy of carbon and iron. Various other metals are alloyed to steel to improve the properties, reduce the heat treatment necessary and provide uniformity in large masses of the material. Manganese is added in amounts up to about 1.8% to improve mechanical properties.
Silicon is added in amounts varying from 0.5% to 3.5% to increase strength and hardness. Nickel, when added as 3 to 3.75% of the content, produces a finer-grained material with increased strength and erosion resistance. Chromium, when added, tends to increase grain size and cause hardness but improves resistance to erosion and corrosion.
Nickel and chromium added to steel as 8% and 18% respectively produce stainless steel. Molybdenum is added in small amounts to improve strength, particularly at high temperatures. Vanadium is added in small amounts to increase strength and resistance to fatigue. Tungsten added at between 12 and 18%, together with up to 5% chromium, produces high-speed steel.
Aluminium
Aluminium is a light material which has a good resistance to atmospheric corrosion. It is usually used as an alloy with small percentages of copper, magnesium, iron, manganese, zinc, chromium and titanium. It is also used as a minor alloying element with other metals. Suitable heat treatment can significantly improve the properties of the alloy.
Copper
Copper has good electrical conductivity and is much used in electrical equipment. It has a high corrosion resistance and also forms some important alloys, such as brasses and bronzes.
Zinc
Zinc has good resistance to atmospheric corrosion and is used as a coating for protecting steel: the process is called 'galvanising'. It is also used as a sacrificial anode material because of its position in the galvanic series. Some alloys are formed using zinc.
Tin
A ductile, malleable metal that is resistant to corrosion by air or water. It is used as a coating for steel and also in various alloys.
Titanium
A light, strong, corrosion-resistant metal which is used as the plate material in plate-type heat exchangers. It is also used as an alloying element in various special steels.
Brass
An alloy of copper and zinc usually a major proportion of copper, A small amount of arsenic may be added to prevent a form of corrosion known as 'dezincification' from occurring. Other alloying metals, such as aluminium, tin and manganese, may be added to improve the properties.
Bronze
An alloy of copper and tin with superior corrosion and wear resistance to brass. Other alloying additions, such as manganese, form manganese bronze or propeller brass. Additions of aluminium and zinc result in aluminium bronze and gunmetal respectively.
Cupro-nickel
An alloy of copper and nickel with 20 or 30% of nickel. Good strength properties combined with a resistance to corrosion by sea or ri¥er waters make this a popular alloy. Monel metal is a particular cupro-nickel alloy with small additions of iron, manganese, silicon and carbon.
White metal
Usually a tin-based alloy with amounts of lead, copper and antimony. It may also be a lead-based alloy with antimony. White metal has a low coefficient of friction and is used as a lining material for bearings.
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