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Resistant MaterialsMetals

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Learning objectives

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Lea

rnin

g o

bje

ctiv

es To know where metals come from and how they are obtained.

To understand the differences between, and properties of, ferrous and non-ferrous metals and alloys.

To understand how the properties of different metals make them suitable for different uses.

To know how the properties of metals can be altered by heating.

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Metals are part of the earth’s crust. Economic, chemical and technological problems have to be solved to obtain them.

How desirable a metal is often depends on how scarce it is.

Gold diggers dig up tonnes to obtain a few grams, whereas there is so much iron that materials technologists are only interested if they can obtain hundreds of kilograms from each tonne of ore.

Where do metals come from?

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Copper ore is mined, then washed to remove other minerals and unwanted materials.

It is heated in a furnace and the molten copper is run off.

This process is known as smelting.

Where do metals come from?

Pure metals like copper form part of the earth’s crust as metal ore.

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Extracting metals – smelting

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Aluminium is the most plentiful metal found in the earth’s crust, and is in high demand because it is both light and strong.

Aluminium is extracted from aluminium oxide (bauxite) by electrolysis. Electricity passes between the electrodes and pure aluminium forms at the cathode.

Extracting metals – electrolysis

molten aluminium metal

cathode lining

carbon anode

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Ferrous metals are metals which contain iron. They will corrode if unprotected. Ferrous metals will be attracted by a magnet.

Non-ferrous are metals which do not contain iron. Pure metals such as aluminium, copper, tin and lead are non-ferrous, and do not rust.

Ferrous and non-ferrous metals

Metals can be classified into three groups: ferrous metals, non-ferrous metals and alloys.

Alloys are metals which are a mixture of two or more metals, benefiting from the properties of both. For example, brass is an alloy of copper and zinc.

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Types of metals

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Examples of ferrous metals

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Non-ferrous metals

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Examples of alloys

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Random alloy generator

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Heat treatment – annealing

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Heat treatment – hardening steel

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Heat treatment – tempering

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Metals are commercially available in a range of stock shapes and sizes.

Market forms of metals

channel

angle

square tube

round tube

flat strip

sheet

round rod

square rod

hexagonal rod

octagonal rod

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Key points

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Key

po

ints

Metals are extracted from the earth’s crust. Iron ore is smelted to obtain iron, while aluminium is obtained by electrolysis.

Ferrous metals come from iron ore and include cast iron and steel. Non-ferrous metals include aluminium, copper and tin.

Alloys such as brass and stainless steel are formed from two or more metals and other elements.

Heating metals alters their properties. Annealing involves heating a metal and then allowing it to cool, which makes the metal more workable. Tempering steel makes it less brittle.