Resistant Materials
Metals
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Learning objectives
Learning objectives
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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Where do metals come from?
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.
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Where do metals come from?
Pure metals like
copper form part of
the earth’s crust as
metal ore.
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.
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Extracting metals – smelting
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Extracting metals – electrolysis
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.
carbon anode
cathode lining
molten aluminium metal
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Ferrous and non-ferrous metals
Metals can be classified into three groups: ferrous metals,
non-ferrous metals and alloys.
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 nonferrous, and do not rust.
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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Market forms of metals
Metals are commercially available in a range of stock
shapes and sizes.
flat strip
round rod
round tube
square rod
hexagonal rod
octagonal rod
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square tube
sheet
angle
channel
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Key points
Key points
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.
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