Page 23 - Curriculum Visions Dynamic Book

a knife. Heating iron or steel in a fire and then beating it mixes some carbon atoms (from the fuel) into the surface. A final heating without beating allows some of the softness to return. This is the process called tempering.
Another way to harden a metal is to work it while it is cold, for example, by passing it under a hammer (a process called forging) or through rollers (called rolling). These actions break up the layers of atoms and so prevent them from easily moving past one another.
KEY
Corrosion resistance
Wear resistance Machinability
Colour Strength
Al
Fe
Alloying
An alternative to physically moving the atoms into new patterns is
Zn Fe
to use mixtures of several metals. Most metals
mix easily when they have been melted. A mixture of metals
is called an alloy.
The metal that
makes up the
majority of an
alloy is called a
base metal. The
most common
base metals are Al iron, aluminium,
and copper. When an
alloying metal is
added, the atoms of
the alloying metal fit in
among the atoms of the
base metal and keep layers of
the base metal from slipping past
one another as easily. That is why the alloy is harder than the base metal.
Sn
Cu
Zr Cr
As
Ni
Si Ag
Ni
Mn
P
Si
Ni
Zn
Sn
Cd
Alloys are made by melting each of the metals and then mixing them in the proportions needed. Because metals oxidise much more easily when they are hot, care has to
(Above) This diagram shows the effects on copper of alloying it with other metals.
Zn
S
Pb
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