3
Design and Technology 8552
Metals and alloys
Unit 3Materials and their working properties
Objectives
• Know the primary sources of materials for
producing metals and alloys
• Be able to recognise and characterise different
types of metals and alloys
• Understand how the physical and working
properties of a range of metals and alloys affect
their performance
Metals and alloys
Unit 3 Materials and their working properties
Starter
• Padlocks are traditionally attached to bridges or
landmarks to signify enduring love and friendship
• How might these padlocks age over time?
Metals and alloys
Unit 3 Materials and their working properties
Metal
• Metals have been essential in the development
of civilisation
• The word ‘metal’ comes from the ancient Greek word ‘metallum’
which means to mine, excavate or extract from the ground
• Prehistoric man used metals to make tools and weapons
• Which common metals would you find in a domestic kitchen?
Metals and alloys
Unit 3 Materials and their working properties
Ore
• The Earth’s crust contains many types of rock
• Metallic minerals are found naturally in rock or ore
• Ore is obtained by mining, and the metals contained
within it are extracted
• The method used for extraction depends on the
metal’s reactivity with air, water or acids
• The more reactive the metal, the more expensive it is
to extract
Metals and alloys
Unit 3 Materials and their working properties
Finding metal
• Some naturally occurring metals are found as lumps
in the rock and don’t require a chemical extraction
• Why is gold expensive in comparison to aluminium?
Metals and alloys
Unit 3 Materials and their working properties
Extraction processes
• Some metals exist as oxides
• Metals such as copper, iron and zinc are oxides
• Oxides are heated with carbon to extract the metal
• Electrolysis is used to extract metals
such as aluminium
• Are metals a
renewable resource?
• How we man reduce the
speed at which we will run
out of natural resources?
Metals and alloys
Unit 3 Materials and their working properties
Classification of metals
• Metals are divided into two main categories
• Ferrous metals and Non-ferrous metals
• Ferrous metals contain the element
iron, also known as ferrite (Fe)
• Non-ferrous metals don’t
contain iron
• You also need to know about ferrous
alloys and non-ferrous alloys
• What is an alloy?
Metals and alloys
Unit 3 Materials and their working properties
Iron ore
• Iron can be extracted from iron ore by using a blast
furnace and the process of smelting
• Smelting extracts common industrial
metals such as iron
• The extreme heat draws off the metals in
a liquid state called ‘hot metal’
• The impurities are removed and the iron
mixed or ‘alloyed’ with a small amount
of carbon to create steel
• The amount of carbon added affects
the strength of the steel
Metals and alloys
Unit 3 Materials and their working properties
Ferrous metals
• Ferrous metals contain iron and may rust
• Iron and steel can corrode – this is known as rust
• Rust is a compound called iron oxide and is formed when iron
and oxygen react in the presence of moisture or water
• Most ferrous metals are magnetic
• Name two types of protective layer
that could be added to metal
to help prevent rust
Metals and alloys
Unit 3 Materials and their working properties
Ductility and malleability
• Ductile metals
• Will stretch without being damaged
• Can be drawn or stretched out into long wires
• Copper is highly ductile and can be
drawn into long, thin wires
• Malleable metals
• Can be hammered into a shape
without breaking
• Can be rolled or pressed into sheets
• Will deform under compression
Metals and alloys
Unit 3 Materials and their working properties
Hard or tough?
• Hardness is the ability to
withstand abrasion
• A very hard metal is likely to crack
or shatter upon impact or force
• Cast iron would be described as
hard but brittle
• Toughness is the ability to
absorb energy and not fracture
• A tough material may scratch
easily on the surface but can
withstand large impacts
Metals and alloys
Unit 3 Materials and their working properties
Tensile strength
• Tensile strength is the amount of
tensile stress (stretching) a
material can withstand before
breaking or failing
• Testing for tensile strength is crucial
in industry
• Suggest two uses for metals with
high tensile strength
• Why is destructive testing
so important?
Metals and alloys
Unit 3 Materials and their working properties
Hard as nails
• Steel is a ferrous metal available in different forms
• Stainless steel has a high resistance to corrosion, staining
and friction, suitable for a wide range of applications
• High speed steel is formed by alloying elements
of carbon, tungsten, vanadium, cobalt,
chromium or molybdenum
• Name three everyday
applications for
stainless steel
Metals and alloys
Unit 3 Materials and their working properties
Material selection
• Ferrous metals have varying properties making them
suitable for different uses
• Low carbon steel is tough, ductile and easily welded
• High carbon steel is very hard wearing, but less ductile
or malleable
• Cast iron is hard and easily cast into shapes, but brittle
• Suggest two items made from each of these metals?
Metals and alloys
Unit 3 Materials and their working properties
Non-ferrous properties
• Non-ferrous metals don’t contain iron
• They are often more expensive than ferrous metals
owing to their desirable properties which include:
• Lightweight
• Good conductivity
• Ductile and malleable
• Resistant to corrosion
• The process of galvanising adds a
protective coat of zinc to iron and
steel to help prevent rusting
Metals and alloys
Unit 3 Materials and their working properties
Electrical conductivity
• Conductivity is how easily an electrical current can
flow through a metal
• As copper is such an efficient conductor, it’s most common
use is in electrical cabling
Metals and alloys
Unit 3 Materials and their working properties
Thermal conductivity
• Thermal conductivity measures the ability of a metal
to conduct heat
• Copper is also an excellent conductor of heat and is
commonly used in air conditioning, water tanks, saucepan
bases and water heaters
• In what environment would it be more appropriate to use
steel than copper?
Metals and alloys
Unit 3 Materials and their working properties
Non-ferrous metals
• Aluminium, copper, tin and zinc are all
non-ferrous metals
• List a selection of household items that
may be made from non-ferrous metals
• In what way do non-ferrous metals
differ from ferrous metals?
Metals and alloys
Unit 3 Materials and their working properties
Tin
• Tin is commonly associated with a ‘tin can’
• In fact, the can is steel, with a thin coating of tin,
‘tin plating’, which helps preserve the contents
• Tin is soft, ductile and malleable
• Alloys of tin include pewter, copper, bronze
and soft-solder
• What other non-ferrous metal is
associated with the production
of cans?
Metals and alloys
Unit 3 Materials and their working properties
Alloys
• Metals are rarely used in their pure form. Alloys are
made by combining two or more elements
• This helps improve the working properties
and appearance
• Brass and steel are common alloys
• Stainless steel is made by combining iron, with
a small amount of carbon and chromium
• This protects the alloy from oxygen –
what will this help prevent?
• What are the advantages of
creating alloys?
Metals and alloys
Unit 3 Materials and their working properties
Worksheet
• Complete Tasks 1 and 2 on your Worksheet
Metals and alloys
Unit 3 Materials and their working properties
Uses of metals
• Given the various properties of metals, list as many
metals as you can that are used to make this bicycle
Metals and alloys
Unit 3 Materials and their working properties
Uses of metals Answers
• A vast range of metals may be used to create
a single product
Frame could be low carbon
steel, aluminium alloy
Aluminium or stainless
steel shopping basket
Aluminium
mud guards
Steel wire in the
tyres, zinc in
the manufacture
of rubber
Twisted strands of steel in the
brake cables, aluminium and
steel in the brake handle
Aluminium alloy
in the pedals
Steel or aluminium
spokes
Fused or welded joints
are usually brass
(a copper / zinc alloy)
High speed steel
in ball bearings,
pedals, wheel
hubs, headstocks,
cranks
Steel springs
Chain made of
carbon steel
Metals and alloys
Unit 3 Materials and their working properties
Worksheet
• Complete Task 3 of the Worksheet
Metals and alloys
Unit 3 Materials and their working properties
Everything but tin?
• Tin probably didn’t feature in your bicycle list
• Working with recycled cans is a technique called Kapoaka
• Used in Madagascar by small scale workshops, crafters
make decorative objects and toys for sale
• It has created sustainable employment and helps the poorest
in Africa attain a living from the profits
Metals and alloys
Unit 3 Materials and their working properties
Oxidisation
• Non ferrous metals such as copper and
bronze, don’t rust, but may oxidise
• Oxidising can be caused by corrosion
or weather exposure over a period of time
• A thin layer of tarnish that appears on the
surface of the metal is known as a patina
• A natural patina occurring on copper
is called Verdigris
• The green hue can be manufactured by
adding acetic acid to copper and is often
used in architecture for aesthetic purposes
Metals and alloys
Unit 3 Materials and their working properties
Plenary
• What are metals commonly extracted from?
• Name three ferrous metals
• Which metal would you select for high conductivity?
• Explain the term ‘alloy’
• Describe the difference between hard and tough
• How can you protect metal from oxidisation?
• Justify one metal used to manufacture cutting tools
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Metals and alloys
Unit 3 Materials and their working properties