UK Aluminium Industry Fact Sheet 4
Aluminium Castings
UK Aluminium Industry Fact Sheet 4 : Aluminium Castings
+44(0)121 601 6363 www.alfed.org.uk
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Diecastings are not easily welded or heat treated
Introduction
because of entrapped gases. Special techniques,
Aluminium castings have the advantage of being such as vacuum diecasting may reduce these
produced to near net shape, maximising the yield entrapped gases. Aluminium alloy diecastings are
and minimising further machining. They have not usually heat treated to improve mechanical
many end uses but the transport industry is the properties, but may be treated to improve
predominant market. dimensional and metallurgical stability.
By 1855 investment and sand castings were being Approximately 85% of aluminium alloy diecastings
produced from the newly discovered aluminium are produced in aluminium-silicon-copper alloys.
metal. By the turn of the century the cost of This family of alloys provides a good combination
refining aluminium had dropped so dramatically of strength and castability at reasonable cost.
that by the 1920’s aluminium was extensively being
Low Pressure Diecasting
alloyed with copper, magnesium, silicon and other
elements and made into foundry ingots to provide Molten metal is introduced into metal moulds at
the modern world with light, durable and versatile pressures up to 170 kPa. Thinner walls can be
aluminium castings. cast by low pressure diecasting than can be cast
by permanent mould castings. This process can
be highly automated.
The Process Gravity Diecasting, Permanent Mould Casting
One of the oldest methods of producing a shape Permanent mould castings are suited to high
in metal is that of casting. Casting involves the production runs, and are normally larger than
melting of the metal in a furnace or ladle and pressure diecastings, the maximum weight of these
pouring this molten metal into a hollow mould, castings is usually about 10 kilograms. Tooling
usually made in sand, or in another suitable costs are high, but less than those for pressure
material. A sand mould is used once and a metal diecasting. Destructible cores may be used and
mould, known as a chill mould or die, may be internal cavities can be fairly complex.
used many times, reproducing the same shape of
Permanent mould castings are gravity fed
casting.
with a relatively low pouring rate, either by
Aluminium may be cast by all of the processes hand or by robot. The metal mould produces
used for casting metal. These processes, in rapid solidification. Castings produced by
decreasing order of amount of aluminium cast the permanent mould method have excellent
in the UK are pressure diecasting, permanent mechanical properties, are generally sound and
mould casting, sand casting, plaster casting and hold good dimensional tolerances. Permanent
investment casting. mould castings may be heat treated, which
Pressure Diecasting further enhances their mechanical properties. For
maximum properties the full heat treatment cycle
The pressure diecasting processes consume of a solution treatment, followed by a quench, and
almost twice as many tonnes of aluminium alloys natural or artificial ageing is used.
as all other casting processes combined. These
processes are especially suited to the production Sand Casting
of large quantities of relatively small parts. Moulds are formed by ramming sand onto a
Aluminium diecast parts may weigh up to around 5 pattern. The pattern is removed leaving a cavity
kilograms. in the sand. Internal cavities for the casting may
High Pressure Diecasting be made with sand cores. Molten metal is poured
into the mould and after it has solidified the mould
High pressure diecastings are made by injecting is broken to remove the casting. Sand casting is a
molten aluminium alloy into a metal mould under versatile and low cost process using a wide range
substantial pressure. Rapid injection and rapid of alloy types. Sand castings do not have the
solidification under high pressure combine to dimensional accuracy of other casting processes
produce a dense, fine grained surface structure, and have a relatively poor surface finish. They
which results in excellent wear and fatigue have the advantage of flexibility of numbers of
properties. Diecastings maintain close tolerances castings produced, it may be very few or many.
and produce good surface finishes.
UK Aluminium Industry Fact Sheet 4 : Aluminium Castings
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Shell Mould Casting properties. In this age of energy conservation the
advantages of lightweight aluminium outweighs the
A mould is made of a resin-bonded sand, in the
initial cost of the material, particularly in transport
form of a shell from 10 – 20mm thick, much thinner
applications where light weight equals less fuel.
than the massive moulds used in sand casting.
During the working life of transport vehicles the
Shell mould castings produce finer surface finishes
total fuel consumption is lowered when the overall
than sand casting and give greater dimensional
weight of the vehicle is reduced by the use of
accuracy. Equipment and production costs are
aluminium castings rather than, for example, cast
relatively high and the size and complexity of the
iron. Over 70% of aluminium castings in Western
castings are limited.
Europe are used in transport applications.
Plaster Casting
General engineering products and processes utilise
In this process the moulds are made of plaster. the corrosion resistance, strength and versatility
The plaster slurry is poured around a pattern, of aluminium castings. In the home aluminium
the plaster is baked, and the pattern removed castings form parts used in cooking pots, washing
leaving a mould cavity. Plaster moulds have high machines, refrigerators, chairs and tables etc. In
reproducibility, permitting castings to be made with offices castings are used in furniture, computers
fine detail and close tolerances. The surface finish and other small lightweight high technology
of plaster casting is good. Although the costs for equipment. Together, these engineering, office and
basic equipment for plaster casting are low, the domestic applications account for up to 20% of
operating costs are high. aluminium castings used.
Investment Casting Architects design private houses or public
This process uses refractory moulds formed over buildings using aluminium casting alloys to
expendable wax or thermoplastic patterns. A enhance the appearance of these structures.
refractory slurry is invested around an arrangement Aluminium casting alloys can be anodised to
of patterns and the refractory is dried and the provide a very corrosion resistant surface with
pattern is melted out, leaving a cavity. The molten coloured finishes to complement any structure.
metal is then cast into the fired mould. Around 8% of aluminium castings are used in the
building and construction industry.
Investment casting produces components
that require almost no further machining. The
advantages of the process, to produce thin walls,
good tolerances and fine surface finishes, lend it to
the production of precision engineered parts.
Centrifugal Casting
The centrifugal casting method forces metal into
spinning multiple moulds arranged around a central
pouring sprue. Mould materials may be of steel,
baked sand, plaster, cast iron or graphite. Cores
may be used in these moulds.
There is a limitation on the shape and size of the
castings available by this method and the casting
cost is high, though the integrity of the castings
comes closer to that of wrought products and
equates well with permanent mould castings.
The Products
Without aluminium castings the world we live in
today would be very different. Aluminium castings
are found in most vehicles in use today from cars,
buses, trains, to ships, aircraft and spacecraft. The
wide variety of aluminium casting alloys available,
allows the selection of materials with good strength
and good corrosion resistance and other special
UK Aluminium Industry Fact Sheet 4 : Aluminium Castings
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The Structure of the
UK Industry
The United Kingdom uses around 140,000 tonnes
of aluminium foundry alloys for the production
of castings for the transport industries, general
engineering and electrical engineering industries,
in the buildings and construction industry, and for
domestic and office equipment.
British Standard BS EN 1706 provides information
on the chemical composition and mechanical
properties of the main aluminium casting alloys in
use today.
The United Kingdom’s foundry industry is made
up of major international companies as well as
small entrepreneurial foundries. Over the last few
decades the total number of foundries in the UK
has decreased although, as market niches are
found, small foundries continue to flourish.
Further information specific to casting is also
available via the Cast Metals Federation
http://www.castmetalsfederation.com/
casting01.asp
Further information about aluminium and
aluminium alloys, their production, fabrication
and end use can be
obtained from:
(1) European Aluminium Association in Brussels
www.eaa.net
(2) International Aluminium Institute in London
www.world-aluminium.org
UK Aluminium Industry Fact Sheet 4 : Aluminium Castings
