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cold as heating will considerably
reduce mechanical properties
(approx. 40 %).
More complex shaping of the
extrusions may be done in the T1
or T4 condition, before ageing to
full hardness in T5 or T6. In this
case it is beneficial to do the
forming within a short time window
of a few days after the solution
heat-treatment to T1 or T4,
1. Introduction
1. Please refer to EN 485-2.
2. For 5000 alloys with Mg content
above 3%, this must be done very carefully
to prevent sensitization to intergranular
corrosion. See also Chapter XI,
section 2.2.6.
3. Please refer to Chapter V section 5,
for an explanation of these tempers.
92
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VII FABRICATION 92 | 93
i.e. before that the material gets
hardened by cold-ageing.
If very extensive shaping is to be
done, it is possible to do this in a
time-span of a few minutes after
the treatment to T1 or T4.
1.3. 7000 series alloys
These extrusions are used in
some high-strength applications
within transportation, automotive
and sports equipment. The
main alloy elements are zinc and
magnesium.
The extrusions are used in the T5,
T6 or a T7 over-aged condition.
The shaping may take place in
the T1 or T4 condition, before
the material is artificially aged.
More complex forming is done in
the T4 condition, shortly after
the solution heat treatment,
before ageing to T6 or T7.
Before using 7000 alloys, prior
consultation with the supplier is
strongly recommended.
The general methods of aluminium
alloy fabrication and the machines
used are not very different from
those used for steel. Aluminium
alloys are easy to fabricate.
However, their relative softness
must be taken into account and
it is essential to use special tools
to avoid damaging aluminium
surfaces. Risks of contamination
from traces of ferrous and
cuprous metals must also be
avoided as these can cause localized
corrosion. It is essential to
work in an environment where
such risks are minimized.
2.1. Storage
Aluminium sheets are classified
by family of alloy and stored
upright when more than 0.8 mm
thick (Figure VII.1). Thin sheets
(less than 0.8 mm) should be
stored flat.
Aluminium sheets should never
be placed directly on the ground,
even if concreted, and should be
kept away from splash water,
condensation and hostile environments.
They are best stored under cover
in a ventilated area and separated
by timber blocks to prevent
condensation stains.
2. Fabrication
of products from plate
STORAGE
FIGURE VII.1
93
EUROPEAN ALUMINIUM ASSOCIATION
2.2. Marking out
Scribing tools should not be
used, since any tracing marks
which might be left on the finished
component can become
crack starters under high loads.
This precaution is not necessary
where the scribe indicates a cutting
line.
As a general rule it is advisable to
trace using a hard pencil (e.g.
5H) which is easier to see and
easy to erase in case of error.
2.3. Cutting to shape
Plate or crocodile shears can be
used to make straight cuts. The
rating of the shear should be
more or less the same as for cutting
non-alloyed steel with low
carbon content and the same
thickness.
Sawing is a common cutting
process which is very economical
for aluminium alloys.
2.3.1. Band saw
The most common type of saw is
the band saw. This can be a simple
timber band saw but with a
blade of specially designed profile
to break and dislodge the
aluminium chips from between
the saw teeth.
This is achieved by the alternation
or pitch of the teeth and by
the clearance angle defined
Figure VII.2.
2.3.2. Circular saw
As with the band saw, the saw
pitch varies with the thickness or
section to be sawn but the process
of cutting, which is a function of
the machine characteristics, makes
it similar to milling (Figure VII.3).
With the band saw and circular
saw, the cutting speeds for
3000, 5000 and 6000 series
alloys are as follows:
• HSS blade: 600 m/min to 1000
m/min.
• Carbide blade: 800 m/min to
1500 m/min.
The portable milling saw is a tool
that can be used to straight cut
products up to 20 mm thick and
with good rates of advance.
It may be preferable to use a jigsaw
for thicknesses of 6 mm or
less. The jigsaw is highly
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