aluminium in commercial vehicles - European Aluminium Association

92 EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER VII
1. Introduction
The forming operations used in
the commercial vehicle industry
are many and various. The manufacturer
will cut, fold, roll and
bend semi-finished sheets and
extrusions to produce a vehicle
or an accessory.
These operations, some of which
such as cutting and drilling can
now be programmed and automated,
are carried out according
to rules which we have summarized
in this chapter. In certain
cases and in some countries they
are also standardized, and the
relevant standards are referred to
where they exist.
In any case, it is very important to
use equipments dedicated to aluminium.
Most aluminium alloys used in
commercial vehicles belong to
the family of aluminium-magnesium
alloys (5000 series) for rolled
products or to the aluminium-silicon-magnesium
family (6000
series) for extruded products.
1.1. 5000 series alloys
In soft conditions, 5000 series
alloys have excellent forming
properties as suggested by the
difference between proof stress
and ultimate tensile strength and
by the level of elongation1 .
As metals are hardened by
mechanical cold working, it may
be necessary to improve ductility
so as to continue forming by
machine or by hand. This is done
by annealing2 , a process that is
easy to accomplish either in a
furnace or with a welding torch,
using tallow as a temperature
indicator which turns a light
brown colour at 340 °C. Heat
indicator crayons or even a stick
pyrometer may also be used.
If necessary, inter-stage annealing
can be repeated between
shaping operations, however
there is one golden rule: only
anneal the metal if it becomes
difficult to work, in other words
when the work-hardening rate
is greater than or at least equal
to the so-called critical workhardening
rate.
1.2. 6000 series alloys
These are used mainly as extruded
sections. The main alloy elements
are magnesium and silicon.
These are heat treatable alloys
supplied in the T6 or T5 condition
and, less commonly, in the
T4 or T1 condition3 .
Generally speaking the shaping
properties of this family of alloys
in the fully heat-treated condition
are limited. Nevertheless
shaping should be performed
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. 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.