5 Series E39 523i (M52TU) SAL
41 00 ...
Basic comments on handling aluminium components
In the following section, the main differences between aluminium and steel are itemised and notes on work safety are
provided.
1.0 Mounting
Special measures
Reason
Store aluminium components in dry situation, and
always store separately, or isolated from, steel
components.
In damp atmosphere and in contact with steel, contact
corrosion occurs.
Do not damage protective surface layer since this would
cause oxidation.
Tendency for contact corrosion and paint migration.
Extra work involved in painting.
Restricted storage life.
1.1 Properties of aluminium
Comparisons with steel
Effects
Aluminium parts are non-magnetic and by up to 50
%
lighter.
Aluminium components are easy to distinguish from
steel parts by using a magnet.
The electrical conductivity is almost 4 times higher.
All electrical welding operations require higher currents
and therefore more advanced equipment.
The elasticity module is only 1/3 as high.
Convertibility is limited in comparison with steel.
Elongation failure is approx. 50
%
slighter.
When the material is stretched, cold strengthening,
restriction of plate thickness and increased tendency to
crack result.
Heat conductivity is 3 times higher, expansion is 2 times
higher.
Heat dissipates more rapidly and the material expands
more markedly.
At temperatures of between 200
°
C and 250
°
C,
convertibility of the material is improved, but the original
properties of the material are altered at the same time
Strength is reduced, elongation characteristics are
improved.
Aluminium shows no thrust traces, the melting point is
650
°
C.
The temperature can only be checked on the basis of
paint discoloration, bulging of the surface and with the
help of thermocouple pins.
1.2 Formation of corrosion
Cause
Effects
Through contact with materials with no special coating,
e.g. copper, tin, nickel, iron and zinc, a plating (galvanic)
process can initiate when moisture is introduced to the
environment.
This plating process causes aluminium to be removed
from the joint. Holes appear (corrosion).
Spare parts and accessories approved by BMW AG for
aluminium manufacture (screws, washers, nuts, sealing
materials etc.) are all subjected to a special form of
surface treatment.
Damaged parts loose their protective coating.
Contact corrosion takes place.
Note:
RA Basic comments on handling aluminium components
BMW AG - TIS
14.02.2013 18:41
Issue status (12/2007) Valid only until next DVD is issued
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