aluminium in commercial vehicles - European Aluminium Association

150 EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER XI
2.2.4. Constructive measures
to prevent corrosion
Some general rules shall be
applied to prevent corrosion (in
most cases to prevent any kind of
water trap or areas where condensation
can occur):
• Constructive gaps should be
avoided or, if not possible, should
be sealed. (Figure XI.6)
FIGURE XI.6
Watertight seal
‰
FIGURE XI.8
Weld discontinuities
‰ ‰
• Water traps should be avoided.
Assemblies should be constructed
with the open side
downwards. (Figure XI.7)
• Weld discontinuities should,
also with regard to other issues
like stress, fatigue etc., be strictly
avoided. (Figure XI.8)
• Materials having different electrochemical
potential have to be
separated from each other by
coatings or insulating materials.
2.2.5. Filiform corrosion
Unsuitable solutions
Run of
Better solutions
Filiform corrosion (also known as
under-film corrosion) occurs
under paint or enamel layers. It
depends mostly on environmental
conditions and the quality of
the surface treatment prior to
painting. The corrosion filaments
FIGURE XI.7
Run of
have a worm-like appearance
and are readily visible. Filiform
corrosion does not attack the
metal surface, but affects the
surface appearance.
The mode of corrosion is quite
similar to pitting with the front of
the attack being supported by
moisture which penetrates the
surface layer and leads to oxygen
concentrated areas and by thus
acting as an anode. Filiform corrosion
is mainly an aesthetic effect,
but could lead in certain construction
parts to delaminating of the
surface layer system.
To prevent this type of corrosion it
is of vital importance to follow the
instructions of the paint supplier,
especially with regard to a proper
surface treatment under the use
of a suitable primer system.