aluminium in commercial vehicles - European Aluminium Association

148 EUROPEAN ALUMINIUM ASSOCIATION ALUMINIUM IN COMMERCIAL VEHICLES CHAPTER XI
There are 3 main prerequisites for
galvanic corrosion:
• 2 different metals with different
electrochemical potential
• presence of an electrolyte
• contact between the 2 metals
The electrolyte enables the flow
of ions between the 2 metals.
This can happen if the metals are
wetted by the electrolyte (e.g.
water containing salt) or
emerged in the electrolyte. In
commercial vehicles, this type of
corrosion can occur where steel
and aluminium parts are bolted,
riveted or screwed together and
where rainwater or road splash
water can come in contact with
the metal parts. (Figure XI.2)
To avoid direct contact between
the 2 metals and to prevent
entrapment of water, it is necessary
to work with insulating
material (such as neoprene or
other elastomers) between the
metals and to use sealing compounds
to close constructive
gaps. (Figure XI.3)
FIGURE XI.2
PRINCIPLE OF A GALVANIC CELL BUILT WITH ALUMINIUM
AS ANODE
Anode
(Aluminium)
Sleeve and
insulating
washers
®e-
Electron Flow
Electrolyte
2Al " 2Al 3+ +6e - 6H + +6e - " 3H 2 #
‰
‰
‰
Bolt
FIGURE XI.3
‰
‰
‰
®
PREVENTION OF GALVANIC CORROSION
Cathode
(e.g. copper)
Aluminium
Gasket ( PVC,
elastomer)
Other metal
(Steel…)