Steel Aluminum Galvanic Corrosion
The likelihood and severity of galvanic corrosion depends on several factors like:
The corrosion potentials of the steels are noble than the corrosion potentials of aluminum, as can be seen in the galvanic series of metals in seawater below.
This mean that there will be no corrosion on steel when placed in contact with aluminum while aluminum will corrodes.
Permissible couples to avoid galvanic corrosion of aluminium when placed in contact with more noble materials are limited to a potential difference of 0.10 V on the galvanic series.
Anodic current density and hence corrosion rates can be reduced by increasing the anode-to-cathode surface area ratio; if a small area of stainless steel is placed in contact with a big area of aluminum the rate of aluminum galvanic corrosion is low due to the effect of the relative areas.
It is possible to avoid steel aluminum galvanic corrosion isolating the two material by means of an electrical insulating material, like rubber.
Steel aluminium galvanic corrosion is used to protect steel structure in seawater, like offshore jackets, placing galvanic anodes made of aluminium alloys on the submerged part of the structures. The galvanic anodes corrode and protect steel.
This type of corrosion control method is called “cathodic protection” and is used also to protect buried steel structures, pipelines or tanks.
This table is taken from: Atlas Steel Technical Note No. 7 "Galvanic Corrosion"
source: Material Deterioration Prevention Control Guide for Army Material - part one MIL-HDBK-735
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