Corrosion handbook

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As a general rule of thumb, a fastener should always be made of the same or a
more noble metal than the part to be fastened, since it typically has the smaller
surface area, and failure of the fastener is usually critical.
Table 2 shows the impact of galvanic corrosion under atmospheric outdoor
conditions for various material combinations.
Fastener (small area)
Fastened part
(large area)
Electro-
galvanized
Duplex-coated
carbon steel
Hot-dip
galvanized
Stainless steel
Electrogalvanized
Hot dip galvanizing
Zn and ZM
Aluminum
Structural
or cast steel
Stainless steel
(CrNi or CrNiMo)
Tin
Copper
Brass
Table 2: Impact on lifetime of the fastener by galvanic (contact) corrosion
No impact on lifetime
Moderate impact on lifetime, technically acceptable in many cases
Strong impact on lifetime
In environments, that are considered non- or very low corrosive (i.e. dry indoor
applications), contact corrosion can generally be neglected and usually there are
little to no susceptible material combinations. In most outdoor applications with
combinations of materials one has always to consider the general guidelines and
limitations for certain materials. For example, even if the accelerating galvanic
effect can be neglected, as in the combination of Zn electroplated parts with
aluminum, in general the service life of such parts is quite short due to their low
coating thickness.
In the selection tables shown in section 5, galvanic corrosion is taken into
account by providing two different rows for the fastened part (divided into “steel”,
“aluminium” and “stainless steel”).