Aluminum appears high in the electrochemical
series of elements and its position indicates that it should corrode very
easily. However, the formation of a tightly adhering oxide film offers
increased resistance under mild corrosive conditions. Most metals in contact
with aluminum form couples,which undergo galvanic corrosion attack. The alloys
of aluminum are subject to pitting, intergranular corrosion and intergranular
stress corrosion cracking.
Battery Electrolyte.
(1) Battery electrolyte used in lead acid
batteries is composed of 35% sulfuric acid and 65% water. When electrolyte is
spilled, it should be cleaned up immediately. A weak boric acid solution may be
applied to the spillage area followed by a thorough flushing with clean, cold
running water. If boric acid is not available, flush the area with clean, cold
water.
(2) If corrosion appears, use an approved repair
method to repair the structure.
(1) The
construction of piano type hinges forms moisture traps as well as the
dissimilar metal couple between the steel hinge pin and the aluminum hinge.
Solid film lubricants are often applied to reduce corrosion problems.
(2) Care and replacement of solid film
lubricants require special techniques peculiar to the particular
solid film being used. Good solid film
lubricants are lubricants conforming to Specification MILPRF- 81322.
(a) Solid film lubricants prevent galvanic
coupling on close tolerance fittings and reduce fretting corrosion. Surface
preparation is extremely important to the service or wear life of solid film
lubricants.
(b) Solid film lubricants are usually applied
over surfaces coated with other films, such as anodize and phosphate. They have
been successfully applied over organic coatings such as epoxy primers.
CAUTION: Solid film lubricants containing
graphite, either alone or in
mixture with any other lubricants, should not be
used since
graphite is cathodic to most metals and will
cause galvanic corrosion in the presence of electrolytes.
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