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Re: Aluminum Base Plate

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>
> Yes, corrosion is a major concern with the connection of aluminum and
> steel.

Although it need not be so.  There are standards for fasteners ideally
suited for such applications, but I can count on one hand (and have lots of
fingers left) the number of firms willing to pay a few extra dollars for
galvanically matched fasteners.  There are producers of aluminum and
aluminum-titanium alloy fasteners to ASTM standards.  B&G Manufacturing in
Hatfield, Pa is one example, Robbins Manufacturing in Fall River, Mass. is
another.

>  If the bolts are regular steel bolts, provide a dielectric
> material material such as a plastic sleeve and washer between the two to
> completely separate them.  For a handrail condition this may not be the
> best choice.

Provided the relaxation of fastener tension caused by creep of the plastic
is acceptable.  Also, depending upon the application, the increased
possibility of vibration-loosening due to the excess relaxation (and
possible falling out of the fasteners,) may need to be considered.

> The other options are to use stainless steel or galvanized bolts.

(passivated) Stainless steel fasteners would be one option, and are a
standard (ASTM F593) item available in the U.S.  Although, probably 90%+ of
the stainless fasteners used in the U.S. today are NOT passivated, as most
specifiers of such fasteners simply specify 'stainless' fasteners ---- which
merely means that the fasteners must contain at least 12% chromium.  Thus,
the common practice of merely specifying use of 'stainless' fasteners almost
guarantees that one will be supplied with Taiwan-made 'stainless' fasteners
that will produced from the cheapest material available (302HQ) and not be
passivated.   Thus, the carbides that remain in the surface of such
unpacivated S/S fasteners quickly corrode and the fasteners get a red-rust
finish in short order.

Zinc, on the other hand, is even less noble than the aluminum, and will
sacrifice itself very quickly (assuming moisture) to protect the base steel
of a standard carbon-steel fastener.  Whereas, fastener materials or
coatings that are slightly MORE noble than aluminum is preferred, as the
natural state of the surface of the exterior-use aluminum is oxide
anyway --- and no one seems to object to that finish.

IMO, the elegant solution is aluminum fasteners for aluminum connections.
The Industrial Fasteners Institute (IFI) in Cleveland Ohio can provide a
list of North American producers for the types of fasteners sought.  (216)
241-1482.

David Sharp
TurnaSure LLC


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