On Mon, 24 Dec 2007 20:50:03 -0500, WaIIy quoted this:

...stainless steel and aluminum do
have a habit of becoming inextricably linked when mated in the marine
environment. The interaction is, however, considered a necessary evil
and not necessarily prohibited as is the use of copper alloys such as
bronze or brass with aluminum. The reaction that takes place between
aluminum and stainless steel is galvanic in nature; the aluminum being
less noble than stainless steel corrodes much like a zinc anode corrodes
in order to protect a nobler propeller or shaft.

The second half of this equation, however, is the byproduct of yet
another type of corrosion called poultice, aluminum oxide, the white
powdery material that is often seen on aluminum that is actively
corroding. Both are undesirable and the latter can cause stainless
fasteners to become seized within aluminum threads. The good news is
this phenomenon is easily avoidable. An essential component in the
galvanic and poultice corrosion equation is moisture, if it can be
excluded then neither will occur with much vigor. Here’s where your
yellow paste, probably zinc chromate, comes in. Applied to the
fastener’s threads it effectively excludes moisture (and air) and while
other proprietary, and often expensive, products are available for this
purpose, others will also work well, including LocTite (I’d use one of
the lower strength varieties such as 242, which is blue) and ordinary
polyurethane sealants such as those offered by Sika and 3M.

As long as what ever you use excludes moisture from the thread
interface, and it’s compatible with the metal substrate, then the
problem should not occur. I’ve successfully used this approach for
years when installing hardware on aluminum masts. Beware, many
anti-seize compounds contain graphite or copper, both of which would be
galvanically incompatible with aluminum (graphite is among the most
noble materials, so it tends to make any metal with which it makes
contact corrode), while some silicone-based sealants utilize an acidic
base, which can me harmful to aluminum.

Steve C. D’Antonio, Technical Editor
http://www.passagemaker.com/UserBlog...0/Default.aspx


Nice note.
I am guessing Wally was quoting Steve wholesale??

Brian W