On Thu, 30 Apr 2009 00:41:21 -0400, "Dr. Barry L. Ornitz"
wrote:

"Michael Coslo" wrote in message
...
Then I guess it's a race between rust and galvanic corrosion?

The aluminum will prevent the steel from rusting at the expense of its
own corrosion.

Use synthetic scrubbies (3M ScotchBrite) instead.

Bronze or stainless steel wool might be a good material to use.
Boaters use it on aluminum.

Because boaters do not understand corrosion and electrochemical
reactions, they often choose poor materials. Brass is more cathodic than
steel, the 400 grade ferritic and martensitic stainless steels are more
cathodic than brass, the 300 grade austenitic stainless steels are more
cathodic than the 400 grades, and precipitation hardenable stainless
steels like 17-4PH lie between 300 and 400 grade stainless in being
cathodic. The more anodic a material is, the faster it corrodes. The
more cathodic (or noble) a metal is, the slower it corrodes.

As I said earlier, I have several good, introductory articles on
corrosion and galvanic series that I can send upon request by email.

As I discovered when I did a restoration and rebuild on my sailboat
about 10 years ago. All of the original interior woodwork fittings on
the boat were held in place by decorative brass screws. As the boat
was built in 1971, but the time I got to it in the late 90's all the
brass screws had "zincified" (probably not the correct term to a
metallurgist, but one that appears in boating literature). This
results in the screws having a pinkish color and they become
very brittle. Any attempt at removing them resulted in the head
breaking off or the Philips cross slot stripping out. I had to remove
all of these with a screw removal tool. They were all replaced with
coated SS screws, the coating for decorative purposes.

At least among sailboaters, who for some reason appear to be more
technically savvy than power boaters, galvanic corrosion is pretty
well understood at least at a layman's level. Most boat repair books
mention this and include the galvanic series and the relative
"nobility" of various metals and alloys. Those of us who sail in salt
water are also well aware of the need to put sacrificial zincs on our
boats to prevent damage to other metal parts. Replacing these is a
regular part of our annual maintenance.

A very high percentage of sailboaters are also hams, far beyond our
normal density in the overall population.


Jon W3JT