In article ,
"Joe" wrote:

We use some decent flat head screws on our units and I've run into a strange
problem. When we tighten them into the aluminum housings, they hold a
galvanized plate in place. After about 10 minutes of being on there, they
are almost impossible to get off.

If you ignore basic chemistry you're going to suffer. Your problem
description lays it out - you're plating the screw in place, for all
intents and purposes, using the very nice battery formed by the
aluminum, steel and zinc. Whoever designed this should be sent back to
their high school chemistry teacher and forced to make an apology.

You could try silicone grease, or anti-seize, but it's not likely to
fully insulate the screw, so it will probably still fail. Change the
materials and the problem will be reduced (as you have seen with the
painted plate), or go away. Make the galvanized plate from aluminum, big
reduction in problem. Make the screw aluminum as well, problem gone (but
you'll need to be sure that the aluminum plate and the aluminum screws
are designed in sizes that will do the job, if that is possible.)

I've seen something similar inside a clothes-washing machine, and there
I'm pretty sure that the materials choice was "malice aforethought" in
making for planned obsolescence and non-repairability - the device held
in place by an aluminum nut was warranteed for a very long time, but
labor to replace it was not, and after a much shorter time than that
warrantee, the nut was well on it's way to being impossibly corroded
(the warrantee on the nut and the non-aluminum part it was screwed to
was much shorter, but you could not get the long-warranteed part off
once the short-warrantee parts had fused).

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