Re: RE: [PSUBS-MAILIST] protecting aluminum parts

[drewacard@charter.net]

6061 is a marine grade if it is harden to T6 hardness it will form a thin oxide layer on it own.  This thin layer will protect the metal from salt water if it is not scratched.  However I would coat the ring with a clear epoxy or polyester paint to prevent galvanic corrosion  

just my 2 cents 
Andy Jensen

From: "Alec Smyth" <Asmyth@changepoint.com>
Date: 2004/01/06 Tue AM 09:52:50 CST
To: <personal_submersibles@psubs.org>
Subject: RE: [PSUBS-MAILIST] protecting aluminum parts

Its 6061.

Thanks,

Alec

-----Original Message-----
From: drewacard@charter.net [mailto:drewacard@charter.net] 
Sent: Tuesday, January 06, 2004 9:50 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] protecting aluminum parts

What grade of Aluminum is it?

From: "Alec Smyth" <Asmyth@changepoint.com>
Date: 2004/01/06 Tue AM 08:14:08 CST
To: <personal_submersibles@psubs.org>
Subject: [PSUBS-MAILIST] protecting aluminum parts

One of the relatively more expensive parts of my sub is a massive
aluminum ring that seats the acrylic bow dome and opens and closes as a
hatch. I know it will form an electrolytic pair with other metals on the
boat, and thus corrode. But I have a practical question... given the sub
is likely to be in the water only an hour or two, and get washed down
with fresh water afterwards, is the need to protect the aluminum real,
or would it only be an issue with longer exposures?
 
I'd be much obliged if anyone with unprotected Al parts on their sub
share their experience on this. Anoziding looks nice but on a part this
size would be very expensive (extrapolating from what I've paid for much
smaller parts, probably in the order of $500). I'm not sure whether to:
 
a)       Do nothing
b)       Use a zinc anode near the hatch
c)       Paint
d)       Anodize
 
Just as background information, I don't have any other metals in direct
contact with the Al on the wet side, except for the hatch seat, but that
should be pretty well protected as it has 4 coats of Gluvit epoxy base
and 5 coats of epoxy paint. On the dry side, the ring is mechanically
connected to bars that go through linear bearings attached to the hull.
This does connect it electrically to the hull as well.
 
Thanks,

Alec