"Pre-Meltdown" wrote in message
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"Ed Huntress" wrote in message
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"Pre-Meltdown" wrote in message
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If the gray oxide finish on fresh/polished aluminum is not so bad
(actually, "natural anodizing", and is itself highly protective and
hard), I wonder if accelerating its formation in an oven would be
practical? Esp. as your parts would fit.
Just don't get fingerprints on it before you put it in the oven....

Strictly speaking, say from a conductivity pov, these oxides start
forming almost immediately, within minutes, enough to effect contact
conductivity.

Sending stuff out to be anodized is expensive, but actually a pretty
easy diy. There were/are some outstanding web sites on how to do this.

I'll have to try the oven ditty myself.

Another cheap and easy finish that works on *most* grades of aluminum is
the bright satin effect you get from dipping it in a lye solution. I use
this for the chassis on electronics projects.

Dissolve a few tablespoons of household lye in a quart of warm water;
wash the oil off the aluminum with strong detergent; submerge the
aluminum in the lye solution. Leave it there until it looks good --
usually minutes. If there are any oil spots on the aluminum that show up
as the lye bath continues, pull the aluminum out, wash with water, brush
the spot with Scotchbrite, and put it back into the solution.

When you like the look, rinse it thoroughly, dry while it's still warm,
and spray with clear lacquer or something tougher, if you prefer.

Very interesting.

There's a guy not far from me with the biggest-assed circular vibratory
tumbler I've seen, the size of a small bedroom/large closet, who puts in
some chemical with the media that gives aluminum an almost galvanized
look, and claims this finish is protective.
I don't know if I like it, it's certainly not like a brushed/satin look, a
little industrial/cobby, but not bad.

Aluminum is so reactive that there have been many chemical finish treatments
cooked up for it over the years. Most of them don't really protect; only a
few produce a tight enough oxide or other compound to really protect the
aluminum. Anodizing, particularly "hard" anodizing (which is no harder, only
thicker) is among the most effective, but there are several types of
anodizing for different purposes. PAA (phosphoric-acid anodizing), for
example, is preferred when you want to make the surface receptive to
adhesives and strong enough for adhesive bonding.

There is a mild acid treatment that gives similar results to the lye
treatment, but I've never used it and can't remember which acid it is. It's
also suitable for home- or small-shop use. Neither the acid nor the lye
treatment provides any protection. They just leave a nice-looking surface
which, if you don't let it sit around for days before coating, is also
chemically active and will make a good bond with paint or clear coats. I try
to coat within a half-hour or so.

Some alloys don't behave very well in this treatment -- they leave a
smutty-looking surface -- but I can't remember which alloys those are. I do
remember using it on 2024 and 1100, and it works well on both of those. I
think it works on 6061, or so I've been told. You may have to experiment
with concentration to get some alloys to work but they make not work anyway.

The lye treatment is well-known among crafty people who make things with
aluminum and I've seen it recommended several times in books about making
electronic projects. I said I use it for chassis; I should have said I use
it for panels and covers.

--
Ed Huntress