Coating aluminum

Ernest Christley wrote:
Smitty Two wrote:
In article ,
"Morgans" wrote:


"Lou" wrote in message
groups.com...

Ok, but why do I want to coat the aluminum? Is this a process just for
metal planes?
should i be doing this on my aluminum hinges attatched to my wooden
spars?


Aluminum will oxidize if left to it's own means. What the etch - alodine
coat process does is prevent the process form continuing on it's own.



Aluminum protects itself. When it rusts (aka oxidizes,) which it does
very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
oxide is about the hardest, most impervious thing you could put on a
piece of metal. The "process" does not "continue on its own." As soon as
a microscopically thin layer forms, your aluminum is protected from
further degradation.


Bingo! You are 100% correct Smitty. The oxide is impervious to water
and is very resisant to abrasion. Many metals form an insoluable oxide,
with the most notable exception being steel. Rust is soluable AND
hygroscopic, so the rust just goes straight through once it starts.

The wild card here is acid. Acid will eat right through the oxide layer
without stopping to ask questions, exposing another microscopic layer,
which then oxidizes. Unfortunately, our culture has spent the last
200years burning tons of coal and dumping all sorts of sulfur in the
air. This sulfur rains back down on us (and our airplanes) as very
dilute sulfuric ACID. That's why the Statue of Liberty needed to be
refubished. The acid rain had worn the copper thin.

Put something on that aluminum, not to protect it from water which is
actually rather benign to aluminum for the reason you state, but to
protect it from the acid that you'll be flying through.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."


Ok, but why alodine, why not rustolium?

Lou

"Lou" wrote

Ok, but why alodine, why not rustolium?

Why? Two reasons.

1. Rustoleum sucks
2. If you put regular ole paint on Aluminum without prep to remove the
oxides, and promote a solid bond, you can scratch off regular paint with
your fingernail.
--
Jim in NC

One of the basic reasons to protect aluminum as unprotected it will develop
Intergranular Corrosion mainly because of the copper in the alloy.


"Lou" wrote in message
oups.com...
Ok, but why do I want to coat the aluminum? Is this a process just for
metal planes?
should i be doing this on my aluminum hinges attatched to my wooden
spars?
Lou

Lou wrote:
Ernest Christley wrote:

Smitty Two wrote:
Aluminum protects itself. When it rusts (aka oxidizes,) which it does
very very quickly, it forms aluminum oxide (duh.) A coating of aluminum
oxide is about the hardest, most impervious thing you could put on a
piece of metal.

Bingo! You are 100% correct Smitty. The oxide is impervious to water
and is very resisant to abrasion. Many metals form an insoluable oxide,
with the most notable exception being steel. Rust is soluable AND
hygroscopic, so the rust just goes straight through once it starts.



Ok, but why alodine, why not rustolium?

Lou


Because, exactly as Smitty wrote, ALUMINUM PROTECTS ITSELF. Not just
from water, but also from paint.

That protection is very hard just like he said and reforms very quickly
in the presence of oxygen after being removed. The purpose of the
alodine is to chemically 'scratch' up the surface in such a way that
paint is able to form a mechanical bond.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Ernest Christley wrote:

...

The wild card here is acid. Acid will eat right through the oxide layer
without stopping to ask questions, exposing another microscopic layer,
which then oxidizes. ...

The other wild card is casutics (bases). Aluminum is equally
susceptible
to caustics. Lye (sodium hydroxide) will react as violently (or even
more so)
as does sulphuric acid.

--

FF

The other wild card is casutics (bases). Aluminum is equally
susceptible
to caustics. Lye (sodium hydroxide) will react as violently (or even
more so)
as does sulphuric acid.

Tell me about it. I used dish soap when checking for fuel tank leaks
(unprimed tanks on a homebuilt project). Result was some mild corrosion
anywhere the aluminum had a scratch on it (2020 coated with 1 mil of pure
aluminum). It'll come off when I prepare the surface for painting (lots of
scuffing with 300 grit).

I had picked up a dish soap bottle from under the sink, and unfortunately it
was not Dawn (some people recommend Dawn due to low causticity, and I have
used Dawn successfully in the past as well).

My motto for 2024... scuff, etch, alodine, prime.

So, let me get this right,
acid bad
Alodine good.

So, let me get this right,
acid bad
Alodine good.


Except when you use the acid to etch the aluminum before alodining it :-)
Shouldn't over-etch either (about 3 minutes in dilute acid solution).

2024 is protected by pure aluminun, but the coating is so thin and delicate,
that you are bound to put scratches in it. For 6061, at the very least,
prime on faying surfaces.

Thanks everyone, I'll be ordering the solution this week.
Lou

"Lou" wrote in message oups.com...
So, let me get this right,
acid bad
Alodine good.


Alodine is acid - chromic acid.