Coating aluminum

What is the best product to use to coat aluminum before I bolt it to
the wood on my spars?
Lou

In article .com,
"Lou" wrote:

What is the best product to use to coat aluminum before I bolt it to
the wood on my spars?
Lou

Alodine + 2-part epoxy primer.

--
Remve "_" from email to reply to me personally.

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

In article ,
"Morgans" wrote:

"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?


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.

The problem arises when the exposed metal is left to water, salts,
dissimilar metals, etc, for long periods of time, which sets up
electrolysis. If you think you're going to protect aluminum from that
kind of damage with some kind of coating, then be my guest. I plan to
keep my plane clean and dry, and let the aluminum oxide that forms
naturally do its job.

Now, I know Mr. Morgans isn't going to flame me for these comments,
because he's already canned me, but I'd love to hear from others who may
disagree.

Jon in California

"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?


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.

Etch- remove oxidation, and roughen the surface (chemically) to make bonding
of new coatings stronger.

Alodine- actually cause a very uniform thin layer of oxidation to form on
the aluminum, that will help the oxidation from continuing on its own, in
un-uniform ways, possibly up to and including consuming the base metal.
Oxidation on the surface actually protects the metal under it.

Coat- Protects the layer of alodine from wearing away, or continuing on its
own, due to contact to other unlike surfaces, or exposure to the
environment. 2 part epoxies are the best (in some (most) people's opinions)
because it is very resistant to chemicals, moisture, and friction of rubbing
against another surfaces. It also has very good adhesion properties,
allowing it to stick to surfaces and not let go.
--
Jim in NC

On Wed, 14 Dec 2005 21:11:09 -0800, Smitty Two
wrote:

In article ,
"Morgans" wrote:

"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?

Ok,I'm no expert on painting, but I'll take both sides here

Aluminum will oxidize if left to it's own means. What the etch - alodine

Wellll, yah, kinda, sorta, but...It really depends on to what it's
exposed.

coat process does is prevent the process form continuing on it's own.

Alodine is pretty fragile and the Aluminum Oxide is pretty tough.
Unfortunately both have their weaknesses.

Aluminum protects itself. When it rusts (aka oxidizes,) which it does
very very quickly, it forms aluminum oxide (duh.) A coating of aluminum

It forms that layer which is only a few molecules thick almost
instantly.

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.

Within reason I agree such as just leaving it alone


The problem arises when the exposed metal is left to water, salts,
dissimilar metals, etc, for long periods of time, which sets up

When it comes to salts it doesn't take much time. Look at the
corrosion around the joints on paint jobs with poor prep.

electrolysis. If you think you're going to protect aluminum from that
kind of damage with some kind of coating, then be my guest. I plan to
keep my plane clean and dry, and let the aluminum oxide that forms
naturally do its job.

Now, I know Mr. Morgans isn't going to flame me for these comments,
because he's already canned me, but I'd love to hear from others who may
disagree.

The Alodine process does two things. It is a prep for painting so it
gives the paint a surface to which it can grip really well.

Alodine itself is relatively fragile. It is very thin and can be
rubbed off, but between the added protection against dissimilar metals
and a good surface for your paint to stick to, I think it's worth the
effort. Give it a good primer and your paint job should last a long
time.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

Jon in California

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.

I'm no expert, however my understanding is...

6061 and 2024 are not pure aluminum. In order to obtain the desired strength
properties, other metals are added to the aluminum. I believe 2024 has
something of the order of a couple percent of copper. The surface will not
be pure aluminum oxide, since there are "impurities" within the metal. You
are now open to pitting corrosion as well as granular corrosion.

The alodine forms a passivated layer, that uniformly protects the whole
surface. Being a delicate surface itself (as a previous poster already
mentioned), the passivated layer needs to be protected against mechanical
abrasion.

6061 is quite immune to most of the above corrosion. It is still a good idea
to protect anywhere you will have metal to metal contact though, since you
can have moisture trapped between the parts which accelerates the corrosion.

I use 2024, so I do the scuff, etch, alodine, 2 part epoxy prime routine.

"RV9" wrote

I'm no expert, however my understanding is...

Obviously your understanding is far above Smitty's

I use 2024, so I do the scuff, etch, alodine, 2 part epoxy prime routine.

As would any sensible person working aluminum in an aircraft.

Strange, isn't it, that the Navy (and I suspect the other armed forces)
spend all of that time with the above procedure on their aircraft? They
must know something that Smitty does not.
--
Jim in NC

6061 and 2024 are not pure aluminum. In order to obtain the desired
strength
properties, other metals are added to the aluminum. I believe 2024 has
something of the order of a couple percent of copper. The surface will not
be pure aluminum oxide, since there are "impurities" within the metal. You
are now open to pitting corrosion as well as granular corrosion.


2024

Cu 3.8 - 4.9
Mg 1.2 - 1.8
Mn 0.30 - 0.9
Fe = 0.50
Si = 0.50
Zn = 0.25
Zr+Ti = 0.20
Total Other = 0.15
Ti = 0.15
Cr = 0.10
Other Elem = 0.05
Al Remainder



6061

Mg 0.40 - 0.8
Si 0.30 - 0.6
Fe = 0.35
Cu = 0.25
Cr = 0.20
Mn 0.05 -0.20
Total Other = 0.15
Zn = 0.15
Ti = 0.10
Other Elem = 0.05
Al Remainder

All compositions in wt%.

"alclad" sheets have a thin layer of pure aluminium on the surface to
improve corrosion resistance.

see http://aluminium.matter.org.uk/aluse...ion_browse.asp for
corrosion and anodizing properties.


--
Geoff
the sea hawk at wow way d0t com
remove spaces and make the obvious substitutions to reply by mail
Spell checking is left as an excercise for the reader.

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)."