Question about Alodine 1201

[Andrew Sarangan]

I am using the following steps for treating my aluminum parts:

- scrub clean with Acetone and scotchbrite
- dry
- scrub clean in Metalprep-79 and scotchbrite
- rinse in water
- repeat until water forms smooth sheet (water break test)
- dip in alodine 1201 until part turns golden brown
- rise in water

After the final rinse, the golden brown coating feels soft and
delicate, and could be rubbed off easily. I have to hang the part and
let it completely dry before touching it.

Now, I can remove the alodine by scrubbing the part again with
Metalprep-79 and recover its original shiny surface. If it repeat the
above surface treatment all over again, I get a more stable coating
that looks more uniform and not so soft, and also appears slightly
darker in color.

I am not sure if I understand why this is happening. This has happened
every time I tried it, not just once, so it is not a random occurence.
Why is the re-coat giving me better results than the first-time coat?

[flybynightkarmarepair]

I can't say why the recoat is giving you "better" results than the
first-time coat, but the Alodine/Iridite passivation treatment IS very
soft when it's first applied. It's never very abrasion resistant (it's
meant to be topcoated), but when it first reacts with the aluminum,
it's a watery gel. That's why the aluminum must be squeaky clean
before you treat it - water don't stick to oily stuff like
fingerprints.

Let the parts hand in the breeze for a day or two after you alodine
them, and they'll be as good as they get.

And remember, no aluminum Piper ever built, and damn few Cessnas ever
got alodined. You're gilding the lily in the first place....only the
Government (and mostly the Navy at that...) could ever afford to be
this picky about corrosion prevention.

[gonefishn]

snipped a good reply<
only the
Government (and mostly the Navy at that...) could ever afford to be
this picky about corrosion prevention.

Agreed. And those steps Andrew listed are right out of Corrosion Control
School. I can still picture that 'crusty old instructor' lecturing us at
Naval Air Station Miramar in 1979. And it was basically the same during the
dozen or so times I sat through those lectures since.

Yep, the Navy is big on Corrosion Prevention. Follow those steps and you'll
have few problems.

[Stealth Pilot]

Post by gonefishn

snipped a good reply<
only the
Government (and mostly the Navy at that...) could ever afford to be
this picky about corrosion prevention.

Agreed. And those steps Andrew listed are right out of Corrosion Control
School. I can still picture that 'crusty old instructor' lecturing us at
Naval Air Station Miramar in 1979. And it was basically the same during the
dozen or so times I sat through those lectures since.
Yep, the Navy is big on Corrosion Prevention. Follow those steps and you'll
have few problems.

between the water break test and the alodining there is sometimes a
prep wash of very dilute phosphoric acid to bite away all corrosion
followed by a distilled water rinse then the alodine.
Stealth Pilot

[Smitty Two]

Post by gonefishn
Yep, the Navy is big on Corrosion Prevention. Follow those steps and you'll
have few problems.

I didn't know the Navy was renting out tie-downs on their carriers, for
the GA fleet. I've taken some heat for my faith in naked aluminum, but
then again I'm not planning to wash my plane in acid rain and soak it in
salt water spray on a daily basis. I'm also hoping that a good coat of
that fancy waterproof paint on the outside will help keep the inside
fairly dry.

[larry]

Post by flybynightkarmarepair
And remember, no aluminum Piper ever built, and damn few Cessnas ever
got alodined.

This is not *exactly* correct. Every zinc chromate painted part in a
Cessna (or Beech or Piper) received iridite before painting. Paint
won't stick right without it. Part of MIL-C-5540 or whatever (I'm
rusty).

If you ordered the hideously expensive "corrosion resistance" package,
you got an extra couple hundred pounds of paint -- but no increase in
useful payload. Guess how popular THAT was?? The oil filter adapter
was treated and then clearcoated leaving it golden color (and priced
accordingly).

You don't mention how "clean" your part is. Are you taking off the
Clad coating? If so, the parts really need to remain *submerged* until
coating. Any exposure to air will instantly start oxidation and reduce
coverage quality (usually judged, as you're doing, by depth of color).

My theory is that your initial coating, utilitzing your stated process,
is merely adhering to an oxidation layer that, of course, scrubs right
off. The most of the surface was "sealed", if you will, against
further oxidation and once re-treated, responded in a more predictable
and acceptable manner. Just a guess.

Larry

[Andrew Sarangan]

Post by larry
You don't mention how "clean" your part is. Are you taking off the
Clad coating? If so, the parts really need to remain *submerged* until
coating. Any exposure to air will instantly start oxidation and reduce
coverage quality (usually judged, as you're doing, by depth of color).
My theory is that your initial coating, utilitzing your stated process,
is merely adhering to an oxidation layer that, of course, scrubs right
off. The most of the surface was "sealed", if you will, against
further oxidation and once re-treated, responded in a more predictable
and acceptable manner. Just a guess.

Larry

Can you explain what you mean by Clad coating?

[larry]

Post by Andrew Sarangan
Can you explain what you mean by Clad coating?

Well... Aluminum is a whitish-gray material, not slick and shiny like
the sheet metal you buy. The sheetmetal product, and much plate stock,
is almost always 'clad-coated' and to my knowledge, not available any
other way. That shiny stuff is the 'clad' which is simply more
aluminum that has been pressed tightly to eliminate natural porosity.
Of course, the *process* has changed over the years but the result is
the same: shiny and slick sheetmetal.

Beneath the clad coating is "raw" aluminum. This has been the bugaboo
of corrosion problems among many. Raw aluminum is quite reactive to
air and water and protects itself with an oxide layer of white powder
(that also turns mysteriously black when you handle it -- kinda weird).
Depending on alloy, once the raw surface is exposed, the oxide layer
can go quite deep -- often deeper than the sheetstock IS. The clad
coating, while still aluminum, keeps corrsion at bay to a much greater
extent because it reacts far, far, slower than 'raw' aluminum. Once
this clad is gone, all bets are off.

Sanding or etching removes this coating pretty much every time. Once
removed, you're gonna hafta treat that surface pretty quickly with
aluminum specific coating (like alodine). Another poster quite rightly
pointed out that color is not supposed to be very 'deep'. "Well-done
fried chicken" brown is too deep. "Light Honey" brown might be more
appropriate. Gotta go, getting hungry alla sudden :-)

Larry

[Orval Fairbairn]

Post by larry

Post by Andrew Sarangan
Can you explain what you mean by Clad coating?

Well... Aluminum is a whitish-gray material, not slick and shiny like
the sheet metal you buy. The sheetmetal product, and much plate stock,
is almost always 'clad-coated' and to my knowledge, not available any
other way. That shiny stuff is the 'clad' which is simply more
aluminum that has been pressed tightly to eliminate natural porosity.
Of course, the *process* has changed over the years but the result is
the same: shiny and slick sheetmetal.
Beneath the clad coating is "raw" aluminum. This has been the bugaboo
of corrosion problems among many. Raw aluminum is quite reactive to
air and water and protects itself with an oxide layer of white powder
(that also turns mysteriously black when you handle it -- kinda weird).
Depending on alloy, once the raw surface is exposed, the oxide layer
can go quite deep -- often deeper than the sheetstock IS. The clad
coating, while still aluminum, keeps corrsion at bay to a much greater
extent because it reacts far, far, slower than 'raw' aluminum. Once
this clad is gone, all bets are off.

Sorry -- but the cladding is *pure* aluminum! The stuff under the
cladding is the alloy, which is usually somewhat prone to corrosion. The
cladding acts as a self-sacrificial protectant and sealant for the
alloy. Materials tables show a slight reduction in allowable stress on
clad vs unclad parts, as the cladding furnishes virtually no matreial
strength.

Post by larry
Sanding or etching removes this coating pretty much every time. Once
removed, you're gonna hafta treat that surface pretty quickly with
aluminum specific coating (like alodine). Another poster quite rightly
pointed out that color is not supposed to be very 'deep'. "Well-done
fried chicken" brown is too deep. "Light Honey" brown might be more
appropriate. Gotta go, getting hungry alla sudden :-)

This part is true. You should not sand clad aluminum, except to remove
existing corrosion.

BTW, to the previous poster, it is the sodium hydroxide etch that should
be warmed to 120 F. The alodine works fine at room temperature.

[larry]

Post by Orval Fairbairn
Sorry -- but the cladding is *pure* aluminum! The stuff under the
cladding is the alloy, which is usually somewhat prone to corrosion.

Where was it that I said the clad was anything other than aluminum??

Ok, after I re-read this a bit, I can see where the misunderstanding
might lie. My bad. Misuse of the word "raw", perhaps. But pure alum
rots right fine. The issue is one of porosity (ok, grain structure).
The clad has none (ok, very little) exposed. It's the form, not the
chemistry, that precludes the corrosion.

Although you bring up a good point that different alloys corrode
differently. Some with remarkable ugliness.

Post by Orval Fairbairn
This part is true. You should not sand clad aluminum, except to remove
existing corrosion

<whew!> glad I did OK :-)
Unfortunately, the manufacturing processes involved in aircraft
sometimes leaves the builder/factory with no choice but to do sanding
and lots of it. The clad is routinely removed for coating and MUST be
removed for alodine/iridite, then paint. Of course, these are
"approved" FAA processes, not just what we might do in our own build.
Relying on old chemistry and old processes that never change isn't
necessarily what the homebuilder needs most so turning to the factory
isn't always the greatest thing.

I'm pretty sure there's lots of fine etching epoxies to paint exposed
parts without iridite. But they don't give 'em away.

[Stealth Pilot]

Post by larry

Post by Orval Fairbairn
Sorry -- but the cladding is *pure* aluminum! The stuff under the
cladding is the alloy, which is usually somewhat prone to corrosion.

Where was it that I said the clad was anything other than aluminum??
Ok, after I re-read this a bit, I can see where the misunderstanding
might lie. My bad. Misuse of the word "raw", perhaps. But pure alum
rots right fine. The issue is one of porosity (ok, grain structure).
The clad has none (ok, very little) exposed. It's the form, not the
chemistry, that precludes the corrosion.
Although you bring up a good point that different alloys corrode
differently. Some with remarkable ugliness.

Post by Orval Fairbairn
This part is true. You should not sand clad aluminum, except to remove
existing corrosion

<whew!> glad I did OK :-)
Unfortunately, the manufacturing processes involved in aircraft
sometimes leaves the builder/factory with no choice but to do sanding
and lots of it. The clad is routinely removed for coating and MUST be
removed for alodine/iridite, then paint. Of course, these are
"approved" FAA processes, not just what we might do in our own build.
Relying on old chemistry and old processes that never change isn't
necessarily what the homebuilder needs most so turning to the factory
isn't always the greatest thing.
I'm pretty sure there's lots of fine etching epoxies to paint exposed
parts without iridite. But they don't give 'em away.

larry, honestly, what you are writing is a load of missunderstood
cobblers.

2024 aluminium is an alloy of aluminium and copper. this alloy has
increased strength over pure aluminium.for this reason it is used in
aircraft construction. its disadvantage is that the copper and
aluminium in the presence of moisture will corrode.
the sheets are made usable by rolling on to each surface a thin layer
of pure aluminium. this cladding in pure aluminium considerably
increases the corrosion resistance of the aluminium sheet.
YOU DO NOT REMOVE THIS CLADDING when passivating the surface of the
sheet. if you are doing lots of sanding then you are considerably
reducing the strength of the components.
in preparing aluminium for corrosion resistance you will never need us
anything more than a scotchbrite pad to scuff the surface.

my suggestion is that you go and read the sections in AC43-13 2b
dealing with the corrosion proofing of aluminium.
Stealth Pilot
Australia

[larry]

Post by Stealth Pilot
larry, honestly, what you are writing is a load of missunderstood
cobblers

<snip>

Post by Stealth Pilot
my suggestion is that you go and read the sections in AC43-13 2b

Stealth Pilot,
While you are (or perhaps not) merely a pilot, I can understand you not
knowing anything about the process of building the plane you fly. As
an Engineer, I'm here to help :-) And I designed quite a few of the
components in your Stealth... well, that is if you're an American in
Auz flying a B-2... elsewise, you're on yer own.

Further, as a jet jock (again, perhaps not) I can certainly believe
you've find yourself with some misunderstandings. That's normal,
really. Possibly, you've attributed more authorship to me than has
actually occured.

Regardless, 2024 is not used simply for its "increased strength" for
there are MANY alloys equally strong and some decidedly stronger at a
much lower price. Perhaps you could tell us the REAL reason. Or
perhaps not. (hint: look up the word "fatigue"). Remarkably, you
missed even more points about 2024, namely its "very high resistance to
corrosion" in T-6 and T-8 tempers (MIL-HNDBK-5H). So even if you shout
while removing the cladding, after quench/aging, it makes no
difference. While you'd have no way of knowing that, and we that
actually build planes do, don't worry, I'm still here to help. It
still has all the copper it ever had, but somehow *doesn't* corrode.
Why is that? Or are you at a loss?

As you knew that 2024 uses a largely copper alloy, that's a good start.
But ALL of the 2xxx series aluminums are mostly copper in alloy, yet
2024 has distictive properties that distinguish it for aircraft use --
and nearly no other 2xxx series is used. Why is that? Do you know?
It involves the silicon content. (ok, I sorta already gave this
away...)

Which is *also* why more and more 6xxx series (6065, 6061) aluminum is
being used. 2024 is out of sight pricewise these days, so why has it
been set aside for a different alloy? 6xxx has far *more* silicon, and
almost no copper, making it much harder to machine, yet far less 2024
is being used per plane than ever before. Curious, don't you think? Or
would you have anyway of knowing.

And, for your edification, *you* may or may not remove this cladding,
as I would never impinge upon what you do with your own property, but
I, personally, have done exactly that in my younger years. Of course,
this was as an employee of Cessna Aircraft, working in an FAA Certified
manufacturing facility, working my way through Engineering school, so
it may not be totally congruent with the various stories told you in
your mil-spec pilot training -- doubtless from other mil-spec pilots
that never knew, either.

So believe as you will and I'll not address the issue again. Rest
assured I'll just nod and smile from half a globe away.

While I may, again, delve into the odd Advisory Circular, I spend most
of my time in FAR25 with occasion to FAR23 and various others. The
branch of the FAA that I deal with worries more about "the letter of
the FAR's" more than the "letter of the AC's".

Stay safe. Fly well. Stick to what you know.

Larry

[Stealth Pilot]

Post by larry

Post by Stealth Pilot
larry, honestly, what you are writing is a load of missunderstood
cobblers

<snip>

Post by Stealth Pilot
my suggestion is that you go and read the sections in AC43-13 2b

Stealth Pilot,
While you are (or perhaps not) merely a pilot, I can understand you not
knowing anything about the process of building the plane you fly. As
an Engineer, I'm here to help :-) And I designed quite a few of the
components in your Stealth... well, that is if you're an American in

if what you have posted previously equates to "engineering" you'll
never have me as a customer.
Stealth Pilot

[Mike]

Post by larry

Post by Andrew Sarangan
Can you explain what you mean by Clad coating?

Well... Aluminum is a whitish-gray material, not slick and shiny like
the sheet metal you buy.

OK

Post by larry
The sheetmetal product, and much plate stock,
is almost always 'clad-coated' and to my knowledge, not available any
other way.

Eh?

Clad coated?

Got a source for that info?

Post by larry
That shiny stuff is the 'clad' which is simply more
aluminum that has been pressed tightly to eliminate natural porosity.
Of course, the *process* has changed over the years but the result is
the same: shiny and slick sheetmetal.

This makes absolutely NO SENSE

Post by larry
Beneath the clad coating is "raw" aluminum. This has been the bugaboo
of corrosion problems among many. Raw aluminum is quite reactive to
air and water and protects itself with an oxide layer of white powder
(that also turns mysteriously black when you handle it -- kinda weird).
Depending on alloy, once the raw surface is exposed, the oxide layer
can go quite deep -- often deeper than the sheetstock IS.

Deeper than the sheetstock?

Like into thin air on the back side?

Post by larry
The clad
coating, while still aluminum, keeps corrsion at bay to a much greater
extent because it reacts far, far, slower than 'raw' aluminum. Once
this clad is gone, all bets are off.

The protective layer IS the oxide

Post by larry
Sanding or etching removes this coating pretty much every time. Once
removed, you're gonna hafta treat that surface pretty quickly with
aluminum specific coating (like alodine). Another poster quite rightly
pointed out that color is not supposed to be very 'deep'. "Well-done
fried chicken" brown is too deep. "Light Honey" brown might be more
appropriate. Gotta go, getting hungry alla sudden :-)

--

[Jean-Paul Roy]

Am I correct assuming only 2024 is clad coated not 6061?

Jean-Paul

Post by larry

Post by Andrew Sarangan
Can you explain what you mean by Clad coating?

Well... Aluminum is a whitish-gray material, not slick and shiny like
the sheet metal you buy. The sheetmetal product, and much plate stock,
is almost always 'clad-coated' and to my knowledge, not available any
other way. That shiny stuff is the 'clad' which is simply more
aluminum that has been pressed tightly to eliminate natural porosity.
Of course, the *process* has changed over the years but the result is
the same: shiny and slick sheetmetal.
Beneath the clad coating is "raw" aluminum. This has been the bugaboo
of corrosion problems among many. Raw aluminum is quite reactive to
air and water and protects itself with an oxide layer of white powder
(that also turns mysteriously black when you handle it -- kinda weird).
Depending on alloy, once the raw surface is exposed, the oxide layer
can go quite deep -- often deeper than the sheetstock IS. The clad
coating, while still aluminum, keeps corrsion at bay to a much greater
extent because it reacts far, far, slower than 'raw' aluminum. Once
this clad is gone, all bets are off.
Sanding or etching removes this coating pretty much every time. Once
removed, you're gonna hafta treat that surface pretty quickly with
aluminum specific coating (like alodine). Another poster quite rightly
pointed out that color is not supposed to be very 'deep'. "Well-done
fried chicken" brown is too deep. "Light Honey" brown might be more
appropriate. Gotta go, getting hungry alla sudden :-)
Larry

[Orval Fairbairn]

Post by Jean-Paul Roy
Am I correct assuming only 2024 is clad coated not 6061?

No -- 2024 comes in both clad and unclad versions. The unclad stuff is
usually heavier stock, for machining and major structural elements.

7075 is usually clad in sheet, but comes in unclad flavor, again, for
major structural elements.

Both 2024 and 7075 (especially) need corrosion protection.

I do not recall seeing clad 6061 or 5052. Other alloys may also exist as
clad.

[b***@msn.com]

A quick search at www.matweb.com using clad as a search criteria, and
looking at the various AMS specs in Mil-HDBK-5H, the following alloys
are available in clad form.

2 Alclad Aluminum 2014-O
3 Alclad Aluminum 2014-T3
4 Alclad Aluminum 2014-T4, T451
5 Alclad Aluminum 2014-T6, T651
6 Alclad Aluminum 2024-O
7 Alclad Aluminum 2024-T3
8 Alclad Aluminum 2024-T361
9 Alclad Aluminum 2024-T4, T351
10 Alclad Aluminum 2024-T81, T851
11 Alclad Aluminum 2024-T861
12 Alclad Aluminum 3003-H12
13 Alclad Aluminum 3003-H14
14 Alclad Aluminum 3003-H16
15 Alclad Aluminum 3003-H18
16 Alclad Aluminum 3003-O
17 Alclad Aluminum 3004-H32
18 Alclad Aluminum 3004-H34
19 Alclad Aluminum 3004-H36
20 Alclad Aluminum 3004-H38
21 Alclad Aluminum 3004-O
22 Alclad Aluminum 6061-O
23 Alclad Aluminum 6061-T4, T451
24 Alclad Aluminum 6061-T6, T651
25 Alclad Aluminum 7075-O
26 Alclad Aluminum 7075-T6, T651
27 Alclad Aluminum 7178-O
28 Alclad Aluminum 7178-T6, T651
29 Alclad Aluminum 7475-T61
30 Alclad Aluminum 7475-T761
from Mil-Hdbk-5H

Al Alclad 2424 is available
in clad form

There may be more. For High strength and corrosion resistance, such as
a marine environment, 5052 is THE alloy to use. Very corrosion
resistant.

[Orval Fairbairn]

Post by Andrew Sarangan
- scrub clean with Acetone and scotchbrite
- dry
- scrub clean in Metalprep-79 and scotchbrite
- rinse in water
- repeat until water forms smooth sheet (water break test)
- dip in alodine 1201 until part turns golden brown
- rise in water
After the final rinse, the golden brown coating feels soft and
delicate, and could be rubbed off easily. I have to hang the part and
let it completely dry before touching it.

Golden brown is too much! All you need for best results is a light
golden hue. Keeping it in the Alodine too long actually reduces the
corrosion protection! About 10 - 20 minutes immersion should suffice.

Post by Andrew Sarangan
Now, I can remove the alodine by scrubbing the part again with
Metalprep-79 and recover its original shiny surface. If it repeat the
above surface treatment all over again, I get a more stable coating
that looks more uniform and not so soft, and also appears slightly
darker in color.
I am not sure if I understand why this is happening. This has happened
every time I tried it, not just once, so it is not a random occurence.
Why is the re-coat giving me better results than the first-time coat?

You can also use a weak mixture of lye and water as a prep. For best
results, heat it to 120 deg F and dip the part for about 5 minutes.

Yes -- the aluminum must be free of dirt and grease befor starting the
process.

[Lou]

Mix the water prep to 120 deg???

[Roger]

On Thu, 06 Apr 2006 03:26:10 GMT, Orval Fairbairn

Post by Orval Fairbairn

Post by Andrew Sarangan
- scrub clean with Acetone and scotchbrite
- dry
- scrub clean in Metalprep-79 and scotchbrite
- rinse in water
- repeat until water forms smooth sheet (water break test)
- dip in alodine 1201 until part turns golden brown
- rise in water
After the final rinse, the golden brown coating feels soft and
delicate, and could be rubbed off easily. I have to hang the part and
let it completely dry before touching it.

Golden brown is too much! All you need for best results is a light
golden hue. Keeping it in the Alodine too long actually reduces the
corrosion protection! About 10 - 20 minutes immersion should suffice.

All that I've done so far (which aint much) looks more like a gold
clear coat, or stain rather than an actual coating. Lots of coating
and lots of washing.

You can get it for steel or aluminum. I think the Alodine is the
same, but the prep solution is different.

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

Post by Orval Fairbairn

Post by Andrew Sarangan
Now, I can remove the alodine by scrubbing the part again with
Metalprep-79 and recover its original shiny surface. If it repeat the
above surface treatment all over again, I get a more stable coating
that looks more uniform and not so soft, and also appears slightly
darker in color.
I am not sure if I understand why this is happening. This has happened
every time I tried it, not just once, so it is not a random occurence.
Why is the re-coat giving me better results than the first-time coat?

You can also use a weak mixture of lye and water as a prep. For best
results, heat it to 120 deg F and dip the part for about 5 minutes.
Yes -- the aluminum must be free of dirt and grease befor starting the
process.

[.Blueskies.]

http://www.pfonline.com/articles/040601.html

Alodine no more...

Post by Andrew Sarangan
- scrub clean with Acetone and scotchbrite
- dry
- scrub clean in Metalprep-79 and scotchbrite
- rinse in water
- repeat until water forms smooth sheet (water break test)
- dip in alodine 1201 until part turns golden brown
- rise in water
After the final rinse, the golden brown coating feels soft and
delicate, and could be rubbed off easily. I have to hang the part and
let it completely dry before touching it.
Now, I can remove the alodine by scrubbing the part again with
Metalprep-79 and recover its original shiny surface. If it repeat the
above surface treatment all over again, I get a more stable coating
that looks more uniform and not so soft, and also appears slightly
darker in color.
I am not sure if I understand why this is happening. This has happened
every time I tried it, not just once, so it is not a random occurence.
Why is the re-coat giving me better results than the first-time coat?

[Stealth Pilot]

On Fri, 07 Apr 2006 11:35:57 GMT, ".Blueskies."

Post by .Blueskies.
http://www.pfonline.com/articles/040601.html
Alodine no more...

an interesting article.
Stealth Pilot