Question about Alodine 1201

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?

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.

"flybynightkarmarepair" wrote in message
oups.com...

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.

On Wed, 05 Apr 2006 05:40:20 GMT, "gonefishn"
wrote:


"flybynightkarmarepair" wrote in message
roups.com...

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

In article 8LIYf.23170$fQ6.1489@trnddc03,
"gonefishn" wrote:



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.

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

larry wrote:

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?

In article .com,
"Andrew Sarangan" wrote:

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.

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.


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.

Mix the water prep to 120 deg???

In article .com,
"larry" wrote:

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.


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.