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  #1  
Old 06-01-2018, 04:21 PM
CheckStein CheckStein is offline
 
Join Date: May 2018
Location: NY NY
Posts: 4
Default Priming and Bonderite (alodine)

Hi folks,
I came here seeking some input for priming 6061 AL. My parts are not aircraft parts but you aircraft folks have some good info.

I am doing a 1k rattle can project and am seeking the best way to get primer to latch onto the AL.

I'll get to Alodine(1200) in a sec.

I am testing out some etching primers (SEM, VHT, SW 988).
I degrease, rinse, then lye etch the 6061, rinse, and then wipe the smut off, then prime. I do no scotchbrite or anything.
1) is nitric acid bath required to get rid of the smut before priming?

2) Next is, does the "Alodine" (now Bonderite) create a conversion layer that is better for primer to latch onto? My understanding of the Alodine conversion is to create a new conversion layer that has migrating properties to protect the AL from corrosion (caused by nicks & scratches, etc). But if I do not need the corrosion properties then is Alodine even needed?

3) Correct me if I am wrong, with the Alodine conversion layer you would not use a etching primer, it would be urethane or epoxy primer?

4) If I were to use Alodine in my process, would it be better to skip the lye etching and just use something more mild, like Alumiprep (also now a Bonderite name)?

5) If I used Alodine in my process, what 1k primer rattle can would make a super bond to the conversion layer?

Thanks for any info.
Chuck

Last edited by CheckStein : 06-01-2018 at 04:24 PM.
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  #2  
Old 06-01-2018, 04:37 PM
wirejock's Avatar
wirejock wirejock is offline
 
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Location: Estes Park, CO
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Default Alodine vs primer

1. Nitric? Never heard anyone use it. Alumiprep is an acid. I suppose nitric would work similar removing the oxide. Dunno.
2. Alodine is a conversion. It stabilizes the outer surface preventing further oxidation and protects against corrosion. Basically you want one something on non Alclad parts at least. Alodine or primer.
3. Nothing is required or specified after. Choice is yours.
4. If you choose Alodine or technically anything, surface prep is key. Remove the aluminum oxide and apply. How you do it is subject to debate. I'll probably get flamed but in my opinion Alodine and primer is a little "belt and suspenders". Nothing wrong with it. Most paint shops will Alodine, prime then paint but it is exterior. I do have opinion on prep. Feel free to read it on my blog.
Basically the idea is to remove the aluminum oxide layer as easy as possible and spray whatever as soon as you can. Easiest method to get a hydrophilic surface is scrub with Scotch Brute and Bon Ami cleanser. Cheap, easy and no caustic chemicals. Alumiprep is fine, but capture the rinse water and wear protection. It's an acid. Lye? Never heard of using it.
5. Primer war. Pick your poison.
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Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 12/01/2017. Plus a little extra.
RV-7A #73391, N511RV reserved (1,800+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.

Last edited by wirejock : 06-01-2018 at 04:47 PM.
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  #3  
Old 06-01-2018, 05:00 PM
1001001's Avatar
1001001 1001001 is offline
 
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Location: Just Minutes from KBVI!
Posts: 752
Default

Quote:
Originally Posted by CheckStein View Post
1) is nitric acid bath required to get rid of the smut before priming?

2) Next is, does the "Alodine" (now Bonderite) create a conversion layer that is better for primer to latch onto? My understanding of the Alodine conversion is to create a new conversion layer that has migrating properties to protect the AL from corrosion (caused by nicks & scratches, etc). But if I do not need the corrosion properties then is Alodine even needed?

3) Correct me if I am wrong, with the Alodine conversion layer you would not use a etching primer, it would be urethane or epoxy primer?

4) If I were to use Alodine in my process, would it be better to skip the lye etching and just use something more mild, like Alumiprep (also now a Bonderite name)?

5) If I used Alodine in my process, what 1k primer rattle can would make a super bond to the conversion layer?
1. I can't see any reason to use nitric acid. It is a strong oxidizing acid that is often used for passivating stainless steels after welding. On aluminumm alloys I can't see why it would be necessary. I have not heard of using lye (sodium hydroxide) as a prep for painting. I would instead use Alumiprep 33 or Klean Strip phosphoric acid "Etch and Prep" (available at home stores). Alumiprep is a solution of phosphoric acid, a small concentration of hydrofluoric acid, and a surfactant to improve contact with the metal surface during treatment. I have used the Klean Strip product as well, and it is I believe a dilute solution of phosphoric acid and possibly a surfactant, but I think it leaves out the HF.

2. If you don't care about corrosion, just chemically etch or, as noted above, physically rough up the surface (for giving the surface "tooth" to improve coating adhesion).

3. You can do whatever you want. Alodine makes for a great paintable surface but you probably can just etch/prep the surface and save your money.

4. I wouldn't bother with the lye. It is going to create a bunch of aluminum hydroxide that is just eating away at the surface. It won't improve the bond other than to give the surface tooth, which is probably easiest done with scotch brite or one of the phosphoric acid etchants mentioned above. You would have to clean the Al(OH)3 off the surface very thoroughly to get a good bond to the base aluminum.

In addition, if you are going to use Alodine, you want to use an acid based etchant, not a basic one like lye. The Alodine solution is acidic itself, and you wouldn't want any residual base reacting with and probably reducing the effectiveness of the Alodine solution.


5. Couldn't really say. Alodine is said to generically improve coating bonding but differences between the various coatings available is probably picking nits if you have otherwise properly prepared the surface before coating.

I wouldn't bother with the Alodine if you don't care about corrosion.

Also, note that if you are going to use Alodine, do not allow the aluminum to dry between the various steps. Soaking the part in water keeps the surface from oxidizing before the Alodine gets a chance to do its work. The chromic acid in the alodine does the oxidation, and you don't want atmospheric air to get in first.
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  #4  
Old 06-01-2018, 05:22 PM
CheckStein CheckStein is offline
 
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Location: NY NY
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Default

A lot of my info comes from finishing.com

Nitric acid will eat smut post lye bath, but will not eat the AL.

The idea for lye bath is to etch away the existing oxide layer, which is around 4nm. This exposes raw AL to the primer.

Some of my parts have inside corners that would be hard to get at with scotchbrite, and I am trying to avoid the "sand" blaster.

If you are just prepping good clean AL using scotchbrite, what 1k rattle can primers have to seen that really latch onto the AL?
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  #5  
Old 06-01-2018, 05:38 PM
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1001001 1001001 is offline
 
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Default

Quote:
Originally Posted by CheckStein View Post
A lot of my info comes from finishing.com

Nitric acid will eat smut post lye bath, but will not eat the AL.

The idea for lye bath is to etch away the existing oxide layer, which is around 4nm. This exposes raw AL to the primer.
That is probably the reason for the hydrofluoric acid in Alumiprep-33 then. I still would avoid combining basic and acidic treatments unless you plan to very thoroughly rinse the parts between the steps. The "smut" is aluminum hydroxide, which you probably won't get if you use a phosphoric acid etchant. Then you only need to rinse with distilled water. Saves you a step.

I don't know about the primer question so I'll leave that to others. I wuold imagine that as long as you have given the surface a good tooth by whatever etching means you choose, most primers would be ok?
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  #6  
Old 06-01-2018, 05:53 PM
CheckStein CheckStein is offline
 
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From what I know of it, the smut is the leftover alloys in 6061 because the lye pulls out AL from the surface (and converts it while releasing H gas) and it falls into the solution, leaving the surface of just the alloys (smut). The nitric acid (other acid work too) will eat the alloy components but not the AL.
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  #7  
Old 06-01-2018, 05:58 PM
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1001001 1001001 is offline
 
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Quote:
Originally Posted by CheckStein View Post
From what I know of it, the smut is the leftover alloys in 6061 because the lye pulls out AL from the surface (and converts it while releasing H gas) and it falls into the solution, leaving the surface of just the alloys (smut). The nitric acid (other acid work too) will eat the alloy components but not the AL.
Interesting, that makes sense. I wonder, since 6061 is 95% - 98% aluminum, if the acid rinse is strictly necessary. I bet the smut could be removed mechanically.

Of course, I prefer to do most things using chemistry if possible. But I wonder if it's more trouble than it's worth to do it for a small number of parts (assuming that's what you're doing).
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  #8  
Old 06-01-2018, 07:18 PM
CheckStein CheckStein is offline
 
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Location: NY NY
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Yes, I have small volume of parts, but some have small pockets and smaller drill throughs, which makes it harder to scuff in those areas. The smut will wipe off and it's like a fine blackish powder.

The reason for using paint is so the parts can be easily fixed if they become nicked or scratched over time. Anodizing and powder coating is by far much more durable, but they cannot easily be fixed after being assembled.

But I think you folks gave me some info that I chomp on.

Thank you.
Chuck.
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  #9  
Old 06-07-2018, 01:35 PM
StressedOut StressedOut is offline
 
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Location: Fullerton, CA
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Default

I just finished priming a big batch of parts using Alumiprep 33 (now called Bonderite C-IC 33 AERO) and Alodine 1201 (now called Bonderite M-CR 1201 AERO) so I thought I'd share my experience here.

My original process was this:
1. Clean off the dirt and oils with Dawn dishwashing soap and water
2. Spray with Prekote and abrade with maroon ScotchBright in one direction
3. Repeat step 2 but abrade perpendicular to the first direction.
4. Rinse thoroughly. Check for a water-break free surface.
5. Dry
6. Prime

The abrading process was laborious, especially on large skins. I used Alumiprep and Alodine in hopes of avoiding abrading. The Alumiprep removes the oxides and the Alodine, as Larry said, prevents its formation. It was my hope that removing the oxides without abrading would give me an adequate surface prep without the labor involved with the ScotchBright.

The new process was this:
1. Clean off the dirt and oils with Dawn dishwashing soap and water
2. Dip the part in Alumiprep for a couple of minutes
3. Rinse thoroughly. Check for a water-break free surface.
4. Dip the part in Alodine for two to five minutes (I chose three minutes).
5. Rinse thoroughly and dry.
6. Prime

Results were disappointing. When I dimpled the parts prepped with the Prekote process, the primer would tolerate it with no flaking or other signs of distress. However, the non-abraded batch flaked off after dimpling. It seems like roughing the surface is a requirement you can't get around no matter which path you choose.
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  #10  
Old 06-07-2018, 07:18 PM
wirejock's Avatar
wirejock wirejock is offline
 
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Location: Estes Park, CO
Posts: 2,979
Default Scuffing

Quote:
Originally Posted by StressedOut View Post
I just finished priming a big batch of parts using Alumiprep 33 (now called Bonderite C-IC 33 AERO) and Alodine 1201 (now called Bonderite M-CR 1201 AERO) so I thought I'd share my experience here.

My original process was this:
1. Clean off the dirt and oils with Dawn dishwashing soap and water
2. Spray with Prekote and abrade with maroon ScotchBright in one direction
3. Repeat step 2 but abrade perpendicular to the first direction.
4. Rinse thoroughly. Check for a water-break free surface.
5. Dry
6. Prime

The abrading process was laborious, especially on large skins. I used Alumiprep and Alodine in hopes of avoiding abrading. The Alumiprep removes the oxides and the Alodine, as Larry said, prevents its formation. It was my hope that removing the oxides without abrading would give me an adequate surface prep without the labor involved with the ScotchBright.

The new process was this:
1. Clean off the dirt and oils with Dawn dishwashing soap and water
2. Dip the part in Alumiprep for a couple of minutes
3. Rinse thoroughly. Check for a water-break free surface.
4. Dip the part in Alodine for two to five minutes (I chose three minutes).
5. Rinse thoroughly and dry.
6. Prime

Results were disappointing. When I dimpled the parts prepped with the Prekote process, the primer would tolerate it with no flaking or other signs of distress. However, the non-abraded batch flaked off after dimpling. It seems like roughing the surface is a requirement you can't get around no matter which path you choose.
Yes, you really need mechanical adhesion. Try this just for grins.
1. Prep the part. Dimple, debur, etc.
2. Wash with maroon Scotch Brite and Bon Ami cleanser. Scrub well. This is both the abrasion and wash step.
3. Rinse well.
4. Dry.
5. Alodine.
6. Rinse.
7. Dry
8. Prime
I have a Kitplanes tip on capturing rinse water. It's on my blog.
Let me know the results.
__________________
Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 12/01/2017. Plus a little extra.
RV-7A #73391, N511RV reserved (1,800+ hours)
HS SB, empennage, tanks, wings, fuse, working finishing kit
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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