Alodine Question

I'm working on my RV-12 wing kit and have decided to alodine and prime/seal the interior parts. That's not what this thread is about, though

I did my first alodining last night and am a little concerned about the results. All of the pieces were Alclad, and I used the following prep procedure:

1) Debur and smooth edges.
2) Glove up
3) Wash in Dawn, then rinse in plain water
4) Etch in EkoEtch (same as Alumiprep), scrub off the Alclad with a Scotchbrite pad, and rinse in distilled water per directions.
5) Dip in alodine solution. Full immersion was used for 2-3 minutes with almost all of the pieces.
6) Rinse by immersing in clean water.
7) Hang up to dry overnight

I immediately noticed a huge variation in coloring of the metal upon removal from the rinse. When I checked on the pieces this morning, the variation (unsurprisingly) was unchanged. The metal ranges from silvery aluminum with a gold sheen all the way to a uniform brown. I also found that wiping the parts with a damp cloth results in some of the color transferring to the cloth (that is, the cloth gets stained and the color on the metal lightens).

I did the stub spar by painting the alodine solution on the piece rather than immersion. The color still showed variation, but not nearly as much as the dipped pieces. And there was much less excess to wipe off.

So, is this normal? Do I need to wipe down all of the pieces before I prime, since the excess may effect the bonding of the primer/sealer?

Or do I need to fix something? Should I actively wipe off the alodine in the rinse phase? Did I skip a step, such as wiping the pieces with paint thinner prior to the Dawn wash? Do I need to be more vigilant about removing all of the Alclad in the etch process?

I'm trying not to be neurotic about the build, but I'd hate to screw up the most internal pieces of the wings for all sorts of reasons. Folding wings = bad. Fixing wings spars and doublers after assembly = almost as bad.

Just a couple of suggestions re. your conversion process:
You didn't indicate how long you are etching. You may or may not be a little too agressive here. Try shortening the soak. Also, I would recommend either rinsing and agitating or running water to ensure full dilution of the etchant.
By using the scotchbright on alclad surfaces you are effectively destroying a valuable element of the corrosion resistance of the part. Proper etching should be all that's needed. If you are planning on prosealing the surface, then scotchbright (no alodine). Otherwise, not necessary.
Unless you're using very cold water, the alodine soak time may also be too long. Try water at ambient and soak for one minute. A rinse/soak coming out of the alodine should be all that's needed to stop the conversion process.
Terry

Are you wiping it down after you rinse it with water? I usually rinse it and then take a dry cloth and wipe any alodine left on the metal off.

Alodine

If you are getting a dark brown color rather than a straw gold color you are soaking in the alodine too long. You should get a light gold color. Also when etching with Alumiprep I use a Scotchbrite pad in the etch to wet scrub the parts along with a soak. Then I rinse in fresh water and, while no longer touching the parts, hang them to dry although compressed air drying is okay but contamination is to be avoided.

After a total rinse and complete drying, I alodine by either a 3-5 minute soak or brush on and keep the alodine wet for 3 to 5 minutes. If the surface tension of the alodine parts or runs off the surface rather than sticking, the surface still has oil or contaminates so the etch process was not done well enough. No matter how deep the color is the alodine will appear streaked.

Rinse with low pressure or a fresh water dip and then be allowed to dry in still air. Without touching for fear of contamination and within 24 hours I prime the parts and you have a good base for paint. One note here...fresh alodine will act rather quickly to color the aluminum a gold color but as the alodine gets used more it will get exhausted. At that point it will take longer to acquire that gold color and after awhile it will hardly be gold at all. Then it is time to replace the Alodine although I have used it when it is pretty exhausted by giving it a real long soak. The length of time you expose the aluminum to the alodine will then have to vary with the strength of your solution.

This is what Heinkel Industries, the maker of Alodine & AlumiPrep, recommend. The product is sold under a few different names but I believe Heinkel is the only manufacturer and they have a website with all the technical data.

Dick DeCramer
RV6 N500DD...entirely alodined
RV8 wings completed...entirely alodined
N9007A C170A...entirely alodined AND for Sale
Northfield, MN 55057

Thanks for the input, guys. I'll be incorporating your suggestions into my process. I've been Scotchbriting along with the etch to promote primer adhesion. However, with the addition of the alodine step, I may be able to forego that part.

Based on your comments and some additional research I think I 1) let the parts soak in the alodine a little too long, 2) did not agitate the parts properly while in the soak, and 3) let the parts overlap inside the soak.

I have gone back and rinsed off the parts, scrubbing with a clean rag. This seems to have removed much of the excess conversion, leaving me with a much more uniform coloration. There are still some lines and variations, but everything seems to be a nice golden hue, at the very least.

If all seems well and good, I'll try to shoot some primer tonight.

Keep the input coming, and thanks for the help so far.

Alodine problems

lawspud said:

snipped
I did my first alodining last night and am a little concerned about the results. All of the pieces were Alclad, and I used the following prep procedure:

1) Debur and smooth edges.
2) Glove up
3) Wash in Dawn, then rinse in plain water
4) Etch in EkoEtch (same as Alumiprep), scrub off the Alclad with a Scotchbrite pad, and rinse in distilled water per directions.
5) Dip in alodine solution. Full immersion was used for 2-3 minutes with almost all of the pieces.
6) Rinse by immersing in clean water.
7) Hang up to dry overnight

I immediately noticed a huge variation in coloring of the metal upon removal from the rinse. When I checked on the pieces this morning, the variation (unsurprisingly) was unchanged. The metal ranges from silvery aluminum with a gold sheen all the way to a uniform brown. I also found that wiping the parts with a damp cloth results in some of the color transferring to the cloth (that is, the cloth gets stained and the color on the metal lightens).

I did the stub spar by painting the alodine solution on the piece rather than immersion. The color still showed variation, but not nearly as much as the dipped pieces. And there was much less excess to wipe off.

So, is this normal? Do I need to wipe down all of the pieces before I prime, since the excess may effect the bonding of the primer/sealer?

Or do I need to fix something? Should I actively wipe off the alodine in the rinse phase? Did I skip a step, such as wiping the pieces with paint thinner prior to the Dawn wash? Do I need to be more vigilant about removing all of the Alclad in the etch process?

I'm trying not to be neurotic about the build, but I'd hate to screw up the most internal pieces of the wings for all sorts of reasons. Folding wings = bad. Fixing wings spars and doublers after assembly = almost as bad.

Click to expand...

Jeff,
Did you allow the parts to dry after you etched them? If you did, that is your main problem. Once the parts are immersed into the etch solution, you should not let them dry, until they come out of the rinse water AFTER they are Alodined. Allowing the etched parts to dry after rinsing allows the parts to start corroding. This happens on a molecular level where you can't even see it happening. This thin film of corrosion will prevent the Alodine from adhering properly. You also must not touch any of the parts during the process.
I will send another post with the proper way to do this.
Charlie Kuss

Proper Alodining Procedure

Jeff,

I've found that dipping is the only completely satisfactory way to get consistently good results with both AlumiPrep and the Alodine. The AlumiPrep instructions say that the parts should be dipped, rinsed, allowed to dry and then Alodined. DON'T ALLOW THE RINSE WATER TO DRY!! I learned this from an A&P friend who works with Alodine every day. Alodine will only bond to clean, corrosion free aluminium. This is THE key to success.

How I do it.

#1 I scuff the parts with a ScotchBrite pad soaked in a good solvent, usually lacquer thinner. Wipe the part off with a clean paper towel before the solvent dries. This accomplishes the following:

Gets rid of any residual adhesive from the plastic coating.

Ensures you haven't left a little bit of the plastic on the part. (Ask me how I know) This isn't much of a problem with the newer, blue colored plastic coating. I had the old, clear plastic coating on my 8A project.

The scuffing helps the Alodine and primer bond to the metal.

#2 Attach wire and hang all parts on a stand. I used an old wardrobe hanger and 2 unairworthy HS-609s. I can supply photos off list if desired.

#3 Suspend several parts in your AlumiPrep tank for 1-3 minutes. I've found that diluting the AlumiPrep 4:1 or 6:1 gives you more solution with less expense. It also takes a little longer than using it straight.

Stronger solutions will cause the edges of 2024 T-3 to turn black with oxidation if you forget a part and leave it in to long.

This gray oxidation is not an unrepairable disaster. Simply submerge the part in a tank of rinse water. Wearing latex gloves, rub your hand against the oxidized area while keeping the entire part submerged. This will remove the black oxide. This is important because any oxidized/unclean area will not "take" the Alodine. Do not touch the parts after starting the etch and Alodine process for any other reason. The oils from your skin will contaminate the surface and affect the quality of the Alodining/priming job.

I try to set up separate tanks for the AlumiPrep and Alodine. This saves time and insures that the rinse water doesn't dry before I can submerge the parts in Alodine. Once the rinse water dries, the aluminium is subject to the rapid start of corrosion. That is what causes most of the poor results with Alodine. Another trick I was taught; If you find that an area of a part (this happens mostly on skins) is not "taking" the Alodine, do the following. Using latex gloves and a fresh, clean ScotchBrite pad, scuff the affected area while holding it submerged in the tank. I have 7 gallons of Alodine solution and 8 gallons of AlumiPrep/water solution. This is sufficient to fill the 5 foot kiddy pools a few inches deep. It will also fill most Beer Cooler type ice chests or the 6" PVC tanks I made. 5 gallon plastic paint or drywall spackling buckets also work good for small parts.
For doing the larger skins you will need larger amounts of Etch and Alodine. I made my own one piece wing main skins. These were over 9 feet long. I had to build 10'X3' tanks out of 2X6s and plastic sheeting to make 3 tanks for these large parts. It took 40 gallons of each chemical to fill these tanks 4 inches deep. I also used these tanks for doing my fuselage tailcone skins and the main longerons. You probably won't need tanks that large for any of your parts.
I suggest you purchase your Alodine or Iridite 14-2 in powder form. It is MUCH cheaper that way (about $2 per liquid gallon).

#4 Rinse the parts. A garden hose is OK, but submerging them in a water tank works better. I use the same rinse water tank for doing both rinse operations. I have never had any problems using this method.

#5 Suspend the rinsed parts in the Alodine tank BEFORE the rinse water dries. This is important for good results. Try to avoid allowing any area of the part to lay against the sides or bottom of the tank. Contact with the tank will inhibit the Alodine conversion process. (converting the surface aluminium to aluminium chromate)

On large parts which will not fit well in your tanks, pour Alodine solution over the exposed parts. Keep all areas wetted with Alodine solution. Do all handling of skins using at least 2 wires while Alodining.

#6 Once the parts have a nice "golden" tint to them, remove and rinse them off. Again, do not touch, handle by the wire(s). After rinsing, hang them up and allow to dry at least 8 hours. If you leave the parts in the Alodine to long, they will look like they have a brown, fuzzy coating. This can be cured, IF you take action before the parts dry. IMMEDIATELY place them back into the tank of rinse water and clean off the excess Alodine using the same method mentioned in step #3.
Don't touch the freshly Alodined parts while they are wet. Handling them will wipe some of the soft, wet Alodine off. It may also contaminate the surface, which will cause problems when you prime them.

#7 You now have nicely Alodined parts, untouched by human hands and all ready for priming.

#8 Prime

#9 Finish paint any fuselage interior panels desired. If you use a polyurathane finish paint, you won't have any damage due to riveting afterwards.

Charlie Kuss

PS Alodine and it's competitors are photochemically reactive. Do NOT set up Alodine dip tanks outside in the sunshine. The sun will neutralize the chemicals. The parts will be converted during the first "in sun" use. However, the sun will ruin the chemicals for further use. A good friend learned this lesson the hard way. The etch chemicals are not affected by the sun.
I suggest you do this stuff in the garage, with the overhead door open to allow good ventilation. When I use large dip tanks like a kiddie pool or my really large tanks, a way to remove the chemicals for reuse is needed. I use an aquirium water pump with automotive fuel hose lines attached to pump out the tanks. I store the chemicals in 5 gallon plastic bucket, like those sold at Lowes and Home Depot. Keep your stored liquid chemicals in a shaded area. I place mine under the work bench at the rear of my work shop. If you have a friend who is a painter or does home remodeling, ask him to clean and save the 5 gallon buckets his paint and dry wall spackling come in for you. That's how I got my buckets for free.

The Rolls Royce specification for chromate conversion coating states "apply the solution until the surface shows an iridescent gold to a light golden-brown colour."

Too much attention

Don't forget that you are corrosion protecting some aluminum, not making jewelry. I had the same reaction when my first alodined parts came out many colored and hued, but eventually I realized that it does not matter. Prime over it and move on. The part is no better protected if it is all one perfect shade of gold or if it is half medium brown and half light gold. The alodining has converted the surface of pure aluminum and made an aluminum oxide coat that is thinner and more durable than the naturely formed aluminum oxide layer. The darker areas are just a thicker layer of the alodine oxide layer. The goal of this alodine oxide layer is to create a layer that primer sticks too not necessarily to be the primary corrosion protection layer, and the darker areas hold paint just as good as the perfect golden hue does. As many have mentioned, not letting the part dry between the etching, rinsing, and alodining is an essential part of getting a nice cosmetic result with alodine.


Kerry Stevens
Have you driven any rivets today ?

Time

Old thread... I know... What is the max time between alodine and prime?

Time

rsrguy3 said:

Old thread... I know... What is the max time between alodine and prime?

Click to expand...

If properly alodined, indefinitely. Theoretically the surface has been converted.
Sure hope everyone is collecting rinse and properly disposing. Stuff is pretty toxic. I collected into a sluice flowing into a large bin. Allowed it to evaporate down to a couple gallons then transferred the remaining to jugs for haz mat disposal.

Hexavalent chromium

Thank you Larry for mentioning proper disposal. Folks, this is the stuff that made Erin Brokovich rich, P,G,&E poor, and the whole town of Hinkley, CA sick with all manor of debilitating disorders.

Really bad stuff to let out into the environment. Let it evaporate into sludge and take to hazmat.

There are better, as well as much safer processes nowadays. The gold standard is AC-130 solgel followed by B-6747 primer. This is the process Boeing uses now. The bummer is that it is hard to buy in small quantities and pretty expensive. And the solver has a short life after mixing.

But your hair and teeth won’t fall out, your liver won’t die, you won’t get lymphoma, etc.