What does Aluminum Corrosion look like?

[snoopyflys]

I have seen rust as most of us have, but I am not sure how to spot corrosion on alumumin. I searched the forums without luck, so anyone have some pics or links to share of misfortune of aluminum corrosion.

Thanks,

[Danny7]

there are different kinds.

I think filiform is the one that looks like little bug tracks, a very small squiggly line. I've seen this starting on edges when moisture was present.

i don't know the names of the other types, but a white frosting look is common.if it is very bad it will flake off from the parent material

here are some pictures : http://www.airforums.com/forums/f441...ion-42647.html

[chaskuss]

Dan,
The types of corrosion are listed in the link below [no photos though]

http://www.eaa1000.av.org/technicl/corrosion/types.htm

Here is an index of a series of articles regarding aircraft aluminum corrosion and how to prevent/fix it. See

http://www.eaa1000.av.org/technicl/c...on/corridx.htm

Charlie Kuss

[apkp777]

Surface corrosion is the most common form. It exists EVERYWHERE on exposed aluminum. It's why we have to polish aluminum aircraft. Usually is appears as just a gray dull discoloration of the skin but does have squiggly lines that look like miniature lighting bolts. All this will come off with a VERY light scotch bright pad (blue or green). However, don't do anything with it until you are ready to treat it with alodine and primer. Left alone on ALCLAD aluminum it will remain without any structural damage for a VERY long time. Don't get freaked out by corrosion. If you live near the coast it will be a bigger deal. I suspect within 5 or 10 miles max will rapidly accelerate the process.

[snoopyflys]

Thanks for the replies. Fortunately I haven't seen of that just yet. And being that I live about 50NM inland from the Gulf of Mexico coast, I wasn't sure what to expect. I haven't used alodine before I primed parts I have built so far. Not sure, maybe a mistake. But I have tried to leave the Alclad parts as is. I don't want to start another big discussion on priming as that topic has been cussed and discussed elsewhere. I just hope that what I have done, will provide me several years of flying once finished.

Regards and thanks again.

[apkp777]

Dan,

50 miles inland shouldn't really be an issue. Primer wars will continue forever. You will be fine. I would alodine and prime any extrusions however.

[Danny7]

Originally Posted by snoopyflys

Thanks for the replies. Fortunately I haven't seen of that just yet. And being that I live about 50NM inland from the Gulf of Mexico coast, I wasn't sure what to expect. I haven't used alodine before I primed parts I have built so far. Not sure, maybe a mistake. But I have tried to leave the Alclad parts as is. I don't want to start another big discussion on priming as that topic has been cussed and discussed elsewhere. I just hope that what I have done, will provide me several years of flying once finished.

Regards and thanks again.

Hey, you should do a little experiment- take some pieces of scrap al, both alclad and "bare" and set them outside somewhere they can get rained on. you could even take a light salt solution - a1/4 teaspoon of salt in a large glass of water and let it sit on the aluminium. You should see some corrosion pretty d q. this would be for you to see for yourself what kind of corrosion is likely to happen in your area.

[snoopyflys]

While removing the vinyl from W-703 skin this evening I found this white feather looking stuff under the protective coating near the edge.

(Sorry for the fuzzy pic.)



Is this what some are calling "filiform" corrosion or just my imagination or paranoia? If it is, is the fix to lightly buff it out, Alodine and prime? Or since I don't have Alodine handy at the moment, use a self-etching primer to slow/stop this from becoming worse? BTW - my completed HS has been hanging in the garage for over a year now and I don't see this on outer skin (inside is primed with self-etching primer).

Danny, I think I just may "plant" some AL in the garden to see how long it takes to chalk up. I have a Rib, alcald sheet and some scape extrusion that I will donate to scientific discovery on my part. Thanks for the suggestion.

Kind Regards,

[Ironflight]

That looks to me to be leftover adhesive scum Dan.

Corrosion is going to look and feel coarse, whereas the normal aluminum surface is wonderfully smooth.

FYI, I have owned airplanes on the south side of Houston for 30 years now. Little primer on the Spam Cans, and no bad corrosion. I have lots of aluminum scrap laying around the hangar, exposed to the temperatures variations and dew - no significant corrosion. If I leave a toolbox open in the hangar, the steel stuff rusts overnight - no aluminum parts corrode.

Your airplane (or airplane parts) are not going to dissolve without warning. Use common sense, check things once in awhile, and you'll be fine. Prime per your desires, but don't be too worried about it. Yes, we live close to the ocean. No, stuff doesn't oxidize away overnight. That's where the sheet metal is all AlClad.

Paul

[apkp777]

Not corrosion from what I can see. Looks more like adhesive from the plastic. Filiform is more gray/black. Remember the pure aluminimum layer (ALCLAD) is supposed to corrode. It will keep the corrosion away from the structural alloy underneath.

I did just remove my blue plastic on the wings and found some light corrosion. I will go to the airport today and see if I can get a good photo and post it later today. I am in no rush to clean it up. When I do, I will polish it away and apply Alodine 1001 (clear).

Again, it's best to leave it alone it is not going to hurt anything. At some point when you prep for paint the painter will scuff the surface and prep accordingly. It'll go away then.

You can "plant some AL in the garden" and it'll still be there in 30 years. Soak it in Pepsi and good bye.