Corrosion Pictures

[nichzimmerman]

Good day all, we talk a lot about corrosion on here and I figured it wouldn't hurt to have a thread dedicated to PICTURES of different types of corrosion, materials, and areas where it's been noticed so that those of us who aren't as metallurgically inclined can benefit from it. It can also be a place to ask questions, like: what is going on with my boot cowl skin?

I made these skins (2024-T3, .025") a couple years ago, then tucked them into a stack of other aluminum pieces like floor boards, wing parts, etc. I'm having a priming marathon, and when I pulled these out I noticed a white powdery substance under the protective plastic along one edge. None of the other parts in the pile had this problem. When I removed the plastic and hit it with a polishing wheel in my dremmel, the "cleaned" aluminum surface is rough and must be sanded smooth.

Is this textbook corrosion? After two years of storage? I live in southern Ohio and my shop does get humid in the cooler months.

IMG_20181001_061052313.jpg
IMG_20181001_061104747.jpg

[Bdflies]

Nick, at first read, I decided not to touch the subject. I misread and thought ALL your parts looked like this. I didn’t want to be the bearer of bad news. Couple more reads and I understood this piece is the only affected part. This could evolve into a flurry of opinions, so I'll go first.
Yes, that piece is a textbook example of corroded aluminum. It’s kind of like a cancer in that it spreads. You can buff it and sand it, but it’s not possible to be absolutely sure it’s all gone. When you’re starting with .025” thickness, there’s not much margin. Like I said, opinions will surely follow, but I wouldn’t put that part on a plane.

Bill

[Chris In Milwaukee]

I had mouse urine do that to some of mine. Any chance it got contaminated by a small critter?

[fairchild]

I have a metal surplus company here in Orlando. This is also home to Lockheed-Martin. About 10 years ago they had a fiasco with roof leaks during the summer tropical season.
They had sheets of aircraft aluminum stacked in the plant. Don't know if it was down flat or up on edge. But the roof leaked on it and the water capillaried inward from the outer edge
of the thick stack. I guess it was some time before anyone got around to noticing that the stack had gotten wet. It ruined the whole stack--and you looked just like your picture.
The only difference was it wasn't as raised up and thick--- but the same look of blooming inward into cauliflower shapes where the water laid there trapped. Now all that sheet is living
outside in the rain at the surplus place.
That plastic film sure could cap up moisture under it if there was any around in quantity.

T

[nichzimmerman]

Thanks for the input all. I removed the corrosion with sandpaper followed by a good polishing until everything was shiny again. Net material removal in the thickest spot was less than .004" as measured by a micrometer.

I plan to prime it anyway and see what happens in the next couple years, as it will be that long before it's ever installed. It's not primary structure, and it's easily removable, so I'm not too worried about it, so long as I can prevent this from happening to other aluminum parts. It makes sense that the loose edge on the plastic sheet could have allowed water to become trapped in there for a very long time. I'm VERY glad this was a boot cowl part and not a wing part!

[Chris In Milwaukee]

I'm glad for you, too! My .125" sheet was contaminated by critters. Imagine how awesome I felt when I saw that mess on that expensive material!

[Steve W]

That almost looks like electrolysis. I had some float skins in contact with a concrete floor in a dry climate for a few years. Edges looked like that.