Corrosion Test

[racaldwell]

One of my projects at work was to build a corrosion R&D Lab. I installed three corrosion test chambers and of course brought some samples from the hangar to test. I have a piece of flap brace from my RV-6 that is 2024-T3 with alumiprep-alodine-Exopy primed, a 6061-T6 with alumiprep-alodine treatment on a wing rib spacer from the Xenos, and a bare 6061-T6 wing rib flange. There are two tests going now. One is with just salt water and the other is with salt water and acetic acid (the SWAAT test.) The tests will run for 30 days or longer. Here is a picture of the corrosion with the various treatments after four days in the salt water test. I am alodining all my parts for the Xenos and this picture shows me it is worthwhile to do since I live next to the ocean.

[dpilot88]

Rick,
I have attached several pieces of 6061 from the Xenos to my dock which is over the very salty Intracoastal Waterway. They have been there for about two years. The pieces that are primed with self-etching primer and alodined are doing okay but the bare pieces have lots of white corrosion. The worst part of all the pieces, including the primed ones are around the rivets. Lots of corrosion there. I don't know what to do with that except dip every rivet.
Bob Perry
Xenos 55

[racaldwell]

Bob, I remember you mentioning your test. I wonder if it is the SS rivet? Maybe a spray like CorrosionX or paraketone? I am using about 50% 2117 AL driven rivets. It would be interesting to compare.

Rick C.

[dpilot88]

Rick,
I'm sure it's the galvanic action between the SS rivets and the 6061. CorrosionX sounds like a good way to treat the rivets. I didn't try riveting two pieces of 6061 together to see how that would hold up but I always try to use self etching primer on every rib flange, spar etc. whenever possible.

Bob

[racaldwell]

Here are the corrosion test samples after 30 days in the chamber. One test salt water only and other test with salt water and acetic acid.

[dbdevkc]

Pretty impressive!

I wonder what percentage of the fleet has no corrosion protection at all?

[kmacht]

Interesting results but you need to.look at the practical side too. I have had my plane parked out on the ramp with nothing more than a canopy cover on it for 2 years now and don't have any evidence of corrosion anywhere. Almost everything on the plane structure is exposed and easily inspected. I suspect that for those that don't alodine or prime the plane will still far out live the builder before it requires any sort of repair from corrosion.

Keith
#554

[dbdevkc]

I suppose some of that depends on the environment. Interesting though, new kits (b-model) will come with the spar pre-assembled and no option of building it up yourself, with no corrosion protection on those mating surfaces in that sandwich assembly...

[Bryan Cotton]

I've restored a 1946 C140. It had some corrosion issues. Cessna did not use a lick of primer back then. If I only get 70 years out of the Waiex I am ok with that. I'll just fly one of my other projects.

[racaldwell]

I am within the salt spray zone of the ocean here in Melbourne. That is why I am alodining all parts. The test shows that the acid component has a dramatic effect. I don't know how rain water acidity varies with location but I'm sure it does. I'm sure many areas of the country would not be corrosive to 6061 in our lifetime. Unfortunately, I don't live in one of those areas. If I knew I was leaving the plane outside for its life, every part would get alodined and epoxy primed.

The next test I want to do in the corrosion chambers would be the SS pulled rivets and 2117 AD rivets and some cad plated bolts. Stay tuned.

Rick