how to stop aluminum corrosion

Thanks. There is no metal to metal contact. I replaced the water damaged parts. Water got trapped between the wood and aluminum and caused corrosion. Replaced wood. Now fixing aluminum.

If the airframe products are too expensive, here's the poor painter's method: Clean surface. Treat with phosphoric acid based deoxidizer. Lately, I've been using water softener cleaner, the green liquid. Humidifier descaler also is phosphoric based and I believe Oshpho may make a conditioner. Prime with Sherwin-Williams DTM (direct to metal) Industrial Primer. I buy it by the gallon but maybe you can get it in quart or even sample sized containers. It can be tinted at the store to any color.

Good luck with your project.

bgum wrote:
Bondo. But that seems to indicate water behind wall.

Please do not use Bondo, all you will do it trap corrosion under it, and you will not know until the whole thing drops out.

GordonThree wrote:
Aluminum is naturally is self protecting, untreated aluminum forms an oxide layer that protects it from further oxidation. However aluminum in contact with steel, iron or copper means trouble.

In its pure state it will protect its self, but we never see pure aluminum in service. we see alloys.

The alloys are two or more different metals, So when there is a electrolyte present there will be two different metal molecules in contact with the electrolyte and it become a galvanic cell and will continue to corrode exposing more and more different molecules to the electrolyte. This will continue until there is no more metal to expose.

The excepted method of treatment is, etch it with a 10% solution of phosphoric acid, remove all corrosive deposits, treat with a 6% solution of chromic acid, rinse well, and protect with paint, the best is a chromate primer used in the marine industry.

All these products can be bought at "Aircraft Spruce and Speciality" on line, they ain't cheap, and they ship with HazMat charges.

Alowdine 1200 is the 6% chromic acid

read the notes at the bottom of the link.

Clean the area with this then rinse really well, then protect with a good Zinkchromate primer form your favorite marine supply store. under the sticker.
If required use a stainless steel platers brush to help clean the heavy spots.
any iron screws or such clean then paint each part prior to replacing them. keep a barrier between each different metal. stop the galvanic cell from forming.

I do aircraft aluminum repair often, That's what we do, :)

Aluminum is naturally is self protecting, untreated aluminum forms an oxide layer that protects it from further oxidation. However aluminum in contact with steel, iron or copper means trouble.

Bondo. But that seems to indicate water behind wall.