[ARC5] Cleaning Aluminum

[Robert Eleazer]

I own a 1946 Ercoupe 415C. It is natural aluminum finish, mostly unpainted. And I live on an island surrounded by salt water. So, I have a lot of experience with corrosion of unpainted aluminum surfaces.

To remove corrosion of bare aluminum, first clean it with a suitable cleaner, such as a mild alkaline solution. They make cleaners just for this purpose but many household products will work as well. Wash it off and then apply a solution of phosphoric acid, sold as an aluminum pre-painting etcher, such as Alumi-Prep, but also available in many home improvement stores under various names as a metal cleaning and painting preparation agent. The phosphoric acid will remove the top layer of metal and get down to a purer finish. Follow the directions for the strength of the solution and rinse it off after a few minutes. This will remove light surface corrosion such as white powder or some of the black marks, but if the surface of the metal has deteriorated so far that it has become rough, it probably won't help that much other than to get it ready for painting. 

You can polish the aluminum after a phosphoric acid wash or just by itself, using any one of many metal polishes. Some companies, such as Rolite, make a harsher polish designed to remove corrosion before applying a final polish designed to buff to a higher finish. I will doubt you would want to do any of this to radios unless you have a fairly localized area that needs some help. 

Alternatively, after the acid etch you can treat the bare, stripped, aluminum with an alodine compound. This is a chromic acid solution that converts the top layer of molecules to aluminum chromate, a ceramic, that is resistant to corrosion. Some alodines color the metal but others that impart no color are available. After keeping the surface wet with the alodine for several minutes you rinse it off thoroughly and you are done.

For bare outer surfaces of radios I recommend a general cleaning, a phosphoric acid etch, and if desired, an alodine treatment. Prompt and thorough rinsing after application of the compounds for the required time period is important. And I would not do this to the inside of the radios.

For a very modest fee I will allow any of you to come practice these techniques on my airplane.

Wayne

WB5WSV