aluminium corrosion product

[aybee]

is there a liquid "solvent" which removes the white/yellow corrosion product from aluminium ? I am thinking of marine grade cast aluminium which has corroded in sea water..obviously the fluid cannot also eat out the aluminium casting in the process...Old sea dog

 

[Metalguy]

That stuff is probably alum. oxide, which is real tough. A dilute sol. of nitric acid *may* remove it without attacking the alum. underneath.

 

[aviat]

The mil spec for chemical corrosion removal compounds for Al. is Mil-C-38334. A web serch under that number finds several suppliers for the product, to that spec. If the part is just stained you could likely remove it mechanically with scotchbright. The following site gives more details.

http://www.eaa72.org/tech/ac43.13-1b/2m-ch6_8.pdf

 

[IRstuff]

The MIL-C-38334 removal agent is phosphoric acid based, which actually removes aluminum.

I recall that we tried to remove aluminum oxide in our processing once and wound up using an ion mill to literally blast the oxide off, since it resisted all of our chemical etchants.

The MIL-C-38334 compound is relatively mild, so you'll probably need to wire-brush or grind off the majority of the corrosion, treat it with MIL-C-38334 compound and then anodize the surface to prevent or minimize future corrosion

TTFN

 

[unclesyd]

Here are two materials that I have had great success with on Al around salt water. I would get a tube of both Autosol and Semichrome. If the link doesn’t work go to the home page and search for Semichrome.
If you have to use an H3PO4 based material the best would be from a chemical supply store. I would try one made for Al fins first. Get the concentrated variety, this will allow you to use higher concentrations if the white rust is heavy

http://www.eastwoodco.com/shopping/...ute15=0&attribute16=0&RS=1&keyword=semichrome

Come back with whether it’s pitted or not.

 

[aybee]

thanks for the help guys,I have used Autosol for years to shine up alloy but this is beyond its capabilities. Now that I know what Mil-C-38334 has in it I can consider my options

 

[kenvlach]

The best solution (in terms of not harming the aluminum substrate) is the 2.0 wt% chromic acid + 3.5 vol.% phosphoric acid, balance DI water, solution used at 50-100^oC. This is the official method of stripping oxide to determine the anodic coating weight per ASTM B137, ISO 2106: 1982, B. S. 6161: part 1: 1984, and EN 12373-2: 1999. Sometimes called “slow stripping” solution, although actually quite rapid at 100^oC. The chromic protects the bare Al from the phosphoric.

The next best method is to use a commercial deoxidizer/desmutting solution. These are either nitric or sulfuric acid based, but contain inhibitors to stop the attack when bare Al is reached.

Concentrated nitric acid (67-70 wt%) is also very safe for cleaning Al (pretty harmful to humans, though). A protective nitrate forms once the bare Al is reached.

http://www.pc.chemie.uni-siegen.de/pci/versuche/english/v44-24-2.html

Dilutions to 50 vol% (38 wt%) are commonly used to reduce the nitric acid fumes, but the reactivity vs. Al goes up fast if the water content is increased. Useful for stripping metallic plating, too, e.g., EN (electroless nickel).

If possible, take your part to a nearby anodizing or plating shop, as they already have the above solutions and can safely handle.

 

[Metalguy]

Kenvlach,
Excellent point about using conc. HNO3. That's what I used way back in my first met. lab. job, in 1960 to clean small pieces of alum.

 

[aybee]

thanks for all the input. I bought a litre of HF/Sulphuric acid Aluminium cleaning liquid from my local autospares outlet. It did work to a point I think the secret is in getting the dilution rate correct. used out of the bottle it ate the aluminium faster than the oxide, used per instructions (7:1 dilution)it was only partly effective..think it needed a lesser dilution and possibly warmer. I was amazed that I could by HF in the store , its very dangerous stuff and can kill in small doses when concentrated