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Aluminum corrosion preventative

 

I am looking for a way to prevent corrosion in the spiral case of a model hydro turbine. The spiral cases are machined from 60x60x10" 6061 T651 aluminum blocks. The water passage is now being spray painted with epoxy tank liner,which is peeling off under the high velocities. Anodizing or any process requiring dipping is not practical due to the size, and the fact that some plastic epoxy fill is usually used to smooth minor machining imperfections. The fluid used for testing the turbine is untreated city water @ 70F. Test time is 1-3 months. I am considering using a wax.

Any ideas appreciated.

Ed Kennell
Voith Siemens Hydro Power Generation - York, PA, U.S.A.

Have you tried active Cathodic Protection?

John Tuohy
- Ireland

No answer on that one? Ok, how about electroless nickel?

John Tuohy
- Ireland

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6061 should hold up well to city water by itself without any treatment. It the corrosion being caused by a physical influence, i.e., cavitational erosion or stress defects in the metal?

Since the item is too large to anodize, and if indeed the water is found to be a source of corrosion, maybe you should consider treating the city water feed to keep the pH close to neutral & to remove the chlorine. There are ways to seal the surface of 6061 to reduce the liquid substrate interface, but again, I am wondering what component of the city water might be affecting the aluminum.

Dale Woika
- Bellefonte, Pennsylvania, USA

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1. Try a light coat of chromate before applying the epoxy. Do not put the chromate on too heavy as it will sheer with the heavier epoxy on top.

2. Also try a complex phosphate (iron phosphate with a little molybdate available as proprietary from several venders)Again, use just a very light coating then either epoxy or powder coat.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina