The authoritative public forum
  for Metal Finishing since 1989
-----

Corrosion Protection for Aluminum in Water

2004

Hello,

I'm designing a simple water-cooled heat sink for use on a long term life test station. For several reasons I'd like to use a machined aluminum block, with water flowing through holes drilled in the block. I've seen corrosion problems with this sort or arrangement in the past, and read many warnings on the web. I strongly suspect the corrosion problems I previously observed were the result of galvanic corrosion from brass fittings used.

I'm considering some coatings to improve the corrosion resistance of the aluminum. I'm considering anodizing but it is not preferred because it reduces heat transfer from the part bolted to the block. I'm also considering an Iridite coating. ( the water is about 20C and is recirculated though the whole plant and is therefore not terribly clean).

My questions are:

1) Will either of these coating really get into the small internal passages of my machined block?
2) Which coating would provide superior corrosion resistance, are either likely to do the job effectively?
3) Are their other coatings I should be considering?

Thank You,

Michael Martin
Mechanical Engineer - Madison, Wisconsin, US

The deeper you go into a small passageway, the less it will anodize. Note that there are contrary opinions on this subject. Alodine basically will not last long in a flowing water situation. I would look at a high phos (possibly a good mid phos) electroless nickel. Not cheap, but very good.Having seen the algal growth in water as well as a tendency for it to plate out salts (like plaque) in tiny passageways, I think that you will find problems with straight aluminum. Only your firm can tell what level of grief is acceptable. Note that there will always be one firm that you sell to that will have a very sour water or extremely dirty water that will defy all of your best engineering.

James Watts
- Navarre, Florida
2004