Compatibility of aluminum and brass

A. Brass is incompatible with aluminum, per MIL-STD-889 (and Notices 1, 2 & 3 thereof) DISSIMILAR METALS.
Galvanized is your best choice.

A. I think an aluminum nipple would be the best choice from the corrosion point of view. You didn't mention it. Why aren't you considering it?

A. Come on guys. A little application perspective here. It is a small engine nipple covered in oil. How much galvanic corrosion will occur? Surely not measurable in my lifetime. Brass, Black Pipe or Galvanized should be fine. For added protection use some good High Temperature anti-seize [on eBay or Amazon] and you will be fine.

Thanks, Thomas ... I certainly can't strongly disagree with you, and if a backyard mechanic was working on his own beater, I'd agree a hundred percent.

But Rhonda is trying to educate herself on the issue of galvanic corrosion to be able to best help her customers, and the answers may be helping her do that.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. The fact that this question is even being asked is commendable! I remember the days I always went to the corner, independent hardware store to get advice. Well, all those corner hardware stores are gone - replaced by the mega-importers such as Lowes and Home Depot! If I can't have my independent corner hardware, at least I have a new found respect for True Value! One of the questions here is how much dissimilar metal area is exposed? The fact that the inside is bathed in oil helps the inside (oil is a really poor electrolyte corrosion wise), however, the outer portion of the aluminum and the brass is where the corrosion will likely progress from. Painting or otherwise covering up the dissimilar metal junction is the best bet if you have to go with brass to aluminum. I'm sure True Value carries either an aluminum or Cold Galvanizing Compound / Zinc Rich Paint. Cadmium plating is used heavily by the aerospace and military industry to interface between aluminum and either steel or stainless, but I wouldn't' suggest this since the result would be a non-RoHS compliant product!

A. Should be fine. Since the aluminum is relative much more anodic that the brass, it would normally experience more corrosion. However since the aluminum is so much more massive than the brass in your situation, it acts as a sink, and won't experience any concentrated corrosion. In a nutshell, galvanic corrosion becomes essentially negligible, and neither metal will corrode any faster than they would normally on their own.

A. Machine cut them out of Aluminum itself and Anodize them to prevent them corroding tight together. Why think about another material?

A. Hi Larry. Almost anything is okay in a climate controlled interior application :-)

Galvanic corrosion requires, in addition to a metal-to-metal contact between dissimilar metals, an "ionic path" (salty moisture).

Regards,

A. Hi Mike.
Such decisions are based upon both the criticality of the situation and the environment.

Such a joint would probably not be permitted to hold a heavy electronic instrument in place over the captain's head even in the air conditioned flight deck of an airliner because the consequence is life-critical; and it would not be okay for even a dollar-store mud flap for a truck because of the corrosive winter environment. But for a hobby application in an air conditioned room, I'm confident that it will be absolutely fine. Good luck.

Regards,

Ted, thanks for your response and your humor. I'll try to remember not to try this technique next time I tackle a mud flap attachment.

Actually, in the unfortunate event of a major disaster this finished product could come into play as a life-support communication instrument ... My hobby is Ham Radio, and this is going to be my effort to create (cheaply) a Morse Code key which can act as a backup as needed, to a Commercially made device on the market for $536. I'm hoping my rendition will cost less than $10. Thanks again for giving me confidence to use on-hand materials (brass screws and aluminum angle iron).

A. Hi David. Yes, aluminum and brass can be "brazed" together, but I'll raise outstretched arms overhead with two crook'd fingers in each hand when I say it because the question is probably more semantics than technology :-)

Metallic materials can be melted to hold the brass and aluminum together, but some people might consider some or all of the methods "soldering" rather than "brazing". If you google "braze aluminum and solder" you will see a number of youtube videos as well as links to proprietary meltable soldering/brazing metals. Good luck.

If you run across John & Debbie B. from Kinnelon, NJ in your little village, say hello from their former next-door neighbors the Mooneys.

Luck & Regards,