How do metals in contact fuse together? 1

[PQ2]

A threaded brass plug screwed into a threaded brass coupling will corrode and become fused together when subjected to warm humid air and undisturbed for a long period of time (10 or 20 years). Since corrosion removes metal, how is it that the plug cannot be removed after it apparently corrodes? Shouldn't corrosion make it easier to remove?

Could it be that cold fusion, diffusion, migration, stress relief, or some other mechanism fuses the mating surfaces together?

 

[PQ2]

I omitted that the pressure is atmospheric, and temperatures normal ambient (40 to 90).

 

[EdStainless]

In most cases like your the metals don't actually bond to each other. They become so mechanically coupled that you can't separate them.
There are a few things working here. One is that the corrosion products take up more volume than the metal.
Secondly the corroded surface become rough. This combination assures a tighter fit over time.
There are some cases where metal will dissolve as it corrodes and then some of it will re-deposit. This just mechanically locks things together tighter.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[strider6]

I agree with Ed, i think that most of the problem is due to the higher volume of the oxide formed during corrosion respect the original volume of metal.

S.

http://www.corrosionist.com

 

[redpicker]

Just a minor nit-pick with your title.

The verb "fuse", in general, does not meet "to join or hold fast", but, rather, "to melt and mix".

I know, I'm fighting a losing battle (most people are going to use the word to mean what they think it means, and I can't stop that), but when you understand the meaning of the word, your question does not even make sense. Yeah, I know what you mean, but when we let "fuse" to take on the meaning "to join", then the whole concept of "non-fusion" welding (ie, friction welding, explosvie bonding) processes is contradictory.

OK, back to our normal programming.

rp