stainless steel & aluminum don't like each other?

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Dave Krall CFII SEL SES
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stainless steel & aluminum don't like each other?

Post by Dave Krall CFII SEL SES »

I've heard this recently and wonder if anyone has seen the results of long term contact between the two?
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scubarider2
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Post by scubarider2 »

Dave, I have heard the same thing.  That is why whenever the two are called to be put together somehow, epoxy is needed.  Have not seen the damage if not done correctly.
Dennis
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Johnny C!
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Post by Johnny C! »

Those two metals create what is know as galvanic corrosion. It's the
green paste that I'm sure you have seen somewhere. That leads
to the break down & failure of the aluminum.

It was the source of Delorean's automotive demise. He used Stainless
screws on Aluminum panels.

You will need some sort of insulator. Epoxy should work...

Later!

Johnny C!
There are many things that happen really fast when you are
flying an airplane. There is no sense in rushing any of the others.

I would much rather be looking down at the runway, than up at it.

Duane Sorenson & Rick Norton Gone West 6/8/09. Godspeed
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Wes
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Stainless on Aluminum

Post by Wes »

Those two materials have to be combined very carefully.
They are pretty far apart on the electromotive series (difference in electrical potential) and the aluminum, being the least noble (more sacrificial) will transform into a white powder under the following conditions:
- the metals are electrically connected (almost guaranteed when SS is used as a fastener)
- moisture is present and wets the metals (absolutely guaranteed in Florida!)
The problem is compounded when the moisture is salty, i.e. by the ocean!
However, having said that, I have been using SS fasteners on aluminum masts on sailboats in Florida for over 30 years and find that if you use a good grade of stainless and INSULATE the exposed boundary between the two metals, the joint will last for 20 plus years. It may be a little tuff to remove the bolt or screw from the part, but it will still be there.

The aluminum parts of our airplanes that are joined with SS rivets are all bonded with epoxy to prevent any moisture sitting in the joint.
Plus,  being Light Sport Airplanes, we are not allowed to fly in moisture (rain), ---  are we?  :lol:

Wes
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jmkota
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Post by jmkota »

Check this site.  The chart shows basically how much galvanic action or whatever the term is between different metals.  The closer together metals are on the list, the better.

http://www.engineersedge.com/galvanic_capatability.htm

Jack
Dave Krall CFII SEL SES
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Post by Dave Krall CFII SEL SES »

jmkota wrote:Check this site.  The chart shows basically how much galvanic action or whatever the term is between different metals.  The closer together metals are on the list, the better.

http://www.engineersedge.com/galvanic_capatability.htm

Jack
Cool, thanks for the chart.
We're also coating all bare metal with Zinc Chromate. Anybody else going that route?
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