stainless steel & aluminum don't like each other?

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stainless steel & aluminum don't like each other?

Postby Dave Krall CFII SEL SES » Tue Apr 01, 2008 2:14 am

I've heard this recently and wonder if anyone has seen the results of long term contact between the two?
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Postby scubarider2 » Tue Apr 01, 2008 1:00 pm

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.
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Postby Johnny C! » Tue Apr 01, 2008 1:06 pm

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!

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Stainless on Aluminum

Postby Wes » Tue Apr 01, 2008 6:40 pm

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:

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Postby jmkota » Thu Apr 03, 2008 5:42 pm

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

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Postby Dave Krall CFII SEL SES » Thu Apr 03, 2008 6:05 pm

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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