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Dave Krall CFII SEL SES
Joined: 14 Mar 2007
Posts: 342
Location: Seattle WA
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| Posted: Tue Apr 01, 2008 1:14 am Post subject: stainless steel & aluminum don't like each other? |
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| 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
Joined: 28 Jan 2008
Posts: 267
Location: Cleveland, GA
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| Posted: Tue Apr 01, 2008 12:00 pm Post subject: |
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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!
Joined: 07 Sep 2006
Posts: 170
Location: Brevard, NC
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| Posted: Tue Apr 01, 2008 12:06 pm Post subject: |
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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! |
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Wes
Joined: 23 Jan 2006
Posts: 105
Location: Satellite Bch, Florida
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| Posted: Tue Apr 01, 2008 5:40 pm Post subject: Stainless on Aluminum |
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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
Joined: 03 Apr 2008
Posts: 1
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| Posted: Thu Apr 03, 2008 4:42 pm Post subject: |
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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 |
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Dave Krall CFII SEL SES
Joined: 14 Mar 2007
Posts: 342
Location: Seattle WA
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| Posted: Thu Apr 03, 2008 5:05 pm Post subject: |
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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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