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Author Topic: Stainless fasteners with Aluminum  (Read 927 times)
WEC4104
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« on: July 15, 2006, 02:37:26 PM »

Was wondering about something today and would like to run it past some of our board's rocket scientists...

Having a GMC4104, much of my coach body is aluminum. The body is holding up well, but I had a lot of rusty screws and bolts. Given the option, I have been replacing some with stainless in hopes of avoiding rust stains and for general appearance. (Not cheap though)

Memories from Chemistry 101 tell me that two dissimilar metals can produce a galvanic reaction and induce corrosion, I started thinking. Is there a "best" metal to be mated with aluminum? Certainly aluminum with aluminum would be the answer, but the softness of the metal limits it's use for screws and bolts.

I am on the correct path using stainless?
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Ross
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« Reply #1 on: July 15, 2006, 02:58:45 PM »

Dissimilar metals produce electrolysis with the help of an electolyte.  Put stainless and aluminum together and put it out in the desert with 0% humidity and it will last forever.  Put the same thing in salt water and it will dissapear in no time.  When I use stainless rivets or oher hardware against aluminum where it will be wet, I put a dab of sikaflex behind the fastener.  That keeps water from getting in behind the fastener where it contacts the aluminum. 
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OneLapper
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« Reply #2 on: July 15, 2006, 03:40:07 PM »

The great thing about stainless steel is that it doesn't react.  They make artifical knees out of the stuff.  But what will happen is that the metal that it is contacting the stainless steel bolts will react, so it is important to use some type of compound to prevent the gaulling of the threads when it comes time to remove them.

I use a lot of stainless, aluminum and titanium on my race car (as seen in the current issue of Car and Driver!).  I simply use Never Sieze on all of the threads and have never had a problem getting the hardware apart.  If I don't use Never Sieze, the threads will gaul every time.

HTH,

Mark
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OneLapper
1964 PD4106-2853
www.markdavia.com
pvcces
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« Reply #3 on: July 15, 2006, 09:11:38 PM »

While silicone has lousy adhesion, there is one area where it works quite well.

When what you want is a thread filler so that contaminants cannot later prevent removal of threaded parts, it will keep electorlytes like dirty water out of the joints, if they are properly tightened. While it does that, it prevents corrosion, as well.

When we were running concrete pumps, we had to bolt together parts that were exposed to cementious water under pressure. If precautions were not taken, it would be hot wrench time upon removal. A film of silicone on assembly completely removed any problems like that. Grease was a very poor second.

For what it's worth.

Tom Caffrey
Suncatcher
Ketchikan, Alaska
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Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska
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