stainless steel bolts with aluminum plates, good or bad ?

Discussion in 'Fiberglass and Composite Boat Building' started by hyboats, Dec 11, 2012.

  1. hyboats
    Joined: Jun 2010
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    Location: Sydney

    hyboats Junior Member

    we usually use stainless steel bolts to fix the canopy frame on the deck, there are aluminum plates laminated in the deck. But yesterday my friend told me that's not good, he said aluminum will accelerate stainless getting rust.
    Is that right ?
    Aluminum plates come with - ion, stainless steel come with + :?::?:
     
  2. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    waterproof and Insulate stainless to aluminium joints with Tefgel.

    Ask any rigging shop, mast builder for Tefgel supplies.

    http://tefgel.com.au/

    Avoid using SLOT head countersunk fastenings on technical joints. The SLOT acts as a scraper, workman bruise the countersink with screwdrivers and the slot holds water.

    Use hex head countersunk fasteners.
     

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  3. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    Your friend is wrong Bruce.
    What does happen is the build up of aluminum salts like chlorides in the gap because some metal is sacrificed. These take up more space than the metal itself and make removal of the bolts hard or sometimes impossible. A smear of anti-seize before installation will prevent that.
     

  4. kvsgkvng
    Joined: Jan 2012
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    Location: *

    kvsgkvng Senior Member

    Combining aluminum and steel (even stainless) in wet/salt exposed environment is not a good practice. Aluminum parts will corrode as a sacrificial metal (similar to zinc coating). As the result, whitish oxides will pit aluminum. It doesn't happen overnight but it will happen. If aluminum oxides are in confined space where it can not expand, then anything what is less strong will break, bend, be pulled out and buckle. It could be adjacent fiberglass, anchor bolt connections, etc.

    Solution - use only same materials in contact, either ss.steel or aluminum, but not different metals in contact. Also, use protective coating, use dielectric gaskets.

    REF: http://en.wikipedia.org/wiki/Galvanic_corrosion
     
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