Material choices to isolate stainless / aluminum

[jordanbettis]

I see a dodgy seven year old video of a guy brazing some aluminum pads onto dirty chrome plated steel pliers. There's no manufacturer documentation on those rods and they're unavailable on amazon. My guess is that's a tube of 4043 or something with a fake label on it.

[coopec43]

Originally Posted by jordanbettis

I see a dodgy seven year old video of a guy brazing some aluminum pads onto dirty chrome plated steel pliers. There's no manufacturer documentation on those rods and they're unavailable on amazon. My guess is that's a tube of 4043 or something with a fake label on it.

"a dodgy seven year old video" If you don't like the message shoot the messenger!!

There is more recent literature on the subject but lets not waste anymore time on the subject as it wouldn't be appropriate for Captain Mark's problem.

Actually I wonder where it would be appropriate?

[Sailmonkey]

Originally Posted by coopec43

You obviously have no idea at all Geez!


Seriously, thank you Sailmonkey for your patience and your erudite response! Have a look at this.

You can braze just about any material together, with a third alloy. Adding a third metal to the galvanic soup is just bad on so many levels when dealing with hulls and the salty electrolyte they float in.

There are techniques like explosive welding that can join the metals, but you’ve still got dissimilar metals in electrically joined in the electrolyte.

https://triclad.com/explosion-bonding/

This is the technique used to join an aluminum superstructure to a steel hull/deck.

[jordanbettis]

Originally Posted by Manateeman

We can always go G10 and 5200. I just wanted to tap into the collective knowledge here as it is always surprising.

I assume you've worked with g10 and know it's stiff as heck. That'd be the only concern with using it. It'll be hard to make it conform, depending on the surface geometry you're working with.


1/8th sheet should work pretty well in most applications though, sanded to key the surface since it comes pretty slick, with polysulfide or polyurethane sealant around it. One trick is to put the sealant on with the fasteners finger-tight. Let it cure then tighten them down. This creates a gasket and then puts it in compression.

[boatpoker]

Originally Posted by coopec43

Just wondering if you could weld the stainless steel to the aluminum hull?

Avery strong galvanic reaction will occur and the stainless will eat
the aluminum in very short order .... weeks.
I know squat about welding but I am a retired Certified Marine Corrosion Analyst.

[coopec43]

Originally Posted by Sailmonkey

You can braze just about any material together, with a third alloy. Adding a third metal to the galvanic soup is just bad on so many levels when dealing with hulls and the salty electrolyte they float in.

There are techniques like explosive welding that can join the metals, but you’ve still got dissimilar metals in electrically joined in the electrolyte.

https://triclad.com/explosion-bonding/

This is the technique used to join an aluminum superstructure to a steel hull/deck.

Many years ago the mining company was using explosive welding?

What’s in a transition joint? “More, much more, than meets the eye – when it’s explosion welded,” says David Gauthier, Market Specialist inMulti-material Transition Joints at NobelClad. Used in shipbuilding for decades, the railway industry is now waking up to the potential of this ‘solid-state’ technique for joining dissimilar metals that, due to their metallurgy, can’t be welded in the traditional manner (by fusion).

https://www.railengineer.co.uk/explo...g-to-rail-now/

[Franziska]

Duplex strips are sometimes used on megayachts to join steel hulls with aluminum superstructures.
Essentialy these are explosion bonded strips of the two materials.

More on the background here:

https://www.cambridge.org/core/journ...FCC016D2A1C75B

[stormalong]

Originally Posted by Manateeman

I would like to hear other opinions on materials to isolate 316 stainless from marine aluminum in above and below waterline applications. Specifically the following. A threaded 316 thru hull flanged adaptor plate from Groco. I’m replacing Forespar marelon.
Currently 1/2 “ thick aluminum backing plates were TIG welded to the hull. They were tapped for bolts prior to welding. The current thru hulls are Marelon and are flush below the waterline. I can add an aluminum or plastic backup plate with new Marelon thru hulls. If I go aluminum, I’m thinking a thin isolation layer between the stainless Groco plate and the aluminum hull backup plate. Lots of choices of materials. The sealant will be 5200. Above the waterline, I’d like to use 316 mushroom thru hulls. Between the inner side of the mushroom and the hull, I’m not sure which plastic to use. Thin, strong and something I can scuff up to grab the 5200. Suggestions?
Thanks to all in advance.
Mark and his manatee crew who have misplaced all their reading glasses.

Please tell us why you want to do this. It seems counter productive to put stainless steel anywhere near aluminum. Why not stick with all Marelon or go to another brand of plastic through hulls and seacocks. Aluminum and stainless do not have to be in direct contact for electrolytic reaction.

You write that you want stainless through hulls above the waterline. Again, why? For appearance? I have some 35 year old Marelon through hulls above and below the waterline. They are still good.