Cast aluminum/stainless bolt galvanic corrosion. Best chemical or compound to add

[Milacron]

to prevent this from getting worse ? In this particular instance, a radar pedestal (the casting below the rotating array that holds the array motor and transmit electronics) on a boat where one of the 3 bolts was very difficult to remove due to corrosion in the aluminum threads. (only in the elements for 4 years) Now need to put it back together but inhibit the cast aluminum thread corrosion from getting worse.

 

[swamp dweller]

We use Tef-Gel. Check out tefgel.com. It works great.

 

[TDegenhart]

Total encapsulation is your best bet. Since the bolt is in metallic contact with the aluminum, water, particularity salt water, will cause the aluminum to corrode. Some other thoughts, change the bolt to a high strength plastic (?), hard anodize the aluminum, bore out the threaded hole and replace with a plastic jacketed stainless shoulder nut, ???.

Some other thoughts on this subject.

Dissimilar metal aluminum/304 stainless galvanic corrosion

Tom

 

[Sea Farmer]

I use the weakest Loctite for the internal threads. It does a pretty good job of excluding water, and is pretty easy to break when you need to remove the bolt.

For the bit of threaded bolt end that protrudes from the end of the fitting or nut or whatever, choices are more limited. This is the bit that is exposed and corrodes more quickly. It helps to cover with some kind of grease then use a plastic end cap to keep the grease in place--something like one of these: McMaster-Carr

Actually I found a better-fitting end cap at my local hardware store, only a few cents.

On edit:

Just recalled that one one set of bolts I didn't use grease, just a dab of oil paint, to cover the exposed threads. Then the end cap. It's still intact, and was less messy to apply.

 

[Cole2534]

I use the weakest Loctite for the internal threads.

Try a thread sealant (loctite 567) in place of a thread locker. Works a treat.

 

[lionelt]

Anyway to get a gasket or O ring in there somehow?

 

[Jorgo]

Another vote for tef-gel here. I do lots of marine work and the commercial fishers swear up and down by a liberal coating of wheel bearing grease.
Jordy

 

[hermetic]

What you are basically producing is a battery! you have two dissimilar metals and an electrolyte, ie water. This works especially well with salt water. To cure the problem you need to eliminate the water from the interface between the metals, using gaskets, O rings, grease or this Tef-gel, which sounds exactly like the product we use in the UK which is called Denso grease. Anything which excludes the electrolyte will work.

 

[Milacron]

Another vote for tef-gel here. I do lots of marine work and the commercial fishers swear up and down by a liberal coating of wheel bearing grease.
Jordy

Can't find any Tef-Gel locally....but can find Permatex Anti Seize Lube....just as good ? (suspect not, as it's considerably cheaper)

 

[Jorgo]

Can't find any Tef-Gel locally....but can find Permatex Anti Seize Lube....just as good ? (suspect not, as it's considerably cheaper)

I can't help with where to get Tef-gel as it's always been supplied to me. If you go with the anti-seize make sure you get the marine grade stuff. Its designed to fight galvanic corrosion. I have no long term data on this stuff but it seems alright so far.
I'd go grease over the neverseize. (I hate the look, smell, texture etc. Of grease. Bleck. My late dad always laughed when I'd have to work myself up to stick my gloved hands in a bucket of grease. I use it as little as possible. But I digress) the thing about fishermen is they've tried pretty well everything to keep bolts from corroding in and come back to grease because they and it are cheap and it works.
Jordy

 

[Trboatworks]

Lanocote is typical for riggers doing assembly work of stainless fittings on aluminum- works.
Boat Lubricant Lanocote

Any decent marine supply shop will have it- if not Call Fawcetts in Annapolis and they will ship a can down to you:
http://www.fawcettboat.com/

I generally try for isolation washers, bushing etc.

That or aluminum bolts eh?

I did some high spec work for builder on this baby- Jimmy Cornells new 45- fittings were specified with aluminum bolts, plastic bushings and washers as needed:

Nos voiliers

 

[thermite]

to prevent this from getting worse ? In this particular instance, a radar pedestal (the casting below the rotating array that holds the array motor and transmit electronics) on a boat where one of the 3 bolts was very difficult to remove due to corrosion in the aluminum threads. (only in the elements for 4 years) Now need to put it back together but inhibit the cast aluminum thread corrosion from getting worse.

Lots of good advice on gaskets, sleeves, and goop.

I'd use those.

But with only THREE fasteners to do? I'd also use one of the better bronzes - bolt and nut same-same, instead of aluminium.

Corrosion or lack-thereof quite aside, the only reason I can fathom for aluminium fasteners is that it is INTENDED the radar be carried away in a gale.. rather than compromise its mount or contribute to capsizing the hull.

It that the case?

Bill

 

[gnorbury]

Helicoils.
TefGel
Loctite
Raymarine's proprietary black goop
...all good solutions.

 

[TDegenhart]

Lots of good advice on gaskets, sleeves, and goop.

I'd use those.

But with only THREE fasteners to do? I'd also use one of the better bronzes - bolt and nut same-same, instead of aluminium.

Corrosion or lack-thereof quite aside, the only reason I can fathom for aluminium fasteners is that it is INTENDED the radar be carried away in a gale.. rather than compromise its mount or contribute to capsizing the hull.

It that the case?

Bill

I think you missed the starting line. Stainless bolt in cast aluminum housing.

Tom

 

[thermite]

I think you missed the starting line. Stainless bolt in cast aluminum housing.

Tom

Yes. Thanks.

Buried in the thread title. Fancy that .... of all places to HIDE s**t.....



That's going to have to relay on a dielectric + gas/liquid barrier, then.

The only electrolytic means to protect the aluminium casting's threads from corrosion and shift it to the replaceable BOLT is to mate it with the same or HIGHER electronegative potential element for the bolt.

Aluminium makes for shit-lousy bolts. Lithium, Sodium, and Potassium don't work for bolts at all.

Nylon and cousins are probably nowhere near strong enough. Not in the as-had count and size, anyway

One does wonder if Aluminium Bronze or Nickel-Aluminium Bronze would be reasonably well-behaved - or at least corrode much more slowly - when used in contact with the very different Aluminium alloy of the casting. Still with goop, regardless, of course.

Anyone done that arredy?

Bill

 

[John Garner]

A long-retired former coworker of mine was a fairly serious deep-water sailor; a couple of years before he retired, he went on a quest to find an effective home-brew corrosion preventive made from ingredients that would be widely available in any major port, for a pittance. He eventually standardized on a mixture of toilet-drain sealing wax, Dexron automatic transmission fluid, and paint thinner, mixed to a potato-soup consistency for brushing on, or coffee cream consistency for spraying. He used it for everything from through-hull fittings to damp-proofing wire connections, and I'm sure he would have recommended it for your application.

Myself, I'd be inclined to fit E-Z Lok stainless inserts to all four of the holes in the cast aluminum, and use Armite Lab's Led-Plate anti-seize compound on the mounting screws. Beyond that, some sort of weather-resistant covering over the exposed hardware would be a damn fine idea . . . especially if the space between the fasteners and weather cover can be completely filled with a very-water-resistant grease.

 

[billzweig]

Why not use aluminum bolts? Those are commonly available in many sizes.

 

[Winterfalke]

Beat me to it, I was going to say I would tap the casting for stainless inserts or heli-coils (make sure they are a different grade than the bolts) and have it anodized or alodine treated. Then have the inserts and bolts passivated, and apply marine grade never-seize or the afore-mentioned Tuf-Gel to both parts. Apply silicone sealant around the mating surface and over the tops of the screws to seal water tight. That's approximately what we did for military grade training equipment.

 

[JST]

Regular Never-Seez is bragged-up as good against salt water corrosion. Might not be good against electrolytic, but if the seawater (electrolyte) cannot get TO the threads, they are not going to corrode. The outside of the nut/bolt might.

That combo of SS and aluminum is actually not a good one. Lots of lit on it if you look around. I like the aluminum bolt idea, even though the differing alloys are likely to still make a weak battery. Use the Never-Seez or similar on those too, though.

 

[thermite]

A long-retired former coworker of mine was a fairly serious deep-water sailor; a couple of years before he retired, he went on a quest to find an effective home-brew corrosion preventive made from ingredients that would be widely available in any major port, for a pittance. He eventually standardized on a mixture of toilet-drain sealing wax, Dexron automatic transmission fluid, and paint thinner, mixed to a potato-soup consistency for brushing on, or coffee cream consistency for spraying. He used it for everything from through-hull fittings to damp-proofing wire connections, and I'm sure he would have recommended it for your application.

Myself, I'd be inclined to fit E-Z Lok stainless inserts to all four of the holes in the cast aluminum, and use Armite Lab's Led-Plate anti-seize compound on the mounting screws. Beyond that, some sort of weather-resistant covering over the exposed hardware would be a damn fine idea . . . especially if the space between the fasteners and weather cover can be completely filled with a very-water-resistant grease.

Beat me to it, I was going to say I would tap the casting for stainless inserts or heli-coils (make sure they are a different grade than the bolts) and have it anodized or alodine treated. Then have the inserts and bolts passivated, and apply marine grade never-seize or the afore-mentioned Tuf-Gel to both parts. Apply silicone sealant around the mating surface and over the tops of the screws to seal water tight. That's approximately what we did for military grade training equipment.

Well, Hell.. if we are going to suggest he works his ARSE off hard enough at it to have to skip meals and visits to the terlet for a whole three days...

How about pulling the dimensions and re-making the whole silly aluminium casting in Bronze, Monel, stainless, or .....Carbon fiber RP?