Corrosion Stainless vs Aluminum

[skipmac]

As mentioned in this thread, the problem is caused by a galvanic reaction between the Al and SS which "welds" the parts together with aluminum oxide. So I've wondered if there is something that will selectively react with the oxide leaving the Al and SS undamaged.

A little googling turned up this discussion and a few suggestions. However, kind of like this forum, every suggestion made by one guy is poo pooed by at least one other.

https://www.researchgate.net/post/Wh...ide_soluble_in

[skipmac]

Regarding vinegar to dissolve the oxide, found this on wikipedia.

Acetic acid is mildly corrosive to metals including iron, magnesium, and zinc, forming hydrogen gas and salts called acetates:
Mg + 2 CH3COOH → (CH3COO)2Mg + H2
Because aluminium forms a passivating acid-resistant film of aluminium oxide, aluminium tanks are used to transport acetic

[David M]

With heat, aluminum expands at a greater rate than does stainless...so the gap between the two materials will increase with heat. So yeah, heating does help along with chemicals to penetrate and torque....all three are sometimes necessary.

Use Tef-Gel. Lanocoat dries out eventually. The guys doing the rigging in the yards no longer use Lanocoat.

[UNCIVILIZED]

For putting things back together, Lancote, Duralac, Blue Loctite, & Never Seez are all viable options, depending on whether you want things bonded in place or not. But all of them will allow you to remove stainless fasteners from aluminum after they've been in place for some time.
Harken actually ships a lot of their hardware with Blue Loctite as of last check.

[SVNeko]

This is why I hate aluminum on a boat. Besides the dissimilar metals corrosion, it looks like crap when it oxidizes. My next boat will have max use of CF, zero aluminum and minimal stainless steel.

[UNCIVILIZED]

Originally Posted by SVNeko

This is why I hate aluminum on a boat. Besides the dissimilar metals corrosion, it looks like crap when it oxidizes. My next boat will have max use of CF, zero aluminum and minimal stainless steel.

Carbon Fiber will cause you a LOT more headaches than aluminum ever will. Unless, & even if you use lots, & lots of titanium.

[noelex 77]

A lot of the more common Never Seez formulations contain copper. I would not use these on an aluminium mast.

There are alternative Never Seez products that dont have copper but things like Tef-gel and Duralac are made for this application and are better in my view.

[SVNeko]

Originally Posted by UNCIVILIZED

Carbon Fiber will cause you a LOT more headaches than aluminum ever will. Unless, & even if you use lots, & lots of titanium.

how so?

[weavis]

Having had British cars from the 70s, an impact driver was essential for this problem for dissimilar metals. Also for some boat engines..

My standard M.O. was heat, easing oil and shocking the bolt. Took hours sometimes and days other times.

Good luck.

[s/v Jedi]

I have had galvanic corrosion between a carbon fiber spinnaker pole, stainless steel fasteners and an aluminum fitting. Had to repair the carbon fiber and buy a new end fitting that was improved with an insulating bushing

Don't forget that carbon conducts.

[SVNeko]

Originally Posted by s/v Jedi

I have had galvanic corrosion between a carbon fiber spinnaker pole, stainless steel fasteners and an aluminum fitting. Had to repair the carbon fiber and buy a new end fitting that was improved with an insulating bushing

Don't forget that carbon conducts.

Yes, I know but I do not think it is as bad as alu vs SS. Anyway, molded attachments and synthetic strop fasteners should be used as much as possible.

[a64pilot]

No, he is correct about carbon fiber, I think there are so few problems with it, cause you see so little of it on cruising type and weekend type of boats.
Even Ti when used on aircraft has to have special precautions as it is so noble, no cadmium plated fasteners can be used for example, and just about all aircraft fasteners are cad plated.

I asked about that with my new Ti chainplates and was told to use Ti thru bolts but the rest as SS was OK, the SS is less noble and will take the brunt of corrosion, it will act as a sort of zinc if you will.

Even the "miracle" materials have their shortcomings, often times there just is no real advantage of it over steel or aluminum, except for the cool factor, do not underestimate the importance of the cool factor in marketing

[hsi88]

I restore vintage motorcycles and some of them were literally in the rain for years at a time. Steel screws in aluminum blocks. Kroil and PBB were best at penetration. Along with a manual impact driver, I could usually remove most of the screws, but there were always a couple that had to be drilled. Didn't take long to buy a good set of cobalt drill bits.

[a64pilot]

I learned about the hammer impact driver as a 12 yr old kid with a Honda trail 70 trying to adjust / replace points

[skipmac]

Originally Posted by a64pilot

I learned about the hammer impact driver as a 12 yr old kid with a Honda trail 70 trying to adjust / replace points

I learned about them from a friend that was one of these can fix anything guys.

Have one that's probably 35 years old. Only problem I have to replace the bits occasionally, especially the flat head bits, and the ones in mine are hex but larger than standard hex driver bits.

Maybe time for a new one. Any recommendations on brands or models?