Galvanic Effects Stainless Steel vs. Aluminum

[Sancho's Horse]

I have some stainless steel bar stock that I was going to use as a spacer on an aluminum trailer I am building. I am a little worried about galvanic effects. Should I be? I was considering using some JB weld to provide some added strength and was hoping that this might slow these effects.

Does anyone have any best practice experience?

I had someone tell me because it is stainless it will be fine, but they based this on nothing. I try to know enough to know when I don't know.

 

[Harold in CR]

From past experience in manufacturing using SS, we always used NON-magnetic 304 Stainless. Outboard motors are used in a very corrosive environment. SS bolts and screws are used, BUT, the corrosive environment will cause the Aluminum to corrode and stick to the SS.

I'm sure there are others with better metallurgy info, and, we were told 304 is NOT non-magnetic and WILL rust or corrode, but, we never had to replace anything we built due to what we used, mostly the product was used in Salt Water.. When in doubt, a tiny dab of a non-stick compound, like "Never Seize" will stop the "Galvanic action" by keeping the corrosive aluminum from sticking to the NON corrosive SS.

18 years of doing the SS stuff, is what I am offering as advice.

 

[marty]

Galvanic corrosion
http://en.wikipedia.org/wiki/Galvanic_corrosion#Galvanic_compatibility

 

[iamsofunny]

The aluminum will corrode in the slightest from the galvanic effect, not the stainless
The stainless will rust by itself eventually

 

[Tench]

The link below is to a Galvanic list, basically the most reactive metals are near the top and least at the bottom, a basic rule is the greater the distance on the list between 2 adjoining metals, the greater the Galvanic reaction. Select materials that are closer together to minimise reaction.

http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm

 

[Kingfish]

I bet if you offered up a sacrificial anode that it will reduce the potential:
Imagine the in-line short check-valve to a water heater, or the replaceable anode rods: The anode takes the brunt of the ionic potential before considering the tasty insides of the water heater and the heating elements… in theory anyway. On Navy ships where steam is employed, the main condenser turns spent steam back into feedwater, and does this by passing seawater through cooling tubes: On the seawater side there are large plates of Cadmium (or Zinc alloy) that act as the sacrificial anode, and these had to be inspected/replaced periodically.

First see if you can get Cadmium washers, and second - place a few on the trailer in easily observed areas… and that should take care of the potential.

Passivated, KF

 

[iamsofunny]

The glue would help if it's waterproof

 

[Sancho's Horse]

Thanks for the responses. The Stainless in question is 316 stainless strip bar (non-magnetic). Tench put up a really useful list from an Army Missile Command Report RS-TR-67-11, thanks for that. I think the Aluminum in question is 6061 T6, but that is just a guess. It is some extruded support for a dry erase board. I have cut it before, many months ago, and had parts in corrosive environments, and didn't notice any big difference in corrosion between the outside and the cut portions, however, there is some sort of coating.

I checked out the JB Weld. They say water-proof, electrically insulating, acid resistant, and good enough for me. There is probably something better suited out there, but I am familiar with it, and it is cheap so, I will end up using it. Above and beyond the usual sanding and cleaning of surfaces, I will put some deep scratches in the aluminum before I apply any of the JB Weld.

Originally, I was going to use some of the 1/4" Aluminum bits from the base of the dry erase board to strengthen the joint, but another idea came along which required those pieces. Of course, inspiration struck only a day or two after I had already made the cuts, so now we have spacers, and I am on my usual path to knowledge. Most of the useful bits usually come after I say, "Oh, no!"

 

[iamsofunny]

Don't use the glue as your only method of adhesion. It's more of a protective layer.
If something is slightly wrong and an aluminum oxide layer forms (that's the stuff you saw on the aluminum) the glue will just come right off
Aluminum doesn't glue well anyway

 

[Sancho's Horse]

Good point. I am using some stainless steel screws to attach to one piece, and SS carriage bolts for the other portion. I have some large HDPE chunks I may stick in one tube to reduce some of the sheer stress on the screws.

Can you tell I reflexively overbuild? But, my stuff lasts...until it doesn't.

 

[Jeremy Harris]

The best stuff for preventing galvanic corrosion is the stuff specifically made for the purpose and used worldwide on ships and aircraft, zinc chromate paste (also known colloquially as "gorilla snot" by those who use it a lot - once you see it you'll realise why.........). It's readily available in tubes or tins and does an excellent job with alloy and ferrous metal bolted/riveted joints. These are the people I've bought the stuff from over the years: http://www.lasaero.com/site/products/article?id=P002OHHP1 but a web search for "zinc chromate paste" should find people in your part of the world that sell it, usually under the Duralac, JC5A or Polycast brand names.

 

[Sancho's Horse]

If I can use something called gorilla snot, and its use is likely best practice, this is among the most compelling arguments in my life. Thanks, Jeremy. I will check it out.

 

[TylerDurden]

If I can use something called gorilla snot, and its use is likely best practice, this is among the most compelling arguments in my life.

:lol:

Around here, we use Permatex Anti-Seize for steel bolts into aluminum cylinder heads. I also dollop the stuff onto alloy wheels to keep them from bonding to steel hubs.

 

[Chalo]

I have some stainless steel bar stock that I was going to use as a spacer on an aluminum trailer I am building. I am a little worried about galvanic effects. Should I be? I was considering using some JB weld to provide some added strength and was hoping that this might slow these effects.

Does anyone have any best practice experience?

I had someone tell me because it is stainless it will be fine, but they based this on nothing. I try to know enough to know when I don't know.

Stainless fasteners in aluminum parts are utterly ubiquitous. If you are worried about it, add some grease to the contact surfaces before assembling. There are probably ten other things that will kill your gizmo before any kind of corrosion does. Why do you want to make this more complicated than it is?

Chalo

 

[Sancho's Horse]

There are experts and some well reasoned thinkers on this forum. If I have a pretty good idea about a wheel question (or whatever), I am still going to research/ask it, because other people know more than I do on many subjects. Even if I think I am an expert, I am often surprised by what I learn by asking.

Hard to argue with results. Look at the information posted. Good stuff.

How did you know my contraption has been designed to fall apart?
I consider it the trailer equivalent of give a penny take a penny.

 

[Chalo]

How did you know my contraption has been designed to fall apart?
I consider it the trailer equivalent of give a penny take a penny.

I said no such thing; I only meant that galvanic corrosion should be somewhere near the bottom of your list of worries. Outside of some problems with carbon fiber and titanium bike parts, I have never known it to be a significant issue with bikes.

Chalo

 

[Sancho's Horse]

Only kidding. You are right about this corrosion for structural integrity, but it is in a very visible spot on a trailer I want people to look at. So, it was purely a cosmetic consideration.

The knowledge gained is structural.

 

[Jeremy Harris]

I've made several trailers out of aluminium alloy rectangular/square tube and stainless bolts/rivets over the years. All have lived outside, some, like the boat trailer pictured below, have been in seawater a few times. None have ever shown any significant corrosion, apart for the normal thin layer of oxide aluminium alloy gets after being outside for a while. All the bolts and rivets get smeared with Duralac zinc chromate paste before being fitted, which 100% prevents any galvanic corrosion. The trailer photo below was taken after a couple of years use and exposure.