Is Stainless Steel Corrosive to Aluminum?

[ts8501]

I thought I understood that Stainless Steel is NOT corrosive when in contact with Aluminum. Is it or is it not?

[Janets Husband]

Originally Posted by ts8501

I thought I understood that Stainless Steel is NOT corrosive when in contact with Aluminum. Is it or is it not?

Take a look at this list. The closer the better. The reactivity of the metals decreases the closer they are in the list.

Metal reactions list
--------------------------------------------
Magnesium
Mg alloy AZ-31B
Mg alloy HK-31A
Zinc (hot-dip, die cast, or plated)
Beryllium (hot pressed)
Al 7072 clad on 7075
Al 2014-T3
Al 1160-H14
Al 7079-T6
Cadmium (plated)
Uranium
Al 218 (die cast)
Al 5052-0
Al 5052-H12
Al 5456-0, H353
Al 5052-H32
Al 1100-0
Al 3003-H25
Al 6061-T6
Al A360 (die cast)
Al 7075-T6
Al 6061-0
Indium
Al 2014-0
Al 2024-T4
Al 5052-H16
Tin (plated)
Stainless steel 430 (active)
Lead
Steel 1010
Iron (cast)
Copper (plated, cast, or wrought)
Nickel (plated)
Chromium (Plated)
Tantalum
AM350 (active)
Stainless steel 310 (active)
Stainless steel 301 (active)
Stainless steel 304 (active)
Stainless steel 430 (active)
Stainless steel 410 (active)
Stainless steel 17-7PH (active)
Tungsten
Niobium (columbium) 1% Zr
Brass, Yellow, 268
Uranium 8% Mo.
Brass, Naval, 464
Yellow Brass
Muntz Metal 280
Brass (plated)
Nickel-silver (18% Ni)
Stainless steel 316L (active)
Bronze 220
Copper 110
Red Brass
Stainless steel 347 (active)
Molybdenum, Commercial pure
Copper-nickel 715
Admiralty brass
Stainless steel 202 (active)
Bronze, Phosphor 534 (B-1)
Monel 400
Stainless steel 201 (active)
Carpenter 20 (active)
Stainless steel 321 (active)
Stainless steel 316 (active)
Stainless steel 309 (active)
Stainless steel 17-7PH (passive)
Silicone Bronze 655
Stainless steel 304 (passive)
Stainless steel 301 (passive)
Stainless steel 321 (passive)
Stainless steel 201 (passive)
Stainless steel 286 (passive)
Stainless steel 316L (passive)
AM355 (active)
Stainless steel 202 (passive)
Carpenter 20 (passive)
AM355 (passive)
A286 (passive)
Titanium 5A1, 2.5 Sn
Titanium 13V, 11Cr, 3Al (annealed)
Titanium 6Al, 4V (solution treated and aged)
Titanium 6Al, 4V (anneal)
Titanium 8Mn
Titanium 13V, 11Cr 3Al (solution heat treated and aged)
Titanium 75A
AM350 (passive)
Silver
Gold
Graphite

[Gene]

As soon as I get my PhD in chemistry, I'll understand what the list means in my world, however, I'll have to start out with whatever comes after Chemistry 1 for arts and science majors (probably more like Chem 1/2). I replaced a grey plastic duplex receptacle cover plate with a stainless one which is now touching the aluminum interior. It looks better than the plastic cover plate. Have I ruined the Safari?

Gene

[hampstead38]

Galvanic corrosion requires an electrolyte. You can have a dry bin of aluminum and stainless fasteners... no big deal. Immerse them in water, you have an electrolyte and corrosion will occur. This is why galvanic corrosion is a big deal for marine applications. When possible, keep water away from metal. When not possible, try to use the same metal. There are other techniques like sacrificial anodes, but it may be helpful to tell us about the specific application.

[Aerowood]

Yes is the simple answer, seperate the two with primer and or sealent to keep the water (electrolyte) from penetrating between the mating surfaces.

Kip

[ts8501]

Here is but one example. I wish to install a stainless steel water filler, used in marine applications. Whitecap Ss Hose Deck Plate with Key (Water) - 6125C - BoatersWorld.com
I note that this particular item is made of "Cast 316 Stainless". It will touch the aluminum skin on my '64. I have also heard that one can use a layer or Mylar between the metals.

[InsideOut]

If I understand Gary's "List" then the 316 SS is pretty far away from the 2024-T4 aluminum of our Airstreams - thus it is more corrosive than if they were closer together on the list - like Stainless 430. We always put either cork, neoprene-type gasket or at a minimum Vulkem at all connections - especially on the outside where water is inevitable.

Shari

[richinny]

in the case of the outlet cover, one of those weather seals for outlet covers might just do the trick.

[mswartz]

As others have mentioned, if stainless steel and aluminum are in contact and moisture is present, the aluminum will sacrifice (corrode).

If your hardware does not already have it, fabricate a 1/8-in thick neoprene gasket that will isolate the stainless steel filler from your aluminum, extending right to the edge of your hardware. It is important that the weather-exposed surface of the stainless is isolated from the aluminum.

If your filler uses through-screws, you may consider pre-drilling the through holes in the aluminum, and before inserting the filler to the hole you've drilled, apply a small amount of vulkem or similar sealant at those pre-drilled screw holes.

If you are inserting stainless sheet metal or machine screws into aluminum where there is a possibility of moisture, it is a good idea to use a corrosion-preventive threading compound, such as Bostik Never-Seez Blue Moly (http://www.bostik-us.com/files/tdsfi...y.pdf#BlueMoly) specifically formulated for such applications. Do not use this on the screws if you are using vulkem, however. Use the Blue Moly on dry-assemblies.

[ts8501]

Originally Posted by mswartz

As others have mentioned, if stainless steel and aluminum are in contact and moisture is present, the aluminum will sacrifice (corrode).

If your hardware does not already have it, fabricate a 1/8-in thick neoprene gasket that will isolate the stainless steel filler from your aluminum, extending right to the edge of your hardware. It is important that the weather-exposed surface of the stainless is isolated from the aluminum.

If your filler uses through-screws, you may consider pre-drilling the through holes in the aluminum, and before inserting the filler to the hole you've drilled, apply a small amount of vulkem or similar sealant at those pre-drilled screw holes.

If you are inserting stainless sheet metal or machine screws into aluminum where there is a possibility of moisture, it is a good idea to use a corrosion-preventive threading compound, such as Bostik Never-Seez Blue Moly (http://www.bostik-us.com/files/tdsfi...y.pdf#BlueMoly) specifically formulated for such applications. Do not use this on the screws if you are using vulkem, however. Use the Blue Moly on dry-assemblies.

This was very helpful Marshall. Where do you find the material to make the 1/8" neoprene gasket?

[rodsterinfl]

Yikes. Yes, now I have learned a bunch on this and it is correct that metal nobility is a factor with dissimilar metals. Last May I finished adding the center rail to my trailer. I decided to use stainless screws as fasteners instead of rivets (the dealer told me I could use either one). Later I learned about galvanic corrosion - the reaction of two different metals. Whoops. I am not so sure how bad it will be as I sealed the rail at the top but it is still a dissimilar match.

The filliform corrosion, when I first read of it, was, in my opinion, a fault of Airstream; however, after further reading I have concluded that it is not as much a product defect as it is a natural occurrence of Aluminum as it is used with Airstreams. A study found that just about any metal that is coated will form filliform corrosion as the coating provides a surface above the top layer of the metal. The 3003 aluminum alloy mixture (used on late model AS) is designed to provide anti-corrosive properties but it will not stop surface filliform. The reason the older Airstreams have no issues with this is due to the alclad layer of solid aluminum over the surface. This protective layer over the alloy only has issues with oxidation compared to the coated aluminum models. The only thing I could find to counter such an attack from chlorides - the main culprit of filliform is a vinegar (acetic acid) wash (by their research and mine).

[r carl]

Originally Posted by ts8501

This was very helpful Marshall. Where do you find the material to make the 1/8" neoprene gasket?

A roofing company that does flat roofs like on a commercial building will give you a scrap piece of rubber roofing if you go there.

[BIGED52]

Originally Posted by ts8501

This was very helpful Marshall. Where do you find the material to make the 1/8" neoprene gasket?

You can buy gasket making (neoprene) sheets at many auto parts stores. Ed

[HeadWest]

Interesting topic since I was wondering about the Airstream exterior stainless parts they offer (range hood vent, water heater, and furnace cover). My local dealer that I'm talking to about buying a 28 International mentioned the stainless goodies to me the other day and I was wondering afterwards about galvanic corrosion issues.

[matthorr]

Now this will really blow your mind...

You can have corrosion even when composite (non-metallic) materials come in contact with metals. All you need is an electron source, an electron receptor and a path for the current (an electrolyte). The farther apart two metals are on the chart above, the more stronger tendency to "swap" electrons. Corrosion is basically a chemical reaction similar to a battery, so preventing the flow of electrons (current) using a coating, a gasket and/or keeping the materials dry and clean is the key. And treat corrosion promptly (by removing it and re-applying oil/coating/sealant).