Does stainless react with aluminium?
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  1. #1
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    Does stainless react with aluminium?

    It's nothing critical, but I have some aluminium with stainless screws in it and I was wondering whether it's going to be a problem.

    The thing is going to be buried in cement - a flooring edge in my bathroom renovation.

    Scott
    Yeah, I carry.

    House keys, wallet, some change, usually a newspaper, maybe a pen.

  2. #2
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    Re: Does stainless react with aluminium?

    Stainless screws are what you should use with aluminum. They react less than any other screws, except plastic, .
    "The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt

  3. #3
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    Re: Does stainless react with aluminium?

    Thanks Sandy.
    Yeah, I carry.

    House keys, wallet, some change, usually a newspaper, maybe a pen.

  4. #4
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    Re: Does stainless react with aluminium?

    I found this chart on another site. I was told that the farther away two metals are from each other the more reactive they are.

    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

    It looks like 304 stainless is better than 316 but a chrome plated bolt/screw is your best choice. If you are submerging into concrete I don’t think you will have a problem. I work in a salt water environment and always have problems with 316 stainless and 6061 aluminum.

    I mentioned the chrome plated screws because that is what is used in my aluminum master cylinders on my motorcycle and have not had any problems with corrosion or screws seizing here in Key West

    I found another chart on this site, http://www.estainlesssteel.com/corrosion.shtml, that seems to suggest zinc/galvanized steel would also be preferred.
    Last edited by nogoa; 08-10-2010 at 12:33 PM. Reason: new information
    "ALL DAMAGE, NO CONTROL"

  5. #5
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    Re: Does stainless react with aluminium?

    Quote Originally Posted by nogoa View Post
    It looks like 304 stainless is better than 316 but a chrome plated bolt/screw is your best choice. If you are submerging into concrete I don’t think you will have a problem. I work in a salt water environment and always have problems with 316 stainless and 6061 aluminum. . . . that seems to suggest zinc/galvanized steel would also be preferred.
    Good chart, but your chemistry is confused.

    Aluminum is a more reactive metal than iron, but the surface chemistry of aluminum and stainless is more complex than that.
    Aluminum forms an oxide crust that protects it from corrosion. Stainless steel forms a colorless oxide layer as well. Its is these oxide layers that interact in air, not the base metals, so your chart doesn't include the appropriate materials for comparison.

    In your example, in salt water, aluminum is more reactive than the stainless, which can prevent the stainless from forming its protective oxide layer (since aluminum will act as a protective anode), which can "activate" the stainless. Unfortunately, once the oxide layer on stainless is compromised, it will rust, and that rust will act as a foot in the door for more rusting, over an expanding area.
    Fortunately, stainless is pretty reactive, and these things tend to happen most in oxygen deprived environments (which is something that will not happen in a bathroom).


    Anyway, back to the OP. Do NOT use chrome plated or galvanized screws. They WILL rust eventually. Stainless is an excellent choice.

  6. #6
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    Re: Does stainless react with aluminium?

    Scott,

    Yes, aluminum and stainless steel can and do corrode when put together.

    The two differing metals set up a galvanic couple (aka a small battery) and corrode.

    The aluminum loses.

    Add in some moisture and the reaction happens faster.

    Add in some other electrolyte or source of ions, like something acidic or basic or salty or etc, and the corrosion reaction will occur even faster.

    So -totally- dry and -totally- clean (anodized aluminum and passivated stainless steel) might last for a while.

    But if you have -any- moisture or ions involved, the aluminum loses.

    And concrete is an alkalai environment, so you really don't want to stick a piece of aluminum in contact with it to begin with. Add in some moisture (bathroom and concrete/mortar/grout pretty much means there is or will be moisture above and beyond just 'regular' atmospheric moisture/humidity) and you really don't want to put stainless and aluminum together there.

    The aluminum loses.

    Go all stainless. Preferably with the SAME stainless alloy (otherwise you can still set up a galvanic couple).
    The best laid schemes ... Gang oft agley ...

  7. #7
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    Re: Does stainless react with aluminium?

    Quote Originally Posted by MoonRise View Post
    Scott,


    And concrete is an alkalai environment, so you really don't want to stick a piece of aluminum in contact with it to begin with. Add in some moisture (bathroom and concrete/mortar/grout pretty much means there is or will be moisture above and beyond just 'regular' atmospheric moisture/humidity) and you really don't want to put stainless and aluminum together there.

    The aluminum loses.
    I learned this first hand! Do not let aluminum contact concrete in a humid environment or the aluminum will corrode very quickly. In the greenhouse we had a concrete walkway poured at at different slope than one of the horizontal pieces of aluminum supporting the polycarbonate siding. Where the concrete ended up partially contacting the aluminum (think it was about 1/8" channel) it was eaten away into nothing in about 5 years.

    We do use a ton of galvanized or zinc dipped self tapping screws though and have never had problems with these. Some of the screws have been in place for 20+ years.

  8. #8
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    Re: Does stainless react with aluminium?

    The concrete in an interior bathroom will NEVER be as moist as a concrete walkway.

    Think about it. If the concrete contained enough water to corrode aluminum, the wood sub-floor and framing underneath it doesn't stand a chance.

    The ground is an unending source of moisture for the concrete to wick. That just doesn't exist within a house (or at least, shouldn't).

    There is a BIG difference between constantly wet (heck, being in contact with the ground is even worse than being submerged for some purposes), and wet on occasion.

  9. #9
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    Re: Does stainless react with aluminium?

    Yeh, we sort of need to keep it in context and keep it reasonable. On this planet, technically everything reacts with something if not a hoard of somethings and all will eventually fail and errode away in one form or another . Our skin ages, plastic crumbles, moutains erode. The concrete floor in the bathroom will probably only have a 75 year life span.

    For these purposes, the hardware store whatever version of stainless screws would be the far better choice than the hardware store anyother screws.
    "The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt

  10. #10
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    Re: Does stainless react with aluminium?

    Oh, and aluminum is frequently used as a divider strip for terazzo, so it should hold up just fine.

    I'm not sure what your application is, but if you're doing a ground concrete floor with an aluminum edge, that would pretty much be equivalent to terazzo, except for using concrete and aggregate, instead of white-concrete and marble chips.
    I had been thinking of doing this in my bathroom, and making similar concrete countertops too.

    Anyway, buried in concrete, or exposed, stainless screws will be fine. Just look to see if the hardware store labels them as a "300 series stainless", or if they're non-magnetic.
    Magnetic stainless, or "400 series" isn't the best choice for corrosion resistance.

    My concern wouldn't be corrosion of the screws, but just enough corrosion to cause a rust stain, or the stainless causing the aluminum to get galvanically eaten, but in the environment you have, that will not be an issue.
    In an outdoor environment (or with VERY thin aluminum), I might consider using aluminum nails, just to be safe.

  11. #11
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    Re: Does stainless react with aluminium?

    Rust never sleeps.

    Neither do other forms of corrosion and material degradation.

    But you can try and pick materials that are more appropriate and compatible for the use and environment that they will be in.

    To me, putting some stainless fasteners into/through some aluminum which is against some at least intermittently wet/moist concrete would NOT be a good choice.

    Stainless steel against aluminum = bad

    Aluminum against concrete = bad

    Stainless against aluminum which is against some moist concrete = double bad

    Putting dissimilar metals in contact with one another in a moist/wet alkalai environment is just not a good plan.

    Heck, sometimes the molecular/granular difference -within- a single piece of metal is enough to set up corrosion (crevice corrosion, intergranular corrosion, etc, etc).

    A flooring edge buried in the concrete? Use a strip of stainless IMHO. It will most likely last better and longer than a strip of aluminum on multiple levels. Corrosion, scuffing, scratching, etc.
    The best laid schemes ... Gang oft agley ...

  12. #12
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    Re: Does stainless react with aluminium?

    At work I sometimes help build Al domes on top of the storage tanks at tank farms and refineries. The huck rivets we use are SS with Al collars. Anytime any metal (usually galvanized) is put in contact with the Al a SS shim is used and sometimes even a teflon shim is used. I haven't heard of any problems caused by the mixing of metals but these domes seem to have a more natural enemy. Depending how close these domes are to the ocean, the seagulls can poop there way through the Al in a couple of years. As far as Al trim for the floor is concerned, you'll find that trim meant to imbed in the mortar when doing tile is made out of Al.

  13. #13
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    Re: Does stainless react with aluminium?

    copper free aluminum with a 300 series stainless is fine. Its what marine engines use that are used in saltwater environments, and we do plenty of corrosion testing. 3003 would be a good choice for aluminum, avoid 5052 and 6061.
    -Aaron

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