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  • Brass and aluminium plates, stainless steel screws = CORROSION?

    Discussion in 'The main mechanical design forum' started by GarethW, May 26, 2012.

    1. MDR

      MDR Active Member

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      I don't envy you! LOL!
       
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    3. proinwv

      proinwv Member

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      Let us know what you do and later how it works out.

      I was wondering if you could make a test model and expose it to an accelerated environment. This might give you advance warning of an impending failure.
       
    4. GarethW

      GarethW Chief Clicker Staff Member

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      Will do, but the kit's already out there so we'll just keep an eye on it for now and see how it goes.... Fortunately it's just a 1-off trial unit so we can afford to make changes if necessary.
       
    5. xinhaikj

      xinhaikj New Member

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      aluminum zinc alloy is better i think
       
    6. MikahB

      MikahB Member

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      Good article in Design News in April (I think) about galvanic corrosion - here it is online.
       
    7. GarethW

      GarethW Chief Clicker Staff Member

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      What is "aluminium zinc alloy"?
      It's better than what?
       
    8. Erich

      Erich Well-Known Member

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      Zinc al alloys are die casting alloys, sometimes going by the name of ZAMAC.

      I suspect your current design will last for the year or two required.

      Look at automobiles, They don't use stainless fasteners, they use a lot of phosphate coated steel screws and they last for years in some agressive conditions.
       
    9. Sobefreedom

      Sobefreedom New Member

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      So I know this may be a little last minute, but you mentioned the size of the screw being M3 which is relatively small as previously noted. how large (mass) of aluminum plate are you using? All those fancy charts are great when you are dealing with relative sizes, however if you have a large chunk of aluminun plate with a tiny M3 SS screw you may not see any corrosion at all. in fact the SS screw could switch to being the anode / cathode (can't remember off the top of my head). And are the plates separate? I think you will be pleasantly surprised with the lack of corrosion (depending again or mass differences) there is after even a year in that harsh environment.

      if you really want to test it out though you could put it in a bath of battery electrolite and apply a voltage to the screws. you would see relatively quickly (a week or two) which is going to corrode first. Or just leave it out there and go from there. Good luck.
       
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    10. MDR

      MDR Active Member

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      Interesting!
       
    11. GarethW

      GarethW Chief Clicker Staff Member

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      Hi - the aluminium plate is approx 100mm diameter and 12mm thick. Yes the M3 screws are pretty small in comparison. We'll probably leave it out and see how it goes to be honest!
       

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