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Bare Aluminum Structure? Why No Protective Coatings?

Discussion in 'Technical' started by James Anders, Apr 30, 2016.

  1. James Anders

    James Anders Member

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    It seems to me that the chassis and much of the under-structure of Model S (and probably Model X) is bare aluminum with no protective coating.

    As a design engineer I've always seen and specified chromate conversion coatings (either a dip or spray) to reduce the possibility of corrosion and oxidation.

    Alodine or Iridite are two well known brands. Can either be clear or a yellowish-straw color.

    It's not very expensive and I wonder why (if I am correct) Tesla doesn't do this?
     
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  2. wdolson

    wdolson Supporting Member

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    The sorts of alloys of aluminum used in aircraft are subject to corrosion and they are often coated with some kind of chromate to protect them, but pure aluminum is very corrosion resistant. It forms a layer of aluminum oxide and then quits corroding.

    During WW II the US developed alclad for aircraft. It's an aircraft aluminum allow that is coated with pure aluminum and it protects the metal quite well from corrosion. That's why most late WW II US aircraft were bare metal, not painting them saved time and weight.

    Alclad is still used on airliners built for airlines that use bare metal areas on their aircraft. American Airlines paints some of their aircraft now, but for many years left most areas of the plane in bare metal.

    I doubt Tesla is using anything as soft as pure aluminum for structural components of the car but they may be using an allow that doesn't corrode or alclad on a stronger alloy.
     
  3. jaguar36

    jaguar36 Active Member

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    I'll have to check when I get home, but I suspect that Tesla uses something like a clear chromic acid anodization on the aluminum parts. Its a pretty standard coating, and theoretically offers more corrosion protection than alodine.
     
  4. JeffC

    JeffC Member

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    Yes. Some alloys of Aluminum form their own protective oxide layer, a bit like anodizing, and a bit like the corrosion protection mechanism of stainless steel or Titanium. (Actually more like Titanium than stainless steel since the latter is an alloy where chromium forms the oxide layer.)
     
  5. DumbIdea

    DumbIdea Member

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    Of all the dumb things I've seen done to a MS, why hasn't anyone brushed a finished Tesla to show off that aluminum?
     
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  6. harry

    harry Member

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    I don't know about the chemistry, but our 5-year old Signatures have zero evidence of any corrosion on the aluminum portions. The steel members (suspension, steering, etc.) are another issue, however, showing a fair amount of rust. Nothing structural or compromising, but I'm just saying...
     
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  7. arnis

    arnis Member

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    Metallic Aluminum is highly reactive metal, not ok to touch it. If it touches air (oxygen in the air) it will immediately oxidize to Al2O3. (Aluminium Oxide). Layer is very thin, 4nm, or 0,004um, or 0,000004 millimeters (that's 0,000004mm/25,4=inches). But it is extremely resistive to corrosion. Absolutely safe to touch. The whole roll of tin-foil is covered with oxide from both sides.

    Though it is possible to very thin oxide with some more harsh chemicals, it is usually just cosmetic (it looks stained).
     
  8. Topher

    Topher Energy Curmudgeon

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    Wonderful! Another FUD post where someone invents some stupid thing that is possible, assumes Tesla is doing that stupid things, doesn't even check what Tesla actually does, and lambastes them for being stupid. Sigh.

    Thank you kindly.
     
  9. bkp_duke

    bkp_duke Member

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    You are a design "engineer" and didn't know that exposed Al formed an Al-oxide protective layer when exposed to air? Tesla uses the same principle that aircraft made of Al use, no need for an additional coating.

    Time to go back to school?
     
  10. Az_Rael

    Az_Rael Supporting Member

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    In the OP's defense, as an engineer who works on aircraft, I would imagine a coating would be required where the aluminum is in contact with steel parts, either bolts, or other components. Galvanic corrosion is a real problem.

    I assume (hope) Tesla has accounted for that, though.
     
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  11. bkp_duke

    bkp_duke Member

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    Sure, but even the bolts in the S/X are Al. I've had both of my S's apart multiple times, and there are very few points of contact with Al and other metals.

    Model 3, which is a mixture, would be something else. Be interesting to see what Tesla did there. Cannot wait to take a Model 3 apart. :)
     
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