Is there a "Corrosion Problem" when 4130 Steel comes into contact with Aluminum?

Discussion in 'General Experimental Aviation Questions' started by Southron, Jun 18, 2012.

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  1. Jun 18, 2012 #1

    Southron

    Southron

    Southron

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    I will start building my 1st Homebuilt aircraft sometimes later this month. So, I have a basic question.

    When 4130 Normalized steel tubing comes in contact with aluminum in an aircraft structure, say for example, a 4130 steel tube Wing Spar in an aluminum wing structure, is there a "Galvanic" (or other) type of Corrosion Problem?

    If such a problem exists, what steps can be taken to prevent that corrosion?

    THANKS!!!
     
  2. Jun 18, 2012 #2

    SVSUSteve

    SVSUSteve

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    There is a potential (pun not intended) for it (as they fall into different categories so far as galvanic potential is concerned) but it's not as severe as you would see if you were using something like titanium. However, I am not exactly sure HOW severe the issue is with aluminum and steel. Orion, Billski or one of the other more experienced members could answer it for you.

    Preventing contact between the two by using a non-conductive barrier would be the most logical one where possible.
     
  3. Jun 18, 2012 #3

    orion

    orion

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    Actually Titanium is the best for all applications in that it is the least reactive with any of the commonly used metals or composites. Titanium is commonly used in direct contact with graphite due to its electrical neutrality.

    Although there can be galvanic corrosion when steel and aluminum come in contact, remember that the reaction is proportional to the moisture content within the interface. Internal components may not show any issues for many years however unprotected parts on the outside of the plane may show signs over a much shorter period of time. If you're talking things like bell-cranks and such, you could use stainless bearings, brass or Oilite bronze bushings or in less loaded applications, even a high density Nylon or a really good material like GSM Blue.

    But aluminum and steel have been used in standard production for many decades, even sliding metal on metal contact, utilizing only mild grease at the interface. It is therefore an issue to keep in the back of your mind during the part design stages but it will not sink your project.
     
  4. Jun 18, 2012 #4

    harrisonaero

    harrisonaero

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    Just a clarification... titanium isn't really "neutral", it just happens to be very close to carbon and the two are often used together. If you combine it with an anodic metal like magnesium or aluminum it's definitely corrosive, especially in the presence of an electrolyte like moisture or seawater.

    To know how to choose dissimilar metals so that they play well together, pick two that are close together on the galvanic chart.

    Also keep in mind what happens during corrosion- the anode metal is consumed. So for example, if you use an aluminum rivet in a bare carbon part the rivet would be consumed and the hole size would not change.
     
  5. Jun 18, 2012 #5

    PTAirco

    PTAirco

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    My old Land Rover in England was a perfect example of what happens when you bolt aluminium and steel together in a damp atmosphere.... It's not pretty.

    On some old British aircraft you could find a thick bituminous paint between fittings of different metal when you disassemble it - it worked very well.
     
  6. Jun 18, 2012 #6

    BBerson

    BBerson

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    All aluminum airplanes are assembled with steel bolts and last 60 years or more. Yes the bolts are usually cad plated but even when the plating wears off very little happens other than light rust on the bolts. The aluminum is usually fine unless you have continuous standing water in the joint. In that case aluminum on aluminum will corrode.

    For bolts, a bit of grease helps. For steel plates touching aluminum, paint is common. For example, the Cessna 172 has some steel angle spar caps riveted to the aluminum spar caps inside the wing strut area.
    BB
     
  7. Jun 19, 2012 #7

    Dan Thomas

    Dan Thomas

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    Steel parts are often primed to minimize contact with aluminum surfaces, and the aluminum is often primed, too. Still, I often see corrosion in bolt holes in aluminum.

    Using the airframe as an electrical ground can aggravate corrosion.

    Dan
     

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