three types of corrosion in aircraft.?

Question

what three types of corrosion in aircraft and what are the affects of them.
thanks.

Answer 1

Intergranular Corrosion
This can be caused by poor processing during manufacture of the alloy (hence the need to be sure it meets a given specification). Usually it is caused by selecting the wrong chemical in attempting a conversion coating on a given alloy. Poor control of heat treatment processing is also a cause.

Over-etching aluminum can cause this type of corrosion.

Exfoliation Corrosion
This type of corrosion is similar to intergranular corrosion except the corrosion follows grain boundaries and "large" chunks fall out. Extrusions can be susceptible where grain boundaries are stretched and/or rough surfaces occur during the extruding process.

If you have a corrosion critical part you may wish to use bar or rod material that has been wrought instead of extruded. In industry extruded stock is used a lot but it usually goes through several inspections before going on an aircraft.

Fretting Corrosion
Fretting corrosion is caused by two surfaces rubbing together at a very small amplitude. I sometimes think that it should not be considered so much a corrosion as a wear. It can be eliminated by placing a very thin sheet of Nylon or Teflon between the surfaces.

Stress Corrosion
The high-strength heat-treatable wrought aluminum alloys in certain tempers are susceptible to stress-corrosion cracking, depending upon the product, section size, direction and magnitude of stress.

Stress corrosion cracking is where the internal stresses (residual stresses) vary across a section so that when they are loaded with additional outside forces, the grain boundaries at the surface start to break. When a part (sheet, extrusion, etc) is quenched and the outside layer cools too quickly, tension stresses are set up on the outside and compression stresses in the middle. This is sometimes taken care of by stretching or shot peening.
Local stresses (assembly stresses) can also be caused by selection of too small diameter of high shear fasteners (such as bolts), shrink or press fits, taper pins, and clevis joints in which tightening of the bolt imposes a sustained bending load on the clevis lugs.
I will never use 7075-T6 because the residual internal stresses can cause cracking without ever being loaded. I will use 7075-T7351.

I am aware of one light airplane that suffered stress corrosion around a bushing in the main spar of a wing. I suspect that particular airplane had been flown many times outside the design envelope.

Galling
Galling is not a corrosion but with all the talk about corrosion between dissimilar metals, galling problems should be discussed.

Galling is a condition where two parts (made from the same alloy) slide over one another and start ripping the surface between them.

Nuts and bolts are not made of the same material. If they were, they would gall and disassembly would be impossible. Each is made from a different alloy. To me it is interesting that the nut is always made the sacrificial member. If there is any shearing of threads, the nut will shear first. Many times if a nut is unknowingly sheared on assembly, it will fall off and the bolt will remain in place, averting disaster. More on bolts and nuts sometime in the future

Answer 2

Aircraft Corrosion

Answer 3

Types Of Corrosion

Answer 4

CorrosionUniform surface attack. This is the most common type and is caused simply by exposing the metal to oxygen in the air, such as when paint is worn off wing skin or the fuselage. Poor pre-paint preparation at the factory, fumes, acid, pollutants, or high humidity accelerate the decay.
Intergranular corrosion. Normally worst on 7000-series alloys (those with an appreciable amount of zinc, like wing spars, stringers and other high-strength aircraft parts), this is not frequently found but is a particularly nasty type of corrosion. It can be difficult to detect, and once you see it, it’s too late: that piece of metal is toast.
Stress corrosion. In highly stressed parts like landing gear or engine crankshafts, this type may develop from a scratch or surface corrosion. Crankshaft failures are often due to undetected corrosion of this type.
Crevice or deposit corrosion. This can occur anywhere there is an area where moisture or other pollutants are trapped. Lapped skin joints or rivets on an oil-stained belly are examples of prime corrosion spots.

Answer 5

Surface corrosion. Causes pitting in the surface of the metal.

Fretting corrosion. Caused by metals rubbing together, makes for a looser fit between parts and more corrosion.

Intergranular corrosion. Essentially cancer of the metal, it bulges and explodes in a white powder. Can cause a major structural failure.

Answer 6

Good answers above; another type is galvanic (dissimiliar metal) corrosion-starts where two different types of metal come in contact.

There's probably more, but my corrosion control knowledge is a little 'rusty'!

Answer 7

This Site Might Help You.

RE:
three types of corrosion in aircraft.?
what three types of corrosion in aircraft and what are the affects of them.
thanks.

Answer 8

What about Cladsorium Resina in the fuel tanks and Mercurian Corrosion, my life there is loads of them.

Answer 9

1. rust
2. alot of rust
3. a damn heck of rust.