Hello everyone, I am working as

[Mohammad041990]

Hello everyone,

I am working as an Aircraft structural repair engineer and I have a case that has a thermal damage to skin made of 2004-F (AMS-4208) material.

How can I evaluate the extent of the damage ?

If electrical conductivity should be carried out, how can I find the limits range ?

Thanks

 

[rb1957]

an odd material (in my experience).

here's a thread on it ... thread330-377823

To understand thermal damage you'll need to understand the temper temperature.


"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

I seriously CANNOT believe 2004-F is used as structural skin material. Now, having said this...

Typically thermal [heat/fire] damage to aluminum sheet metal starts with knowing what it is...

Alloy, temper and bare or clad?

Known electrical conductivity [%IACS, eddy current] for the alloy/temper/type?

Also... IF finishes were damaged, then to what extent? Discolor, blistering, flaking, charring, burned-off... etc

Any wrinkling/buckling, stretching, sagging, 'broom-strawing', etc... etc?

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[RoarkS]

Last week I challenged one of the higher up eddy current NDT techs for a major airline engine shop to identify a material based off air normalized lift off curves against known samples...
His best attempt to convince me of the difference between major alloy groups... I wasn't convinced. At best the indication difference between 2xxx 5xxx 6xxx and 7xxx samples was almost nothing. He settled on a 7xxx but XRF nailed it as 2024 a few days later. I would be stunned if a composition change due to thermal effects would be detectable with typical professional eddycurrent equipment.

That said depending on the extent, there could be thermal related flaws that could at least let you map what's different.

I'd suggest having a serious conversation with a level 2 tech and have them inspect the area and see if there are any abnormal indications keeping an open mind. Have a "good" sample for comparison. You might have to back your way into an answer. My guy had a pretty complete chart of materials and their associated values they look for.

I hate to say it, but... you might have to go pretty deep into metallurgy. Maybe even cut out some "known damage" and have it micrographed to determine its current temper state, hardness, or do tensile tests. I know that won't help much for a boundary to damage... but it's a start to see what you have left. I'm curious why you wouldn't just replace the whole panel... probably $. G650 upper wing skin? lol.

I've had to talk to mill metallurgist on a few occasions for really crazy deep info like micrographs. Usually the more metal you buy the more they're willing to talk to you.

Weird metal. Not much out there. I've never used it.

 

[rb1957]

why do you think it might be G650 upper skin ? "Surely" they used a "sensible" alloy ... 7xxx plate ? This stuff (2004) isn't in MMPDS ??



"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[edmeister]

Never even heard of a 2004-F .. very doubtful.
Suspect Alclad 2024-T3 .. almost every time except nacelles-intakes or interior structural members.
1/ How large of a suspect area? Replace or cut & patch. this would be a 100% soln.
2/ otherwise .. locate an area outside the heat damage. Ensure no Alum cladding ..
- remove .002/.003 (blend - avoid heat during blending) of the cladding to reach bare core material.
perform a NDT conductivity from outside the Heat affected area inward towards the critical areas.
Draw a profile mapping of the conductivity values. Obviously when values start changing - this would be the limits of your "good" material. Note that conductivity has to be performed on a fairly flat surface - thus the .002/.003 blends should be at about 1" dia.
- any curvature will affect the probe. I suggest a 2-3 inch spacing / density of test locations.
Note: had many dealing attempting to match up conductivity results with published numbers .. do not have much faith in this. Too many variables .. equipment calibration / technician experience / correct probe / surface contamination / remnants of cladding , etc. Comparison to a "known" region outside the heat -affected area is the best calibration standard.

 

[rb1957]

I think it is 2004 ... he has the AMS right. Possibly it's not structural ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[RoarkS]

@rb1957

For damage that can't be easily determined and on an atypical metal my only thought is it would be something not economically repairable by simply replacing a skin section... made me think of a recent example for me that's fresh on my mind, got pretty deep into a g650 and was stunned how the upper wing skin is made. I thought I knew the alloy but their processing method is pretty off the wall so they might of went with something weird for some reason or another. I know what i was told but never saw an official callout. Probably not... but again just something that came across my table recently. Ended up replacing the entire wing.

Edit... AMS 4208 is legit. $61 on SAE.

 

[rb1957]

it is weird, the things we grow to accept !?

The G650 wing was a bit of a "bastard orphan". Started with Vought, then Spirit, now ? Triumph ??
I know they had the usual weight issues so maybe tried to be creative ? rarely works out well.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

I looked at AMS4208 Aluminum Alloy Sheet 6.0Cu - 0.40Zr (2004-F) As Rolled.

That alloy/temper appears to be intended for super-plastic forming [SPF]... which then must be heat-treated [SHT+PHT, as-defined in the spec] to attain a useable strength [as-defined in the spec].

Is that skin assembled [skin +stiffeners +splices +doublers +etc] with diffusion bonding [DB] and/or friction stir welding [FSW]???

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov