Alodine aluminum AFTER installing nutplates

[Stephan Nelle]

Having a debate with another group internally. Here's the scenario: 6061-T6 plate welded to a 5052-O tube. The plate gets NAS680A3 nutplates riveted on with (alodined) AD rivets. Group 1 is pushing to weld the plate to the tube, then rivet the nutplates to the plate, then alodine the whole assembly (MIL-DTL-5541, Type 1, Class 1A), and Group 2 (my group) is pushing to weld the plate to the tube, then alodine the weldment, then rivet the nutplates to the plate. Group 1 acknowledges it isn't standard practice to alodine after nutplates are installed, but they are insisting it won't cause any issues. My argument is that the deoxidizer dip step will allow the deoxidizer liquid (essentially acid) to get between the faying surfaces (between nutplates and plate, between rivets and nutplates, and between rivets and plate). There is of course a rinse after the deoxidizer, but my concern is that not 100% of the deoxidizer will be removed in the rinse step and this will cause corrosion in the future, starting between the faying surfaces.

My position is a hard 'no'; we should not alodine after the nutplates are riveted on, but rather before they are riveted on. Do any of you have experience that shows alodining after riveting on the nutplates doesn't cause corrosion issues later on?

 

[rb1957]

"Group 1 acknowledges it isn't standard practice to alodine after nutplates are installed," ... ok, red flag ...
"but they are insisting it won't cause any issues." ... and their evidence for this is ?

5052-O ... not a high strength installation ! what is this ?

6061T6 should be pretty good for corrosion.

"My argument is that the deoxidizer dip step will allow the deoxidizer liquid" ... you wouldn't brush alodine ?

Fay seal under the a/nuts (= wet install) ? ... probably not ... does anyone ??

Depending on situation, I'd maybe build up as you suggest, then bathe the whole thing in WDC ...

but wait a little ... Will'll educate us all (not a dig, smile !)

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

 

[Stephan Nelle]

rb,

They (Group 1) don't have any evidence to support their claim. I think just wishful thinking on their part, really.

I know 5052-O is not high strength. I purposefully left out details of what it is or what it does because I don't want to derail the topic with those details. It isn't structural and the 5052-O is sufficient for what it is and does.

It is an automated alodine process line in a GA OEM production environment, so no, not brush alodining.

"...bathe the whole thing in WDC..." What is WDC?

Yes, anxious to see Wil's reply!

 

[rb1957]

Water Displacing Compound ... basic anti-corrosion treatment.

I get "don't want to derail the topic" but the whole thing with Engineering is the nuance of the specific installation may allow things that are not normally considered sensible.



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

 

[Stephan Nelle]

rb,

Oh duh, on the WDC acronym. This assembly is a location not terribly accessible, so we want a more long-term solution than WDC.

I hear what you are saying about the nuance of the specific installation, but I'm not trying to debate with them (or Eng-Tips) about this specific installation, but at a higher level of "is this a good idea or not", not so much "can we get away with it in this specific scenario/installation". The fact is, in this specific installation, a bit of corrosion probably won't hurt a thing. But if a little corrosion is ok on this installation, we might as well not even alodine it at all, then we'd bypass the deox acid concern.

But, I don't want to set a precedent for doing things out of order in the name of production efficiency. In many cases, obviously, corrosion is a big problem.

 

[SWComposites]

Sounds like a bad idea. Just tell them "No" and move on.

 

[rb1957]

"I don't want to set a precedent for doing things out of order in the name of production efficiency." ... oh, ain't that the truth ! ... the thin end of the wedge ... and we know where the thick end ends up ...

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

 

[rb1957]

I get a lot of similar arguments settled with "what is common good practice ?"

Of course I can always say "Sure, do it, but get someone else to sign for it" (the delegate trump card !)

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

 

[TugboatEng]

Aluminum is subject to crevice corrosion. Attaching the nut plate to bare aluminum creates the conditions to cause crevice corrosion. If this part will always remain very dry, this may not be a problem. If it's exposed to moisture this will be no good.

 

[MintJulep]

NAS 680 Nut, Self-Locking, Plate-Two Lug, Low Height, C'Bore
Inactive for New Design after 1 January 1989 Use MS21047 and MS21048.

MS21047 itself is now superseded by NASM21047

https://www.aircraftspruce.com/catalog/pdf/K1000tech.pdf

They:
Are Steel
Cadmium plated (yuck)
Have a dry film lube applied

I don't see how dipping them in an acid wash, and then in the Alodine cocktail could possibly be a good thing for them.

 

[RoarkS]

"but my concern is that not 100% of the deoxidizer will be removed in the rinse step and this will cause corrosion in the future, starting between the faying surfaces."

YOU ARE 100% correct! I don't know which chemical it was, but some of something stayed behind and DESTROYED a lot of parts/time/money.

Don't let them do it. It will take exactly long enough for the parts to get shipped to the customer, sit on their shelves, possibly even get installed... before the crustyness starts growing out of the parts.

It was really bad in our situation. It was a new vendor who didn't know better and we didn't have any instructions that specified HOW/When. They assembled the entire assembly with VERY expensive machined fittings, rivets, sheet work... Holy crap. It was a massive service bulletin/recall. Cost a lot of money.

 

[TugboatEng]

Have you considered Click Bond nut plates? In this case it would seem acceptable to perform Alodine treatment after installation.

 

[TugboatEng]

5052-O ... not a high strength installation ! what is this ?

6061T6 should be pretty good for corrosion.

In the marine industry we use 5052 for skins and 6016T6 for structure. 5052 is used for the hull of the vessel as it can be drawn into position by chain hoist or dogs and wedges. High strength 6061 extruded shapes are welded to the 5052 skin to stiffen it. 6061T6 lacks formability or it would be used everywhere.

Corrosion resistance of both materials is good, even in salt water.

 

[Stephan Nelle]

Thanks, all, for the replies. I'll stick to my position and demand a "no". I knew it was a bad idea, but nice to hear other confirming opinions.

 

[WKTaylor]

OK... guys... there are actually [2] ways to approach this situation. Both will work in either pathway. BUT... sequence and accessibility are everything...as well as Rule #1.

Rule #1 with process coatings... NEVER have any parts attached that can trap process fluids fay-surface... and beware... process solutions compatible with aluminum WILL damage other alloys. Nutplates, bushes, pins, washers/bolts etc CANNOT experience process solutions for this reason. Another side of this is that process solutions will be cross-contaminated by the chemistry [alloy, coatings, etc] of the non-compatible parts... worst would be alloys/finishes that experience oxidation/erosion, IE: rust, zinc, cadmium, silver, etc will degrade process bath chemistries.... and processors will usually say 'ohhellno'.

SO... how can either of the pathways mentioned be taken and be successful... without violating rule #1??

SN... YOUR POSITION is typical for conventional production process for bath Chromate Conversion Coating [CCC, MIL-DTL-5541 Class 1A]... something like a pressurized tube Assy... would be to: clean in preparation for welding, accomplish Assy-welding, NDI, proof-test, re-work A/R, clean... then apply the CCC in a bath for the bare-weld [typically to exterior surfaces, only - mask-off interior]. Many of these same tube Assys would also receive primer after CCC. OK... NOW is the appropriate time to install all attaching/embedded parts.

OTHERS... so how could this be done 'otherwise'... somewhat like the 'other crowd' is suggesting... it CANNOT BE DONE EXACTLY as they describe... it WILL violate Rule #1. But there is a variation to consider... that I've used for parts-replacement-repairs... not ideal/straightforward.

Trim and 100% clean individual parts for welding. Mask-off interior 100% and exterior surface areas within +4.0-inches of the weld heat affect zones. Apply CCC [and epoxy primer] to exposed surfaces away from the weld-zone... and install attached/imbedded parts to the areas that have been CCC/primed, ONLY. Unmask the areas to be welded, fixture the parts, weld-the-parts, NDI, proof-test, rework A/R, final clean bare aluminum areas/welds... then brush-apply CCC [no-rinse is OK] and apply primer to the bare/welded areas. Ta-Da done... the right way... but definitely NOT the economical/production-friendly way.

BTW... Welding 5052-O to 6061-T4 is the preferred combination. Be cautious when welding 6061-T6 to anything... it can can develop hot-short cracks... and besides... 5052-O and 6061-T4 have relatively similar strength/toughness/weld durability. Also the weld-filler should be compatible to both... not necessarily heat treatable. On my jet, common ER4043 is preferred for this material combination... with a couple of other ER5xxx alloys allowed for specific purposes.

xxxxxxxxxx

Tug... I am curious... WHY 5052-xxx for hull alloy? What size vessels are you used to assembling... I assumed You worked on larger sea-going vessels? Here is WHY I am asking...

ASTM B928 Standard Specification for High Magnesium Aluminum-Alloy Sheet and Plate for Marine Service specifies 5083, 5086 and 5456 for sea-water service. Alloys 5052 and 6061 are definitely NOT on the spec list.

HOWEVER... I checked AWS D3.1 Guide for Aluminum Hull Welding... and yes it appears that... 5052, 5083, 5086, 5454, and 5456... are the common 5xxx plate-hull alloys... although it states that 5052 is used typically for 'small pleasure craft' due to lowest strength. OH and 6061, 6063, 6151, 6356 and A356 are the commonly used heat treatable aluminums compatible with 5xxx alloys for internal details/stiffening/strengthening... exactly as You describe.

Gotta crawl back-to-work.

Extra credit for knowing what 'ER' stands for when describing weld filler alloys... IE: ER4043

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

 

[Sparweb]

Read the spec, folks.

NAS680 > MS21047, Note 7: Lubricant. Dry film lubricant approved in accordance with Mil-N-25027...

Explain how that lubricant will still be there and still useful after immersion in an acid bath followed by a caustic bath.

These nuts are carbon steel, not CRES... as if I have to point that out...

Just beyond belief.