2024-T81 bare has contamination after FPL etch. Any ideas why? 1

[KirbyWan]

Howdy all,

So we have a PAA line and we had one piece of metal that had a brown color when it came out of the FPL tank. Here's the process:

Solvent wipe
15-30 minutes in Cee-Bee 300LF
5 minute rinse in tap water
10 minutes in Sulfuric acid/sodium dichromate etch
5 minute rinse in tap water
We would normally go on the Phosphoric acid anodize step, but our process operator stopped because it had a streaks. She re-ran it and it got even worse. Check out the pictures below.

The material is 2024-T3 bare per QQ-A-250/4 which had been aged to the -T81 condition before processing.

This was run at the same time as other details made of 2024, though different sheets, which did not have a problem, see the sheet just above in the first picture. I can't figure out why one piece of 2024 would come out so different from parts run at the same time.

Has anyone seen this issue before or recommend a plan for determining the root cause?

Thanks for your help.

-Kirby

Pictures:

http://files.engineering.com/getfil...e-46be-8118-e875ac6b8a04&file=20150604_082309

[1].jpg

http://files.engineering.com/getfil...3-4b15-bb0d-cf8281ff672b&file=20150604_082320

[1].jpg

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[MikeHalloran]

Contamination?

One of my machinist friends found a complete micrometer caliper in an aluminum bar; it ruined an expensive cutter.



Mike Halloran
Pembroke Pines, FL, USA

 

[3DDave]

Maybe the sheet was mislabeled. I've had shops 'substitute' called for material with other material they have lying around. In fact one place that deals in scrap has any material you want; by magic apparently.

 

[MikeHalloran]

By magic _marker_. ;-)

My marine exhaust shop, where 316L is the 'cheap stuff', had a sheet of '304' lying around that they used for some incidental brackets welded to some very expensive and very complicated custom tubework made of 25-6SMO or AL6XN or something similar.

The brackets disappeared completely in the pickling bath.

The sheet was mild steel that someone had acquired for a home project.

Mike Halloran
Pembroke Pines, FL, USA

 

[KirbyWan]

I could actually read the mill printing on the sheet. So if the material was wrong it looks like it was marked wrong at the foundry. And just to double check we spark tested it and didn't get any sparks, so I felt confident it was at least aluminum and most likely 2024-T3. The -T3 had been marked over and -T81 added, so I figure someone performed an artificial age to change the temper.

thanks for the stories of suspect material.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[3DDave]

I would try

http://www.finishing.com/letters/index.html

as they seem to have a lot of participation from experts in the plating and finishing industry. A lot of questions are from platers.

For example, some results on FPL

http://www.finishing.com/191/21.shtml

 

[MikeHalloran]

Another vote for finishing.com. Lots of real old timers (older than me, and smarter about finishing), have been contributing to the associated trade rag for decades.


Mike Halloran
Pembroke Pines, FL, USA