No passwords, No popups, No cost, No AI
we earn from your eBay & Amazon purchases

Home /
T.O.C.
Fun
FAQs
Good
Books
Ref.
Libr.
Adver-
tise
Help
Wanted
Current
Q&A's
Site 🔍
Search
curated with aloha by
ted_yosem
Ted Mooney, P.E. RET
- Pine Beach, NJ
finishing.com -- The Home Page of the Finishing Industry


  pub
  The authoritative public forum
  for Metal Finishing since 1989

-----

Pitting in Aluminum Threads after Alodine




March 17, 2021

Q. I am in incoming inspection for an aerospace supplier.
We have a "Pitting" issue in threads, two separate parts from two separate platers.
Material for both parts: 7050-T7451 thicknesses is 6-inch plate and 3.5" plate.
During the machining process, we use TRIM MicroSol 690XT parts that are washed and dry before shipping.
Etch for Penetrant Inspection, holes are masked prior to etching, Chemical conversion Coating using Alodine 1200 or equivalent.
From the attached photos, you can clearly see the "pitting" in the threads. This is typical of what we are seeing on the last several shipments.

61225-1a

61225-1b

Any suggestions?

Kevin Willis
- Decatur, Alabama


A. This may be a "stretch", but let's consider that the heat from heat treating and/or dull machine threading, has brought the 5% zinc out which then fell out and left pits. "Been there done that".

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
March 19, 2021


A. You say the holes get masked, but the pattern seems to suggest that there might be ingress of something (etching solution perhaps?) into the threaded hole and then it may be sitting there un-rinsed doing the damage.

Ask how the holes are masked and part orientation on the rack to see if the damage is occurring on the bottom of the holes -- suggesting the etchant pooling there.

Janis Ziemelis
- Riga, Latvia
March 27, 2021


thumbs up sign Thank you for your comments.

Kevin Willis [returning]
- Huntsville, Alabama
April 5, 2021


A. Kevin

The part in the upper photo looks to have galling as opposed to pitting. But it does show signs for retailing / touch-up.

The part in the second photo appears to include another process in addition to pre-penetrant etch and conversion coating. It almost looks like anodize on the surface surrounding the hole.

The slots for the locking insert make it challenging to get a good seal to keep solution out, as evidenced by the leakage / coating on the chamfer.

The pitting is likely not from the etch process, but possible etch remaining in the threaded hole (wasn't unmasked & rinsed properly). If the additional process was anodize, the same inadequate masking could cause the same. The same path that allows the acid to enter will also allow some current to enter. That creates a rather hostile environment for aluminum.

Willie Alexander
- Green Mountain Falls, Colorado
April 15, 2021




(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Finishing
Jobshops
Capital
Equipment
Chemicals &
Consumables
Consult'g,
& Software


About/Contact  -  Privacy Policy  -  ©1995-2024 finishing.com, Pine Beach, New Jersey, USA  -  about "affil links"