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topic 44433

6061-T6 Panels Fail Salt Spray after Treatment with Alodine 600

A discussion started in 2007 & continuing through 2017


Q. Hello All,

We are an aerospace processing facility that utilizes Alodine 600 for our chromate conversion coating needs. Recently we have experienced off and on failures (3 out of 6 testing cycles) of 6061-T6 for both class 1A & class 3 per Mil-DTL-5541 [link is to free spec at Defense Logistics Agency,]. We are diligent in the preparation and post treatments of the processed coupons with extensive flow down of requirements of the process to all applicable personnel. These failures are extremely vexing due to the amount of care and attention to detail associated with the processing. We even go to the lengths to map out any suspect indications observed on the coupons prior to treatment. We carefully store the panels in an temperature controlled environment and the panels are laminated with mylar so as to protect the surface integrity. Our solution analysis results are well within parameters, but we cannot explain the recent rash of failures. Please note that the 6061 panels pass successfully through the chromic anodize tests for corrosion resistance. It is just the Conversion coating for 6061 we are having issues with, the submitted 2024 coupons for both classes are fine and exhibit no pitting.

My question is this; is there any objective evidence that the adhesive used on the mylar film can degrade the 6061 panel surface so as to cause failure during the corrosion resistance testing?

If anyone has an answer, please feel free to give your input to me on what may be occurring. Thank you.


John Overstreet
Quality Manager - Lewisville, Texas

simultaneous (2007)

A. If you search this site, 99% of the recommendations are to throw away your panels and get brand new ones. Something happens to the surface chemistry as aluminum ages. If you keep using the same lot of panels, your fail rate will increase.

James Watts
- Navarre, Florida


A. I'm fairly sure that the protective film on test panels uses a non-injurious adhesive.

If the Alodine® solution is within specs. and the coating appears OK, failure is likely due to contamination from preceding steps. E.g., iron from the deox/desmut or hard water residue from a flowing rinse.
To check: deox/desmut in 20 vol% nitric acid, DI water rinse, Alodine®, drag-out rinse and DI rinse.

Ken Vlach
- Goleta, California
contributor of the year honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.


A. You need to call in your supplier, meanwhile, try another source for the panels and inspect the panels for pits with a 10X loop before chromating.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como


A. It is unlikely the protective wrapping is causing failure unless you are going straight from unwrapping to the Alodine bath. If you are using a caustic cleaning process followed by an acid deoxidizing process prior to chemical conversion -- a small amount of surface has been removed from the panels. So long as you attain a water break free surface after cleaning and prior to chemical conversion it would be moot if it were degrading the surface as the degraded surface would have been removed.

Test your Alodine 600 for sulfate and chloride contamination - keep it under 400 ppm. Henkel suggested you could potentially see salt spray failures over 15 ppm phosphate contamination. This is good to know as some parameters might have the high limit set to 25 ppm.

The bath should also have a certain level of Fluoride in it to work properly as well. Have your bath tested and call your Henkel rep to see what the target should be.

Lastly, you are not alone in this dilemma. It IS vexing. If we come up with something spectacular and brilliant - I'll let you know. If enough people throughout the country admit they are having SS failures with Alodine 600 - I might focus on the product being the failure mode.

Christopher D. Arfman
- Seattle, Washington


A. Hi all -

My experience has been that this problem will be most difficult when using an iron based deoxidizer. If you can use a chromated deox it should be easier to pass.

Terry Tomt
- Auburn, Washington


A. Update!
Although our passes have been nominal, and our failures miserable, we have found what seems to work, and what doesn't at all.

The key is removing the natural oxide coating from the test panel without going too deep into the base metal prior to Alodine. There is no set times, you have to find what the 'sweet spot' of your chemistry is. If you skip alkaline etch altogether, extend your acid deoxidizer times a bit. Try another set with a little etch and shorter deox. Be sure to look at your panels prior to process (10X loop is best) as the panel starting with pits will certainly end with pits.

The key is not to focus on 'why' - you'll go mad. Send several sets into salt spray with a wide variety of process times and parameters, whichever set(s) passes becomes the way you certify your work to.

There are enough people in this area now having troubles with Alodine salt spray that there is a little comfort knowing we are not alone.

Christopher D. Arfman [returning]
- Seattle, Washington

Q. Surtec 650 treated aluminum panels failing Salt Fog test

-- this entry appended to this thread by editor in lieu of spawning a duplicative thread February 22, 2014

Q. Hello, I work for a small metal finishing company in Michigan and we are completely stumped on an issue with Surtec 650.

We are running 2024 panels and 6061 panels to the MIL-DTL-81706B spec by the immersion method. Our tanks are well within pH and temp. ranges when panels are being ran. We have constant overflow rinses and are very careful with the times that the panels are in the tanks.

Once the panels have been ran, they are put into our salt fog test cabinet to run for the 7 day test, but the panels often fail within the first couple days. At the end of the 7 days, the panels come out with very large pits and it's very obvious that they have failed.

Is there a common reason why Surtec 650 panels fail and is there any easy things I can try to remedy this?

P.S. I just found this site and think it will be an awesome resource. Thanks for your help.

Scott Czarnik
Plating shop employee - Jackson, Michigan, USA

February 2014

A. Hi Scott. We appended your inquiry to a thread about 6061 panels rather than to one of our dozen threads about 2024 panels because every once in a while the failure of 6061 panels is actually related to the process -- whereas it's essentially unheard of for the failure of 2024 panels to be related in any way to their processing :-)

As Robert suggests and implies, throw away your test panels, get several sets of new test panels from various vendors, and get back to us if you're still having trouble; but there's a good chance you'll be fine. Salt spray testing of chromate conversion coated aluminum test panels is only a joke, and must be accepted as such or you'll go nuts. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

February 23, 2014

A. Hi Scott, what kind of salt fog tests did you perform? NSS or AASS?

Davey Shaw
Shenzhen, Guangdong, China

Salt spray result on 6061 T6-51 with chemical conversion per MIL DTL 5541 Type1 Class3

March 24, 2016

Q. One of our products was subjected to salt corrosion test as per MIL-STD-810 [link is to spec at / Defense Logistics Agency] F for 96 hours. Raw material is Aluminum Al 6061 T6-51 We have observed decolorisation as per the photo:

(Click graphic for hi-rez version)

Please let us know whether it is corrosion and what type of corrosion? We would be grateful if you could tell us the type of corrosion and what could be the root cause. How to prevent it from occurring.


Nandaki Devi R
Employee - Quality Control - Chennai Tamil Nadu India
^- Privately contact this inquirer -^

April 1, 2016

A. Good day Nandaki.

Google "rainbow" on this site.
There is a lot of good info.


Eric Bogner, Lab. Tech
Aerotek Mfg. Ltd. - Whitby, Ontario, Canada

November 2, 2017

Q. I have been struggling with getting visually passing coupons samples.
I am processing two Alloys 6061-T6 and 2024-T3 .032 x 3" x 10" premium prepared panels to pass the MIL-DTL-5541F Class 3 requirement.

I process four sets of coupons, Qty five (5) of each alloy 6061-T6, 2024-T3 for 168 hour Salt Spray, Contact Resistance testing and process two (2)of each alloy for Paint Adhesion testing.

These coupons are processed using sst film clips and all 14 coupons are processed at the same time.

The 2024-T3 Alloy looks great as it should, no signs of smut and appealing finish.

The 6061-T6 coupons are streaked and have surface smut on them, the finish is not appealing. The streaked surface is lighter in color as well.

The coupons are not processed thru the etch. This step is reserved for extrusions and welded assemblies.

I have mechanically removed the Oxide layer on the 6061-T6 panels with abrasive pad then processed thru the Wash, Rinse, Spray Rinse, 1200S, Rinse and then Spray Rinse with great results.

The Deox is my focus.

Any recommendations of how to proceed to get better results?

Our Line is as follows.


MATERIAL: 6061-T6, 2024-T3 Aluminum

Degrease      C-AK 6849 14% per/vol H2O             5 Min.
Dip Rinse     DI Water                             15 Sec.
Spray Rinse   DI Spray Water                       15 Sec.
Etch          SD-1 Granules 5.3 oz/gal               N/A
Dip Rinse     DI Water                               N/A
Spray Rinse   DI Spray Water                         N/A
Nitric Deox   C-IC 6MU 10% Nitric & 9% C-IC 6MU     5 Min.
Dip Rinse     Cascade DI Water                     15 Sec.
Dip Rinse     Cascade DI Water                     15 Sec.
Spray Rinse   DI Spray Water                       15 Sec.
Chem Film     1200s 	                           90 Sec.
Dip Rinse     DI Water                             15 Sec.
Spray Rinse   DI Spray Water                       15 Sec.
Kurt Krueger
- Lexington, Massachusetts

November 10, 2017

A. Kurt

I would first look at the sst clips. Have you tried an aluminum rack? If you process a panel by hand (no rack) do you get favorable results?

Willie Alexander
- Green Mountain Falls, Colorado

November 11, 2017

A. Has that abrasive pad been used on any other metal than aluminum? Is the pad abrading other metals into the soft Kleenex-like aluminum? Did you inspect the panels with a 10X loop to look for pits and scratches?

robert probert
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina

November 13, 2017

Good Afternoon Ted Mooney

Thank you for this forum.

Attached are the photos that go with the initial question and process posed last week.

... the coupon made out of the Alloy 6061-T6.

... the coupon made out of the Alloy 2024-T3.

... both sets of coupons side by side.

Thank you,

Kurt Krueger
- Lexington, Massachusetts

November 13, 2017

Q. Good Afternoon Willie

Thank you for your input. I have processed one 6061-T6 aluminum coupon by double gloved hand. No Rack. The results were still less than desirable. The process steps were the same as listed previously,except no rack was used.

Last week I a ran a series of additional testing. My variable was the immersion time in the Deox. Still using a 6061-T6 test panel.
Immersion time of 2 minutes,3 minutes and 4 minutes was my variation. All three showed the same washed out streaky look. I do not believe these are of visual passing quality to send out for salt spray analysis.

I then processed two 6061-T6 coupons thru the same 140 °F DI Immersion Wash, DI Immersion Rinse, DI Spray Rinse, then 2 minute immersion in 140 degree Sodium Hydroxide at 40 g/l solution concentration, DI Immersion Rinse, DI Spray Rinse, then one coupon was immersed for 30 seconds C-IC 6MU Deox and one for 60 seconds. Then the same final steps DI Immersion Rinse, DI Immersion Rinse, DI Spray Rinse, 90 second 1200S immersion, then DI Immersion Rinse, DI Spray Rinse.

Both of the coupons processed thru the Sodium Hydroxide looked better than any previous results with the 60 second Deox immersion variation looking the best. The results of this testing look good enough to send out for salt spray, resistivity and paint adhesion testing.

I am still at a loss for why the 2024-T3 coupons were not showing similar visual streaky, washed out look.

Thank You all for your responses.


Kurt Krueger
- Lexington, Massachusetts

November 13, 2017

Q. Good Afternoon Robert

Thank you for you interest and input. In response to your inquiry:

"Has that abrasive pad been used on any other metal than aluminum? Is the pad abrading other metals into the soft Kleenex-like aluminum? Did you inspect the panels with a 10X loop to look for pits and scratches?"

The premium test panels were processed with a(new)never used red(Trade Name)abrasive pad.

After the abrasive pad treatment these panels were visually inspected under 10x magnifiers the panel looked uniform and no visual imbedded particulate.

Then the panels were Washed in the C-AK Immersion product, 15 sec DI Immersion Rinse, 15 sec DI Spray Rinse.

Then the 90 second Immersion in the 1200S Chromate, DI Immersion Rinse and finally DI Spray Rinse

These test panels had no issue. The chromate looked great. These part would most likely pass the salt spray, resistivity and paint adhesion if I tested them.

So this tells me the 1st and last chemistries are working as designed.

The Deox chemistry is suspect.

Thank You

Kurt Krueger
- Lexington, Massachusetts

November 16, 2017

A. Your pretreatment process sounds okay, but pictures look like a too thin chromate coating.

Clean/etch a bit more aggressively, make certain your deox is up to snuff, and chromate for a bit longer time.

jeffrey holmes
Jeffrey Holmes, CEF
      South Carolina

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