finishing.com -- The Home Page of the Finishing Industry

HomeFAQsSuggested
Books
Help
Wanteds
Advertise
on this site
FORUM
current topics
The world's most popular metal finishing site, and striving to be the internet's friendliest corner

topic 19342

Chemical conversion coating on aluminum: what is default color?


A discussion started in 2003 but continuing through 2019


2003

TUTORIAL:

Alodine is a Henkel trade name for a line of conversion coating processes.

Q. I have an aluminum part to be chemical conversion coated per Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil], class 1A. Is this colorless Alodine or gold Alodine?

Norm Dang
an instrument manufacturer - Santa Ana, California


2003

A. Hello,

The Mil-Spec states that unless otherwise requested the default color is Gold. That pertains to Class 3 coatings as well.

Bill Grayson
- Santa Cruz, California


2003

A. Class 1A is a paint base coating. It can be gold or clear, but the coating should be gold unless a clear chromate is directly specified.

Patrick Patton
lab products - Westlake, Ohio


2003

A. Gold. Alodine is one of many trade names for aluminum chromate meeting Mil-C-5541 [link is to free spec at Defense Logistics Agency, dla.mil].

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


TUTORIAL:

Iridite is a Macdermid trade name.

Clear chromating is sometimes done by leaching the color out of yellow/gold coatings in hot water, but many professionals believe that "no color left = no chromate left".

2003

A. Alodine (or Iridite or whatever) is sort of an opinion, isn't it? Anyway, MIL-C-5541 (or AMSC5541, both are "active" if anyone wants to toss stones at a NADCAP auditor) has Class 1A and Class 3. Class 1A is the "corrosion protection" and could be described as the "dark" and Class 3 is the "electrically conductive" and is the "light". In any case, don't confuse "clear" and "colorless" ... it should be (depending on which "proprietary" chemical, prep and cleaning (mechanical and chemical, the immersion time, temperature, alloy type, et. al) faintly yellowish ... again, this is subjective.

My personal gripe is design engineers who spec "colorless" and want you to "bleach" (hot water) ... what are they thinking!

Doug Hahn
- Mason, Ohio


2003

A. Color can vary from colorless to golden - iridescent - brown. Materials conform to Mil-QPD-81706 [link is to free spec at Defense Logistics Agency, dla.mil]. Coatings shall be continuous free from powdery areas, breaks, scratches, etc. Sometimes called yellow Iridite. No dimensional change are effected with Iridite finishes. Class 1A is used as a corrosion preventative film (unpainted) or to improve adhesion of paint finish systems.

Robert D Lilley
- Singapore



Electroless procedure for aluminium plating in a brass color

October 29, 2018

Q. Hi I wish to plate aluminium zipper in yellow (brass) color thru electroless procedure. Please guide process and chemicals.
Please help.

Mukand Garg
Bdmpl - Delhi


October 2018

probert book
Aluminum How-To

"The Chromating - Anodizing - Hardcoating Handbook"
by Robert Probert
$89

A. Hi Mukand. I think you have yellow (gold) chromate conversion coating in mind. The main step in the process is immersing the aluminum into a vat of Alodine, Iridite, Chemion TCP [from Chemetall, a finishing.com supporting advertiser], or other brand of chromate conversion coating chemistry for the formation of the conversion coating. These days, trivalent chromates should be specified.

This step is preceded by mechanical finishing, non-etch alkaline cleaning, etching (usually), desmutting (with the specific chemistry dependent on what aluminum alloy you are using). We have dozens, maybe hundreds of threads about chromate conversion coating of aluminum in this forum, but books are probably a faster, more tutorial, path to general learning. Good luck.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha



March 11, 2019

Q. Where in Mil-Spec Mil-DTL-5541 [link is to free spec at Defense Logistics Agency, dla.mil] F does it state that "unless otherwise requested" the default color is Gold?

Glen Boreman
- Oceanside California


March 2019

A. Hi Glen. It doesn't, although it did say more or less that it in the earlier days of MIL-C-5541 (copies of which are no longer on line at quicksearch.dla.mil).

MIL-C-5541E says in Section 3.5: "Clear (colorless) coating shall only be used when specifically authorized by the procurement authority,"
and in section 6.2: "Ordering data. Acquisition documents should specify the following: ... d. Clear coatings, if desired ..."

It seems that the color expectation went away with MIL-C-5541F, concurrent with inclusion of Class II (non-hexavalent) coatings.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


July 30, 2019

A. Glen,

There are a couple of trivalent chromium conversion coatings on the market that meet this 5541-F spec and exceed the performance of hexavalent alternatives. Currently all trivalent conversion coatings are clear, producing an almost imperceptible iridescent look. It is a complaint with many customers that they cannot tell if the coating has been applied especially with untrained operators on-line.

In the next year there is a USA based company that is fast tracking a dyed trivalent conversion coating through the QPL process to conform to this spec. It is commercially available now though distributors as an unspecified product.

Isaac Brown
Technical Sales Rep - Cleveland, Ohio, USA


July 2019

thumbs up sign  Thanks for the update, Isaac!
opinion! Is it too much to hope that the dye color is spring green or something other than the yellow/gold natural color of the toxic, carcinogenic, hexavalent chromium and identified with it for so long?

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha

Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Disclaimer: It's not possible to 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 may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices


©1995-2019 finishing.com, Inc., Pine Beach, NJ   -   About finishing.com   -  Privacy Policy
How Google uses data when you visit this site.