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"Gold Color Finish for Hard Anodize"

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Current question:

November 22, 2021

We are facing some similar color issues after hard anodizing II.

Our customer needs dark golden colour after hard anodizing process and we are now getting grey colour after hard anodizing.

Can you please advise me how to fix this types of issue.

Many thanks in advance.

Dedania Sandeep
Employee - Rajkot -India
^


November 2021

A. Hi Dedania.

Was that a typo in "hard anodizing II"? Not sure if you're doing type II or type III.

1. You could try type 2-1/2 anodizing or oxalic acid chemistry if it doesn't violate your specs.
2. Although hard anodize isn't usually sealed, you could try a chromic acid seal.
3. Although hard anodize isn't usually dyed, you could use a dye of the color you want.

Please return the favor by keeping us appraised of of your progress or lack of progress. Many thanks in advance.

Luck & Regards,

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

simultaneous
November 24, 2021

A. Hi Dedania.

You may have read the threads that ted has attached to your question...(thank you Ted, that is always much appreciated).

A question to ask is what is the thickness requirement, meaning is higher thickness necessary to the function of the parts? If not, you can always apply a lower thickness of like .0003"/.0005" and then dye gold. This should allow you to achieve color with no issue. If however thickness is critical (.002" or thereabouts), then I suggest changing alloys. Different alloys do yield different natural colors when thickness is at or about .002.

Philip J. Verzal
Saporito Finishing Co.
supporting advertiser
Cicero, Illinois
saporito
^


November 24, 2021

thumbs up sign Dear Mooney sir ,

Many many thanks for your advice.

We will follow your advise and do the needful.

We are currently using sulphuric acid 10% to 15% as a electrolyte in our anodizing bath process with standard per Mil-A-8625 [link is to free spec spec at Defense Logistics Agency, dla.mil] Type 2 class1 non dyed and natural color . We are suffering a lot to get gold color finish in 6061 T6 aluminium grade . Now we get grey and black color from this sulphuric concentration. We are now using Nickel Acetate sealing process after anodizing as per our customer request.

Q. Can you also advise me how to control aluminium sulphate in anodizing bath? Is aluminium sulphate the cause for burning issues or color variations?

Currently we are applying current 25 to 26 V and 30 amps with 4 °C and 30 minutes for our 8" round aluminium plates with 40 mm thickness. I need 25 microns anodic thickness.

Is this above formula correct? Or we need some changes in this calculation?
So please give your advise so we can make as per standard.

With best regards,

Sandeep Dedania [returning]
Engineer - Rajkot -India
^


November 2021

A. Hi Sandeep. Philip's reply crossed in the mail with your posting. It has good ideas including dyeing. 25 microns (0.001") is fairly thin for type III hardcoat but very thick for type II. Even architectural and black anodizing is rarely over 0.0007". Also, 4 °C (40 °F) is neither conventional type II nor type III temperature.

It sounds to me like your customer is looking for and has become familiar with type 2-1/2 anodizing. Usually this will require a proprietary additive or additions of glycolic acid and glycerine rather than just sulphuric acid. Do a search for "MAE anodizing process". But read the rest of this thread first and there is interesting info about doping the aluminum before anodizing.

We want to help you out with all of your problems and not hassle you, but this site has hundreds of readers for every poster, and it's a disservice to the readers if the threads all wander to such a wide extent that it loses most of its usefulness as a research site. So please search the site for the issues that you mentioned that are not related to getting a gold coloration, like "controlling aluminum sulphate in anodizing", "burning in hardcoat anodizing", "estimating anodizing time vs. thickness" (search for "the 720 rule"), and post your continuing questions on relevant threads. Thanks!

Luck & Regards,

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




Closely related Q&A's, oldest first:

2004

Q. We are an engineering company manufacturing factory automation part, and we have a customer's requirement that needs hard anodize parts with a gold finish. We've sent parts for anodizing to our suppliers and they usually come back with a dark finish. How can I get the gold finish?

Edward Lay
engineering - Kuala Lumpur, Malaysia
^


2004

A. What is your means of gold color, is it gold plating on the aluminum parts? Do you know different grade of aluminum will come out the different color after you do the anodizing?

Goh Boon Han
- Muar, Johor, Malaysia
^


simultaneous

probertEthumbAluminum How-To
"The Chromating - Anodizing - Hardcoating Handbook"
by Robert Probert
(How good is it? Finishing.com has sold over 750 copies without a single return request)

2004

A. "Hard Anodizing" means different things to different people. To the Military Specification writers it merely means a heavier thickness, usually about 0.002 inches thick, and hardness it not addressed. To me it means a small pore which which is created by a cold temperature and high current density. So far your gold color is dark because the pore is very small and that tells me that you are getting one kind of "hard coat".

By anodizing at a higher temperature with a glycolic/glycerin type additive you can get thickness (so called "hard coat") and a larger enough pore to get bright gold dye adsorption.

Another way is to use what some call "Architectural Hard Coat" which takes place in an electrolyte that contains sulfatholic acid and derives it's gold color from the oxide formed from manganese that is alloyed (or mixed) into the metal. Here you buy a special metal from the aluminum supplier that is "doped" with an impurity (usually manganese) that comes out bright gold color when anodized in sulfuric with sulfatholic acid. Any of the four big aluminum suppliers can furnish the details.

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


2004

A. Mr Goh

It is not gold plating on the aluminum, rather gold color. the aluminum grade is 6061. I know different grades will affect the color. I've run test for black anodizing before. Even the country of origin affects the color. What I require is for a hard anodize treatment that will also yield a gold color finish.

Edward Lay [returning]
engineering - Kuala Lumpur, Malaysia
^


2004

A. Try having the parts hard anodized at lower current density (18 ASF) and only anodize .0005-.0008" thickness. A 5% nitric acid dip before dying might help also.

Good luck,

Bill Grayson
Metal Finishing - San Jose, California
^


2004

A. The color of Hard coat is a factor of what alloy, that is being hard coated. A Gold color after hard coating means the alloy is a 7000 series, like 7075, A dark gray hard coat is 6000 series like 6061-T6, different heat treats different machining temps can cause different shades of color.

Chris Snyder
plater - Charlotte, North Carolina
^

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