Gold Color Finish for Hard Anodize

A. Hi Sandeep.

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,

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 sulfuric 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,

A. Hi Sandeep,
If you start with type III traditional hard anodize, your substrate is going to be some sort of grey or bronze, depending on alloy. So you need to talk to your customer about the limitations of the process, and how important added abrasion resistance vs. color is to them, and work to find a process that works, or if they are stubborn... return a no-quote. In my experience, true sulfuric hardcoat and any pale color are incompatible. And depending on the alloy, sometimes even the promised color of the dye will be nowhere near what you expect.
Best of luck.

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?

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,

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.