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Gold Color Finish for Hard Anodize
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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 Layengineering - Kuala Lumpur, Wilayah Persekutuan, Malaysia
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What is your means of gold color, is it gold plating on the aluminum parts? Do you know different grade of alu. will come out the different color after you do the anodizing?
Goh Boon Han- Muar, Johor, Malaysia
First of two simultaneous responses -- ++++
"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.
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Robert H Probert Robert H Probert Technical Services  Garner, North Carolina
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Second of two simultaneous responses -- ++++
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- Kuala Lumpur
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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 GraysonMetal Finishing - San Jose, California
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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 Snyderplater - Charlotte, North Carolina