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Ted Mooney, P.E. RET
Pine Beach, NJ

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Color Anodizing

2002

Dear sir,

I want to know that if I am trying diecast aluminium containing .0003% of silicon in it and I am trying color anodising on it but some black spots are coming on it. So please help me out whether I can do it on it or not.

Sharad Kathuria
- Faridabad (Haryana), India

2002

Nobody believes that such an animal exists -- an aluminum diecast alloy with only 0.0003 % silicon! Yes, diecast aluminum is commonly anodized and dyed, although some alloys are more suitable than others, and the quality of the casting process matters. Anodize 'spots' on diecast are most commonly due to 1) porosity and 2) silicon grains, especially the coarse ones occurring in slowly solidified, hyper-eutectic alloys lacking grain refiner additives. Presuming that you have a typical, silicon-containing diecast alloy, be sure to use a nitric acid-fluoride etch rather than a caustic solution. After anodizing, use extra rinsing, perhaps even including a warm DI water dip, to flush out any acid prior to dyeing.

Ken Vlach [deceased]
- Goleta, California

Finishing.com 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, and we at finishing.com, continue to benefit from.

I want to color the aluminium alloy 2014/2024 with green dye? suggest dye & why absorption of dye is not occurring?

Ibrar Shah
hobbyist - Rawalpindi, Punjab, Pakistan
2004

What were your anodizing conditions. How thick is the anodized layer?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

Anodizing conditions are ;

concentration of bath(sulfuric acid)=10%by volume
current density=12 asf
voltage =18 volts
temperature=25 c
thickness achieved = 8-12 microns

Ibrar Shah
- Rawalpindi, Punjab, Pakistan
2004

You can use dyes for cotton fabric (cheapest but not best), or try to find proprietary product.

Good luck!

Goran Budija
- Cerovski vrh Croatia
2004

2004

The conditions sound good, and the anodizing thickness is probably sufficient. Are you heating the dye tank?

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