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topic 52830

Minimum thickness for black anodizing

A discussion started in 2009 but continuing through 2019

August 9, 2009

Q. Hi anyone

I intend to anodize sheets of aluminium (AA5182) with the size of 3 * 1.5 m. The desired color is black and I am wondering what would be the minimum thickness for obtaining a reasonable aesthetic effect. The scratch resistance is not that relevant as the products will be used in office environment and I think that any type of anodizing will offer that required resistance.
Another question is related to the panel sizes: I was reading on several posts about the problems with big sheets as they might create uneven color. Do you know anything about this? Do you have suggestions for the process?

Thank you

Marius Moldovan
ergonomics - Dubai, UAE

simultaneous South CarolinaAugust 11, 2009

A. Marius,

You should specify a minimum of .0006" (15.2 microns) thickness of a Type II (sulfuric acid) anodize to achieve a coating that will take the dye well. But remember that the anodize thickness is 50% penetration and 50% surface build-up.

Tim Hamlett
Decorative Plating - North Miami, Florida, USA

August 11, 2009

A. It is very difficult to get the current evenly distributed on thin sheets, make contact in several places. Better still, use an aluminum v-block on the bottom and just depend on titanium clips at the top to hold the panel in place.

Thickness for quality is 0.0008 inch, thickness for bare minimum with quality dyes is 0.0005 inch.

If the color is uneven then the anodize coating is uneven due to (1) probably uneven current distribution, (2) pick up of floating oil anywhere in the process line (do not use compressed air for agitation).

If you will set the panel down in a bottom v-block and hold it in place with titanium clips at the top, ramp up very slowly to 10 or 12 amps per square foot, the color should be uniform.

robert probert

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

Aluminum Alloy 6061 Black Anodizing: Coating Thickness

September 4, 2019

Q. I am new to anodizing and am curious about measuring the coating thickness of the piece being anodized. For instance, if I were to anodize a piece and dye it black, would the coating thickness be the layer of oxide after anodizing, or would it be the combined layer of oxide plus dye (correct me if I am wrong, but I assume that the dye also adds a certain thickness)?

Chiraag Bhawnani
- Atlanta, Georgia, USA

September 2019

A. Hi Chiraag. No, the dye has no thickness. The dye is absorbed into pores, microscopic 'drill holes' in the anodizing. When you read that black anodizing is thicker than other anodizing, what people are actually referring to is the fact that to get a good, saturated, black color the anodizing has to be rather thick to be able to absorb enough dye -- as Tim & Robert Probert say, 0.0005" or preferably more. When doing a light pastel color, not requiring much saturation, it is possible to use thinner anodizing like 0.0002".


pic of Ted Mooney
Ted Mooney, P.E. RET - Pine Beach, New Jersey
Aloha -- an idea worth spreading

Minimum aluminium thickness for anodising

September 17, 2019

Q. We have some very thin, very small components for black sulphuric anodize (25µm). They are less than half a mm thick and are partially dissolving during the etch process. This is the second time we've attempted this job and we've had the same result both times. Any advice?

Jane McMullen
Plater - Dorset, UK

simultaneous September 17, 2019

A. Firstly I advice trying acid etch process which does not involve as much as in normal etch process, or secondly if I were you I'd skip the etch process for this black anodizing. Etching is not necessary for black anodizing if custumer accepts that appearance.
Good Luck

alaattin tuna
- TURKEY,sakarya

September 17, 2019

A. Even if you get by the etch loss by skipping it, be reminded that, from both sides, the coating goes 50% under the original surface and 50% over the original surface +/- 10%, then all you would have left is solid aluminum oxide (very brittle and would fall apart).

robert probert

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

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