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topic 56585

Cold Anodizing Of 6061 and 2024 Aluminum

A discussion started in 2011 but continuing through 2017

January 23, 2011

Q. I have absolutely no idea what I'm doing. I am a first year member (11th grade) of a high school robotics team, and the team decided to do a cold anodizing (which I am told is anodizing that does not require the use of an electrical current). Lucky me, I was tasked with the assignment of researching anodizing. As of right now, the team is considering either green or black anodizing of 6061 and 2024 Aluminum.

The two types of parts the team seeks to anodize include

1" x 1" 1/16" thick wall 6061 aluminum tubing
2" wide 1/8" thick 2024 aluminum flat stock

Preferably, we would like to keep the costs to a minimum.
If you need any more info, send me a followup.

Alexander N. [last name deleted for privacy by Editor]
Student - Detroit, Michigan

simultaneous January 25, 2011

In order to do anodizing on aluminum, you need electrical current, period. There should be several companies in the Detroit area that could provide this service for you. If you want the colors to match (between the two alloys), you'd probably be better off going with black, as opposed to green.

The way the anodizing process works is:

Parts are racked for electrical current
Parts are cleaned/etched in multiple baths
Parts are anodized (this is where the electrical part comes in play)
Parts are rinsed, and then dyed to whatever color you want
Then parts are sealed (to keep the color from fading.

I've never heard of the term "cold anodizing", but this could mean two things.

1. The temperature of the anodizing bath, where if colder, will produce a harder coating when used with higher current densities. This is typically called hard anodizing.

2. There is also a sealing process called "cold sealing", which, in my opinion, is generally inferior to mid-temp, or high temp sealing.

Just call around and get a quote. Not sure what your budget is, or the quantity of parts you need coated..but I would imagine you're looking somewhere around $50 to $75, if you're just talking a few small parts.

You could always try to attempt to do this yourself by researching online, but believe me, in the long run, you'd be better off spending a few bucks to let someone that knows what they're doing handle the job. Will save you quite a few headaches. Either that, or buy a $5 can of spray paint :)

Marc Green
Marc Green
anodizer - Idaho

January 25, 2011

You have been at least partially misinformed. All anodizing requires DC current. Cold anodizing may refer to hard anodizing (also called hardcoat, or Type III) which is often performed in cold (~30 degrees F) sulfuric acid. That may not be what you need, however. What are your requirements for your piece? Are you just wanting the color green or black? If so, you would probably just find a shop to perform standard Type II sulfuric acid anodizing, followed by the dye in the desired color. Black is probably more common, but green is also common. If you are dead set on trying to figure out how to do the anodizing yourself, then Robert Probert's book "Aluminum How To" would be a good place to start. Good luck.

Jon Barrows
Jon Barrows, MSF, EHSSC
Springfield, Missouri

January 26, 2011

A. Alexander

To add to what Marc & Jon have provided and considering the scope of your project, it sounds like you just need some aluminum robot parts anodized so your project looks better than your competition.

I would suggest finding a local anodizer (search metal finishing, anodize, plating, electroplate) who would do the job gratis in exchange for mention of his services as part of your project. If you are not picky about the colors, you'll make it easier for them to help you. Maybe he has a sticker you can put on the bumper of your robot.

Willie Alexander
- Colorado Springs, Colorado

October 12, 2017

A. Here's a backyard , or home hobby shop way to dye anodize Al parts. I know all you industry professionals don't believe in this, but for us "Makers", and Robotics Team members (and mentors) we must, by necessity and financial constraints, find ways and workarounds for a LOT of manufacturing processes. Hell, I used to use a black wide tip sharpie to "black anodize" very small parts, and even touch up previously plated, but scratched, parts. In the (commercial) Nuclear industry, no less.

Ray Straub
Accurate Engineering Services - Williams, Arizona, USA

October 2017

thumbs up sign Thanks Ray. When it comes to hobbies and education, whatever satisfies the needs of the project is good enough! Titanium can be anodized in anything from Coca-Cola to Spic 'n Span.

If you've anodized aluminum with bisulfate, that's good news. We're not opposed to simple and safe: our FAQs include instructions for elementary school children to do zinc & copper electroplating in the kitchen with vinegar and a penlight battery.

I too have seen anodizing 'rack marks' disguised with a black magic marker.

Part of what makes production plating and anodizing difficult is not just the need for extremely high reliability, robustness of the process, and warrantability, but the need to maintain an equilibrium process because shops can't afford the cost and environmental damage of dumping their plating and anodizing solutions, but must keep them running for decades. It's not solely a matter of getting the solution to produce a satisfactory part, but also for the plating or anodizing operations they conduct to not throw their solutions too badly out of balance. Thanks again.


pic of Ted Mooney
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"

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