First experiments... Smut pics identify alloys, voltage curves at 6A CD

[acidrain]

Hello all,
I have been busy with experiments... here's what I've been up to:
I was able to obtain some different alloys... 2024, 5058, 6061, and 7075. First part of the experiments involve observing the smut produced from the etch process. I use 1 can of Red Devil Chrystal drain cleaner per 3 gal. RO water. The parts were allowed to etch for about 3 minutes at 70F, then rinsed in RO water, and arranged for photos... top left-7075, top right-6061, bottom left-5086, and bottom right-2024.
7075- Black, almost sooty smut appears quickly, and is easily wiped with a rag.
6061- No smut to speak of.
5086- Very little smut, slightly yellow smut that can be wiped with medium ease with a rag.
2024- Gray/black smut appears with medium speed. Not easily wiped with a rag.


Next was the individual anodizing of each of the alloys. Anodizing was temperature controlled to 70F as close as possible, and notes were taken at 5min intervals all through the process checking volts and temperature. Surface areas were carefully measure, and amps were controlled with a digital CC/CV power source. Racking was with Ti racks (previously pickled), and agitation was with thorough air bubbling.
Titration of my ano bath shows the acid concentration at ~200g/litre of water, and aluminum content at 1.8g/litre. I'm not sure exactly what this means, but it is a standard 1:3 acid/water mix that I have been using for about a year now with no problems. Here are the graphs:

[acidrain]

[acidrain]

Each of the alloys were individually anodized at 6amps per sq. ft. current density for a period of 90 minutes for a projected ano thickness of .75mil. Dying was done with black, because that color typically requires a full 1mil thickness (at least for 6061) to come out good. Each of the samples were laid out in the same order as above for side-by-side color comparison. As expected, the 2024, and the 7075 dyed deep black, and the 5086, and 6061 were a bit light.

[acidrain]

Next, the parts were stripped, de-smut'd, and run at the same CD all together in a mixed batch. Here is the really interesting part... This entire effort began with the goal being a scientific approach to CV anodizing. All the while in the back of my mind I'm thinking that I really want to get away from having to calculate the surface areas of irregular parts, but knowing full well the consistency of the CC LCD method will yield the best results. Well, after studying the volts curves, and trying to come up with the best of two worlds, here is what I did:
I picked a number... 15 volts.
I racked the freshly cleaned parts, checked the temperature, turned on the air agitation, turned the amps all the way up, started with the volts all the way down, and turned on the power supply.
Now, I slowly ramped up the volts (really slowly) to 15 volts. After 5 minutes of the start, I noted the amps (they were steady now), and slowly turned down the amps until they just began to drop, then bumped them back to the steady number. Now I turn the volts all the way up. This move produced a seamless transition from CV to CC. Now I ran the rest of the duration at this setting for two hours. At the end of the process the parts were dyed black with outstanding (normal) results. BTW, at the arrived amps, I reverse calculated the current and known SA, and guess what? The CD was just a tad over my target of 6A CD. YAY! Here is a pic of the finished mixed batch. The 2024, and 7075 came out ever so slightly darker, but that is somewhat normal. I often have to adjust dye times of mixed batches so that all the parts come out the same... hopefully with the smut info, I'll be able to predict (and you, now) which parts will give me dye problems.


Any comments/feedback is greatly appreciated. Did I leave anything out? Did I make any mistakes?
Hopefully somebody out there can use some of this info. I know I'm pretty excited to try the same method with other colors. I hope to have some real thickness measurement to go with these results soon as well.
Enjoy! -Acid

[rclint]

acidrain could you shoot me a email ?

rclint@alltel.net

[destroyer125]

weird...on 6061 aluminum I get a medium grey smut similar to your 2024 only it whipes off easy

Also, How much would the colors vary if you were to use non-black colors?

[acidrain]

Originally Posted by destroyer125

weird...on 6061 aluminum I get a medium grey smut similar to your 2024 only it whipes off easy

Also, How much would the colors vary if you were to use non-black colors?

Great question... I don't know because I have'nt done any other colors yet, but I will in the next day or two.
I'll use the same four samples, and dye them blue this time.

[blackcote]

Originally Posted by acidrain

Next, the parts were stripped, de-smut'd, and run at the same CD all together in a mixed batch. Here is the really interesting part... This entire effort began with the goal being a scientific approach to CV anodizing. All the while in the back of my mind I'm thinking that I really want to get away from having to calculate the surface areas of irregular parts, but knowing full well the consistency of the CC LCD method will yield the best results. Well, after studying the volts curves, and trying to come up with the best of two worlds, here is what I did:
I picked a number... 15 volts.
I racked the freshly cleaned parts, checked the temperature, turned on the air agitation, turned the amps all the way up, started with the volts all the way down, and turned on the power supply.
Now, I slowly ramped up the volts (really slowly) to 15 volts. After 5 minutes of the start, I noted the amps (they were steady now), and slowly turned down the amps until they just began to drop, then bumped them back to the steady number. Now I turn the volts all the way up. This move produced a seamless transition from CV to CC. Now I ran the rest of the duration at this setting for two hours. At the end of the process the parts were dyed black with outstanding (normal) results. BTW, at the arrived amps, I reverse calculated the current and known SA, and guess what? The CD was just a tad over my target of 6A CD. YAY!

I've been toying with this idea for quite some time as well. But temps have been killing my calculations as well as lack of precision measurements of volts amps and temps. acidrain check your CD at different temps when you make the switch between CV and CC... I'd be real happy to know if you get any drastically different results in terms of CD. I find that when I calculate CD at different times through a constant CV process... The results are too scattered because of temp variation and I have no idea how to compensate for the effect temp has on resistance of the system. I think more testing needs done.. and I'd be glad to help in any way we can. On our next run I may try to keep a thorough log of the variations to see if we can identify something to help.

We're in the process of upgrading the system to a more permanent and larger basis than we currently have and at the same time we want to keep rework to a minumum so we are on the fence about switching to LCD acid concentration and using both CC and CV when applicable. We'd like to use higher concentrations to keep the process time down [it's not helping right now though, we still have to run parts 80-90 min to get a good black.], but I think we'll need more time for study and experience, before we can take that step.

Calculation of surface area for one off or a few parts is too time consuming as this seems to be the most of what we do. So we've been using CV anodizing for quite some time and sacrificing the consistency somewhat of CC ano over shorter times and not having to calculate SA (ever try to calc area of a gun reciever or a trigger housing?)

[Canute7]

Hey acidrain, this is great, I just ran a part that came out of ecthing with a kind of dark gray-greenish-black film on it, since I don't have any de-smut, I just wiped them off and ran them, they came out a little lighter than I had hoped.
Thanks for sharing this info
Canute

[acidrain]

Blackcote, I have not run at different temps, because I REALLY make an effort to control the temp very precisely. I learned early on that tank temps are one of the first variables that need to be controlled if you want to have consistant results (to the point of desilution after 70F).
I can tell you the difference between 70F, and 68F, is about .5v higher (for a cooler tank).