We are anodizing 2011 on Ti racking too, and it’s definitely more troublesome for us than 6061 and 6063. At first it gave us fits, now we are quite consistently getting nice results and things seem to go better and better. The commercial anodizer that we have used was especially inconsistent with it (2011), they didn’t like it either. I will say that over 90% of the 2011 we do is dyed black, the balance is fairly evenly divided between clear, red, and blue. The red with 2011 is by far the hardest to get right.
I realized sometime back that the Ti racking makes it difficult if not impossible to calculate the exact amperage that the parts are anodizing at. We started out using 4.5 amps with aluminum hanging wire. Once that was going fairly well, we needed to increase volume and went to Ti racking. We still don’t have a large operation (shopping for a 1,000 amp power supply now), and the most parts per run are 100-200 parts. We started to anodize at “6-8” amps per square foot (1:2.5 electrolyte), to reduce cycle times. The reason I put quotes on the amperages is because that was the calculated amperage for part surface area. Anyway, we were doing ok (not super great) after some experimenting on times and so forth. Then we went to a deeper and larger anodizing tank, and were able to fully submerge our racking (we were only submerging it about 40-50% before that). All of a sudden things got weird. I decided to try more amperage and we are now using 10-12 amps per part square foot (not including racks). It made a huge improvement, the parts are turning out very nice and have very little or no haze that needs wiping off. If we have problems with haze now, it is almost always with 2011. The electrolyte is now the same (1:2.5 electrolyte) as we used with the smaller tank.
It appears to me that anodizing with Ti racking does require compensation in the amperage amount. Too low of amperage causes haze (smut or what ever you call it) and other inconsistencies like black dye being reddish, and etc. Since the Ti racking is altering the electrical calculations, I’m not sure what the actual amperage for parts really is. Like Fibergeek suggested already, I would suggest trying more. I suspect that since you increased the electrolyte concentration so much in addition to the amperage, that you are still low on the actual part amperage and dissolution is occurring now and was before.
You do need to be sure the parts are de-oxidized well, because that positively will cause problems. You might try increasing the soak time, or concentration of the etch solution, if it doesn’t degrade the surface. Are you de-smutting them after the lye etch? I know that very thorough rinsing is needed, and racking multiple parts makes it more difficult than doing a single part that has free access to all sides.
I know none of this information is precise, but is might give you a direction to try. I think with the Ti racking you may need to stick with loads that are fairly consistent, and experiment with the amperage and times until you get good results. If you change the part load, then I believe there will need to be an adjustment on current density. Maybe with time Fibergeek and I will find a formula were it can be calculated before hand.
Added in Edit: I also thing that doing some test pieces with aluminum wire would help. If they turn out good and the results are consistent, and the Ti racked loads don't, it shows the problem is CD related.
I would think a deficiency in the cathodes would cause problems. I have been using aluminum sheet (stays in the tank). I have 2 pieces of 7 square feet each on opposite sides in a 55 gallon tank, connected with a 12 guage wire with solder terminals. The connections are several inches about the solution, but I try to clean them regularly as the acid mist finds it way around.
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