Sid,
Since you are using CC the electrolyte concentration won't make much difference in the thickness of the anodize. This is not the case with voltage (CV) anodizing. The concentration will effect pore size. I would prefer a 1:2 ratio at 12 ASF, and still use 30-45 min. If everything else is right, this will get you 0.5 to 0.7 mils coating thickness. Recall that dye won't penetrate any deeper than 0.7 mils. regardless of pore size.
The anodizing time is from the "720 rule". I have found; since I can measure the anodize thickness, that it holds up well at any ASF from 3 to 24 ASF.
The measured voltages look OK for 1:1 electrolyte, you should expect to see higher voltages (a little higher) with weaker electrolyte.
As M_D and other Ti racking users will agree here; racking in general is tricky, the two main issues:
1. Connection variance; your spring tension or how and where it makes contact may not be right, or not right most of the time. The sporadic nature of the problem supports this.
2. The parasitic resistance of the rack itself. If the SA of the rack itself is close to or larger than the work, it dominates. Since the Ti won't anodize here this resistance is constant with anodizing time; the resistance won't go up like it does for the work. This can defeat CC; the ASF for the work actually going down, not remaining constant, the power supply can't tell the difference between the rack's resistance, and the work's resistance. A fudge factor added to the ASF will help, I don't know how much extra ASF you will need to compensate.
Just as a test to see if this is the problem; do a test anodization with a piece of 6061, with soft Al wire bolted tightly. I know you can't do this with your real work, this is only to isolate the problem.
By "hazy film that you can sometimes wipe off"; could this be described as "chalky"? If so; it would be a sign of excessive dissolution, and the stronger electrolyte is working against you. Other things that can do this are; too low ASF, too high a temp., too long an anodization time.
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