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Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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Sulfric acid anodize on 7050 T7451 color changing
2007
We are bring on line a sulfuric acid anodize line for MIL-A-8625 / MIL-PRF-8625 [on DLA]. We are having great results on color(non-dyed),salt spray and coating weight on 2024 test panels. However on 7050 T7451(actual parts) we running into a bronze color. We have reduced the anodizing time down to 15 minutes and seal time 23 minutes in Hot DI water(205°F±5°F). The color stays the same. Our requirement is a clear color on the 7050 parts. The other test we ran are anodizing 2024, 7050 and 7075 all the same process variables, The 7075 was the darkest, 7050 next and 2024 clear. Any advice on how to get a clear anodize on 7050 is welcome.
Todd Kingplating shop employee - Arkansas
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Although I'm not familiar with that particular alloy, being a 7000 series, I would wager the zinc content is on the high side, which is giving you that "bronze" color. The color of the anodic coating depends on several things, one being the alloy. I don't know if this can be overcome. The mil spec minimum coating thickness is .0002" I believe (for type 2). I would go as thin as possible, using the lowest current density, and the highest temperature (I wouldn't go higher than 74 °F). With all this being said, you may not be able to overcome the main issue, which is the zinc in the alloy. Is there another alloy you, or your customer could use?  Marc Green anodizer - Boise, Idaho 2007 You did not give us any concentrations, current densities, or temperatures, so here are the general rules for "clarity". Clarity in the anodizing tank increases with higher concentration, higher temperature, and lower current density.  Robert H Probert Robert H Probert Technical Services  Garner, North Carolina  2007 |
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