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Difference between Mil-s-A8625 Type II Class 2, and BiFluoride etch Alum Anodize





December 20, 2011

Q. My name is Beverly. One of our customers wants to anodize alum 6061 T651 "Flat Black". The print however calls for Mil-s- Std A8625 Type II Class 2. and Flat Black, BiFluoride etch. It isn't even a military part , and I think it is a contradition. Type II Class 2 is shiny and "BiFluoride" is matte or flat . Is this true?

Beverly Hartman
buyer, shipper, proof reader,jobshop employee - Vista, California



December 21, 2011

The anodize can be either shiny or flat depending on the surface of the aluminum. The bifluoride etch is a finer etch than a sodium hydroxide etch. It tends to dissolve all of the metals in the alloy, whereas lye only attacks the aluminum and zinc, thus leaving a black smut.
It can be very aggressive, but within a normal range, you will get a consistent product until you have dissolved too much aluminum and other alloys.

James Watts
- Navarre, Florida


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