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HAE Post-Treatment Dip

January 17, 2012

Q. Hi All,
I am currently dealing with a foreign supplier who is conducting HAE treatment on magnesium castings. Our requirement is HAE per MIL-M-45201, Class A, Grade 2 (i.e., tan coating with bifluoride-dichromate post-treatment). The supplier has inquired about the fact that the specification does not allow for a rinse following the bifluoride-dichromate dip, so there is concern that there is hex-chrome residue lingering on the parts, that are subsequently headed to be partially machined...

My question is three-fold, and I hope some of you out there can help me understand a bit about this process which is relatively new to me.
1. what is the purpose of the bifluoride-dichromate dip?
2. why does the MIL spec prohibit a rinse following this treatment?
and 3. are my supplier's concerns about hex-chrome residue legit?

Thank you for your time and consideration, I appreciate any information you all can provide.

Marco Ciccone
Materials Engineer - Philadelphia, Pennsylvania, USA

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