Summary for hae post-treatment dip Discussion
HAE post-treatment dip is the focus of this question about magnesium castings treated to MIL-M-45201, Class A, Grade 2. Marco Ciccone asks why the bifluoride-dichromate post-treatment is used, why the spec forbids a rinse afterward, and whether his supplier is right to worry about hex-chrome residue before partial machining. The thread excerpt provided contains only the question and no answers, so there is no documented resolution or expert opinion to summarize from the source. Based on the question alone, the practical concern is that the post-treatment appears intended to create the tan coating required by the spec, while the no-rinse instruction raises a legitimate process-control and contamination question for downstream machining. Because no replies are included, any explanation of purpose, rinse prohibition, or residue risk would be speculative.
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