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Etching Aluminum - MIL-C-5541 Class 1A

Q. A customer part calls out "MIL-C-5541, Class 1A - DO NOT ETCH". Chem Film Supplier is telling me that in order to be compliant with MIL-DTL-5541, a minimal mild etch must be applied, therefore the "No Etch" instruction must be changed to "minimal etch".

These parts were designed ages ago ... and used to be machined from castings. Today they are machined 6061.

We've asked the customer how they wish to proceed but wanted to ask here if indeed etching, even mild, is "required". The 'do not etch' instruction has been in-place for years and this is the first time we've been told about it from the supplier.

C Fisher
- Illinois
January 25, 2024

A. Hello C,
As a practical matter, the issue probably could become moot these days because the reason for not etching was probably to not bring about discoloration by etching a casting :-)

If your customer is made aware that the update of the substrate material might render the 'Do Not Etch' requirement unnecessary, hopefully everything can be simplified. Of course if this is an aerospace part, it might be a little more complicated than that.

As for exactly what the spec says, you and your customer will first need to decide if the ruling spec is an old version of MIL-C-5541 or the current version of MIL-DTL-5541 [on DLA], and then carefully read the applicable spec. The supplier may be acting 100% in good faith or might be slightly shading their interpretation because they've found that the process is more robust with a slight etch :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey

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