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Post baking E-Ni on Alum. for adhesion -per specifications

My particular concern requires some knowledge of specification plating, ENi specs, as well as which series of alum. are heat treatable and non heat treatable. To try to be as concise as possible, I have witnessed SEVERAL customers (some in the aviation industry) calling out an incorrect post-bake class ( for adhesion on alum) for the series of alum. that their parts are machined from. For example,a customers parts are 6061 alum. According to MIL-C-26074 [on DLA], heat-treatable alum.(which 6061 is) should be class 4 (250 F) however the customers purchase order will call for class 3 ( 375 F), which according to Mil-C-26074 is for non-heat treatable aluminum. It is my concern that this could anneal their material. I am not however, AS concerned about a non-heat treatable series of alum being baked at a lower temp. It has remained my companies policy to continue post baking the parts at whatever the customer has requested on their purchase order and not contacting them. Should I continue be concerned about these heat treatable alum parts being annealed if they are baked at too high a temp?

Katrina Pelletier
Plating shop, QA - KC, Kansas, USA
June 2, 2008

June 5, 2008


If you have been in the business long enough, you know (or will find out) that some of your customers are quite knowledgable about what they are asking for, and other are not. If you are distinguishing your company from the competition, you should consider advising (educating) your customer when they are asking for something that does not seem right. Ultimately, the PO is the bible, but the added customer service goes a long way in maintaining a good business relationship with your customers.

Willie Alexander
- Colorado Springs, Colorado

Thanks Willie, however, I am still looking for more specific information on the subject, from a metallurgical standpoint.If heat-treatable alum. like 6061 is baked at a higher temp. class, intended for non-heat treatable alum., will the structure of the alum be adversely effected? (Example, per Mil-C-26074 heat treatable alum should be class 4 and baked at 250 f for 1 hr (approx.) and non-heat treatable alum should be class 3 and baked at 375 F for 1 hr.)

Katrina Pelletier
Plating Shop, QA - KC, Kansas, USA
June 9, 2008


I apologize for not being able to give you more information. Our MF department does not perform EN, and our HT department does not treat aluminum, yet!. However, in talking with the HT manager, aluminum will begin to change the temper at around 375 F. Time and temperature are the factors for tempering/annealing. But once tempered, we do not know if additional exposure will change the temper. Sorry.

Willie Alexander
- Colorado Springs, Colorado
June 13, 2008

You've hit on what separates the "good" shops from the "great" shops. The easy thing to do is just doing what the PO states as any PO or drawing would take precedence over the specification. My guess would be that this part was initially designed using a non-heat treatable alloy such as 5052 and at some point the alloy was changed without taking into account the impact on the electroless nickel callout. The "great" shops, as Willie pointed out, would contact the customer informing them of the apparent discrepancy and very likely getting permission to use the lower, albeit proper, baking temperature. There is no doubt that this type of scrutiny in contract review costs more, however, it's value that aerospace primes demand and Nadcap auditors insist on. Good catch!

milt stevenson jr.
Milt Stevenson, Jr.
Syracuse, New York
June 21, 2008

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