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MIL-A-8625 Type II adhesion test




We currently produce many parts that require finishing to MIL-A-8625 / MIL-PRF-8625 [affil link or DLA] type II. Some are dyed some are not. We are being rejected for failing the adhesion test. Our customer is performing the adhesion test after heating the part to 250 deg. My question is if this is the proper way to test.

Robert Aleksiewicz
customer / plating houses - Seymour, Connecticut, USA
August 27, 2008



simultaneous replies

I cannot tell you if it is proper or not but: The thermal expansion of the oxide is 1/5 that of the underlying aluminum, cracking will start to occur at 80 °C and up. My source is Sheasby and Pinner's latest books, they do not mention adhesion, but surely with that difference in thermal expansion of 5 times, then something has got to give.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
probertbanner
August 29, 2008



Did your customer tell you that you needed to meet this requirement? If not and you are certifying to MIL-A-8625 Type II then I cannot see how they can reject them. If you agreed to this in the original contract then you have no option other than to comply.

Added to this I wouldn't ever consider a thermal test for adhesion due to the differences in thermal expansion rates of aluminum and aluminum oxide, the oxide having a much lower coefficient of linear expansion than the aluminum.

Brian Terry
Aerospace - Yeovil, Somerset, UK
September 1, 2008

 



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