Discoloration of EN plated Aluminum 6061-T6

We had some parts returned to us from our customer. They are circular Aluminum connectors that are Electroless nickel plated per MIL-C-26074 [⇦ this spec on DLA] Class 3, Grade B. When returned, they are almost totally discolored. They have a "smoky" & blueish color all over them, almost like they were in a fire. These were plated around 8/9/05, assembled by us on 8/25 and shipped to our customer. They left our plant clean and our customer just noticed them changing color last week. These parts have an o-ring groove in them with an o-ring installed. The area underneath the ring is clean...

My questions are:
-Does this sound like a plating issue? Would Aluminum tarnish?
-Any ideas on what, if any, chemical reaction might cause this?
-Any other possible causes?

Thanks

It is caused by tarnish of the EN. You need a post tratment.Unfurtuanetlly the good post dips are hexa-chromates. There are post treatments used by dipping but I prefer those used as an electrical treatment. Ask your supplier. In case you cannot find a product, you can use the rinse of a chromium containing solution.

First of two simultaneous responses --

That sounds like the Pepsi syndrome. Some one spilled a softdrink on the parts. Change the spec to call for a high phos. EN or tell your customer to be more careful with his drink.

Second of two simultaneous responses --

Hi,

I think you have a bad rinses after EN and that can shows like disscoularation on your part after rinses.

Regards,