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Letter 31036
Corroding AL A380 with resin impreg and
Iridite
++++
We have manufactured several thousand Al A380 Die casted parts in
Asia that are starting to show signs of corrosion.
The parts were cast, machined, then resin impregnated with
Ultraseal PC504/66, then clear Iridited to
Mil-C-5541 [link is to spec at TechStreet]-class-3.
The customer has tested some units in a salt spray chamber as per
Mil-810F [link is to spec at TechStreet] Method 509.4
Procedure I. They failed miserably.
We have built similar parts in this grade with these post
treatments, with great success. But that customer did not test them
the same way.
I'm looking for comments and opinions on if these 2 post
treatments should stand up to the test/environment.
Please note that I may use your responses in dealing with this
customer. If you are not comfortable with that, please do not
respond.
John Jamael
Contract Manufacturer - Ottawa, Ontario, Canada
++++
Clear chromate on aluminum castings usually do not do well in salt
spray. MIL C5541 specifies ASTM
B-117 [link is to spec at TechStreet] 5% salt spray.
With vacuum sealing and everything proper using Iridite 14-2 clear
(class three) can pass. However, yellow chromate stands a much better
chance of passing salt spray and other corrosion test methods. The
difficulty in passing corrosion tests lies in the fact that the
alloying constituents in the aluminum form corrosion cells. Silicon
is one of the bad ones. Fluoride-Nitric acid treatment prior to
chromating helps some in minimizing the silicon left on the surface
to cause trouble. Porosity and a rough surface works against good
corrosion protection.
Dear Reader, please --
- Answer or follow-up on this subject (in non-commercial
fashion).
-
- Post a new
question or inquiry on a different subject.
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