Metal finishing Q&As since 1989

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Galvanic potential of RoHS compliant chromate chemical conversion coating

2005

I am a mechanical design engineer working at a telecom company that makes RF filters out of aluminium 6061-T6. The body/cavity design of the filter products need to be corrosion protected and we used to use chromate chemical conversion coating per MIL-C-5541E Class 1A or Class 3. We are now switching over to use an RoHS compliant chromate chemical conversion coating (finish spec number is not yet finalized as testing is ongoing).

We have customers that demand in their product design specifications minimum galvanic potential differences for dissimilar metals in contact. Our aluminium chromate coated RF filter bodies come in contact with silver plated lids.

I know the galvanic potential of sliver. The questions I have are:

1) Does chromate chemical conversion coating (RoHS compliant or otherwise) change the galvanic potential of the base material when in contact with dissimilar metals?

2) What is the galvanic potential of chromate chemical conversion coated aluminum when using MIL-C-5541E Class 1a? Also MIL-C-5541E Class 3?

3) Does anyone yet know the galvanic potential for an RoHS compliant chromate chemical conversion coating?

Many thanks in advance for your help.
Christopher Paci

Christopher Paci
Telecom RF Filter Design - Montreal, Quebec, Canada

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Hello Mr Paci,

Its my guess that a chromated aluminium will be far less active than bare Al. However if you wish to contact other metals, you might want to look at anodising the Al instead of Chromating.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2005