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Electrical Resistance of Chromate Coatings

2004

We have been making bus work out of Aluminum (6061-T6 for straight pieces and 5052-H32 for bent pieces) for many years. As a general practise, we have called out "clear Iridite" as the finish on the parts. We have come to understand that this has been getting us a Class 1A (max corrosion protection) MIL-C-5541 E Chemical Conversion Coating rather than a Class C (lower electrical resistance). We have thousands of operating hours on these joints with no over heating issues but are wondering if anyone has any experience or test information on the relative electrical resistance between the class 1A and the class C coatings.

For joint preparation we use Penetrox A and do not abraid the surfaces prior to assembly.

Tom Dyer
Electronics Mfgr - Orlando, FL, USA

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If the Iridite coating is clear it is low resistance. If it is yellow it is not low resistance.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])
2004