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Zinc chromate finish is rusting (red) very badly at seam

I have an old zinc chromate finished part that has been re-plated. The part is two pieces spot welded together. At the area that they over lap they are rusting (red) very badly. This has happened in about 4 weeks. The parts have been maintained in a class A storage area (65-80 degree F and below the dew point). What could cause them to rust so quickly? I have contacted the vendor, they stated that these were not plated on an automated line but done manually. Also they were cleaned and blown off with compressed air vs. baking.

John Strange
TVA - Chattanooga, TN, US
2006

Having the parts plated in alkaline zinc rather than acid zinc (if that was the case) may help due both to better covering power in the recesses and a less corrosive solution trapped by capillary action. But the parts must be very thoroughly rinsed and completely dried. I think it will be necessary to dry them in an oven rather than with compressed air.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
2006

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