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Spots appear on zinc plating after 48 hours under normal environment

Base metal is 4130, with zinc plating. Being put in stock in plastic bags for 2 or 3 days, corrosion spot appears on the surface. Other parts were plated at the same line does not have this problem. Even several replatings can't solve this problem. Cyanide plating bath, 8-10 µm thickness, Pavco trivalent chromate. The parts were replated at another plater, alkaline plating bath, 10um, Yuken trivalent chromate, but with same issue. What is the root cause?

Sharon Luo
Supplier chain - Shenzhen, GuangDong, China
April 21, 2010

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First of two simultaneous responses --

Pitted parts, cold shuts and bad alloy comes to mind.

James Watts
- Navarre, Florida
April 23, 2010

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Second of two simultaneous responses -- April 26, 2010

Hi,
Is it a cast iron, may be its too porous, I would suggest to have an acid zinc plating, then heat it and then passivation followed by a silicate sealant.

Hope this would help to achieve better corrosion protection.
Best Regards

Praveen Kumar
plating process supplier
Mumbai, India

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Sounds like you are plating castings to me. Correct?

Trent Kaufman
electroplater - Galva, Illinois
April 26, 2010

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Sharon

What happens if you do NOT bag the part? Are the parts dry when you bag them? Have you tried a different supplier of bags, or material? Do you bag other parts without issue?

Willie Alexander
- Colorado Springs, Colorado
April 28, 2010