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Zinc plating defects - quality of surface

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We had a housing made from cold rolled carbon steel sheet and zinc plated with yellow passivation.

After opening it recently from the package after three months we noticed some fungus like white powder on the surface of the sheet.The housing was packed in an air tight polyethelene sheet. I would like to know the technical reason for this problem.

Thanks,

Ravi G
sa graphics - Bangalore, Karnataka, India

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It is, most likely, white corrosion product due either to the poor chromating job or the entrapped moisture (source/origin of which will need further investigation). A chemical analysis/characterization of white powder found on the part will be helpful in determining the root cause.

Raj Singh
- Cleveland, OH, U.S.A.

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