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Copper plated aluminum sand casting gets brown dots

Q. we are doing Zincating, bright nickel, acid copper on aluminium sand cast decorative items. We face brown dots after 2 or 3 days after spray lacquering. Our process sequence after copper plating: rinse, sulfur 15% concentration, 2 rinses, tamarind water for removing sulfur, then again rinse, anti-tarnish, then lacquering, our components are having some small pin holes due to sand casted.

61145-1b 61145-1a

I attach photocopy. Please help

vasanth karunakaran
- Chennai India
August 17, 2020

Please check your zincating process and let us explore more.

Prof. Karthikeyan Sambantham
- Vellore TAMILNADU India
August 22, 2020

Nadcap Chemical Processing Auditor - PRI, traveling
Process Engineer / Chemist - Denver Metal Finishing, Colorado

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