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Problems in Passivated Zinc deposit

A job shop plater using acid zinc chemistry for barrel plating of small mild steel components on a very large scale. Zinc deposit is yellow passivated using conventional hexavalent yellow iridiscent passivation. The problem encountered is of discolouration of passivated film on storage in LCD area of the component. Yellow colour turns dark bluish purple.

My questions are ;

1. what can cuse this?

2. Can this discolouration be responsible for white rust formation during storage and transit, even though NSS life of freshly plated components is OK. 2. Is yellow trivalent Cr. passivation possible.

With Regards ,

Kishore Lokhande
Field Engineer - Mumbai, Maharashtra State, India
2003

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Very low plating thickness in the LCD can cause this. The part will be compromised if the plating thickness is low; that is obvious. It sounds that you have to balance the acid zinc plating brightener system to allow for better throw in the LCD area.

Khozem Vahaanwala
Saify Ind

Bengaluru, Karnataka, India

2003

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