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Is electropolishing of hard chrome plating possible?

2007

Hi,

We have requirement of achieving 0.1 micron Ra finish on hardchrome plated 15-5PH steel pins. Plating thickness requriement after grinding is 30-127 micron. We have been trying to get a suitable grinding wheel to grind to this finish. The plating required to meet AMSQQC320.

Wondering whether electropolishing can be performed on the hard chrome plated area after grinding to 0.4-0.5 micron Ra finish to get 0.1 micron Ra finish.

If electropolishing can be can be done on electroplated area, any guidelines on current density, bath control etc.? What are the risk factors shall we consider while doing so?

I am aware that elecropolishing is a reverse process of electroplating, but if any other way it can be performed.

Thanks in advance.

Biren Desai
Metallurgist - Bangalore, India

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Yes you can electropolish chromium but you will need a specialised solution. I suggest you ask your chemical supply house if they offer one. It would be based on a sulfuric acid/ phosphoric acid mixture, but with other additives. I would not recommend you try to formulate one yourself as these solutions can be quite complex and require chemical balancing to optimise their efficiency.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2007