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Trouble in black chromium plating

2003

I work in an automatic plating line as production manager and I have a frequent problem with the coating of black chromium (hexavalent). Sometimes, without alteration of the conditions of the process they appear small located bubbles in the piece, characterized by the rising of the interior coating of nickel after the chromium deposition. With the same baths conditions, cleaning and preparation of surfaces I don't attribute this defect the low adhesion of the nickel. The pattern of bubbles appears located in the zones of larger current density or in interior zones of the surface, but always with only on of this pattern in each production series. Will it be provoked by the distribution of currents in the piece or in the electrolyte?

Thank you,

Ricardo Silva
- Braga, Minho, Portugal

You have two choices, the nickel is blistering on the substrate metal or the chrome is blistering on the nickel. For the nickel blister, it is normally because the substrate was not properly cleaned and activated. On a few metals, it can be caused by too much cleaning and activation. (several reasons, but you left out a lot of useful information) The chrome would normally blister because you let the nickel passivate and then did not aggressively etch it in an etch tank prior to your chrome tank.

James Watts
- Navarre, Florida
2003