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Blisters on Copper Nickel Chrome (Cu-Ni-Cr) plated zamak#3 die castings

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We are having some problem with plating blisters on plated zinc die casting (zamak#3). We plating it with 0.003" copper 0.003" nickel and 0.00001" chromium. but after max 1 day some blisters like bubbles appear on surface.

Our available zamak have about %0.05 Pb (it must be less than %0.003)and we think this is the cause of the bubbles.

How we can omit Pb from of our alloy, or is there any way in plating to decrease influence of the Pb? any ideas would be greatly appreciated

Amir Khosravi
pajeh - Pishavar, Aser, Pakistan

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Hi there, firstly check the activation dip( powdered hf acid) after ur soak cleaning , and also don't use any cathodic cleaning, secondly build good copper cyanide or alkaline base electrolytes , with a minimum current apprx 0.1 - 0.2 amp/dm sqr........hope this will help.

Regards

Praveen [last name deleted for privacy by Editor]
- Mumbai, India

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ZINC IS A REACTIVE METAL AND ALL PRE-PLATING TREATMENTS SHOULD BE AS SHORT AS POSSIBLE.

POOR DEPOSITION OCCURS EITHER OVER CLEANED OR INSUFFICIENTLY CLEANED.

PROPERLY WASHED AFTER CLEANING IN RUNNING WATER AND THEN DIPPED IN HYDROFLUORIC ACID OR SULPHURIC ACID ABOUT 5% MOMENTARILY UNTIL GAS EVOLUTION IS OBSERVED,OXIDE FILMS ARE TO BE REMOVED.

WASH AGAIN PROPERLY THEN COPPER PLATE.

CHROMIUM CONTAMINATION ALSO CAUSES BLISTERING,CHROMIUM ENTERS USUALLY BY BEING CARRIED ON PLATING RACKS.

Ajay Raina Punjab, India

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Dear Amir,

If you do metal pretreatment as suggested by Mr Praveen and still get blisters I doubt gas entrapment during casting. Bake parts in oven at 200 deg centigrade for 2-3 hours and check , if you see some gas escaping marks (white grey dots) on surface , then you have to work out in your casting or otherwise you have to do degassing prior to plating.

Best of luck

Qutub Saify
- Ajman, UAE

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December 30, 2009

Blisters can come from many sources, and it is sometimes very difficult to diagnose, unless you do a microscopic analysis to determine the root cause of the blisters.

Often, blisters are due to surface cold shuts on the casting surface. These are very shallow crack like defects that can seep in cleaning fluids during pretreatments. During the plating process these fluids evaporate, leaving blister like defects in the plating.

There are many other possibilities, but a thorough examination is required to accurately diagnose the defect first.

Ryan Winter
- maybrook, New York, USA