Letter 34030

Blisters on 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 omi 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

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
- Mumbai

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 HYDROFLUORICACID 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

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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