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Pyrophosphate copper for zinc problems

Q. We are plating aluminum parts (nickel, acid copper, nickel, chrome) . We use only non-cyanide baths. We plate zinc parts and for that reason we made up a pyrophosphate copper bath. (pH=8,5 ; Temp=55 grad C ; I=1 A/dm2 ; P2O7:Cu=7:1). At the beginning everything was great. We were doing pyrophosphate copper strike then acid copper. After 3 months, when we plated in the pyrophosphate copper bath, the copper layer falls off the zinc (layer has micro holes). In the acid copper bath under the layer rise blisters. Maybe in the bath is too much orthophosphates? How to remove it? Could you help me solve this problem. Any suggestions would be greatly appreciated.

Waldemar Tomankiewicz
Metal finishing - Cracow, Malopolska, Poland
2003

A. Hi Waldermar,

To lower the ortophosphite content is only one way to do it that's is to discarded to reduce its concentration in the solution. If you have a high contamination of zinc that will shows by producing brassy looking deposit and should be dummied out at medium current density.

Regards,

Anders Sundman
4th Generation Surface Engineering
Consultant - Arvika,
Sweden
2003