Correct copper content of zinc for ideal copper nickel chroming?

+++++++

We operate a zinc foundry and a copper nickel chrome plating plant in South Africa where grades of zinc alloys are fairly limited. As we experience fluctuating quality within our factory we are trying to correct this by a process of elimination. One area of concern is whether or not our base material is of a standard conducive to quality diecasting and finishing. Our focus is at present on the copper content of the alloy where we can have fairly large differences between batches. What should the copper content be for best quality diecasting/finishing.

Don Scott
Operations manager - Durban, South Africa