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Porosity in HP Zinc Castings

We are required to produce mirror finish (chrome plated) zinc high pressure castings for bathroom fittings and are having our share of porosity problems after plating. The porosity is not visible to the naked eye at casting or after polishing. At 50x magnification it is very apparent at casting. Our question is at what magnification level could we reasonably expect the plating to "level" any porosity. We are trying to set a standard that would eliminate defects at the casting stage.

Graham Wilson
Die Casting & Electroplating - Durban, South Africa
February 7, 2008

Most plating baths will not cover porosity at all, indeed, they will magnify it. Physics tells us that electricity refuses to flow inside pores, so metal does not cover them. Plating liquids, on the other hand, do penetrate causing corrosion inside them. Only exception appears to be acid copper but it cannot be plated directly on top of zinc. You need an underplate which in turn, may accentuate the original problem rendering deeper pores which in turn will difficult the acid copper to fully bridge them. Bottom line, work on the casting process ionstead and avoid pores.

Guillermo Marrufo
Monterrey, NL, Mexico
February 12, 2008