Zamak used for model train castings is an alloy with a base metal of Zinc with additional elements of Aluminum, Magnesium and Copper. If the Zamak alloy contains impurities (can we say low cost) then Zinc Pest will be a problem. This problem was eliminated back in the 1940's by the NJ Zinc Company by casting with 99.99% pure zinc. Most PW engines were cast of that alloy. Today 70% of the No. American Zamak castings are 96% zinc and 4% aluminum. This alloy is called Zamak 3 and it doesn't easily deteriorate. There are 7 different grades of Zamak and the one used in Asia is typically Zamak 4 and they produce it cheaply. I'll make the argument that cast parts should be made of brass but they doesn't agree with the low cost manufacturing attractiveness of Chinese manufacturing that produces mainly disposable products.
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