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Is 'white' and 'black' rust considered 'ferrous corrosion'?

Q. We have some 1050 steel parts that are clear zinc plated and then sent through a 50-hr salt spray test. The test samples exhibit the "white" and "black" corrosion but no red rust. I've read on this website before that the white corrosion is a result of the zinc and not the underlying material, so I'm guessing that it cannot be classified as ferrous corrosion. But what about the black rust? Is this a result of the underlying material, and could it be classified as ferrous corrosion? How does this black rust affect the material compared to any red rust?

Thanks for the insight.

Tyler

Tyler Butel
Engineer - Edmond, Oklahoma, USA
February 16, 2012

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