Summary for white and black rust Discussion
white and black rust on clear zinc-plated 1050 steel is discussed as a distinction between zinc corrosion and possible steel corrosion. Tyler asks whether the white corrosion seen after a 50-hour salt spray test is from the zinc coating rather than the base metal, and whether the black rust should be considered ferrous corrosion and treated like red rust. The excerpt provided does not include any expert replies, so no definitive answer is shown here. Based on Tyler’s question alone, the key issue is whether the black discoloration indicates attack on the underlying steel or is simply a zinc-related corrosion product. The thread title suggests the discussion is about whether these appearances count as ferrous corrosion, but the actual conclusion is not present in the excerpt.
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