When selecting corrosive liquids, attention should be paid to selective corrosion
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Industrial alloys contain different components and impurities, have varying structures, and exhibit different corrosion resistances. In a certain solution, some active components dissolve, leaving behind loose, inactive components that lose all of their strength and ductility. A common example of this type of selective corrosion is the dezincification of brass. Zinc dissolves in the solution, forming a loose red film on the surface of the brass. In fact, copper also dissolves, but then deposits on the surface of the alloy. In addition to uniform layered zinc removal, there is also localized plug-like zinc removal. Increasing the copper content (red brass: Cu85%) can prevent zinc loss, and adding 1% tin, or small amounts of arsenic, antimony, and phosphorus can also improve resistance to zinc loss. The graphitization of gray cast iron is also a form of selective corrosion: the iron corrodes and leaches away, leaving behind a graphite network structure that loses much of its strength. Ductile or malleable cast iron does not undergo graphitization because it lacks a network structure held together by residues.
When selecting materials for corrosive liquids, the composition of the alloy and its corrosion resistance must be taken into account. To avoid selective corrosion, such as the dezincification of brass, corrosion resistance can be improved by increasing the copper content or by adding small amounts of elements such as tin, arsenic, antimony, and phosphorus. To address the graphitization issue in gray cast iron, ductile iron or malleable iron can be used to improve the overall strength and corrosion resistance of the material. .