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Because electrolytically zinc-plated surfaces provide comparatively little corrosion protection, and in the case of galvanic zinc coatings on high-strength steel (e.g. category 10.9 and 12.9 high-strength bolts) there is a risk of hydrogen embrittlement, the industry needed a better corrosion protection system.
The chromate coating acts as paint does, protecting the zinc from white corrosion, thus making the part considerably more durable, depending on the chromate layer's thickness. [8] [9] [10] The protective effect of chromate coatings on zinc is indicated by color, progressing from clear/blue to yellow, gold, olive drab and black.
Phosphate conversion coating is a chemical treatment applied to steel parts that creates a thin adhering layer of iron, zinc, or manganese phosphates to improve corrosion resistance or lubrication or as a foundation for subsequent coatings or painting. [1] [2] [3] It is one of the most common types of conversion coating.
Galvanization (also spelled galvanisation) [1] is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are coated by submerging them in a bath of hot, molten zinc. [citation needed]
There are aftermarket electronic "rustproofing" technologies claimed to prevent corrosion by "pushing" electrons into the car body, to limit the combination of oxygen and iron to form rust. The loss of electrons in paint is also claimed to be the cause of “paint oxidisation” and the electronic system is also supposed to protect the paint. [4]
The salt spray test (or salt fog test) is a standardized and popular corrosion test method, used to check corrosion resistance of materials and surface coatings.Usually, the materials to be tested are metallic (although stone, ceramics, and polymers may also be tested) and finished with a surface coating which is intended to provide a degree of corrosion protection to the underlying metal.
Immersion zinc plating is an electroless (non-electrolytic) coating process that deposits a thin layer of zinc on a less electronegative metal, by immersion in a solution containing a zinc or zincate ions, Zn(OH) 2− 4. A typical use is plating aluminum with zinc prior to electrolytic or electroless nickel plating.
Such zinc electroplating or zinc alloy electroplating maintains a dominant position among other electroplating process options, based upon electroplated tonnage per annum. According to the International Zinc Association, more than 5 million tons are used yearly for both hot-dip galvanization and electroplating. [ 1 ]