Conversion coating
A Conversion coating is a chemical or electro-chemical treatment applied to manufactured parts that superficially converts the material into a thin adhering coating of an insoluble compound. These coatings are commonly applied to protect the part against corrosion, to improve the adherence of other coatings, for lubrication or for decoration. [1][2][3][4]
Types
The most common conversion coating processes for metal parts with industrial use include
- Chromate (aluminum, steel)
- Phosphate (steel)
- Bluing (steel)
- Blackening (steel)
- Anodizing (aluminum)
- Stannate (magnesium)[5]
- Molybdate (zinc, zinc-nickel)[6][7]
- Zirconate (steel, aluminum, magnesium, galvanized steel).[1][8][9]
- Titanate (steel, aluminum, magnesium).[1]
- Plasma electrolysis (aluminum, magnesium, titanium)[10][11]
Non-metallic substrates
Conversion coatings have been studied for non-metallic substrates, such as for protection of fluorozirconate glasses used in optoelectronics.[12]
Regulations
US military specifications for conversion coatings include MIL-DTL-81706 and MIL-DTL-5574.
References
- I. Milošev and G. S. Frankel (2018): "Review—Conversion Coatings Based on Zirconium and/or Titanium". Journal of the Electrochemical Society, volume 165, issue 3,pages C127-C144. doi:10.1149/2.0371803jes
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- "Fastener Surface Conversion", In: FastenerData.co.uk
- M. A. Gonzalez-Nunez, C. A. Nunez-Lopez, P. Skeldon, G. E. Thompson, H. Karimzadeh, P. Lyon, and T.E.Wilks (1995): "A non-chromate conversion coating for magnesium alloys and magnesium-based metal matrix composites". Corrosion Science, volume 37, issue 11, pages 1763-1772. doi:10.1016/0010-938X(95)00078-X
- A. A. O. Magalhães, I. C. P. Margarita, O. R. Mattos (2004): "Molybdate conversion coatings on zinc surfaces". Journal of Electroanalytical Chemistry, volume 572, issue 2, pages 433-440. doi:10.1016/j.jelechem.2004.07.016
- J. A. Wharton, G. D. Wilcox, and K. R Baldwin (1996): "Non-Chromate Conversion Coating Treatments For Electrodeposited Zinc-Nickel Alloys". Transactions of the IMF - The International Journal of Surface Engineering and Coatings, volume 74, issue 6, pages 210-213. doi:10.1080/00202967.1996.11871128
- Charles E. Tomlinson (1998): "Chromate-free conversion coatings for metals". US Patent 5759244, filed on 1996-10-09, granted on 1998-06-02, expired on 2016-10-09.
- Raoling Wang (2018): "Chromium-free aluminum conversion coating agent, aluminum material, and surface conversion coating treatment method". Patent WO2018006270, filed on 2016-07-05, granted on 2018-01-11.
- Lishi Wang, Tao Feng, Shanwen Yu, Yihang Cheng, Zhixiang Bu and Xinbin Hu (2020): "Fluoride effect on plasma electrolytic oxidation coating formed on Mg-Al alloy in alkaline electrolytes". Materials Research Express, volume 7, issue 1, article 016412. doi:10.1088/2053-1591/ab60a7
- Liu Feng, Shan Dayong, Song Yingwei, Liu Xianbin, and Han Enhou (2012): "Highly corrosion-resistant ceramic coating solution prepared through magnesium alloy surface micro-arc oxidation and application thereof". Chinese patent 101994145, filed on 2009-08-19, granted on 2012-05-23.
- A. P. Rizzato, C. V. Santilli, S. H. Pulcinelli, Y. Messaddeq, and P. Hammer (2004): "XPS Study of the Corrosion Protection of Fluorozirconate Glasses Dip-Coated with SnO2 Transparent Thin Films". Journal of Sol-Gel Science and Technology, volume 32, pages 155–160. doi:10.1007/s10971-004-5781-9
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