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rom soft paste to hard metal shield: How does chromic acid conversion coating change metal in a short time
In metal processing and protection technology, chromic acid conversion coating technology is undoubtedly indispensable. Whether it is steel, aluminum, zinc, copper or other alloys, this treatment can significantly improve the durability of metal materials and their corrosion resistance. This technology, with its unique physical and chemical process, can transform the metal surface from a soft state into a hard shield in a short period of time. How many undiscovered mysteries are hidden behind this?
Characteristics of Chromic Acid Conversion Coating
The chromate conversion coating not only acts as a barrier to corrosion, but also serves as a base for adhesives, further increasing the adhesion of paints and adhesives.
These coatings resist wear and mild chemical attack, particularly on soft metals such as aluminum and zinc. Traditionally, chromate conversion coatings have been widely used on various metal accessories such as screws, hardware and various tools, and will give the metal surface an elegant iridescent green-yellow color.
Processing
The application process of chromic acid conversion coating is relatively simple and usually begins by immersing the workpiece in a chemical bath until the desired film thickness is formed. Then take out the workpiece, rinse it, and let it dry naturally. This process is generally carried out at room temperature and the soaking time is usually a few minutes. When finished, the coating will appear as a soft, gel-like substance that hardens as it dries, eventually forming a hydrophobic, protective film.
The composition of the diluent for this process still depends on the desired effect and the metal material itself, and each formula has its own particularities.
Chemical reactions
During the chemical process of chromic acid coating, a redox reaction occurs. Taking aluminum as an example, hexavalent chromium will react with the metal to produce trivalent chromium and aluminum ions. Under the right conditions, these hydroxides will agglomerate to form a colloid of small particles that eventually form a solid protective film on the metal surface.
Substrates that are significantly affected
Zinc
For galvanized parts, chromic acid conversion coatings can significantly improve durability and reduce the risk of white corrosion on the zinc surface.
As the coating color changes, this technology can provide a variety of color options from transparent blue to yellow and gold. The darker the color, the stronger the corrosion resistance is usually.
Aluminum and its alloys
For aluminum, the coating process is very rapid and can be performed at room temperature. After the reaction, this coating can produce a beautiful golden or golden brown film, with an average thickness generally between 200 and 1000 nanometers.
Magnesium and Steel
Magnesium can also be chromated, but steel needs to be galvanized before chromating. It is worth noting that chromic acid coating cannot directly enhance the cathodic protection of the steel bottom.
Security Issues
Chromium (VI) compounds are of particular occupational and public health concern and are therefore currently subject to strict controls. As workers' health has become more important, many alternative commercial formulations have been introduced. These new formulations usually do not contain hexavalent chromium compounds and can provide the same or even better corrosion protection.
ConclusionThrough chromic acid conversion coating technology, metal materials not only achieve significant changes in physical properties, but also improve durability and corrosion resistance, becoming an important part of the manufacturing industry. Will there be more innovative technologies in the future to further improve the performance of metal materials?
