Chromium plating companies12/27/2023 A thin layer of copper is plated over the chromium deposit and microscopically examined to determine the extent of porosity and cracking. However, if the temperature is too high, the plating layer becomes soft and the original properties cannot be obtained.This extremely simple test has been poorly described in the literature due to its clandestine origin. For example, a higher plating bath temperature will reduce the number of cracks. It is known that the number and size of microcracks correlate with the plating bath temperature and current density during the chromium plating process. As countermeasures against corrosion itself, there are methods such as increasing the thickness of the chromium plating layer or plating another metal, such as nickel plating, under the chromium plating layer. Therefore, it is believed that this type of structure can inhibit overall corrosion. On the other hand, in the case of microcracks, where there are many tiny cracks, the current is distributed to each location, thus slowing down the corrosion process. Since the current flowing in a corrosion cell is proportional to its surface area, in the case of large cracks, the current is concentrated there and corrosion progresses rapidly. If we consider the chromium as the anode and the metal inside as the cathode, we can see that a corrosion cell is formed in which different metals are in indirect contact with each other due to moisture and dirt. On the other hand, this structure is thought to inhibit the progress of corrosion. These cracks extend from the surface to the interior, allowing moisture and dirt to penetrate through the surface to the interior material, causing corrosion. Rust and Microcracks in Chromium PlatingĬhromium plating is known to have cracks called microcracks. In addition, it is harmless to the human body, making it an easy-to-use plating method in terms of workability. Trivalent chromium plating is superior in terms of uniformity, and methods have been developed that provide corrosion resistance equivalent to that of conventional plating. In recent years, however, the toxicity of hexavalent chromium has become widely known, and plating processes using trivalent chromium as an alternative have come into use. Specific examples of hexavalent chromium toxicity include damage to skin and mucous membranes to which hexavalent chromium adheres, as well as liver and kidney failure.Īs for chromium plating treatment, the use of hexavalent chromium has been mainstream in the past. Hexavalent chromium is a substance whose use is prohibited by the RoHS and RoHS2 directives due to its reported environmental pollution and toxicity to the human body. Intermediate plating of copper and nickel is done before chromium plating.Ĭhromium is classified into trivalent chromium and hexavalent chromium, depending on the oxidation number. In decorative chromium plating, not only metal materials but also plastic parts are used as materials. The process of hard chromium plating is as follows: In most cases, steel parts are used as materials for hard chromium plating. There are two types of chromium plating: hard chromium plating and decorative chromium plating. When a direct current is applied to both poles, a reduction reaction occurs at the cathode, and chromium plating is deposited. The product to be plated is the cathode, and the lead alloy is the anode. The typical composition of a Sargent bath is 250 g/L chromic anhydride and 2.5 g/L sulfuric acid. The most basic method of chromium plating is to use a solution called a Sargent bath. Examples of where decorative chromium plating is used include the exterior parts of automobiles and motorcycles, faucet fittings, and decorative accessories. This plating is used for parts that require corrosion resistance and a beautiful luster design. Examples of applications where hard chromium plating is used include automobile engine parts, rollers for metal rolling, molds, and drill blades. Hard chromium plating is used for parts in industrial equipment that require abrasion resistance and low wear. The following is a description of the uses of chromium plating for each of the hard chromium plating and decorative chromium plating. The reason for this is that hexavalent chromium is harmful to the human body, and the RoHs directive, enforced by the European Union in 2006, restricted the use of hazardous substances in electrical and electronic equipment. Chromium plating generally has the following characteristics:Ĭhromium plating can be broadly divided into decorative chromium plating and hard chromium plating.Ĭonventionally, hexavalent chromium was used for chromium plating, but in recent years, trivalent chromium has been increasingly used.
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