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Dacromet is the transliteration and abbreviation of DACROMET; it is also known as Dacro, Dak Rust, or Dickron. In China, it is known as a zinc-chromium coating; it is a new type of anti-corrosion coating whose main components are zinc powder, aluminum powder, chromic acid, and deionized water. I. There are many types of Dacromet coating solutions, but their basic composition can be summarized as follows: 1. Metals: Composed of materials such as zinc and aluminum, primarily in the form of ultra-fine flake-shaped zinc and ultra-fine flake-shaped aluminum. 2. Solvent: An inert organic solvent, such as ethylene glycol, etc. 3. Inorganic acid components: such as chromic acid, etc. 4. Special organic substances: These serve as components that increase the viscosity and promote dispersion of the coating liquid; their main component is a cellulose-based white powder. II. Anticorrosion mechanism: The protective effect of the Dacromet coating on the steel substrate can be summarized as follows: 1. Barrier effect: Due to the layered overlap of zinc and aluminum flakes, it prevents corrosive agents such as water and oxygen from reaching the substrate, thereby providing an isolating shielding effect. 2. Passivation: During the Dacromet treatment process, chromic acid reacts chemically with zinc, aluminum powder, and the base metal to form a dense passivation film, which possesses excellent corrosion resistance. 3. Cathodic protection effect: The main protective function of the zinc-aluminum-chromium coating, just like that of a galvanized layer, is to provide cathodic protection for the substrate. III. Advantages and Disadvantages Advantages: Dacromet is a new type of surface treatment technology; compared to traditional electroplating processes, it represents a \"green electroplating\" option. Its advantages are as follows: 1. Excellent corrosion resistance: The thickness of the Dacromet coating is only 4–8 μm, yet its rust prevention efficiency is 7–10 times higher than that of traditional electro-galvanizing, hot-dip galvanizing, or coating methods. Standard parts and pipe fittings treated using the Dacromet process showed no red rust after undergoing a salt spray test for over 1200 hours. 2. No hydrogen embrittlement: The coating process of Dacromet ensures that it does not suffer from hydrogen embrittlement; therefore, Dacromet is highly suitable for coating components that are subject to stress. 3. High heat resistance: Dacromet can resist corrosion at high temperatures, with a heat resistance capacity of over 300°C. In contrast, with the traditional galvanizing process, the material starts to peel and become unusable at a temperature of 100°C. 4. Good adhesion and recoatability: The Dacromet coating exhibits good adhesion to the metal substrate, as well as strong bonding with other additional coatings. Parts treated with this coating are easy to spray-color, and its adhesion to organic coatings is even greater than that of a phosphating film. 5. Good permeability: Due to the electrostatic shielding effect, it is difficult to plate zinc on deep holes, narrow slots, and the inner walls of tubes in workpieces; therefore, these areas of the workpieces cannot be protected by electroplating. Dacromet can enter these areas of the workpiece to form a Dacromet coating. 6. No pollution or environmental hazards: During the entire process of Dacromet production, processing, and coating of workpieces, no wastewater or waste gases that can pollute the environment are generated; thus, there is no need for waste treatment, which reduces processing costs. Disadvantages: Although Dacromet has many advantages, it also has some shortcomings, mainly as follows: 1. Some Dacromet formulations contain chromium ions that are harmful to the environment and human health; in particular, hexavalent chromium ions are carcinogenic. (Under current environmental regulations, modern Dacromet coatings no longer contain hexavalent chromium ions.) 2. Dacromet requires a high sintering temperature and a long duration, resulting in high energy consumption. 3. Dacromet has a low surface hardness and poor wear resistance; moreover, products coated with Dacromet are not suitable for coming into contact with or being connected to components made of copper, magnesium, nickel, and stainless steel, as this can lead to contact corrosion, affecting the surface quality and corrosion resistance of the products. 4. The surface color of the Dacromet coating is uniform, limited to silver-white and silver-gray, which does not meet the needs for personalization in the automotive industry. However, different colors can be achieved through post-treatment or composite coatings to enhance the aesthetic appeal and compatibility of heavy truck components. 5. The electrical conductivity of the Dacromet coating is not very good; therefore, it is not suitable for use in components that require electrical conductivity, such as grounding bolts in electrical devices. IV. Precautions 1. Dacromet ages rapidly when exposed to light, so its coating process should be carried out indoors. 2. If the baking temperature for Dacromet is too low or too high, it will result in the loss of its anti-corrosion properties; Dacromet should be baked within an appropriate temperature range. 3. The service life of Dacromet is very short, so it should be used up as soon as possible. 4. Dacromet has poor wear resistance; therefore, it should be applied as a top coat, followed by the application of other coatings with better wear resistance. V. Technical Applications 1. Corrosion protection of various high-strength chassis components such as brackets, connectors, exposed parts, and fasteners in trucks, including various shaped steel brackets, bolts (including carriage bolts, wheel bolts, etc.), nuts, etc. 2. Corrosion protection of metal components in high-temperature environments around the engine, such as insulation panels, exhaust pipes, radiators, engine cylinder heads, and other similar parts. 3. Corrosion protection of various elastic components in trucks, such as bands, semi-circular clamps, various springs, leaf springs, etc. 4. Corrosion protection of various complexly shaped tubular and chambered components on trucks, such as engine exhaust pipes and mufflers.