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What is Dacromet Coating?

dacromet coating processDacromet is the translation and abbreviation of DACROMET, abbreviated as Dacromet, Dacromet Rust, Dicron. The domestic name is zinc-chromium coating, a new type of anti-corrosion coating with zinc powder, aluminum powder, chromic acid and deionized water as the main ingredients. Dacromet is a process of degreasing--shot blasting-- coating-- curing-- cooling-- finished product. so that the surface of the workpiece to form a sheet of zinc powder, aluminum powder and metal chromium salt composed of silver gray anti-corrosion coating. Dacromet film, in the forming process of metal surface, the volatile material is almost all the water through the gasification,and no pollution, has been widely used in industrial developed countries, is gradually replacing the serious pollution of electroplating zinc, chromium, hot dip galvanizing, hot spray zinc, mechanical galvanizing, zinc-based alloy coating, oxidation, phosphating and other traditional surface treatment processes,fundamentally reduce the occurrence of environmental pollution, and has the advantages and characteristics incomparable to other surface treatments. The whole set of Dacromet process equipment adopts the whole process of closed circuit coating method, which revolutionizes the plating process and eliminates the pollution problems such as acid, alkali, zinc, chromium and the emission of sewage and exhaust gas produced during the plating process.

Main Components of Dacromet Coating

There are many different types of Dacromet coating solutions, but the basic composition of the coating solution can be summarized as follows:
 Metallic substances: composed of zinc, aluminum and other substances, mainly ultra-fine scale-like zinc and ultra-fine scale-like aluminum.
 Solvent: Inert organic solvents, such as ethylene glycol, etc.
 Inorganic acid component: such as chromic acid, etc.
 Special organic material: the viscosity increasing and dispersing component of the coating liquid, the main component is cellulose type white powder.

Anti-Corrosion Mechanism of Dacromet Coating

The protective effect of the Dacromet film layer on the steel substrate can be summarized as follows:
number 1
Barrier effect
due to the lamellar zinc, aluminum lamellar overlap, hinder the process of water, oxygen and other corrosive media to reach the substrate, can play a kind of isolation shielding effect.
number 2
In the process of Dacromet treatment, chromic acid reacts chemically with zinc, aluminum powder and the base metal to produce a dense passivation film, which has good corrosion resistance.
number 3
Cathodic protection role
The most important protection role of zinc aluminum chromium coating is the same as galvanized layer, which is cathodic protection of the substrate.

Advantages and Disadvantages of Dacromet Coating


Dacromet is a new type of surface treatment technology, compared with the traditional plating process, Dacromet is a kind of "green plating". Its advantages are as follows.
 Super corrosion resistance: The thickness of Dacromet film layer is only 4-8μm, but its antirust effect is more than 7-10 times of traditional electrogalvanizing, hot-dip galvanizing or coating method. No red rust appeared in the standard parts and pipe joints treated by Dacromet process after salt spray resistance test for 1200h.
 No hydrogen embrittlement: The treatment process of Dacromet decides that there is no hydrogen embrittlement in Dacromet, so Dacromet is very suitable for the coating of stressed parts.
 High heat resistance: Dacromet can resist high temperature corrosion, heat-resistant temperature up to 300 ℃ or more. The traditional galvanizing process, when the temperature reaches 100 ℃, the surface of workpiece has peeling and scrapped.
 Good bonding and recoating performance: Dacromet coating has good binding force with metal matrix, and has strong adhesion with other additional coatings. The processed parts are easy to spray and color, and the binding force with organic coating even exceeds that of phosphating film.
 Good permeability: Due to the electrostatic shielding effect, it is difficult to electroplate the deep holes and slits of the workpiece and the inner wall of the pipe, so the above parts of the workpiece cannot be protected by electroplating. Dacromet can enter these parts of the workpiece to form Dacromet coating.

 No pollution and public hazards: In the whole process of Dacromet production and coating process on the workpiece, Dacromet does not produce waste water and waste gas that pollute the environment, Dacromet does not produce waste water and waste gas that pollute the environment.


Although Dacromet has many advantages, it also has some shortcomings, which are mainly reflected as follows:

 Some Dacromet contains chromium ions which are harmful to the environment and human body, especially hexavalent chromium ions which are carcinogenic. (Under the environmental protection policy, Dacromet no longer contains hexavalent chromium ions)

 The sintering temperature and time of Dacromet are higher and longer, and the energy consumption is high.
 The surface hardness of Dacromet is not high, wear resistance is not good, and the products with Dacromet coating are not suitable for contact and connection with copper, magnesium, nickel and stainless steel parts, because they will produce contact corrosion, affecting the product surface quality and corrosion resistance.
 The surface color of Dacromet coating is single, only silver white and silver gray, which is not suitable for the development of individualization of the car. However, different colors can be obtained by post-treatment or composite coating to improve the decorative and matching properties of load-carrying auto parts.
 The electrical conductivity of Dacromet coating is not too good, so it is not suitable for electrically connected parts, such as electrical grounding bolts.

Process Flow of Dacromet Coating

Organic solvent grease removal——Mechanical polishing——Spraying——Baking——Second spraying——Baking——Drying
Process Flow of Dacromet Coating


 Dacromet will deteriorate rapidly when exposed to light, so the coating process of Dacromet should be carried out indoors.
 No matter Dacromet baking temperature too low or too high, will make Dacromet lose its anti-corrosion ability, Dacromet should be baked in the appropriate temperature range.
 Dacromet has a very short use cycle, so it should be used up as soon as possible.
 The wear resistance of Dacromet is poor, so it should be top coated with Dacromet, and then coated with other coatings with wear resistance.

Technology Applications of Dacromet Coating


dacromet coating processAnti-corrosion of small and medium-sized brackets, connectors, exposed parts and fasteners of various high-strength chassis on laden vehicles, such as various special-shaped steel brackets, bolts (including riding bolts, wheel bolts, etc.), nuts, etc. Foreign countries have clearly recommended the use of Dacromet coating to achieve anti-corrosion protection for fasteners on the car ≥ 10.9 grade, because Dacromet coating not only has high corrosion resistance, but also can ensure no hydrogen embrittlement. High strength steel has the risk of hydrogen embrittlement in the process of pickling and electroplating, etc. Although the hydrogen can be removed by heat treatment, it is difficult to remove completely. Dacromet coating process does not require pickling and activation, and there is no electrochemical reaction leading to hydrogen precipitation, which avoids the phenomenon of hydrogen embrittlement.

Brake disc coatingAnti-corrosion of metal parts around the engine and other high heat environments, such as heat shields, exhaust pipes, radiators, engine cylinder heads and other parts.
The passivation film on the surface of the traditional galvanized layer will be destroyed at about 70°C, and the corrosion resistance decreases sharply, while the curing temperature of Dacromet coating is about 300°C. The chromate polymer in the coating does not contain crystalline water, and the coating is not easily destroyed at high temperature, showing excellent anti-corrosion performance. The appearance of the parts treated with Dacromet process is almost unchanged in long-term use at 250℃, and the corrosion resistance is very strong.
dacromet coating vs galvanizedAnti-corrosion of various elastic parts on load vehicles, such as ring hoops, semi-circular clamps, various springs, leaf springs, etc. These parts require high strength and hardness, electroplating treatment will produce hydrogen embrittlement, such as incomplete hydrogen removal, long time to bear dynamic load is prone to tearing or corrosion fatigue, will bring safety hazards to the car driving, especially for heavy vehicles, the operating environment is relatively harsh, so the surface treatment requirements of these pieces are correspondingly high, and Dacromet coating has high corrosion resistance, high weather resistance. It is very suitable for the surface treatment of this kind of auto parts.
Zinc Flake CoatingAnti-corrosion of various complex shaped tubes and cavities of parts on laden vehicles, such as exhaust pipes of engines, mufflers, etc. If such parts are treated by electroplating, due to the complexity of the shape of such parts and the limitations of the electroplating process, the formation of the coating is not uniform, and may even occur leakage plating, which will cause the corrosion resistance of the parts to drop sharply, directly affecting the performance and service life of automotive parts. The Dacromet process uses impregnation and other methods, there is no problem in the plating process of uniform coating ability and depth ability is not good, and Dacromet treatment solution has excellent penetration ability, in close contact with the gap can also form a good protective film, especially for the anti-corrosion of tube and cavity complex automotive parts , some assembly parts after assembled is also suitable for Dacromet treatment. In addition, Dacromet coating is not subject to the erosion of various oils, antifreeze, cleaning agents and other chemicals, chemical resistance, weather resistance are also very good, so Dacromet is very suitable for the anti-corrosion of the chassis of heavy vehicles and automotive exterior parts.
Initially only used for national defense industry and auto parts, and then developed to electric power, construction, marine engineering, household appliances, small hardware and standard parts, railroads, bridges, tunnels, highway guardrails, petrochemical, biological engineering, medical equipment powder metallurgy and many other industries.
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