1, the basic principle of powder zinc infiltration
The basic principle of powder zinc infiltration is to utilize the diffusion and diffusion of metal atoms under heating. Under the condition that the temperature is lower than AC1 and the base metal has no phase transformation, the metal zinc is infiltrated into the surface of the fastener of steel material to form different ratios of Zn-Fe. Alloy protective layer (referred to as infiltration layer or coating). The main purpose of powder zincizing surface alloying is to improve and improve the corrosion resistance, surface oxidation and wear resistance of steel material fastener surfaces.
The powder zinc infiltration anti-corrosion coating technology is based on the traditional powder zinc infiltration process, and uses the special thermal properties (high surface performance and high activity) of the zinc-filling agent added with composite materials (CeO2, powder zinc-plated La2O3, LaF3, etc.). , low temperature of metal atom diffusion process) and chemical properties (high diffusion rate, solid state diffusion bonding of metal materials), and the development of a comprehensive upgrade technology that can achieve mechanized production and improve product performance; Composite (zinc, aluminum, cadmium, chromium, oxide, etc.) powder thermal diffusion coating anti-corrosion technology.
Powder zinc infiltration consists of five layers of FeZn7+Zn, FeZn7, Fe11Zn40 zinc-rich layer, solid solution of Zn in Fe and steel matrix. If the surface is coated with Dacromet coating, the salt spray resistance test time can be more than 1000 h.
2, powder zinc infiltration process characteristics
1 The coating thickness is uniform and can be accurately controlled. The thickness of the coating depends only on the process, regardless of the shape and location of the fastener. For shapes and complex fasteners such as internal threads, blind holes, inner walls or grooves, etc., the thickness of the layer can be changed between 20 and 110 μm by the control specification, and the thickness is almost the same.
2 The coating has high hardness and strong resistance to abrasion and scratching. The microhardness of the powder zinc-coated zinc-iron alloy is generally 220-420 HV0.2, which is the hardest of the current zinc coatings.
3 The bonding strength of the coating with the base metal is high. The galvanized coating is a diffusion of zinc-iron alloy, and the coating is difficult to peel off and can only be removed by chemical means. The tensile strength of the interface between the coating and the base material is 600 to 700 MPa; and the tensile strength of the surface layer is 300 to 350 MPa.
4 coating is strong in corrosion resistance. Especially suitable for a variety of environments such as the ocean atmosphere, harsh industrial atmosphere, corrosion resistance is better than hot dip galvanizing, electroplating zinc. It can resist high temperature oxidation corrosion of less than 1000 °C.
5 coating coating performance is good. The galvanized coating has good adhesion strength with various paint and polymer coating materials.
6 galvanized coating without the harm of wood hydrogen embrittlement. The processing temperature is low and does not affect the mechanical properties of the fastener components. The zinc infiltration temperature of the powder is 320-500 ° C, which does not affect the mechanical properties of high-strength fasteners. And the zinc infiltration technology is a green cleaning technology, and there is no “three wastes†in the production process, which saves raw materials.
Table 1 Comparison of common zinc metal coating properties
3. Application fields
Powder zinc infiltration fasteners can be widely used in railways, rail transit, bridges, power communications, municipal construction and other fields. In recent years, with the extensive application of large-scale railways, municipal engineering, and steel structural engineering, high requirements have been placed on the corrosion resistance of various fasteners and connectors used. These provide practical applications for powder zinc anti-corrosion technology.
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