Bridge cable steel wire alloy coating and preparation method thereof

Abstract

The invention discloses a bridge cable steel wire alloy coating and a preparation method thereof, and belongs to the technical field of anti-corrosion coatings. The alloy for preparing the bridge cable steel wire alloy coating is Sn-xZn alloy, X is the mass ratio of Zn in the alloy and ranges from 25 wt.% to 60 wt.%, x is the mass ratio of Zn in the alloy, x is the mass ratio of Zn in the alloy, and x is the mass ratio of Zn in the alloy. A plating assistant agent for preparing the bridge cable steel wire alloy plating layer is prepared from NH4Cl, ZnCl2, SnCl2 and H2O. The Sn-Zn alloy with a low melting point and good corrosion resistance is used as a hot-dip coating of the bridge cable steel wire, so that the hot-dip temperature is reduced, spheroidization of cementite in the bridge cable steel wire is avoided, reduction of the strength of the bridge cable steel wire after hot-dip coating is reduced, and meanwhile, on the premise that the tensile strength of the steel wire is guaranteed, the service life of the bridge cable steel wire is prolonged. And compared with the existing zinc-aluminum alloy coating, the corrosion resistance is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of anti-corrosion coatings, and particularly relates to an alloy coating for bridge cable steel wires and a preparation method thereof. Background Art

[0002] Suspension bridges have the advantages of large span, light weight and less material loss. Therefore, most of the long-span bridges that have been built and are being designed in the world are suspension bridges. The bridge cable system of a long-span bridge is a prerequisite for realizing the modernization and large span of the bridge. Existing bridge cables are mainly composed of high-strength hot-dip galvanized alloy steel wires and are important components for bearing the weight of the bridge and transmitting dynamic and static loads. Bridges usually span complex terrains such as rivers, lakes, seas, and canyons and are in a windy, rainy and humid atmospheric environment for a long time, and even often suffer from acid rain erosion. Therefore, bridge cable steel wires not only require high strength, good toughness and excellent torsion performance, but also must have good corrosion resistance. The corrosion resistance of bridge cable steel wires is crucial for the durability and safety of the structure and is the key to extending and ensuring the long-term safety of the bridge. Common anti-corrosion measures include electroplating, hot-dip plating (referred to as hot plating for short) and spraying. Among many protection measures, hot-dip galvanizing and its alloys are the most commonly used and economical corrosion protection methods for bridge cable steel wires. At present, the hot-dip coatings for bridge cable steel wires are divided into three categories: pure Zn, Zn-Al and Zn-Al-Mg coatings. The coatings that have been actually applied to bridge cable steel wires are only pure Zn coatings and Zn-Al coatings, while the Zn-Al-Mg coating is currently in the R & D and test stage.

[0003] The principle of the hot-dip galvanizing process is to immerse the metal substrate in the zinc bath. Through metallurgical reactions, diffusion, etc. between the substrate and the zinc bath, a composite coating composed of an Fe-Zn alloy layer and a pure Zn free solidification layer is obtained on the surface of the substrate. Usually, the hot-dip galvanizing temperature is around 450 - 460 °C. Adding Al element to the zinc bath can reduce the grain size, improve the uniformity of the coating, and significantly improve the corrosion resistance. Its hot-dip galvanizing temperature is around 450 °C. Moreover, since the affinity between Al and Fe is greater than that between Zn and Fe, Al and Fe preferentially form intermediate alloy layers of Fe2Al5 and FeAl3, which hinders the diffusion of iron ions into the zinc layer and inhibits the formation of the brittle Fe-Zn alloy layer. Due to the presence of Al element, a dense Al2O3 protective film will be formed on the surface of the coating, which has both passivation protection and electrochemical protection effects, and its corrosion resistance is 2 - 4 times higher than that of the pure Zn coating. However, with the continuous increase of environmental pollution and the scale of bridge construction, the above coatings are difficult to meet the requirements of the centennial life of bridge cables. To further improve the corrosion resistance and appearance quality of the coating, it is found that adding a small amount of Mg element to the Zn-Al alloy bath can improve the brightness of the coating surface, further refine the grains, and at the same time play a role in strengthening the grain boundaries and inhibiting intergranular corrosion. The Zn / MgZn2 binary eutectic structure and Zn / Al / MgZn2 ternary eutectic structure appearing in the coating greatly improve the corrosion resistance of the coating. Its hot-dip galvanizing temperature is above 500 °C. The Zn-Al-Mg ternary alloy coating is currently mainly used for the surface anti-corrosion of low-carbon steel plates. Due to the particularity of bridge cable steel wires, they are very sensitive to the hot-dip galvanizing temperature. The addition of Mg element will cause the fluidity of the molten pool to become poor and the hot-dip galvanizing temperature to rise, resulting in a significant reduction in the tensile strength of bridge cable steel wires, and at the same time, the surface coating quality is poor and easy to peel off.

[0004] For the hot-dip galvanized pure Zn, Zn-Al coatings on bridge cable steel wires, and the Zn-Al-Mg coatings under research, under the existing production conditions, the strength of the steel wires will drop significantly after hot-dip galvanizing, and the higher the strength, the more it drops after hot-dip galvanizing. The reason is that the hot-dip galvanizing temperature during hot-dip galvanizing with zinc or zinc-aluminum is relatively high, around 450 - 460 °C. At this temperature, the cementite in the structure of the heavily deformed steel wire gradually changes from lamellar to spherical, and with the increase of the hot-dip galvanizing temperature and the prolongation of time, the degree of cementite spheroidization becomes more and more serious, resulting in a serious reduction in its tensile strength.

[0005] Therefore, there is an urgent need for a coating with a low melting point and good corrosion resistance to solve the above problems. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a bridge cable steel wire alloy coating and its preparation method.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides an alloy coating for bridge cable wires. The alloy for preparing the alloy coating of the bridge cable wires is Sn-xZn alloy, where X is the mass proportion of Zn in the alloy, and the value is 25-60 wt.%.

[0009] The flux for preparing the alloy coating of the bridge cable wires is composed of NH4Cl, ZnCl2, SnCl2 and H2O.

[0010] Technical principle: The present invention uses Sn-Zn alloy with low melting point and good corrosion resistance as the hot-dip coating of bridge cable wires, reduces the hot-dip temperature, avoids the spheroidization of cementite in bridge cable wires, reduces the reduction of the strength of bridge cable wires after hot-dip coating, and at the same time, on the premise of ensuring the tensile strength of the wires, the corrosion resistance is further improved compared with the existing zinc-aluminum alloy coating.

[0011] Optionally, the X is 25 wt.%, 30 wt.%, 40 wt.%, 50 wt.% or 60 wt.%.

[0012] Further, the preparation method of the Sn-xZn alloy includes the following steps: melting pure tin ingots, then heating up and adding pure zinc ingots. After the pure zinc ingots are melted, they are refined to remove slag and cast into shape to obtain the Sn-xZn alloy.

[0013] Further, the melting temperature of the pure tin ingots is 300 °C; the heating up is to heat up to 450 °C.

[0014] Further, the mass ratio of NH4Cl, ZnCl2, SnCl2 and H2O is 15:10:5:70.

[0015] The present invention also provides a preparation method of the alloy coating for bridge cable wires described in the above technical solutions, including the following steps:

[0016] (1) Grinding, alkali washing and acid washing the bridge cable wires to obtain clean bridge cable wires;

[0017] (2) Putting the clean bridge cable wires obtained in step (1) into the flux for fluxing treatment to obtain fluxed bridge cable wires;

[0018] (3) Using Sn-xZn alloy as the plating solution, subjecting the fluxed bridge cable wires obtained in step (2) to hot-dip coating to obtain bridge cable wires with a hot-dip Sn-xZn alloy coating.

[0019] Further, in step (1), the caustic solution used for caustic washing is a NaOH solution with a mass concentration of 15%; the temperature of the caustic washing is 40°C, and the time of the caustic washing is 3 minutes.

[0020] Further, in step (1), the acid solution used for pickling is a HCl solution with a mass concentration of 15%; the temperature of the pickling is 40°C, and the time of the pickling is 3 minutes.

[0021] Further, in step (2), the temperature of the fluxing treatment is 60 - 80°C, and the time of the fluxing treatment is 3 minutes.

[0022] Further, in step (3), the temperature of the hot dip plating is 400 ± 5°C, and the time of the hot dip plating is 30 - 60 seconds.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] (1) The surface of the hot dip plated Sn-Zn alloy bridge cable wire of the present invention is bright, smooth, has good adhesion, and there is no case of missing plating, and the quality is excellent.

[0025] (2) For the Sn-Zn alloy coating of the present invention, the coating thickness is thinner than that of the Zn-Al alloy coating, only about 20μm, effectively reducing the consumption of tin and zinc.

[0026] (3) For the Sn-Zn alloy coating bridge cable wire of the present invention, its tensile strength not only does not decrease, but also has a certain increase, effectively avoiding the reduction of the tensile strength of the bridge cable wire during the hot dip plating process.

[0027] (4) On the premise of ensuring the tensile strength of the wire, the corrosion resistance of the coating of the present invention has been further improved compared with the currently mainstream zinc-aluminum alloy coating, fully meeting the comprehensive performance requirements of the bridge cable wire in a complex environment, and having great application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0029] Figure 1 is a physical diagram of the hot dip plated Sn-xZn alloy coating bridge cable wire in Examples 1 - 5;

[0030] Figure 2 is a SEM diagram of the Sn-60Zn alloy coating in Example 5. DETAILED DESCRIPTION OF THE INVENTION

[0031] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0033] The embodiment of the present invention provides an alloy coating for bridge cable steel wires. The alloy for preparing the alloy coating for bridge cable steel wires is Sn-xZn alloy, where X is the mass percentage of Zn in the alloy, and its value is 25-60 wt.%, further preferably 25 wt.%, 30 wt.%, 40 wt.%, 50 wt.%, or 60 wt.%. The present invention uses the Sn-Zn alloy with low melting point and good corrosion resistance as the hot-dip coating of bridge cable steel wires, effectively improving the tensile strength and corrosion resistance of bridge cable steel wires.

[0034] In a preferred embodiment, the preparation method of the Sn-xZn alloy includes the following steps: melting pure tin ingots, then heating up and adding pure zinc ingots. After the pure zinc ingots are melted, they are refined to remove slag and cast into shape to obtain the Sn-xZn alloy.

[0035] In a preferred embodiment, the melting temperature of the pure tin ingots is 300 °C.

[0036] In a preferred embodiment, the heating up is to 450 °C; the adding method of the pure zinc ingots is the pressing method; after the pure zinc ingots are melted, it also includes a heat preservation step; the heat preservation time is 60 min.

[0037] In a preferred embodiment, the slag remover for refining and removing slag is ZS-ZJ1 industrial slag remover; after refining and removing slag, it also includes a stirring step; the stirring time is 30 min.

[0038] In a preferred embodiment, the reagent for preparing the alloy coating of the bridge cable wire further includes a flux; the flux is composed of NH4Cl, ZnCl2, SnCl2 and H2O; the mass ratio of NH4Cl, ZnCl2, SnCl2 and H2O is 15∶10∶5∶70. The present invention uses NH4Cl, ZnCl2 and SnCl2 as the main components of the flux. The introduction of SnCl2 effectively reduces the decomposition temperature of the flux, making it more suitable for low-temperature hot dip plating. During the fluxing treatment, the flux cleans impurities such as oxides and iron salts on the surface of the wire. In addition, a thin salt film is formed on the surface to prevent the wire from secondary oxidation. During the hot dip plating process, the gas generated by the high-temperature decomposition of the flux plays a role of reactivation and cleaning. At the same time, the flux also improves the wettability between the plating solution and the wire, promotes the formation of the alloy layer, and effectively improves the coating quality.

[0039] The present invention also provides a method for preparing the alloy coating of the bridge cable wire according to the above technical solution, including the following steps:

[0040] (1) Grinding, alkali washing and acid washing the bridge cable wire to obtain a clean bridge cable wire;

[0041] (2) Placing the clean bridge cable wire obtained in step (1) into the flux for fluxing treatment to obtain a fluxed bridge cable wire;

[0042] (3) Using Sn-xZn alloy as the plating solution, performing hot dip plating on the fluxed bridge cable wire obtained in step (2) to obtain a bridge cable wire with a hot dip plated Sn-xZn alloy coating.

[0043] In a preferred embodiment, in step (1), the grinding is specifically: grinding successively with sandpapers of 400#, 1000# and 2000# meshes. The present invention roughly removes rust by grinding.

[0044] In a preferred embodiment, in step (1), the alkali solution used for alkali washing is a NaOH solution with a mass concentration of 15%; the temperature of alkali washing is 40°C, and the time of alkali washing is 3 min. The present invention removes the grease on the surface of the bridge cable wire by alkali washing.

[0045] In a preferred embodiment, in step (1), the acid solution used for acid washing is a HCl solution with a mass concentration of 15%; the temperature of acid washing is 40°C, and the time of acid washing is 3 min. The present invention further removes the rust on the surface of the bridge cable wire by acid washing.

[0046] In a preferred embodiment, in step (2), the temperature of the fluxing treatment is 60 - 80°C, and the time of the fluxing treatment is 3 min. The fluxing treatment of the present invention can improve the wettability of the surface of the bridge cable steel wire, enabling the coating metal to uniformly cover the surface of the workpiece and avoiding the phenomena of uneven coating or missing plating.

[0047] In a preferred embodiment, in step (2), after the fluxing treatment, there is also a drying step; the drying temperature is 100°C, and the drying time is 3 min.

[0048] In a preferred embodiment, in step (3), before hot dip coating, there is also a step of remelting the Sn - xZn alloy.

[0049] In a preferred embodiment, in step (3), the temperature of the hot dip coating is 400 ± 5°C, and the time of the hot dip coating is 30 - 60 s. By using the Sn - xZn alloy as the plating solution, the present invention reduces the temperature of the hot dip coating, avoids the transformation of cementite in the steel wire structure from lamellar to spherical at high temperatures, and thus avoids the reduction of the tensile strength of the bridge cable steel wire during the hot dip coating process.

[0050] In the embodiments of the present invention, room temperature refers to "25 ± 2°C".

[0051] Unless otherwise specified, the raw materials in the embodiments of the present invention are all obtained through commercial channels.

[0052] Example 1

[0053] A method for preparing an alloy coating on a bridge cable steel wire, the specific steps are as follows:

[0054] (1) Weigh pure tin ingots and pure zinc ingots according to the alloy composition of the coating. Heat the resistance furnace to 200°C, then put the crucible in, dry the crucible for 2 h, then add pure tin ingots to the crucible and heat to 300°C until completely melted, then heat to 450°C and add pure zinc ingots by the pressing method. After the pure zinc ingots are completely melted, keep warm for 60 min, then add ZS - ZJ1 industrial slag removing agent for refining and slag removing. After removing the surface scum, stir evenly for 30 min and pour into a mold to obtain the hot dip coating alloy Sn - 25Zn alloy.

[0055] (2) Take high - carbon bridge cable steel wire as a sample, and successively polish the surface rust with sandpapers of 400#, 1000#, and 2000# meshes to obtain the polished sample;

[0056] (3) Put the polished sample into a 15 wt.% NaOH solution for degreasing treatment by alkali washing. The alkali washing temperature is 40°C, the alkali washing time is 3 min, take it out and rinse with clean water.

[0057] (4) The pickled sample after alkali washing is put into a 15 wt.% HCl solution for pickling and rust removal treatment. The pickling temperature is 40 °C and the pickling time is 3 min. After taking it out, it is rinsed with clean water.

[0058] (5) The pickled sample is put into a flux for fluxing treatment. The fluxing temperature is 70 °C and the fluxing time is 3 min. The flux is composed of the following components by mass percentage: 15% NH4Cl, 10% ZnCl2, 5% SnCl2 and 70% H2O.

[0059] (6) The fluxed sample is put into an oven to dry and remove the moisture on the surface of the sample. The drying temperature is 100 °C and the drying time is 3 min.

[0060] (7) The Sn-25Zn alloy in step (1) is remelted as the plating solution, and the dried sample in step (6) is subjected to hot dip plating. The hot dip plating temperature is 400 ± 5 °C and the hot dip plating time is 30 s. After water cooling, the hot dip plated Sn-25Zn alloy coated bridge cable wire is obtained.

[0061] Example 2

[0062] A method for preparing an alloy coating on a bridge cable wire, different from Example 1 in that in step (7), the Sn-30Zn alloy is used as the plating solution, and the others are the same as in Example 1.

[0063] Example 3

[0064] A method for preparing an alloy coating on a bridge cable wire, different from Example 1 in that in step (7), the Sn-40Zn alloy is used as the plating solution, and the others are the same as in Example 1.

[0065] Example 4

[0066] A method for preparing an alloy coating on a bridge cable wire, different from Example 1 in that in step (7), the Sn-50Zn alloy is used as the plating solution, and the others are the same as in Example 1.

[0067] Example 5

[0068] A method for preparing an alloy coating on a bridge cable wire, different from Example 1 in that in step (7), the Sn-60Zn alloy is used as the plating solution, and the others are the same as in Example 1.

[0069] Comparative Example 1

[0070] The Zn-5Al coated wire is purchased from Guizhou Wire Rope Co., Ltd.

[0071] Figure 1 It is a physical diagram of the hot dip plated Sn-xZn alloy coated bridge cable wire in Examples 1-5. FromFigure 1 It can be seen that the surface of the hot-dip Sn-Zn alloy bridge cable steel wire of the present invention is bright, smooth, has good adhesion, and there is no case of missing plating, and the quality is excellent.

[0072] Figure 2 It is the SEM image of the Sn-60Zn alloy coating in Example 5. From Figure 2 It can be seen that the Sn-Zn alloy coating of the present invention has a thickness of only about 20 μm.

[0073] The steel wires of Examples 1-5 and Comparative Example 1 were subjected to a full immersion test in 5% (mass concentration) NaCl solution to test the corrosion resistance, and the results are shown in Table 1.

[0074] Table 1 Coating thickness and corrosion resistance of Examples 1-5 and Comparative Example 1

[0075] Coating type Coating thickness / μm <![CDATA[NaCl full immersion test corrosion rate / g·m -2 ·h -1 > Example 1 Sn-25Zn 18.54 0.0781 Example 2 Sn-30Zn 18.78 0.0812 Example 3 Sn-40Zn 19.87 0.0982 Example 4 Sn-50Zn 22.43 0.1066 Example 5 Sn-60Zn 24.83 0.1213 Comparative example 1 Zn-5Al 55.32 0.1839

[0076] It can be seen from Table 1 that the Sn-Zn alloy coating of the present invention has a thinner coating thickness compared to the Zn-Al alloy coating, only about 20 μm, effectively reducing the consumption of tin and zinc. And as the Zn content increases, the coating thickness gradually becomes thicker. At the same time, compared with the Zn-Al alloy coating, the corrosion resistance has been further improved.

[0077] Examples 6 and Comparative Examples 2-5

[0078] The difference from Example 1 is that in step (7), the hot-dip plating times are 0 s (Comparative Example 2), 60 s (Example 6), 120 s (Comparative Example 3), 300 s (Comparative Example 4), 600 s (Comparative Example 5), and the others are the same as Example 1.

[0079] According to GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", the tensile strengths of the steel wires of Example 1, Example 6 and Comparative Examples 2-5 were tested, and the results are shown in Table 2.

[0080] Table 2 Tensile strengths of the steel wires of Example 1, Example 6 and Comparative Examples 2-5

[0081] Hot dip coating time / s Tensile strength / MPa Comparative example 2 0 1875 Example 1 30 1922 Example 6 60 1969 Comparative example 3 120 1941 Comparative example 4 300 1923 Comparative example 5 600 1900

[0082] As can be seen from Table 2, the hot-dip coating time affects the tensile strength of bridge cable steel wires. Within 0-60s, as the hot-dip coating time increases, the tensile strength of the bridge cable steel wire increases briefly. Within 60-600s, as the hot-dip coating time continues to increase, the tensile strength of the bridge cable steel wire slowly decreases. This is because long-term heat preservation will cause the lamellar cementite to spheroidize, resulting in a decrease in tensile strength. However, in general, when the hot-dip coating temperature is 400±5℃ and the hot-dip coating time is within 30-600s, it will not cause a significant decrease in the tensile strength of the bridge cable steel wire.

[0083] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A bridge cable steel wire alloy coating, characterized in that, The alloy used to prepare the alloy coating of the bridge cable steel wire is a Sn-xZn alloy, wherein X is the mass percentage of Zn in the alloy, which is 25 to 60 wt.%; The plating aid for preparing the bridge cable steel wire alloy coating consists of NH4Cl, ZnCl2, SnCl2 and H2O.

2. The alloy coating for bridge cable steel wire according to claim 1, characterized in that, The X is 25 wt.%, 30 wt.%, 40 wt.%, 50 wt.% or 60 wt.%.

3. The alloy coating for bridge cable steel wire according to claim 1, wherein, The preparation method of the Sn-xZn alloy comprises the following steps: melting a pure tin ingot, then heating it and adding a pure zinc ingot; and after the pure zinc ingot is melted, refining, deslagging and casting to obtain the Sn-xZn alloy.

4. The alloy coating for bridge cable wires according to claim 3, characterized in that, The melting temperature of the pure tin ingot is 300° C.; the heating is increased to 450° C.

5. The alloy coating of the bridge cable wire according to claim 1, wherein The mass ratio of NH4Cl, ZnCl2, SnCl2 and H2O is 15:10:5:

70.

6. A method for preparing an alloy coating on a bridge cable steel wire according to any one of claims 1 to 5, characterized in that, The following steps are involved: (1) Grinding, alkali washing and pickling the bridge cable steel wire to obtain clean bridge cable steel wire; (2) placing the clean bridge cable steel wire obtained in step (1) into a fluxing agent for fluxing treatment to obtain fluxed bridge cable steel wire; (3) Using Sn-xZn alloy as the plating solution, the bridge cable steel wire obtained in step (2) is hot-dip plated to obtain a hot-dip Sn-xZn alloy-coated bridge cable steel wire.

7. The preparation method according to claim 6, characterized in that, In step (1), the alkali solution used for the alkali washing is a NaOH solution with a mass concentration of 15%; the temperature of the alkali washing is 40° C., and the time of the alkali washing is 3 minutes.

8. The preparation method according to claim 6, characterized in that, In step (1), the acid solution used for pickling is a 15% mass concentration HCl solution; the pickling temperature is 40° C., and the pickling time is 3 minutes.

9. The preparation method according to claim 6, wherein In step (2), the temperature of the plating-assist treatment is 60-80° C., and the time of the plating-assist treatment is 3 minutes.

10. The preparation method according to claim 6, characterized in that, In step (3), the hot-dip coating temperature is 400±5°C, and the hot-dip coating time is 30-60s.

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