A coating and a method of plating the same in steel wire and a steel wire rope

Abstract

This application relates to a zinc-aluminum-magnesium rare earth alloy coating, its coating method in steel wire, and steel wire rope. The zinc-aluminum-magnesium rare earth alloy coating comprises: Al, Mg, at least one microalloying element selected from Nb, Ti, and V, rare earth elements, with the balance being Zn and unavoidable impurities; the rare earth elements are introduced into the coating in the form of organic rare earth compounds. In the coating of this application, during the hot-dip galvanizing process, the organic rare earth compounds undergo thermal decomposition, releasing active rare earth atoms in situ. The CO and H2 generated by the cracking of the organic groups constitute a micro-reducing atmosphere that protects the rare earth from secondary oxidation. The release of rare earth atoms at the interface improves the wettability of the plating solution to the steel substrate, reduces residual oxide films, purifies grain boundaries, and trace amounts of carbon form a RE-C grain boundary composite segregation layer with the rare earth, thereby improving the performance of the steel wire product.

Description

Technical Field

[0001] This application relates to the field of steel wire rope surface treatment technology, specifically to a zinc-aluminum-magnesium rare earth alloy coating, its coating method in steel wire, and steel wire rope. Background Technology

[0002] To improve the corrosion resistance of steel wire, the existing technology mainly adopts the protective scheme of hot-dip galvanizing a metal coating on the surface of the steel wire. Common coating systems include hot-dip zinc coating, copper coating, and zinc-aluminum-magnesium alloy coating.

[0003] Traditional hot-dip galvanizing technology is mature and inexpensive, but the corrosion resistance of the galvanized layer is limited. In harsh environments such as marine and industrial atmospheres, the salt spray corrosion life is usually only 200-300 hours. In addition, the galvanized layer is prone to uneven coating thickness, incomplete coating, zinc marks, "bamboo joints" and other surface defects during the hot-dip galvanizing process, which affect the appearance quality and service performance of the wire rope.

[0004] To improve the corrosion resistance of coatings, zinc-aluminum-magnesium (Zn-Al-Mg) ternary alloy coating technology has been developed and gradually applied to steel wire products. The addition of Al can form a dense alumina protective film on the coating surface, while Mg can enhance the self-healing ability of the coating and inhibit localized cathodic corrosion. However, the following shortcomings still exist: insufficient adhesion between the coating and the steel substrate, affecting the service life of the steel wire rope under repeated bending and tensile loads; and the coating is prone to intergranular corrosion, which propagates along grain boundaries in long-term humid and hot environments, leading to premature coating failure.

[0005] Adding microalloying elements to zinc-aluminum-magnesium alloy coatings is an important technical approach to further improve coating performance. For example, CN110004390A discloses a zinc-aluminum-magnesium alloy coating with Al 10%-18%, Mg 3%-6%, and added microalloying elements such as Nb 0.1%-1.0%, Ti 0.05%-0.3%, and V 0.01%-0.1%. The Nb, Ti, and V form carbonitride precipitates with C / N, which act as heterogeneous nucleation sites to refine the grains. However, this patent does not add rare earth elements, failing to utilize the interfacial activity of rare earth elements to improve the wettability of the plating solution to the steel substrate, nor does it utilize rare earth elements to purify grain boundaries to inhibit intergranular corrosion.

[0006] Rare earth elements, due to their unique electronegativity and chemical reactivity, play a role in the modification of metallic materials by reducing solid-liquid interfacial tension, purifying grain boundaries, and refining solidification structure, and have been introduced into zinc-aluminum-magnesium alloy coating systems. For example, CN109252125A discloses a zinc-aluminum-magnesium rare earth alloy coating with the composition Zn:Al:Mg:RE=(86.50-98.49):(1-10):(0.5-3):(0.01-0.5), where RE is La, Ce, or a mixture of rare earth elements. However, the corrosion resistance of this coating remains limited.

[0007] In summary, in existing zinc-aluminum-magnesium alloy coatings for steel wire ropes, rare earth elements are directly added to the plating bath in the form of pure metals or intermediate alloys. This results in severe oxidation and burn-off at high temperatures, low effective utilization of rare earth elements, and the generation of large amounts of RE2O3 slag, leading to an increase in the amount of slag in the plating bath. Furthermore, excessively concentrated rare earth elements in certain areas react with Al and Mg to form brittle intermetallic compounds such as CeAl4 and LaAl3, which deteriorate the mechanical properties of the coating. Summary of the Invention

[0008] In view of the above-mentioned defects in the prior art, the technical problem to be solved by this application is to provide a zinc-aluminum-magnesium rare earth alloy coating. By using organic rare earth compounds to replace traditional pure rare earth metals or rare earth intermediate alloys as the form of rare earth introduction, the problems of low effective utilization rate of rare earth elements in high-temperature plating bath, increased plating bath slag, and brittle side reactions caused by local overconcentration are solved. At the same time, the wettability of the coating interface and the grain boundary purification effect of rare earth are effectively improved.

[0009] To address the aforementioned technical problems, this application provides a zinc-aluminum-magnesium rare earth alloy coating, comprising: Al, Mg, at least one microalloying element selected from Nb, Ti, and V, rare earth elements, with the balance being Zn and unavoidable impurities; wherein the rare earth elements are introduced into the coating in the form of organic rare earth compounds.

[0010] In this application, during the thermal decomposition of the organic rare earth compounds, the CO and a small amount of H2 generated by the cracking of the organic groups form a micro-reducing atmosphere around the rare earth atoms, which protects the newly released active rare earth atoms and slows down the rate of secondary oxidation by dissolved oxygen in the plating solution. Simultaneously, the organic rare earth compounds preferentially decompose at the steel substrate / plating solution interface due to the effects of temperature gradient, interfacial catalysis, and concentration gradient, causing the released active rare earth atoms to accumulate in the interfacial region, improving the wetting and spreading ability of the plating solution on the steel substrate. Furthermore, the trace carbon remaining from the decomposition of the organic rare earth compounds forms a RE-C composite segregated layer with rare earth atoms at the grain boundaries during solidification, which can further reduce the grain boundary energy and enhance the grain boundary cohesive strength.

[0011] Optionally, the organic rare earth compound is one or more of the following: rare earth naphthenate salts, rare earth stearate salts, and rare earth neodecanoate salts.

[0012] Optionally, the rare earth elements in the organic rare earth compound include La, Ce, or a combination of La and Ce.

[0013] Furthermore, the rare earth elements are a combination of La and Ce, with a mass ratio of La to Ce ranging from 1:1 to 3:1. La primarily reduces solid-liquid interfacial tension and reduces oxide films, while Ce primarily purifies grain boundaries and suppresses impurity segregation. Each element plays its role at different spatial locations and at different time stages.

[0014] Preferably, by mass percentage, the coating composition contains 3%-25% Al, 0.3%-8% Mg, 0.01%-2% total microalloying elements, and 0.02%-0.20% total rare earth elements.

[0015] Furthermore, by mass percentage, the coating composition contains 10%-18% Al, 2%-5% Mg, 0.01%-2% total microalloying elements, and 0.10%-0.20% total rare earth elements.

[0016] The further technical problem to be solved by this application is to provide a coating method for the above-mentioned zinc-aluminum-magnesium rare earth alloy coating, so as to further improve the interfacial bonding quality between the coating and the steel substrate.

[0017] This application provides a method for coating steel wire with zinc-aluminum-magnesium rare earth alloy coatings, including the following steps: The surface-pretreated steel wire is immersed in a flux solution containing organic rare earth compounds to form a rare earth organic active film on the surface of the steel wire. After the steel wire is reduced in a protective gas in an annealing furnace, it is immersed in a molten zinc-aluminum-magnesium alloy plating bath containing organic rare earth compounds for hot-dip plating. The coating thickness is controlled by wiping with inert gas, and post-treatment is performed to obtain coated steel wire.

[0018] Preferably, the protective gas is at least one of nitrogen and hydrogen, and can be nitrogen or a mixture of nitrogen and hydrogen, preferably 95% N2 + 5% H2. Optionally, the plating bath temperature is 430-460°C.

[0019] Preferably, the concentration of organic rare earth compounds in the flux solution, calculated as rare earth elements, is 5-15 g / L.

[0020] This application also provides a steel wire rope, wherein the surface of the steel wire is coated with the aforementioned zinc-aluminum-magnesium rare earth alloy coating.

[0021] Compared with the prior art, the technical solution of this application has the following advantages: 1. This application uses organic rare earth compounds instead of traditional pure rare earth metals or rare earth intermediate alloys as the form of rare earth introduction. When organic rare earth compounds are thermally decomposed during hot-dip plating, the CO and H2 generated by the cracking of organic groups constitute a micro-reducing atmosphere, which protects the newly released active rare earth atoms and slows down their rate of secondary oxidation in the plating solution, thereby improving the utilization rate of rare earths.

[0022] 2. Because organic rare earth compounds preferentially decompose at the steel substrate / plating bath interface due to the effects of temperature gradient, interfacial catalysis and concentration gradient, the released active rare earth atoms accumulate in the interfacial region, reducing the amount of ineffective consumption of rare earth in the plating bath and the amount of RE2O3 slag generated by oxidation, thus reducing the increase in plating bath slag.

[0023] Organic rare earth compounds release rare earth atoms through thermal decomposition, avoiding the problem of local overconcentration caused by directly adding pure rare earth metals to the plating bath in traditional methods, which leads to the formation of brittle intermetallic compounds such as CeAl4 and LaAl3 with Al and Mg, thus reducing the brittle RE-Al phase.

[0024] 3. The active rare earth atoms released by organic rare earth compounds at the interface effectively improve the wettability of the plating solution on the steel substrate, reduce residual oxide film at the interface, and purify grain boundaries. The residual trace carbon from the decomposition of organic rare earth compounds forms an RE-C composite segregated layer with rare earth atoms at the grain boundaries, which can reduce grain boundary energy. This, combined with the grain refinement effect of Nb / Ti / V microalloying elements, produces a cross-layer synergy, improving salt spray test life. Due to the combined effect of improved interfacial wettability from organic rare earth compounds and grain refinement by Nb / Ti / V microalloying elements, the coating is uniform and smooth, with a significant reduction in defects such as incomplete plating, zinc marks, and "bamboo joints."

[0025] 4. This application uses an annealing furnace to reduce the residual FeO film on the steel wire surface to an active Fe surface in a protective gas environment. Combined with the interfacial modification effect of organic rare earth compounds, rare earth atoms can directly exert interfacial activity on the clean active surface without being consumed in reducing the oxide film, thereby enhancing the bonding strength between the coating and the substrate. No delamination or cracking was observed in the winding test. Detailed Implementation

[0026] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0027] Unless otherwise specified, all percentages in this application are by mass; unless otherwise specified, the rare earth content in organic rare earth compounds is expressed as rare earth elements (RE).

[0028] This application provides a zinc-aluminum-magnesium rare earth alloy coating that uses organic rare earth compounds instead of traditional pure rare earth metals or rare earth master alloys as the form of rare earth introduction. During the hot-dip plating process, the organic rare earth compounds undergo thermal decomposition, releasing active rare earth atoms in situ. The CO and H2 generated by the cracking of organic groups form a micro-reducing atmosphere that protects the rare earth atoms from secondary oxidation. At the same time, rare earth atoms are released at the steel substrate / plating bath interface, achieving improved interfacial wettability and grain boundary purification.

[0029] The zinc-aluminum-magnesium rare earth alloy coating of this application comprises: Al, Mg, at least one microalloying element selected from Nb, Ti, and V, rare earth elements, and the balance being Zn and unavoidable impurities; the rare earth elements are introduced into the coating in the form of organic rare earth compounds.

[0030] Rare earth elements are introduced into the coating in the form of organic rare earth compounds, which are one or more of naphthenic acid rare earth salts, stearic acid rare earth salts, and neodecanoic acid rare earth salts.

[0031] The characteristics of the three organic rare earth compounds are as follows: Rare earth cycloalkanoates: chemical formula RE(C n H 2n-1 COO)3, RE is La, Ce or a mixture thereof. In the following examples of this application, the selected naphthenic acid n ranges from 5 to 8, the naphthenic acid acid value is ≥ 220 mg KOH / g, it is a dark red viscous liquid, and the thermal decomposition temperature is 350-420℃.

[0032] Rare earth stearate: Chemical formula RE(C 17 H 35 COO)3, RE is La, Ce or a mixture thereof, is a white to pale yellow powder or waxy solid, with a thermal decomposition temperature of 300-380℃. 17 During thermal decomposition, a greater amount of reducing gases are released.

[0033] Neodecanoic acid rare earth salt: Chemical formula RE(C9H) 19 COO)3, RE is La, Ce or a mixture thereof, is a pale yellow to brown viscous liquid, and has a thermal decomposition temperature of 320-390℃.

[0034] The aforementioned organic rare earth compounds undergo thermal decomposition at the plating bath temperature (430-460℃) during the hot-dip plating process, releasing active rare earth atoms in situ.

[0035] Optionally, the coating composition, by mass percentage, includes: Al 3%-25%, Mg 0.3%-8%, at least one microalloying element selected from Nb, Ti, and V, with a total amount of 0.01%-2%, rare earth elements 0.02%-0.20%, and the balance being Zn and unavoidable impurities; preferably, the Al content is 10%-18%, the Mg content is 2%-5%, the total amount of microalloying elements is 0.01%-2%, and the total amount of rare earth elements is 0.10%-0.20%. Further, the Al content is 18%, the Mg content is 5%, the Nb content is 0.3%, the Ti content is 0.2%, the V content is 0.03%, and the total amount of rare earth elements is 0.20% (of which La 0.15% and Ce 0.05% are added in the form of rare earth naphthenic acid salts).

[0036] The plating method of this application employs a hot-dip plating process, in which the pretreated steel wire is immersed in a plating solution containing the aforementioned components at a plating temperature of 430℃-460℃. During the plating process, a protective gas containing reducing components is applied, and the CO generated from the thermal decomposition of organic rare earth compounds synergistically forms a dual reducing atmosphere protection mechanism with the protective gas.

[0037] In the following embodiments, the design principle of the plating bath composition is as follows: the Al content in the plating bath is 1.05-1.15 times the target Al content of the coating, the Mg content is 1.10-1.25 times the target Mg content of the coating, the organic rare earth compound content is higher than the target RE content of the coating, and the Nb, Ti, and V contents are consistent with the target contents of the coating. The Al, Mg, and rare earth contents in the plating bath are proportionally higher than the target coating contents to compensate for high-temperature burn-off and slag formation losses.

[0038] The concentration of organic rare earth compounds in the flux, calculated as rare earth elements, is 2-15 g / L, preferably 5-15 g / L. The protective gas is nitrogen, or a mixture of nitrogen and hydrogen, preferably 95% N2 + 5% H2. The reduction temperature is 450-600℃, and the reduction time is 30-60 s. The plating solution temperature is 430-460℃, the wire speed is 120-135 m / min, and the coating thickness is controlled at 60-80 μm. The nitrogen wiping parameters are: pressure 0.15-0.25 MPa, flow rate 15-25 L / min, nozzle-to-wire angle 10-20°, and spray distance 20-40 mm.

[0039] The present application will now be illustrated through specific embodiments and comparative examples.

[0040] The rare earth naphthenic acid salts (lanthanum naphthenic acid La(naph)3, cerium naphthenic acid Ce(naph)3), rare earth stearate salts (lanthanum stearate, cerium stearate), and rare earth neodecanoate salts (lanthanum neodecanoate, cerium neodecanoate) used in the following embodiments of this application can be prepared by conventional methods or obtained from commercial channels. An optional preparation method is to first dissolve rare earth oxides (La2O3, CeO2, etc.) in hydrochloric acid to obtain a rare earth chloride aqueous solution (RECl3), wherein trivalent rare earth oxides such as La2O3 can be directly dissolved in hydrochloric acid, while CeO2 needs to be dissolved by adding an appropriate amount of hydrogen peroxide (H2O2) to hydrochloric acid to assist in reduction; then react the corresponding organic acid (naphthenic acid, stearic acid, or neodecanoic acid) with sodium hydroxide to prepare an aqueous solution of sodium organic acid salt; mix the rare earth chloride aqueous solution and the sodium organic acid salt aqueous solution under stirring to undergo a metathesis reaction to generate rare earth organic acid salt precipitate; the product is obtained after washing with water, filtration, and vacuum drying.

[0041] For example, the preparation of lanthanum neodecanoate: Lanthanum oxide (La₂O₃) is dissolved in 6 mol / L hydrochloric acid and heated and stirred until completely dissolved to obtain an aqueous solution of LaCl₃. Separately, sodium neodecanoate is prepared by reacting neodecanoic acid with an aqueous solution of sodium hydroxide at a molar ratio of 1:1. Under stirring at 60-70℃, the aqueous solution of sodium neodecanoate is slowly added dropwise to the LaCl₃ aqueous solution, resulting in a metathesis reaction to form a precipitate of lanthanum neodecanoate. The product is washed three times with deionized water, filtered, and dried under vacuum at 80℃ for 12 hours to obtain a pale yellow product.

[0042] Preparation of cerium stearate: Cerium oxide (CeO2) was dissolved in 6 mol / L hydrochloric acid, and an appropriate amount of hydrogen peroxide (H2O2) was added to assist in reduction and dissolution. The mixture was heated and stirred until completely dissolved to obtain an aqueous solution of CeCl3. Separately, an aqueous solution of sodium stearate was prepared by reacting stearic acid with an aqueous solution of sodium hydroxide in a 1:1 molar ratio. Under stirring conditions at 70-80℃, the aqueous solution of sodium stearate was slowly added dropwise to the aqueous solution of CeCl3, resulting in a metathesis reaction to form a precipitate of cerium stearate. The product was washed three times with deionized water, filtered, and dried under vacuum at 80℃ for 12 h to obtain a pale yellow waxy solid.

[0043] Preparation method of rare earth naphthenic acid salts (La:Ce = 3:1): Lanthanum oxide (La₂O₃) and cerium oxide (CeO₂) are mixed at a mass ratio of La:Ce = 3:1 and dissolved in 6 mol / L hydrochloric acid. An appropriate amount of hydrogen peroxide (H₂O₂) is added to assist in the reduction and dissolution of CeO₂. The mixture is heated and stirred until completely dissolved to obtain an aqueous solution of mixed rare earth chlorides (LaCl₃ + CeCl₃). Separately, naphthenic acid is reacted with an aqueous solution of sodium hydroxide at a molar ratio of 1:1 to prepare an aqueous solution of sodium naphthenate. Under stirring conditions at 60-70℃, the aqueous solution of sodium naphthenate is slowly added dropwise to the aqueous solution of the mixed rare earth chlorides, resulting in a metathesis reaction to generate rare earth naphthenic acid salts. The product is washed three times with deionized water, filtered, and dried under vacuum at 80℃ for 12 h to obtain a dark red product.

[0044] Preparation method of rare earth stearate (La:Ce = 3:1): La2O3 and CeO2 are mixed at a mass ratio of La:Ce = 3:1 and dissolved in 6 mol / L hydrochloric acid. An appropriate amount of hydrogen peroxide (H2O2) is added to assist in the reduction and dissolution of CeO2. The mixture is heated and stirred until completely dissolved to obtain a mixed rare earth chloride aqueous solution. Separately, stearic acid and sodium hydroxide aqueous solution are reacted at a molar ratio of 1:1 to prepare sodium stearate aqueous solution. The sodium stearate aqueous solution is added dropwise to the mixed rare earth chloride aqueous solution under stirring at 70-80℃, and a metathesis reaction occurs to generate rare earth stearate precipitate. The product is washed three times with deionized water, filtered, and vacuum dried at 80℃ for 12 h to obtain rare earth stearate.

[0045] Preparation of cerium naphthenate: CeO2 was dissolved in 6 mol / L hydrochloric acid, and an appropriate amount of hydrogen peroxide (H2O2) was added to assist in the reduction and dissolution to obtain an aqueous solution of CeCl3. The solution was then reacted with an aqueous solution of sodium naphthenate under stirring at 60-70℃ to undergo a metathesis reaction. The product was washed with water, filtered, and dried under vacuum at 80℃ for 12 h to obtain cerium naphthenate.

[0046] The raw materials used in this application, such as pure rare earth metals and Zn-10%RE master alloy, can all be obtained through commercial channels. The steel wire substrate used in this application is high-carbon steel wire rod (SWRH82B), which is drawn to the required wire diameter and then subjected to alkaline washing, pickling, fluxing, hot-dip galvanizing, wiping, and post-treatment processes to obtain coated steel wire.

[0047] Example 1 High-carbon steel wire rods are cleaned and dried with hydrochloric acid, then drawn to 1.6 mm. After electrolytic alkaline washing (NaOH 40 g / L, 55℃), water washing, and acid washing (HCl 20%, 42℃), they enter the fluxing process. The fluxing solution consists of ZnCl2 250 g / L + NH4Cl 120 g / L + lanthanum neodecanoate (10 g / L as RE), with the remainder being water. The wire is immersed for 8 seconds. After fluxing, a rare earth organic active film forms on the surface of the wire. The wire is then annealed in a pure N2 protective atmosphere at 500℃ for 40 seconds, followed by immersion in a 440℃ plating solution. The plating solution composition (by mass percentage) is: Al 3.3%, Mg 0.36%, V 0.01%, lanthanum neodecanoate (0.027% as RE), with the balance being Zn. The wire speed is 125 m / min, and the immersion time is 4 minutes. After being wiped with N2 (pressure 0.20 MPa, flow rate 20 L / min, nozzle angle 15°, spray distance 30 mm), the steel wire is obtained after air cooling, water cooling, and passivation treatment. See Table 1 for detailed control parameters.

[0048] The thickness of the steel wire coating was found to be 72 μm. The coating composition (by mass percentage) was: Al 3%, Mg 0.3%, V 0.01%, RE 0.02% (introduced as rare earth neodecanoate (lanthanum neodecanoate), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0049] Example 2 Method for coating steel wire with zinc, aluminum, magnesium and rare earth alloy: The main process is the same as in Example 1, the only difference is that the composition of the plating solution is (mass percentage): Al 27.5%, Mg 9.6%, Nb 2%, cerium stearate (0.14% as RE), and the balance is Zn. For specific control parameters, please refer to Table 1.

[0050] The coating thickness was measured to be 72 μm. The coating composition (mass percentage) was: Al 25%, Mg 8%, Nb 2%, RE 0.11% (introduced as rare earth stearate salt, Ce alone), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0051] Example 3 Method for coating steel wire with zinc-aluminum-magnesium rare earth alloy: The pretreatment of the steel wire is the same as in Example 1. The flux is 250 g / L ZnCl2 + 120 g / L NH4Cl + rare earth naphthenic acid salt (5 g / L as RE, La:Ce=1:1), with the remainder being water. The steel wire is immersed for 8 seconds. After treatment with the flux, the steel wire is annealed in a furnace at 450℃ for 30 seconds under a 95% N2 + 5% H2 protective atmosphere, and then immersed in a 430℃ plating solution. The composition of the plating solution is (mass percentage): Al 11%, Mg 2.4%, Nb 0.3%, Ti 0.2%, V 0.03%, rare earth naphthenic acid salt (0.23% as RE, La:Ce=1:1), with the balance being Zn. The wire speed is 120 m / min, and the immersion time is 4 min. After being wiped with N2 (0.15 MPa, 15 L / min, 10°, 20 mm), the steel wire is obtained after air cooling, water cooling, and passivation treatment. The control parameters are detailed in Table 1.

[0052] The coating thickness was found to be 64 μm. The coating composition (mass percentage) was: Al 10%, Mg 2%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.18% (introduced as rare earth naphthenic acid salt, La:Ce=1:1), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0053] Example 4 Method for coating steel wire with zinc-aluminum-magnesium rare earth alloy: High-carbon steel wire rod is cleaned and dried with hydrochloric acid, then drawn to 1.6 mm. After electrolytic alkaline washing (NaOH 40 g / L, 55℃), water washing, and acid washing (HCl 20%, 42℃), it enters the fluxing process. The fluxing solution is ZnCl2 250 g / L + NH4Cl 120 g / L + naphthenic acid rare earth salt (15 g / L as RE, La:Ce=3:1), with the remainder being water. The steel wire is immersed for 8 seconds. After treatment with the fluxing solution, the steel wire is annealed in an annealing furnace at 500℃ for 40 seconds under a 95% N2 + 5% H2 protective atmosphere. The wire was immersed in a 440℃ plating solution with the following composition (by mass percentage): Al 19.8%, Mg 6%, Nb 0.3%, Ti 0.2%, V 0.03%, rare earth naphthenate salt (0.24% as RE, La:Ce = 3:1, of which La 0.18% and Ce 0.06%), with the balance being Zn. The wire speed was 125 m / min, and the immersion time was 4 min. After wiping with N2 (pressure 0.20 MPa, flow rate 20 L / min, nozzle angle 15°, spray distance 30 mm), the wire was air-cooled, water-cooled, and passivated to obtain the coated steel wire. Detailed control parameters are shown in Table 1.

[0054] The coating thickness was measured to be 72 μm. The coating composition (mass percentage) was as follows: Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.20% (introduced in the form of rare earth naphthenic acid salts, La:Ce=3:1, of which La 0.15% and Ce 0.05%), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0055] Example 5 Method for coating steel wire with zinc-aluminum-magnesium rare earth alloy: The pretreatment of the steel wire is the same as in Example 4. The flux is 250 g / L ZnCl2 + 120 g / L NH4Cl + rare earth naphthenic acid salt (10 g / L as RE, La:Ce=1:1), with the remainder being water. The steel wire is immersed for 8 seconds. After treatment with the flux, the steel wire is annealed in an annealing furnace at 600℃ for 60 seconds under a 95% N2 + 5% H2 protective atmosphere, and then immersed in a 460℃ plating solution. The composition of the plating solution is (mass percentage): Al 19.8%, Mg 6%, Nb 0.3%, Ti 0.2%, V 0.03%, rare earth naphthenic acid salt (0.26% as RE, La:Ce=1:1, of which La 0.13% and Ce 0.13%), with the balance being Zn. The wire speed is 135 m / min, and the immersion time is 4 minutes. After being wiped with N2 (pressure 0.25 MPa, flow rate 25 L / min, nozzle angle 20°, spray distance 40 mm), the steel wire is obtained after air cooling, water cooling, and passivation treatment. See Table 1 for detailed control parameters.

[0056] The coating thickness was measured to be 79 μm. The coating composition (mass percentage) was as follows: Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.20% (introduced in the form of rare earth naphthenic acid salts, La:Ce=1:1, of which La 0.10% and Ce 0.10%), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0057] Example 6 The coating composition and coating process parameters are the same as in Example 4, except that the flux does not contain organic rare earth compounds. See Table 1 for detailed control parameters.

[0058] The coating thickness was measured to be 72 μm. The coating composition (mass percentage) was as follows: Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.17% (introduced in the form of rare earth naphthenic acid salts, La:Ce=3:1, of which La 0.127% and Ce 0.043%), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0059] Example 7 The plating process is the same as in Example 4, except that Nd-Ce organic rare earth salt (neodymium naphthenate, 0.18% based on Nd) + organic cerium compound (cerium naphthenate, 0.06% based on Ce) is used instead of La-Ce organic rare earth salt in the plating solution, with a total RE of 0.24%.

[0060] Preparation of neodymium naphthenate: Nd2O3 was dissolved in 6 mol / L hydrochloric acid to obtain an aqueous solution of NdCl3, which was then reacted with an aqueous solution of sodium naphthenate under stirring at 60-70℃ in a metathesis reaction. The product was washed with water, filtered, and dried under vacuum at 80℃ for 12 h.

[0061] Preparation of cerium naphthenate: CeO2 was dissolved in 6 mol / L hydrochloric acid, and an appropriate amount of hydrogen peroxide (H2O2) was added to assist in the reduction and dissolution to obtain an aqueous solution of CeCl3. The solution was then reacted with an aqueous solution of sodium naphthenate under stirring at 60-70℃ for metathesis reaction. The product was washed with water, filtered, and dried under vacuum at 80℃ for 12 h.

[0062] The fluxing solution is ZnCl2 250 g / L + NH4Cl 120 g / L + rare earth naphthenic acid salt (15 g / L as RE, Nd:Ce=3:1). The composition of the plating solution is as follows (by mass percentage): Al 19.8%, Mg 6%, Nb 0.3%, Ti 0.2%, V 0.03%, neodymium naphthenate (0.18% as Nd) + cerium naphthenate (0.06% as Ce), with the balance being Zn. The total amount of RE added to the plating solution is 0.24%.

[0063] The control parameters are detailed in Table 1.

[0064] The coating thickness was measured to be 72 μm. The coating composition (mass percentage) was as follows: Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.196% (introduced in the form of rare earth naphthenic acid salts, Nd:Ce=3:1, of which Nd 0.147% and Ce 0.049%), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0065] Comparative Example 1 The plating process is the same as in Example 4, except that the flux does not contain rare earth elements. In the plating bath, an organic rare earth compound (rare earth naphthenate salt) replaces the La-Ce metal (La:Ce=3:1, total RE 0.66%, calculated as RE), and La and Ce are directly added to the plating bath in the form of metal blocks. The control parameters are detailed in Table 1.

[0066] The obtained coating thickness was 72 μm, and the coating composition (mass percentage) was: Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.20% (introduced by direct immersion of metal in the plating bath, La:Ce=3:1). See Table 2 for detailed coating composition.

[0067] Comparative Example 2 The plating process is the same as in Example 4, except that rare earth elements are not added.

[0068] Testing revealed that the coating composition was Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, with the balance being Zn and unavoidable impurities. Process parameters remained unchanged. Control parameters are detailed in Table 1, and coating composition is detailed in Table 2.

[0069] Comparative Example 3 The plating process is the same as in Example 4, except that the protective gas reduction step in the annealing furnace is omitted, and the steel wire is directly immersed in the plating solution without undergoing N2 / H2 reduction. See Table 1 for detailed control parameters.

[0070] The coating thickness was measured to be 72 μm. The coating composition (mass percentage) was as follows: Al 18%, Mg 5%, Nb 0.3%, Ti 0.2%, V 0.03%, RE 0.15% (introduced in the form of rare earth naphthenic acid salts, La:Ce=3:1, of which La 0.1125% and Ce 0.0375%), with the balance being Zn and unavoidable impurities, as detailed in Table 2.

[0071] The control parameters for each of the above embodiments and comparative examples are detailed in Table 1. The coating compositions obtained from each of the above embodiments and comparative examples are detailed in Table 2.

[0072] Table 1 Control parameters for each embodiment and comparative example

[0073] Table 2. Coating composition of each embodiment and comparative example

[0074] The coating performance of the above embodiments and comparative examples was tested using the following standard methods, and the test results are detailed in Table 3.

[0075] Neutral Salt Spray Test: The test was performed according to the NSS (Neutral Salt Spray Test) method in GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test". Sample Preparation: Straight steel wire segments of 300 mm in length were cut from the coated steel wires of the examples and comparative examples. Both ends were sealed with epoxy resin, with a sealing length of approximately 20 mm. The effective test length was 260 mm, and the effective test area was approximately 1307 mm². 2 (Calculated as π×d×L, d=1.6mm, L=260mm). Test conditions: NaCl aqueous solution concentration 50±5 g / L, pH value 6.5~7.2, test chamber temperature 35℃, continuous spraying. During the test, the surface condition of the sample was visually inspected through the observation window of the test chamber. The time (in hours) at which the first visible red rust spots appeared on the coating surface was recorded, which is the salt spray test life. The observation cycle is 10h / time. For example, if red rust spots appear 354 hours after the start of the test, then the time at which the first visible red rust spots appeared is recorded as 360h. Three parallel samples were tested for each example and comparative example, and the average value was taken.

[0076] Winding Test: Performed according to GB / T 2976-2020 "Metallic Materials Wire Winding Test Method". Sample Preparation: Cut straight steel wire segments with a length of not less than 500 mm from the coated steel wires of each embodiment and comparative example. Test Parameters: Using the diameter of the steel wire itself (d=1.6 mm) as the mandrel diameter, i.e., winding mandrel diameter D=1d, 8 winding turns, winding speed 10 turns / min. Result Evaluation: Check whether the coating has cracked, peeled off, or delaminated to the point that it can be wiped off with a bare finger. If there is no cracking, peeling, or delamination to the point that it can be wiped off with a bare finger, the sample is considered qualified.

[0077] Coating weight deviation: The chemical peeling and weighing method in GB / T 1839-2003 "Determination of Zinc Coating Quality of Zinc Coating on Steel" was followed. Five 100mm long samples were cut at equal intervals from the coated steel wires of each example and comparative example. The test was carried out according to the procedure in Section 6 of the standard. The mass of the samples before and after peeling was weighed, and the weight of the coating per segment (g / m) was calculated. The coating weight deviation was calculated by the following formula: Weight deviation (%) = (Maximum coating weight per segment - Minimum coating weight per segment) / Average coating weight per segment × 100%.

[0078] Rare earth utilization rate: The initial rare earth content of the plating solution and the rare earth content in the slag are measured and calculated according to the following formula: Rare earth utilization rate (%) = (Amount of rare earth actually consumed in the plating solution / Total amount of rare earth added to the plating solution) × 100%.

[0079] The RE addition amount in the plating solution is the mass percentage of rare earth compounds added during the preparation of the plating solution, converted into rare earth elements. The measured RE content of the coating is the mass percentage of rare earth elements determined by ICP-OES after the coating is chemically peeled from the steel wire substrate. The increase in plating solution slag volume is measured as the percentage increase in slag volume after adding rare earth, based on the slag volume within the same plating solution operating cycle without rare earth addition. Measurement timing: After the plating solution has been running continuously at the target temperature for 8 hours, all floating slag and bottom slag are collected, dried, weighed, and the slag volume (kg / ton of plating solution) is recorded. The slag volume increase (%) is calculated using the following formula: (Slag volume after adding rare earth - Slag volume without adding rare earth) / Slag volume without adding rare earth × 100%. The baseline slag volume without adding rare earth is 2.9 kg / ton of plating solution (measured value in Comparative Example 2).

[0080] Coating thickness: The thickness was measured according to GB / T4956-2020 "Magnetic Method for Measuring the Thickness of Non-Magnetic Coatings on Magnetic Substrates". Sample preparation: A 100mm long straight steel wire segment was cut from the coated steel wire of each embodiment and comparative example. Measurement was performed in the middle area within 10mm from both ends. Measurement method: A magnetic thickness gauge was used. Measurements were taken at 90° intervals along the circumference of the steel wire, with 4 points measured at each cross-section. The above measurements were repeated at 3 equidistant cross-sections along the axial direction of the steel wire, for a total of 12 measurement points. Result processing: The arithmetic mean of the 12 measurement points was the coating thickness (μm) of the sample. Three parallel samples were tested for each embodiment and comparative example, and the average value was taken.

[0081] Table 3 Test results for each embodiment and comparative example

[0082] The test results of the above embodiments and comparative examples were analyzed, and the results are as follows: 1. The difference between Example 4 and Comparative Example 1 lies in the form of rare earth introduction. Example 4 uses an organic rare earth compound (a naphthenic acid rare earth salt), while Comparative Example 1 uses pure La-Ce metal directly added to the plating bath. All other components and process parameters are the same. Comparative results show that: the rare earth utilization rate of Example 4 reaches 83.3%, while that of Comparative Example 1 is only 30.3%, representing an improvement of 175%; after 8 hours of operation, the slag volume of Example 4 is 3.2 kg / ton of plating bath, with a slag volume increase of 10.3%, while the slag volume of Comparative Example 1 is 4.8 kg / ton of plating bath, with a slag volume increase as high as 65.5%; the neutral salt spray lifetime of Example 4 is 730 hours, an 18% improvement compared to the 620 hours of Comparative Example 1.

[0083] Based on the above data, it is speculated that the CO generated by the cracking of organic groups during the thermal decomposition of organic rare earth compounds constitutes a micro-reducing atmosphere, which effectively delays the secondary oxidation of rare earth atoms and greatly improves the utilization rate of rare earths. At the same time, the "interface release" mechanism causes rare earth atoms to preferentially accumulate in the interface region, avoiding the ineffective consumption and oxidation slag formation of rare earths inside the plating solution.

[0084] 2. The difference between Example 4 and Comparative Example 2 is whether or not rare earth elements are added; all other parameters are the same. The comparative results show that the neutral salt spray lifetime of Example 4 is 730 hours, which is 37% higher than that of Comparative Example 2 (530 hours); the coating weight deviation of Example 4 is ±2.6%, which is better than that of Comparative Example 2 (±7.6%).

[0085] Based on the above data, it is speculated that rare earth elements play a role in improving interfacial wettability, reducing residual oxide film, and purifying grain boundaries during hot-dip galvanizing, which helps to improve the corrosion resistance of the coating and enhance surface quality.

[0086] 3. The difference between Example 4 and Comparative Example 3 lies in whether a protective gas reduction process is used. The comparative results show that the neutral salt spray lifetime of Example 4 is 730 hours, which is 12% higher than that of Comparative Example 3 (650 hours); Comparative Example 3 showed delamination in the winding test, while Example 4 showed no delamination or cracking.

[0087] Based on the above data, it is speculated that the protective gas reduction creates an active Fe surface on the steel substrate, allowing the rare earth atoms released from the decomposition of organic rare earth compounds to directly exert interfacial activity on the clean active surface without being consumed by the reduced oxide film.

[0088] 4. Examples 1 (coating: Al 3%, Mg 0.3%, RE 0.02%), 2 (coating: Al 25%, Mg 8%, RE 0.11%), and 4 (coating: Al 18%, Mg 5%, RE 0.20%) all passed the winding test, with salt spray lifetimes of 630 hours, 680 hours, and 730 hours, respectively. Example 1, due to its lower Al and Mg content and lower rare earth element content, had a relatively shorter salt spray lifetime, but it was still longer than that of ordinary zinc plating.

[0089] 5. The flux solution in Example 6 does not contain organic rare earth elements, and the rare earth utilization rate of the product is weaker than that in Example 4, indicating that adding organic rare earth elements to the flux solution is beneficial to improving the immersion plating effect.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A zinc-aluminum-magnesium rare earth alloy coating, comprising: Al, Mg, at least one microalloying element selected from Nb, Ti, V, rare earth elements, with the balance being Zn and unavoidable impurities; characterized in that the rare earth elements are introduced into the coating in the form of organoravenous earth compounds.

2. The zinc-aluminum-magnesium rare earth alloy coating according to claim 1, characterized in that, The organic rare earth compounds include one or more of naphthenic acid rare earth salts, stearic acid rare earth salts, and neodecanoic acid rare earth salts.

3. The zinc-aluminum-magnesium rare earth alloy coating according to claim 1, characterized in that, The rare earth elements in the organic rare earth compound include La, Ce, or a combination of La and Ce.

4. The zinc-aluminum-magnesium rare earth alloy coating according to claim 1, characterized in that, The rare earth elements in the organic rare earth compound include a combination of La and Ce, wherein the mass ratio of La to Ce is 1:1 to 3:

1.

5. The zinc-aluminum-magnesium rare earth alloy coating according to claim 1, characterized in that, By mass percentage, the coating composition contains 3%-25% Al, 0.3%-8% Mg, 0.01%-2% total microalloying elements, and 0.02%-0.20% total rare earth elements.

6. The zinc-aluminum-magnesium rare earth alloy coating according to claim 1, characterized in that, The coating composition contains 10%-18% Al, 2%-5% Mg, 0.01%-2% total microalloying elements, and 0.10%-0.20% total rare earth elements.

7. A method for plating a zinc-aluminum-magnesium rare earth alloy coating in steel wire as described in any one of claims 1-6, characterized in that, Includes the following steps: The surface-pretreated steel wire is immersed in a flux solution containing organic rare earth compounds to form a rare earth organic active film on the surface of the steel wire. After the steel wire is reduced in a protective gas in an annealing furnace, it is immersed in a molten zinc-aluminum-magnesium alloy plating bath containing organic rare earth compounds for hot-dip plating. The coating thickness is controlled by wiping with inert gas, and post-treatment is performed to obtain coated steel wire.

8. The plating method according to claim 7, characterized in that, The concentration of organic rare earth compounds in the fluxing solution, calculated as rare earth elements, is 5-15 g / L.

9. The plating method according to claim 7, characterized in that, The protective gas is nitrogen, or a mixture of nitrogen and hydrogen.

10. A steel wire rope, characterized in that, The surface of the steel wires of the steel wire rope is coated with a zinc-aluminum-magnesium rare earth alloy coating as described in any one of claims 1-6.

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