A dezincification-resistant alloy and its preparation method and application

Abstract

This invention provides a de-galvanizing alloy, its preparation method, and its application, belonging to the field of hot-dip galvanizing technology. The de-galvanizing alloy of this invention comprises the following elements by mass percentage: aluminum 7.0%~10.0%, gadolinium 0.7%~1.0%, tin 0.4%~0.6%, with the remainder being zinc and unavoidable impurities. The gadolinium in this invention can react with bismuth in the zinc plating solution to form a high-melting-point alloy with a density of 7.1 g / cm³. 3 GdBi, this compound is solid in zinc plating solution and has a density greater than that of zinc solution (6.8 g / cm³ at 440°C). 3 The bismuth will sink to the bottom of the zinc bath to form bottom dross, which can effectively remove bismuth and solve the zinc spangle problem at its source; tin can promote the uniform dispersion of residual bismuth in the zinc bath and reduce bismuth segregation. The zinc spangle removal alloy described in this invention effectively solves the zinc spangle problem caused by excessive bismuth content in the zinc bath during ultra-thin zinc plating production, without affecting the thickness and corrosion resistance of the zinc coating.

Description

Technical Field

[0001] This invention relates to the field of hot-dip galvanizing technology, and in particular to a dezincification alloy, its preparation method, and its application. Background Technology

[0002] In the hot-dip galvanizing industry, to achieve ultra-thin zinc coatings (reducing zinc plating thickness to save zinc resources and improve production efficiency), the aluminum content in the zinc bath is typically increased from the conventional 0.006%~0.008% to 0.03%~0.08%. Aluminum preferentially reacts with iron to form Fe2Al5 compounds, hindering the interdiffusion of iron and zinc atoms and inhibiting the iron-zinc reaction, thereby reducing the zinc coating thickness from over 80μm in traditional galvanizing to below 40μm. However, high-aluminum zinc baths lead to increased surface tension, reducing the wettability of the zinc bath on the steel. Simultaneously, aluminum readily reacts with chlorides in the flux to form high-boiling-point aluminum trichloride, which condenses on the steel surface, causing serious incomplete coating problems.

[0003] To address the issue of incomplete plating in high-aluminum zinc baths, the industry commonly uses bismuth-containing anti-incomplete plating agents. However, bismuth accumulates continuously in the zinc bath. When the bismuth content reaches 0.003% or higher, zinc spangles appear on the surface of the galvanized workpiece; when the bismuth content exceeds 0.010%, the zinc spangle problem becomes quite severe. Furthermore, higher aluminum content requires more anti-incomplete plating agent, leading to even higher bismuth content in the zinc bath and more severe zinc spangle formation. Simultaneously, aluminum exacerbates zinc spangle formation; with the same bismuth content, higher aluminum content results in more severe zinc spangle formation. Ultra-thin galvanizing inevitably creates a vicious cycle of "high aluminum - high bismuth - severe zinc spangle." Traditional methods for removing bismuth from zinc baths have many limitations: 1. Calcium and magnesium cannot be used to remove bismuth: The removal of bismuth impurities in liquid lead usually involves adding metallic calcium and magnesium. This causes bismuth to form intermetallic compounds with higher melting points, lower densities, and insolubility in molten lead, which then float to the surface of the lead, thus removing bismuth. However, using calcium and magnesium can only reduce the bismuth content in the molten lead to 0.02%~0.03%. 2. Bismuth in molten zinc is difficult to remove with zinc slag through gravity segregation. At 440℃, the density of bismuth is 9.8 g / cm³. 3 The concentration was much higher than that of zinc liquid (6.88 g / cm³). 3 Theoretically, bismuth should settle to the bottom of the molten zinc and separate with the zinc dross due to its density. However, in actual production, because the bismuth content is very low, the solubility of bismuth in the molten zinc is over 0.1% at galvanizing temperatures, while the actual bismuth content is below 0.01%. Therefore, it dissolves in the molten zinc and does not settle into the zinc dross, thus preventing separation of zinc and bismuth. Furthermore, bismuth is a more inert metal than zinc and will not be oxidized into bismuth oxide, which is carried away with the zinc ash. Currently, the only way to remove bismuth is to continuously replenish new zinc ingots to dilute the bismuth in the molten zinc, allowing it to be slowly carried away by the zinc plating layer on the surface of the galvanized workpiece. However, this process is time-consuming, inefficient, and cannot meet the need for rapid control of zinc spangles in continuous production.

[0004] Therefore, there is an urgent need to develop an efficient and convenient technology for removing bismuth and zinc spangles from molten zinc to meet the production requirements of ultra-thin galvanized layers. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a de-galvanizing alloy, its preparation method, and its application. The gadolinium in the de-galvanizing alloy provided by this invention can fully react with bismuth in the zinc plating solution to generate gadobismuth compounds, thereby reducing the bismuth content in the zinc plating solution and eliminating the root cause of zinc spangle formation.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a zinc-aluminum-gadolinium-tin alloy, comprising the following elements by mass percentage: aluminum 7.0%~10.0%, gadolinium 0.7%~1.0%, tin 0.4%~0.6%, with the remainder being zinc and unavoidable impurities.

[0007] Preferably, the mass percentage of aluminum is 8.0% to 9.0%.

[0008] Preferably, the gadolinium has a mass percentage of 0.75% to 0.8%.

[0009] Preferably, the tin has a mass percentage of 0.45% to 0.5%.

[0010] Preferably, the mass percentage of the impurities does not exceed 0.01%.

[0011] This invention also provides a method for preparing the zinc-free alloy described in the above technical solution, comprising the following steps: Aluminum ingots and gadolinium ingots are first smelted to obtain an aluminum-gadolinium master alloy; The zinc and tin ingots are then subjected to a second smelting process to obtain a zinc-tin master alloy. The aluminum-gadolinium master alloy, zinc-tin master alloy, and zinc ingot are subjected to a third smelting process to obtain the dezincified alloy.

[0012] Preferably, the mass percentage of gadolinium in the aluminum-gadolinium master alloy is 9.0% to 11.0%.

[0013] Preferably, the zinc-tin master alloy contains 5% to 20% tin by mass.

[0014] The present invention also provides the application of the dezincification alloy described in the above technical solution or the dezincification alloy prepared by the preparation method described in the above technical solution in the field of hot-dip galvanizing.

[0015] Preferably, the application includes the following steps: The mass percentages of bismuth and aluminum in the zinc plating solution were determined. After dissolving the zinc-removing alloy in the zinc plating solution, let it stand, then remove the scum, and then perform hot-dip galvanizing. The amount of zinc-removing alloy added is determined by the following steps: When the mass percentage of aluminum is ≤0.04%, the amount of dezincification alloy added is 1000×a×c / d, where a is the mass percentage of bismuth, c is the weight of the zinc plating solution in tons, and d is the mass percentage of gadolinium in the dezincification alloy. When the mass percentage of aluminum is >0.04%, the amount of dezincification alloy added is 1200×a×c / d, where a is the mass percentage of bismuth, c is the weight of the zinc plating solution in tons, and d is the mass percentage of gadolinium in the dezincification alloy.

[0016] This invention provides a zinc-free alloy comprising the following elements by mass percentage: aluminum 7.0%~10.0%, gadolinium 0.7%~1.0%, tin 0.4%~0.6%, with the remainder being zinc and unavoidable impurities.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The gadolinium element in the zinc-removing alloy of this invention can react with bismuth in the zinc plating solution to form a high-melting-point (2110℃) alloy with a density of 7.1 g / cm³. 3 The gadolinium-bismuth intermetallic compound (GdBi) exists as a solid in the zinc plating solution and has a density greater than that of the zinc solution (6.8 g / cm³ at 440°C). 3 The bismuth will sink to the bottom of the zinc bath to form bottom dross, which can effectively remove bismuth and solve the zinc spangle problem at its source; tin can promote the uniform dispersion of residual bismuth in the zinc bath and reduce bismuth segregation. The zinc spangle removal alloy described in this invention effectively solves the zinc spangle problem caused by excessive bismuth content in the zinc bath during ultra-thin zinc plating production, without affecting the thickness and corrosion resistance of the zinc coating.

[0018] The present invention also provides a method for preparing the zinc-free spangle alloy described in the above technical solution. The preparation method of the present invention is simple and convenient to operate and is suitable for industrial production.

[0019] This invention also provides the application of the aforementioned de-galvanizing alloy in the hot-dip galvanizing process, effectively solving the problem of zinc spangle caused by bismuth accumulation in high-alumina zinc bath. Detailed Implementation

[0020] This invention provides a zinc-free alloy comprising the following elements by mass percentage: aluminum 7.0%~10.0%, gadolinium 0.7%~1.0%, tin 0.4%~0.6%, with the remainder being zinc and unavoidable impurities.

[0021] In this invention, the mass percentage of aluminum is preferably 8.0% to 9.0%, specifically 7.0%, 8.0%, 9.0%, 9.6% or 10.0%.

[0022] In this invention, the mass percentage of gadolinium is preferably 0.75% to 0.8%, specifically 0.7%, 0.75%, 0.8% or 1.0%.

[0023] In this invention, the mass percentage of tin is preferably 0.45% to 0.5%, specifically 0.4%, 0.45%, 0.5% or 0.6%.

[0024] In this invention, the mass percentage of the impurities is preferably no more than 0.01%.

[0025] The principle of the zinc-free alloy formulation of the present invention is as follows: (1) The preparation of zinc-gadolinium alloy is very difficult: the melting point of gadolinium is 1312℃, while the boiling point of zinc is only 907℃. If the temperature is raised above the melting point of gadolinium, all the zinc will be converted into steam, and the steam pressure will be huge, making alloy production impossible. Therefore, the preparation of zinc alloy is generally carried out at a lower temperature, such as 600~700℃, so that other metals dissolve in the zinc liquid. According to the gadolinium-zinc phase diagram, the solubility of gadolinium in zinc liquid is very small. For example, the solubility is only 0.3% at 720℃. To produce a gadolinium-zinc alloy with a gadolinium content of 0.3%, the melting temperature must be raised to above 850℃. Under high temperature conditions, zinc is easily volatilized and gadolinium is easily oxidized, and the preparation cycle is very long, making it unsuitable for large-scale industrial production; (2) Aluminum-gadolinium alloys are easy to prepare: As can be seen from the aluminum-gadolinium binary phase diagram, when gadolinium is 10.5wt%, there is a eutectic point with a eutectic temperature of 650℃, which is lower than the melting point of aluminum, 660.5℃. Near the eutectic point, the alloy components melt very quickly. Therefore, this invention first prepares gadolinium and aluminum into an aluminum-gadolinium master alloy, and then uses the aluminum-gadolinium master alloy to prepare a zinc-aluminum-gadolinium-tin de-zincification alloy; (3) The hot-dip galvanizing industry currently uses zinc-aluminum alloys with an aluminum content of 7wt%~10wt%: the melting point of zinc-10wt% aluminum alloy is about 435℃, the normal galvanizing temperature is 440℃, and the aluminum content in the existing zinc-aluminum alloys in the batch hot-dip galvanizing industry is generally 7.0wt%~10wt%, ensuring that the zinc-aluminum alloy can melt in the zinc liquid of galvanizing and improving the production efficiency of the alloy addition process. If the aluminum content is too high, the alloy melting point is high, and it cannot melt at the galvanizing temperature of 440℃, but can only gradually dissolve, resulting in low production efficiency during use. If the aluminum content is too low, the required alloy weight will increase significantly under the same aluminum weight, which will increase the cost of alloy production, transportation and use. This invention introduces gadolinium into the dezincification alloy through aluminum, wherein the aluminum content is preferably between 7.0 wt% and 10 wt%; (4) There is an upper limit to the gadolinium content in the dezincification alloy: the gadolinium content in the aluminum-gadolinium eutectic alloy is 10.5 wt%, and the aluminum-gadolinium eutectic alloy is prepared together with zinc to form an alloy containing 7.0 wt% to 10 wt% aluminum, wherein the maximum gadolinium content is determined by the aluminum content. Calculated based on the gadolinium content in the aluminum-gadolinium eutectic alloy being 10.5 wt%, when the aluminum content in the dezincification alloy is 10 wt%, the gadolinium content can reach a maximum of 1.15 wt%; (5) The gadolinium content in the dezincification alloy can be arbitrarily reduced: the gadolinium content can be deliberately reduced when preparing the aluminum-gadolinium intermediate alloy. Alternatively, an aluminum-gadolinium eutectic alloy can be prepared, and in the subsequent preparation of the dezincification alloy, the aluminum and gadolinium contents can be reduced by decreasing the amount of aluminum-gadolinium eutectic alloy. Alternatively, aluminum can be added to the zinc-aluminum alloy formula to reduce the gadolinium content while maintaining a high aluminum content; (6) In the zinc-aluminum alloy liquid, the solubility of gadolinium also increases with the increase of aluminum content.At 440℃, the solubility of gadolinium is 0.0002% when there is no aluminum in the zinc bath, 0.002% when the aluminum content is 0.03wt%, 0.006% when the aluminum content is 0.10wt%, 0.4% when the aluminum content is 5wt%, 0.7% when the aluminum content is 7wt%, and 1.06% when the aluminum content is 10wt%. Considering both production efficiency and gadolinium solubility, the gadolinium content in the de-galvanized alloy is determined to be 0.7wt%~1.0wt%. (7) Determination of tin content in the alloy: Tin in the zinc plating bath can reduce zinc spangles. When the tin content in the zinc plating bath is greater than 0.006wt% and the bismuth content in the zinc plating bath is less than 0.003wt%, no zinc spangles are produced. When designing the alloy formulation, the tin content in the alloy is determined based on a tin content of 0.006wt%~0.008wt% in the zinc plating bath. During the bismuth removal process, gadolinium reacts with bismuth to form an intermetallic compound GdBi with an atomic ratio of 1:1. The atomic weight of gadolinium is 157, and the atomic weight of bismuth is 209. If gadolinium is added at the same weight as the bismuth in the zinc plating bath during bismuth removal, the gadolinium excess is 33wt%, which can ensure sufficient bismuth removal reaction. Based on actual ultra-thin galvanizing production with a daily output of 150 tons, consuming 25kg of anti-leakage plating agent and 5 tons of zinc, the total zinc weight in the zinc pot is 400 tons. The anti-leakage plating agent introduces 0.6kg of bismuth, therefore, the daily required zinc spangle removal alloy contains 0.6kg of gadolinium. Based on the above data and through continuous cycling, to achieve a tin content of 0.006wt%~0.08wt% in the zinc plating solution, the daily tin addition would be: 5 tons × (0.006%~0.008%) = 0.3~0.40 kg. It is evident that adding 0.3~0.40 kg of tin daily ensures a balance between the tin carried away by the galvanized workpiece and the tin brought in by the desiccant alloy, thus stabilizing the tin content in the zinc plating solution at 0.006wt%~0.008wt%. Calculations suggest that a tin content of 0.4wt%~0.6wt% in the alloy formulation is optimal.

[0026] The zinc-removing alloy of the present invention can: (1) Highly efficient removal of bismuth and zinc spangles: The gadolinium element in the zinc spangle removal alloy of this invention can react with bismuth in the zinc melt to form a high melting point (2110℃) and density of 7.1 g / cm³. 3 The gadolinium-bismuth intermetallic compound (GdBi) exists as a solid in molten zinc and has a density greater than that of molten zinc (6.8 g / cm³ at 440°C). 3Bismuth will sink to the bottom of the zinc bath to form bottom slag, which can effectively remove bismuth and solve the zinc spangle problem at its source. Table 1 shows the data of the main elements that can form intermetallic compounds with bismuth. It can be seen that the formation free energy of alkaline earth metals with bismuth is not as low as that of rare earth metals. Therefore, this invention selects rare earth metals as the main raw materials for removing bismuth from zinc bath. Among rare earth elements, the binding ability of each rare earth element with bismuth gradually increases with the increase of atomic weight (the formation free energy of intermetallic compounds gradually shifts to the negative direction). When it comes to neodymium, the binding force of neodymium-bismuth compound is the strongest, and then it gradually decreases. From the perspective of binding force alone, neodymium has the best effect on removing bismuth. The prices of rare earth metal products also vary greatly. For example, praseodymium and neodymium are priced at around RMB 1 million / ton, while yttrium, lanthanum, and cerium are less than RMB 100,000 / ton, gadolinium is RMB 230,000 / ton, and dysprosium is RMB 280,000 / ton. Considering the bismuth removal effect and cost, gadolinium is selected as the main element for bismuth removal. Table 1. Data on major elements that can form intermetallic compounds with bismuth.

[0027] Note: To facilitate comparison of the formation free energy of each mole of alkaline earth element forming compounds with bismuth, Ca3Bi2, Mg3Bi2, and Sr3Bi2 are expressed as MgBi2. 2 / 3 CaBi 2 / 3 、SrBi 2 / 3 express; (2) Synergistic dispersion effect: At a zinc plating temperature of 440℃, tin has good compatibility with the zinc plating solution and also with bismuth. The atomic radius of tin is between that of zinc and bismuth atoms, which promotes the uniform dispersion of bismuth in the zinc solution, ensures that gadolinium and bismuth fully contact and react to form gadolinium-bismuth compounds, reduces the bismuth content in the zinc solution, and eliminates the root cause of zinc spangle formation. During the cooling process of the zinc plating layer, the solubility of bismuth in the zinc plating layer decreases rapidly. Bismuth, whose atomic radius is much larger than that of zinc, will be squeezed to the surface of the zinc plating layer by zinc atoms, resulting in surface segregation. When a certain amount of tin is present in the zinc plating solution, it can effectively reduce bismuth segregation and reduce the formation of zinc spangle. (3) Does not affect the thickness of the ultra-thin zinc plating layer: The aluminum content in the de-galvanizing alloy of the present invention is matched with the high-aluminum zinc plating solution of the ultra-thin zinc plating process. When adding the de-galvanizing alloy of the present invention, the balance of aluminum content in the zinc plating solution can be ensured by reducing the amount of zinc-aluminum alloy added, and the aluminum content in the zinc plating solution will not be too high. The gadolinium and tin elements in the zinc-aluminum-gadolinium-tin alloy of the present invention will not interfere with the process of aluminum and iron forming Fe2Al5 compounds, and have no effect on the thickness of the zinc plating layer; (4) Convenient preparation and application: The preparation process of zinc-aluminum-gadolinium-tin alloy is simple and suitable for large-scale production; when applying it, there is no need to modify the existing galvanizing equipment. Just add the alloy in proportion and let it settle. The operation is convenient and the production cost is low.

[0028] This invention also provides a method for preparing the zinc-free alloy described in the above technical solution, comprising the following steps: Aluminum ingots and gadolinium ingots are first smelted to obtain an aluminum-gadolinium master alloy; The zinc and tin ingots are then subjected to a second smelting process to obtain a zinc-tin master alloy. The aluminum-gadolinium master alloy, zinc-tin master alloy, and zinc ingot are subjected to a third smelting process to obtain the dezincified alloy.

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available products in the field.

[0030] The present invention involves a first smelting of aluminum ingots and gadolinium ingots to obtain an aluminum-gadolinium master alloy.

[0031] In this invention, the purity of the aluminum ingot is preferably ≥99.7wt%, and the purity of the gadolinium ingot is preferably ≥99.5wt%.

[0032] Because gadolinium reacts readily with oxygen, nitrogen, and water vapor at high temperatures, and exposure to air can lead to severe oxidation and nitridation, this invention preferably places commercially available aluminum ingots and gadolinium ingots into a vacuum induction melting furnace, controlling the vacuum level inside the furnace to ≤1×10⁻⁶. -3 Expel air from the furnace and introduce high-purity argon gas (purity ≥ 99.999 vol%) into it. Adjust the pressure to be higher than atmospheric pressure (1.04~1.08 atm, specifically 1.04, 1.05, 1.06 or 1.08 atm). Then start the induction furnace to heat and carry out the first melting.

[0033] In this invention, the temperature of the first melting is preferably 750~800℃, specifically 750, 760, 770, 780, 790 or 800℃, and the time is preferably 30~60min, specifically 30, 35, 40, 45, 50, 55 or 60min.

[0034] After the first melting is completed, the resulting alloy liquid is preferably cast to obtain the aluminum-gadolinium master alloy.

[0035] In this invention, the mass percentage of gadolinium in the aluminum-gadolinium master alloy is preferably 9.0% to 11.5%, specifically 9.0%, 10.0%, or 11.1%.

[0036] The present invention involves a second smelting of zinc ingots and tin ingots to obtain a zinc-tin master alloy.

[0037] In this invention, the zinc ingot and tin ingot are preferably placed in a graphite crucible and heated to carry out the second smelting.

[0038] In this invention, the purity of the zinc ingot is preferably ≥99.99wt%, and the purity of the tin ingot is preferably ≥99.99wt%.

[0039] In this invention, the second melting temperature is preferably 500~550℃, specifically 500, 510, 520, 530, 540 or 550℃.

[0040] After the second smelting is completed, the present invention preferably stirs for 5 to 15 minutes (specifically 5, 8, 10, 11, 12, 13, 14 or 15 minutes), and then casts to obtain the zinc-tin master alloy.

[0041] In this invention, the mass percentage of tin in the zinc-tin master alloy is preferably 5% to 20%, specifically 5%, 10%, 15% or 20%.

[0042] After obtaining the aluminum-gadolinium master alloy and the zinc-tin master alloy, the present invention performs a third smelting of the aluminum-gadolinium master alloy, the zinc-tin master alloy and the zinc ingot to obtain the dezincified alloy.

[0043] In this invention, the aluminum-gadolinium master alloy, zinc-tin master alloy, and zinc ingot are preferably placed in a melting furnace and the third melting is carried out under argon protection.

[0044] In this invention, the purity of the zinc ingots during the third smelting is preferably ≥99.99wt%.

[0045] In this invention, aluminum ingots are preferably added during the third smelting process to make the mass percentage of aluminum in the dezincified alloy reach 7.0% to 10.0%.

[0046] In this invention, the temperature of the third melting is preferably 550~580℃, specifically 550, 560, 570 or 580℃.

[0047] After the third smelting is completed, the present invention preferably stirs for 10 to 20 minutes, specifically 10, 13, 15, 17, 19 or 20 minutes, to make the components evenly mixed, and then cast into an alloy ingot to obtain the zinc-free alloy.

[0048] The present invention also provides the application of the dezincification alloy described in the above technical solution or the dezincification alloy prepared by the preparation method described in the above technical solution in the field of hot-dip galvanizing.

[0049] In this invention, the application preferably includes the following steps: The mass percentages of bismuth (a) and aluminum (b) in the zinc plating solution were determined. After dissolving the zinc-removing alloy in the zinc plating solution, let it stand, then remove the scum, and then perform hot-dip galvanizing. Because higher aluminum content results in more pronounced zinc spangles, the amount of zinc spangle-removing alloy added is preferably adjusted according to the aluminum content in the zinc plating bath. The amount of zinc spangle-removing alloy added is determined by the following steps: When the mass percentage of aluminum is ≤0.04%, the amount of dezincification alloy added is 1000×a×c / d, where a is the mass percentage of bismuth, c is the weight of the zinc plating solution in tons, and d is the mass percentage of gadolinium in the dezincification alloy. When the mass percentage of aluminum is >0.04%, the amount of dezincification alloy added is 1200×a×c / d, where a is the mass percentage of bismuth, c is the weight of the zinc plating solution in tons, and d is the mass percentage of gadolinium in the dezincification alloy.

[0050] The present invention does not impose any particular limitation on the specific method for detecting the mass percentage of bismuth (a) and the mass percentage of aluminum (b) in the zinc plating solution; any method known to those skilled in the art can be used.

[0051] The present invention does not impose any special limitations on the composition of the zinc plating solution.

[0052] In this invention, the dezincification alloy is preferably pressed into the zinc plating liquid at a depth of 0.5 to 1.5 m below the surface of the zinc plating liquid (specifically, it can be 0.5, 1, 1.2 or 1.5 m) to allow the dezincification alloy to dissolve uniformly.

[0053] In this invention, the settling time is preferably 20-30 minutes, specifically 20, 25 or 30 minutes, and the temperature is preferably 440-443°C, specifically 440, 441, 442 or 443°C. During the settling process, the gadolinium in the dezincification alloy reacts with the bismuth in the zinc plating solution to generate gadolinium-bismuth compound, and the gadolinium-bismuth compound settles completely, thus achieving bismuth removal.

[0054] The present invention preferably removes the scum, which preferably includes zinc oxide. Removing the scum before galvanizing can ensure that the surface of the galvanized layer is bright and clean.

[0055] The present invention does not impose any special limitations on the specific parameters of the hot-dip galvanizing, and any method known to those skilled in the art can be used.

[0056] The present invention preferably involves daily, timed detection of the aluminum and bismuth content in the zinc plating solution, and bismuth removal according to the above method.

[0057] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0058] Example 1 A dezinc-speckled alloy was prepared, with the following mass percentages of elements: aluminum 8.0%, gadolinium 1.0%, tin 0.6%, and the remainder being zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 100.0 kg of aluminum ingot with a purity of 99.7 wt% and 12.5 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 5 × 10⁻⁶. -4 Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.05 atm. Induction heating was started, and melting was carried out at 800℃. After melting, the mixture was stirred and reacted for 35 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 11.1 wt% gadolinium. (2) Preparation of zinc-tin master alloy: Take 85 kg of zinc ingot with a purity of 99.99 wt% and 15 kg of tin ingot with a purity of 99.9 wt%, put them into a graphite crucible, heat to 500℃ to melt, stir for 15 min, and cast to obtain a zinc-tin master alloy containing 15 wt% tin. (3) Preparation of zinc-free alloy: Take 304.1 kg of zinc ingot with a purity of 99.99 wt%, 31.9 kg of aluminum-gadolinium master alloy (containing 3.5 kg of gadolinium), and 14.0 kg of zinc-tin master alloy (containing 2.1 kg of tin), put them into a melting furnace, purify with argon gas, heat to 550℃ to melt, stir for 15 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-8.0%Al-1.0%Gd-0.6%Sn.

[0059] A zinc plating bath in a galvanizing plant contained 0.03 wt% aluminum and 0.010 wt% bismuth, with noticeable zinc spangles. A zinc spangle-removing alloy (1000 × 0.010% / 1.0% × 1 = 10.0 kg) was added to 1 ton of this zinc plating bath. The alloy was then pressed 0.8 m below the surface of the zinc plating bath and moved, dissolving completely in 4 minutes. The solution was then held at 442℃ for 25 minutes, after which the scum was removed. After treatment, the bismuth content in the zinc plating bath was found to be 0.0025 wt%, no visible zinc spangles were observed on the surface of the galvanized workpiece, and the zinc plating layer thickness stabilized at 28.5 μm.

[0060] Example 2 A dezinc-speckled alloy was prepared, with the following mass percentages of elements: aluminum 10.0%, gadolinium 0.8%, tin 0.4%, and the remainder consisting of zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 91.0 kg of aluminum ingot with a purity of 99.7 wt% and 9.0 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 8 × 10⁻⁶. -4Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.06 atm. Induction heating was started, and melting was carried out at 750℃. After melting, the mixture was stirred and reacted for 60 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 9.0 wt% gadolinium. (2) Preparation of zinc-tin master alloy: Take 90 kg of zinc ingot with a purity of 99.99 wt% and 10 kg of tin ingot with a purity of 99.9 wt%, put them into a graphite crucible, heat to 520℃ to melt, stir for 8 min, and cast to obtain a zinc-tin master alloy containing 10 wt% tin. (3) Preparation of zinc-free alloy: Take 298.2 kg of zinc ingot with a purity of 99.99 wt%, 6.6 kg of aluminum ingot, 31.2 kg of aluminum-gadolinium master alloy (containing 2.81 kg of gadolinium), and 14.0 kg of zinc-tin master alloy (containing 1.4 kg of tin), put them into a melting furnace, purify with argon gas, heat to 580℃ to melt, stir for 13 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-10.0%Al-0.8%Gd-0.4%Sn.

[0061] The zinc plating solution in a galvanizing plant contained 0.08 wt% aluminum and 0.004 wt% bismuth, with noticeable zinc spangles. A zinc spangle-removing alloy (1200 × 0.004% / 0.8% × 1 = 6.0 kg) was added to 1 ton of this solution. The solution was then pressed 1.2 m below the surface and moved, dissolving completely in 3.5 minutes. After reacting at 441℃ for 20 minutes, the scum was removed. After treatment, the bismuth content in the zinc plating solution was found to be 0.0019 wt%, no visible zinc spangles were observed on the surface of the galvanized workpiece, and the zinc plating thickness stabilized at 26.3 μm.

[0062] Example 3 A dezinc-speckled alloy was prepared, with the following mass percentages of elements: aluminum 9.0%, gadolinium 1.0%, tin 0.5%, and the remainder being zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 90.0 kg of aluminum ingot with a purity of 99.7 wt% and 10.0 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 9 × 10⁻⁶. -4 Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.04 atm. Induction heating was started, and melting was carried out at 780℃. After melting, the mixture was stirred and reacted for 40 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 10.0 wt% gadolinium. (2) Preparation of zinc-tin master alloy: Take 80 kg of zinc ingot with a purity of 99.99 wt% and 20 kg of tin ingot with a purity of 99.9 wt%, put them into a graphite crucible, heat to 550℃ to melt, stir for 10 min, and cast to obtain a zinc-tin master alloy containing 20 wt% tin. (3) Preparation of zinc-free alloy: Take 306.25 kg of zinc ingot with a purity of 99.99 wt%, 35 kg of aluminum-gadolinium master alloy (containing 3.5 kg of gadolinium), and 8.75 kg of zinc-tin master alloy (containing 1.75 kg of tin), put them into a melting furnace, purify with argon gas, heat to 570℃ to melt, stir for 10 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-9.0%Al-1.0%Gd-0.5%Sn.

[0063] The zinc plating solution in a galvanizing plant contained 0.06 wt% aluminum and 0.004 wt% bismuth, with noticeable zinc spangles. A zinc spangle-removing alloy (1200 × 0.004% / 1.0% × 1 = 4.8 kg) was added to 1 ton of this solution. The solution was then pressed 1.5 m below the surface and moved, dissolving completely in 4.2 minutes. After reacting at 440℃ for 28 minutes, the scum was removed. After treatment, the bismuth content in the zinc plating solution was found to be 0.0021 wt%, no visible zinc spangles were observed on the surface of the galvanized workpiece, and the zinc plating thickness remained stable at 25.7 μm.

[0064] Example 4 A dezinc-speckled alloy was prepared, with the following mass percentages of elements: aluminum 7.0%, gadolinium 0.75%, tin 0.5%, and the remainder being zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 89.5 kg of aluminum ingot with a purity of 99.7 wt% and 10.5 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 7 × 10⁻⁶. -4 Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.05 atm. Induction heating was started, and melting was carried out at 790℃. After melting, the mixture was stirred and reacted for 30 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 10.5 wt% gadolinium. (2) Preparation of zinc-tin master alloy: Take 88 kg of zinc ingot with a purity of 99.99 wt% and 12 kg of tin ingot with a purity of 99.9 wt%, put them into a graphite crucible, heat to 530℃ to melt, stir for 8 min, and cast to obtain a zinc-tin master alloy containing 12 wt% tin. (3) Preparation of zinc-free alloy: Take 308.25 kg of zinc ingot with a purity of 99.99 wt%, 2.15 kg of aluminum ingot, 25 kg of aluminum-gadolinium master alloy (containing 2.63 kg of gadolinium), and 14.6 kg of zinc-tin master alloy (containing 1.75 kg of tin), put them into a melting furnace, purify with argon gas, heat to 550℃ to melt, stir for 20 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-7.0%Al-0.75%Gd-0.5%Sn.

[0065] The zinc plating solution in a galvanizing plant contained 0.035 wt% aluminum and 0.007 wt% bismuth, with noticeable zinc spangles. A zinc spangle-removing alloy (1000 × 0.007% / 0.75% × 1 = 9.33 kg) was added to 1 ton of this solution. The solution was then pressed 0.5 m below the surface and moved, dissolving completely in 3.2 minutes. After reacting at 443℃ for 24 minutes, the scum was removed. Testing showed that the bismuth content in the treated zinc plating solution was 0.0026 wt%, no visible zinc spangles were found on the surface of the galvanized workpiece, and the zinc coating thickness stabilized at 21.5 μm.

[0066] Example 5 A dezinc-speckled alloy was prepared, with the following mass percentages of elements: aluminum 9.6%, gadolinium 0.7%, tin 0.45%, and the remainder consisting of zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 90 kg of aluminum ingot with a purity of 99.7 wt% and 10 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 8 × 10⁻⁶. -4 Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.08 atm. Induction heating was started, and melting was carried out at 760℃. After melting, the mixture was stirred and reacted for 45 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 10.0 wt% gadolinium. (2) Preparation of zinc-tin master alloy: Take 95 kg of zinc ingot with a purity of 99.99 wt% and 5 kg of tin ingot with a purity of 99.9 wt%, put them into a graphite crucible, heat to 535℃ to melt, stir for 5 min, and cast to obtain a zinc-tin master alloy containing 5 wt% tin. (3) Preparation of zinc-free alloy: Take 282.3 kg of zinc ingot with a purity of 99.99 wt%, 11.6 kg of aluminum ingot, 24.5 kg of aluminum-gadolinium master alloy (containing 2.45 kg of gadolinium), and 31.6 kg of zinc-tin master alloy (containing 1.58 kg of tin), put them into a melting furnace, purify with argon gas, heat to 560℃ to melt, stir for 17 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-9.6%Al-0.7%Gd-0.45%Sn.

[0067] The zinc plating solution in a galvanizing plant contained 0.047 wt% aluminum and 0.0036 wt% bismuth, with noticeable zinc spangles. A zinc spangle-removing alloy (1200 × 0.0036% / 0.7% × 1 = 6.2 kg) was added to 1 ton of this solution. The solution was then pressed 1.0 m below the surface and moved, dissolving completely in 3 minutes. After reacting at 442℃ for 30 minutes, the scum was removed. After treatment, the bismuth content in the zinc plating solution was 0.0018 wt%, no visible zinc spangles were found on the surface of the galvanized workpiece, and the zinc plating thickness stabilized at 26.4 μm.

[0068] Comparative Example 1 Without adding the zinc spangle-removing alloy of this invention, the method of diluting bismuth by simply adding new zinc ingots was adopted. The initial aluminum content in the zinc plating solution was 0.04 wt%, and the bismuth content was 0.008 wt%. New zinc ingots were added each time, at a rate of 5% of the weight of the zinc plating solution in the zinc pot, once a day. After 10 consecutive days of replenishment, the bismuth content decreased to 0.0059 wt%, and the aluminum content in the zinc plating solution was maintained at 0.04 wt% by adding a zinc-aluminum alloy. The galvanized workpiece still had obvious zinc spangles on the surface, with a zinc plating layer thickness of 23.6 μm. After 20 consecutive days of replenishment, the bismuth content decreased to 0.0035 wt%, the zinc spangles basically disappeared, and the zinc plating layer thickness was 23.2 μm.

[0069] Comparative Example 2 An aluminum-10% gadolinium master alloy (containing 10 wt% gadolinium) was directly added to a zinc plating bath containing 0.05 wt% aluminum and 0.008 wt% bismuth. The addition amount was 1200 × 0.008% / 10% × 1 = 0.96 kg per ton of zinc plating bath. Due to the high melting point of this alloy and the low temperature of the zinc bath (only 440℃), the alloy melted extremely slowly in the zinc bath. The alloy ingot was pressed 1.0 m below the surface of the zinc bath and moved back and forth along the length of the zinc pot. After 30 minutes, a portion of the alloy remained undissolved. The alloy was continued to be moved until it was completely dissolved after 46 minutes. After standing and holding the reaction at the same temperature for 30 minutes, the surface dross was removed. The bismuth content in the zinc bath was measured to be 0.0075 wt%, and there was no change in the zinc bloom on the surface of the galvanized workpiece. The zinc plating layer thickness was 24.1 μm.

[0070] Comparative Example 3 A de-galvanized alloy was prepared, with the following mass percentages of elements: aluminum 15.0%, gadolinium 1.67%, tin 0.45%, and the remainder being zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 90 kg of aluminum ingot with a purity of 99.7 wt% and 10 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 8 × 10⁻⁶. -4 Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.08 atm. Induction heating was started, and melting was carried out at 760℃. After melting, the mixture was stirred and reacted for 45 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 10.0 wt% gadolinium. (2) Preparation of zinc-tin master alloy: Take 95 kg of zinc ingot with a purity of 99.99 wt% and 5 kg of tin ingot with a purity of 99.9 wt%, put them into a graphite crucible, heat to 535℃ to melt, stir for 5 min, and cast to obtain a zinc-tin master alloy containing 5 wt% tin. (3) Preparation of zinc-free alloy: Take 260.1 kg of zinc ingot with a purity of 99.99 wt%, 58.3 kg of aluminum-gadolinium master alloy (containing 5.83 kg of gadolinium), and 31.6 kg of zinc-tin master alloy (containing 1.58 kg of tin), put them into a melting furnace, purify with argon gas, heat to 560℃ to melt, stir for 18 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-15.0%Al-1.67%Gd-0.45%Sn.

[0071] The zinc plating solution in a galvanizing plant contained 0.047 wt% aluminum and 0.006 wt% bismuth, with noticeable zinc spangles. A zinc spangle removal alloy (1200 × 0.006% / 1.67% × 1 = 4.3 kg) was added to 1 ton of this solution. The alloy was then pressed 1.0 m below the surface of the solution and moved, dissolving completely in 9.5 minutes. After reacting at 442℃ for 30 minutes, the scum was removed. Testing revealed that the bismuth content in the treated zinc plating solution was 0.0039 wt%, and zinc spangles remained on the surface of the galvanized workpieces, failing to achieve the intended zinc spangle removal.

[0072] Comparative Example 4 A dezinc-speckled alloy was prepared, with the following mass percentages of elements: aluminum 8.0%, gadolinium 0.88%, tin 0%, and the remainder consisting of zinc and unavoidable impurities (total content ≤0.01%). The preparation method is as follows: (1) Preparation of aluminum-gadolinium master alloy: Take 90 kg of aluminum ingot with a purity of 99.7 wt% and 10 kg of gadolinium ingot with a purity of 99.5 wt%, put them into a vacuum induction furnace, and evacuate the furnace to a vacuum degree of 8 × 10⁻⁶. -4 Air was removed from the furnace, and then high-purity argon gas was introduced into the furnace, adjusting the furnace pressure to 1.08 atm. Induction heating was started, and melting was carried out at 760℃. After melting, the mixture was stirred and reacted for 45 minutes, and then cast to obtain an aluminum-gadolinium master alloy containing 10.0 wt% gadolinium. (2) Preparation of zinc-free alloy: Take 318.9 kg of zinc ingot with a purity of 99.99 wt% and 31.1 kg of aluminum-gadolinium master alloy (containing 3.11 kg of gadolinium), put them into a melting furnace, purify with argon gas, heat to 560℃ to melt, stir for 18 min, and cast into ingots to obtain the target alloy with the alloy composition of Zn-8.0%Al-0.88%Gd.

[0073] A zinc plating bath in a galvanizing plant contained 0.06 wt% aluminum and 0.007 wt% bismuth, with noticeable zinc spangles present. A zinc spangle removal alloy (1200 × 0.007% / 0.88% × 1 = 9.5 kg) was added to 1 ton of this zinc plating bath. The alloy was then pressed 1.0 m below the surface of the zinc plating bath and moved, dissolving completely in 3 minutes. The solution was then kept at 442℃ for 30 minutes, after which the scum was removed. After treatment, the bismuth content in the zinc plating bath was found to be 0.0027 wt%, and zinc spangles remained on the surface of the galvanized workpieces, indicating that the zinc spangle removal was not achieved.

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A zinc-removing alloy, characterized in that, It includes the following elements by mass percentage: aluminum 7.0%~10.0%, gadolinium 0.7%~1.0%, tin 0.4%~0.6%, with the remainder being zinc and unavoidable impurities.

2. The zinc-removing alloy according to claim 1, characterized in that, The mass percentage of aluminum is 8.0% to 9.0%.

3. The zinc-removing alloy according to claim 1, characterized in that, The gadolinium has a mass percentage of 0.75% to 0.8%.

4. The zinc-removing alloy according to claim 1, characterized in that, The tin content is 0.45% to 0.5% by mass.

5. The zinc-removing alloy according to claim 1, characterized in that, The mass percentage of the impurities does not exceed 0.01%.

6. The method for preparing the zinc-free alloy according to any one of claims 1 to 5, characterized in that, Includes the following steps: Aluminum ingots and gadolinium ingots are first smelted to obtain an aluminum-gadolinium master alloy; The zinc and tin ingots are then subjected to a second smelting process to obtain a zinc-tin master alloy. The aluminum-gadolinium master alloy, zinc-tin master alloy, and zinc ingot are subjected to a third smelting process to obtain the dezincified alloy.

7. The preparation method according to claim 6, characterized in that, The mass percentage of gadolinium in the aluminum-gadolinium master alloy is 9.0% to 11.0%.

8. The preparation method according to claim 6, characterized in that, The zinc-tin master alloy contains 5% to 20% tin by mass.

9. The application of the dezincification alloy according to any one of claims 1 to 5 or the dezincification alloy prepared by the preparation method according to any one of claims 6 to 8 in the field of hot-dip galvanizing.

10. The application according to claim 9, characterized in that, Includes the following steps: The mass percentages of bismuth and aluminum in the zinc plating solution were determined. After dissolving the zinc-removing alloy in the zinc plating solution, let it stand, then remove the scum, and then perform hot-dip galvanizing. The amount of zinc-removing alloy added is determined by the following steps: When the mass percentage of aluminum is ≤0.04%, the amount of dezincification alloy added is 1000×a×c / d, where a is the mass percentage of bismuth, c is the weight of the zinc plating solution in tons, and d is the mass percentage of gadolinium in the dezincification alloy. When the mass percentage of aluminum is >0.04%, the amount of dezincification alloy added is 1200×a×c / d, where a is the mass percentage of bismuth, c is the weight of the zinc plating solution in tons, and d is the mass percentage of gadolinium in the dezincification alloy.

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