High-corrosion-resistance hot-dip galvanized steel coating and preparation method thereof

Abstract

The invention relates to the technical field of hot-dip galvanized steel manufacturing, in particular to a high-corrosion-resistance hot-dip galvanized steel coating and a preparation method thereof. The coating comprises a Zn-Al-Mg matrix and doping elements, the doping elements are Ni and rare earth elements, and the rare earth elements are La, Ce and Sc. The Zn-Al-Mg-Ni alloy is composed of 5.0%-7.0% of Al, 2.5%-3.5% of Mg, 0.4%-0.6% of Ni, 0.03%-0.06% of La, 0.03%-0.06% of Ce, 0.01%-0.02% of Sc and the balance Zn. The plating layer is thinned by Ni, and the compactness is improved; the rare earth elements hinder zinc liquid oxidation. Trace nickel and rare earth elements are added to Zn-Al-Mg, and the compactness and corrosion resistance of a plating layer are improved through the synergistic effect of inhibiting permeation of a corrosive medium and promoting formation of a passive film. And the obtained plating layer has excellent corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot-dip galvanized steel manufacturing, in particular to a high-corrosion-resistant hot-dip galvanized steel coating and a preparation method thereof. BACKGROUND

[0002] Hot-dip galvanizing is an effective method to improve the corrosion resistance of steel materials and prolong their service life. After pretreatment processes such as rust removal, cleaning, and plating aid, the steel products are immersed in liquid zinc for a certain period of time, and a beautiful and well-protected zinc layer is formed on the surface of the steel material through iron-zinc reaction and diffusion. The zinc layer has good adhesion and compactness, which can effectively improve the corrosion resistance of steel. The hot-dip galvanized coating combines physical barrier protection with electrochemical protection, which can significantly improve the service life of steel.

[0003] The corrosion resistance of the coating is always an important problem, which mainly depends on the composition of the coating, the method of hot-dip plating, and the process conditions. Good corrosion resistance can only be achieved by combining composition control and advanced hot-dip plating technology. With the expansion of the application field of hot-dip galvanizing, the traditional pure zinc coating cannot meet the performance requirements of the coating, and adding alloying elements to the coating is one of the effective means to improve its corrosion resistance. The composition of the coating is a key factor affecting the corrosion resistance of the steel plate, so the composition design of the coating has become a focus. Currently, there are two main compositions of hot-dip galvanized coatings in wide commercial use: Zn-Al and Zn-Al-Mg. The Zn-Al-Mg coating is a widely used coating system, and the ternary eutectic structure produced by the addition of Mg has excellent corrosion resistance. However, with the increasing complexity of steel service conditions, users have higher requirements for the corrosion resistance of steel plates. Therefore, the current problem is that the poor corrosion resistance of steel plates leads to resource waste and safety hazards caused by corrosion of steel. SUMMARY

[0004] To solve the above problems, the present application provides a high-corrosion-resistant hot-dip galvanized steel coating and a preparation method thereof. The coating includes a Zn-Al-Mg matrix and a doping element, the doping element is Ni and a rare earth element, the rare earth element is La, Ce and Sc, and the coating is composed of the following components by mass percentage: Al: 5.0%~7.0%; Mg: 2.5%~3.5%; Ni: 0.4%~0.6%; La: 0.03%~0.06%; Ce: 0.03%~0.06%; Sc: 0.01%~0.02%; and the rest is Zn, totaling 100%. The present application adds a small amount of nickel and rare earth elements to the Zn-Al-Mg coating. Through the synergistic effect of nickel and rare earth elements in inhibiting the penetration of corrosive media and promoting the formation of passivation film, the coating density is improved, thereby significantly improving the corrosion resistance of the coating.

[0005] To achieve the above object, the present application adopts the following technical solutions: The present application aims to provide a high corrosion-resistant hot-dip galvanized steel coating, which comprises a Zn-Al-Mg matrix and doping elements, the doping elements being Ni and rare earth elements, the rare earth elements being La, Ce and Sc; the coating is composed of the following components in mass percentage: Al: 5.0%-7.0%; Mg: 2.5%-3.5%; Ni: 0.4%-0.6%; rare earth elements: 0.07%-0.14%, the rest being Zn, and the total being 100%.

[0006] In a preferred embodiment of the present application, the mass percentage of La in the coating is 0.03%-0.06%, the mass percentage of Ce in the coating is 0.03%-0.06%, and the mass percentage of Sc in the coating is 0.01%-0.02%.

[0007] In a preferred embodiment of the present application, the mass percentage of the doping elements in the coating is 0.52%-0.58%.

[0008] In a preferred embodiment of the present application, the mass percentage of the rare earth elements in the coating is 0.08%-0.12%.

[0009] Another object of the present application is to provide a preparation method of the above high corrosion-resistant hot-dip galvanized steel coating, comprising the following steps: hot-dip galvanizing the surface of the cold-rolled steel sheet to form a hot-dip galvanized coating on the surface of the cold-rolled steel sheet, thereby obtaining the high corrosion-resistant hot-dip galvanized steel coating.

[0010] In a preferred embodiment of the present application, the temperature for hot-dip galvanizing is 460-470℃, and the time is 15-25s.

[0011] In a preferred embodiment of the present application, the steel sheet after hot-dip galvanizing needs to be cooled at a cooling speed of 1-5℃ / s to a room temperature. In a preferred embodiment of the present application, the preparation method of the cold-rolled steel sheet comprises the following steps: smelting and casting a steel base material to obtain a forged blank; heating and holding the forged blank for hot continuous rolling to obtain a hot-rolled steel sheet; and cooling the hot-rolled steel sheet and then performing cold continuous rolling to obtain the cold-rolled steel sheet.

[0012] In a preferred embodiment of the present application, the heating temperature of the forged blank is 1200-1250℃, and the holding time is 50-80min.

[0013] In the preferred embodiment of the present application, the hot continuous rolling adopts a two-stage controlled rolling method, which is divided into rough rolling and finish rolling; the rough rolling has a rough rolling starting temperature of 1100-1150 DEG C and a rough rolling final rolling temperature of 1000-1050 DEG C; the finish rolling has a finish rolling starting temperature of 900-950 DEG C and a finish rolling final rolling temperature of 850-880 DEG C; and the specific process of cooling the hot-rolled steel plate is first cooled to 600-650 DEG C at a cooling speed of 20-30 DEG C / s, and then cooled to room temperature at a cooling speed of 10-15 DEG C / s.

[0014] Compared with the prior art, the present application has the beneficial effects that: 1. The high corrosion-resistant hot-dip galvanized steel coating provided by the present application comprises a Zn-Al-Mg base and doping elements, the doping elements are Ni and rare earth elements, and the rare earth elements are La, Ce and Sc; the coating is composed of the following components in mass percentage: Al: 5.0-7.0%; Mg: 2.5-3.5%; Ni: 0.4-0.6%; rare earth elements: 0.07-0.14%, and the rest is Zn, with a total of 100%. The Ni thins the coating, makes the coating denser, and eliminates the abnormal growth tendency of ζ-FeZn 13 phase. The rare earth elements form oxides to hinder the oxidation and evaporation of the zinc liquid, reduce the viscosity of the zinc liquid to reduce the amount of zinc used, and improve the appearance, density and processing performance of the coating. The core improvement of the present application is that trace amounts of nickel and rare earth elements are added to the traditional Zn-Al-Mg coating at the same time, the synergistic effect of the two is utilized to improve the coating density, thin the coating thickness, and significantly improve the corrosion resistance of the coating. The synergistic effect of the two is reflected in: first, the penetration of the corrosion medium is inhibited: the addition of nickel improves the electrode potential of the coating, forming a synergistic effect of "sacrificial anode-cathode protection"; at the same time, after the formation of a solid solution of nickel and zinc, the grain boundary defects such as vacancies and dislocations of the coating are reduced, and the diffusion channel of the corrosion medium is reduced. The rare earth elements improve the coating density by refining the grains and purifying the inclusions, and prevent the penetration of the corrosion medium into the substrate. Second, the formation of the passivation film is promoted: the rare earth elements are easily adsorbed on the surface of the coating during corrosion, and combined with the corrosion products to form a stable composite passivation film (containing rare earth oxides / hydroxides), which is dense and has strong adhesion, and can delay the dissolution rate of zinc. Nickel can enhance the conductivity of the passivation film, and avoid the concentrated occurrence of local corrosion.

[0015] 2. The preparation method of the high corrosion-resistant hot-dip galvanized steel coating provided by the present application, by the coating of different chemical components, reasonable control of the zinc plating temperature, zinc plating time and cooling speed, the corrosion resistance is improved, and the average corrosion rate of the obtained hot-dip galvanized steel coating is 0.021 g / h·m 2 , which has excellent corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1SEM morphology of the cross section of the zinc layer of Example 1 of the present application.

[0017] Figure 2 SEM morphology of the cross section of the zinc layer of Example 1 of the present application. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be apparently and completely described in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the present application.

[0019] It should be noted that the professional terms used in the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the protection scope of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present application can be purchased from the market or prepared by the existing method.

[0020] The main components of the widely used hot-dip galvanized coating are Zn-Al and Zn-Al-Mg. The Zn-Al-Mg coating is a widely used coating system, and the ternary eutectic structure produced by the addition of Mg has excellent corrosion resistance. However, with the complication of the service conditions of steel materials, users have higher requirements for the corrosion resistance of steel plates. Therefore, improving the corrosion resistance of steel plates and improving the resource waste and safety hazards caused by corrosion of steel are the current problems. Based on this, the present application uses a coating with different chemical components, controls the galvanizing process at the same time, and uses the synergistic effect of nickel and rare earth elements to improve the corrosion resistance of the coating, and prepares a hot-dip galvanized steel with excellent performance.

[0021] In one aspect, the present application provides a high-corrosion-resistant hot-dip galvanized steel coating, the coating comprising a Zn-Al-Mg base and a doping element, the doping element being Ni and a rare earth element, the rare earth element being La, Ce and Sc; the coating being composed of the following components in mass percentage: Al: 5.0%~7.0%; Mg: 2.5%~3.5%; Ni: 0.4%~0.6%; rare earth element: 0.07%~0.14%, the rest being Zn, and the total being 100%.

[0022] The mass percentage of La in the coating is 0.03%~0.06%, the mass percentage of Ce in the coating is 0.03%~0.06%, and the mass percentage of Sc in the coating is 0.01%~0.02%.

[0023] It should be noted that the reason for adopting the above range for the chemical composition of the hot-dip galvanized steel coating is as follows: (1) Aluminum: Aluminum is the most common alloying element in hot-dip galvanizing. If there is Al in the zinc liquid, Fe in the steel substrate will react with Al first, and a layer of Fe-Al intermetallic compound will be formed on the surface of the coating, which will inhibit the diffusion and reaction of Zn and hinder the formation of Fe-Zn compound layer, thereby reducing the coating thickness, improving the coating quality and improving the adhesion of the coating. The Fe-Al compound layer exhibits high corrosion resistance in electrochemical corrosion, which can improve the corrosion resistance of the coating to some extent. In addition, the addition of Al will form an Al203 passivation film on the surface of the coating, which has a passivation protection effect. However, a high Al content will increase the hot-dip plating temperature to 600°C, causing resource waste and reducing the processing performance, welding performance and cathodic protection ability of the steel plate.

[0024] (2) Magnesium: Adding an appropriate amount of magnesium to the zinc plating liquid can significantly improve the corrosion resistance of the coating and eliminate the adverse effects of lead in the zinc liquid. Mg has a significant refining effect on alloy coatings and can effectively inhibit the occurrence of intergranular corrosion. However, when the Mg content is too high, the viscosity of the zinc liquid will increase significantly, causing the wettability of the zinc liquid to the steel substrate to decrease. In addition, high Mg content coatings will produce primary MgZn2 brittle phases after solidification, making the coating surface turn white and brittle, and reducing the adhesion of the coating.

[0025] (3) Nickel: The addition of Ni can significantly thin the coating and make the coating structure more dense, which can effectively eliminate the abnormal growth tendency of ζ-FeZn 13 phase. However, Ni is a valuable element, and excessive addition will significantly increase the use cost.

[0026] (4) Rare earth (La, Ce, Sc): On the one hand, rare earth elements are active elements and are easily oxidized. The addition of rare earth elements to the zinc liquid can form rare earth oxide and accumulate on the surface of the zinc liquid, which can hinder the contact between the zinc liquid and the air, reduce the oxidation and evaporation of zinc, and reduce the amount of zinc left on the surface of the plated part, thereby reducing the production cost of hot-dip galvanizing. In addition, the addition of rare earth elements can increase the surface gloss and machining performance of the hot-dip galvanized layer, prolong the service life of the coating, reduce the coating thickness, and improve the appearance quality and density of the coating to some extent. However, excessive addition will reduce the corrosion resistance and increase the use cost.

[0027] The doping element constitutes 0.52% to 0.58% of the coating by mass. Hot-dip galvanized steel coatings utilize the synergistic effect of rare earth elements and nickel to improve coating density and corrosion resistance. Specifically, this is achieved in two ways: First, it inhibits the penetration of corrosive media: the addition of nickel increases the electrode potential of the coating, creating a synergistic effect of "sacrificial anode-cathode protection." Simultaneously, the formation of a solid solution between nickel and zinc reduces grain boundary defects such as vacancies and dislocations in the coating, lowering the diffusion channels for corrosive media (such as Cl⁻). Rare earth elements further improve coating density by refining grains and purifying inclusions (reducing oxide / sulfide porosity), preventing corrosive media from penetrating the substrate. Second, it promotes the formation of a passivation film: rare earth elements readily adsorb onto the coating surface during corrosion, combining with corrosion products to form a stable composite passivation film (containing rare earth oxides / hydroxides). This film is dense and has strong adhesion, significantly slowing down the zinc dissolution rate. The presence of nickel enhances the conductivity of the passivation film, preventing the concentrated occurrence of localized corrosion. In specific embodiments, the coating exhibits optimal corrosion resistance when the combined amount of rare earth elements and nickel is 0.52% to 0.58%.

[0028] The mass percentage of rare earth elements in the hot-dip galvanized steel coating is 0.08%~0.12%.

[0029] On the other hand, the present invention provides a method for preparing a high corrosion-resistant hot-dip galvanized steel coating, comprising the following steps: S1. The steel substrate is smelted and cast to obtain a forging billet.

[0030] S2. The forging billet is heated and held at a certain temperature to remove the iron oxide scale, and then hot-rolled to obtain a hot-rolled steel plate.

[0031] S3. After cooling the hot-rolled steel sheet, cold rolling is performed to obtain a cold-rolled steel sheet.

[0032] S4. After cleaning and annealing the cold-rolled steel sheet, hot-dip galvanize it to form a hot-dip galvanized coating on the surface of the cold-rolled steel sheet, thus obtaining the hot-dip galvanized steel sheet.

[0033] S5. Flatten the hot-dip galvanized steel sheet to obtain a high corrosion-resistant hot-dip galvanized steel coating.

[0034] In a preferred embodiment of the present invention, the heating temperature of the forging billet is 1200℃~1250℃, and the holding time is 50min~80min; the forging billet is composed of the following components by mass percentage: C: 0.05%~0.10%; Si: 0.25%~0.30%; Mn: 1.0%~1.5%; Ti: 0.12%~0.18%; Nb: 0.02%~0.04%; S≤0.005%; P≤0.015%; the remainder is iron and unavoidable impurities, totaling 100%.

[0035] In a preferred embodiment of the present invention, hot continuous rolling adopts a two-stage controlled rolling method, which is divided into roughing rolling and finishing rolling; the initial rolling temperature of roughing rolling is 1100℃~1150℃, and the final rolling temperature of roughing rolling is 1000℃~1050℃; the initial rolling temperature of finishing rolling is 900℃~950℃, and the final rolling temperature of finishing rolling is 850℃~880℃.

[0036] In a preferred embodiment of the present invention, the specific process of cooling the hot-rolled steel plate is to first cool it to 600°C to 650°C at a cooling rate of 20°C to 30°C / s, and then cool it to room temperature at a cooling rate of 10°C / h to 15°C / h.

[0037] In a preferred embodiment of the present invention, cold continuous rolling requires 5 passes.

[0038] In a preferred embodiment of the present invention, the hot-dip galvanizing temperature is 460℃~470℃. The galvanizing temperature is a core parameter for controlling the fluidity of the zinc bath, the growth of alloy phases, and the adhesion of the coating: If the temperature is too low: the viscosity of the zinc bath increases, the fluidity decreases, and the wettability to the steel substrate deteriorates, easily leading to defects such as incomplete coating and pinholes, resulting in discontinuous coatings and reduced corrosion resistance. Simultaneously, the diffusion reaction between zinc and the iron substrate is slow, and the formation of alloy phases (such as δ-phase and Γ-phase) is insufficient, resulting in weak adhesion between the coating and the substrate, making it prone to peeling. If the temperature is too high: the surface tension of the zinc bath decreases. Although the fluidity increases, the solubility of iron in the zinc bath increases significantly, leading to excessive growth of the zinc-iron alloy phase, uneven coating thickness, increased brittleness, and easy cracking. Furthermore, high temperatures accelerate the oxidation of the zinc bath, generating more zinc dross, which forms pores in the coating, becoming channels for corrosive media penetration and reducing corrosion resistance.

[0039] In a preferred embodiment of the present invention, the hot-dip galvanizing time is 15s to 25s. The galvanizing time determines the thickness and distribution of the zinc-iron alloy phase. If the time is too short: the reaction between the zinc liquid and the substrate is insufficient, the alloy phase is too thin, and the coating is mainly composed of pure zinc. Although it has good toughness, its adhesion to the substrate is weak, making it prone to detachment due to mechanical action. Simultaneously, the corrosion resistance of the pure zinc layer is limited, making it difficult to meet high corrosion resistance requirements. If the time is too long: excessive zinc-iron diffusion occurs, the alloy phase continues to thicken, and coarse columnar crystals may appear, leading to increased coating brittleness and easy cracking upon bending or impact. Furthermore, an excessively thick alloy phase reduces the efficiency of the coating's "sacrificial anode protection" of the substrate, increasing the risk of localized corrosion.

[0040] In a preferred embodiment of the present invention, the single-sided zinc layer weight of the hot-dip galvanized steel is 70 g / m². 2 ~90g / m 2 .

[0041] In a preferred embodiment of the present application, the hot galvanized steel plate needs to be cooled, and the cooling speed is 1-5℃ / s, and the cooling temperature is room temperature. The cooling speed affects the grain structure and stress state of the coating: if the cooling is too slow, the coating grains have sufficient time to grow, and coarse zinc-based solid solution or alloy phase is easily formed, the grain boundary defects increase, and the corrosion medium easily penetrates along the grain boundary; at the same time, the stress accumulated due to the difference in thermal expansion between the coating and the substrate increases the risk of coating cracking. If the cooling is too fast, although the grains can be refined, the internal stress of the coating is too large, which may cause micro-cracks; in addition, if the cooling medium directly contacts the high-temperature coating, the coating may peel off due to the large local temperature difference, destroying the continuity.

[0042] The present application provides a preparation method of a high-corrosion-resistant hot galvanized steel coating, which improves the corrosion resistance by using coatings with different chemical compositions and reasonably controlling the galvanizing temperature, galvanizing time and cooling speed. The average corrosion rate of the obtained hot galvanized steel coating is 0.021g / h·m 2 , and the coating has excellent corrosion resistance.

[0043] The present application is further illustrated by specific examples.

[0044] Example 1 A high-corrosion-resistant hot galvanized steel coating, which is composed of the following components in mass percentage: Al: 6.0%; Mg: 3.0%; Ni: 0.5%; La: 0.03%; Ce: 0.03%; Sc: 0.02%; and the rest is Zn, totaling 100%. The sum of the mass percentages of Ni, La, Ce and Sc is 0.58%; and the sum of the mass percentages of La, Ce and Sc is 0.08%.

[0045] The preparation method of the above high-corrosion-resistant hot galvanized steel coating comprises the following steps: S1, smelting and casting a steel base material to obtain a forged blank.

[0046] S2, heating the forged blank at 1250℃ and holding for 60min, removing the iron oxide scale, and then performing hot continuous rolling, i.e. first performing rough rolling, the rough rolling opening temperature is 1100℃, the final rolling temperature is 1000℃, then performing finish rolling, the finish rolling opening temperature is 900℃, the final rolling temperature is 850℃, then cooling the hot-rolled steel plate to 650℃ at a speed of 20℃ / s, and then cooling to room temperature at a speed of 10℃ / s, to obtain a cooled hot-rolled steel plate.

[0047] S3, cold continuous rolling the cooled hot-rolled steel plate, and performing 5 passes of cold continuous rolling to obtain a cold-rolled steel plate.

[0048] S4, after the cold-rolled steel plate is cleaned and annealed, hot galvanizing is carried out at 470 DEG C for 20s, so that a hot galvanizing coating layer is formed on the surface of the cold-rolled steel plate, and a steel plate after hot galvanizing is obtained.

[0049] S5, after the steel plate after hot galvanizing is cooled to room temperature at a speed of 5 DEG C / s, leveling is carried out, and a high-corrosion-resistant hot galvanizing steel coating layer is obtained.

[0050] Embodiment 2 A high-corrosion-resistant hot galvanizing steel coating layer, which is composed of the following components in percentage by mass: Al: 6.0%; Mg: 3.0%; Ni: 0.45%; La: 0.05%; Ce: 0.04%; Sc: 0.01%; and the rest is Zn, totaling 100%. Among them, the sum of the percentages by mass of Ni, La, Ce and Sc is 0.55%; and the sum of the percentages by mass of La, Ce and Sc is 0.10%.

[0051] The preparation method of the above high-corrosion-resistant hot galvanizing steel coating layer, comprising the following steps: S1, a steel material base material is smelted and cast, and a forged blank is obtained.

[0052] S2, the forged blank is heated at 1250 DEG C and kept for 60 min, after the iron oxide scale is removed, hot continuous rolling is carried out, that is, rough rolling is carried out first, the rough rolling opening rolling temperature is 1100 DEG C, and the final rolling temperature is 1000 DEG C, then finish rolling is carried out, the finish rolling opening rolling temperature is 900 DEG C, and the final rolling temperature is 850 DEG C, then the hot-rolled steel plate is cooled to 650 DEG C at a speed of 20 DEG C / s, and then cooled to room temperature at a speed of 10 DEG C / s, and a cooled hot-rolled steel plate is obtained.

[0053] S3, the cooled hot-rolled steel plate is cold continuous rolled for 5 passes, and a cold-rolled steel plate is obtained.

[0054] S4, after the cold-rolled steel plate is cleaned and annealed, hot galvanizing is carried out at 470 DEG C for 20s, so that a hot galvanizing coating layer is formed on the surface of the cold-rolled steel plate, and a steel plate after hot galvanizing is obtained.

[0055] S5, after the steel plate after hot galvanizing is cooled to room temperature at a speed of 5 DEG C / s, leveling is carried out, and a high-corrosion-resistant hot galvanizing steel coating layer is obtained.

[0056] Embodiment 3 A high-corrosion-resistant hot galvanizing steel coating layer, which is composed of the following components in percentage by mass: Al: 6.0%; Mg: 3.0%; Ni: 0.46%; La: 0.06%; Ce: 0.04%; Sc: 0.02%; and the rest is Zn, totaling 100%. Among them, the sum of the percentages by mass of Ni, La, Ce and Sc is 0.58%; and the sum of the percentages by mass of La, Ce and Sc is 0.12%.

[0057] The preparation method of the high corrosion-resistant hot-dip galvanized steel coating comprises the following steps: S1, smelting and casting a steel base material to obtain a forged blank.

[0058] S2, heating and holding the forged blank at 1250 DEG C for 70 min, removing the iron oxide scale, and then performing hot continuous rolling, i.e., first performing rough rolling with a rough rolling starting temperature of 1100 DEG C and a final rolling temperature of 1000 DEG C, then performing finish rolling with a finish rolling starting temperature of 950 DEG C and a final rolling temperature of 850 DEG C, and then cooling the hot-rolled steel plate to 650 DEG C at a speed of 20 DEG C / s and then to room temperature at a speed of 20 DEG C / s to obtain a cooled hot-rolled steel plate.

[0059] S3, performing cold continuous rolling on the cooled hot-rolled steel plate to obtain a cold-rolled steel plate.

[0060] S4, cleaning and annealing the cold-rolled steel plate, and then performing hot-dip galvanizing at 470 DEG C for 20 s to form a hot-dip galvanized coating on the surface of the cold-rolled steel plate to obtain a hot-dip galvanized steel plate.

[0061] S5, cooling the hot-dip galvanized steel plate to room temperature at a speed of 5 DEG C / s, and then performing skin pass rolling to obtain a high corrosion-resistant hot-dip galvanized steel coating.

[0062] Comparative Example 1 A high corrosion-resistant hot-dip galvanized steel coating, which is composed of the following components in mass percentage: Al: 6.0%; Mg: 3.0%; Ni: 0.6%; La: 0.08%; Ce: 0.08%; Sc: 0.04%; and the rest is Zn, with the total being 100%. The sum of the mass percentages of Ni, La, Ce and Sc is 0.80%; and the sum of the mass percentages of La, Ce and Sc is 0.20%.

[0063] The preparation method of the high corrosion-resistant hot-dip galvanized steel coating comprises the following steps: S1, smelting and casting a steel base material to obtain a forged blank.

[0064] S2, heating and holding the forged blank at 1250 DEG C for 80 min, removing the iron oxide scale, and then performing hot continuous rolling, i.e., first performing rough rolling with a rough rolling starting temperature of 1150 DEG C and a final rolling temperature of 1050 DEG C, then performing finish rolling with a finish rolling starting temperature of 950 DEG C and a final rolling temperature of 880 DEG C, and then cooling the hot-rolled steel plate to 650 DEG C at a speed of 20 DEG C / s and then to room temperature at a speed of 10 DEG C / s to obtain a cooled hot-rolled steel plate.

[0065] S3, performing cold continuous rolling on the cooled hot-rolled steel plate to obtain a cold-rolled steel plate.

[0066] S4. After cleaning and annealing the cold-rolled steel sheet, hot-dip galvanize it at 470℃ for 20 seconds to form a hot-dip galvanized coating on the surface of the cold-rolled steel sheet, thus obtaining the hot-dip galvanized steel sheet.

[0067] S5. After the hot-dip galvanized steel sheet is cooled to room temperature at a rate of 5℃ / s, it is flattened to obtain a high corrosion-resistant hot-dip galvanized steel coating.

[0068] Comparative Example 2 A high corrosion-resistant hot-dip galvanized steel coating is composed of the following components by mass percentage: Al: 6.0%; Mg: 3.0%; Ni: 0.4%; La: 0.02%; Ce: 0.02%; Sc: 0.02%; with the remainder being Zn, totaling 100%. The sum of the mass percentages of Ni, La, Ce, and Sc is 0.46%; and the sum of the mass percentages of La, Ce, and Sc is 0.06%.

[0069] The method for preparing the above-mentioned high corrosion-resistant hot-dip galvanized steel coating includes the following steps: S1. The steel substrate is smelted and cast to obtain a forging billet.

[0070] S2. The forging billet is heated at 1250℃ and held for 80 minutes to remove the iron oxide scale. Then, it is hot continuous rolling, that is, rough rolling is performed first, with a rough rolling start temperature of 1150℃ and a finish rolling temperature of 1050℃. Then, finish rolling is performed, with a finish rolling start temperature of 950℃ and a finish rolling temperature of 880℃. The hot-rolled steel plate is then cooled to 650℃ at a rate of 20℃ / s, and then cooled to room temperature at a rate of 10℃ / s to obtain the cooled hot-rolled steel plate.

[0071] S3. The cooled hot-rolled steel sheet is subjected to cold continuous rolling for 5 passes to obtain a cold-rolled steel sheet.

[0072] S4. After cleaning and annealing the cold-rolled steel sheet, hot-dip galvanize it at 470℃ for 20 seconds to form a hot-dip galvanized coating on the surface of the cold-rolled steel sheet, thus obtaining the hot-dip galvanized steel sheet.

[0073] S5. After the hot-dip galvanized steel sheet is cooled to room temperature at a rate of 5℃ / s, it is flattened to obtain a high corrosion-resistant hot-dip galvanized steel coating.

[0074] Comparative Example 3 A high corrosion-resistant hot-dip galvanized steel coating is composed of the following components by mass percentage: Al: 6.0%; Mg: 3.0%; Ni: 0.3%; La: 0.04%; Ce: 0.04%; Sc: 0.02%; with the remainder being Zn, totaling 100%. The sum of the mass percentages of Ni, La, Ce, and Sc is 0.40%; and the sum of the mass percentages of La, Ce, and Sc is 0.10%.

[0075] The method for preparing the above-mentioned high corrosion-resistant hot-dip galvanized steel coating includes the following steps: S1. The steel substrate is smelted and cast to obtain a forging billet.

[0076] S2. The forging billet is heated at 1250℃ and held for 80 minutes to remove the iron oxide scale. Then, it is hot continuous rolling, that is, rough rolling is performed first, with a rough rolling start temperature of 1150℃ and a finish rolling temperature of 1050℃. Then, finish rolling is performed, with a finish rolling start temperature of 950℃ and a finish rolling temperature of 880℃. The hot-rolled steel plate is then cooled to 650℃ at a rate of 20℃ / s, and then cooled to room temperature at a rate of 10℃ / s to obtain the cooled hot-rolled steel plate.

[0077] S3. The cooled hot-rolled steel sheet is subjected to cold continuous rolling for 5 passes to obtain a cold-rolled steel sheet.

[0078] S4. After cleaning and annealing the cold-rolled steel sheet, hot-dip galvanize it at 470℃ for 20 seconds to form a hot-dip galvanized coating on the surface of the cold-rolled steel sheet, thus obtaining the hot-dip galvanized steel sheet.

[0079] S5. After the hot-dip galvanized steel sheet is cooled to room temperature at a rate of 5℃ / s, it is flattened to obtain a high corrosion-resistant hot-dip galvanized steel coating.

[0080] The structure and performance of the high corrosion-resistant hot-dip galvanized steel coatings of Examples 1 to 3 and Comparative Examples 1 to 3 were tested.

[0081] Figure 1 This is a SEM image of the zinc layer surface in Embodiment 1 of the present invention. Figure 2 This is a SEM image of the cross-section of the zinc layer in Embodiment 1 of the present invention. Figure 1 and Figure 2 It can be seen that the surface structure of the zinc layer is relatively uniform and dense, with a large number of banded structures. The cross-section of the zinc layer is relatively smooth, with an average thickness of about 6μm to 8μm, and it is tightly integrated with the base structure, with no obvious cracks found.

[0082] The corrosion resistance of the hot-dip galvanized steel coatings prepared in Examples 1-3 and Comparative Examples 1-3 was evaluated by immersion weight loss tests. The specific procedure for the immersion weight loss test was as follows: First, a standard-sized hot-dip galvanized steel sample was selected, and the surface oil was cleaned with alcohol or acetone. After drying, the initial mass m0 was accurately weighed, and the surface area A exposed to the corrosive environment was measured, with units of m². 2 Secondly, the sample is placed in a specific corrosive environment, such as a 3.5 wt.% NaCl solution, and exposed for a certain period of time t (specifically 30 days), in hours. Finally, the sample is removed, and the surface corrosion products are removed with an acidic rust remover. After cleaning and drying, the mass m1 after corrosion is measured. The corrosion resistance of the coating is measured by the corrosion rate, which is calculated using the following formula: v=Δm / (A×t), where Δm is the mass loss rate, Δm=m0-m1.

[0083] Table 1 shows the corrosion rate and single-sided zinc layer weight of the galvanized steel in Examples 1-3 and Comparative Examples 1-3. As can be seen from Table 1, the average corrosion rate of the coating in Examples 1-3, using the preparation process and zinc layer composition of the present invention, is approximately 0.021 g / h·m. 2 Below 0.023 g / h·m 2 The coating exhibits excellent corrosion resistance. However, in Comparative Example 1, the sum of the mass percentages of Ni, La, Ce, and Sc is 0.80%; the sum of the mass percentages of La, Ce, and Sc is 0.20%, both exceeding the composition range limited by this invention, resulting in a significant decrease in the corrosion resistance of the coating. In Comparative Example 2, the sum of the mass percentages of Ni, La, Ce, and Sc is 0.46%; the sum of the mass percentages of La, Ce, and Sc is 0.06%, both below the composition range limited by this invention, also leading to a significant decrease in the corrosion resistance of the coating. In Comparative Example 3, the sum of the mass percentages of Ni, La, Ce, and Sc is 0.40%, below the composition range limited by this invention. Although the sum of the mass percentages of La, Ce, and Sc is within the composition range limited by this invention, it still results in a significant decrease in the corrosion resistance of the coating.

[0084] Table 1. Corrosion rates and single-sided zinc layer weights of galvanized steel in Examples 1-3 and Comparative Examples 1-3 It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended scope of protection is intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of this invention.

[0085] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of protection of this invention and its equivalents, this invention also intends to include these modifications and variations.

Claims

1. A high corrosion-resistant hot-dip galvanized steel coating, characterized in that, The coating comprises a Zn-Al-Mg matrix and doping elements, namely Ni and rare earth elements, specifically La, Ce, and Sc; the coating consists of the following components by mass percentage. composition: Al：5.0%~7.0%； Mg: 2.5%~3.5%； Ni: 0.4%~0.6%; Rare earth elements: 0.07%~0.14%, the remainder is Zn, totaling 100%.

2. The high corrosion-resistant hot-dip galvanized steel coating according to claim 1, characterized in that, The mass percentage of La in the coating is 0.03%~0.06%, the mass percentage of Ce in the coating is 0.03%~0.06%, and the mass percentage of Sc in the coating is 0.01%~0.02%.

3. The high corrosion-resistant hot-dip galvanized steel coating according to claim 1, characterized in that, The mass percentage of dopant elements in the coating is 0.52%~0.58%.

4. The high corrosion-resistant hot-dip galvanized steel coating according to claim 3, characterized in that, The mass percentage of rare earth elements in the coating is 0.08%~0.12%.

5. A method for preparing a high corrosion-resistant hot-dip galvanized steel coating according to any one of claims 1 to 4, characterized in that, Includes the following steps: Hot-dip galvanizing is applied to the surface of cold-rolled steel sheets to form a hot-dip galvanized coating, resulting in a highly corrosion-resistant hot-dip galvanized steel coating.

6. The method for preparing a high corrosion-resistant hot-dip galvanized steel coating according to claim 5, characterized in that, The hot-dip galvanizing temperature is 460℃~470℃, and the time is 15s~25s.

7. The method for preparing a high corrosion-resistant hot-dip galvanized steel coating according to claim 5, characterized in that, The hot-dip galvanized steel sheet needs to be cooled at a rate of 1℃ / s to 5℃ / s, and the cooling temperature is room temperature.

8. The method for preparing a high corrosion-resistant hot-dip galvanized steel coating according to claim 5, characterized in that, The method for preparing cold-rolled steel sheet includes the following steps: The steel substrate is smelted and cast to obtain a forged billet; the forged billet is heated and held at a certain temperature for hot continuous rolling to obtain a hot-rolled steel plate; the hot-rolled steel plate is cooled and then cold-rolled to obtain a cold-rolled steel plate.

9. The method for preparing a high corrosion-resistant hot-dip galvanized steel coating according to claim 8, characterized in that, The heating temperature of the forging billet is 1200℃~1250℃, and the holding time is 50min~80min.

10. The method for preparing a high corrosion-resistant hot-dip galvanized steel coating according to claim 8, characterized in that, Hot rolling adopts a two-stage controlled rolling method, which is divided into roughing and finishing rolling. The initial rolling temperature of roughing is 1100℃~1150℃, and the final rolling temperature of roughing is 1000℃~1050℃. The initial rolling temperature of finishing is 900℃~950℃, and the final rolling temperature of finishing is 850℃~880℃. The specific cooling process of hot-rolled steel plate is to first cool it to 600℃~650℃ at a cooling rate of 20℃~30℃ / s, and then cool it to room temperature at a cooling rate of 10℃ / s~15℃ / s.

Images