A zinc alloy plating capable of effectively suppressing silicon reactivity and having excellent corrosion resistance

Abstract

The application designs a hot-dip galvanizing alloy with higher corrosion resistance and inhibiting silicon reactivity. The design method is as follows: the composition of the hot-dip galvanizing alloy is designed according to the composition range of the hot-dip galvanizing alloy, the hot-dip galvanizing alloy coating is prepared by using the drying solvent method, the microstructure of the alloy coating is observed and analyzed, the thickness of each compound layer is counted and compared, the composition is optimized for electrochemical testing, and the corrosion resistance is evaluated. The content of each component of the alloy is 0.4% in terms of atomic percentage, and the content of Zn is 99.6%.

Description

Technical Field

[0001] This invention relates to an alloy material, and more particularly to the design of a Zn-In zinc plating alloy that can effectively suppress silicon reactivity and has higher corrosion resistance. Background Technology

[0002] Hot-dip galvanizing is a simple and inexpensive process, widely used to improve the corrosion resistance of steel materials. However, hot-dip galvanizing silicon-containing steel has always been a technical challenge for the hot-dip galvanizing industry. Silicon, as a deoxidizer in steel smelting, inevitably exists in steel. However, silicon in the steel matrix can cause the explosive growth of the ζ phase in the hot-dip galvanized coating, reducing the adhesion between the coating and the substrate, resulting in a dark and rough coating surface, severely affecting the appearance quality and corrosion resistance of the coating. This phenomenon is called silicon reactivity. Besides affecting coating quality, the silicon reactivity during galvanizing also significantly increases zinc consumption with the explosive growth of the ζ phase, raising the cost of hot-dip galvanizing. To control the explosive growth of the ζ layer, improve coating quality, and reduce zinc consumption, alloying elements are often added to the zinc bath. However, the various alloying elements developed so far still have their own shortcomings. Therefore, developing a galvanizing alloy that can suppress silicon reactivity and has excellent corrosion resistance is of great significance for promoting the development of the hot-dip galvanizing industry for silicon-containing steel. Summary of the Invention

[0003] The main objective of this invention is to design a zinc-plating alloy that can effectively suppress silicon reactivity and has higher corrosion resistance.

[0004] The technical solution adopted by this invention to solve its technical problem is as follows: Zinc alloy molten pools with different In contents are designed, with an In atomic percentage of 0.1-0.8; zinc alloys with different In contents are prepared and placed in an alumina crucible for complete melting at 450℃, and held at that temperature for 3 hours to obtain a molten pool with uniform chemical composition; then, Q235 steel is used as the base material and hot-dip galvanized in the zinc pool for different times, and the obtained coatings are subjected to microstructure analysis and corrosion experiments. A Zn-In alloy that exhibits significant inhibition of silicon reactivity and excellent corrosion resistance is preferred.

[0005] The atomic percentage of each component of the hot-dip galvanized alloy is: In 0.1-0.8, Zn 99.9-99.2.

[0006] The preferred atomic percentage content of each component in the hot-dip galvanized alloy is: In 0.1-0.8, Zn 99.9-99.2.

[0007] Preferred embodiment 1: The preferred atomic percentage content of each component of the hot-dip galvanized alloy is: In 0.1, Zn 99.99.

[0008] Preferred embodiment 2: The preferred atomic percentage content of each component of the hot-dip galvanized alloy is: In 0.2, Zn 99.98.

[0009] Preferred embodiment three: The preferred atomic percentage content of each component of the hot-dip galvanized alloy is: In 0.4, Zn 99.96.

[0010] Preferred embodiment four: The preferred atomic percentage content of each component of the hot-dip galvanized alloy is: In 0.6, Zn 99.94.

[0011] Preferred embodiment five: The preferred atomic percentage content of each component of the hot-dip galvanized alloy is: In 0.8, Zn 99.92.

[0012] Preferred implementation method: The preferred atomic percentage content of each component of the hot-dip galvanized alloy is: In 0.4, Zn 99.96.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: By studying the influence of In content in the hot-dip galvanizing alloy on the coating structure and corrosion resistance of the hot-dip galvanized layer, the present invention discovered a hot-dip galvanizing alloy that can effectively suppress the reactivity of silicon and has higher corrosion resistance. Compared with the coating obtained by immersion in a pure zinc molten pool, the coating obtained by immersion in this galvanizing alloy on Q235 steel showed the following reductions in compound layer thickness (5.01 μm, 12.50 μm, 27.00 μm, and 52.54 μm) and ζ layer thickness (4.04 μm, 9.77 μm, 22.96 μm, and 32.11 μm) at immersion times of 20 s, 40 s, 80 s, and 160 s, respectively. Furthermore, at an immersion time of 160 s, the compound layer consisted of dense ζ, δ, and Γ layers, and the reactivity of silicon was significantly suppressed. Electrochemical analysis showed that, compared with pure zinc coating, the zinc alloy coating had a larger capacitive arc radius, a positive shift in corrosion potential of 0.0319 V, and a decrease in self-corrosion current density of 9.585 μA / cm². 2 It can increase corrosion life by 2.5 times and has higher corrosion resistance. Attached Figure Description

[0014] Figure 1 Microstructure of Q235 steel after immersion plating in a molten pool with an In content of 0.1 at.% for different times: (a) 20s; (b) 40s; (c) 80s; (d) 160s

[0015] Figure 2 Microstructure of Q235 steel after immersion plating in a molten pool with an In content of 0.2 at.% for different times: (a) 20s; (b) 40s; (c) 80s; (d) 160s

[0016] Figure 3 Microstructure of Q235 steel after immersion plating in a molten pool with an In content of 0.4 at.% for different times: (a) 20s; (b) 40s; (c) 80s; (d) 160s

[0017] Figure 4 Microstructure of Q235 steel after immersion plating in a molten pool with an In content of 0.6 at.% for different times: (a) 20s; (b) 40s; (c) 80s; (d) 160s

[0018] Figure 5 Microstructure of Q235 steel after immersion plating in a molten pool with an In content of 0.8 at.% for different times: (a) 20s; (b) 40s; (c) 80s; (d) 160s

[0019] Figure 6 Potentiodynamic polarization curves of Zn-0.4at.%In coating and pure Zn coating

[0020] Figure 7 Nyqusit spectra of Zn-0.4at.%In coating and pure Zn coating

[0021] Figure 8 Bode spectra of Zn-0.4at.%In and pure Zn coatings: frequency-impedance curves and frequency-phase angle curves Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments, but the present invention is not limited thereto.

[0023] Example 1

[0024] The preferred atomic percentage content of each component in the hot-dip galvanizing alloy of this invention is: In 0.1%, Zn 99.99%. The microstructure of the coatings obtained by immersing Q235 steel in this molten pool for 20s, 40s, 80s, and 160s using this composition ratio is described in the reference document. Figure 1 It can be observed that a visible but discontinuous δ layer exists when the hot-dip galvanizing time is 20s, with the ζ phase near the δ layer being relatively dense. When the hot-dip galvanizing time is 40s and 80s, the compound layer of the coating consists of a continuous grid-like ζ phase and a continuous δ phase. When the hot-dip galvanizing time is 160s, a thin Γ phase layer is generated, without strong silicon reactivity. At immersion times of 20s, 40s, 80s, and 160s, the average thicknesses of the compound layer are 16.82μm, 23.70μm, 34.44μm, and 44.48μm, respectively. The thicknesses of the ζ phase layer are 15.23μm, 20.18μm, 26.44μm, and 33.18μm, respectively, and the average thicknesses of the δ phase layer are 1.62μm, 3.52μm, 7.93μm, and 11.3μm, respectively.

[0025] Example 2

[0026] The preferred atomic percentage content of each component in the hot-dip galvanizing alloy of this invention is: In 0.2%, Zn 99.98%. The microstructure of the coatings obtained by immersing Q235 steel in this molten pool for 20s, 40s, 80s, and 160s using this composition ratio is described in the reference document. Figure 2 It was observed that dense δ and ζ layers were present in all samples with hot-dip galvanizing times. A thin Γ layer also appeared in the coating when the immersion time was 160 s. The average thicknesses of the compound layers at immersion times of 20 s, 40 s, 80 s, and 160 s were 15.99 μm, 22.58 μm, 26.47 μm, and 31.76 μm, respectively. The thicknesses of the ζ layers were 14.18 μm, 16.48 μm, 18.33 μm, and 22.66 μm, respectively, and the average thicknesses of the δ layers were 1.81 μm, 6.10 μm, 8.14 μm, and 9.10 μm, respectively.

[0027] Example 3

[0028] The preferred atomic percentage content of each component in the hot-dip galvanizing alloy of this invention is: In 0.4%, Zn 99.96%. The microstructure of the coatings obtained by immersing Q235 steel in this molten pool for 20s, 40s, 80s, and 160s using this composition ratio is described in the reference document. Figure 3 It can be observed that when the hot-dip galvanizing time is less than 40 s, the Fe-Zn compound layer consists entirely of dense ζ and δ layers. When the hot-dip galvanizing time is 80 s, a thin Γ layer appears in the Fe-Zn compound layer. At galvanizing times of 20 s, 40 s, 80 s, and 160 s, the average thicknesses of the compound layers are 17.44 μm, 20.09 μm, 23.12 μm, and 28.27 μm, respectively. The thicknesses of the ζ phase layers are 14.29 μm, 16.48 μm, 18.33 μm, and 21.65 μm, respectively, and the average thicknesses of the δ layers are 3.15 μm, 3.61 μm, 4.79 μm, and 6.62 μm, respectively.

[0029] Example 4

[0030] The preferred atomic percentage content of each component in the hot-dip galvanizing alloy of this invention is: In 0.6%, Zn 99.94%. The microstructure of the coatings obtained by immersing Q235 steel in this molten pool for 20s, 40s, 80s, and 160s using this composition ratio is described in the reference document. Figure 4It can be observed that the Fe-Zn compound layer in the coating is mainly composed of dense δ and ζ layers, with a Γ layer present when the hot-dip galvanizing time is 160 s. At immersion times of 20 s, 40 s, 80 s, and 160 s, the average thicknesses of the compound layers are 16.63 μm, 21.02 μm, 26.24 μm, and 29.94 μm, respectively. The thicknesses of the ζ phase layer are 14.07 μm, 16.10 μm, 20.07 μm, and 25.11 μm, respectively, and the average thicknesses of the δ layer are 2.56 μm, 4.92 μm, 6.17 μm, and 4.83 μm, respectively.

[0031] Example 5

[0032] The preferred atomic percentage content of each component in the hot-dip galvanizing alloy of this invention is: In 0.8, Zn 99.92. The microstructure of the coatings obtained by immersing Q235 steel in this molten pool for 20s, 40s, 80s, and 160s using this composition ratio is described in the reference document. Figure 5 It can be observed that In-rich particles appeared in the free layer. The In content of these In-rich particles is twice that of the In content in the molten pool. The Fe-Zn compound layer in the coating is mainly composed of dense δ and ζ layers, and a Γ layer exists when the hot-dip galvanizing time is 160s. At immersion times of 20s, 40s, 80s, and 160s, the average thicknesses of the compound layers are 16.55μm, 23.83μm, 25.34μm, and 30.74μm, respectively. Among them, the thicknesses of the ζ phase layer are 15.20μm, 17.78μm, 20.62μm, and 23.75μm, respectively, and the average thicknesses of the δ layer are 1.35μm, 6.05μm, 4.72μm, and 6.99μm, respectively.

[0033] Example 6

[0034] The optimal atomic percentage content of each component in the hot-dip alloy of this invention is: In 0.4%, Zn 99.6%. Two molten pools were prepared: Zn-0.4 at.% In and pure zinc. Q235 steel was used for immersion plating in each pool for 160 seconds. The resulting plating samples were encapsulated in epoxy resin and then immersed at 25°C for 720 hours before undergoing potentiodynamic polarization curve testing. The results are shown in [reference needed]. Figure 6 The corrosion kinetic parameters obtained by fitting the results in the figure are shown in Table 1.

[0035] Table 1 Corrosion kinetic parameters of In-coated and pure Zn-coated layers.

[0036]

[0037] It can be observed that the self-corrosion current of the Zn-0.4at.%In alloy coating is significantly lower than that of the pure zinc coating, and the corrosion potential shifts positively by 0.0319V. Based on the corrosion parameters in Table 1, the Rp of this hot-dip alloy coating is calculated to be 3235.12 Ω·cm. 2 The Rp value is greater than that of pure zinc plating, which is 1362.59 Ω·cm. 2 It is expected that the corrosion life can be increased by 2.5 times, showing higher corrosion resistance.

[0038] AC impedance spectroscopy was used to test the two coatings; the comparison results are shown in [link to relevant documentation]. Figure 7 and Figure 8 It can be observed that the compressive arc radius of the Zn-0.4at.%In alloy coating is larger than that of the pure zinc coating, indicating that the alloy has higher corrosion resistance.

[0039] The experimental method of this invention is as follows:

[0040] (1) Prepare molten pools with different In contents. The atomic percentage of In added to the molten pool is 0.1-0.8. Five hot-dip alloy molten pools with different In contents and one comparative pure Zn molten pool are designed. The composition of the molten pools is shown in Table 2.

[0041] Table 2. Molten Pool Composition Design

[0042]

[0043] (2) Cut the Zn blocks into suitable sizes and place them in an alumina crucible. Melt them in a crucible resistance furnace at a melting temperature of 480℃. Then lower the temperature to 450℃, retaining one pure Zn molten pool. Remove the surface oxide layer from the remaining molten pools and add 0.1 at.%, 0.2 at.%, 0.4 at.%, 0.6 at.%, and 0.8 at.% In to each molten pool, respectively, and hold for 2 hours. Then stir the molten pools 1-2 times with long strip ceramic pieces and hold for 1 hour to ensure that In is evenly dispersed in the molten pools.

[0044] (3) Grind the surface of the Q235 steel substrate to remove cutting marks and surface oxide layer. Use ultrasonic cleaning to remove some oil and debris from the substrate. The ground steel substrate needs to retain a certain roughness, which is beneficial to enhance the bonding between the coating and the substrate.

[0045] (4) Prepare an 80 g / L NaOH solution using analytical grade NaOH solid and distilled water. Place the cleaned steel substrate into the solution and heat it to 50°C. Stir the steel substrate in the solution for 5 minutes to remove residual oil stains from the surface.

[0046] (5) After alkaline washing, the steel substrate needs to be washed with flowing distilled water to remove the residual alkaline solution on the surface, so as not to interfere with the next process.

[0047] (6) Prepare a 4% HCl aqueous solution using 35% HCl and distilled water. Place the cleaned steel substrate into the solution and stir repeatedly for 5 minutes to remove the oxide layer on the surface of the steel substrate.

[0048] (7) The pickled steel substrate needs to be washed with flowing distilled water to remove the residual acid on the surface, so as not to interfere with the next step.

[0049] (8) Flushing is a key step in hot-dip plating to obtain a good coating, and the use of flux and the fluxing method are particularly important. This article uses solvent-based fluxing, and the composition of the flux is shown in Table 3.

[0050] Table 3 Composition of hot-dip galvanizing flux

[0051]

[0052] After multiple experiments, this flux formulation yielded the optimal plating effect. The sample needed to be completely immersed in the flux and heated to 80°C. The plating time was 3 minutes, at which point the steel substrate surface achieved maximum activity, resulting in the best immersion plating effect.

[0053] (9) The sample after the plating is completed should be taken out immediately and the surface moisture dried to form a thin salt film on the substrate surface. Removing moisture can prevent zinc explosion during the immersion plating process, prevent zinc liquid splashing, ensure operational safety, and also improve the adhesion between the coating and the substrate.

[0054] (10) When the temperature of the molten pool stabilizes at 450℃, quickly open the furnace door, peel off the oxide layer on the surface of the molten pool, immerse the steel substrate that has completed the fluxing into the Zn pool, and then close the furnace door, holding it for 20s, 40s, 80s, and 160s respectively. Then take out the sample, shake off the excess molten metal on the surface, and quickly immerse it in distilled water for quenching.

[0055] (11) The hot-dip galvanized sample was ground to remove one side of the coating, embedded in epoxy resin, and polished step by step. The side was then etched with a 2% HNO3 alcohol solution. The microstructure of the compound layer was analyzed by SEM-EDS. The thickness of each compound layer was measured using ImageJ software, and the optimal In content hot-dip galvanizing alloy composition that could suppress the Sandelin effect was selected.

[0056] (12) The preferred alloy composition from Example 4 and the pure Zn coating were selected as controls. The two coating samples were encapsulated in epoxy resin, with one side exposed, covering an area of ​​100 mm². 2 And solder Cu wires to the other side to connect the circuit.

[0057] (13) The sample was immersed in a naturally aerated 35 g / L NaCl solution for 720 h at a constant immersion temperature of 25 °C.

[0058] (14) Electrochemical testing

[0059] Electrochemical tests were performed on a VersaSTAT V3F electrochemical workstation using a three-electrode system. All potentials mentioned are relative to a saturated calomel reference electrode. The platinum sheet electrode had an area of ​​400 mm². 2 The open-circuit potential test lasted 1 minute. The Tafel curve test potential was scanned at a rate of 5 mV / s from the open-circuit potential of -0.125 V towards the positive direction, up to +0.250 V, and then from the relative open-circuit potential of +0.125 V towards the negative direction at the same rate, down to -0.250 V. Throughout the experiment, the sample was kept at a constant temperature, and oscillation of the solution cell was avoided as much as possible. The results are shown in [Figure number missing]. Figure 6 The calculated corrosion kinetic parameters are shown in Table 1. The AC impedance test scan frequency range was 1MHz to 100mHz, and the excitation voltage was 10mV. The results are shown in [Table 1]. Figure 7 and Figure 8 .

[0060] The conclusions drawn are as follows:

[0061] (1) Adding In to the coating can effectively reduce the thickness of the compound layer. In addition to the ζ and δ phases, a dense Γ phase layer also appears in the coating. With the increase of In content, the δ phase layer is continuous and dense. The dense δ and Γ phase layers hinder Fe-Zn interdiffusion and inhibit the explosive growth of the ζ phase. For the same hot-dip coating time, when the In content is 0.1-0.4 at.%, the average thickness of the compound layer gradually decreases with the increase of In content. When the In content is 0.4-0.8 at.%, the thickness change is not obvious with the increase of In content. The optimal hot-dip coating alloy composition is, in atomic percentage: In 0.4, Zn 99.6.

[0062] (2) After immersion in 35 g / L NaCl solution for 720 h, the corrosion potential of the Zn-0.4 at.%In alloy coating shifted positively by 0.0319 V compared to the corrosion potential of the pure Zn coating, and the self-corrosion current density of the Zn-0.4 at.%In alloy coating was 6.294 μA / cm. 2 The self-corrosion current density is less than that of pure Zn coating, which is 15.879 μA / cm². 2 This indicates that the corrosion rate of the In-containing coating is lower than that of the pure Zn coating, and the expected corrosion life can be increased by 2.5 times. In the AC impedance test, the capacitive arc radius of the Zn-0.4at.%In alloy coating is larger than that of the pure Zn coating, indicating that this hot-dip alloy has higher corrosion resistance.

Claims

1. A zinc-plating alloy that effectively inhibits silicon reactivity and exhibits excellent corrosion resistance, characterized in that, The atomic percentages of each component in the alloy are: In 0.4%, Zn 99.6%. The zinc alloy is prepared by: preparing a zinc alloy with an atomic percentage of In 0.4 and Zn 99.6, placing the zinc alloy in an alumina crucible and melting it fully at 450°C, holding it at that temperature for 3 hours to obtain a molten pool; Using Q235 steel as the base material, hot-dip galvanizing is performed in a molten pool for 160 seconds to obtain the zinc-plated alloy that effectively inhibits silicon reactivity and has excellent corrosion resistance.

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