Zinc liquid based on multi-component alloy and galvanizing method thereof

Abstract

The invention belongs to the technical field of hot galvanizing, and relates to a liquid zinc based on a multicomponent alloy, which is characterized by comprising the following components in percentage by weight: 0.30-0.40% of Al, 0.05-0.15% of Ni or Mg, 0.01-0.03% of rare earth element RE and the balance of Zn and inevitable impurities. A liquid zinc plating method based on a multi-element alloy is characterized in that a workpiece to be plated is placed in molten liquid zinc based on the multi-element alloy, and a plating layer is formed on the surface of the workpiece to be plated. According to the method, the aluminum content of the zinc liquid is increased to 0.30-0.40 wt.%, Ni / Mg and rare earth elements are cooperatively added, and the technology of dynamically adding the alloy in batches is combined, so that the viscosity of the zinc liquid is remarkably reduced, the performance of a plating layer is optimized, and the method is suitable for efficient low-consumption zinc plating production.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-dip galvanization, and relates to a zinc bath and a galvanizing method thereof, specifically a zinc bath based on a multi-element alloy and a galvanizing method thereof. Background Art

[0002] As the core process for steel anti-corrosion, the core of hot-dip galvanization technology lies in forming a dense coating through the reaction between molten zinc bath and steel substrate. However, with the improvement of industrial requirements for coating quality, cost control and environmental protection, the limitations of traditional galvanizing processes have become increasingly prominent, specifically:

[0003] Contradiction between zinc bath composition design and fluidity

[0004] Traditional galvanizing baths are mainly pure zinc or low-aluminum zinc alloys (Al ≤ 0.15 wt.%). The aluminum content in traditional zinc baths is relatively low, generally 1.5 per ten thousand, resulting in poor fluidity of the molten zinc bath, too high viscosity of the zinc bath (viscosity ≥ 4.5 mPa·s at 440 °C), and it is difficult to uniformly control the thickness of the zinc layer on the workpiece surface. The high-viscosity zinc bath forms turbulence on the workpiece surface, resulting in uneven coating thickness (local deviation can reach ±50 g / m 2 ), and it is easy to form zinc nodules at complex structures such as the inner wall of steel pipes and welds. The zinc consumption caused by the over-thick coating (≥ 350 g / m 2 ) accounts for 45%-50% of the total cost, and the waste of zinc resources is serious. To solve this technical problem, the industry has tried to increase the aluminum content to 0.20 wt.%, but the problem of composition fluctuation caused by aluminum oxidation has not been solved, and the actual production stability is poor.

[0005] Vicious cycle of aluminum oxidation and alloy addition efficiency

[0006] As a key alloying element, aluminum is extremely easy to oxidize to form Al2O3 slag (oxidation rate ≥ 30%) in high-temperature zinc bath, resulting in a decrease in the effective aluminum content. To maintain the aluminum concentration in the zinc bath, traditional processes need to frequently add alloys (5-10 times a day, 40-60 kg per alloy), but intermittent addition causes the following problems:

[0007] Fluctuation of zinc bath composition: The deviation of aluminum content reaches ±0.10 wt.%, and the coating performance fluctuates significantly;

[0008] Serious alloy waste: The oxidation of aluminum and the entrainment of zinc slag result in an alloy utilization rate of less than 70%, and a large amount of waste slag (8-10 kg / ton of steel) is generated, increasing the treatment cost.

[0009] Coarsening of coating structure and deterioration of performance

[0010] In low-aluminum zinc liquid (Al ≤ 0.15 wt.%), the growth rate of the Fe-Zn alloy layer is fast and the crystal grains are coarse (≥ 50 μm), resulting in high brittleness and poor adhesion of the coating (3 levels by the cross-cut method). In addition, the coarse crystal structure accelerates the penetration of corrosive media, and the salt spray resistance is only 650 - 720 h.

[0011] When the aluminum content is insufficient, there is a lack of effective elements in the zinc liquid to inhibit the Fe-Zn reaction, and the thickness of the Γ-phase layer exceeds 10 μm (the ideal value ≤ 5 μm), which exacerbates the risk of coating spalling.

[0012] To improve the above problems, in the prior art, there is a technology of adding silicon (Si) to the alloy to refine the crystal grains, but Si causes the viscosity of the zinc liquid to further increase, and the surface roughness (Ra) of the coating increases from 1.2 μm to 2.5 μm. There is also a technology of improving fluidity through electromagnetic stirring, but the equipment investment increases by 30%, the energy consumption increases by 15%, and the economy is poor. Summary of the Invention

[0013] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a zinc liquid based on multi-element alloy and its galvanizing method that is scientifically and reasonably designed, has high fluidity of the zinc liquid, uniform coating, low zinc consumption, and is easy to implement.

[0014] The present invention solves its technical problems by adopting the following technical solutions:

[0015] A zinc liquid based on multi-element alloy, characterized in that its components include: Al: 0.30 - 0.40 wt.%, Ni or Mg: 0.05 - 0.15 wt.%, rare earth element RE: 0.01 - 0.03 wt.%, and the balance is Zn and inevitable impurities.

[0016] Moreover, the rare earth element includes but is not limited to Ce and La.

[0017] A galvanizing method for a zinc liquid based on multi-element alloy, characterized in that the workpiece to be plated is placed in the molten zinc liquid based on multi-element alloy to form a coating on the surface of the workpiece to be plated.

[0018] Moreover, the method of placing the workpiece to be plated in the molten zinc liquid based on multi-element alloy is as follows:

[0019] Alloy addition: 20 - 25 alloys are put into the small tank of the zinc pot in 4 - 6 batches every day, and the weight of each alloy is 100 - 130 kg;

[0020] Temperature control: The temperature of the zinc liquid is controlled at 435 - 445 °C, and the dipping time of the workpiece is 30 - 50 s;

[0021] Dynamic adjustment of aluminum content: Real-time monitoring is carried out by a spectrometer, and the fluctuation range ≤ ± 0.05 wt.%.

[0022] The advantages and positive effects of the present invention are as follows:

[0023] By increasing the aluminum content in the zinc bath to 0.30 - 0.40 wt.%, synergistically adding Ni / Mg and rare earth elements, and combining the process of dynamically adding alloys in batches, the present invention significantly reduces the viscosity of the zinc bath and optimizes the coating properties, which is applicable to high - efficiency and low - consumption galvanizing production. Specifically:

[0024] Improved fluidity of the zinc bath: The viscosity is reduced by 40%, and the coating thickness is reduced from 300 - 400 g / m 2 to 180 - 220 g / m 2 , and the zinc consumption is reduced by 35 - 45%;

[0025] Optimized coating properties: The adhesion reaches level 1 (cross - hatch method), and the salt spray resistance performance is ≥1200 h;

[0026] Process stability: The alloy utilization rate is increased to 95%, and the component volatility is reduced to 1 / 3 of the traditional process. Detailed implementation manners

[0027] The following further details the embodiments of the present invention:

[0028] A zinc bath based on a multi - element alloy, its innovation lies in: its composition includes: Al: 0.30 - 0.40 wt.% (3.0 - 4.0 ten - thousandths), Ni or Mg: 0.05 - 0.15 wt.%, rare earth element RE: 0.01 - 0.03 wt.%, and the balance is Zn and inevitable impurities. The rare earth elements include but are not limited to Ce and La.

[0029] The mechanism of action of Al is as follows:

[0030] Reducing the viscosity of the zinc bath: Al atoms replace some Zn - Zn bonds in the zinc bath, weakening the inter - metallic force, and reducing the viscosity from 4.8 mPa·s (0.15% Al) to 2.9 mPa·s (0.35% Al).

[0031] Inhibiting the Fe - Zn reaction: Al preferentially reacts with Fe in the steel substrate to form a dense Fe2Al5 barrier layer, reducing the thickness of the Γ phase (Fe - Zn alloy layer) (from ≥10 μm to ≤5 μm), and improving the adhesion of the coating.

[0032] When it is lower than 0.30 wt.%, the improvement in fluidity is insufficient; when it is higher than 0.40 wt.%, the amount of zinc slag generated surges. The experimental data are shown in the following table:

[0033] Al content (wt.%) Viscosity of zinc bath (mPa·s) Amount of zinc dross (kg / ton of steel) 0.15 4.8 8.5 0.35 2.9 6.2 0.45 2.7 10.8

[0034] The mechanism of action of Ni is as follows:

[0035] Antioxidation: Ni forms a composite oxide film of NiAl2O4 with Al, covering the surface of the zinc bath, reducing the aluminum oxidation rate from 30% to ≤10%.

[0036] Grain refinement: Ni reacts with Zn and Al to form micron-sized NiZn3 phase, which serves as heterogeneous nucleation sites, making the grain size of the coating ≤20μm.

[0037] The mechanism of action of Mg is as follows:

[0038] Reducing surface tension: The addition of Mg reduces the surface tension of the zinc bath from 0.75 N / m to 0.52 N / m, and the wetting angle shrinks from 75° to 42°, reducing the defect of missing plating.

[0039] Fixing free Fe: Mg reacts with Fe to form a stable MgZn 11 Fe phase, reducing the amount of zinc slag generated by 30% (from 8 kg / ton of steel to 5.6 kg / ton of steel).

[0040] Ni is suitable for high-aluminum systems (0.35 - 0.40 wt.% Al), and Mg is more suitable for scenarios requiring high wettability.

[0041] The mechanism of action of rare earth elements (RE) is as follows:

[0042] Adsorption and purification: Rare earth elements are preferentially adsorbed on the surface of oxide inclusions in the zinc bath, promoting the aggregation and floating of slag particles, and purifying the zinc bath.

[0043] Synergistic grain refinement: RE forms Al4RE phase with Al and Mg, further inhibiting grain growth, making the grain size of the coating ≤18μm.

[0044] A zinc plating method based on a multi-element alloy, the innovation of which lies in: placing the workpiece to be plated in a molten zinc bath based on a multi-element alloy to form a coating on the surface of the workpiece to be plated.

[0045] The method of placing the workpiece to be plated in a molten zinc bath based on a multi-element alloy is as follows:

[0046] Alloy addition: Add 20 - 25 alloys to the small tank of the zinc pot in 4 - 6 batches every day. The weight of each alloy is 100 - 130 kg, and the interval between each batch is 2 - 3 hours, ensuring that the fluctuation of aluminum content ≤±0.05 wt.%;

[0047] High-frequency addition can reduce the single addition amount and avoid composition segregation caused by excessive local concentration. When added in 4 times, the aluminum utilization rate reaches 92%, while the single addition is only 68%.

[0048] Temperature control: The temperature of the zinc bath is controlled at 435 - 445°C, and the dipping time of the workpiece is 30 - 50 s;

[0049] When the temperature is below 435°C, the fluidity of the zinc bath decreases and the viscosity increases by 15%; when the temperature is above 445°C, the oxidation rate of aluminum doubles and the oxidation rate increases from 10% to 25%.

[0050] The coating is not completely covered within 30 seconds, and the coating is too thick after 50 seconds (thickness > 220 g / m 2 ).

[0051] Dynamic adjustment of aluminum content: Real-time monitoring by spectrometer, fluctuation range ≤ ±0.05 wt.%.

[0052] Use an inductively coupled plasma spectrometer (ICP-OES) to monitor the Al and Ni / Mg contents in the zinc bath in real time.

[0053] Automatically adjust the alloy addition amount according to the monitoring data to ensure that the fluctuation of aluminum content is ≤ ±0.05 wt.%.

[0054] Post-plating treatment

[0055] Air knife control: After plating, precisely control the coating thickness through the air knife pressure (0.4 - 0.6 MPa), and the tolerance is controlled within ±10 g / m 2 .

[0056] Cooling rate: Adopt segmented cooling (first water-cooled to 200°C, then air-cooled to room temperature) to inhibit the internal stress of the coating and avoid cracking.

[0057] Example 1

[0058] Zinc bath formula: Al 0.35 wt.%, Ni 0.10 wt.%, Ce 0.02 wt.%, balance Zn;

[0059] Process parameters: Add 22 alloys per day, each alloy weighs 115 kg, and is added in 5 batches; zinc bath temperature 440°C, immersion plating time 40 s;

[0060] Effect: Coating thickness 210 g / m 2 , adhesion level 1, zinc consumption reduced by 38%.

[0061] Example 2

[0062] Zinc bath formula: Al 0.38 wt.%, Mg 0.12 wt.%, La 0.025 wt.%, balance Zn;

[0063] Process parameters: Add 24 alloys per day, each alloy weighs 125 kg, and is added in 6 batches; zinc bath temperature 438°C, immersion plating time 35 s;

[0064] Effect: Coating thickness 195 g / m 2 , salt spray resistance time 1350 h.

[0065] Example 3

[0066] Zinc bath formula: Al 0.32 wt.%, Si 0.08 wt.%, mixed rare earth (Ce + La) 0.03 wt.%, the balance is Zn;

[0067] Process parameters: Add 20 alloys per day, each alloy weighs 105 kg, and is added in 4 times; the zinc bath temperature is 442 °C, and the dipping time is 45 s;

[0068] Effect: The viscosity of the zinc bath is reduced by 42%, and the grain size of the coating is 18 μm.

[0069] Comparative example

[0070] Adopt the traditional process (Al 0.15 wt.%, add 8 alloys per day, each alloy weighs 50 kg):

[0071] Coating thickness 350 g / m 2 , the adhesion is grade 3, the zinc consumption increases by 40%, and the salt spray resistance time is only 650 h.

[0072] The following is a comparison table of the effects of the embodiments of the present invention and the traditional comparative examples. The data are based on the actual test results of the embodiments and the comparative examples

[0073] Table 1: Performance comparison table of the present invention and the comparative example

[0074]

[0075]

[0076] Data source: The measured average values of the laboratories and production lines of Examples 1-3 and the comparative example;

[0077] The adhesion grade is based on the GB / T 9286-1998 standard (cross-cut method);

[0078] The salt spray test is carried out according to the ASTM B117 standard.

[0079] Key comparison description

[0080] Zinc bath fluidity: Through the increase of aluminum content and the synergistic effect of rare earth elements, the viscosity of the zinc bath is reduced by 40%, reducing the risk of coating accumulation.

[0081] Coating uniformity: The grains are refined to ≤20 μm (≥50 μm in the comparative example), significantly improving the denseness and adhesion of the coating.

[0082] Economy: The zinc consumption is reduced by 35-45%, combined with the improvement of alloy utilization rate, and the comprehensive cost is reduced by 25%-30%.

[0083] Environmental friendliness: Reduces the generation amount of zinc dross (by 30%), meeting the requirements of green manufacturing.

[0084] The main innovation points of the present invention are as follows:

[0085] Breakthrough in high-aluminum zinc liquid system:

[0086] In the traditional process, it is difficult to stably maintain a high aluminum content (>0.20 wt.%) due to aluminum oxidation. The present invention realizes the industrial application of an aluminum content of 0.30 - 0.40 wt.% for the first time through the synergistic antioxidant effect of Ni / Mg and rare earth.

[0087] Innovation in dynamic addition process:

[0088] Proposes a "batch-by-batch high-frequency addition + on-line feedback regulation" mode, reducing the aluminum content fluctuation from ±0.10 wt.% to ±0.05 wt.%, and improving the component stability by 50%.

[0089] Synergistic mechanism of multi-element alloy:

[0090] Ni-Al-RE ternary system: Ni inhibits oxidation, RE refines grains, and Al adjusts fluidity. The three work together to more than double the comprehensive performance of the coating.

[0091] Mg-RE synergistic wetting: Mg reduces the surface tension, RE purifies the zinc liquid, and the non-plating rate is reduced from 5% to 0.3%.

[0092] Through the high-aluminum zinc liquid formulation design, dynamic addition process optimization, and multi-element alloy synergistic effect, the present invention systematically solves the problems of poor fluidity, high zinc consumption, and insufficient coating performance in the traditional galvanizing process, achieving a technical breakthrough of a 43% reduction in zinc consumption and an 87% improvement in corrosion resistance, and has significant industrial application value.

[0093] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art can understand that various substitutions, changes, and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the content disclosed in the embodiments.

Claims

1. A zinc liquid based on a multi-element alloy, characterized in that: Its components include: Al: 0.30 - 0.40 wt.%, Ni or Mg: 0.05 - 0.15 wt.%, rare earth element RE: 0.01 - 0.03 wt.%, and the balance is Zn and inevitable impurities.

2. The zinc solution based on a multi-component alloy according to claim 1, characterized in that: The rare earth elements mentioned above include but are not limited to Ce and La.

3. A zinc plating method for zinc liquid based on multi-element alloy, characterized in that: Place the workpiece to be plated in the molten zinc bath based on multi - element alloy as described in any one of claims 1 - 2 to form a coating on the surface of the workpiece to be plated.

4. A zinc plating method for zinc liquid based on multi - element alloy according to claim 1, characterized in that: The method of placing the workpiece to be plated in the molten zinc bath based on multi - element alloy is as follows: Alloy addition: Add 20 - 25 alloy bars to the small tank of the zinc pot in 4 - 6 batches every day, and the weight of each alloy bar is 100 - 130 kg; Temperature control: Control the temperature of the zinc bath at 435 - 445 °C, and the dipping time of the workpiece is 30 - 50 s; Dynamic adjustment of aluminum content: Monitor in real time through a spectrometer, and the fluctuation range is ≤ ±0.05 wt.%.

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