Process for hot dipping and bleaching of zinc-aluminum-magnesium alloy liquid

Abstract

The technology comprises the following steps that a workpiece is subjected to hot-dip galvanizing, before the workpiece is taken out of a pot after hot-dip galvanizing, zinc-aluminum-magnesium alloy is molten and spread on the zinc liquid surface, the workpiece is taken out of the pot, and therefore a zinc-aluminum-magnesium alloy coating is formed on the surface of a zinc coating of the workpiece. According to the method, a layer of zinc-aluminum-magnesium alloy liquid is quantitatively bleached when hot galvanizing is taken out of a pot, a zinc-aluminum-magnesium alloy coating with a certain aluminum-magnesium content can be obtained by adjusting the components of the alloy liquid, and due to the fact that the zinc-aluminum-magnesium alloy coating is plated at a time and is good in adhesive force, the zinc-aluminum-magnesium alloy coating is free of blistering and falling-off phenomena after a drop weight test; meanwhile, the zinc-aluminum-magnesium alloy liquid only exists on the surface of the zinc liquid of the zinc bath, the usage amount of the alloy liquid can be adjusted, and balance can be formed within a certain concentration range along with consumption brought out by a workpiece, so that scum on the surface of the zinc bath is controlled at a small level, the appearance of a zinc-aluminum-magnesium alloy coating is smooth, and the problems of skip plating and scum are solved at the same time.

Description

Technical Field

[0001] The invention relates to a process for hot-dip plating of zinc-aluminum-magnesium alloy liquid, belonging to the technical field of hot-dip plating. Background Art

[0002] Batch hot-dip galvanizing usually refers to a hot-dip galvanizing process based on dry-assisted plating. The main components of the zinc bath in this process are more than 99% (mass percentage) zinc, 0.003-0.10% aluminum, 0.005-0.060% nickel and trace rare earth elements, as well as about 0.03% iron that is inevitably dissolved in the zinc bath due to the zinc-iron reaction. The working temperature of the zinc bath is 435-445℃, and the galvanizing time is 2-10 minutes.

[0003] At present, the only process that can obtain the zinc-aluminum-magnesium alloy layer and is applied in actual production is continuous hot-dip plating, and the substrate is limited to steel wire and steel coil, while steel components such as angle steel, pipe rod, beam column, and footing can only be hot-dip plated in batches. Studies have shown that the corrosion resistance of the zinc-aluminum-magnesium alloy layer is 3-20 times that of the zinc layer.

[0004] There are two existing hot-dip galvanizing aluminum-magnesium alloy process routes: 1) Special plating agent process: degreasing → water washing → pickling → water washing → special plating agent plating → drying → hot-dip galvanizing aluminum-magnesium → air cooling → passivation → drying. 2) Secondary hot-dip plating process: degreasing → water washing → pickling → water washing → plating → drying → hot-dip galvanizing → hot-dip galvanizing aluminum-magnesium → air cooling → passivation → drying. Among them, the process problems that need to be solved by the special plating agent process are: ① Plating leakage: By adding bismuth salts and stannous salts to the conventional plating solution to prepare a special plating solution, although it can solve the problem of low aluminum and low magnesium leakage, for zinc baths containing 0.5% aluminum and 0.5% magnesium or more, the coating often has pinhole leakage and plaque leakage; ② Rough appearance caused by scum: With the increase of aluminum and magnesium content in the zinc bath, a scum layer with a thickness of about ten centimeters is formed on the surface of the zinc bath. Because the batch hot-dip galvanizing pot cannot be equipped with an air knife, a large amount of scum adheres to the surface of the workpiece when it comes out of the pot, making it very rough, and the thickness of the coating on the surface is extremely uneven. The secondary hot-dip process solves the problem of plating leakage, but it needs to solve three other problems: ① The adhesion between the external zinc-aluminum-magnesium coating and the internal zinc coating is poor, and part of the alloy layer is prone to peeling off; ② Due to the generation of scum on the surface of the zinc-aluminum-magnesium zinc bath, the coating appearance is relatively rough; ③ Since the secondary hot-dip plating requires the use of two zinc pots, the production cost is greatly increased. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a process for hot-dip bleaching of zinc-aluminum-magnesium alloy liquid.

[0006] In order to achieve the above-mentioned purpose, the present invention adopts a process of hot-dip galvanizing of zinc-aluminum-magnesium alloy liquid, comprising the following steps: hot-dip galvanizing a workpiece, before the workpiece is taken out of the hot-dip galvanizing pot, molten zinc-aluminum-magnesium alloy is spread on the surface of zinc liquid, and the workpiece is taken out of the pot, thereby forming a zinc-aluminum-magnesium alloy coating on the surface of the zinc coating of the workpiece.

[0007] As an improvement, the zinc solution for hot-dip galvanizing includes, by mass percentage, 0.003-0.008% aluminum, 0.015-0.040% nickel, 0.01-0.03% iron and the balance zinc. The galvanizing temperature is 430-450° C. and the galvanizing time is 2-10 minutes.

[0008] As an improvement, before the workpiece is hot-dip galvanized, a drift plating tool is used to spread the molten zinc-aluminum-magnesium alloy on the surface of the zinc liquid while removing the ash, and then the workpiece is slowly removed from the pot, thereby drift plating a zinc-aluminum-magnesium alloy coating on the surface of the zinc coating of the workpiece.

[0009] As an improvement, the plating tool includes an ash shovel, one side of which is provided with a mesh cage for placing zinc-aluminum-magnesium alloy strips. During operation, the ash is beaten through the ash shovel, and the zinc-aluminum-magnesium alloy strips are placed through the mesh cage. The zinc-aluminum-magnesium alloy strips are melted and spread in the high-temperature zinc liquid, thereby forming a thin layer of zinc-aluminum-magnesium alloy liquid on the surface of the zinc liquid.

[0010] As an improvement, when the bleaching and plating equipment is being plastered, the zinc-aluminum-magnesium alloy strips in the mesh cage are 5-10 cm below the liquid surface of the zinc liquid.

[0011] As an improvement, the time for the drift plating tool to spread the molten zinc-aluminum-magnesium alloy on the surface of the zinc liquid while removing the dust is 30-60 seconds.

[0012] As an improvement, the zinc-aluminum-magnesium alloy includes, by mass percentage, 3-6% aluminum, 1-3% magnesium and the balance zinc.

[0013] As an improvement, the thickness of the zinc-aluminum-magnesium alloy coating is 4-10 microns, and the total thickness of the zinc coating and the zinc-aluminum-magnesium alloy coating is 65-80 microns.

[0014] As an improvement, the following steps are specifically included: degreasing → water washing → pickling → water washing → plating assistance → drying → hot-dip galvanizing → bleaching zinc-aluminum-magnesium alloy liquid before taking out of the pot → air cooling → passivation → drying.

[0015] As an improvement, the workpiece is a steel wire, a steel coil or a steel component, and the steel component includes, for example, angle steel, pipe rod, beam column, foundation foot and the like.

[0016] Compared with the prior art, the process of hot-dip bleaching zinc-aluminum-magnesium alloy liquid of the present invention quantitatively bleachs a layer of zinc-aluminum-magnesium alloy liquid when hot-dip galvanizing is taken out of the pot, and by adjusting the composition of the alloy liquid, a zinc-aluminum-magnesium alloy coating with a certain aluminum-magnesium content can be obtained. Since the zinc-aluminum-magnesium alloy coating is plated out at one time, the coating adhesion is good, and the zinc-aluminum-magnesium alloy coating is subjected to a drop hammer test, and the coating has no bubbling or shedding phenomenon; at the same time, since the zinc-aluminum-magnesium alloy liquid only exists on the zinc liquid surface of the zinc bath, and the amount of the alloy liquid used can be adjusted, a balance can be formed within a certain concentration range as the workpiece is consumed, thereby controlling the scum on the surface of the zinc bath to a less level, making the zinc-aluminum-magnesium alloy coating smooth in appearance, and solving the problems of missed plating and scum at the same time; since the process of hot-dip bleaching zinc-aluminum-magnesium alloy liquid only uses one zinc pot, the production cost is equivalent to that of hot-dip galvanizing.

[0017] The zinc coating + zinc-aluminum-magnesium alloy coating of the present invention is subjected to a neutral salt spray test (refer to GB / T 10125-2021 "Artificial atmosphere corrosion test salt spray test"), and the coating has red rust appearing time of 1848-3840 hours, while the hot-dip galvanized layer of the same thickness has red rust appearing in 360 hours, and the corrosion resistance is improved by 5-10 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the structure of the bleaching and plating tool of the present invention:

[0019] Figure 2 Schematic diagram of SEM of the coating (zinc coating and zinc-aluminum-magnesium alloy coating) of Example 1 of the present invention;

[0020] Figure 3 This is the EDS spectrum of the coating (zinc coating and zinc-aluminum-magnesium alloy coating) of Example 1 of the present invention. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clear, the technical solutions of the present application are described in detail below with the help of accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical solutions of the present application, rather than limitations on the technical solutions of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.

[0022] The present invention studies the influence of four factors, namely, zinc-aluminum-magnesium alloy composition (C), zinc bath temperature (T), alloy immersion depth (h), and dusting time (t) on the zinc-aluminum-magnesium alloy coating composition (C), through single factor experiments, determines the value range of each factor, and thus constructs a suitable response surface experimental model.

[0023] Conduct experiments according to the designed experimental points, collect experimental data, and fit the regression equation (for example, use the linear regression model: C=M+m1c+m2T+m3h+m4t+N; where C is the dependent variable, which is the composition of the zinc-aluminum-magnesium alloy coating; c, T, h, and t are independent variables, where c is the composition of the aluminum-magnesium alloy, T is the zinc bath temperature, h is the alloy immersion depth, and t is the lime-beating time; in the model, M, m1, m2, m3, and m4 are the coefficients of the model, and N is the error term. The values ​​of M, m1, m2, m3, and m4 can be estimated through the least squares method, thereby obtaining the fitted regression equation).

[0024] Analyze the interaction between various factors and their impact on the response value. Use response surface analysis software for optimization, and intuitively find the best value combination of c, T, h, and t corresponding to any target composition value C of zinc-aluminum-magnesium alloy coating by drawing response surface diagrams and contour diagrams. Similarly, by appropriately expanding the value range of the four factors, the control range of each parameter that is convenient for actual operation of the production line can be obtained.

[0025] Example 1

[0026] 1. Batch hot dip coating conditions

[0027] Steel grade Q355B;

[0028] Zinc bath composition: 0.0053% aluminum, 0.0157% nickel, 0.0181% iron, and the balance is zinc;

[0029] Composition of zinc-aluminum-magnesium alloy strip: 5.88% aluminum, 2.6% magnesium, and the balance is zinc;

[0030] According to the conventional hot-dip galvanizing method, degreasing, pickling, plating assistance, drying, etc. are carried out, and then hot-dip galvanizing is carried out;

[0031] Before hot-dip galvanizing, the molten zinc-aluminum-magnesium alloy is spread on the surface of the zinc liquid while the ash is removed. Figure 1 As shown, the adopted drift plating tool comprises an ash shovel 1, one side of the ash shovel 1 is provided with a mesh cage 2 for placing zinc-aluminum-magnesium alloy strips (an opening for placing zinc-aluminum-magnesium alloy strips is provided above the mesh cage 2), during operation, the ash is beaten by the ash shovel 1, and the zinc-aluminum-magnesium alloy strips loaded in the mesh cage 2 are melted and spread in a high-temperature zinc bath, thereby forming a thin layer of zinc-aluminum-magnesium alloy liquid on the surface of the zinc bath, and then the workpiece is slowly lifted out of the pot, thereby forming a zinc-aluminum-magnesium alloy coating on the surface of the zinc coating of the workpiece;

[0032] Then air-cool, passivate and dry; the zinc bath temperature is 440°C, the galvanizing time is 5 minutes, the zinc-aluminum-magnesium alloy strip is 10 cm below the zinc liquid surface, and the time for plating the ash and spreading the zinc-aluminum-magnesium alloy melt on the zinc liquid surface is 40 seconds;

[0033] 2. Test results:

[0034] The total thickness of the coating (zinc coating and zinc-aluminum-magnesium alloy coating; the same below) is 76.8 microns, of which the thickness of the zinc-aluminum-magnesium alloy coating is 6.4 microns, the aluminum content of the alloy coating is 2.162%, and the magnesium content is 1.470%. The SEM image is as follows Figure 2 As shown, A is a zinc-aluminum-magnesium alloy coating, and B is a zinc coating;

[0035] The EDS spectra of the coating (zinc coating and zinc-aluminum-magnesium alloy coating) are as follows: Figure 3 As shown,

[0036] Table 1 Spectrum1

[0037]

[0038] Table 2 Spectrum2

[0039]

[0040] Table 3 Spectrum3

[0041]

[0042] Table 4 Spectrum4

[0043]

[0044] Table 5 Spectrum5

[0045]

[0046]

[0047] The drop hammer test showed no blistering or shedding of the coating. The neutral salt spray test showed red rust after 3228 hours.

[0048] Example 2

[0049] 1. Batch hot dip coating conditions

[0050] Steel grade Q355B;

[0051] Zinc bath composition: 0.0055% aluminum, 0.0204% nickel, 0.0221% iron and the balance zinc;

[0052] Composition of zinc-aluminum-magnesium alloy strip: 5.88% aluminum, 1.8% magnesium and the balance zinc;

[0053] According to the conventional hot-dip galvanizing method, degreasing, pickling, plating assistance, drying, etc. are performed, and then hot-dip galvanizing, bleaching zinc-aluminum-magnesium alloy liquid before being taken out of the pot, air cooling, passivation, and drying are performed; wherein, the zinc bath temperature is 440°C, the galvanizing time is 5 minutes, the zinc-aluminum-magnesium alloy strip is 8 cm below the zinc liquid surface, and the time for bleaching and plating tooling to dust and spread the zinc-aluminum-magnesium alloy melt on the zinc liquid surface is 40 seconds;

[0054] 2. Test results:

[0055] The total thickness of the coating is 72.4 microns, of which the thickness of the zinc-aluminum-magnesium alloy coating is 5.6 microns, and the aluminum content of the alloy coating is 2.26% and the magnesium content is 1.07%.

[0056] The drop hammer test showed no blistering or peeling of the coating. The neutral salt spray test showed red rust after 28-32 hours.

[0057] Example 3

[0058] 1. Batch hot dip coating conditions

[0059] Steel grade Q355B;

[0060] Zinc bath composition: 0.0075% aluminum, 0.0262% nickel, 0.0168% iron and the balance zinc;

[0061] Composition of zinc-aluminum-magnesium alloy strip: 5.88% aluminum, 2.6% magnesium and the balance zinc;

[0062] According to the conventional hot-dip galvanizing method, degreasing, pickling, plating assistance, drying, etc. are performed, and then hot-dip galvanizing, bleaching zinc-aluminum-magnesium alloy liquid before being taken out of the pot, air cooling, passivation, and drying are performed; wherein, the zinc bath temperature is 440°C, the galvanizing time is 5 minutes, the zinc-aluminum-magnesium alloy strip is 10 cm below the liquid surface of the zinc liquid, and the time for ash removal of the bleaching tool and spreading the molten zinc-aluminum-magnesium alloy on the surface of the zinc liquid is 60 seconds;

[0063] 2. Test results:

[0064] The total thickness of the coating is 68.8 microns, of which the thickness of the zinc-aluminum-magnesium alloy coating is 8.4 microns, and the aluminum content of the alloy coating is 3.65% and the magnesium content is 1.88%.

[0065] There was no blistering or shedding of the coating in the drop hammer test. Red rust appeared in the neutral salt spray test for 3840 hours.

[0066] Example 4

[0067] 1. Batch hot dip coating conditions

[0068] Steel grade Q355B;

[0069] Zinc bath composition: 0.0075% aluminum, 0.0255% nickel, 0.0218% iron and the balance zinc;

[0070] Composition of zinc-aluminum-magnesium alloy strip: 5.88% aluminum, 2.6% magnesium and the balance zinc;

[0071] According to the conventional hot-dip galvanizing method, degreasing, pickling, plating assistance, drying, etc. are performed, and then hot-dip galvanizing, bleaching zinc-aluminum-magnesium alloy liquid before being taken out of the pot, air cooling, passivation, and drying are performed; wherein, the zinc bath temperature is 440°C, the galvanizing time is 5 minutes, the zinc-aluminum-magnesium alloy strip is 5 cm below the zinc liquid surface, and the time for bleaching and plating tooling to dust and spread the zinc-aluminum-magnesium alloy melt on the zinc liquid surface is 40 seconds;

[0072] 2. Test results:

[0073] The total coating thickness is 77.6 microns, of which the zinc-aluminum-magnesium alloy coating thickness is 6.6 microns, and the aluminum content of the alloy coating is 3.15% and the magnesium content is 1.87%.

[0074] The drop hammer test showed no blistering or shedding of the coating. The neutral salt spray test showed red rust after 3408 hours.

[0075] Example 5

[0076] 1. Batch hot dip coating conditions

[0077] Steel grade Q355B;

[0078] Zinc bath composition: 0.0065% aluminum, 0.0215% nickel, 0.0231% iron and the balance zinc;

[0079] Composition of zinc-aluminum-magnesium alloy strip: 3.08% aluminum, 1.48% magnesium and the balance zinc;

[0080] According to the conventional hot-dip galvanizing method, degreasing, pickling, plating assistance, drying, etc. are performed, and then hot-dip galvanizing, bleaching zinc-aluminum-magnesium alloy liquid before being taken out of the pot, air cooling, passivation, and drying are performed; wherein, the zinc bath temperature is 440°C, the galvanizing time is 5 minutes, the zinc-aluminum-magnesium alloy strip is 5 cm below the zinc liquid surface, and the time for bleaching and plating tooling to dust and spread the zinc-aluminum-magnesium alloy melt on the zinc liquid surface is 60 seconds;

[0081] 2. Test results:

[0082] The total thickness of the coating is 86.7 microns, of which the thickness of the zinc-aluminum-magnesium alloy coating is 5.5 microns, and the aluminum content of the alloy coating is 1.76% and the magnesium content is 0.87%.

[0083] There was no blistering or shedding of the coating in the drop hammer test. Red rust appeared after 2112 hours of neutral salt spray test.

[0084] Example 6

[0085] 1. Batch hot dip coating conditions

[0086] Steel grade Q355B;

[0087] Zinc bath composition: 0.0045% aluminum, 0.0155% nickel, 0.016% iron and the balance zinc;

[0088] Composition of zinc-aluminum-magnesium alloy strip: 3.08% aluminum, 1.48% magnesium and the balance zinc;

[0089] According to the conventional hot-dip galvanizing method, degreasing, pickling, plating assistance, drying, etc. are performed, and then hot-dip galvanizing, bleaching zinc-aluminum-magnesium alloy liquid before being taken out of the pot, air cooling, passivation, and drying are performed; wherein, the zinc bath temperature is 440°C, the galvanizing time is 5 minutes, the zinc-aluminum-magnesium alloy strip is 5 cm below the zinc liquid surface, and the time for bleaching and plating tooling to dust and spread the zinc-aluminum-magnesium alloy melt on the zinc liquid surface is 40 seconds;

[0090] 2. Test results:

[0091] The total coating thickness is 69.8 microns, of which the zinc-aluminum-magnesium alloy coating thickness is 6.4 microns, and the aluminum content of the alloy coating is 1.31% and the magnesium content is 0.47%.

[0092] The drop hammer test showed no blistering or peeling of the coating. The neutral salt spray test showed red rust after 1848 hours.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A process for hot-dip bleaching zinc-aluminum-magnesium alloy liquid, characterized in that: The following steps are involved: The workpiece is hot-dip galvanized. Before the workpiece is taken out of the hot-dip galvanizing pot, the molten zinc-aluminum-magnesium alloy is spread on the surface of the zinc liquid, and the workpiece is taken out of the pot, thereby forming a zinc-aluminum-magnesium alloy coating on the surface of the zinc coating of the workpiece.

2. The process of hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 1, characterized in that: The hot-dip galvanizing zinc solution includes, by mass percentage, 0.003-0.008% aluminum, 0.015-0.040% nickel, 0.01-0.03% iron and the balance zinc. The galvanizing temperature is 430-450° C. and the galvanizing time is 2-10 minutes.

3. The process of hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 1, characterized in that: Before the workpiece is taken out of the hot-dip galvanizing pot, a drift plating tool is used to spread the molten zinc-aluminum-magnesium alloy on the surface of the zinc liquid while removing the dust. Then the workpiece is slowly taken out of the pot, thereby drift plating a zinc-aluminum-magnesium alloy coating on the surface of the zinc coating of the workpiece.

4. The process of hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 3, characterized in that: The plating tool includes an ash shovel, one side of which is provided with a mesh cage for placing zinc-aluminum-magnesium alloy strips. During operation, the ash shovel is used to beat the ash, and the zinc-aluminum-magnesium alloy strips are placed in the mesh cage. The zinc-aluminum-magnesium alloy strips are melted and spread in the high-temperature zinc liquid, thereby forming a thin layer of zinc-aluminum-magnesium alloy liquid on the surface of the zinc liquid.

5. The process of hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 4, characterized in that: When the bleaching and plating equipment is being plastered, the zinc-aluminum-magnesium alloy strips in the mesh cage are 5-10 cm below the liquid surface of the zinc liquid.

6. The process for hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 4, characterized in that: The time for the plating tool to spread the molten zinc-aluminum-magnesium alloy on the surface of the zinc liquid is 30-60 seconds.

7. The process for hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 1, characterized in that: In terms of mass percentage, the zinc-aluminum-magnesium alloy includes 3-6% aluminum, 1-3% magnesium and the balance zinc.

8. The process for hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 1, characterized in that: The thickness of the zinc-aluminum-magnesium alloy coating is 4-10 microns, and the total thickness of the zinc coating and the zinc-aluminum-magnesium alloy coating is 65-80 microns.

9. The process for hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 1, characterized in that: The specific steps include: Degreasing → washing → pickling → washing → auxiliary plating → drying → hot dip galvanizing → bleaching zinc aluminum magnesium alloy liquid before leaving the pot → air cooling → passivation → drying.

10. The process for hot-dip bleaching zinc-aluminum-magnesium alloy liquid according to claim 1, characterized in that: The workpiece is a steel wire, a steel coil or a steel component.

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