CN113463003A

CN113463003A - Plating assistant agent and hot galvanizing process applying same

Info

Publication number: CN113463003A
Application number: CN202110581220.8A
Authority: CN
Inventors: 马光耀
Original assignee: Hangzhou Longyao Power Accessories Co ltd
Current assignee: Hangzhou Longyao Power Accessories Co ltd
Priority date: 2021-05-26
Filing date: 2021-05-26
Publication date: 2021-10-01

Abstract

The application relates to the field of hot galvanizing, in particular to a plating assistant and a hot galvanizing process applying the plating assistant. The plating assistant agent comprises 4-9 g/L of stannic chloride and 3-7 g/L of sodium hexametaphosphate; the plating assisting process comprises the following steps: s1, sequentially carrying out degreasing, washing, acid pickling for rust removal and washing on the steel base to obtain a pretreated steel base; s2, dipping the pretreated steel base into a plating assistant agent, applying a sine alternating electric field between two ends of the pretreated steel base while dipping, taking out and drying after 1-2 min to obtain the pretreated steel base; and S3, placing the pre-plated steel base in a galvanizing solution for hot dipping. The plating layer prepared by the plating assistant agent and the hot galvanizing process has excellent apparent mass and higher adhesive force.

Description

Plating assistant agent and hot galvanizing process applying same

Technical Field

The application relates to the field of hot galvanizing, in particular to a plating assistant and a hot galvanizing process applying the plating assistant.

Background

Hot galvanizing is to dip steel base in molten zinc for galvanizing and form a protective layer on the surface to improve the rust-proof and corrosion-proof performance.

After the hot-dip galvanized workpiece is subjected to degreasing, pickling, cleaning and other production processes, iron salt, residual acid and other residues still exist on the surface of the hot-dip galvanized workpiece; before the workpiece is immersed in the galvanizing liquid, the workpiece steel base can react with air to generate an oxide film (rust) under the action of residues, so that the subsequent galvanizing quality is influenced, and the phenomenon of plating leakage is caused. In order to prevent this phenomenon, before the zinc immersion, the immersion treatment is usually carried out by using a plating assistant agent, on one hand, the oxide film on the surface of the workpiece can be removed; on the other hand, the method is favorable for reducing the resistance in the galvanization, and reducing the phenomena of plating leakage and the like.

The Chinese invention application with the application number of CN201910616757.6 discloses a hot-dip galvanizing plating assistant and a hot-dip galvanizing process, wherein the plating assistant comprises the following components: 110-200 g/L of zinc chloride, 20-96 g/L of potassium chloride and 20-48 g/L of sodium chloride, wherein the weight ratio of the potassium chloride to the sodium chloride is 1: 1-2, wherein the total weight of potassium chloride and sodium chloride is 40-70% of the weight of zinc chloride.

In view of the above technical solutions, the inventors believe that when the galvanizing solution contains aluminum, the plating assistant is liable to react with aluminum chloride to generate aluminum chloride, which results in failure of the plating assistant effect of the plating assistant, and the steel substrate is not protected before hot dipping to generate an oxide film, thereby resulting in defects such as pinholes, bubbles, and plating leakage on the surface of the plating layer.

Content of application

In order to reduce the defects of pinholes, bubbles, plating leakage and the like generated on the surface of a plating layer, the application provides the plating assistant agent and the hot galvanizing process applying the plating assistant agent, and the plating assistant agent is matched with the hot galvanizing process to effectively improve the galvanizing quality.

In a first aspect, the application provides a plating assistant agent, which adopts the following technical scheme:

the plating assistant agent is prepared from an aqueous solution containing the following mass concentrations:

ammonium chloride: 50-60 g/L;

zinc chloride: 70-90 g/L;

potassium chloride: 15-30 g/L;

tin chloride: 4-9 g/L;

sodium hexametaphosphate: 3-7 g/L;

film-forming auxiliary agent: 15-25 g/L.

After the dipping of the plating assistant agent, the residual impurities on the surface of the steel base steel are removed, and a plating assistant agent film can be formed on the surface of the steel base steel. The plating assistant agent film can play a role in preventing the steel piece after acid washing from being secondarily oxidized, dissolving the generated FeO and generating iron salt which can be reduced by zinc liquid;

in the second aspect, when entering the zinc liquid, the zinc liquid can be quickly gasified and reacted, and the reaction product can adsorb impurities in the zinc liquid;

in the third aspect, after the plating assistant agent is decomposed, the surface of the workpiece has activity, so that zinc liquid can be well attached to the surface of the workpiece, and the generation of an alloy layer in the hot dip plating process is accelerated;

in the fourth aspect, the plating assistant agent has the function of reducing the surface tension of the zinc liquid, increasing the infiltration capacity of the steel base to the zinc liquid and reducing the plating leakage phenomenon.

According to the tin chloride added in the application, tin ions can perform a replacement reaction with simple substance iron of the steel base to form a tin film on the surface of the steel base, so that the effect of preventing the surface of the steel base from being oxidized and rusted is achieved, and the steel base is effectively protected before galvanization; during the galvanizing process, the defects of the galvanizing layer on the surface of the steel base are obviously reduced.

If the iron ions generated by the above-mentioned reaction remain on the surface of the steel base, the zinc coating becomes rough and uneven during hot galvanizing; the sodium hexametaphosphate added in the method can perform a complex reaction with iron ions to form a precipitate for removal, so that the surface defects of the zinc coating are reduced.

Preferably, the surfactant is one or more of dipropylene glycol methyl ether, ethanol and tetrafluoropropanol.

By adopting the technical scheme, the non-film-forming auxiliary agent can improve the wettability and the adhesive force of the plating assistant agent to the surface of the steel substrate, so that the plating assistant agent is more uniformly and stably attached to the surface of the steel substrate, and the apparent quality of a zinc coating is improved.

In a second aspect, the present application provides a hot dip galvanizing process, which adopts the following technical scheme:

a hot galvanizing process applying the plating assistant agent in the claim 1 or 2, comprising the following steps:

s1, sequentially carrying out degreasing, washing, acid pickling for rust removal and washing on the steel base to obtain a pretreated steel base;

s2, dipping the pretreated steel base into a plating assistant agent, applying a sine alternating electric field between two ends of the pretreated steel base while dipping, taking out and drying after 1-2 min to obtain the pre-plated steel base;

and S3, placing the pre-plated steel base in a galvanizing solution for hot dipping.

According to the method, a sine alternating electric field is applied between two ends of the pretreated steel base, so that the components of the plating assistant agent, particularly the diffusion of tin ions in the length direction of the steel base, can be promoted, and the distribution uniformity of the plating assistant agent is improved, so that a uniform and compact tin film is formed on the steel base on the plating assistant agent layer, the protection effect on the steel base is improved, the improvement of the galvanizing quality is facilitated, and the galvanizing defects are reduced.

In addition, the tin film formed on the surface of the steel substrate can induce aluminum element to form Fe on the surface of the steel substrate₂And the iron-aluminum compound layer such as Al and the like can play a medium role in forming a zinc coating, so that the adhesion of the zinc coating is improved, the coating is not easy to fall off, and the corrosion resistance of the steel base is improved.

Preferably, in step S2, the sinusoidal alternating electric field has a current density of 1 to 2.5a.dm^-2。

By adopting the technical scheme, when the current density is too low, the effect of fully improving the diffusion speed of the plating assistant cannot be achieved; when the current density is too high, the components such as ammonium chloride in the plating assistant agent are easily decomposed, and the plating assistant effect is reduced.

Preferably, in step S2, the frequency of the sinusoidal alternating electric field is 30 to 60 Hz.

By adopting the technical scheme, when the frequency is too low, the diffusion effect of the plating assistant agent is poor,

uniform tin film is difficult to form on a steel base; when the frequency is too high, the disturbance to the solution is large,

it is difficult to form a dense tin film on a steel base.

Preferably, in step S2, the temperature of the plating assistant is 40 to 55 ℃.

By adopting the technical scheme, the temperature of the plating assistant agent is properly increased, and the sedimentation speed of the plating assistant agent on the surface of the steel substrate can be increased. When the plating assistant temperature is too low, the plating assistant time is increased, the hot galvanizing efficiency is reduced, and when the plating assistant temperature is too high, the solvent volatilization is serious, so that the concentration of the plating assistant is difficult to control.

Preferably, in the step S2, the drying initial temperature is 70-85 ℃, then the temperature is increased to 120-140 ℃ at the speed of 4-7 ℃/min, and the temperature is maintained for 10-15 min.

By adopting the technical scheme, after plating assistant is finished, the plating assistant agent salt film is dried at a lower temperature, and then the tin film is dried at a higher temperature to obtain a uniform and compact plating assistant agent layer.

Preferably, in step S3, the zinc plating solution is prepared by melting the following raw materials in percentage by mass:

Al：3％～5.5％；

Ni：0.1％～0.25％；

Mn：1％～2％；

Mg：0.3％～1％；

Si：0.05％～0.2％；

Sn：0.5％～1％；

La₂O₃：0.05％～0.2％；

the balance of Zn.

By adopting the technical scheme, the aluminum element can react with the steel base before the zinc element to form an iron-aluminum compound layer, so that the adhesive force of the coating is improved; the nickel element can increase the fluidity of the zinc plating solution, improve the infiltration degree of the zinc plating solution to steel base, and reduce the defects of plating leakage and the like; manganese can improve the oxidation resistance and corrosion resistance of the coating; the silicon can improve the adhesive force and the corrosion resistance of the coating; the tin element can form spangles on the surface of the coating, and the attractiveness of the coating is improved.

The lanthanum oxide can slow down the layered fluctuation range of the coating, refine the coating structure, reduce the pores and obtain a more uniform and compact coating. In addition, the rare earth element can also reduce the surface tension of the galvanizing solution, so that the wettability of the galvanizing solution and the steel substrate is improved, and the adhesion of the plating layer to the steel substrate is improved.

In summary, the present application has the following beneficial effects:

1. the tin chloride and the sodium hexametaphosphate are matched together, so that the steel base can be effectively protected from being oxidized, and the surface defects of the plating layer are reduced.

2. In the plating assistant process, the sine alternating current is applied to the steel base in the length direction, so that the dispersion of the plating assistant agent is promoted, and a more uniform and dense tin film and a plating assistant agent salt film are formed on the surface of the steel base, and the quality of a plating layer and the adhesive force of the plating layer are obviously improved.

3. By adopting the aluminum and nickel elements in the galvanizing solution, the adhesion of the coating is effectively improved, and the galvanizing defects are reduced.

Detailed Description

The present application will be described in further detail with reference to examples.

Preparation example

Preparation example 1, a plating assistant, each raw material component was selected and its corresponding amount as shown in table 1, and each raw material component was sequentially added to water and stirred to mix.

Preparation examples 2 to 7, a plating assistant, were different from preparation example 1 in that the selection of each raw material component and the corresponding amount thereof were as shown in table 1.

TABLE 1 selection of raw material components in plating assistant agents and their respective contents (g) in preparation examples 1 to 7

Preparation example a, a zinc plating bath, the selection of the raw material components and their respective contents are shown in table 2, and was prepared by melting the respective raw materials.

Preparation examples b to e, a zinc plating bath, were different from preparation example a in that the selection of the raw material components and their respective contents were as shown in Table 2.

TABLE 2 selection of raw materials and their respective contents (kg) of the galvanising solutions of preparation examples a to e

	Preparation example a	Preparation example b	Preparation example c	Preparation example d	Preparation e
						Al	4.8	3	5.5	4.8	0
Ni	0.13	0.1	0.25	0.13	0.13
						Mn	1.2	1	2	1.2	1.2
Mg	0.45	0.3	1	0.45	0.45
						Si	0.08	0.05	0.2	0.08	0.08
Sn	0.8	0.5	1	0.8	0.8
						La2O3	0.17	0.15	0.2	0	0.17
Zn	92.37	94.9	89.85	92.54	97.17

Examples

Embodiment 1, a hot dip galvanizing process includes the steps of:

s1, sequentially carrying out degreasing, washing, acid pickling for derusting and washing on the steel plate to obtain a pretreated steel plate;

s2, putting the plating assistant agent prepared in the preparation example 1 into a galvanizing bath, heating the solution of the plating assistant agent to 45 ℃, respectively placing a nickel metal plate at two ends of the bath, wherein the two nickel metal plates are parallel to each other, and then adding sinusoidal alternating current to the two nickel metal plates; the pretreated steel plate is placed between two nickel metal plates, and the plating assistant solution is immersed in the pretreated steel plate, and the current density of a sine alternating electric field is 1.5A.dm^-2Dipping for 2min at the frequency of 50Hz, taking out, drying at the temperature of 80 ℃, heating to 130 ℃ at the speed of 5 ℃/min, and preserving heat for 15min to obtain a pre-plated steel plate;

and S3, placing the pre-plated steel plate into the galvanizing solution prepared in the preparation example a for hot dipping, wherein the temperature of the galvanizing solution is 455 ℃, the dipping time is 50S, and after the dipping is finished, taking out the pre-plated steel plate and placing the pre-plated steel plate into water at 30 ℃ for water cooling to obtain a finished galvanized steel plate.

Example 2, a hot dip galvanizing process, was different from example 1 in that the plating assistant prepared in preparation example 2 was used in step S2.

Example 3, a hot dip galvanizing process, was different from example 1 in that the plating assistant prepared in preparation example 3 was used in step S2.

Example 4, a hot dip galvanizing process, was different from example 1 in that the plating assistant prepared in preparation example 4 was used in step S2.

Example 5, a hot galvanizing process, was different from example 1 in that the galvanizing solution prepared in preparation example b was used in step S3.

Example 6, a hot galvanizing process, was different from example 1 in that the galvanizing solution prepared in preparation example c was used in step S3.

Example 7, a hot galvanizing process, was different from example 1 in that the galvanizing solution prepared in preparation example d was used in step S3.

Example 8, a hot dip galvanizing process, was different from example 1 in that the galvanizing solution prepared in preparation example e was used in step S3.

Example 9 a Hot galvanizing Process, difference from example 1In step S2, the current density is 0.5A.dm^-2。

Example 10, a hot dip galvanizing process, differs from example 1 in that in step S2, the current density was 3a.dm^-2。

Example 11, a hot dip galvanizing process, was different from example 1 in that the current frequency was 20Hz in step S2.

Example 12, a hot galvanizing process, was different from example 1 in that in step S2, the current frequency was 80 Hz.

Example 13, a hot dip galvanizing process, differs from example 1 in that in step S2, the flux temperature is 65 ℃.

Example 14, a hot dip galvanizing process, differs from example 1 in that in step S2, the plating assistant is dipped, taken out and dried, and then dried at 85 ℃ for 30 min.

Example 15 is different from example 1 in that, in the step S2, when the plating assistant agent is dipped, taken out and dried, the hot dip galvanizing process is performed by drying at 130 ℃ for 25 min.

Example 16, a hot galvanizing process, differs from example 1 in that the specific operation of step S2 is as follows:

putting the plating assistant agent prepared in the preparation example 1 into a galvanizing bath, heating the plating assistant agent solution to 45 ℃, putting the pretreated steel plate into the galvanizing bath, immersing the pretreated steel plate in the plating assistant agent solution, taking out after immersing for 2min, drying at 80 ℃, then heating to 130 ℃ at the speed of 5 ℃/min, and preserving heat for 15min to obtain a pre-plated steel plate; namely, a sine alternating electric field is not applied to the steel plate during the plating assisting.

Comparative example

Comparative example 1, a hot dip galvanizing process, differs from example 1 in that in step S2, the plating assistant prepared in preparation example 5 was used, i.e., tin chloride was not added to the plating assistant.

Comparative example 2, a hot dip galvanizing process, differs from example 1 in that the plating assistant prepared in preparation example 5 was used in step S2, i.e., sodium hexametaphosphate was not added to the plating assistant.

Comparative example 3, a hot dip galvanizing process, differs from example 1 in that the plating assistant prepared in preparation example 5 was used in step S2, i.e., tin chloride and sodium hexametaphosphate were not added to the plating assistant.

Comparative example 4, a hot galvanizing process, is different from example 1 in that the specific operation of step S2 is:

adding metered water into a plating assistant tank, heating the water to 40-70 ℃, gradually adding the components of the plating assistant agent, stirring and dissolving, and then adjusting the pH value to 3.5-4.5 by hydrochloric acid to obtain a plating assistant solution; and soaking the workpiece to be plated in the plating assistant solution until the workpiece is plated in the plating assistant solution for 3min, lifting the workpiece out and pouring out the plating assistant solution.

Wherein the plating assistant agent comprises the following components in percentage by weight: 110g of zinc chloride, 30g of potassium chloride, 25g of sodium chloride, 12 g of ammonium chloride and 1000g of water.

Performance test

Test 1: coating surface quality evaluation test

The test method comprises the following steps: the coating surface quality of the test specimens was evaluated with reference to the standard sheet for zinc coating defects of Table 3, and the evaluation results are shown in Table 4.

TABLE 3 standard list of zinc coating defects (minutes)

0

1

2

3

4

5

Area of skip plating

<15％

<12％

<9％

<6％

<3％

Non-skip plating

Number of pinholes

<15％

<12％

<9％

<6％

<3％

No pinhole

Number of zinc nodules

>10％

<8％

<6％

<4％

<2％

Without zinc nodules

Table 4 coating surface quality evaluation test results (minutes)

And (3) analyzing test results:

(1) in combination with examples 1 to 16 and comparative examples 1 to 4 and table 4, it can be seen that the plating assistant agent adopts tin chloride and sodium hexametaphosphate to cooperate together, which can effectively improve the plating quality of hot galvanizing. The reason for this may be that tin chloride is capable of undergoing a substitution reaction with elemental iron in the steel substrate, precipitating a tin film on the surface of the steel substrate, and generating Fe²⁺. The tin film can protect the steel base matrix from oxidation and corrosion before entering the zinc liquid, and ensure the infiltration and adhesive force of the zinc liquid to the steel base surface, thereby reducing the quality problems of leakage stoppage, pin holes and the like.

In addition, the tin film can also induce and promote aluminum elements to form Fe on the surface of the steel substrate₂Al、Fe₂Al₅When the iron-aluminum compound layer is formed, the iron-aluminum compound layer can be used as an intermediate medium layer to improve the adhesive force of the iron-zinc alloy layer and the steel base, so that the integral adhesive force of the zinc coating is enhanced. Meanwhile, the tin film can relieve the problem of poor wettability of zinc liquid on the surface of the steel substrate due to the reaction of aluminum element and the plating assistant components such as ammonium chloride, zinc chloride and the like on the surface of the steel substrate, and reduce quality defects such as plating leakage, pinholes and the like.

Fe produced by the above substitution reaction²⁺The zinc is carried into the galvanizing liquid, which causes quality problems such as zinc nodules and the like, and the galvanized layer becomes rough and uneven. Sodium hexametaphosphate employed in the present application can react with Fe²⁺Complex reaction occurs to form zinc slag precipitate, thereby reducing Fe²⁺And the quality of the plating layer is improved.

In conclusion, the effect of improving the quality of the plating layer is achieved through the matching of the tin chloride and the sodium hexametaphosphate.

(2) By combining the embodiment 1 and the embodiment 4 and combining the table 4, it can be seen that the coating quality of the hot dip galvanizing can be effectively improved by adopting the film forming assistant in the plating assistant. The reason for this may be that the film-forming assistant can improve the wettability of the surface of the plating assistant steel base; the dipropylene glycol methyl ether has a coupling effect, so that the adhesive force of the plating assistant agent on the surface of the steel substrate can be improved, the salt film layer of the plating assistant agent is not easy to fall off, and the plating quality is improved.

(3) Combine example 1 with example 16It can be seen from table 4 that the coating quality of hot galvanizing can be effectively improved by applying a sine alternating electric field to two ends of a steel base matrix during plating assistance. The reason for this may be that the sinusoidal alternating electric field can significantly improve the dispersibility of the components in the plating assistant solution, particularly Sn²⁺To promote a more dense and uniform tin film formation; in addition, sodium hexametaphosphate and Fe can be promoted²⁺Thereby improving the quality of the plating layer.

(4) As can be seen from the combination of examples 1 and 9 to 10 and Table 4, the plating aid used has a current density of 1 to 2.5A.dm^-2The quality of the prepared coating is better. The reason for this may be that, when the current density is too low, it does not function to sufficiently increase the diffusion rate of the plating assistant; when the current density is too high, the components such as ammonium chloride in the plating assistant agent are easily decomposed, and the plating assistant effect is reduced.

(5) By combining the embodiment 1 and the embodiments 11 to 12 and combining the table 4, it can be seen that the plating assistant is performed by using a sinusoidal alternating electric field with a current frequency of 30 to 60Hz, and the quality of the prepared plating layer is good. The reason for this may be that, when the frequency is too low, the plating assistant diffusion effect is poor, and it is difficult to form a uniform tin film on the steel substrate; when the frequency is too high, the disturbance of the solution is large and it is difficult to form a dense tin film on the steel substrate.

(6) By combining the embodiment 1 and the embodiments 11 to 12 and combining the table 4, it can be seen that after the plating assistant is completed, the tin film layer and the plating assistant salt film layer are dried in a segmented drying manner and at a constant temperature, and the quality of the prepared plating layer is good. The reason for this is probably that after the plating assistant is finished, the tin film layer is attached to the surface of the steel substrate, and the salt film layer of the plating assistant agent is attached to the surface of the tin film layer, so if the drying is not thorough, the residual moisture is too much, which will cause the plating assistant effect to be greatly reduced, and influence the formation and quality of the zinc coating.

In the application, the plating assistant agent salt film layer and the tin film layer are sequentially dried by adopting a sectional drying mode, and the internal stress of the film layer during drying is reduced by a uniform temperature rise mode, so that the film layer is more compact in forming, and the quality of the plating layer is improved.

Test 2: adhesion test of plating layer

Sample preparation: by using the galvanizing processes corresponding to examples 1 to 16 and comparative examples 1 to 4, respectively, plating layers were formed on Q235 steel sheets having dimensions of 60mm × 50mm × 2mm, and test samples 1 to 15 and comparative samples 1 to 4 were prepared, and 6 specimens were prepared for each group.

The test method comprises the following steps: the detection is carried out according to the detection standard in GB/T5210-2006 adhesion test by paint and varnish pulling method. Directly bonding a test column of a tension tester to the surface of a coating of a sample by using an adhesive, placing the bonded test combination on a proper tension tester after the adhesive is cured, and measuring the tension required for damaging the adhesion between the coating and the sample steel plate by the bonded test combination through a tension test. The surface adhesion of the coating to the steel sheet is expressed by a tensile force to break the interfacial (adhesion failure) or a tensile force to break the coating by itself (cohesive failure). The average value of the surface adhesion force of 6 specimens was used as the test result, and the test result is shown in Table 5.

Test equipment: the tensile testing machine adopts an XH-M adhesion tester.

TABLE 5 coating adhesion test results

And (3) analyzing test results:

(1) in combination with examples 1 to 16 and comparative examples 1 to 4 and table 5, it can be seen that the plating assistant agent adopts tin chloride and sodium hexametaphosphate to cooperate together, so that the adhesion of the plating layer on the surface of the steel substrate can be effectively improved. The reason may be that tin chloride is added to generate a tin film on the surface of the steel substrate, and the tin film has the functions of ensuring the cleanness of the surface of the substrate and improving the quality of a plating layer; the tin film on the other hand has the function of inducing the aluminum element to form a more compact iron-aluminum compound layer on the surface of the steel substrate. Because the activity of the aluminum element is higher than that of zinc, the aluminum element can form an iron-aluminum compound layer on the surface of the steel substrate earlier than the zinc element, and then form an iron-zinc alloy layer and a pure zinc layer, and the iron-aluminum compound layer can play the role of an intermediate medium layer, so that the adhesive force of the iron-zinc alloy layer and the pure zinc layer is improved, and the integral adhesive force of the coating is improved. Therefore, the tin film also has a function of enhancing the adhesion of the plating layer.

(2) By combining the embodiment 1 and the embodiment 16 and combining the table 4, it can be seen that the adhesion between the plating layer and the steel base can be effectively improved by applying a sinusoidal alternating electric field to the two ends of the steel base during the plating assisting. The reason may be that the sine alternating electric field can promote the dispersion of the plating assistant, especially tin ions, and form a more compact and stable tin film layer and a plating assistant salt film layer on the surface of the steel substrate, thereby promoting the formation of each alloy layer of the plating layer and enhancing the adhesion of the plating layer.

The present embodiment is only for explaining the present application and is not limited to the present application, and those skilled in the art can make modifications of the present embodiment without inventive contribution as required after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present application.

Claims

1. The plating assistant is characterized by being prepared from an aqueous solution containing the following mass concentrations:

ammonium chloride: 50-60 g/L;

zinc chloride: 70-90 g/L;

potassium chloride: 15-30 g/L;

tin chloride: 4-9 g/L;

sodium hexametaphosphate: 3-7 g/L;

film-forming auxiliary agent: 15-25 g/L.

2. The plating assistant agent as recited in claim 1, wherein the surfactant is one or more selected from the group consisting of dipropylene glycol methyl ether, ethanol, and tetrafluoropropanol.

3. A hot galvanizing process applying the plating assistant agent of claim 1 or 2, which is characterized by comprising the following steps:

s2, dipping the pretreated steel base into a plating assistant agent, applying a sine alternating electric field between two ends of the pretreated steel base while dipping, taking out and drying after 1-2 min to obtain the pretreated steel base;

4. The hot dip galvanizing process according to claim 3, wherein in the step S2, the sinusoidal alternating electric field has a current density of 1 to 2.5A.dm^-2。

5. A hot dip galvanizing process according to claim 3, characterized in that in the step S2, the frequency of the sinusoidal alternating electric field is 30-60 Hz.

6. A hot dip galvanizing process according to claim 3, wherein in the step S2, the temperature of the plating assistant agent is 50-55 ℃.

7. A hot dip galvanizing process according to claim 3, characterized in that in the step S2, the initial drying temperature is 70-85 ℃, and then the temperature is raised to 120-140 ℃ at a speed of 4-7 ℃/min, and the temperature is maintained for 10-15 min.

8. A hot galvanizing process according to claim 3, characterized in that in step S3,

the zinc plating solution is prepared by melting the following raw materials in percentage by mass:

Al：3%～5.5%；

Ni：0.1%～0.25%；

Mn：1%～2%；

Mg：0.3%～1%；

Si：0.05%～0.2%；

Sn：0.5%～1%；

La₂O₃：0.05%～0.2%；

the balance of Zn.