A pre-formation treatment agent for a metal surface film forming method and use thereof

Abstract

The application discloses a pre-formation treatment agent for a metal surface film forming method and application thereof. The pre-formation treatment agent is an alkaline liquid composition, and main components are copper element, silane coupling agent, resin, ammonia compound, and the rest is pure water. The pre-formation treatment agent can cooperate with subsequent formation surface treatment process, enhance the physical strength and chemical resistance of the metal surface film, and can adjust the charge state of the metal surface, increase the matching force between the pretreatment conversion film and the cathode electrophoresis of the subsequent process.

Description

Technical Field

[0001] This invention belongs to the field of low-carbon and environmentally friendly metal surface pretreatment, and particularly relates to the field of thin film pretreatment based on conversion film structures such as copper oxide, zirconium oxide, organosilane and resin. Background Technology

[0002] Traditional phosphating pretreatment processes have undergone over 100 years of development, application, and technological iteration, and are widely used in industries and applications such as automotive, steel, home appliances, parts processing, and plastic forming where short-term rust prevention, wear resistance, lubrication, and enhanced adhesion to subsequent coating materials (cathodic electrophoresis, electrostatic powder coating, painting, etc.) are required. While traditional phosphating is still used in most applications, with increasing environmental awareness and the use of new metallic / non-metallic materials (such as color-coated steel sheets), traditional phosphating is being replaced by more environmentally friendly and lower-carbon thin-film metal surface treatment processes. Currently, the home appliance industry has achieved 100% replacement, and the automotive / parts industry has a replacement rate of approximately 8-10%. Other applications, such as plastic forming and wear resistance, have not yet adopted thin-film pretreatment processes.

[0003] In thin film pretreatment processes, the loss of adhesion between the treated metal material and the primer (usually cathodic electrophoresis) is a serious failure mode. This can cause large-area peeling of the surface coating of related products (such as automobiles) under certain external forces, or a sharp increase in the rate and area of ​​metal corrosion at the damaged coating site. This can lead to rapid feedback from the end market, or even mass recalls. The loss of adhesion between the treated metal material and the primer (referred to as poor adhesion) manifests in two forms: dry failure and wet failure. Dry failure refers to the failure of a metal substrate after pretreatment, primer coating, and drying and curing, when it is left to stand for a certain period of time under certain conditions according to the corresponding standard methods (such as GB-T 1732-1993 "Test Method for Impact Resistance of Coating Films", which stipulates that the test pieces should be conditioned at 23±2℃ and 50±5% relative humidity for at least 16 hours) and subjected to tests related to the adhesion of the coating film (such as cupping, impact, cross-cut adhesion, etc.). Wet failure, on the other hand, refers to the large-scale peeling of the coating film in non-corroded areas near the scribing line of a test sample after pretreatment, primer coating, and drying and curing, after a period of accelerated aging corrosion testing (such as neutral salt spray, cyclic alternating corrosion test). Traditional phosphating pretreatment electrophoresis has a certain probability of dry failure, but wet failure is extremely rare; while thin film pretreatment electrophoresis can result in both dry and wet failure. Wet failure of coatings is a relatively insidious failure mode. It usually requires samples to be tested under certain temperature, humidity and salinity conditions for a period of time (about 1 month) before it becomes apparent. During this period, vehicles produced have coating quality risks, so corresponding measures must be taken to reduce the risks to an acceptable level.

[0004] Currently, the most widely accepted solution in the industry for reducing poor adhesion after film pretreatment is to add a certain amount of copper-containing compound to the film pretreatment working solution. However, while adding a certain amount of copper-containing compound to the film pretreatment working solution can effectively reduce the risk of poor coating adhesion, it also brings the following problems:

[0005] ① Excessive copper adhesion can lead to poor appearance in subsequent electrophoretic coating (such as increased roughness);

[0006] ② When the copper content in the thin film pretreatment bath is too high and needs to be reduced, the only way to dilute and reduce the concentration is to discharge a portion of the bath solution, which leads to an increase in processing costs.

[0007] ③ The pretreatment formation process will carry liquid to the subsequent process, resulting in the enrichment of copper elements in the electrophoresis tank. Excessive copper elements are detrimental to the electrophoresis tank solution.

[0008] ④ Copper elements co-exist with organic substances such as silanes in the same tank, which accelerates the self-condensation and other reactions of organic components, leading to waste or even failure of the reagents. Summary of the Invention

[0009] To address the aforementioned problems caused by the co-existence of copper and thin film pretreatment agents in the same bath, this invention provides a pre-forming treatment agent for metal surface coating methods and its application. Specifically, by incorporating a pre-forming treatment step before the thin film pretreatment step, the above problems can be significantly improved.

[0010] The technical solution adopted in this invention is as follows: a pre-forming treatment agent for a metal surface coating method, the pre-forming treatment agent comprising: copper element, silane coupling agent, resin, ammonia compound and pure water.

[0011] Preferably, the pre-forming agent for the above-mentioned metal surface coating method comprises, by mass percentage: 0.5-5% copper element, 0.5-5% silane coupling agent, 0.5-5% resin, 1-5% ammonia compound and the balance being pure water.

[0012] Preferably, in the above-mentioned pre-forming agent for metal surface coating method, the copper element is a combination of I-valent copper and II-valent copper; with a molar ratio of I-valent copper:II-valent copper = 1:0.2-5.

[0013] More preferably, the molar ratio is I-valent copper:II-valent copper = 1:0.8 to 1.25.

[0014] Preferably, in the above-mentioned pre-forming agent for metal surface coating method, the copper element is derived from at least one of copper nitrate, copper sulfate, cuprous sulfate, basic copper carbonate, cuprous iodide, and organic phosphonate cuprous salt.

[0015] Preferably, in the above-mentioned pre-forming treatment agent for metal surface coating method, the organosphinic acid cuprous salt has the general structural formula shown in (I):

[0016]

[0017] R1 and R2 are C1 to C6 alkyl groups.

[0018] Preferably, in the above-mentioned pre-forming treatment agent for metal surface coating method, the silane coupling agent is at least one of acyloxysilane, aminosilane, and epoxysilane.

[0019] More preferably, in the above-mentioned pre-forming agent for metal surface coating method, the aminosilane is at least one of monoaminosilane, diaminosilane, triaminosilane and polyaminosilane.

[0020] Preferably, in the above-mentioned pre-forming agent for metal surface coating method, the resin is at least one selected from polyethylene glycol, ethanolamine ester (EPO), organic amine ester (TPP), and tripropylene glycol (TPG).

[0021] Preferably, in the above-mentioned pre-forming agent for metal surface coating method, the ammonia compound is at least one selected from ammonia water, ammonium bicarbonate, monoethanolamine, diethanolamine and diethylene glycolamine.

[0022] The application of the pre-forming treatment agent provided by this invention in the pre-forming process of a metal surface coating method.

[0023] Preferably, in the pre-forming process, the pre-forming agent is dissolved in pure water (conductivity ≤20μs / cm) to obtain a pre-forming working solution; the content of the pre-forming agent in the pre-forming working solution is in the range of 1 to 5‰ by mass percentage.

[0024] Preferably, the pre-formation treatment agent contributes no less than 8.5 to the pH of the pre-formation working solution. This pH contribution of no less than 8.5 means that after adding the pre-formation agent to pure water at a concentration of 1-5‰, the pH of the pre-formation working solution should be no less than 8.5.

[0025] A method for coating a metal surface, using the pre-forming treatment agent provided by this invention, includes the following steps:

[0026] 1) First hot water wash: Spray the sample with hot water at 35-42℃ for 90-100 seconds;

[0027] 2) Pre-degreasing: After the first hot water wash, the sample is pre-treated by spraying it with a degreasing agent at 35-42℃ for 60-70 seconds;

[0028] 3) Degreasing treatment: Immerse the pre-degreased sample in a degreasing agent at 35-42℃ for 120-150 seconds;

[0029] 4) Second wash: After degreasing, the sample is sprayed with industrial water at room temperature for 60-90 seconds, and then immersed in industrial water at room temperature for 180-240 seconds.

[0030] 5) Pre-treatment: Immerse the sample after the second water wash in a pre-treatment working solution containing 1-5‰ of the pre-treatment agent at room temperature for 30-40 seconds;

[0031] 6) Formation: Immerse the pre-formed sample in a forming agent at room temperature for 150-180 seconds;

[0032] 7) Third pure water wash: Spray the chemically treated sample with pure water at room temperature for 30-40 seconds; then immerse it in pure water at room temperature for 60-90 seconds.

[0033] The beneficial effects of this invention are:

[0034] 1. By applying the pre-formation treatment agent of the present invention, the concentration of copper in the pre-formation working solution can be flexibly adjusted to adapt to different materials being treated and differences in production line design at the application site.

[0035] 2. The pre-conversion treatment agent provided by the present invention can be used separately from the subsequent conversion agent, which can avoid the problem of uneven distribution of copper elements on the surface of the treated material, and make the pre-treatment chemical conversion film more uniform and complete.

[0036] 3. The pre-forming treatment agent provided by the present invention can be used separately from the subsequent forming agent, which can reduce the influence of copper element on organic components such as silane in the forming agent and extend the life of the forming working fluid.

[0037] 4. The pre-formation treatment agent provided by the present invention allows the process containing copper elements to be further away from the electrophoresis station, which can reduce the enrichment of copper elements in the electrophoresis tank due to liquid carryover.

[0038] 5. The pre-treatment agent provided by this invention is added to the water washing tank of the corresponding station using a suitable feeding device (usually a pneumatic diaphragm pump system) and circulated for more than 15 minutes. The pre-treatment agent provided by this invention can, for vehicle body metal materials (cold-rolled, hot-rolled, galvanized, aluminum, etc.), synergistically enhance the physical strength and chemical resistance of the metal surface coating in subsequent chemical surface treatment processes, and can also adjust the charge state of the metal surface and increase the bonding force between the pretreatment conversion film and the subsequent cathodic electrophoresis process.

[0039] 6. The pre-forming agent provided by this invention uses a combination of I-valent and II-valent copper. Through substitution reactions with the treated metals (Fe, Zn, Al, etc.) and other redox reactions, the copper element transforms from an ionic state to an elemental or oxide molecular state and is distributed on the surface of the treated object. This catalyzes and accelerates the main reactions in the pretreatment of the film (i.e., the hydrolysis deposition reaction of fluorozirconic acid and the cross-linking reaction of silanes). In particular, when the copper element forms Cu2O-CuO heterojunctions, it plays a very important role in the rate and morphology of the cross-linking reaction of organic substances such as silanes. The cross-linking morphology of organic substances such as silanes also plays a significant role in reducing the risk of poor coating adhesion after the pretreatment of the film. Attached Figure Description

[0040] Figure 1 This is a flowchart of the pretreatment process in a vehicle manufacturing plant using the pre-formed treatment agent of this invention (applied to the red-marked workstations).

[0041] Figure 2 This is an energy dispersive spectroscopy (EDS) elemental analysis of the surface of the cold-rolled sheet in Example 1 after (a) / without (b) pre-forming treatment.

[0042] Figure 3This is an energy dispersive spectroscopy (EDS) elemental analysis of the galvanized sheet surface in Example 1 after (a) / without (b) pre-treatment.

[0043] Figure 4 The energy dispersive spectroscopy (EDS) elemental analysis of the aluminum alloy plate surface in Example 1 after (a) / without (b) pre-forming treatment.

[0044] Figure 5 The results are the coating adhesion test results of the cold-rolled sheet after electrophoresis in Example 2, after (a) / without (b) pre-forming treatment.

[0045] Figure 6 The results are the adhesion test results of the paint film after electrophoresis of the galvanized sheet in Example 2 after (a) / without (b) pre-forming treatment.

[0046] Figure 7 The results are the adhesion test results of the paint film after electrophoresis of the aluminum alloy plate in Example 2 after (a) / without (b) pre-forming treatment.

[0047] Figure 8 The results of the neutral salt spray test on the coating film of the cold-rolled sheet after electrophoresis (a) / without (b) pre-forming treatment in Example 2 are as follows.

[0048] Figure 9 The results are from the electrophoretic coating cycle test of the galvanized sheet in Example 2 after (a) / without (b) pre-treatment.

[0049] Figure 10 The results are from the electrophoretic coating cycle test of the aluminum alloy plate in Example 2 after (a) / without (b) pre-treatment. Detailed Implementation

[0050] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0051] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0052] Example 1: A pre-forming agent for a metal surface coating method and its application (I) A pre-forming agent for a metal surface coating method

[0053] Preparation of pre-constitution treatment agent: Take 16g of cuprous iodide (calculated as copper element), 16g of copper nitrate (calculated as copper element), 30g of diaminosilane, 5g of tripropylene glycol, and 30g of diethanolamine, add pure water (conductivity ≤20μs / cm) to 1000g, stir evenly to obtain the pre-constitution treatment agent.

[0054] (II) A method for coating metal surfaces in vehicle manufacturing

[0055] This embodiment uses cold-rolled steel sheet, galvanized steel sheet, and aluminum alloy sheet from a certain vehicle manufacturer as samples for illustration.

[0056] The metal surface coating method used in vehicle manufacturing includes a first hot water wash, pre-degreasing, degreasing treatment, a second water wash, and pre-curing. The pre-curing treatment agent includes the following steps:

[0057] 1. First hot water wash

[0058] Spray the sample with hot water at 35-42℃ for 90-100 seconds.

[0059] 2. Pre-degreasing

[0060] After the first hot water wash, the sample was pretreated by spraying it with a degreasing agent at 35-42℃ for 60-70 seconds.

[0061] 3. Degreasing treatment

[0062] The pre-degreased sample was immersed in a degreasing agent at 35–42°C for 120–150 seconds.

[0063] The degreasing agent used is a product currently sold by Shenyang Pakase Precision Co., Ltd., brand name SF-4018.

[0064] 4. Second wash

[0065] After degreasing, the sample was sprayed with industrial water at room temperature (25±3℃) for 60-90 seconds, and then immersed in industrial water at room temperature (25±3℃) for 180-240 seconds.

[0066] 5. Pre-treatment

[0067] The sample after the second water wash was immersed in the pre-formed working solution at room temperature (25±3℃) for 30-40 seconds.

[0068] Preparation of pre-formed working solution: Dissolve the pre-formed treatment agent obtained in (I) in pure water (conductivity ≤20μs / cm), the content of the pre-formed treatment agent is 1wt‰, stir evenly to obtain the pre-formed working solution.

[0069] (III) Effects

[0070] Cold-rolled steel, galvanized steel, and aluminum alloy steel samples were divided into two groups. One group underwent the above five steps, while the other group skipped step five and, after step four, underwent drying treatment, serving as a control group. All three types of samples treated in the above steps were dried at 110℃ and subjected to SEM energy dispersive spectroscopy analysis.

[0071] Figure 2 This is an energy dispersive spectroscopy (EDS) elemental analysis of the surface of cold-rolled steel sheets after (a) / without (b) pre-treatment.

[0072] Figure 3 This is an energy dispersive spectroscopy (EDS) elemental analysis of the galvanized sheet surface after (a) / without (b) pre-treatment.

[0073] Figure 4 This is an energy dispersive spectroscopy (EDS) elemental analysis of the surface of an aluminum alloy plate after (a) / without (b) pre-treatment.

[0074] It is evident that the surfaces of the three sample materials that underwent pre-forming treatment all exhibited uniform spherical copper compound structures, while the surfaces of the unpre-formed sample materials did not exhibit this structure.

[0075] Example 2: A pre-forming agent for a metal surface coating method and its application (I) A pre-forming agent for a metal surface coating method

[0076] Preparation of pre-constitution treatment agent: Take 16g of organic phosphonate cuprous salt (calculated as copper element), 16g of copper sulfate (calculated as copper element), 25g of triaminosilane, 10g of ethanolamine ester, and 15g of diethylene glycolamine, add pure water (conductivity ≤20μs / cm) to 1000g, stir evenly to obtain the pre-constitution treatment agent.

[0077] The structural formula of the organic phosphonic acid cuprous salt is as follows:

[0078]

[0079] R1 and R2 are both C3 alkyl groups.

[0080] (II) A method for coating metal surfaces in vehicle manufacturing

[0081] This embodiment uses cold-rolled steel sheets, galvanized steel sheets, and aluminum sheets from a certain vehicle manufacturer as samples for illustration.

[0082] The metal surface coating method used in vehicle manufacturing includes a first hot water wash, pre-degreasing, degreasing treatment, a second water wash, pre-chemical forming, chemical forming, a third pure water wash, and electrophoresis. Pre-chemical forming agents, such as... Figure 1 The steps include the following:

[0083] 1. First hot water wash

[0084] Spray the sample with hot water at 35-42℃ for 90-100 seconds.

[0085] 2. Pre-degreasing

[0086] After the first hot water wash, the sample was pretreated by spraying it with a degreasing agent at 35-42℃ for 60-70 seconds.

[0087] 3. Degreasing treatment

[0088] The pre-degreased sample was immersed in a degreasing agent at 35–42°C for 120–150 seconds.

[0089] The degreasing agent used is a product currently sold by Shenyang Pakase Precision Co., Ltd., brand name SF-4018.

[0090] 4. Second wash

[0091] After degreasing, the sample was sprayed with industrial water at room temperature (25±3℃) for 60-90 seconds, and then immersed in industrial water at room temperature (25±3℃) for 180-240 seconds.

[0092] 5. Pre-treatment

[0093] The sample after the second water wash was immersed in the pre-formed working solution at room temperature (25±3℃) for 30-40 seconds.

[0094] Preparation of pre-formed working solution: Dissolve the pre-formed treatment agent obtained in (I) in pure water (conductivity ≤20μs / cm), the content of the pre-formed treatment agent is 1wt‰, stir evenly to obtain the pre-formed working solution.

[0095] 6. Chemical treatment

[0096] The pre-treated sample was immersed in a forming agent at room temperature (25±3℃) for 150–180 s.

[0097] The chemical agent is a product currently sold by Shenyang Pakase Precision Co., Ltd., with the brand name BM-2021.

[0098] 7. Third rinse with pure water

[0099] After the chemical reaction, the sample was sprayed with pure water at room temperature (25±3℃) for 30-40 seconds, and then immersed in pure water at room temperature (25±3℃) for 60-90 seconds.

[0100] 8. Electrophoresis

[0101] The samples after the third pure water wash were subjected to electrophoresis using a conventional electrophoresis process.

[0102] (III) Effects

[0103] The cold-rolled sheet, galvanized sheet, and aluminum alloy sheet samples were divided into two groups. One group went through the above 8 steps, while the other group skipped step 5 and went directly through steps 6, 7, and 8 after step 4, serving as a control group.

[0104] 1. Dry failure test

[0105] Dry failure tests are conducted using cross-cut adhesion, impact resistance, and cupping tests.

[0106] Cross-cut adhesion test and impact resistance test: conducted in accordance with GB / T 1732-1993 standard.

[0107] Cupping test: Performed according to GB / T 9753-2007 standard.

[0108] Figure 5 The results are the coating adhesion test results of the cold-rolled sheet after electrophoresis with (a) or without (b) pre-treatment.

[0109] Figure 6 The results are the adhesion test results of the paint film after electrophoresis of galvanized steel sheets after (a) / without (b) pre-treatment.

[0110] Figure 7 The results are the adhesion test results of the paint film after electrophoresis on aluminum alloy plates with (a) or without (b) pre-treatment.

[0111] Depend on Figures 5-7 It is evident that the pre-treated cold-rolled, galvanized, and aluminum alloy samples did not exhibit poor bonding strength and dry failure effects. However, some galvanized sheets from the three materials that were not pre-treated showed dry failure due to impact failure (NG).

[0112] 2. Wet failure test

[0113] The wet failure test was conducted using a cyclic alternating test.

[0114] Cyclic alternation experiment: conducted in accordance with GB / T26323—2010 standard.

[0115] Figure 8 The results are from the neutral salt spray test of the coating film of cold-rolled steel sheet after electrophoresis with (a) or without (b) pre-treatment.

[0116] Figure 9 The results are from the electrophoretic coating cycle test of galvanized steel sheets after (a) / without (b) pre-treatment.

[0117] Figure 10 The results are from the electrophoretic coating cycle test of aluminum alloy plates after (a) / without (b) pre-treatment.

[0118] Depend on Figures 8-10It is evident that the cold-rolled, galvanized, and aluminum alloy samples that have undergone pre-treatment do not exhibit poor bonding strength and do not show wet failure effects; while the cold-rolled and galvanized sheets that have not undergone pre-treatment all show wet failure after accelerated corrosion testing.

[0119] It is evident that the samples treated with the pre-forming agent of this invention exhibit excellent performance after electrophoretic coating, meeting both national standards and current enterprise standards of various automobile manufacturers.

[0120] Example 3: A pre-constitution treatment agent for metal surface coating method and its application (I) The effect of the combination of I-valent and II-valent copper in copper element on the pre-constitution treatment agent

[0121] 1. Preparation of pre-treatment agent:

[0122] Take cuprous iodide (as shown in Table 1), copper nitrate (as shown in Table 1), 30g of diaminosilane, 5g of tripropylene glycol, and 30g of diethanolamine, add pure water (conductivity ≤20μs / cm) to 1000g, stir evenly, and obtain the pre-formation treatment agent.

[0123] 2. Effects

[0124] Using cold-rolled steel sheets, galvanized steel sheets, and aluminum alloy sheets from a certain vehicle manufacturer as samples, the metal surface coating method of the vehicle manufacturer includes a first hot water wash, pre-degreasing, degreasing treatment, a second water wash, pre-forming, forming, a third pure water wash, and electrophoresis. The method is the same as in Example 2.

[0125] The ratio of cuprous iodide to copper nitrate in the pre-forming agent was adjusted (based on copper elemental content), and experiments were conducted according to the dry failure and wet failure tests in Example 2. The results are shown in Table 1:

[0126] Table 1

[0127]

[0128]

[0129] Note: S represents cold-rolled sheet, E represents galvanized sheet, and A represents aluminum alloy sheet; 8%NG(E) means that 8% of the galvanized sheet is defective, and the rest of the sheet is OK.

[0130] As shown in Table 1, different combinations of I-valent and II-valent copper have varying degrees of influence on wet failure after pretreatment and coating of cold-rolled and galvanized sheets.

[0131] (II) The effect of silane coupling agents on pre-formation treatment agents

[0132] 1. Preparation of pre-treatment agent:

[0133] Take 16g of cuprous iodide (calculated as copper element), 16g of copper nitrate (calculated as copper element), 30g of silane coupling agent, 5g of tripropylene glycol, and 30g of diethanolamine, add pure water (conductivity ≤20μs / cm) to 1000g, stir evenly, and obtain the pre-formation treatment agent.

[0134] 2. Effects

[0135] Using cold-rolled steel sheets, galvanized steel sheets, and aluminum alloy sheets from a certain vehicle manufacturer as samples, the metal surface coating method of the vehicle manufacturer includes a first hot water wash, pre-degreasing, degreasing treatment, a second water wash, pre-forming, forming, a third pure water wash, and electrophoresis. The method is the same as in Example 2.

[0136] The type of silane coupling agent in the pre-formation agent was adjusted, and experiments were conducted according to the dry failure and wet failure tests in Example 2. The results are shown in Table 2:

[0137] Table 2

[0138]

[0139] Note: S represents cold-rolled sheet, E represents galvanized sheet, and A represents aluminum alloy sheet; 5%NG(E) means that 5% of the galvanized sheet is defective, and the rest of the sheet is OK.

[0140] As shown in Table 2, different types of silane coupling agents have varying degrees of influence on wet failure after pretreatment coating of galvanized sheets.

Claims

1. A pre-treatment agent for a metal surface coating method, characterized in that, The composition comprises, by mass percentage: 0.5-5% copper element, 0.5-5% diaminosilane, 0.5-5% resin, 1-5% ammonia compounds, and the balance being pure water. The copper element is a combination of I-valent and II-valent copper, with a molar ratio of I-valent copper:II-valent copper = 1:0.8-1.

25. The resin is at least one of polyethylene glycol, ethanolamine ester, organic amine ester, and tripropylene glycol; the ammonia compound is at least one of ammonia water, ammonium bicarbonate, monoethanolamine, diethanolamine, and diethylene glycolamine.

2. The pre-treatment agent for a metal surface coating method according to claim 1, characterized in that, The divalent copper is derived from at least one of copper nitrate, copper sulfate, and basic copper carbonate; the ionic copper is derived from at least one of cuprous sulfate, cuprous iodide, and organic phosphonate cuprous salts.

3. The pre-treatment agent for a metal surface coating method according to claim 2, characterized in that, The organic phosphonic acid cuprous salt has the general structural formula shown in (I): （I） R1 and R2 are C1 to C6 alkyl groups.

4. The application of the pre-forming treatment agent according to claim 1 in the pre-forming process of the metal surface coating method.

5. The application according to claim 4, characterized in that, In the pre-forming process, the pre-forming agent is dissolved in pure water to obtain the pre-forming working solution; the content of the pre-forming agent in the pre-forming working solution ranges from 1 to 5‰ by mass percentage.

6. The application according to claim 5, characterized in that, The pre-formation treatment agent contributes no less than 8.5 to the pH of the pre-formation working solution.

7. A method for coating a metal surface, characterized in that, The method using the pre-formation treatment agent according to claim 1 includes the following steps: 1) First hot water wash: Spray the sample with hot water at 35-42℃ for 90-100 seconds; 2) Pre-degreasing: After the first hot water wash, the sample is pre-treated by spraying it with a degreasing agent at 35-42℃ for 60-70 seconds; 3) Degreasing treatment: Immerse the pre-degreased sample in a degreasing agent at 35-42℃ for 120-150 seconds; 4) Second wash: After degreasing, the sample is sprayed with industrial water at room temperature for 60-90 seconds, and then immersed in industrial water at room temperature for 180-240 seconds. 5) Pre-treatment: Immerse the sample after the second water wash in a pre-treatment working solution containing 1-5‰ of the pre-treatment agent at room temperature for 30-40 seconds; 6) Formation: Immerse the pre-formed sample in a forming agent at room temperature for 150-180 seconds; 7) Third pure water wash: After the chemical treatment, spray the sample with pure water at room temperature for 30-40 seconds, and then immerse it in pure water at room temperature for 60-90 seconds.

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