WO2014036785A1

WO2014036785A1 - Plating solution and plating process for multi-layer cyanide-free plating copper-tin alloy coating, and coins made by the process

Info

Publication number: WO2014036785A1
Application number: PCT/CN2012/084571
Authority: WO
Inventors: 张勃; 徐伟; 王卓新; 徐岷; 宋金华; 张高军; 陆懿; 王斌; 曹雅哲
Original assignee: 上海造币有限公司; 中国印钞造币总公司
Priority date: 2012-09-06
Filing date: 2012-11-14
Publication date: 2014-03-13
Also published as: CN103668359A; CA2883815C; CN103668359B; CA2883815A1

Abstract

The present invention relates to the technical field of coinage, and particularly to a plating solution and a plating process for a multi-layer cyanide-free plating copper-tin alloy coating, and coins made by the process. The pyrophosphate plating solution for a multilayer cyanide-free plating copper-tin alloy coating of the present invention comprises a cyanide-free main brightener based on tin-brass consisting of brighteners A and B, and the concentration of the brightener A in the main brightener is 1-10 g/L; the concentration of the brightener B in the main brightener is 0.05-0.5 g/L. With this pyrophosphate plating solution and the plating process for a multi-layer cyanide-free plating copper-tin alloy coating, the thickness of the coating of more than 20 μm can be achieved, and coin products with a dense and uniform coating can be obtained. A coating on a coin formed after high-temperature heat treatment has a single-layer structure, the content of tin in the single-layer coating by weight is 11% to 14%; the appearance of the coating is even and golden without chromatic aberration. Therefore, the well-recognized difficult problem in the plating industry that a single-layer cyanide-free plating alloy coating is thin is solved.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the field of coinage technology, and in particular to a plating solution for electroplating of a multi-layer cyanide-free electroplating copper-tin alloy coating, electroplating Process and coin products obtained by the process.

BACKGROUND OF THE INVENTION The history of cyanide-containing electroplating dates back to 1831, and the practical electroplating process began with the silver cyanide silver plating patent obtained by Elkington in 1840. Cyanide galvanizing has been used in the first world war. Subsequently, cyanide electroplating technology has been widely used in zinc, copper, cadmium, silver, gold and other single metal or alloy plating. However, cyanide is a highly toxic substance, and its lethal dose is only 5 mg. Therefore, high management is required for the management of highly toxic cyanide and the discharge of wastewater containing cyanide plating solution. In the 1970s, the research on cyanide-free galvanizing process first achieved breakthroughs. So far, technologies such as cyanide-free copper plating, cyanide-free gold plating, and cyanide-free copper plating alloy have been developed and started in some industrial fields. Get the app. At present, the electroplating materials used in the international coinage industry mainly include copper plating, nickel plating, copper plating alloy, etc. Among them, the electroplating copper-tin alloy technology is formed by using a cyanide-containing electroplating method or a single metal plating method to form an alloy layer by heat treatment. Copper-tin alloy plating is a traditional electroplating process for nickel plating. It can be used for hanging plate plating. Cyanide system copper-tin alloy is a relatively mature nickel-based layer process. Due to environmental protection and human health requirements, research and development of new cyanide-free copper-tin alloy plating processes have been widely concerned in recent years. Currently reported cyanide-free copper-tin alloy plating solutions mainly include pyrophosphate, pyrophosphate-stannate, citrate-stannate and HEDP, but the most potential alternative to cyanide solution system is pyrophosphate. Salt solution system. At this stage, there is no cyanide brass tin plating process. If the plating time is too long, problems such as fogging and looseness of the plating layer will occur. Therefore, this process is mostly used for decorative coatings, and there are few breakthroughs in functional coatings. Therefore, the object of the present invention is to solve the problems encountered in the use of a brass tin plating layer for a functional plating layer, namely, continuous thickening of the plating layer, uniform density of the plating layer, and stability of the plating solution.

SUMMARY OF THE INVENTION In view of the disadvantages of the prior art that cyanide-free electroplating brass tin cannot be plated thickly and the plating layer is uneven, the object of the present invention is to provide a pyrophosphate plating solution for a multi-layer cyanide-free electroplating copper-tin alloy plating layer and a Electroplating process for multi-layer cyanide-free electroplating copper-tin alloy plating layer and coin product produced by the electroplating process, using the pyrophosphate plating solution and multi-layer cyanide-free plating The electroplating process of copper-tin alloy plating can obtain a coin product with a coating thickness of more than 20 m and a uniform and dense coating. The electroplating process of the multi-layer cyanide-free electroplating copper-tin alloy plating layer of the invention and the coin product produced by the electroplating process, the blank cake is made of a low carbon steel coinage billet, and the first layer and the second layer are sequentially plated thereon The layer, the third layer and the surface layer, the electroplating process is a multi-layer electroplating process using a pyrophosphate solution system, and the main electroplating process has the same main salt system, thereby avoiding the risk of contamination of the plating solution between different plating layers, and each layer is plated with clean water. Rinsing can save the activation process; multi-layer electroplating is used to compensate for the problem that the single-layer cyanide-free electroplated copper-tin alloy coating is thinner than the cyanide-plated copper-tin alloy coating; the plating solution used in each layer of the electroplating process is The pyrophosphate solution system is a cyanide-free environment-friendly type, which greatly reduces the management cost of highly toxic cyanide, improves the plating environment, reduces the pressure of wastewater on the environment, and greatly improves the coin plating coating material. The level of production. The electroplating process of the multi-layer cyanide-free electroplating copper-tin alloy coating provided by the invention and the coin structure thereof are different from the traditional cyanide-containing electroplated copper-tin alloy coins and other electroplated copper-tin alloy coins currently provided at home and abroad. Crafting process and coin structure. The conventional cyanide-plated copper-tin alloy coin is made by electroplating a copper-tin alloy directly on a steel core blank, and the coin structure is a single-layer structure. Other electroplated copper-tin alloy processes provided at home and abroad, such as plating the underlayer on the iron cake, and then performing single metal alternate plating, after the electroplating is completed, a certain thickness of the alloy layer is obtained by heat treatment diffusion. In order to achieve the above and other objects, the present invention adopts the following technical solutions: a pyrophosphate plating solution for a multi-layer cyanide-free electroplating copper-tin alloy plating layer, comprising a cyanide-free brass tin main light agent, the cyanide-free yellow The solute of the copper tin main light agent is composed of a brightener Α and a brightener ;; wherein the concentration of the brightener A in the cyanide-free brass tin main light main light agent is 1-10 g/L; the brightener B is in the absence The concentration of the cyanide brass tin main light agent in the main light agent is 0.05-0.5 g/L. Preferably, the concentration of the cyanide-free brass tin main light agent in the pyrophosphate plating solution is 3-20 mL/L. Preferably, the solute of the cyanide-free brass tin main light agent is composed of brightener A and brightener B; the solvent is a mixture of water and an organic solvent; wherein the ratio of water and organic solvent is just enough to dissolve the brightener A and brightener B are optimal. In the mixture of water and an organic solvent, the organic solvent may be selected from the group consisting of an organic solvent capable of dissolving the brightener A and the brightener B and water. Preferably, the brightener A is a Mimpol WT brightener produced by the French company Rhodia; the brightener B is 2-mercaptobenzimidazole. The addition of the above Mimpol WT can significantly shorten the plating time, improve the uniformity of the plating layer and the deep plating ability, and at the same time improve the corrosion resistance of the plating layer, and the coating is excellent in salt spray resistance and flexibility. The present invention adds a brightener A and a brightener B to the plating solution, and the two synergistically act to obtain a uniform and dense brass tin plating layer over a wide range of current densities. Preferably, the pyrophosphate plating solution of the multi-layer cyanide-free electroplated copper-tin alloy plating layer has a _P H value of 8.0-10.0; and a density of 1.30 to 1.45 g/cm ³ . The pH of the above pyrophosphate plating solution of the present invention can be adjusted with hydrogen phosphate and phosphoric acid to achieve the desired pH value. Further, the pyrophosphate plating solution of the multi-layer cyanide-free electroplating copper-tin alloy plating layer further comprises the following components: pyrophosphate 350-450 g/L; soluble copper salt 20-35 g/L; soluble tin Salt 1.8~3.0g/L; conductive salt 0~80g/L;

Cyanide-free brass tin adjuvant 10 - 50 mL / L. The solvent of the above pyrophosphate plating solution is water. Preferably, the pyrophosphate is selected from the group consisting of potassium pyrophosphate and sodium pyrophosphate. Preferably, the pyrophosphate is selected from the group consisting of potassium pyrophosphate. Preferably, the soluble copper salt is selected from the group consisting of copper pyrophosphate, copper sulfate, copper chloride, basic copper carbonate, copper methanesulfonate, copper sulfamate, two or more. Preferably, the soluble copper salt is selected from the group consisting of copper pyrophosphate. Preferably, the soluble tin salt is selected from the group consisting of stannous pyrophosphate, stannous sulfate, stannous chloride, tin fluoroborate, and tin alkyl sulfonate, two or more. Preferably, the soluble tin salt is selected from the group consisting of stannous pyrophosphate. Preferably, the conductive salt is selected from the group consisting of potassium chloride, sodium chloride, dipotassium hydrogen phosphate, ammonium chloride, potassium sulfate, sodium sulfate, potassium carbonate, sodium carbonate, two or more. Preferably, the conductive salt is selected from the group consisting of dipotassium hydrogen phosphate. Preferably, the solute of the cyanide-free brass tin adjuvant is composed of the auxiliary complexing agent A and the auxiliary complexing agent B; wherein the concentration of the auxiliary complexing agent A in the cyanide-free brass tin adjuvant is 5-10 g. /L, the concentration of the auxiliary complexing agent B in the cyanide-free brass tin adjuvant is 5~10g/L. The solvent of the above cyanide-free brass tin adjuvant is water. More preferably, the auxiliary complexing agent A and the auxiliary complexing agent B are both selected from the group consisting of glycolic acid, sodium gluconate, HEDP (hydroxyethylidene diphosphonic acid), citric acid, sodium citrate, citrate amine, potassium tartrate One, two or more of sodium, methanesulfonic acid, triethanolamine, oxalic acid, glycine, and the auxiliary complexing agent A and the auxiliary complexing agent B are not simultaneously selected from the same substance. Preferably, the auxiliary complexing agent A is selected from the group consisting of glycolic acid; and the auxiliary complexing agent B is selected from the group consisting of sodium gluconate. The pyrophosphate plating solution of the multilayer cyanide-free electroplated copper-tin alloy plating layer of the present invention may further comprise a stabilizer; The concentration of the stabilizer is 0.01 to 0.05 g/L. Preferably, the stabilizer is selected from the group consisting of hydroquinone, catechol, resorcinol, β-naphthol, ascorbic acid, and hydroxybenzenesulfonic acid. The electroplating solution of the invention has the advantages of simple composition and easy maintenance, and can be applied to a wide current density range, and the plating thickness can be more than 20 m without brittleness, and the weight percentage of tin in the plating layer is 11% to 14%; The appearance is uniform golden yellow, and there is no color difference. The invention also provides a method for electroplating a multi-layer cyanide-free electroplated copper-tin alloy plating layer, which sequentially electroplats two layers of -4 layers of copper-tin alloy plating on the coin substrate, and then obtains multi-layer cyanide-free electroplating copper by high temperature heat treatment- A tin alloy coated coin; wherein the even plating layer and the surface layer are plated by the above-mentioned multi-layer cyanide-free electroplating copper-tin alloy plating pyrophosphate plating solution. Preferably, the number of layers of the electroplated copper-tin alloy plating layer is 2 layers or 4 layers. Preferably, the temperature of the high temperature treatment is 600-800° C. The plating method of the multi-layer cyanide-free copper-tin alloy plating layer of the present invention specifically includes the following steps:

1. Electroplating first layer: The low carbon steel coinage billet is used as the coin base, and the degreased and pickled activated coinage billet is placed in the first plating solution, and the plating thickness is about 1 at 20~30 °C. A first layer of 5 microns, a first layer of copper-tin alloy containing less than 2% tin is obtained; then washed with water. Preferably, in step 1, the current density of the first layer of electroplating is 0.5 to 1.5 A/dm ² ; and the plating time is 30 to 60 minutes.

The first plating solution used in the first step and the fifth step is a cyanide-free low-tin copper-tin alloy plating solution, and the cyanide-free low-tin copper-tin alloy plating solution commonly used in the prior art can be used, for example, it is a plating solution containing the following solute concentration. Potassium pyrophosphate 250-370g/L; copper pyrophosphate 20-30g/L; stannous pyrophosphate 0. 2—0. 5 g/U dipotassium hydrogen phosphate 0— 80 g/U Cyanide-free copper additive 10-20 The solvent is water. The density is 1.25-1.35; Preferably, the water washing after the plating of the first layer is performed by immersing the coinage material after the plating of the first layer in deionized water at normal temperature. The total thickness of the coating of the blank or the blank of the invention is not less than 20 micrometers, and the bonding strength, corrosion resistance, abrasion resistance and hardness of the coating of the blank or the blank cake satisfy the requirements of the coinage application.

2. Electroplating the second layer: the water-washed coinage obtained in step 1 is placed in the above-mentioned multi-layer cyanide-free electroplating copper-tin alloy plating pyrophosphate plating solution at a temperature of 25 to 35 ° C. Electroplating a second layer with a thickness of approximately 10-20 microns, A second layer of copper-tin alloy having a tin content of 14-18% was obtained; then washed with water. Preferably, in step 2, the current density of the second layer of electroplating is 0.5 to 1.5 A/dm ² ; and the plating time is 200 to 550 minutes. Preferably, the water washing after the plating of the second layer is performed by immersing the coinage material after the second layer plating in deionized water at normal temperature.

3. Electroplating the third layer: The water-washed coinage obtained in step 2 is placed in the first plating solution, and the third layer having a thickness of about 3 to 5 μm is plated at a temperature of 20 to 30 ° C to obtain a tin content. Less than 2% of the third layer of copper-tin alloy; then washed with water. Preferably, in step 3, the current density of the third layer of the electroplating is 0.5 to 1.5 A/dm ² ; the electroplating time is 60 to 90 minutes; preferably, the water washing after the third layer is electroplated is to be electroplated after the third layer The coinage billet is rinsed in deionized water at room temperature.

4, electroplating the fourth layer (also referred to as the surface layer): the rinsed coinage obtained in step 3 is placed in the above-mentioned multi-layer cyanide-free electroplating copper-tin alloy plating pyrophosphate plating solution, A fourth layer having a thickness of about 10 to 12 μm is electroplated at a temperature of 20 to 30 ° C to obtain a fourth layer of a copper-tin alloy containing 14-18% of tin; and then washed with water. Preferably, in step 4, the current density of the fourth layer of electroplating is 0.5 to 1.5 A/dm ² ; and the plating time is 200 to 270 minutes. Preferably, the water washing after the fourth layer is electroplated is performed by immersing the coinage material after the fourth layer plating in deionized water at normal temperature.

5. The electroplated billet obtained by the second step and the water-washed coinage obtained in the step 2 or the electroplated billet obtained by the fourth step and the water-washed coinage billet are sequentially dried and subjected to high-temperature heat treatment to obtain a multi-layer cyanide-free copper-tin alloy plating layer. The coin, the copper-tin alloy single-coated coin. Further, the degreasing step in the step 1 includes an alkaline degreasing step and an electric deoiling step in sequence; the pickling activation step in the step 1 is a pickling activation of the coinage billet with a hydrochloric acid solution. Preferably, the alkaline degreasing step, the electric deoiling step and the pickling activation step further comprise a water washing step. The water washing is preferably a normal temperature rinsing using deionized water. The alkaline deoiling step, the electric deoiling step and the pickling activating step of the present invention may employ an alkaline degreasing step, an electric deoiling step and a pickling activation step which are conventional in the prior art. The present invention also provides a coin product for use in the above-described multi-layer cyanide-free electroplating copper-tin alloy plating layer of the present invention. The multi-layer cyanide-free copper-tin alloy coated coin obtained by the plating method is subjected to high temperature heat treatment to form a single layer of copper-tin alloy coated coin, and the weight percentage of tin in the single layer coating is 11% to 14%. The coating has a uniform golden color and no color difference. Further, the above-mentioned multi-layer cyanide-free copper-tin alloy plating coin has a coin plating thickness of 20-24 micrometers obtained by using two plating layers, and a coin plating thickness of 25-31 micrometers obtained by using four plating layers. The electroplating bath used in each coating of the coin product of the invention adopts a pyrophosphate solution system, fully utilizing the advanced and superiority of the cyanide-free alloy electroplating, combined with the multi-layer electroplating method, through the thickness of the multi-layer coating and the composition of the alloy The reasonable combination solves the difficult problem of the thinning of the single-layer cyanide-free plating alloy coating which is recognized by the current plating. The electroplating method of the multi-layer cyanide-free electroplating copper-tin alloy plating layer of the invention can save the management cost of the highly toxic cyanide; greatly improve the plating conditions, and is beneficial to the health of the worker and the protection of the environment; The system uses a pyrophosphate system to avoid the risk of mutual contamination between the plating solutions, making the entire process smooth and easy to control.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart of the electroplating process of the present invention; FIG. 2 is an effect of the brightener A on the appearance of the Hull test piece; FIG. 3 is the effect of the brightener B on the appearance of the Hull test piece; And the appearance of the Hull cell test piece at different currents after B; Fig. 5 Effect of adding auxiliary complexing agent A on the coating composition; Figure 6 Effect of adding auxiliary complexing agent B on the coating composition; Figure 7 Adding auxiliary complex The effect of agents A and B on the composition of the coating.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described by way of specific specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the disclosure of the present specification. The invention may be practiced or applied in various other specific embodiments, and the details of the invention may be variously modified or changed without departing from the spirit and scope of the invention.

Table 1 - Table 7 below and the cyanide-free brass tin main light agent in each of Examples 1-6, from Mimpol at a concentration of 1-10 g/L WT brightener (brightener A) and 2-mercaptobenzimidazole (brightener B) at a concentration of 0.05-0.5 g/L.

The cyanide-free brass tin adjuvants in Tables 1 to 7 below and in Examples 1-6 were composed of glycolic acid having a concentration of 5-10 g/L and sodium gluconate having a concentration of 5-10 g/L.

The following table 1 - Table 7 and the cyanide-free copper additive in each of Examples 1-6 are composed of glycolic acid having a concentration of 50-100 g/L and 2-mercaptobenzimidazole having a concentration of 0.05-0.5 g/L. .

The process parameters of the plating method of the multilayer cyanide-free copper-tin alloy plating layer in the following Tables 1 to 7 and the respective examples are preferably shown in Tables 1 to 7.

Table 1 Alkaline degreasing process parameters

Alkaline degreasing parameter range Degreaser 50-70g/L

Temperature 55- 65 ° C

Table 2 Electric oil removal process parameters

Electric release oil Parameter range Degreaser 60— 80g/L

1 I

Temperature 55- 65 ° C

Current density 0.5-1.3 A/dm ² Table 3 Hydrochloric acid activation process parameters

Hydrochloric acid activation Parameter range Concentrated hydrochloric acid (35%) 350-500mL/L Temperature 20-30°C

Table 4 Electroplating first layer plating process parameters

Plating process parameters Parameter range Pyrolysis potassium

Pyrolysis copper

Pyrolysis

Pity acid dipotassium

Cyanide-free copper additive

Table 7 plating surface process parameters

Example 1: A low carbon steel coinage blank is used as a base, and a first layer and a second layer are sequentially plated thereon, and then as a product, the specific steps are as follows:

(1) Alkaline degreasing puts the coinage billet into the alkaline degreasing liquid, the degreasing agent is 50g/L degreaser, the temperature is 55 °C for 20 minutes, then the deionization with 60 °C Water rinsing;

(2) Electro-de-oiling oil The above-mentioned alkali-washed coinage billet is placed in an electric de-oiling liquid, the degreaser is a degreaser of 60 g/L, the temperature is 55 V, and the current density is 0.5 A/dm ² for 20 minutes. The anode was electrolytically cleaned and then rinsed with deionized water at 60 ° C;

(3) Hydrochloric acid activation The coinage blank after the above-mentioned electric de-oiling was placed in a HCL solution having a concentration of 350 mL/L at a temperature of 20. C, for 7 minutes of acid activation, and then rinsed with normal temperature deionized water;

(4) Electroplating the first layer The activated coinage billet is placed in a first layer of plating solution having a pH of 8.0, and the first layer is electroplated at a temperature of 20 ° C, and the current density is 0.5 A/dm ² . Time is 60 minutes. The first layer of plating solution consists of the following components: potassium pyrophosphate, 250 g / L _; copper pyrophosphate, 20 g / L; stannous pyrophosphate, 0.2 g / L; cyanide-free copper additive, 10 ml / L; the first layer thickness of about 2-4 microns.

(5) Washing The coinage blank after the first layer of the above plating is placed in deionized water and rinsed with deionized water at room temperature.

(6) Electroplating the second layer The coinage material rinsed with the above deionized water is placed in a second layer of plating solution having a pH of 8.0, and the second layer is electroplated at a temperature of 20 ° C, and the current density is 0.5 A/dm. ² , plating time 540 minutes. The second layer of plating solution consists of the following components: potassium pyrophosphate, 350g / L; copper pyrophosphate, 20 g / L; stannous pyrophosphate, 1.8g / L; cyanide-free brass tin main light agent, 3ml / L ; Cyanide-free brass tin adjuvant, 10ml / L _{; The} second layer is about 18-20 microns thick, and the tin content is 14-18%.

(7) Washing and drying the coinage blank after the above plating surface is placed in deionized water, rinsing with normal temperature deionized water, and then drying the coinage blank;

(8) High-temperature heat treatment The above-mentioned dried coinage billet is placed in a high-temperature heat treatment furnace, and the furnace is subjected to a reducing protective atmosphere. The heat treatment is carried out by a process of 650 ° C, 7 min, and addition to 680 ° C for 7 min. The coating diffuses into a layer with a tin content of 11-14% and a coating thickness of 20-24 microns. Embodiment 2: A low carbon steel coinage blank is used as a base, and a first layer and a second layer are sequentially plated thereon, and then as a product, the specific steps are as follows:

(1) Alkaline degreasing puts the coinage billet into the alkaline degreasing liquid, the degreasing agent is 60g/L degreaser, the temperature is 60 ° C for 20 minutes, then the deionization with 60 ° C Water rinsing;

(2) Electric de-oiling oil The above-mentioned alkali-washed coinage billet is placed in an electric de-oiling liquid, the degreasing agent is 70 g/L degreaser, the temperature is 60 ° C, and the current density is 1.0 A/dm ² . A minute of electrolytic cleaning of the anode, followed by rinsing with deionized water at 60 ° C;

(3) Hydrochloric acid activation The above-mentioned electric degreased coinage blank was placed in a HCL solution having a concentration of 480 mL/L at a temperature of 25 ° C for 7 minutes of acid activation, and then rinsed with normal temperature deionized water;

(4) Electroplating the first layer The activated coinage billet is placed in a first layer of plating solution having a pH of 9.0, and the first layer is electroplated at a temperature of 25 ° C, and the current density is 1.0 A/dm ² . Time is 60 minutes. The first layer of plating solution consists of the following components: potassium pyrophosphate, 300g / L; copper pyrophosphate, 25 g / L; stannous pyrophosphate, 0.35 g / L; cyanide-free copper additive, 20ml / L; The layer thickness is about 2-4 microns.

(6) Electroplating the second layer The coinage material after rinsing the above deionized water is placed in a second layer of plating solution having a pH of 9.0, and the second layer is electroplated at a temperature of 25 ° C, and the current density is 1.2 A/dm. ² , plating time 540 minutes. The second layer of plating solution consists of the following components: potassium pyrophosphate, 400g / L; copper pyrophosphate, 25 g / L; stannous pyrophosphate, 2.2g / L; dipotassium hydrogen phosphate, 45 g / L; Brass tin main light agent, 20ml / L; cyanide-free brass tin adjuvant, 50ml / L; the second layer thickness is about 18-20 microns, tin content is 14-18%.

(8) High-temperature heat treatment The above-mentioned dried coinage billet is placed in a high-temperature heat treatment furnace, and the furnace is subjected to a reducing protective atmosphere. The heat treatment is carried out by a process of 650 ° C, 7 min, and addition to 680 ° C for 7 min. The coating diffuses into a layer with a tin content of 11-14% and a coating thickness of 20-24 microns. Example 3: A low carbon steel coinage blank was used as a substrate, and the first layer and the second layer were sequentially electroplated thereon, and then as a product, the specific steps were as follows:

(1) Alkaline degreasing, the coinage billet is placed in an alkaline degreaser, the degreaser is 70g/L degreaser, and the temperature is 65°C for 20 minutes. Washed and then rinsed with deionized water at 60 ° C;

(2) Electro-de-oiling oil The above-mentioned alkali-washed coinage billet is placed in an electric de-oiling liquid, the degreaser is 80 g/L degreaser, the temperature is 65, and the current density is 1.2 A/dm ² for 20 minutes. The anode was electrolytically cleaned and then rinsed with deionized water at 60 ° C;

(3) Hydrochloric acid activation The coinage blank after the above-mentioned electric deoiling was placed in a HCL solution having a concentration of 480 mL/L at a temperature of 29. C, for 7 minutes of acid activation, and then rinsed with normal temperature deionized water;

(4) Electroplating the first layer The activated coinage billet is placed in the first layer of plating solution having a pH of 9.8, and the first layer is electroplated at a temperature of 28 ° C, and the current density is 1.4 A/dm ² . Time is 60 minutes. The first layer of plating solution consists of the following components: potassium pyrophosphate, 360g / L; copper pyrophosphate, 28 g / L; stannous pyrophosphate, 0.45 g / L; cyanide-free copper additive, 15ml / L; The layer thickness is about 2-4 microns.

(6) Electroplating the second layer The coinage material rinsed with the above deionized water is placed in a second layer of plating solution having a pH of 9.8, and the second layer is electroplated at a temperature of 28 ° C, and the current density is 1.8 A/dm. ² , plating time 540 minutes. The second layer of plating solution consists of the following components: potassium pyrophosphate, 450g / L; copper pyrophosphate, 32 g / L; stannous pyrophosphate, 2.8g / L; dipotassium hydrogen phosphate, 70 g / L; Brass tin main light agent, 10ml / L; cyanide-free brass tin adjuvant, 30ml / L; the second layer thickness is about 18-20 microns, tin content is 14-18%.

(8) High-temperature heat treatment The above-mentioned dried coinage billet is placed in a high-temperature heat treatment furnace, and the furnace is subjected to a reducing protective atmosphere. The heat treatment is carried out by a process of 650 ° C, 7 min, and addition to 680 ° C for 7 min. The coating diffuses into a layer with a tin content of 11-14% and a coating thickness of 20-24 microns. Embodiment 4: The low carbon steel coinage blank is used as a base, and the first layer, the second layer, the third layer and the surface layer are sequentially plated thereon, and then as a product, the specific steps are as follows:

(4) Electroplating the first layer The activated coinage billet is placed in a first layer of plating solution having a pH of 8.0, and the first layer is electroplated at a temperature of 20 ° C, and the current density is 0.5 A/dm ² . Time is 30 minutes. The first layer of plating solution consists of the following components: potassium pyrophosphate, 250g / L; copper pyrophosphate, 20 g / L; stannous pyrophosphate, 0.2 g / L; cyanide-free copper additive, 10ml / L _; The layer thickness is about 1-2 microns.

(6) Electroplating the second layer The coinage material rinsed with the above deionized water is placed in a second layer of plating solution having a pH of 8.0, and the second layer is electroplated at a temperature of 20 ° C, and the current density is 0.5 A/dm. ² , plating time is 270 minutes. The second layer of plating solution consists of the following components: potassium pyrophosphate, 350g / L; copper pyrophosphate, 20 g / L; stannous pyrophosphate, 1.8g / L; cyanide-free brass tin main light agent, 3ml / L ; Cyanide-free brass tin adjuvant, 10ml / L _{; the} second layer thickness is about 10-12 microns, the tin content is about 14-18%.

(7) Washing The coinage blank after the first plating was placed in deionized water and rinsed with deionized water at normal temperature.

(8) Electroplating the third layer The above-mentioned washed mint material is placed in a third layer of plating solution having a pH of 8.0, and the third layer is electroplated at a temperature of 20 ° C, and the current density is 0.5 A/dm ² . Time is 90 minutes. The third layer of plating solution consists of the following components: potassium pyrophosphate, 250g / L; copper pyrophosphate, 20 g / L; stannous pyrophosphate, 0.2 g / L; cyanide-free copper additive, 15ml / L; The layer thickness is approximately 3-5 microns.

(9) Washing The coinage blank after the third layer of the above plating is placed in deionized water and rinsed with deionized water at room temperature.

(10) Electroplated surface layer The coinage material after rinsing the above deionized water is placed in a surface plating solution with a pH of 8.0, and the surface layer is plated at a temperature of 20 ° C, the current density is 0.5 A/dm ² , and the plating time is 270 minutes. . The surface plating solution consists of the following components: potassium pyrophosphate, 350g/L; copper pyrophosphate, 20 g/L; stannous pyrophosphate, 1.8g/L; cyanide-free brass tin main light, 10ml/L _; Cyanide brass tin adjuvant, 30ml / L; surface layer thickness of about 10-12 microns, tin content of 14-18%.

(11) Washing and drying The coinage blank after the above electroplated surface layer is placed in deionized water, rinsed with normal temperature deionized water, and then the coinage billet is dried;

(12) High-temperature heat treatment The above-mentioned dried coinage billet is placed in a high-temperature heat treatment furnace, and the furnace is passed through a reducing protective atmosphere, and heat-treated after heat treatment at 650 ° C for 7 minutes, added to 680 ° C for 7 minutes. The coating diffuses into a layer with a tin content of 11-14% and a coating thickness of 25-31 microns. Embodiment 5: The low carbon steel coinage blank is used as a base, and the first layer, the second layer, the third layer and the surface layer are sequentially plated thereon, and then used as a product, and the specific steps are as follows:

(1) Alkaline degreasing puts the coinage billet into the alkaline degreasing liquid, the degreasing agent is 60g/L degreaser, the temperature is 60 ° C for 20 minutes, then the deionization with 60 ° C Water rinsing; (2) Electric de-oiling oil The above-mentioned alkali-washed coinage billet is placed in an electric de-oiling liquid, the degreasing agent is 70 g/L degreaser, the temperature is 60 ° C, and the current density is 1.0 A/dm ² . A minute of electrolytic cleaning of the anode, followed by rinsing with deionized water at 60 ° C;

(3) Activation of hydrochloric acid The coinage blank after the above-mentioned electric de-oiling was placed in a HCL solution having a concentration of 400 mL/L at a temperature of 25. C, for 7 minutes of acid activation, and then rinsed with normal temperature deionized water;

(4) Electroplating the first layer The activated coinage billet is placed in a first layer of plating solution having a pH of 9.0, and the first layer is electroplated at a temperature of 25 ° C, and the current density is 1.0 A/dm ² . Time is 30 minutes. The first layer of plating solution consists of the following components: potassium pyrophosphate, 300g / L; copper pyrophosphate, 25 g / L; stannous pyrophosphate, 0.3 g / L; cyanide-free copper additive, 20ml / L; The layer thickness is about 1-2 microns.

(6) Electroplating the second layer The coinage material after rinsing the above deionized water is placed in a second layer of plating solution having a pH of 9.0, and the second layer is electroplated at a temperature of 25 ° C, and the current density is 1.2 A/dm. ² , plating time is 270 minutes. The second layer of plating solution consists of the following components: potassium pyrophosphate, 400g / L; copper pyrophosphate, 25 g / L; stannous pyrophosphate, 2.2g / L; cyanide-free brass tin main light agent, 20ml / L ; Cyanide-free brass tin adjuvant, 50ml / L; The second layer is about 10-12 microns thick, and the tin content is about 14-18%.

(7) Washing The coinage blank after the second layer of the above plating is placed in deionized water and rinsed with deionized water at room temperature.

(8) Electroplating the third layer The above-mentioned washed mint material is placed in a third layer of plating solution having a pH of 9.0, and the third layer is electroplated at a temperature of 25 ° C, and the current density is 1.0 A/dm ² . Time is 90 minutes. The third layer of plating solution consists of the following components: potassium pyrophosphate, 300g / L; copper pyrophosphate, 25 g / L; stannous pyrophosphate, 0.3 g / L; cyanide-free copper additive, 18ml / L; The layer thickness is approximately 3-5 microns.

(9) Washing The coinage blank after the third layer plating was placed in deionized water and rinsed with deionized water at normal temperature.

(10) Electroplated surface The minted material after rinsing the above deionized water is placed in a surface plating solution with a pH of 9.0, and the surface layer is plated at a temperature of 25 ° C. The current density is 1.0 A/dm ² and the plating time is 270 minutes. . The surface plating solution consists of the following components: potassium pyrophosphate, 400g/L; copper pyrophosphate, 25g/L; stannous pyrophosphate, 2.2g/L; cyanide-free brass tin main light, 18ml/L; Brass tin adjuvant, 40ml/L; surface layer thickness is about 10-12 microns, tin content is 14-18%.

(12) High-temperature heat treatment The above-mentioned dried coinage billet is placed in a high-temperature heat treatment furnace, and the furnace is passed through a reducing protective atmosphere, and heat-treated after heat treatment at 650 ° C for 7 minutes, added to 680 ° C for 7 minutes. The coating diffuses into a layer with a tin content of 11-14% and a coating thickness of 25-31 microns. Embodiment 6: The low carbon steel coinage blank is used as a base, and the first layer, the second layer, the third layer and the surface layer are sequentially plated thereon, and then used as a product, and the specific steps are as follows:

(1) Alkaline degreasing puts the coinage billet into the alkaline degreasing liquid, the degreasing agent is 70g/L degreaser, the temperature is 65 °C for 20 minutes, then the deionization with 60 °C Water rinsing;

(2) Electric de-oiling The above-mentioned alkali-washed coinage billet is placed in an electric de-oiling liquid, the degreasing agent is 80 g/L degreaser, the temperature is 65, and the current density is 1.3 A/dm ² for 20 minutes. The anode was electrolytically cleaned and then rinsed with deionized water at 60 ° C;

(3) Hydrochloric acid activation The coinage blank after the above electric deoiling is placed in a HCL solution having a concentration of 500 mL/L at a temperature of 30 ° C for 7 minutes of acid activation, and then rinsed with normal temperature deionized water;

(4) Electroplating first layer The activated coinage billet was placed in a first layer of plating solution having a pH of 9.8, and the first layer was electroplated at a temperature of 30 ° C with a current density of 1.5 A/dm ² and a plating time of 30 minutes. The first layer of plating solution consists of the following components: potassium pyrophosphate, 370g / L; copper pyrophosphate, 30 g / L; stannous pyrophosphate, 0.4 g / L; cyanide-free copper additive, 15ml / L; The layer thickness is about 1-2 microns.

(6) Electroplating the second layer The coinage material after rinsing the above deionized water is placed in a second layer of plating solution having a pH of 10.0, and the second layer is electroplated at a temperature of 28 ° C, and the current density is 1.8 A/dm. ² , plating time is 270 minutes. The second layer of plating solution consists of the following components: potassium pyrophosphate, 450g / L; copper pyrophosphate, 35 g / L; stannous pyrophosphate, 3.0g / L; cyanide-free brass tin main light agent, 10ml / L _; Cyanide-free brass tin adjuvant, 30ml / L; The second layer thickness is about 10-12 microns, the tin content is about 14-18%.

(8) Electroplating the third layer The above-mentioned washed mint material is placed in a third layer of plating solution having a pH of 10.0, and the third layer is electroplated at a temperature of 28 ° C, and the current density is 1.5 A/dm ² . Time is 90 minutes. The third layer of plating solution consists of the following components: potassium pyrophosphate, 370g / L; copper pyrophosphate, 30g / L; stannous pyrophosphate, 0.5 g / L; cyanide-free copper additive, 12mlL; It is 3-5 microns.

(10) Electroplated surface The minted material after rinsing the above deionized water is placed in a surface plating solution with a pH of 10.0, and the surface layer is plated at a temperature of 30 ° C. The current density is 1.8 A/dm ² and the plating time is 270 minutes. . The surface plating solution consists of the following components: potassium pyrophosphate, 450g/L; copper pyrophosphate, 32g/L; stannous pyrophosphate, 2.8g/L; cyanide-free brass tin main light, 18ml/L; Brass tin adjuvant, 40ml/L; surface layer thickness is about 10-12 microns, tin content is 14-18%.

(11) Washing and drying the coinage blank after plating the above surface layer into deionized water, rinsing with normal temperature deionized water, and then The coinage billet is dry;

(12) High-temperature heat treatment The above-mentioned dried coinage billet is placed in a high-temperature heat treatment furnace, and the furnace is passed through a reducing protective atmosphere, and heat-treated after heat treatment at 650 ° C for 7 minutes, added to 680 ° C for 7 minutes. The coating diffuses into a layer with a tin content of 11-14% and a coating thickness of 25-31 microns. Copper-tin alloy in Mirapol WT brightener A (additive A) and brightener B (2-mercaptobenzimidazole, additive B) and cyanide-free brass tin adjuvant in cyanide-free brass tin main light agent The effects of sedimentation:

(1) The synergistic test and test results of the separate brightener A, the brightener B, the brightener A and the brightener B are as follows:

1. Brightener A (WT) Additive A can effectively improve high-area charring and increase the brightness of the coating. The addition of A causes the electrodeposition characteristics of the alloy plating solution to be controlled by the electrochemical step control to the diffusion step. Therefore, in the high current density region, it is only necessary to reduce the concentration polarization of the metal ions, so that electrodeposition can be better achieved. At the same time, the diffusion adsorption and inhibition of the additive A on the surface of the electrode increase the polarization of the cathode, so that the crystal of the alloy coating is fine and bright. In the plating solution, Cu ₂ P ₂ O 3H ₂ 0 25 g/L; Sn ₂ P ₂ 0 ₇ 3.0 g/L; Κ4Ρ ₂ 0 ₇ ·3Η ₂ 0 450 g/L; Κ ₂ ΗΡ0 ₄ ·3Η ₂ 0 60 g/L; pH 8.5; temperature 25. C, Brightener A 0.1 g / L at different currents, the appearance of the Hull cell is shown in Figure 2, Figure 2 is the effect of additive A on the appearance of the Hull cell test piece. It can be seen from Fig. 2 that the addition of brightener A can effectively improve the scorch in the high current density region, and also has a certain effect on the alloy co-deposition in the low current region, so that the appearance of the Hull trough is brighter, and the gold-yellow alloy co-deposition region has Increased. However, as the current increases, the range of scorching in the high current region is larger and larger, indicating that the range of operable current of the plating is narrow.

2. Brightener B (2-mercaptobenzimidazole) brightener B acts as a grain refiner for copper ion electrodeposition, enhances the cathodic polarization of copper ions in a low current density region, and makes the metal copper crystal fine and inhibits The precipitation of copper increases the tin content in the coating of the low current density region. In the plating solution, Cu ₂ P ₂ O _r 3H ₂ 0 25 g/L; Sn ₂ P ₂ 0 ₇ 3.0 g/L; Κ4Ρ ₂ 0 ₇ ·3Η ₂ 0 450 g/L; Κ ₂ ΗΡ0 ₄ ·3Η ₂ 0 60 g / L; pH 8.5; temperature 25 ° C, brightener B 0.0015 g / L at different currents, the appearance of the Hull trough is shown in Figure 3, Figure 3 is the brightener B vs. Hull trough test piece The impact of appearance. It can be seen from Fig. 3 that the addition of brightener B can effectively improve the co-deposition of the low current density region, and the appearance of the Hull trough in the low current density region changes from pink to golden yellow. As the current increases, the range of pink plating in the low current density region becomes smaller and smaller. However, with the increase of current, the range of scorch in the high region is getting larger and larger, indicating that the range of operable current of electroplating is narrow.

3. Synergistic effect of brightener A and brightener B: In the plating solution, Cu ₂ P ₂ O 3H ₂ 0 25 g/L; Sn ₂ P ₂ 0 ₇ 3.0 g/L; Κ4Ρ ₂ 0 ₇ ·3Η ₂ 0 450 g/L; Κ ₂ ΗΡ0 ₄ ·3Η ₂ 0 60 g/L; pH 8.5; brightener A 0.1 g/L, brightener B 0.0015 g/L, temperature 25 ° C, the appearance of the Hull cell under different current conditions is shown in Figure 4, Figure 4 is after adding the additive Appearance of Hull test strips at different currents. As can be seen from Fig. 4, in the plating solution having the brightener A and the brightener B at the same time, when the current is 0.3 A, the high region has no scorch phenomenon, and the range of the pink plating layer in the low current density region is narrow. When the current is 0.5A, the entire Hull channel is golden yellow. As the current increases, scorching occurs in the high current density region, but the range is narrow. Therefore, when the brightener A and the brightener B are simultaneously present in the plating solution, a synergistic effect is produced, which not only effectively solves the scorching phenomenon in the high current density region, but also eliminates the appearance of the pink plating layer in the low current density region.

(2) The synergistic test and test results of the separate auxiliary complexing agent A, the separate auxiliary complexing agent B, the auxiliary complexing agent A and the auxiliary complexing agent B are as follows:

1. Auxiliary complexing agent A (glycolic acid) An auxiliary complexing agent for tin ions, which can enhance the complexation of tin ions, can eliminate the reaction of free divalent tin with copper ions to form monovalent copper powder, and can effectively inhibit tin. Oxidation of ions. In the plating solution, Cu ₂ P ₂ O 3H ₂ 0 25 g/L; Sn ₂ P ₂ 0 ₇ 3.0 g/L; Κ4Ρ ₂ 0 ₇ ·3Η ₂ 0 450 g/L; Κ ₂ ΗΡ0 ₄ ·3Η ₂ 0 60 g/L; pH 8.5; temperature 25. C; auxiliary complexing agent A 0.3 g / L, the composition of the coating at different current densities is shown in Figure 5, Figure 5 is the effect of the addition of auxiliary complexing agent A on the coating composition. In Figure 5, the abscissa indicates the current density and the ordinate indicates the mass percentage of tin in the coating. Curve B is the composition of the plating solution at the different current densities of the plating solution without the auxiliary complexing agent A, and the curve C is the composition of the plating solution at the different current densities of the plating solution to which the auxiliary complexing agent A is added. It can be seen from Fig. 4 that as the current density increases, the tin content of the coating increases gradually. When the current density is Ο.ΙΑ/dm ² , the tin content in the coating is 12.45%; when the current density is 2A/dm ² , in the coating The tin content can reach 15.67%. After adding auxiliary complexing agent A, the effect of tin content in the coating layer is small in the low current density region; however, tin precipitation is effectively suppressed in the high current density region, when the current density is 2 A/dm ² , in the plating layer The tin content was 14.73%, a decrease of 0.94% year-on-year. It can be seen that the addition of the auxiliary complexing agent A effectively suppresses the difference in tin content of the plating layer at different current densities, and improves the uniformity of the plating layer.

2. Auxiliary complexing agent B (sodium gluconate) An auxiliary complexing agent for copper ions in an alkaline solution system, which can enhance the complexation of copper ions and synergistic effect with glycolic acid, greatly improving the stability of the plating solution. . In the plating solution, Cu ₂ P ₂ O 3H ₂ 0 25 g/L; Sn ₂ P ₂ 0 ₇ 3.0 g/L; Κ4Ρ ₂ 0 ₇ ·3Η ₂ 0 450 g/L; Κ ₂ ΗΡ0 ₄ ·3Η ₂ 0 60 g/L; pH 8.5; temperature 25. C; auxiliary complexing agent B 0.3 g / L, the composition of the coating at different current densities is shown in Figure 6, Figure 6 is the effect of the addition of auxiliary complexing agent B on the coating composition. In Figure 6, the abscissa indicates the current density and the ordinate indicates the mass percentage of copper in the coating. Curve B is the composition of the plating solution at different current densities of the plating solution without the auxiliary complexing agent B, and curve C is the composition of the plating solution at the different current densities of the plating solution to which the auxiliary complexing agent B is added. It can be seen from Fig. 5 that the copper content of the coating gradually decreases with the increase of the current density. When the current density is Ο.ΙΑ/dm ² , the copper content in the coating is 87.62%; when the current density is 2A/dm ² , the coating is in the coating. The copper content dropped to 84.33%. After the addition of auxiliary complexing agent B, the effect of copper content in the coating is small in the high current density region; however, copper precipitation is effectively suppressed in the low current density region. When the current density is Ο.ΙΑ/dm ² , the coating is in the coating. The copper content was 86.21%, a decrease of 1.41% year-on-year. It can be seen that the addition of the auxiliary complexing agent B effectively suppresses the difference in the copper content of the plating layer at different current densities, and improves the uniformity of the plating layer.

3. Synergistic effect of auxiliary complexing agent A and auxiliary complexing agent B: in the plating solution, Cu ₂ P ₂ O 3H ₂ 0 25 g/L; Sn ₂ P ₂ 0 ₇ 3.0 g/L; Κ4Ρ ₂ 0 ₇ · 3Η ₂ 0 450 g/L; Κ ₂ ΗΡ0 ₄ ·3Η ₂ 0 60 g/L _; ρΗ value 8.5 ; temperature 25 ; auxiliary complexing agent A 0.3 g/L, auxiliary complexing agent B 0.3 g/L, different current The composition of the coating under density is shown in Figure 7, and Figure 7 is the effect of the addition of an auxiliary complexing agent on the composition of the coating. In Fig. 7, the abscissa indicates the current density, and the ordinate indicates the mass percentage of copper in the plating. Curve B is the composition of the plating solution without the auxiliary complexing agent at different current densities. Curve C is added with the auxiliary complexing agent A 0.3 g/L, and the auxiliary complexing agent B 0.3 g/L is different. The composition of the coating at current density. It can be seen from Fig. 6 that in the case where the auxiliary complexing agent A and the auxiliary complexing agent B are simultaneously present, the auxiliary complexing agent A in the low current density region effectively suppresses the precipitation of copper and lowers the mass percentage of copper in the plating layer; In the high current density region, the auxiliary complexing agent B effectively suppresses the precipitation of tin, and the mass percentage of tin in the plating layer is lowered, so that the mass percentage of copper is increased. The auxiliary complexing agents A and B in the plating solution produce a synergistic effect by inhibiting the electrodeposition of copper and tin in different current density regions, so that the copper-tin alloy plating layer remains relatively stable under different current density conditions. Alloy plating composition.

The above is only the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. It should be noted that those skilled in the art will not A number of improvements and additions may be made which are also considered to be within the scope of the invention. The equivalents of the changes, modifications, and evolutions that can be made by the above-disclosed technical contents are all those skilled in the art without departing from the spirit and scope of the present invention. Equivalent embodiments; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above-described embodiments in accordance with the essential art of the present invention are still within the scope of the technical solutions of the present invention.

Claims

Claims: A pyrophosphate electroplating solution for multi-layer cyanide-free copper-tin alloy plating, including a cyanide-free brass tin main gloss agent, and the cyanide-free brass tin main gloss agent is in the pyrophosphate electroplating solution The concentration of the cyanide-free brass tin main bright agent is 3-20 mL/L; the solute of the cyanide-free brass tin main bright agent is composed of brightener A and brightener B; wherein the concentration of brightener A in the cyanide-free brass tin main bright agent is 1 - 10g/L; The concentration of brightener B in the cyanide-free brass tin main brightener is 0.05-0.5 g/L. . The pyrophosphate electroplating solution for multi-layer cyanide-free copper-tin alloy plating as claimed in claim 1, wherein the brightener A is Mirapol WT brightener; the brightener B is 2-mercaptobenzene. imidazole. . The pyrophosphate electroplating solution for multi-layer cyanide-free electroplating copper-tin alloy coating as claimed in claim 1, characterized in that the pH value of the pyrophosphate electroplating solution for multi-layer cyanide-free electroplating copper-tin alloy coating is 8.0-10.0; the density is 1.25-1.45g/cm, and the multi-layer cyanide-free electroplating copper-tin alloy plating pyrophosphate electroplating solution according to any one of claims 1-3 is characterized in that it also includes the following concentration Components: pyrophosphate 350~450g/L; soluble copper salt 20-35g/L; soluble tin salt 1.8~3.0g/L; conductive salt 0~80g/L; cyanide-free brass tin auxiliary 10-50 mL/L, the pyrophosphate electroplating solution for multi-layer cyanide-free copper-tin alloy plating as claimed in claim 4, characterized in that the solute of the cyanide-free brass-tin auxiliary agent is composed of auxiliary complexing agent A and Composition of auxiliary complexing agent B; wherein the concentration of auxiliary complexing agent A in the cyanoacrylate tin auxiliary is 5~10g/L, and the concentration of auxiliary complexing agent B in the cyanoacrylate tin auxiliary is 5~10g/L L. . The pyrophosphate electroplating solution for multi-layer cyanide-free electroplating of copper-tin alloy coating as claimed in claim 5, wherein the pyrophosphate is selected from one of potassium pyrophosphate and sodium pyrophosphate; The soluble copper salt is selected from one or more of copper pyrophosphate, copper sulfate, copper chloride, basic copper carbonate, copper methane sulfonate, and copper sulfamate; the soluble tin salt is selected from stannous pyrophosphate , one or more of stannous sulfate, stannous chloride, tin fluoroborate, and tin alkyl sulfonate; the conductive salt is selected from potassium chloride, sodium chloride, dipotassium hydrogen phosphate, ammonium chloride, One or more of potassium sulfate, sodium sulfate, potassium carbonate, and sodium carbonate; the auxiliary complexing agent A and the auxiliary complexing agent B are selected from glycolic acid, sodium gluconate, HEDP (hydroxyethylidene diphosphonic acid) ), citric acid, sodium citrate, citrate amine, potassium sodium tartrate, one or more of methylsulfonic acid, triethanolamine, oxalic acid, glycine, and auxiliary complexing agent A and auxiliary complexing agent B are not selected at the same time same substance. . The pyrophosphate electroplating solution for multi-layer cyanide-free copper-tin alloy plating as claimed in claim 4, further comprising a stabilizer; the concentration of the stabilizer is 0.01~0.05g/L. , an electroplating method for multi-layer cyanide-free electroplating copper-tin alloy plating, sequentially electroplating 2 to 4 layers of copper-tin alloy plating on the coin substrate, and then using high-temperature heat treatment to obtain multi-layer cyanide-free electroplating copper-tin alloy plating. Coins; wherein the even-numbered plating layer and the surface layer are all electroplated using the multi-layer cyanide-free electroplating copper-tin alloy plating pyrophosphate electroplating solution described in any one of claims 1 to 7. The electroplating method for multi-layer cyanide-free electroplating copper-tin alloy plating as claimed in claim 8, characterized in that the number of electroplated copper-tin alloy plating layers is 2 or 4 layers; the temperature of the high-temperature treatment is 600 -800° C o 0. The electroplating method for multi-layer cyanide-free copper-tin alloy plating as claimed in claim 9, which is characterized in that it specifically includes one of the following steps: Method 1:

1. The first layer of electroplating: Use the low carbon steel coinage blank as the coin base. Put the coinage blank after degreasing, pickling and activation into the first plating solution. The plating thickness is about 1 at 20~30°C. A first layer of 5 microns to obtain a first layer of copper-tin alloy containing less than 2% tin; then wash with water;

2. Electroplating the second layer: Put the washed coinage blank obtained in step 1 into the pyrophosphate electroplating solution of the multi-layer cyanide-free electroplated copper-tin alloy coating, and perform electroplating at a temperature of 25~35°C. The second layer is about 10-20 microns thick, and the second layer of copper-tin alloy with a tin content of 14-18% is obtained; then washed;

3. The coinage blank obtained in step 2 after electroplating with two layers and washed with water is dried in sequence and heat treated at high temperature to obtain a coin with multi-layer cyanide-free electroplated copper-tin alloy coating. Method Two:

2. The second layer of electroplating: Put the washed coinage blank obtained in step 1 into the multi-layer cyanide-free electroplated copper-tin alloy In the pyrophosphate electroplating solution of the plating layer, a second layer with a thickness of about 10-20 microns is electroplated at a temperature of 25~35°C to obtain a second layer of copper-tin alloy with a tin content of 14-18%; then washed;

3. Electroplating the third layer: Put the washed coinage blank obtained in step 2 into the first electroplating solution, and electroplate a third layer with a thickness of about 3-5 microns at a temperature of 20~30°C to obtain the tin content. The third layer of copper-tin alloy with less than 2%; then washed;

4. The fourth layer of electroplating (also called the surface layer): Put the rinsed coinage blank obtained in step 3 into the pyrophosphate electroplating solution of the multi-layer cyanide-free electroplated copper-tin alloy coating, and place it at 20 Plate a fourth layer with a thickness of about 10-12 microns at a temperature of ~30°C to obtain a fourth layer of copper-tin alloy with a tin content of 14-18%; then wash with water;

5. The four-layer electroplated and water-washed coinage blanks obtained in step 4 are dried and heat-treated at high temperatures to obtain coins with multi-layer cyanide-free electroplated copper-tin alloy coatings. The electroplating method for multi-layer cyanide-free copper-tin alloy plating as claimed in claim 10, characterized in that, in step 1, the current density of the first layer of electroplating is 0.5~1.5A/ ^dm2 ; the electroplating time is 30 ~60 minutes; in step 2, the current density of the second layer of electroplating is 0.5~1.5A/ ^dm2 ; the electroplating time is 200~550 minutes; in step 3, the current density of the third layer of electroplating is 0.5~1.5A/dm ² ; The electroplating time is 60 to 90 minutes; In step 4, the current density of the fourth layer of electroplating is 0.5 to 1.5A/dm ² ; The electroplating time is 200 to 270 minutes. The water washing described in Step 1 to Step 4 is to use deionized water at room temperature for rinsing. . The electroplating method for multi-layer cyanide-free copper-tin alloy plating as claimed in claim 10, wherein the degreasing step in step 1 also includes an alkaline degreasing step and an electrolytic degreasing step in sequence; The pickling and activation step is to use hydrochloric acid solution to pickle and activate the coinage blank. The electroplating method of multi-layer cyanide-free copper-tin alloy plating as claimed in claim 10, characterized in that the obtained multi-layer cyanide-free copper-tin alloy plating coin is obtained by using two layers of plating. The thickness of the coin coating is 20-24 microns; the thickness of the coin coating obtained by using 4 layers of coating is 25-31 microns. , a coin, produced by the electroplating method of multi-layer cyanide-free electroplating copper-tin alloy coating as described in any one of claims 8-13, the weight percentage of tin in the coating of the coin is 11%~14 %. , The coin according to claim 14, characterized in that the coating thickness of the coin is 20-24 microns or 25-31 microns.