Hard gold plating layer with nanoscale roughness and high gloss and method for preparing same

Abstract

The application provides a hard gold plating layer with nanoscale roughness and high gloss and a preparation method thereof, and relates to the technical field of gold plating layers.The roughness Ra of the hard gold plating layer is less than or equal to 15 nm, the gloss is not less than 600 GU, the hardness is 160-175 HV, and after annealing at 300 DEG C, the hardness is reduced by not more than 20 HV.The electroplating method uses a cyanide-free gold salt electroplating solution, and the raw material components include a gold source, a main complexing agent, an auxiliary complexing agent, a bright leveling agent, a stress relieving agent, a conductive salt and a pH regulator.

Description

Technical Field

[0001] This invention belongs to the field of gold plating technology, and relates to a high-gloss hard gold plating with nanoscale roughness and its preparation method. Background Technology

[0002] Low-roughness gold plating exhibits excellent infrared reflectivity, conductivity, chemical stability, and effective resistance to signal attenuation. It can serve as a highly reliable conductive material and coating material, for example, in millimeter-wave antennas for high-frequency transmission signals in 5G / 6G communication equipment. Ultra-smooth device surfaces can significantly reduce electromagnetic wave scattering; gold mirrors in high-power lasers can effectively reduce energy absorption; and high-gloss gold layers on the infrared windows of optical sensors can improve the sensitivity of gas detection. In particular, when the gold plating has high hardness, it exhibits good wear resistance and also reduces the plating thickness required for device use.

[0003] Cyanide-free gold plating solutions are environmentally friendly, but the resulting gold plating layers, while achieving low roughness, generally have low hardness. Chinese patent CN118256968A discloses a cyanide-free gold plating solution comprising cyanide-free gold salts, complexing agents, buffers, surfactants, stabilizers, grain refiners, hardeners, and antioxidants. The resulting gold plating layer has low roughness, but poor gloss, exhibiting a matte finish. Its initial hardness is 90-120 HV, and after annealing (280℃, 30 min), the hardness only remains at 60-80 HV. Chinese patent CN114934302A discloses a cyanide-free gold plating solution containing a gold source, conductive salts, buffers, auxiliary complexing agents, additives, and cerium salts. However, the additives in this cyanide-free gold plating solution contain at least one of the environmentally unfriendly antimony compounds, arsenic compounds, and thallium compounds, and the hardness of the prepared gold plating layer is between 50-110 HV.

[0004] Therefore, existing technologies urgently need to be improved to provide gold plating with lower roughness and higher hardness. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-gloss hard gold coating with nanoscale roughness and its preparation method.

[0006] The technical solution of the present invention is as follows:

[0007] A high-gloss hard gold coating with nanoscale roughness, wherein the roughness Ra of the hard gold coating is ≤15nm and the hardness is 160-175HV;

[0008] After the hard gold plating is annealed at 300°C, the hardness decreases by no more than 20 HV.

[0009] Preferably, the thickness of the hard gold plating layer is 1-20 μm, and the gloss of the hard gold plating layer is not less than 600 GU.

[0010] Preferably, the annealing time does not exceed 1 hour, the annealing is carried out in a vacuum, inert gas atmosphere or reducing gas atmosphere, and the hardness reduction after annealing does not exceed 20 HV.

[0011] A method for preparing a high-gloss hard gold plating layer with nanoscale roughness, wherein the hard gold plating layer is applied using a cyanide-free gold salt electroplating solution;

[0012] The raw material components of the cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster.

[0013] The pH of the cyanide-free gold salt electroplating solution is 5.5-7.0;

[0014] The roughness Ra of the hard gold plating is ≤15nm, and the hardness is 160-175HV.

[0015] Preferably, the main complexing agent is selected from one or a combination of two of sodium sulfite and ammonium sulfite, and the concentration of the main complexing agent is 10-150 g / L.

[0016] Preferably, the gloss and smoothing agent is selected from one or a combination of two or more imidazole salts and pyridine salts; the concentration of the gloss and smoothing agent is 3-20 mg / L;

[0017] Preferably, the imidazole salt is selected from N-substituted imidazole salts;

[0018] Preferably, the pyridine salt is selected from N-substituted pyridine salts.

[0019] More preferably, the structure of the imidazole salt is shown in formula (1).

[0020]

[0021] Among them, R1 - For organic and / or inorganic anions, m = 2-5.

[0022] More preferably, the structure of the pyridine salt is shown in formula (2) below.

[0023]

[0024] Among them, R2 - The anions are organic and / or inorganic, n = 2-5.

[0025] Preferably, the stress-relieving agent is selected from one or a combination of several of the following: organic sulfonic acids and their salts, organic sulfuric acids and their salts, and organic phosphoric acids and their salts;

[0026] The concentration of the stress reliever is 10-60 mg / L.

[0027] Preferably, the auxiliary complexing agent is a short peptide containing a cysteine ​​structure, and the concentration of the auxiliary complexing agent is 1-10 g / L;

[0028] The plating process is pulse plating.

[0029] The beneficial effects of this invention are:

[0030] (1) The hard gold plating of the present invention has an ultra-smooth metal surface with a roughness Ra≤15nm, a gloss of not less than 600GU, high reflectivity, and a hardness of 160-175HV. The hardness changes little after annealing.

[0031] (2) The present invention uses a cyanide-free electroplating gold solution. By adjusting the auxiliary complexing agent and adding a brightening and smoothing agent and a stress-relieving agent, a gold plating layer with both low roughness and high hardness is achieved. Moreover, the hardness of the high-hardness gold plating layer changes little after annealing. Attached Figure Description

[0032] Figure 1 This is an image showing the reflection of text on paper after the gold plating obtained in Example 2 is stood up.

[0033] Figure 2 This is a SEM image of the gold plating obtained in Example 2. Detailed Implementation

[0034] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0035] On the one hand, the present invention proposes a high-gloss hard gold coating with nanoscale roughness, wherein the roughness Ra of the hard gold coating is ≤15nm and the hardness is 160-175HV;

[0036] After annealing at 300℃, the hardness of the hard gold plating decreases by no more than 20 HV.

[0037] The hard gold plating of this invention has low roughness, with a roughness Ra as low as 15 nm or less, resulting in an ultra-smooth metallic surface. Its hardness can reach 160-175 HV, achieving the goal of obtaining a gold plating with both low roughness and high hardness. Furthermore, the hard gold plating of this invention exhibits good stability; the hardness reduction after heat treatment does not exceed 20 HV. For example, the hardness reduction can be 20 HV, 18 HV, 16 HV, 15 HV, 13 HV, 12 HV, 11 HV, 10 HV, 9 HV, 8 HV, 7 HV, etc.

[0038] In some embodiments, the thickness of the hard gold plating is 1-20 μm, and the gloss of the hard gold plating is not less than 600 GU. For example, the thickness of the hard gold plating can be any value or any value between 1 μm, 3 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 13 μm, 15 μm, 16 μm, 18 μm, 20 μm, etc.; further, the thickness of the hard gold plating can be 1-10 μm. For example, the gloss of the hard gold plating can be any value or any value between 600 GU, 620 GU, 630 GU, 650 GU, etc.

[0039] In some embodiments, the annealing time does not exceed 1 hour, and the annealing is performed in a vacuum, inert gas atmosphere, or reducing gas atmosphere. The hardness reduction after annealing does not exceed 15 HV. For example, annealing is performed in a vacuum, inert gas atmosphere, or reducing gas atmosphere, and the annealing time can be any value or any value between 10 min, 15 min, 20 min, 30 min, 40 min, 50 min, and 60 min, which can prevent oxidation of the hard gold coating during annealing and thus avoid affecting the performance of the hard gold coating. For example, under a nitrogen atmosphere, annealing at 300°C for 30 min results in a hard gold coating hardness reduction of 10 HV, 11 HV, etc.

[0040] On the other hand, the present invention also proposes a method for preparing a high-gloss hard gold plating layer with nanoscale roughness, wherein the hard gold plating layer is applied using a cyanide-free gold salt electroplating solution.

[0041] The raw material components of the above-mentioned cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster; the pH of the cyanide-free gold salt electroplating solution is 5.5-7.0;

[0042] The obtained hard gold coating has a roughness Ra≤15nm and a hardness of 160-175HV.

[0043] There are no particular restrictions on the gold source for cyanide-free gold salt electroplating solutions. For example, sodium gold sulfite and / or ammonium gold sulfite can be used. The concentration of the gold source can be 5-25 g / L, or further, 5-15 g / L, depending on the gold content.

[0044] In some embodiments, the primary complexing agent is selected from one or a combination of two of sodium sulfite and ammonium sulfite, and the concentration of the primary complexing agent is 10-150 g / L. For example, the concentration can be any value among 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, etc. Further, the concentration of the primary complexing agent can be 15-110 g / L.

[0045] In some embodiments, the brightening and smoothing agent is selected from one or a combination of two or more imidazole salts and pyridine salts; the concentration of the brightening and smoothing agent is 3-20 mg / L; in this invention, pyridine salts and / or imidazole salts are used as brightening and smoothing agents, which adsorb onto the surface of the substrate where the current density is high, making it difficult for gold ions to deposit at high currents without affecting reduction in low current regions, thus promoting the acquisition of a hard gold plating layer with low roughness and high gloss. Examples of the concentration of the brightening and smoothing agent include 3 mg / L, 4 mg / L, 5 mg / L, 6 mg / L, 7 mg / L, 8 mg / L, 9 mg / L, 10 mg / L, 11 mg / L, 12 mg / L, 13 mg / L, 14 mg / L, 15 mg / L, 16 mg / L, 17 mg / L, 18 mg / L, 19 mg / L, and 20 mg / L.

[0046] In some embodiments, the imidazole salt is selected from N-substituted imidazole salts, and further, the imidazole salt has the structure shown in formula (1).

[0047]

[0048] Among them, R1 - The anion is an organic anion and / or an inorganic anion, where m = 2-5. For example, the imidazole salt can be 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium chloride, 1-propyl-3-methylimidazolium sulfate, 1-propyl-3-methylimidazolium acetate, etc.

[0049] In some embodiments, the pyridinium salt is selected from N-substituted pyridinium salts, and further, the structure of the pyridinium salt is shown in formula (2).

[0050]

[0051] Among them, R2 - The anions are organic and / or inorganic, with n = 2-5. For example, pyridine salts can be butylpyridine bromide, butylpyridine chloride, butylpyridine sulfate, butylpyridine maleate, propylpyridine bromide, butylpyridine acetate, etc.

[0052] In some embodiments, stress-relieving agents can reduce the internal stress of hard gold plating, improve the uniformity, wear resistance, and stability of hard gold plating on various shaped devices, and better maintain the hardness of the gold plating during annealing. Stress-relieving agents can be selected from one or more combinations of organic sulfonic acids and their salts, organic sulfuric acids and their salts, and organic phosphoric acids and their salts, such as sodium saccharin-N-3-propanesulfonate, 2-naphthalenesulfonic acid, sodium dodecyl sulfate, dodecylbenzenesulfonic acid, sodium dodecylbenzenesulfonate, sodium dodecyl sulfonate, etc.

[0053] The concentration of the stress reliever is 10-60 mg / L. For example, the concentration can be any value from 10 mg / L, 15 mg / L, 20 mg / L, 25 mg / L, 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, etc. Further, the concentration of the stress reliever can be 25-40 mg / L.

[0054] In some embodiments, the auxiliary complexing agent is a short peptide containing a cysteine ​​structure, and the concentration of the auxiliary complexing agent is 1-10 g / L. For example, the short peptide containing a cysteine ​​structure can be cysteyl alanine, cysteyl aspartic acid, cysteyl lysine, and cysteyl tyrosine, etc., containing amino, carboxyl, thiol, amide, etc., which have a good complexing effect on gold elements and are therefore effective as an auxiliary complexing agent. For example, the concentration of the auxiliary complexing agent can be any value or any value between 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, and 10 g / L.

[0055] The conductive salt can be an inorganic salt, such as sodium chloride, potassium chloride, or sodium nitrate. The concentration of the conductive salt can be 10-70 g / L, or even further, 15-45 g / L.

[0056] The pH adjuster can be either an acid or a base to adjust the pH of the cyanide-free gold salt electroplating solution to 5.5-7.0. Acids can be sulfuric acid, sodium dihydrogen phosphate, tartaric acid, malic acid, citric acid, etc., while bases can be sodium hydroxide, sodium carbonate, sodium phosphate, sodium monohydrogen phosphate, etc.

[0057] The plating process is pulse plating, such as single-pulse plating or dual-pulse plating. Further, pulse plating is specifically single-pulse plating.

[0058] For example, one method for applying the cyanide-free gold salt electroplating solution of the present invention may be as follows: adjusting the temperature of the plating solution to 45-60℃, using a Pt-coated titanium mesh as the anode and the workpiece to be plated as the cathode. The distance between the anode and cathode is 1-2.5cm, the duty cycle is 10-40%, the frequency is 500-1200Hz, and the current density is 20-60mA / cm. 2 The electroplating process involves moving the cathode or stirring the plating solution with magnetic force, and the electroplating is completed when the desired thickness is reached.

[0059] The hard gold coating of the present invention has low roughness, high gloss, high hardness, and good high temperature resistance. It can be plated on the surface of metals such as nickel and copper as a coating material and is used in signal transmitters such as high-end communication equipment, high-power devices and sensors.

[0060] The technical solution of the present invention will be further described and illustrated below with reference to various embodiments. Unless otherwise specified, the parts mentioned in the following embodiments are parts by weight.

[0061] Example 1

[0062] The raw material components of the cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster.

[0063] The gold source is ammonium gold sulfite, with a concentration of 5 g / L based on the gold content. The main complexing agent is ammonium sulfite, with a concentration of 15 g / L. The auxiliary complexing agent is cysteine ​​alanine, with a concentration of 10 g / L. The brightening and smoothing aid is butylpyridine bromide, with a concentration of 3 mg / L. The stress-relieving aid is sodium saccharin-N-3-propanesulfonate, with a concentration of 25 mg / L. The conductive salt is sodium chloride, with a concentration of 15 g / L. The pH adjuster is 10 wt% dilute sulfuric acid, adjusting the pH of the plating bath to 6.0.

[0064] Single-pulse electroplating was performed at a bath temperature of 45℃. The anode was a Pt-coated titanium mesh, and the cathode was a nickel sheet to be plated. The anode-cathode distance was 1.0 cm, the duty cycle was 10%, the frequency was 500 Hz, and the current density was 20 mA / cm². 2 The electroplating process employed magnetic stirring to obtain a gold plating layer with an average thickness of 10 μm. The gold plating layer was uniform and bright, with a roughness Ra = 15 nm, a gloss level of 628 GU, and a micro Vickers hardness of 163 HV. After annealing at 300℃ for 30 min in a nitrogen atmosphere, the micro Vickers hardness of the plating layer decreased to 151 HV, representing a decrease of 12 HV after annealing.

[0065] Example 2

[0066] The raw material components of the cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster.

[0067] The gold source is sodium gold sulfite, with a concentration of 10 g / L based on the gold content. The main complexing agent is sodium sulfite, with a concentration of 45 g / L. The auxiliary complexing agent is cysteyl aspartic acid, with a concentration of 7 g / L. The brightening and smoothing agent is 1-butyl-3-methylimidazolium thiocyanate, with a concentration of 6 mg / L. The stress-relieving agent is 2-naphthalenesulfonic acid, with a concentration of 30 mg / L. The conductive salt is sodium chloride, with a concentration of 25 g / L. The pH adjuster is a 10 wt% NaOH solution, adjusting the pH of the plating bath to 6.5.

[0068] Single-pulse electroplating was performed at a bath temperature of 50℃. The anode was a Pt-coated titanium mesh, and the cathode was a nickel sheet to be plated. The anode-cathode distance was 1.5 cm, the duty cycle was 20%, the frequency was 800 Hz, and the current density was 40 mA / cm². 2 The electroplating process employed a cathode-moving method to obtain a gold plating layer with an average thickness of 8 μm. The gold plating layer was uniform and bright, with a roughness Ra = 13 nm, a gloss level of 647 GU, and a micro Vickers hardness of 173 HV. After annealing at 300℃ for 30 min in a nitrogen atmosphere, the micro Vickers hardness of the plating layer decreased to 162 HV, representing a decrease of 12 HV after annealing.

[0069] The gold plating obtained in this embodiment reflects the text on the paper when the paper is stood upright, as shown in the attached image. Figure 1 As shown, the golden yellow layer on top is the gold plating layer of this invention, and the silvery white layer below is paper. It can be seen that the surface smoothness of the gold plating layer of this invention is very high, achieving a smooth mirror-like effect. The SEM image of the gold plating layer obtained in this embodiment is attached. Figure 2 As shown.

[0070] Comparative Example 1

[0071] The difference between this comparative example and Example 2 is that in Example 2, the single-pulse electroplating was adjusted to constant current electroplating (i.e., not pulse electroplating), the anode-cathode distance was 1.5 cm, and the current density was 8 mA / cm². 2 The remaining steps remained unchanged, and the resulting gold coating had a roughness Ra = 75 nm, a gloss of 356 GU, and a micro Vickers hardness of 135 HV. After annealing at 300℃ for 30 min, the micro Vickers hardness of the coating was 117 HV, a decrease of 18 HV.

[0072] Comparative Example 2

[0073] The difference between this comparative example and Example 2 is that in Example 2, the auxiliary complexing agent was changed from cysteyl aspartic acid to sodium citrate, while the concentration remained unchanged. The remaining steps remained the same, and the resulting gold coating had a roughness Ra = 28 nm, a gloss of 415 GU, and a micro Vickers hardness of 137 HV. After annealing at 300°C for 30 min, the micro Vickers hardness of the coating decreased to 117 HV, a decrease of 20 HV.

[0074] Comparative Example 3

[0075] The difference between this comparative example and Example 2 is as follows: In Example 2, the brightening and smoothing agent was changed from 1-butyl-3-methylimidazolium thiocyanate to a combination of vanillin and sodium propargyl sulfonate in a weight ratio of 2:3, while the concentration remained unchanged. The remaining steps remained the same. The resulting gold coating had a roughness Ra of 15 nm, a gloss of 498 GU, and a micro Vickers hardness of 128 HV. After annealing at 300°C for 30 min, the micro Vickers hardness of the coating was 107 HV, a decrease of 21 HV.

[0076] Comparative Example 4

[0077] The difference between this comparative example and Example 2 is that in Example 2, the stress-relieving agent 2-naphthalenesulfonic acid was not added, and the other steps remained unchanged. The roughness of the obtained gold coating was Ra=14nm, the gloss was 640GU, ​​the micro Vickers hardness of the coating was 165HV, and after annealing at 300℃ for 30min, the micro Vickers hardness of the coating was 126HV, which is a decrease of 39HV.

[0078] Example 3

[0079] The raw material components of the cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster.

[0080] The gold source is sodium gold sulfite, with a concentration of 10 g / L based on the gold content. The main complexing agent is sodium sulfite, with a concentration of 80 g / L. The auxiliary complexing agent is cysteyl lysine, with a concentration of 5 g / L. The brightening and smoothing aids are butylpyridine bromide and 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, both with a concentration of 3 mg / L. The stress-relieving aid is sodium dodecyl sulfate, with a concentration of 35 mg / L. The conductive salt is potassium chloride, with a concentration of 35 g / L. The pH adjuster is 10 wt% dilute sulfuric acid, adjusting the pH of the plating bath to 7.0.

[0081] Single-pulse electroplating was performed at a bath temperature of 60℃. The anode was a Pt-coated titanium mesh, and the cathode was a nickel sheet to be plated. The anode-cathode distance was 2cm, the duty cycle was 30%, the frequency was 1000Hz, and the current density was 50mA / cm². 2The electroplating process employed a cathode-moving method to obtain a gold plating layer with an average thickness of 8 μm. The gold plating layer was uniform and bright, with a roughness Ra = 12 nm, a gloss level of 650 GU, and a micro Vickers hardness of 168 HV. After annealing at 300 °C for 30 min in a nitrogen atmosphere, the micro Vickers hardness of the plating layer decreased to 155 HV, representing a decrease of 13 HV after annealing.

[0082] Example 4

[0083] The raw material components of the cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster.

[0084] The gold source is ammonium gold sulfite, with a concentration of 15 g / L based on the gold content. The main complexing agent is ammonium sulfite, with a concentration of 110 g / L. The auxiliary complexing agent is cysteyl tyrosine, with a concentration of 1 g / L. The brightening and smoothing aid is 1-hexyl-3-methylimidazolium trifluoromethanesulfonate, with a concentration of 20 mg / L. The stress-relieving aid is sodium dodecyl sulfate, with a concentration of 40 mg / L. The conductive salt is sodium chloride, with a concentration of 45 g / L. The pH adjuster is 30 wt% dilute sulfuric acid, adjusting the pH of the plating bath to 6.0.

[0085] Single-pulse electroplating was performed at a bath temperature of 60℃. The anode was a Pt-coated titanium mesh, and the cathode was a nickel sheet to be plated. The anode-cathode distance was 2cm, the duty cycle was 40%, the frequency was 1200Hz, and the current density was 60mA / cm². 2 The electroplating process employed a cathode-moving method to obtain a gold plating layer with an average thickness of 5 μm. The gold plating layer was uniform and bright, with a roughness Ra = 15 nm, a gloss level of 653 GU, and a micro Vickers hardness of 167 HV. After annealing at 300℃ for 30 min in a nitrogen atmosphere, the micro Vickers hardness of the plating layer decreased to 157 HV, representing a decrease of 10 HV after annealing.

[0086] As described above, the basic principles, main features, and advantages of the present invention have been shown and described. Those skilled in the art should understand that the present invention is not limited to the above embodiments, which are merely preferred embodiments and should not be construed as limiting the scope of the invention. All equivalent changes and modifications made in accordance with the scope of the patent and the description should still fall within the scope of the present invention. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-gloss hard gold coating with nanoscale roughness, characterized in that, The hard gold plating layer is applied using a cyanide-free gold salt electroplating solution. The pH of the cyanide-free gold salt electroplating solution is 5.5-7.0; The raw material components of the cyanide-free gold salt electroplating solution include: gold source, main complexing agent, auxiliary complexing agent, brightening and smoothing agent, stress relief agent, conductive salt and pH adjuster. The gloss and smoothing agent is selected from one or two of imidazole salts and pyridine salts, and the concentration of the gloss and smoothing agent is 3-20 mg / L; The imidazole salt is selected from N-substituted imidazole salts, and the pyridine salt is selected from N-substituted pyridine salts; The stress-relieving agent is selected from one or more of saccharin-N-3-propanesulfonate sodium, 2-naphthalenesulfonic acid and sodium dodecyl sulfate, and the concentration of the stress-relieving agent is 10-60 mg / L; The auxiliary complexing agent is selected from one of cysteyl alanine, cysteyl aspartic acid, cysteyl lysine and cysteyl tyrosine, and the concentration of the auxiliary complexing agent is 1-10 g / L. The plating process is pulse plating. The roughness Ra of the hard gold plating layer is ≤15nm, and the hardness is 160-175HV. After the hard gold plating is annealed at 300°C, the hardness decreases by no more than 20 HV.

2. The method for preparing a high-gloss hard gold coating with nanoscale roughness according to claim 1, characterized in that, The thickness of the hard gold plating is 1-20 μm, and the gloss of the hard gold plating is not less than 600 GU.

3. The method for preparing a high-gloss hard gold coating with nanoscale roughness according to claim 1, characterized in that, The annealing time shall not exceed 1 hour, the annealing shall be carried out in a vacuum, inert gas atmosphere or reducing gas atmosphere, and the hardness reduction after annealing shall not exceed 20 HV.

4. The method for preparing a high-gloss hard gold coating with nanoscale roughness according to claim 1, characterized in that, The main complexing agent is selected from one or both of sodium sulfite and ammonium sulfite, and the concentration of the main complexing agent is 10-150 g / L.

5. The method for preparing a high-gloss hard gold coating with nanoscale roughness according to claim 1, characterized in that, The structure of the imidazole salt is shown in formula (1) below. （1） Among them, R1 - For organic and / or inorganic anions, m = 2-5.

6. The method for preparing a high-gloss hard gold coating with nanoscale roughness according to claim 1, characterized in that, The structure of the pyridine salt is shown in formula (2) below. （2） Among them, R2 - The anions are organic and / or inorganic, n=2-5.

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