Ag-graphene composite plated metal parts and their manufacturing method

Abstract

To provide a component comprising a substrate coated with an Ag-graphene composite plating film improved in both electroconductivity and abrasion resistance relative to a silver-plating film.SOLUTION: A component 10 comprising a substrate 2 coated with an Ag-graphene composite plating film 1, is characterized in that the size of graphene 8 dispersed in the Ag-graphene composite plating film 1 is from 0.05 to 6 μm, the content of the graphene 8 is from 3.0 to 30 at%, and the arrangement direction of the graphene 8 in the Ag-graphene composite plating film 1 is vertical to, parallel to, or tilted to the substrate 2.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a metal part having an Ag-graphene composite plating film and a method for producing the same. [Background technology]

[0002] With the growing concern for the global environment, the rapid spread of electric vehicles (EVs) and plug-in hybrid vehicles (PHVs) has replaced fossil fuel-powered vehicles, and the demand for pure silver (Ag) plating materials, which have the highest electrical conductivity of all metals, is increasing in order to save energy. However, Ag is soft and prone to adhesion, resulting in low wear resistance. Graphene is also more electrically conductive than silver and has excellent lubricity and thermal stability, but it cannot be used as a standalone material, so the biggest challenge is how to combine it with other materials.

[0003] Patent Document 1 describes a silver plating material that achieves both high hardness and low electrical resistance by further using graphene oxide in addition to a curing agent. Patent Document 2 describes an electrical contact material that contains silver or copper, 0.1% to 6% by mass of graphite, calcium, etc., and has a relative density of 97% or more.

[0004] Meanwhile, Non-Patent Document 1 describes that by dropping an ethanol solution containing graphene onto a silver plate, drying it, and conducting a wear test with a silver-plated material, it is possible to significantly reduce the friction coefficient of the silver plate to one-tenth by using graphene as a lubricant. Non-Patent Document 2 describes that a commercial graphene sheet is added to a silver plating solution, and a silver-graphene plating with an uneven surface is formed by electroplating, and the formed silver-graphene plating exhibits a lower friction coefficient and corrosion current than the silver plating in a wear test against a GCr15 steel ball.

[0005] Conventional techniques have primarily improved wear resistance by hardening Ag plating, but this reduces electrical conductivity and limits the effectiveness of improving wear resistance. Attempts have also been made to combine Ag with non-metallic materials such as solid lubricants like MoS2, graphite, and Teflon® particles, but these have always led to problems such as a decrease in electrical conductivity. Meanwhile, the inventors have already developed a hybrid plating technology to create Ag-graphene composite plating, which significantly improved wear resistance while maintaining electrical conductivity (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-199839 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-99839 [Patent Document 3] Patent application No. 2019-196958 [Non-patent literature]

[0007] [Non-Patent Document 1] “Graphene as a lubricant on Ag for electrical contact applications”, Fang Mao, Urban Wiklund, Anna M. Andersson, Ulf Jansson. Journal of Materials Science, vol.50, pp.6518-6525,2015. [Non-patent document 2] “Performance studies of Ag, Ag-graphite, and Ag-graphene coatings on Cu substrate for high-voltage isolation switch”, Wang Yan Lv, Ke Qin Zheng, Zeng Guang Zhang, Materials and Corrosion,vol.69. pp.1847-1853, 2019. Summary of the Invention [Problem to be solved by the invention]

[0008] However, the electrical conductivity of Ag-graphene composite plating films remains lower than that of pure silver plating, and there is room for further improvement in their wear resistance. In particular, there is a problem in that both electrical conductivity and wear resistance have not yet been improved. [Means for solving the problem]

[0009] (1) A metal part having a substrate coated with an Ag-graphene composite plating film, wherein the size of the graphene dispersed in the Ag-graphene composite plating film (graphene size) is 0.05 to 6 μm, the content of the graphene (graphene content) is 3.0 to 30 at %, and the arrangement direction of the graphene in the Ag-graphene composite plating film is at least one selected from perpendicular, parallel, and oblique to the substrate. The remainder of the Ag-graphene composite plating film is Ag and unavoidable impurities. (2) The metal part according to (1), wherein the Ag-graphene composite plating film has an electrical contact resistance of 0.1 to 0.7 mΩ. (3) The metal part according to (1) or (2), characterized in that the wear coefficient with respect to the Ag-graphene composite plating film is 0.1 to 0.4, and the amount of wear is reduced to 1 / 10 to 1 / 30. (4) The metal part according to any one of (1) to (3), wherein the Ag-graphene composite plating film has a Vickers hardness of 80 HV or more. (5) The metal part according to any one of (1) to (4), characterized in that it is used for an automobile on-board terminal, a charging connector, or a power transmission part. (6) A method for manufacturing a metal part having a substrate coated with an Ag-graphene composite plating film, the method comprising: electroplating the substrate with a plating solution containing Ag and graphene, the plating solution being supplied in one of the following ways: flowing the plating solution in a direction approximately vertical to the surface to be plated of the substrate (so-called coaxial stirring); flowing the plating solution in a direction approximately horizontal to the surface to be plated (so-called torsional stirring); or flowing the plating solution in a direction approximately horizontal to the surface to be plated (so-called orthogonal axis stirring). (7) The electric field strength (current density) during the electroplating is 0.1 A / dm 2 ~10A / dm 2 The method for manufacturing a metal part according to (6) is characterized in that: [Effects of the Invention]

[0010] According to the present invention, it is possible to improve the electrical conductivity, which has not been realized in the prior art. In particular, it is possible to consciously control the electrical conductivity and the wear resistance (lubricity) in a well-balanced manner, and it is possible to provide various plating specifications depending on the actual terminal mounting location, i.e., metal parts with those plating specifications. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1A shows a manufacturing method for coating a Cu substrate with an Ag-graphene composite plating film by electroplating, and FIG. 1B shows schematic diagrams of four representative embodiments of a Cu substrate coated with an Ag-graphene composite plating film by the manufacturing method. [Figure 2] 1A and 1B are diagrams each showing a schematic diagram of an electrode arrangement, a liquid flow, and stirring methods, namely, coaxial stirring and torsional stirring, during electroplating. [Figure 3]When using a commercially available non-cyanide silver plating solution, Solution A (general Ag plating), the following factors affect conductivity as determined by electrical contact resistance measurement are shown: (a) a schematic diagram of the electrical contact resistance measurement method, (b) the influence of the graphene size and current density to be combined, (c) the influence of the stirring method and current density (graphene size 3-5 μm), and (d) the influence of current density (graphene size 3-5 μm, coaxial stirring). [Figure 4] This figure shows the effect of stirring strength on the conductivity (electrical contact resistance) of Ag-graphene composite plating films when using commercially available non-cyanide silver plating solution Solution B, with graphene size and stirring method as influencing factors, for (a) coaxial stirring with graphene size of 1 to 3 μm, (b) coaxial stirring with graphene size of 6 μm or less (mixed), (c) torsional stirring with graphene size of 1 to 3 μm, and (d) torsional stirring with graphene size of 6 μm or less (mixed). [Figure 5] The figures show the effect of graphene size on wear resistance in sliding wear tests for (a1) and (a2) pure Ag plating film (plating solution B, hard Ag plating), (b1) and (b2) Ag-graphene composite plating film (graphene size 1 μm or less), and (c1) and (c2) Ag-graphene composite plating film (graphene size 3 to 5 mm). [Figure 6] The figures show the results of the sliding friction test for (a1) to (a4) pure Ag (plating solution A), and (b1) to (b4) Ag-graphene (graphene size 1 to 3 μm, stirring intensity 6 with torsional stirring). [Figure 7] The effect of graphene size on hardness (Vickers hardness) measured by microhardness measurement is shown in (a) a schematic diagram of the microhardness measurement, (b) a graphene size of 3 to 5 μm or 1 μm with torsional stirring, and (c) a graphene size of 3 to 5 μm or 1 μm with coaxial stirring. The Ag plating solution used was Solution A (general Ag plating solution). [Figure 8]These figures show the effect of graphene size on hardness (Vickers hardness) measured by microhardness measurement, when plating is performed using Ag plating solution B (hard Ag plating solution) with graphene sizes of 1 to 3 μm, with (a) coaxial stirring and (b) torsional stirring. [Figure 9] FIG. 1 is a diagram showing the influence of graphene size on the pinning effect when (a) the graphene size is 1 μm or less and (b) the graphene size is 3 to 5 μm. [Figure 10] The effect of current density on the bonding state of carbon in Ag-graphene composite plating films is shown by (a) Raman spectroscopy measurement, and (b) EDS analysis of the plating film composition. [Figure 11] (a) TEM image of graphene in the Ag-graphene composite plating film during torsional stirring, and (b) a schematic diagram of (a). DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments, and changes, modifications, and improvements can be made without departing from the scope of the invention.

[0013] Figure 1(a) shows a manufacturing method for coating a Cu substrate with an Ag-graphene composite film by electroplating, and Figure 1(b) shows schematic diagrams of four representative embodiments of Ag-graphene composite film plating produced by this manufacturing method. The Cu substrate is coated with an Ag-graphene composite plating film 1. Therefore, a metal part having a Cu substrate has a substrate coated with an Ag-graphene composite plating film 1. Graphene flakes, or graphene, can be produced by electrolytic exfoliation, which involves breaking down graphite into layers under a high electric field.

[0014] As shown in Figure 1(b), Ag-graphene composite plating film 1 can impart various performance properties to metal terminals depending on the dispersion state of graphene in the Ag matrix. Because electricity flows easily along the graphene sheet, when mating with a mating terminal, selecting a high-conductivity specification like (2) is preferable to achieve high conductivity in a metal terminal coated with Ag-graphene composite plating film (Ag-graphene composite plating film-coated metal terminal). On the other hand, to create a highly lubricious Ag-graphene composite plating film-coated metal terminal, selecting a high-lubricity specification like (3) is preferable to ensure that the graphene slides easily on the copper substrate. Furthermore, because graphene has high strength parallel to the sheet, it is preferable to arrange the graphene sheet diagonally in a jagged pattern on the Ag film and select a high-strength specification like (4). This improves both conductivity and lubricity.

[0015] The conditions for electrolytic peeling were as follows: graphite was immersed in an aqueous solution, and a strong electric field and electrochemical reaction were used to decompose the graphite into layers, producing stacked graphene flakes. The decomposed layered graphene was then separated into the following graphene sizes by classification: graphene sizes of less than 1 μm, 1-3 μm, 3-5 μm, and a mixture of 6 μm and less. Note that graphene size was determined by the mesh of the filter paper used during filtration.

[0016] A silver plating solution L containing a graphene dispersion was placed in a plating tank 5 of an electroplating apparatus 20 shown in Figure 2. A Cu alloy substrate 2 (cathode) and a counter electrode (anode, silver plate) 3, which are the objects to be plated, were immersed vertically and an electric current was applied to the objects to be plated. A forced flow of the silver plating solution L can be induced, for example, by a stirrer or a propeller. If a flow direction indicated by r1 is induced in the silver plating solution L at the bottom of the plating tank 5 by a stirrer, the flow direction will be horizontal (parallel to the bottom of the plating tank 5). In this case, the silver plating solution L includes silver plating solution L that contacts the plating surface 4 of the Cu alloy substrate 2 from a horizontal direction. In this case, the axis x1 of the flow indicated by r1 is vertical and can be said to be "coaxial" with the vertical axes x3 and x4 of the Cu alloy substrate 2 and the counter electrode 3. In other words, a stirring method that induces such a flow (flow) is called coaxial stirring.

[0017] On the other hand, if forced convection in the direction of r2, r2' occurs in the silver plating solution L on the side of the plating tank 5, for example, by a stirrer, the flow direction will be vertical. In this case, the silver plating solution L will contain silver plating solution L that contacts the plating target surface 4 of the Cu alloy substrate 2 from a direction perpendicular to the plating target surface. In this case, the flow axis x2 of r2, r2' is horizontal, and x2 can be said to be an "orthogonal axis" that is perpendicular to the vertical axes x3, x4 of the Cu alloy substrates 2, 3. In other words, the stirring method that causes such a flow (fluidity) can be called "orthogonal axis stirring." Furthermore, when the flow direction of r2 and the flow direction of r2' are opposite to each other, it can be called a "torsion axis." In other words, a mixing method that causes such a flow (convection) is called torsion axis mixing (sometimes called "torsion mixing"). [Example]

[0018] For the copper shown in Figure 1(b), a Cu alloy substrate (20 × 60 × 0.3 mm) was prepared as the starting sample. The Cu alloy substrate was pretreated by alkaline electrolytic degreasing and acid pickling to remove the oxide film, and thoroughly washed after each pretreatment. Two types of commercially available non-cyanide Ag plating solutions (Ag 30 g / L) were used for Ag plating. Graphene was prepared from graphite by electrolytic peeling and dispersed ultrasonically using an organic dispersant. The prepared graphene dispersion was added to the Ag plating solution (graphene dispersion / Ag plating solution = 20 mL / L) to prepare the Ag-graphene plating solution. Tables 1 and 2 summarize the manufacturing conditions and measured values of the manufactured sample (Ag-graphene composite plating film coated Cu substrate (Example)). Table 3 summarizes the manufactured samples (Ag plating film coated Cu substrate (Comparative Example) and various commercially available Ag-plated materials for on-board terminals and charging connectors and thick Ag-plated materials for power transmission switches (Comparative Example)) and their measured values. An explanation of these tables is added below.

[0019] [Table 1] [Table 2] [Table 3]

[0020] (electrical contact resistance measurement) By measuring the electrical contact resistance as shown in the schematic diagram in Figure 3(a), we investigated the graphene size, stirring method (graphene size 3–5 μm), and current density (graphene size 3–5 μm, coaxial stirring) as factors affecting conductivity. The conditions for measuring the electrical contact resistance were as follows: Conditions: Variable load type (0-0.5-0N, with sliding), sliding type (value at 0.5N load), Measuring device: Electrical contact resistance measuring device (electrical contact simulator CRS-1 type). The mating terminal was 24K gold wire, and the fixed terminal was 18K gold plated. Figures 3(b) to (d) show the results of electrical contact resistance measurements (sliding type) of the composite plating film obtained using Ag plating solution A, and Figures 4(a) to (d) show the results of electrical contact resistance measurements (sliding type) of the composite plating film obtained using Ag plating solution B.

[0021] 3(b), all of the Ag-graphene composite plating films (Examples 1 to 8) were found to have lower electrical contact resistance, i.e., better conductivity, than the pure Ag plating film (Comparative Example 1). Furthermore, composites containing graphene with a graphene size of 3 to 5 μm had better conductivity than composites containing graphene with a size of 1 μm or less.

[0022] 3(c) shows that all of the Ag-graphene composite plating films (Examples 9 to 12) had lower electrical contact resistance, i.e., better conductivity, than the pure Ag plating film (Comparative Example 1). In particular, coaxial stirring was more effective at improving conductivity than torsional stirring.

[0023] From Figure 3(d), it was found that all of the Ag-graphene composite plating films (Examples 13-17) had lower electrical contact resistance than the pure Ag plating film (Comparative Example 1), and that the contact resistance decreased significantly as the current density increased, resulting in a significant improvement in conductivity. Furthermore, the resistance value was reduced by up to 59% compared to the pure Ag plating film (Example 17). It was also found that in all cases, increasing the current density significantly improved the conductivity.

[0024] 4(a) to 4(d), improved conductivity was confirmed for all Ag-graphene composite plating films (Examples 18 to 29) when silver plating solution B was used. That is, by combining the stirring strength, stirring method, and graphene size, the electrical contact resistance was 42 to 71% of that of the pure Ag plating film of Comparative Example 2.

[0025] (Sliding wear test) The effect of graphene size on wear resistance was investigated by a sliding wear test for a pure Ag plating film (Comparative Example 1), an Ag-graphene composite plating film (graphene size 1 μm or less), and an Ag-graphene composite plating film (graphene size 3 to 5 μm). The conditions for the sliding wear test were as follows: Load: 3N, Frequency: 1Hz, Sliding distance: 500μm, Measuring device: Precision wear friction tester (CRS-B type), Counterpart material (Emboss): R=3mm, commercially available general Ag-plated material (80HV), Ag plating film: 5μm, Ni-plated undercoat. Each sample was measured twice. In addition, the wear tracks were photographed using a white laser microscope to create a three-dimensional image. Next, using the digital data from the three-dimensional image, the unworn area was set as the reference surface, and the adhesive wear amount was calculated for the area above the reference surface, and the abrasive wear amount for the area below the reference surface. The adhesive wear amount and abrasive wear amount were then added together to calculate the wear amount of the entire sample.

[0026] Figures 5(a1) to (c1) show the correlation between the number of abrasion cycles and the friction coefficient for pure silver plating (Comparative Example 2), and Ag-graphene composite plating films with graphene sizes of 1 μm or less (Example 7), and 3 to 5 μm (Example 11), respectively. The results of two measurements are plotted. The pure silver plating shown in (a1) has a high friction coefficient of 0.6 to 0.9 due to adhesion, while the Ag-graphene composite plating films with graphene sizes of 3 to 5 μm shown in (c1) have less adhesion in the early stages of abrasion and a low friction coefficient in the stable region of 0.28 to 0.32, a reduction of approximately 62% compared to pure Ag plating.

[0027] Furthermore, from the three-dimensional images taken by a laser microscope shown in Figure 5 ((a2) to (c2)), it can be seen that the pure Ag plating film has wear marks with severe irregularities, while the Ag-Graphene composite plating film is so smooth that wear marks are barely detectable. In particular, from the three-dimensional images mentioned above, the adhesive wear amount and abrasive wear amount were calculated, and the wear amount of the entire sample was calculated and the two measured values were averaged. As a result, the wear amounts of Comparative Example 2, Example 7, and Example 11 were each 167 × 10 4 μm 3 , 116.0×10 4 μm 3and 5.9 x 10 4 μm 3 In addition, when the wear amounts of Examples 7 and 11 were compared with the wear amount of the pure Ag plating film, the wear amount was 116.0 × 10 4 μm 3 / 167×10 4 μm 3 = 1 / 1.42, which is also 5.9 × 10 4 μm 3 / 167×10 4 μm 3 = 1 / 28.3, which was less than 1 / 28. It was found that the best wear resistance was achieved when graphene with a graphene size of 3 to 5 μm was used.

[0028] (For charging connector) For the charging connector, a sliding wear test similar to that shown in Figure 5 was performed on Example 25 and the pure Ag plating film (Comparative Example 2) to determine the amount of wear, etc. (measurements were performed under the same conditions for the on-board terminal and the charging connector, and the amount of wear was calculated). Figure 6(a1) shows a graph of the number of abrasion passes and the coefficient of friction for two measurements of a pure Ag plating film (Comparative Example 2). Figure 6(a2) shows a laser microscope photograph of the plating state after the sliding abrasion test, Figure 6(a3) shows a three-dimensional image taken with the laser microscope, and Figure 6(a4) shows the elevation of the plated surface 16 after the sliding abrasion test, with the non-friction surface 15 in Figure 6(a2) as the reference surface. The wear volume of the entire sample was then calculated for the abrasion marks in the same manner as described above.

[0029] Figure 6(b1) shows a graph of the number of abrasion passes and the coefficient of friction for two measurements of the Ag-graphene composite plating film (Example 25). Figure 6(b2) shows a laser microscope photograph of the plating state after the sliding wear test, Figure 6(b3) shows a three-dimensional image taken with the laser microscope, and Figure 6(b4) shows the height of the plated surface 18 after the sliding wear test, with the non-friction surface 17 in Figure 6(b2) used as the reference surface. The wear volume of the entire sample was then calculated based on the wear scars in the same manner as described above.

[0030] 6(a1) and (b1), the pure Ag plating film (Comparative Example 2) was generally unstable and had a large friction force, whereas the Ag-graphene composite plating film (Example 25) had a stable region for sliding. The friction coefficient in this stable region was low at 0.26, approximately 61% lower than that of pure Ag plating. 6(a2), (a4) and (b2), (b4), it is clear that the Ag-graphene composite plating film (Example 25) suffered less damage due to abrasion than the pure Ag plating film (Comparative Example 2), with the ratio of the abrasion loss being 13 × 10 4 μm 3 / 167×10 4 μm 3 =1 / 10.5, which is less than 1 / 10.

[0031] (a4) and (b4) show the surface roughness profiles across the wear scar. Compared to the dotted reference surface of the unworn area, the pure Ag plating film shown in (a4) has been worn away by 6.49 μm, which is deeper than the thickness of the plating film (5 μm). However, the Ag-graphene composite plating film shown in (b4) has only a maximum wear depth of 2.51 μm, demonstrating that the Ag-graphene composite plating film is less susceptible to wear.

[0032] (Microhardness measurement) Using microhardness measurements as shown in the schematic diagram in Figure 7(a), the effect of graphene size on hardness was investigated for graphene sizes of 3–5 μm or 1 μm with torsional stirring and (c) for graphene sizes of 3–5 μm or 1 μm with coaxial stirring. The conditions for measuring microhardness (Vickers hardness) were as follows: Load: 490.3 mN, Holding time: 20 seconds, Measuring device: Vickers hardness tester (HMV-1 ADW J).

[0033] Figures 7(b) and (c) show that graphene of 1 μm or less is at the same level as pure Ag-plated film, while graphene of 3 to 5 μm is 1.2 times harder than pure Ag-plated film. Figure 8 shows the results of an investigation into the effect of stirring intensity on the hardness of the composite plating film when using a commercially available hard Ag plating solution (solution B) and adding 1-3 μm graphene with (a) coaxial stirring and (b) torsional stirring. In both cases, when the stirring intensity was increased to a weak level of 4 or higher, the Ag-graphene composite plating was found to be approximately 1.2 times harder than the hard Ag plating film. In other words, it was clear that the addition of graphene to the plating film made it harder. As shown in Figures 9(a) and (b), the size of the graphene affects the effectiveness of the pinning effect, and it is thought that larger graphene sizes (same (b)) have a stronger pinning effect and become harder than smaller graphene sizes (same (a)).The pinning effect is the effect of one graphene connecting multiple Ag matrix crystals, which hardens the Ag matrix.

[0034] Comparing Examples 1 to 17, which use ordinary Ag plating, and Examples 18 to 29, which use hard Ag plating, with Comparative Examples 3 to 6 (Ag-plated materials for automotive terminals (Companies C to D)) and Comparative Examples 7 to 9 (Ag-plated materials for power transmission switches (Companies F to H)), it was found that the contact resistance of all of the Examples of the present invention was lower than that of Comparative Examples 1 to 9, achieving higher conductivity than current products. Furthermore, by optimizing the plating conditions, the Vickers hardness of the composite plating film was about 1.2 times harder than the pure Ag plating of Comparative Examples 1 and 2, demonstrating that high conductivity and hardness were both achieved.

[0035] (Raman spectrometry, EDS analysis) Figure 10 shows the results of investigating the effect of current density on the chemical composition of Ag-graphene composite plating films (graphene size 3 to 5 μm) using (a) Raman spectroscopy and (b) EDS analysis. In (a), the D-band is due to defects, and the G-band is due to sp 2 This indicates the presence of bonds, and the 2D-band is derived from graphene, so the presence of graphene was confirmed in all of Example 13, Example 15, Example 16, and Example 17. Regarding Raman spectroscopy, model name: Laser Raman spectrophotometer (NRS-3300), measurement range: 254.896 cm -1 ~3899.87cm -1 , Center wave number: 2301.01cm -1 The excitation wavelength was 532.08 nm, the laser intensity was 7.9 mW, and the EDS analysis was carried out as follows: acceleration voltage was 15 kV, and the magnification of the photograph was 2000 times.

[0036] 10(b) shows that for the similar Examples 13 to 17, the composition of the plating film remains unchanged even at high current densities (carbon atomic concentration 11.6 to 13.7 at.%), making it possible to produce Ag-graphene composite plating films at high speed. On the other hand, with general composite plating, there is a problem in that metal deposition takes precedence at high current densities, resulting in a decrease in the amount of composite.

[0037] The graphene size is preferably 6 μm or less so as not to protrude from the plating surface, from the viewpoint of not exceeding the thickness (5 μm) of the plating film for automotive terminals and connectors, and more preferably 1 μm to 6 μm from the viewpoint of improving both the hardness and conductivity of the plating film. The graphene content dispersed in the Ag-graphene composite plating film is 3.0 at% to 30 at%, preferably 5 at% to 25 at%, and more preferably 8 at% to 20 at%, from the viewpoints of wear resistance and conductivity. Note that the temperature of 40°C of the silver plating solution during electroplating is an example, and can be changed as appropriate depending on the type of plating solution (e.g., cyanide-based bath and various non-cyanide baths).

[0038] The electrical contact resistance of the Ag-graphene composite plating film should be as low as possible from the viewpoint of reducing power consumption, but taking into consideration wear resistance and mechanical strength (hardness), the electrical contact resistance is preferably 0.1 mΩ to 0.7 mΩ, more preferably 0.1 mΩ to 0.6 mΩ, and even more preferably 0.1 mΩ to 0.4 mΩ. The wear coefficient of the Ag-graphene composite plating film should be as low as possible from the viewpoint of extending the life of the connector, and it is preferable that it be 0.4 or less, and the amount of wear should be reduced to 1 / 10 to 1 / 30 of that of current products. Considering the conductivity of the plating film and its aggressiveness against the abrasion mating material, the Vickers hardness of the Ag-graphene composite plating film is preferably 80 HV or more, which is the same as that of current general Ag plating, more preferably 100 HV or more, and even more preferably 120 HV or more. In addition, in the case of hard Ag plating (added with antimony Sb or bismuth Bi), the hardness is preferably higher than 120 HV of current hard Ag plating and up to 300 HV, and more preferably 140 HV to 200 HV.

[0039] Figures 11(a1) and (b1) show images of Ag-graphene composite plating films processed by FIB perpendicular to the substrate using coaxial stirring and torsional stirring, respectively, and observed under a transmission microscope. (a2) and (b2) show schematic diagrams. When the stirring method was coaxial stirring (Example 3), the distribution of graphene in the Ag-graphene composite plating film included graphene aligned approximately parallel and oblique to the Cu substrate. On the other hand, when the stirring method was torsional stirring (Example 11), the distribution of graphene in the Ag-graphene composite plating film included graphene aligned approximately perpendicular and perpendicular to the Cu substrate. In the case of coaxial stirring, the graphene sheets were aligned parallel and oblique to the substrate, which was found to be more preferable from the results of the electrical contact resistance, friction coefficient, and hardness described above. On the other hand, in the case of torsional stirring, the gloss and uniformity of the plating film were found to be superior.

[0040] Furthermore, by comparing the electrical contact resistance of commercially available Ag-plated materials (Comparative Examples 3 to 6) currently used for automotive terminals and connectors, it was found that the Ag-graphene composite plating film of the present invention has conductivity 2.5 times (0.72 / 0.29) to 5.9 times (1.7 / 0.29) higher than that of the commercially available products.

[0041] Furthermore, when compared with the electrical contact resistance of current Ag-plated materials (Comparative Examples 7 to 9) used in power transmission components, it was found that the Ag-graphene composite plating film of the present invention had conductivity 2.9 times (0.83 / 0.29) to 4.8 times (1.40 / 0.29) higher than the current products. From the above, it was confirmed that the Ag-graphene composite plating film of this invention has significantly improved both conductivity and wear resistance, making it suitable for use in automotive terminals, connectors, and power transmission components. This will enable a significant reduction in the amount of Ag used compared to current products, while still ensuring product quality. This reduction in power consumption is expected to have a significant ripple effect on the creation of a clean society. [Industrial Applicability]

[0042] As electronic control becomes more sophisticated with the advancement of automated driving in automobiles, higher performance and durability are required for the terminals connecting wire harnesses to various electronic devices. Furthermore, with the predicted further expansion of EVs and PHVs, there is likely to be a strong need for higher performance and durability in charging equipment connectors. Furthermore, in order to reduce power loss in high-voltage, high-current power transmission switches that supply electricity, this plating material can be used as an even more conductive and wear-resistant material. [Explanation of symbols]

[0043] 1, 11: Ag-graphene composite plating film 2:Cu alloy substrate (cathode) 3: Counter electrode (anode, silver plate) 4: Surface to be plated 5: Plating tank 15, 17: Non-friction surface 16, 18: Plated surface after sliding wear test 20: Electroplating equipment L: Silver plating solution r1: Horizontal flow direction of silver plating solution r2, r2´: Vertical flow direction of silver plating solution flow axis such as x1:r1 x2: flow axis such as r2 and r2´ x3, x4: Vertical axes of the Cu alloy substrate

Claims

1. A metal part having a substrate coated with an Ag-graphene composite plating film, wherein the graphene dispersed in the Ag-graphene composite plating film has a size (graphene size) of 0.05 to 6 μm, a content of the graphene (graphene content) of 3.0 to 30 at %, an arrangement direction of the graphene in the Ag-graphene composite plating film is at least one selected from perpendicular, parallel, and oblique to the substrate, the graphene is dispersed throughout the Ag-graphene composite plating film, even to the interior thereof, and the graphene has a pinning effect in which each graphene connects a plurality of crystals of the Ag matrix.

2. The metal part according to claim 1, characterized in that the electrical contact resistance of the Ag-graphene composite plating film is 0.1 to 0.7 mΩ.

3. The metal part according to claim 1 or 2, characterized in that the friction coefficient of the Ag-graphene composite plating film is 0.1 to 0.

4.

4. The metal part according to any one of claims 1 to 3, characterized in that the Ag-graphene composite plating film has a Vickers hardness of 80 HV or more.

5. The metal part according to any one of claims 1 to 4, which is used for an automobile terminal, a charging connector, or a power transmitter switch.

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