Method for producing plated product

Abstract

The purpose of the present invention is to provide a method for producing a plated product capable of efficiently forming an aluminum plating layer with high adhesion to a base material comprising magnesium or a magnesium alloy.　Therefore, a method for producing a plated product according to an embodiment of the present invention has a zinc layer formation step for forming a zinc layer on the surface of a base material comprising magnesium or a magnesium alloy, a copper plating layer formation step for performing copper plating treatment on the zinc layer and forming a copper plating layer on the zinc layer, and an aluminum plating layer formation step for performing aluminum plating treatment on the copper plating layer and forming an aluminum plating layer on the copper plating layer. The aluminum plating solution used in the aluminum plating layer formation step contains dimethyl sulfone, an aluminum halide, ammonium chloride, and tetramethylammonium chloride.

Description

Manufacturing method for plated products

[0001] The present invention relates to a method for producing a plated product in which a plate is applied to the surface of a substrate made of magnesium or a magnesium alloy.

[0002] Magnesium alloys, for example, are used as lightweight, high-strength materials. Compared to aluminum, magnesium alloys are lighter and stronger, making them suitable for use in a variety of fields. However, it is difficult to directly apply durable decorations to the surface of magnesium alloys. Therefore, a method has been proposed in which an aluminum plating layer is formed on the surface of a magnesium alloy by electrolytic aluminum plating (see, for example, Patent Document 1). In the method disclosed in Patent Document 1, the surface is thoroughly cleaned by degreasing or other methods before the aluminum plating layer is formed on the magnesium alloy substrate. Furthermore, to improve the adhesion of the aluminum plating layer, a method has been proposed in which a copper layer and a nickel layer are sequentially formed on the surface of the magnesium alloy, and then an aluminum plating film is formed on the nickel layer (see, for example, Patent Document 2).

[0003] JP 2004-292858 A JP 2006-161155 A

[0004] An aluminum plating film formed on magnesium or a magnesium alloy is required to have high adhesion, while also being formed efficiently. The present invention has been made in consideration of these problems, and an object of the present invention is to provide a method for producing a plated product that can efficiently form an aluminum plating layer with high adhesion on a substrate made of magnesium or a magnesium alloy.

[0005] In order to achieve the above-mentioned object, one embodiment of the present invention provides a method for producing a plated product, comprising: a zinc layer forming step of forming a zinc layer on the surface of a base material made of magnesium or a magnesium alloy; a copper plating layer forming step of copper plating the zinc layer to form a copper plating layer on the zinc layer; and an aluminum plating layer forming step of aluminum plating the copper plating layer to form an aluminum plating layer on the copper plating layer, wherein the aluminum plating solution used in the aluminum plating layer forming step contains dimethyl sulfone, aluminum halide, ammonium chloride, and tetramethylammonium chloride.

[0006] The thickness of the copper plating layer is preferably 1 μm or more and 30 μm or less, and the copper plating layer is preferably formed to be thicker than the zinc layer. The thickness of the aluminum plating layer is preferably 1 μm or more and 100 μm or less.

[0007] It is also preferable that the method further comprises an anodizing treatment step of anodizing the aluminum plating layer to form an anodized film. Furthermore, it is preferable that the total thickness of the aluminum plating layer and the anodized film is 21 μm or more and 100 μm or less, and the film thickness of the anodized film is 11 μm or more and 30 μm or less.

[0008] The aluminum plating solution preferably contains 3.5 to 4.2 moles of the aluminum halide, 0.1 to 0.5 moles of the ammonium chloride, and 0.1 to 1.5 moles of the tetramethylammonium chloride relative to 10 moles of the dimethyl sulfone.Furthermore, the aluminum plating solution preferably contains 0.2 to 0.5 moles of ammonium chloride relative to 10 moles of the dimethyl sulfone.

[0009] In the aluminum plating layer forming step, when the substrate on which the copper plating layer has been formed in the copper plating layer forming step and the anode electrode are immersed in the aluminum plating solution and a voltage is applied between the substrate on which the copper plating layer has been formed and the anode electrode, the current density flowing between the substrate on which the copper plating layer has been formed and the anode electrode is 15 mA / cm ２ 200mA / cm or more ２ Furthermore, the anode electrode preferably contains an aluminum alloy containing silicon or copper.

[0010] According to the plated product and the method for producing the same of the present invention, it is possible to efficiently obtain a plated product of magnesium or a substrate made of magnesium having an aluminum plating layer with high adhesion.

[0011] Fig. 2 is a schematic cross-sectional view of a plated product manufactured by the method for manufacturing a plated product according to an embodiment of the present invention; Fig. 3 is a flowchart showing the method for manufacturing a plated product according to an embodiment of the present invention; Fig. 4 is an enlarged cross-sectional view of the surface of the substrate 1 after performing the zinc layer forming step S001 in the method for manufacturing a plated product according to an embodiment of the present invention shown in Fig. 2; Fig. 5 is an enlarged cross-sectional view of the surface of the substrate 1 after performing the copper plating layer forming step S002 in the method for manufacturing a plated product according to an embodiment of the present invention shown in Fig. 2; Fig. 6 is an enlarged cross-sectional view of the surface of the substrate 1 after performing the aluminum plating layer forming step S003 in the method for manufacturing a plated product according to an embodiment of the present invention shown in Fig. 2;

[0012] A schematic cross-sectional view of a plated product obtained by the method for producing a plated product according to an embodiment of the present invention is shown in Figure 1. Figure 1 shows the cross-sectional structure near the surface of magnesium or magnesium alloy obtained by the method for producing a plated product according to this embodiment. The plated product obtained by the method for producing a plated product according to this embodiment has a zinc layer 2, a copper plating layer 3, and an aluminum plating layer 4 formed in this order on a substrate 1 made of magnesium or a magnesium alloy, and then an anodized film layer 5 obtained by anodizing the surface of the aluminum plating layer 4, thereby obtaining a plated product with a high design quality.

[0013] The substrate 1 used in the method for manufacturing a plated product according to this embodiment may be made of magnesium or an alloy thereof. In particular, magnesium (Mg)-aluminum (Al)-zinc (Zn) alloys (e.g., ASTM AZ91 and AZ31), Mg-Zn-zirconium (Zr) ternary alloys (e.g., ASTM ZK60 and ZK61), and Mg-Zn-yttrium (Y) ternary alloys are preferred. The overall shape of the substrate 1 may be any shape, including a plate or a rod. As long as the zinc layer 2, copper plating layer 3, and aluminum plating layer 4 can be formed on the surface of the substrate 1, other shapes, such as a polygonal column, sphere, or hemisphere, may also be used.

[0014] In order to obtain such a plated product, the method for manufacturing a plated product in this embodiment can be performed based on the flowchart shown in Fig. 2. As shown in Fig. 2, the method for manufacturing a plated product in this embodiment includes a zinc layer forming step S001 for forming a zinc layer on the surface of a substrate 1 made of magnesium or a magnesium alloy, a copper plating layer forming step S002 for forming a copper plating layer on the surface of the zinc layer, an aluminum plating layer forming step S003 for forming an aluminum plating layer on the copper plating layer, and an anodizing treatment step S004 for anodizing a portion of the vicinity of the surface of the aluminum plating layer.

[0015] In the zinc layer formation step (S001), the surface of the substrate 1 is degreased, followed by a well-known zincate treatment to replace the oxide film formed on the surface of the substrate 1 made of magnesium or its alloy with zinc, thereby forming a zinc layer 2 on the surface of the substrate 1. The zincate treatment is preferably performed using the well-known double zincate method. The double zincate method involves forming a zinc layer 2 on the degreased surface of the substrate 1 by zincate treatment, then removing the zinc layer 2 formed by the previous zincate treatment with nitric acid, and then performing zincate treatment on the surface of the substrate 1 again to form the zinc layer 2. The double zincate method involves forming a zinc layer on the surface of the substrate 1 once by zincate treatment, stripping the zinc layer with acid, and then forming another zinc layer by zincate treatment. Therefore, the zinc particles forming the zinc layer 2 are dense and fine, which enhances adhesion to the substrate and enables more uniform coating. Figure 3 is an enlarged cross-sectional view of the surface of the substrate 1 after the zinc layer formation step S001. As shown in Figure 3, when the zinc layer forming step S001 is performed, a zinc layer 2 is formed on the surface of the substrate 1. Zinc has a lower ionization tendency than magnesium, so the corrosion resistance is increased compared to the state where the substrate 1 is formed alone. This allows the subsequent surface treatment to be performed smoothly. Note that in the zinc layer forming step S001, the substrate 1 may be degreased and then etched with acid to remove the oxide film, and then zinc plating may be performed.

[0016] In this way, by performing the zinc layer forming step S001 on the magnesium or magnesium alloy substrate 1, the zinc layer 2 can be formed on the surface of the substrate 1. The thickness of the zinc layer formed in the zinc layer forming step (S001) is preferably 0.01 μm or more and 2 μm or less. If the thickness is 0.01 μm or more, most of the surface of the substrate 1 is covered with the zinc layer 2, so that the surface of the substrate 1 can be efficiently covered by the subsequent surface treatment. On the other hand, if the thickness is 2 μm or less, the crystal grain size of the zinc layer 2 is less likely to vary, and it is possible to prevent significant surface roughness from occurring due to the coating performed in the subsequent surface treatment.

[0017] Next, the base material 1 having the zinc layer 2 formed thereon is subjected to a copper plating layer forming step S002. In the copper plating layer forming step S002, the base material 1 having the zinc layer 2 formed thereon is immersed in a known electrolytic copper plating solution, and a voltage is applied so that the base material 1 having the zinc layer 2 formed thereon serves as a cathode electrode and copper, platinum, or the like serves as an anode electrode, and copper plating is performed under known temperature conditions and current density set according to the electrolytic copper plating solution used. By performing this copper plating layer forming step S002, a copper plating layer 3 is formed on the zinc layer 2.

[0018] By forming the copper plating layer 3 on the surface of the substrate 1 on which the zinc layer 2 has been formed in this manner, it is possible to minimize the exposure of the surface of the substrate 1, which is made of magnesium or a magnesium alloy. Furthermore, copper has a lower ionization tendency than zinc. Therefore, the formation of the copper plating layer 3 makes it easier to handle the substrate 1 when moving to the aluminum plating layer forming step S003. Therefore, in the method for manufacturing a plated product according to an embodiment of the present invention, by performing the copper plating layer forming step S002 after the zinc layer 2 has been formed on the surface of the substrate 1, it is possible to efficiently cover the surface of the substrate 1 with the zinc layer 2 and the copper plating layer 3.

[0019] Furthermore, the oxide film of the copper plating layer 3 is less chemically stable than the oxide film of nickel plating, which is a typical metal plating. Therefore, even if an oxide film forms on the surface of the copper plating layer 3, the oxide film can be easily removed, allowing for efficient production of plated products having an aluminum plating layer. Furthermore, the copper plating layer 3 has lower internal stress than nickel plating. Therefore, the copper plating layer 3 has the advantage of being less likely to peel off from the plating layer formed on top of it. For these reasons, the copper plating layer 3 is used as the underlayer for the aluminum plating layer to improve the production efficiency of plated products having an aluminum plating layer.

[0020] The thickness of the copper plating layer 3 is preferably thicker than the thickness of the zinc layer 2. Therefore, the thickness of the copper plating layer 3 is preferably 1 μm or more. A thickness of 1 μm or more facilitates the formation of the copper plating layer 3 on most of the surface of the zinc layer 2, thereby preventing untreated portions of the copper plating layer from being formed. On the other hand, a thickness of 30 μm or less is preferred to avoid unnecessarily prolonging the takt time of the copper plating layer forming step S002. Furthermore, in the present invention, the copper plating layer forming step S002 is not limited to a method of forming the copper plating layer 3 by electrolytic copper plating or a combination of electrolytic copper plating and electroless copper plating. The copper plating layer forming step S002 may also be performed by electroless copper plating. FIG. 4 is an enlarged cross-sectional view of the surface of the substrate 1 after the copper plating layer forming step S002. As shown in FIG. 4, when the copper plating layer forming step S002 is performed, a zinc layer 2 and a copper plating layer 3 are formed on the surface of the substrate 1.

[0021] Next, an aluminum plating layer forming step S003 is performed on the base material 1 on which the copper plating layer 3 has been formed. In the aluminum plating layer forming step S003, the base material 1 on which the copper plating layer 3 has been formed is immersed in an electrolytic aluminum plating solution, and a voltage is applied so that the base material 1 on which the copper plating layer 3 has been formed serves as a cathode electrode and the other electrode, such as aluminum, serves as an anode electrode, thereby forming an aluminum plating layer 4 on the base material 1 on which the copper plating layer 3 has been formed.

[0022] In the method for manufacturing a plated product according to an embodiment of the present invention, in the aluminum plating layer 4 forming step S003, even if an oxide film is formed on the surface of the copper plating layer 3 as described above, the oxide film can be removed and the aluminum plating layer 4 can be formed at the same time. Therefore, the method for manufacturing a plated product according to an embodiment of the present invention uses the following aluminum plating solution. This aluminum plating solution contains at least (1) dimethyl sulfone, (2) aluminum halide, (3) ammonium chloride, and (4) tetramethylammonium chloride.

[0023] This aluminum plating solution is a mixture of dimethyl sulfone, aluminum halide, ammonium chloride, and tetramethylammonium chloride. The oxide film on the copper plating layer 3 is reduced by the halogen ions obtained from the aluminum halide mixed in dimethyl sulfone, as well as the chloride ions obtained from the ammonium chloride and tetramethylammonium chloride, thereby achieving the effect of removing the oxide film on the copper plating layer 3. In this aluminum plating solution, the ammonium chloride or tetramethylammonium chloride mixed in dimethyl sulfone dissociates as shown in the following formula 1: where R represents hydrogen (H) or a methyl group (CH ３ ) where DM is a dimethyl group and N is nitrogen. ４ Cl -> NR ４ ＋ +Cl － ... (Formula 1) In addition, when aluminum chloride is used as the aluminum halide, some dimethyl sulfone (DMSO ２ ) and aluminum chloride (AlCl ３ ) reacts with Al(DMSO ２ ) ３ ３＋ and chloroaluminate (AlCl), in which four chloride ions are coordinated to one aluminum ion. ４ ― ) containing chloride ions are formed.

[0024] As described above, the aluminum plating solution of this embodiment generates chloride ions in the plating solution. These chloride ions have the effect of reducing the oxide film formed on the copper plating layer 3 and removing the oxide film from the copper plating layer 3. Therefore, by immersing a substrate 1 made of magnesium or a magnesium alloy having a copper plating layer 3 formed on its outermost surface in the aluminum plating solution of this embodiment of the present invention, the oxide film formed on the copper plating layer 3 can be removed. This eliminates the need for an operation to remove the oxide film, and enables the efficient production of plated products having an aluminum plating layer.

[0025] In particular, since the standard oxidation-reduction potential of aluminum is lower than the hydrogen evolution potential (-1.66 V vs. SHE), if water molecules adhere to the surface of the copper plating layer 3, the growth of the aluminum plating layer is suppressed in the areas where they adhere. On the other hand, when an aluminum plating layer is formed on a metal layer other than the copper plating layer 3, an oxide film removal process is usually required for the reasons mentioned above, and the surface is cleaned after the oxide film removal process. An aqueous solution is generally used for this cleaning, but if even a small amount of moisture adheres to the surface where the aluminum plating layer is to be formed, the formation of the aluminum plating layer is suppressed in that area only, causing unevenness on the surface of the aluminum plating layer 4. Note that, although increasing the thickness of the aluminum plating layer reduces surface unevenness, areas where adhesion is reduced between the aluminum plating layer and the underlayer still occur, resulting in a decrease in the adhesion of the aluminum plating layer.

[0026] On the other hand, in the aluminum plating layer formation step S003 of this embodiment, the oxide film formed on the copper plating layer 3 is removed by the aluminum plating solution of this embodiment. That is, the aluminum plating layer formation step S003 can also remove the oxide film, making it possible to omit the oxide film removal step after forming the copper plating layer 3. Furthermore, it is possible to eliminate the subsequent process of exposing the substrate 1 to moisture, enabling the efficient formation of an aluminum plating layer with good adhesion. Note that this oxide film removal step can also be performed in this embodiment. For example, even if the oxide film cannot be completely removed, the oxide film removal step may be performed to thin the oxide film or reduce the area covered by the oxide film. In this case, it is not necessary to completely remove the oxide film. By doing so, the reliability of oxide film removal by the aluminum plating solution can be improved. Note that a cleaning step is required after the oxide film removal step. A drying process or the like is performed after the cleaning step to remove moisture, and during this process, an oxide film may be formed on the copper plating layer 3. Even in such cases, performing the aluminum plating layer formation step using this aluminum plating solution eliminates the need for additional oxide film removal. Therefore, efficiency is improved. Furthermore, the aluminum plating solution used in this embodiment makes it possible to narrow or eliminate the region in which the formation of the aluminum plating layer 4 is suppressed due to the presence of an oxide film on the surface of the copper plating layer 3, thereby enabling the production of a plated product with a good design and reduced surface irregularities of the aluminum plating layer 4. Furthermore, when anodizing the surface of the aluminum plating layer 4, there is a possibility that depressions and holes in the aluminum plating layer 4 caused by the oxide film on the copper plating layer 3 may become enlarged, but the aluminum plating solution used in this embodiment makes it possible to suppress the occurrence of such a phenomenon.

[0027] To improve the oxide film removal capability of the aluminum plating solution, in the aluminum plating layer formation step S003, it is preferable to agitate the plating solution using a plating solution agitator or move or vibrate the cathode electrode itself in the plating solution before applying a voltage between the cathode and anode electrodes immersed in the aluminum plating solution, thereby causing the aluminum plating solution to flow on the surface of the copper plating layer 3. This allows chloride ions and halide ions to be supplied to the surface of the copper plating layer 3, thereby enabling efficient removal of the oxide film formed on the surface of the copper plating layer 3. It is also preferable to avoid applying a voltage to the substrate 1 having the copper plating layer 3 formed on its surface for at least one second after immersion in the aluminum plating solution. Applying a negative potential to the substrate 1 having the copper plating layer 3 formed on its surface one minute or more, preferably three to ten minutes, after immersion in the aluminum plating solution makes it possible to form the aluminum plating layer 4 in a state in which the oxide film formed on the surface of the copper plating layer 3 has been removed, thereby improving the adhesion and surface smoothness of the aluminum plating layer 4. In this way, by immersing the magnesium or magnesium alloy substrate 1 on which the copper plating layer 3 has been formed in the aluminum plating solution for 3 minutes or more while maintaining a state in which no voltage is applied, the oxide film on the copper plating layer 3 can be more easily removed. In addition, since the temperature of the magnesium or magnesium alloy substrate approaches that of the aluminum plating solution, the formation of the aluminum plating layer 4 is more smoothly carried out. Note that by immersing the substrate for 10 minutes or less, it is possible to suppress the effect of dissolution of the copper plating layer by the aluminum plating solution.

[0028] Furthermore, the aluminum plating solution used in the method for producing a plated product according to this embodiment also has the effect of maintaining the film formation efficiency of the aluminum plating layer 4. The reason for this will be explained below.

[0029] In order to investigate the effect on the ion species in the aluminum plating solution, the present inventors performed nuclear magnetic resonance (NMR) measurements while changing the amounts of ammonium chloride and tetramethylammonium chloride added, and analyzed the amount of ions in the aluminum plating solution.２７ By Al-NMR measurement, it was found that adding ammonium chloride or tetramethylammonium chloride to an aluminum plating solution consisting of dimethyl sulfone and aluminum chloride increased the Al (DMSO ２ ) ３ ３＋ It was found that the amount of Al(DMSO ２ ) ３ ３＋ is produced by the reaction of dimethyl sulfone with aluminum halide. This suggests that chloride ions (Cl) dissociated from ammonium chloride or tetramethylammonium chloride － ) in the plating solution. ２ ) ３ ３＋ is expected to change as follows:

[0030] 4NR ４ Cl+Al(DMSO ２ ) ３ ３＋ + 3AlCl ４ － -> 4NR ４ ＋ +4AlCl ３ +3DMSO ２ ...(Formula 2)

[0031] According to the findings of the present inventors, increasing the concentration of aluminum halide relative to dimethyl sulfone reduces the electrical conductivity of the plating solution. This reduces the rate at which the aluminum plating layer 4 is formed. ２ The greater the amount, the greater the electrical conductivity of the plating solution. ４It is preferable to increase the amount of ammonium chloride or tetramethylammonium chloride, expressed as Cl. That is, it is preferable to increase the concentration of ammonium chloride and tetramethylammonium chloride relative to dimethyl sulfone without increasing the concentration of aluminum chloride relative to dimethyl sulfone, thereby increasing the amount of chloride ions. This makes it possible to suppress a decrease in the electrical conductivity of the aluminum plating solution, maintain high film formation efficiency of the aluminum plating layer 4, and improve the oxide film removal ability of the copper plating layer 3.

[0032] In addition, as shown in formula 2, by adding ammonium chloride or tetramethylammonium chloride, NR ４ ＋ NH represented by ４ ＋ and N (CH ３ ) ＋ These cations have the effect of suppressing the increase in the surface roughness of the aluminum plating layer 4 even when multiple different types of metals are exposed on the surface on which the aluminum plating layer 4 is to be formed. This is because the overpotential, which is the potential required for the initiation of aluminum electrodeposition, differs for each type of metal, but the amount of NH ４ ＋ This is because the difference in overpotential between the surfaces of the materials decreases when ammonium ions represented by the following formula (1) are attached to the surface of the material onto which aluminum is electrodeposited.

[0033] For example, in the plated product of this embodiment, a magnesium or magnesium alloy substrate 1, a zinc layer 2, and a copper plating layer 3 are formed on an aluminum plating layer 4. It is preferable that at least the surface of the substrate 1 on which the aluminum plating layer 4 is to be formed is uniformly covered with the copper plating layer 3. However, there are cases in which the zinc layer 2 does not completely cover the surface of the substrate 1, and pores extending to the surface of the substrate 1 are formed in some areas. In the method for manufacturing a plated product of this embodiment, forming the copper plating layer 3 on the zinc layer 2 functions to block pores formed in the zinc layer 2. However, because magnesium in the substrate 1 has a greater ionization tendency than copper, magnesium may dissolve during the copper plating layer forming step S002, and the through-holes in the zinc layer 2 may not be completely blocked by the copper plating layer 3. In such cases, in addition to the surface of the copper plating layer 3, the surface on which the aluminum plating layer 4 is formed will also have extremely small exposed areas of the zinc layer 2 and the surface of the magnesium or magnesium alloy substrate 1. If a conventional aluminum plating process is performed under such conditions, unlike the present embodiment, the difference in overpotential between the metals will cause the growth of the aluminum plating layer 4 to be non-uniform, resulting in a decrease in the smoothness of the surface of the aluminum plating layer 4.

[0034] The aluminum plating solution used in the method for producing a plated product according to the embodiment of the present invention contains NR as described above. ４ ＋ NH represented by ４ ＋ and N (CH ３ ) ＋ When the substrate 1 on which the copper plating layer 3 is formed is immersed in an aluminum plating solution containing such cations and a voltage is applied so that the substrate 1 becomes the cathode, the NR of the aluminum plating solution is increased. ４ ＋Cations such as these are deposited on the entire surface of the substrate 1. Therefore, the difference in overpotential between the exposed portion of the copper plating layer 3 and the exposed portion of other metals, such as the zinc layer 2 and magnesium of the substrate 1, becomes small, and it is believed that if the aluminum plating layer is formed until it has a sufficient film thickness, the surface smoothness of the aluminum plating layer 4 will be improved compared to the surface of an aluminum plating layer 4 formed using an aluminum plating solution to which ammonium chloride or tetramethylammonium chloride is not added.

[0035] In addition, the surface on which the aluminum plating layer 4 is formed is ４ ＋ In order to facilitate the supply of cations represented by the formula (I) above, it is preferable to vibrate the substrate 1 on which the copper plating layer 3, which serves as the cathode, has been formed, or to stir the aluminum plating solution, during the electrodeposition of aluminum on the substrate 1 on which the copper plating layer 3 has been formed.

[0036] In the aluminum plating solution used in the method for producing a plated product according to an embodiment of the present invention, the blending ratio of dimethyl sulfone, aluminum halide, ammonium chloride, and tetramethylammonium chloride is, for example, preferably 3.5 to 4.2 moles, more preferably 3.8 to 4.2 moles, of aluminum halide per 10 moles (mol) of dimethyl sulfone. Furthermore, the blending ratio of ammonium chloride per 10 moles of dimethyl sulfone is preferably 0.1 to 0.5 moles, more preferably 0.2 to 0.3 moles. Furthermore, the blending ratio of tetramethylammonium chloride per 10 moles of dimethyl sulfone is preferably 0.1 to 1.5 moles, more preferably 0.3 to 1.5 moles.

[0037] By using 4.2 moles or less of aluminum halide per 10 moles of dimethyl sulfone, the decrease in the electrical conductivity of the aluminum plating solution is suppressed, contributing to preventing a decrease in the diffusion rate of aluminum ions. Furthermore, an increase in the solution resistance of the aluminum plating solution can be suppressed, thereby suppressing heat generation during aluminum electrodeposition using the aluminum plating solution, suppressing deterioration and evaporation of the aluminum plating solution, and suppressing a decrease in the quality of the aluminum plating layer 4. On the other hand, if the aluminum halide is 3.5 moles or more, an increase in the melting point of the aluminum plating solution can be suppressed, making it less likely for the solution to solidify within the aluminum plating solution circulation path. Furthermore, if the aluminum halide is 3.8 moles or more, the melting point of the aluminum plating solution can be further reduced. Among aluminum halides, aluminum chloride is preferred. The gas generated during aluminum plating is chlorine gas, which reduces the chemical impact on the solvent, dimethyl sulfone.

[0038] Furthermore, when the amount of ammonium chloride and tetramethylammonium chloride is 0.1 moles or more per 10 moles of dimethyl sulfone, the amount of chloride ions in the aluminum plating solution increases, which contributes to improving the ability to remove the oxide film from the copper plating layer 3. ４ ＋ Furthermore, cations represented by NH ４ ＋ This also increases the amount of ammonium ions, thereby increasing the effect of reducing the difference in overpotential for different metal species that appears on the surface of the substrate 1 on which the aluminum plating layer 4 is formed. Therefore, the method for producing a plated product according to this embodiment makes it possible to reduce the influence of surface irregularities and pores on the surface of the zinc layer 2 and the copper plating layer 3 on the surface smoothness of the aluminum plating layer 4. Furthermore, if the amount of ammonium chloride is 0.2 mol or more per 10 mol of dimethyl sulfone, it becomes possible to further suppress blackening of the aluminum plating layer 4.

[0039] Incidentally, by using ammonium chloride at a ratio of 0.5 mol or less per 10 mol of dimethyl sulfone, it is possible to suppress an increase in the amount of gas generated from the surface of the cathode electrode during the production of an aluminum coating, thereby contributing to suppressing a decrease in electrodeposition efficiency. Furthermore, by using an amount of 0.3 mol or less, gas generation can be further suppressed, which is preferable in terms of improving the surface smoothness of the aluminum plating layer 4. Furthermore, if the content ratio of tetramethylammonium chloride is 0.1 mol or more per 10 mol of dimethyl sulfone, the effect of increasing the electrical conductivity of the aluminum electroplating solution can be expected. If the content ratio is 0.3 mol or more, it is possible to further increase the electrical conductivity of the aluminum electroplating solution, which is more desirable in terms of improving the film formation rate and efficiency. If the content ratio is 1.5 mol or less, the Al(DMSO) in the plating solution can be reduced. ２ ) ３ ３＋ This can suppress a decrease in the amount of aluminum ions, making it difficult for black deposits (called burns) to occur due to an insufficient supply of aluminum ions to the surface of the cathode electrode, and can suppress a decrease in electrodeposition efficiency.

[0040] In the aluminum plating layer forming step using the aluminum plating solution described above, it is preferable to set the temperature of the aluminum plating solution to, for example, 80° C. or higher and 110° C. or lower. In addition, it is preferable that the current density between the anode electrode and the cathode electrode immersed in the aluminum plating solution is 15 mA / cm. ２ 200mA / cm or more ２ The lower limit of the temperature of the aluminum plating solution should be determined taking into consideration the melting point of the aluminum plating solution, and is preferably 85°C, more preferably 95°C. On the other hand, by setting the upper limit of the temperature of the aluminum plating solution to 110°C, deformation of the substrate 1 can be suppressed. If the temperature is 110°C or less, the activity of the reaction between the aluminum plating layer 5 and the aluminum plating solution can be suppressed, and an increase in the amount of impurities in the aluminum plating layer 4 can be suppressed. In addition, when the current density is 15 mA / cm ２ If the film formation efficiency is maintained, the NR ４ ＋Since the effect of the cations represented by the formula (I) covering the substrate 1 on which the copper plating layer serving as the cathode is formed can be sufficiently maintained, it is expected that pinholes formed in the aluminum plating layer 4 will be reduced. ２ If the current is less than 100 mA / cm, decomposition of nitrogen compounds such as ammonium chloride and tetramethylammonium chloride is suppressed, and stable plating processing can be easily continued. ２ Since stable plating is possible even when the above current density is applied, the film formation rate can be improved. The plating time depends on the desired film thickness of the aluminum plating layer 4, the temperature of the electrolytic solution, the applied current density, etc., but is usually preferably 1 to 90 minutes, and more preferably 1 to 60 minutes in consideration of production efficiency.

[0041] FIG. 5 is an enlarged cross-sectional view of the surface of the substrate 1 after the aluminum plating layer forming step S003. As shown in FIG. 5 , after the copper plating layer forming step S002, there is a zinc layer 2 formed on the surface of the substrate 1, a copper plating layer 3 formed on the zinc layer 2, and an aluminum plating layer 4 formed on the copper plating layer 3. In the method for manufacturing a plated product according to the embodiment of the present invention, the thickness of the aluminum plating layer 4 is made thicker than the thickness of the copper plating layer 3. This is because a portion of the aluminum plating layer 4 is anodized in the subsequent anodizing treatment step S004. If the entire aluminum plating layer 4 were anodized, the anodized coating 5 would come into contact with the copper plating layer 3. This would result in reduced adhesion, as described above. Therefore, in the aluminum plating layer forming step S003, the anodized coating 5 is formed at least 1 μm thicker than the designed thickness, as described above. If smoothness is desired on the surface of the plated product, the surface may be polished in the aluminum plating layer forming step S003. In such a case, it is preferable to form the aluminum plating layer 4 even thicker, taking into consideration the thickness to be polished. When polishing the surface of the aluminum plating layer 4, it is preferable to polish it to a roughness having an arithmetic mean roughness Ra of 1.5 μm or less.

[0042] Reducing the crystal grain size of the aluminum plating layer 4 can reduce the surface roughness of the aluminum plating layer 4 after aluminum plating. Therefore, by intentionally adding impurities such as copper (Cu) or silicon (Si) during the aluminum plating layer formation process, the crystal grains can be refined and the surface roughness can be reduced. For example, by ionizing a certain amount of Cu or the like in the aluminum plating solution, the purity of the aluminum plating layer 4 can be reduced and the crystal grains can be refined. For example, in the aluminum plating layer formation process, it is preferable to use an aluminum alloy containing either Cu or Si, or an aluminum alloy containing 0.1% by mass or more and 24% by mass or less of Si, 0.1% by mass or more and 5% by mass or less of Cu, and 0.15% by mass or more and 1.8% by mass or less of iron (Fe), for the anode electrode. For example, the anode electrode can be obtained by molding used AC2A alloy material into an electrode shape by casting or the like. Furthermore, it is preferable to set the current density at the anode electrode during aluminum plating to 10 mA / cm. ２ 200mA / cm or more ２ By setting the following, it is possible to cause Cu to be contained in the formed electrodeposited film. Note that, in the aluminum plating layer 4 of this embodiment, it is preferable that aluminum accounts for 90 mass % or more and the contents of other contained elements are kept to less than 10 mass %.

[0043] Next, the substrate 1 having the aluminum plating layer 4 formed thereon is subjected to anodizing treatment S004. The anodizing treatment method is not particularly limited and can be performed by a known method. The anodizing treatment conditions are set appropriately depending on the desired thickness of the anodic oxide coating 5, the anodizing treatment solution to be used, and the like. If necessary, the aluminum plating layer 4 may be divided into multiple sections, and anodizing treatment may be performed under different conditions for each section. In the anodizing treatment, a color tone may be imparted to the anodic oxide coating 5 by natural color development, or by coloring (so-called color anodizing).

[0044] For these reasons, the total thickness of the aluminum plating layer 4 and the anodic oxide coating 5 formed in the anodizing treatment step S004 is preferably 21 μm or more and 100 μm or less. In this case, the film thickness of the aluminum plating layer 4 after the anodizing treatment step S004 is preferably 11 μm or more and less than 100 μm, more preferably 11 μm or more and 70 μm or less. The film thickness of the anodic oxide coating 5 after the anodizing treatment step S004 is preferably 10 μm or more and 30 μm or less. That is, when performing electrolytic plating, it is preferable to form the aluminum plating layer 4 with a thickness that takes into account the change in thickness due to the anodic oxide coating 5 formed in the anodizing treatment step S004. Note that the anodizing treatment step S004 may not be performed if the color tone or texture of the aluminum metal is utilized. In this case, the aluminum plating layer 4 becomes the outermost layer, and the preferred film thickness at this time is preferably 1 μm or more and 100 μm or less, more preferably 1 μm or more and 70 μm or less.

[0045] As described above, according to this embodiment, the surface of magnesium or a magnesium alloy can be given a highly decorative appearance. For example, any color, such as white, black, red, or blue, can be colored or developed, and the color can be varied depending on the location. The method for manufacturing a plated product according to this embodiment ensures good adhesion, making it possible to obtain plated magnesium or magnesium alloy products that can be used in a wider range of applications than conventional methods. Furthermore, since the method can improve corrosion resistance and oxidation resistance, it is also suitable for surface treatment of various exterior parts, such as electronic devices, automotive components, optical components, and machine components.

[0046] In this specification, roughness measurements, film thickness measurements, and adhesion tests were performed as follows. Arithmetic mean roughness measurements were performed in accordance with the international standard ISO 4288:1996. Roughness measurements were performed particularly for non-periodic roughness curves, with the cutoff value λc set to 0.08 mm or more and 0.8 mm or less, the reference length L set to 0.08 mm or more and 0.8 mm or less, and the evaluation length Ln set to a range of 0.4 to 4 mm, depending on the surface smoothness. Next, film thickness measurements were performed by photographing the cross section of the plated product using a scanning electron microscope, measuring the film thickness at multiple arbitrary positions on the photographed cross section, excluding the vicinity of the periphery of each layer, and calculating the average film thickness. The adhesion test was conducted in accordance with the cross-cut method defined in Japanese Industrial Standard JIS K 5600-5-6:1999, in which 25 squares in total were cut with 2 mm width, 5 squares vertically and 5 squares horizontally, and cellophane adhesive tape was used to press the tape against the aluminum plating layer or the anodized coating, and the tape was pulled vertically to evaluate whether peeling occurred. In this specification, this is referred to as the cross-cut test.

[0047] The disclosure of the present specification also includes the following aspects of the invention, which are intended to provide plated products and the like that can achieve high designability on magnesium or magnesium alloy substrates. Another aspect of the present invention, which is intended to achieve the above-mentioned object, is a plated product having a substrate made of magnesium or a magnesium alloy, a zinc layer formed on the surface of the substrate, a copper plating layer formed on the zinc layer, and an aluminum plating layer formed on the copper plating layer.

[0048] According to this aspect, the thickness of the copper plating layer is preferably 1 μm or more and 30 μm or less, and the copper plating layer is preferably thicker than the zinc layer. The thickness of the aluminum plating layer is preferably 1 μm or more and 100 μm or less. An anodized coating is preferably provided on the aluminum plating layer. The thickness of the aluminum plating layer is preferably 1 μm or more and 70 μm or less, and the thickness of the anodized coating is preferably 10 μm or more and 30 μm or less.

[0049] In another embodiment of the present invention, to achieve the above-mentioned object, a method for producing a plated product preferably includes a zinc layer forming step of forming a zinc layer on the surface of a substrate made of magnesium or a magnesium alloy, a copper plating layer forming step of copper plating the zinc layer to form a copper plating layer on the zinc layer, and an aluminum plating layer forming step of aluminum plating the copper plating layer to form an aluminum plating layer on the copper plating layer. An anodizing step of anodizing the aluminum plating layer is preferably further performed. The aluminum plating solution used in the aluminum plating layer forming step is preferably a solution containing (i) a dialkyl sulfone, (ii) an aluminum halide, and (iii) ammonium halide, a hydrogen halide salt of a primary amine, a hydrogen halide salt of a secondary amine, a hydrogen halide salt of a tertiary amine, and an aluminum halide having the general formula: R １ R ２ R ３ R ４ N.X. (R １ ~R ４ are the same or different alkyl groups, and X represents a counter anion to the quaternary ammonium cation). １ ~R ４ Examples of the alkyl group represented by the formula (I) include those having 1 to 6 carbon atoms (which may be linear or branched), such as methyl, ethyl, propyl, and hexyl groups. X may be a halide ion such as chloride ion, bromide ion, or iodide ion, as well as BF ４ － and PF ６ － Examples of the nitrogen-containing compound include tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, and tetraethylammonium boron tetrafluoride. A suitable nitrogen-containing compound is a tertiary amine hydrochloride, such as trimethylamine hydrochloride, which facilitates the formation of a high-purity aluminum plating layer 4 at a high film-forming rate.

[0050] Next, an aluminum plating layer 4 or an anodized coating was formed according to the following examples. In all examples, when the substrate 1 had a plate shape (board), at least two surfaces were coated with the aluminum plating layer 4. When the substrate 1 had a round stick shape, one bottom surface and one cylindrical surface were coated with the aluminum plating layer 4. The surface roughness of each of these substrates 1 was 0.74 μm or less in Ra, providing a satisfactory smooth surface. These substrates 1 were subjected to a zincate treatment corresponding to the zinc layer formation step S001, electrolytic copper plating corresponding to the copper plating layer formation step S002, and electrolytic aluminum plating corresponding to the aluminum plating layer formation step S003. Furthermore, in some examples, as shown in Table 1 below, the aluminum plating layer formed in the aluminum plating layer formation step S003 was anodized to form an anodized coating.

[0051] The zincate treatment carried out in the zinc layer forming step S001 was a double zincate treatment carried out after degreasing the substrate 1. The zinc layer 2 was formed to a film thickness of approximately 1 μm or less.

[0052] Next, in the copper plating layer forming step S002, each substrate was immersed in a copper plating solution containing copper cyanide to form a copper plating layer 3 under conditions that resulted in a thickness of more than 8 μm and less than 22 μm.

[0053] Next, the aluminum plating solution used in this example was prepared by mixing 10 moles of dimethyl sulfone with 3.8 moles of aluminum chloride, 0.2 moles of ammonium chloride, and 1.0 moles of tetramethylammonium chloride. Two liters of this prepared aluminum plating solution was placed in a plating tank, and an aluminum plating layer 4 was formed at a solution temperature of 95°C or higher and 100°C or lower. In all of the examples and comparative examples, after the copper plating layer 3 was formed on the substrate 1, the substrate was immersed in the plating tank of the aluminum plating solution for about 5 minutes without applying a voltage, without performing any oxide film removal treatment on the copper plating layer 3, thereby performing the aluminum plating layer forming step S003.

[0054] Table 1 shows the details of the plated products from Example 1 to Example 18. Item (a) of Table 1 shows the material of the substrate, item (b) the shape of the substrate, item (c) the configuration of the layers formed in order from the substrate 1 side, item (d) the results of the cross-cut test, item (e) the results of the visual appearance inspection, and item (f) the current density (mA / cm) passed through the aluminum plating solution during the aluminum plating layer formation process. ２ ), item (g) shows the total film thickness (μm) of the zinc layer 2 and the copper plating layer 3, item (h) shows the film thickness (μm) of the aluminum plating layer 4, and item (i) shows the film thickness (μm) of the anodic oxide coating. In Table 1, "-" indicates that no testing or film thickness measurement was performed. In item (b), "Board" indicates that the substrate has a flat plate shape, and "Round Stick" indicates that the substrate has a cylindrical rod shape. In item (d), "○" indicates that no peeling was observed in the cross-cut test. In item (e), "○" indicates that no pinholes were observed in the plated product by appearance, and no peeling was observed when touched with a finger. Meanwhile, in item (e), "△" indicates that no peeling was observed when touched with a finger, but pinholes were observed. In item (h), the numerical values ​​written in parentheses are estimated values ​​of film thickness calculated from the current density and plating treatment time (current application time) during the aluminum plating treatment set in the aluminum plating layer formation step S003, and the other values ​​are actual film thickness measurements after the formation of a plated product.

[0055] In Example 1 (Ex. 1) to Example 8 (Ex. 8), and Example 18 (Ex. 18), the aluminum plating layer forming step S003 was performed, but the anodizing treatment step S004 was not performed. On the other hand, in Example 9 (Ex. 9) to Example 17 (Ex. 17), the aluminum plating layer forming step S003 was performed, followed by the anodizing treatment step S004. In Examples 12, 15, and 16, the thickness of the anodized coating was measured by cross-sectional observation. The aluminum plating layer forming step was performed with different current densities for each Example.

[0056]

[0057] According to the results in Table 1, the cross-cut test results were good in Examples 1 to 5 and Examples 14 to 18, and no peeling was observed. Furthermore, in all Examples and Comparative Examples, no peeling from the substrate 1 was observed when touched with a hand. These findings demonstrate that by performing the aluminum plating layer formation step S003 using the aluminum plating solution of this Example, an aluminum plating layer with good adhesion could be formed without removing the oxide film formed on the copper plating layer 3. Although the cross-cut test was not performed in Examples 6 to 13, it was performed under the same conditions as in Examples 3 and 4, where the cross-cut test was performed (a copper plating layer was formed on the substrate, and the current density during aluminum plating layer formation was also the same), and therefore it is presumed that the cross-cut test results are similar to those of Examples 3 and 4.

[0058] In Example 18, it was confirmed that pinholes were formed on the surface of the aluminum plating layer 4. This is thought to be due to the low current density flowing through the aluminum plating solution in the aluminum plating layer formation step S003. Because the current density is low, NR, which has the effect of reducing the difference in overvoltage between different metal species, was used. ４ ＋ It is presumed that this is because the cations represented by the formula (I) are unable to sufficiently cover the substrate 1, which is the cathode electrode, and as a result, the aluminum plating layer is unable to completely seal the holes that have formed in the copper plating layer 3. Therefore, it is preferable to set the current density flowing through the aluminum plating solution to 15 mA / cm or more.

[0059] 1: Base material, 2: Zinc layer, 3: Copper plating layer, 4: Aluminum plating layer, 5: Anodized layer, S001: Zinc layer forming step, S002: Copper plating layer forming step, S003: Aluminum plating layer forming step, S004: Anodized treatment step

Claims

1. A method for manufacturing a plated product, comprising: a zinc layer forming step of forming a zinc layer on the surface of a substrate made of magnesium or a magnesium alloy; a copper plating layer forming step of copper plating the zinc layer to form a copper plating layer on the zinc layer; and an aluminum plating layer forming step of aluminum plating the copper plating layer to form an aluminum plating layer on the copper plating layer, wherein the aluminum plating solution used in the aluminum plating layer forming step contains dimethyl sulfone, aluminum halide, ammonium chloride, and tetramethylammonium chloride.

2. The method for manufacturing a plated product according to claim 1, characterized in that the copper plating layer has a thickness of 1 μm or more and 30 μm or less, and the copper plating layer is formed so as to be thicker than the zinc layer.

3. The method for manufacturing a plated product according to claim 2, characterized in that the film thickness of the aluminum plating layer is 1 μm or more and 100 μm or less.

4. The method for manufacturing a plated product according to claim 1, further comprising an anodizing step of anodizing the aluminum plating layer to form an anodized film.

5. The method for manufacturing a plated product according to claim 4, wherein the total thickness of the aluminum plating layer and the anodic oxide coating is 21 μm or more and 100 μm or less, and the thickness of the anodic oxide coating is 11 μm or more and 30 μm or less.

6. A method for manufacturing a plated product according to any one of claims 1 to 5, characterized in that the aluminum plating solution contains 3.5 mol or more and 4.2 mol or less of the aluminum halide, 0.1 mol or more and 0.5 mol or less of the ammonium chloride, and 0.1 mol or more and 1.5 mol or less of the tetramethylammonium chloride relative to 10 mol of the dimethyl sulfone.

7. The method for manufacturing a plated product according to claim 6, wherein the aluminum plating solution contains 0.2 moles or more and 0.5 moles or less of ammonium chloride per 10 moles of dimethyl sulfone.

8. In the aluminum plating layer forming step, when the substrate on which the copper plating layer has been formed in the copper plating layer forming step and the anode electrode are immersed in the aluminum plating solution and a voltage is applied between the substrate on which the copper plating layer has been formed and the anode electrode, the current density flowing between the substrate on which the copper plating layer has been formed and the anode electrode is 15 mA / cm ２ 200mA / cm or more ２ 7. The method for producing a plated product according to claim 6, wherein 9. The method for manufacturing a plated product according to claim 8, wherein the anode electrode comprises an aluminum alloy containing silicon or copper.

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