JPH07157884A - Method for plating tungsten alloy - Google Patents

Abstract

PURPOSE:To execute plating of a W allay excellent in chemical resistance by cleaning the surface of metal stock, applying Sn-Ni plating thereon and thereafter applying a Pd-Ni-W or Ni-W alloy thereon as finish plating according to the application. CONSTITUTION:The surface of Al or an Al allay is cleaned by degreasing, pickling or the like, and next, a zinc-substituted film is formed thereon. After that, this metal stock is applied with substrate plating. The surface of this substrate plating is applied with intermediate plating constituted of an Sn-Ni alloy excellent in corrosion resistance. In the case the metal stock is constituted of Cu or a Cu allay, immediately after the cleaning of the surface, the Sn-Ni allay is applied. Moreover, in the case the metal stock is constituted of a stainless steel, after the cleaning of the surface, preferably, a passive film formed on the surface is removed, and furthermore, after the application of strike plating, the Sn-Ni alloy plating is executed. After that, the surface of the Sn-Ni allay plating is moreover applied with a Pd-Ni-W or Ni-W allay plating as finish plating according to the application.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal for forming a highly corrosion-resistant alloy film by performing alloy plating having a composition of tungsten on the surface of a metal such as aluminum, copper, alloys thereof, stainless steel or the like. The present invention relates to a method for plating a tungsten alloy on the surface of the above.

[0002]

2. Description of the Related Art Metal bond radius 1.43Å, density 2.70.
g / cm ³ (20 ° C.), Young's modulus 68.3 × 10 ⁹ N /
Aluminum having a m ² and a melting point of 660.4 ° C. is lightweight and soft, has excellent ductility and malleability, and has many advantages in use, and thus has a wide range of applications. Aluminum alloys most widely used as light alloys to strengthen the mechanical properties lacking in this high-purity aluminum include duralumin, super duralumin, ultra super duralumin, etc. for the purpose of strengthening mechanical properties. There are high-strength alloys, and for the purpose of corrosion resistance, Al-Mg type, Al-Mn type, A
There are l-Mg-Si type, Al-Cu type, A for casting
1-Cu-Si system (Lautal etc.), Al-Si system (Silmine etc.), Al-Mg system (Hydrosodium etc.), A
There exists an l-Cu-Mg-Ni system (Y alloy or the like). However, aluminum is an amphoteric metal and has the property of being soaked in both alkali and acid, and thus it is necessary to perform a surface treatment operation on the metal. As the surface treatment operation of this metal,
Surface coating, surface oxidation treatment of aluminum, which is generally called alumite, and immediately anodizing method such as electrolytic oxidation method using oxalic acid bath, chromic acid bath, sulfuric acid bath, etc. have been proposed.

Metal bond radius 1.28Å, density 8.96g
/ Cm ³ (20 ° C.), Young's modulus 110 × 10 ⁹ N /
Copper alloys such as m ^{2 having} a melting point of 1083.4 ° C., bronze that is an alloy with tin, brass that is an alloy with brass, etc. are particularly weak in chlorine-based and fluorine-based environments, and under these environments. Corrodes easily and cannot be used. In order to eliminate the above-mentioned drawbacks, the surface of the metal is plated with nickel or nickel chrome by electroplating.
Further, by electroplating, plating using gold or silver is performed on a very small part.

As the stainless steel, a ferrite system called 18Cr stainless steel, an austenite system called 18-8 stainless steel, a martensite system called 13Cr stainless steel, a ferrite / austenite with improved stress corrosion cracking resistance and pitting corrosion resistance. Two-phase stainless steel having a two-phase mixed structure, that is, 25% Cr and 5% Ni as the base, with a small amount of Mo, Cu, Si, etc. added,
It is roughly classified into PH stainless steel for which precipitation strengthening is intended. 12
Stainless steels containing more than 50% chromium have excellent corrosion resistance. Chromium in the composition is a highly reactive metal and reacts remarkably with oxygen in the atmosphere, forming an oxide film on the surface of the steel to passivate it and stop further corrosion. Immediately, oxygen in the solution or air chemically protects the stainless steel and improves the corrosion resistance of the stainless steel. In addition, in recent years, Japanese Patent Publication No. 53-41623 and Japanese Patent Laid-Open No. 53-11
131, JP-A-53-57138, JP-B-59-10437, JP-A-57-31447, JP-A-61-6291, and JP-A-61-960.
No. 96, Japanese Patent Laid-Open No. 1-147087, and Japanese Patent Publication No. 4
The alloy plating methods disclosed in JP-A-38838 and JP-A-2-258994 have been proposed.

[0005]

However, among those described in the above-mentioned prior art, the surface treatment operation for the purpose of corrosion resistance on the surface of aluminum or aluminum alloy has the effect compared with aluminum itself from the industrial viewpoint. Then, although it is much larger, the film obtained by the oxalic acid bath has a thickness of about 25 μm and is rich in peelability due to its porosity, and the film obtained by the chromic acid bath is dense and smooth.
Since the film is 0μ or less, it is easily worn, and the film obtained by the sulfuric acid bath is hard and transparent and can be dyed, but the wear resistance is low, and the plating obtained by either treatment method is remarkable in corrosion resistance and the like. No effect is seen. Therefore, there has been a problem that it is rarely used in, for example, a chemical agent using apparatus, especially a semiconductor manufacturing apparatus, which requires corrosion resistance especially in an acidic environment.

In the surface treatment operation for the purpose of anticorrosion of copper or copper alloy, gold and silver are used, so that the cost is high, no remarkable anticorrosion effect is observed, and it is said that there is almost no anticorrosion plating. is the current situation.

[0007] As described in the above-mentioned prior art, stainless steel reacts with oxygen to passivate and stop corrosion, so that it exhibits excellent corrosion resistance. However, stainless steel is not a steel that does not rust at all. In particular, in a specific environment such as a fluorine-based, chlorine-based, or other acidic environment, localized corrosion such as pitting corrosion, crevice corrosion, intergranular corrosion, and stress corrosion cracking occurs. And these corrosions result in the dramatic destruction of stainless steel. Conventionally, various methods such as electrodeposition and glassy enamel have been attempted for surface treatment of stainless steel, but it is extremely difficult to coat the stainless steel. The present situation is that there are only a few for decorative purposes, and none for the purpose of improving corrosion resistance.

Also, Japanese Patent Publication No. 53-41623, Japanese Patent Publication No. 53-11131, Japanese Patent Publication No. 53-57138, Japanese Patent Publication No. 59-10437 and Japanese Patent Publication No. 57-3.
1447, JP 61-6291, JP 61-96096, JP 1-147087, JP 4-38838, JP 2-2589.
The alloy plating method disclosed in Japanese Patent Publication No. 94 has excellent wear resistance, but has a problem that corrosion resistance is not preferable in a specific chemical environment.

In order to solve the above-mentioned problems of the prior art, the present invention uses a metal having good corrosion resistance as an intermediate layer and further coats nickel, tungsten, or palladium alloy having good corrosion resistance as a finish to obtain chemical resistance. It is an object of the present invention to improve the properties and provide a material that can be used for various purposes as a material for chemicals and semiconductor manufacturing equipment.

[0010]

To achieve the above object, in the method for plating a tungsten alloy of the first invention of the present application, the metal surface such as aluminum or aluminum alloy is degreased, pickled, etc. In addition to cleaning, the zinc-substituted film was plated with an alloy having a composition of nickel and tungsten to form a base plating, and then an alloy plating having a composition of nickel and tungsten was subjected to intermediate plating. After that, finish plating is palladium, nickel, tungsten, or an alloy plating of any composition of nickel and tungsten depending on the intended use.

In the tungsten alloy plating method of the second invention of the present application, the metal surface is cleaned by degreasing or pickling a metal material such as copper or a copper alloy, and the cleaned metal surface is tinned. After plating with an alloy having a composition of nickel, an alloy plating having a composition of nickel, tungsten, palladium, or nickel or tungsten is further applied as a finish plating depending on the intended use.

In the tungsten alloy plating method of the third invention of the present application, after degreasing and pickling the stainless steel material to remove the passivation film formed on the stainless steel surface, tin and nickel Alloy plating consisting of composition, nickel, tungsten,
An alloy plating having a composition of palladium, nickel, or tungsten is applied as finish plating.

[0013]

The functions of degreasing, pickling, and forming a zinc-substituted film have the functions of cleaning the surface, improving the plating of the undercoat, preventing the subsequent peeling of the plating, and enhancing the adhesion.

Nickel containing 1% to 10% of tungsten and tungsten alloy plating are applied to the base plating, and it is more resistant to humidity than conventional nickel plating and has strong corrosion resistance in acidic environments such as acetic acid and hydrogen chloride. The accepted tin and nickel alloy plating is used as an intermediate plating between the material and the finish plating, and the interaction improves the corrosion resistance. The tin / nickel alloy plating has a softer film and a higher humidity resistance than nickel plating. Tungsten, which is used as a strong acid corrosion resistant material, is alloyed with nickel for finish plating. However, because of the property that it cannot be plated because it is not tungsten alone, for example, when co-deposited with another metal such as nickel, it is within a range of about 2 to 50%. Tungsten co-deposits. Nickel, tungsten alloy and nickel, tungsten, palladium alloy plating show strong corrosion resistance especially in chlorine or fluorine environment. Thus, when tungsten, which is a strong acid corrosion resistant material, is plated as an alloy, palladium, which has a stronger corrosion resistance, is co-deposited and contained in the plating film, which serves to strengthen the corrosion resistance.

Further, as described above, the plating having each characteristic is laminated to form a plating film having high corrosion resistance.

In the finish plating, whether or not palladium is added is determined depending on the use of the metal, and the hardness of the plating film is adjusted by changing the composition of the bath.

When forming a plated film on the surface of stainless steel, strike plating is performed because if the plating is performed before the formation of the passivation film, the adhesion of the plating becomes good.

[0018]

Example 1 An example of the present invention will be described below.

Silicon (Si), iron (Fe), copper (C
u), manganese (Mn), magnesium (Mg), zinc (Zn), titanium (Ti), aluminum (Al) containing aluminum (Al) as a composition component, for example, JIS standard aluminum alloy No. 1070, degreasing, etching pickling Go and clean the surface, then Super Z Z
Double substitution of zinc with II (trade name of Kizai Co., Ltd.) is performed, and base plating is performed for about 5 minutes under the electrolytic conditions shown in Table 1 below.

[0020]

[Table 1]

After the above-mentioned base plating, it is washed with water and intermediate plating is performed under the electrolytic conditions shown in Table 2 below.

[0022]

[Table 2]

After carrying out uniform intermediate plating on the surface of the base plating, it was washed with water and further subjected to finish plating under the electrolytic conditions shown in Table 3 below. Finish plating depends on the corrosive environment used, and bath A containing no palladium amine chloride
And bath B containing paradium amine chloride.

[0024]

[Table 3]

The obtained product has a plating thickness of 20 μm.
Then, the composition of the alloy plating carried out under the electrolytic conditions of the bath B containing paradium amine chloride as one of the composition components shown in Table 3 above is as shown in Table 4 below. The thickness of the plating can be changed to any thickness in consideration of the corrosion resistance limit according to the application and the corrosive environment used.

[0026]

[Table 4]

[0027]

TEST EXAMPLE 1 The alloy-plated aluminum plate obtained in this example was immersed in a hydrochloric acid aqueous solution prepared by mixing 1 part of hydrochloric acid and 2 parts of water at room temperature for about 48 hours. In order to compare the test results, an aluminum plate under the same conditions as those described above, an aluminum plate plated with nickel having a thickness of 10 μm, a substrate plated under the electrolytic conditions of Table 1 above, and an electrolysis of Table 2 above. Those subjected to intermediate plating under the conditions were also immersed in the same manner. The results are shown in Table 5 below.

[0028]

[Table 5]

[0029]

[Test Example 2] The alloy-plated aluminum plate obtained in this example is hung in the upper chamber of a desiccator in which chlorine gas is generated.
It was left for an hour and exposed to chlorine gas. In order to compare the test results, an aluminum plate under the same conditions as those described above, an aluminum plate plated with nickel having a thickness of 10 μm, a substrate plated under the electrolytic conditions of Table 1 above, and an electrolysis of Table 2 above. Those subjected to intermediate plating under the conditions were also suspended in the same manner.
The results are shown in Table 6 below.

[0030]

[Table 6]

[0031]

Test Example 3 The alloy-plated aluminum plate obtained in this example was suspended in a transparent plastic container with a lid having a 48% hydrofluoric acid aqueous solution at the bottom, and the humidity in the container was 90% or more. It was left for about 72 hours in a room temperature environment and exposed to hydrogen fluoride gas. In order to compare the test results, an aluminum plate under the same conditions as above, a nickel plate plated on the aluminum plate, a base plating under the electrolytic conditions of Table 1 above, and an intermediate condition under the electrolytic conditions of Table 2 above. The plated ones were also hung in the same way. The results are shown in Table 7 below.

[0032]

[Table 7]

[0033]

Example 2 Silicon (Si), iron (Fe), copper (C
u), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), silconium (Zr), and an alloy of titanium oxide (TiO), an aluminum alloy containing aluminum (Al) as a composition component, for example, After JIS standard aluminum alloy No. 2017 was cleaned to the surface by degreasing, etching, and pickling treatment in exactly the same process as in the above-mentioned embodiment, zinc substitution was performed, for example, Super Z Z.
Double replacement process with II (trade name of Kizai Co., Ltd.),
Under the electrolytic conditions shown in Tables 1, 2, and 3, base plating, intermediate plating, and finish plating were sequentially performed to perform alloy plating on the surface of the aluminum alloy.

[0034]

[Test Example 4] Regarding the alloy plating obtained in this example,
Similar to the alloy plating shown in Example 1, the corrosion resistance tests shown in Test Examples 1 to 3 were performed. Also in this example, the same good test results as those in Tables 5, 6, and 7 were obtained as in Example 1.

[0035]

Example 3 Silicon (Si), iron (Fe), copper (C
u), manganese (Mn) magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), and aluminum (Al) as a compositional component, for example, JIS standard aluminum alloy No. 5052 is also described above. After cleaning the surface by degreasing, etching, and pickling in the same manner as in Example 1, zinc substitution was performed by double substitution treatment with, for example, Super ZET ZII (trade name of Kizai Co., Ltd.). Underlying, intermediate, and finish plating were performed under the electrolytic conditions shown.

[0036]

[Test Example 5] Regarding the alloy plating obtained in this example,
The corrosion resistance tests shown in Test Examples 1 to 3 were performed in the same manner as in Example 1. Similar to the above example, the same good test results as in Table 5, Table 6 and Table 7 were obtained.

[0037]

Example 4 Silicon (Si), iron (Fe), copper (C
u), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), titanium (Ti), aluminum alloy having a compositional component, for example, JIS standard aluminum alloy No. 6061 is also described above. The surface treatment operation was performed by the same procedure as in the above example.

[0038]

[Test Example 6] The corrosion resistance test shown in Test Examples 1 to 3 was performed on the alloy plating obtained in this example, and the same good test results as those in Table 5, Table 6 and Table 7 were obtained. It was

[0039]

Example 5 Silicon (Si), iron (Fe), copper (C
u), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn), an alloy of zirconium (Zr) and titanium oxide (TiO), an aluminum alloy of titanium (Ti), and aluminum (Al) is a core material. And a composite material using an aluminum alloy composed of an alloy of silicon (Si) and iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), zinc (Zn), and aluminum (Al) as a skin material, For example, JIS standard aluminum alloy number 70
75 was subjected to a surface treatment operation by the same procedure as in Example 1 described above.

[0040]

[Test Example 7] Regarding the alloy plating obtained in this example,
As a result of performing the corrosion resistance test shown in the above-mentioned Test Examples 1 to 3, the same good test results as those in Table 5, Table 6 and Table 7 were obtained.

In the above-mentioned embodiment, after the base plating and the intermediate plating, further finish plating is carried out to obtain a plating film having good corrosion resistance. However, the final stage finish plating is a bath containing the palladium shown in Table 3. It is determined according to the electrolysis condition of B or the electrolysis condition of the bath A containing no paradium, the application of the obtained product, and the corrosive environment to be used.

[0042]

[Example 6] A copper (Cu) material was degreased and pickled to clean the surface, and then plated for 10 minutes under the electrolytic conditions shown in Table 8 below to obtain plating with good softness and corrosion resistance. It was

[0043]

[Table 8]

Then, after washing with water, finish plating was performed under the electrolytic conditions shown in Table 9 below. The finish plating was divided into a bath C containing no palladium, a bath D containing palladium, and a bath E containing palladium and having an increased PH. For example, bath C and bath D have a citric acid concentration of 80 to 200 g /
However, in the bath E, the citric acid concentration was 150 g / l, and tartrate was added in an amount of 50 to 100 g / l.
1 is added to increase the PH.

[0045]

[Table 9]

The alloy compositions of the plating films obtained by the baths C, D and E were in the ranges shown in Table 10 below, and there was no great difference in the composition ratio.

[0047]

[Table 10]

The plating hardness at the time of plating deposition is shown in Table 11 below.
As shown in, a bath E containing tartaric acid can be remarkably softened as compared with a bath obtained by another bath, and the thickness of the plating film is as thick as 20 μm, and a material requiring corrosion resistance and flexibility. As a result, the optimum plating could be obtained. In this way, the bath can be used properly according to the application of the product.

[0049]

[Table 11]

[0050]

Test Example 8 The alloy-plated copper plate obtained in this example was immersed in a hydrochloric acid aqueous solution in which water was mixed at a ratio of 1 to 1 for about 72 hours at room temperature. In order to compare the test results, under the same conditions as above, 1
The 0 μm nickel plating, and the finish plating with each of bath C, bath D and bath E were similarly immersed in the hydrochloric acid aqueous solution.
The results were as shown in Table 12 below.

[0051]

[Table 12]

[0052]

[Test Example 9] The alloy-plated copper plates obtained in each of the baths C, D, and E according to this example were hung in a desiccator in a room temperature environment where chlorine gas was constantly generated and humidity was 40% or more, and chlorine was suspended. I hit the gas. In order to compare the test results, a copper substrate and a copper plate plated with 10 μm nickel were also exposed to chlorine gas under the same conditions as described above. The results were as shown in Table 13 below.

[0053]

[Table 13]

[0054]

[Test Example 10] The alloy-plated copper plates obtained in each of the baths C, D, and E according to this example were suspended in a transparent plastic container with a lid having a 48% hydrofluoric acid aqueous solution at the bottom. did. Humidity in the container is 90% or more, and it is about 48 at room temperature.
The same state was maintained for a time. In order to compare the test results, a nickel-plated copper plate having a copper base material of 10 μm was also exposed to hydrogen fluoride gas under the same conditions as above. The results are shown in Table 14 below.

[0055]

[Table 14]

[0056]

Example 7 A copper alloy of 60% copper and 40% zinc, a so-called brass plate, was degreased and acid-activated to clean the surface in the same process as in Example 6, and the results are shown in Table 8 above. After plating under the conditions, the plate was washed with water and further plated under the conditions shown in Table 9 above.

[0057]

Test Example 11 The alloy plating obtained in this example was subjected to a corrosion resistance test in the same manner as in Test Examples 8 to 10 above. Also in this example, as in the case of Example 6, Tables 12 to 14 were used.
The same good test result was obtained.

[0058]

Example 8 The surface of an 18Cr-8Ni stainless steel plate is cleaned by degreasing and pickling, and then strike plating is performed for about 3 to 5 minutes under electrolytic conditions shown in Table 15 below to form a base plating film. This activation method is not necessarily limited to cathodic electrolysis, and anodic electrolysis may be used in combination.

[0059]

[Table 15]

After the strike plating, the plate is washed with water and the following Table 1 is shown.
Under the electrolytic conditions shown in No. 6, intermediate plating by tin, nickel and alloy plating was performed. Tin-nickel alloy plating is used as an intermediate plating because it shows strong corrosion resistance in a chlorine-based environment.

[0061]

[Table 16]

The intermediate plated product was washed with water and then subjected to final plating under the electrolytic conditions shown in Table 17 below. The finishing plating is divided into a bath F containing no palladium and a bath G containing palladium according to the environment in which it is used. The plating with the bath G had a wall thickness of 20 μm. The alloy plating composition is shown in Table 18.

[0063]

[Table 17]

[0064]

[Table 18]

[0065]

TEST EXAMPLE 12 Three adhesion tests were carried out on strike-plated undercoating under the conditions shown in Table 15. Firstly, a bending test after heating at high temperature, a second test in which a cut surface was rubbed with a file, and a third scissors bending test in a vise were performed. For the second and third tests, which were not performed, neither peeled off. Thus, the destructive test showed a strong adhesion.

[0066]

[Test Example 13] For comparison, the alloy-plated stainless steel plate obtained in Example 8 was immersed in a concentrated hydrochloric acid aqueous solution for 148 hours together with an 18Cr-8Ni stainless steel plate and an 18Cr.12Ni-2.5Mo stainless steel plate in a room temperature environment. . The results are shown in Table 19 below.

[0067]

[Table 19]

[0068]

[Test Example 14] For comparison, the alloy-plated stainless steel sheets obtained in this Example were used together with 18Cr-8Ni stainless steel sheet and 18Cr.12Ni-2.5Mo stainless steel sheet, and the humidity at which chlorine gas was generated was 90% or more at room temperature. It was hung in the desiccator for 72 hours. The results are shown in Table 20 below.

[0069]

[Test Example 15] For comparison, the alloy-plated stainless steel sheets obtained in this Example were put together with 18Cr-8Ni stainless steel sheet and 18Cr.12Ni-2.5Mo stainless steel, and 48% hydrofluoric acid aqueous solution was added to the bottom thereof to fluorinate. It was hung in a transparent plastic container filled with hydrogen gas for 72 hours. The results are shown in Table 21 below.

[0070]

[Table 21]

[0071]

[Example 9] 18Cr / 8Ni stainless steel plate, 18C
The r.12Ni-2.5Mo stainless steel plate and the 18Cr stainless steel plate were also subjected to degreasing, pickling, strike plating, intermediate plating and finish plating in the same process as in Example 8 described above. A plating film having a wall thickness of 20 μm for the 18Cr-8Ni stainless steel plate, a thickness of 15 to 20 μm for the 18Cr / 12Ni-2.5Mo stainless steel plate, and a thickness of 10 to 15 μm for the 18Cr stainless steel plate was obtained.

[0072]

[Test Example 16] The alloy plating obtained in Example 9 was also subjected to the corrosion resistance test shown in Test Examples 13 to 15 described above. As a result, the same results as in the baths F and G in these test examples were obtained, and it was found that the corrosion resistance was good against chlorine-based and fluorine-based environments.

[0073]

According to the first aspect of the present invention, the zinc film is formed after cleaning the surface by degreasing and pickling, so that the plating is easily applied, the adhesion is improved, and peeling is difficult. Since the coating is formed on the metal by the three-layer plating, there is an effect that the corrosion resistance can be improved.

The invention according to claim 2 makes the plating soft by only slightly changing the composition of the bath of the finish plating, and is not limited to the application to the chemical manufacturing equipment, and can be used for those requiring flexibility. The effect is that the range of applications is widened.

The invention according to claim 3 has the effect of enabling the plating of the stainless steel surface, which has been difficult in the past, to prevent corrosion such as pitting corrosion and stress corrosion cracking of stainless steel, and to improve the corrosion resistance.

The inventions according to claims 1 to 3 can be used as a chemical manufacturing apparatus, a material or a material used for a semiconductor manufacturing apparatus that requires strong chemical resistance by forming a multilayer of an alloy having good corrosion resistance. There is an effect.

[Table 20]

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Claims (3)

[Claims] 1. A base material obtained by cleaning a metal material such as aluminum or an aluminum alloy by degreasing and pickling, and forming a zinc substitution film on the metal surface, and then plating the alloy with a composition of nickel and tungsten. After plating, then alloy plating consisting of nickel and tungsten composition is performed and then intermediate plating is performed, and then alloy plating consisting of palladium, nickel, tungsten, or nickel or tungsten composition is applied according to the intended use. A method for plating a tungsten alloy, characterized by being applied as finish plating. 2. Degreasing a metal material such as copper or copper alloy,
After the metal surface is cleaned by pickling, etc., and after the cleaned metal surface is plated with an alloy having a composition of tin and nickel, either nickel, tungsten, palladium or nickel, or tungsten may be used depending on the intended use. A method for plating a tungsten alloy, which comprises applying an alloy plating having the above composition as a finish plating. 3. A stainless steel material is degreased and pickled to remove a passivation film formed on the surface of the stainless steel, and then plated with an alloy having a composition of tin and nickel, and further, depending on the intended use. A method for plating a tungsten alloy, which comprises performing, as finish plating, an alloy plating having a composition of nickel, tungsten, barium or nickel, tungsten.