JP2962496B2 - Magne-based alloy plating method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for plating a magnesium alloy (magne-base alloy), and more particularly, to a plating film having good dimensional accuracy by directly applying electroless nickel plating having good adhesion and good corrosion resistance. It is devised to obtain.

[0002]

2. Description of the Related Art Magnesium is a very noble metal,
Even when the plating pretreatment is performed, the chemical activity is high and an oxide film is immediately formed, so that handling is very difficult.
An example of a plating method for such a magnesium alloy is described below. After the surface is first degreased, acid cleaning is performed with phosphoric acid, chromic acid, or the like, acid or alkaline activation treatment is performed, and then Zn impregnated coating and Cu plating are performed. , Tin, chrome, silver, etc.

[0003] Other plating methods include a Dow method using fluoride as a pretreatment, a Norsk method and a WCM method in which acid treatment is performed with sulfuric acid followed by treatment with pyrophosphoric acid and zincate treatment. Further, as a method of directly plating a magnesium alloy, there is a method of chemically etching, pretreating with a fluoride, and then performing nickel plating (see JP-A-61-67770).

[0004]

In the plating method according to the prior art, since the pretreatment for pickling is performed, the surface of the raw material is significantly etched and the surface is roughened, and it is difficult to secure dimensional accuracy. Further, since fluoride is used for the activation, a film of magnesium fluoride (MgF ₂ ) is formed, and the adhesion of the plating film is hindered in a later step. Further, since it is necessary to use copper cyanide plating as a plating base, there are problems in pollution control and health and safety. Further, since hydrofluoric acid is used in the pickling before plating, a thick MgF ₂ film is generated, and the subsequent deposition of the electroless plating film is disturbed, resulting in poor adhesion. Further, it is known that the plating film has poor corrosion resistance in this method. In the Dow method, the surface is roughened in the pretreatment pickling, and the pretreatment is based on fluoride. MgF ₂ is generated, and the zincate film tends to be porous. In both the Norsk method and the WCM method, pickling with oxalic acid is performed, followed by treatment with a pyrophosphate system to perform zincate. After pyrophosphoric acid treatment, the magnesium surface is oxidized unevenly, and the plating adheres. Gets worse. Further, both methods require cyan copper plating and have problems in pollution control and health and safety. Furthermore, in these methods, when the thickness of the underlying copper plating is small, the existence of pinholes cannot be prevented, so that it is difficult to ensure corrosion resistance. The corrosion resistance can be improved by increasing the thickness of the copper plating, but the dimensional accuracy is remarkably deteriorated. JP-A-61-6
In the method disclosed in Japanese Patent No. 7770, since a fluoride is used for a pretreatment bath, an MgF ₂ film is formed, and electroless nickel plating is directly performed thereon, so that adhesion of the film is not good. In addition, the coating is apt to crack, and the corrosion resistance is insufficient.

[0005] In view of the circumstances described above, the present invention provides a method of etching a magnesium alloy without roughening the back surface thereof and without generating magnesium fluoride, and directly performing electroless nickel plating after zincate treatment. An object of the present invention is to provide a method of plating a magne-based alloy having good adhesion and remarkably improved corrosion resistance and good dimensional accuracy.

[0006]

In order to achieve the above object, a method of plating a magne-based alloy according to the present invention is characterized in that, when electroless nickel plating is performed on the surface of a magne-based alloy, an organic acid nickel salt and a hypophosphite are used. Immersion in an electroless nickel plating solution containing at least one member selected from the group consisting of sodium benzenesulfinate, sodium saccharin and sodium allylsulfonate, in addition to sodium, pyrophosphate, phosphoric acid and ammonia.

That is, the nickel-plated magne-based alloy produced by the production method according to the present invention has good adhesion and good corrosion resistance because nickel plating is applied directly on the magnesium alloy.

Hereinafter, the contents of the present invention will be described in detail. Here, the magne-based alloy in the present invention refers to an alloy for MC1 to MC8 specified in JIS. FIG. 1 shows a preferred flowchart of the pretreatment method and the subsequent plating method according to the method of plating a magne-based alloy according to the present invention. As shown in the figure, the surface of the magne-based alloy is polished, the surface is degreased, and then a weak alkaline cleaning is performed with a pretreatment liquid containing pyrophosphate as a main component. Next, after washing with water, an alkali treatment is performed, followed by washing with water. Next, after a Zn coating treatment (zincate treatment) is performed as a base, a Ni plating treatment is performed to obtain a Ni plating product in which a magne-based alloy is nickel-plated.

Hereinafter, this processing step will be described step by step. Surface polishing and degreasing are performed using a magnesium alloy as a normal pretreatment method. For these treatments, the conventional methods can be used as they are.
Puff polishing, blasting or the like is used. Degreasing can be performed by a method using an organic solvent, alkali degreasing, cathodic electrolytic degreasing, or the like, and is used in combination according to the surface condition.

After degreasing, chemical etching is performed. In this chemical etching, pyrophosphate is used as a main component and a small amount of a surfactant is contained. As the salt, a sodium salt, a potassium salt, and an ammonium salt are preferable. The concentration of pyrophosphate is 10 to 50 g / L, more preferably 3 to 50 g / L.
It is preferably 0 g / L. This is because pyrophosphate has the effect of preferentially dissolving magnesium in the magnesium alloy and magnesium oxide on the surface, and its effect is not exhibited at 10 g / L or less, and the amount of dissolution increases at 50 g / L or more and the surface dissolves. Is coarse, which is not preferable.
As the surfactant, a commercially available surfactant that operates in an alkali can be used. The amount of addition is 0.01 to
It is preferred to be about 0.1% by weight. Processing temperature is 25 ~
The temperature is preferably in the range of 60 ° C, more preferably 40 to 50 ° C, and the treatment time is preferably 1 to 5 minutes, more preferably 2 to 3 minutes. The reason for setting the above temperature range is that if the temperature is 25 ° C. or lower, the dissolving power is low, and if the temperature is 60 ° C. or higher, the amount of dissolution increases, and it becomes difficult to control the dissolution.
The addition of sulfates, nitrates, chlorides, etc. to this bath is not preferred because it promotes the etching action and deteriorates the surface condition.

After the etching, the material washed with water is treated with an alkaline solution. As the alkaline solution, a hydroxide of an alkali metal such as sodium hydroxide or potassium hydroxide is used. The concentration is preferably in the range of 10 to 100 g / L, more preferably 30 to 60 g / L. this is,
If the alkali concentration is 10 g / L or less, the reaction with the zinc aluminum component is not sufficient, and if the alkali concentration is 100 g / L or more, the reaction is not accelerated and handling problems increase, which are both undesirable. Processing temperature is 30
The temperature is preferably from 80 to 80C, more preferably from 40 to 60C. This is because if the temperature is 30 ° C. or lower, the alkali reaction is weak, and if the temperature is 80 ° C. or higher, the reaction becomes excessive, which is not preferable. The treatment time is preferably 1 to 10 minutes, more preferably 3 to 5 minutes. When treated with an alkaline solution, magnesium is not eluted at all, and the aluminum and zinc components in the alloy are eluted preferentially and oxide hydroxide is formed on the surface to form a film. In this state, magnesium is maintained in the state of most metals, E
It has been confirmed as a result of SCA analysis. In addition, zinc aluminum oxide hydroxide is formed in a mesh shape corresponding to the form of existence in the alloy.

After the alkali treatment, the substrate is washed with water and zinc-coated. In this zincate treatment, for example, zinc sulfate (Zn
SO ₄ ), sodium pyrophosphate (Na ₂ P ₂ O ₇ ) or potassium pyrophosphate (K ₄ P ₂ O ₇ ), potassium fluoride (K
F) or lithium fluoride (LiF), sodium fluoride (NaF), or an immersion liquid made of sodium carbonate (Na ₂ CO ₃ ).

[0013] After the zincate treatment, washing with water is performed sufficiently, and then nickel plating is performed. This nickel plating process was developed by the present inventors, and was previously described in Japanese Patent Application No. Hei.
87537 (filed on April 3, 1990). By using the nickel plating bath according to the above-mentioned application, it becomes possible to obtain a dense and good crack-free corrosion-resistant film having good adhesion on a zincate film. Here, when plating is performed using an ordinary commercially available acidic electroless plating bath, the zincate film is porous, so that it rapidly reacts with the underlying magnesium alloy to form a substituted nickel film having extremely poor adhesion. Only a film having extremely poor appearance and corrosion resistance can be obtained. The electroless nickel plating is performed under the conditions shown in Japanese Patent Application No. 2-87537 (the details will be described later). The plating time can be adjusted according to the desired film thickness.

After the plating is completed, the product is thoroughly washed with water and then dried to obtain a product. It is also possible to further perform surface treatment such as electroplating using the plating film according to the present invention as a base.

Next, a plating method according to the above application will be described. After the above-described pretreatment, electroless nickel plating is performed, and a plating solution containing an organic acid nickel salt is used to directly form a good and dense coating film on the magne-based alloy. The electroless nickel plating solution contains a hypophosphite as a reducing agent and ammonia, pyrophosphate and phosphoric acid as additives in addition to a nickel salt of an organic acid. Contains at least one member selected from the group consisting of sodium benzenesulfinate, sodium saccharin and sodium allylsulfonate.

As a normal electroless nickel plating solution, nickel sulfate, nickel chloride or the like is used as a nickel salt, but these are not preferable because they act as a catalyst for elution of zinc from the zinc coating film into the plating bath. In the present invention, the use of the organic acid nickel salt minimizes the elution of zinc. Here, examples of the organic acid nickel salt include nickel formate, nickel acetate, nickel lactate, nickel citrate and the like. N in electroless nickel plating solution
Usually, the i content is preferably 0.05 mol / l to 0.2 mol / l. This is because the plating life is short if the amount is less than 0.05 mol / l, and it is not practical.
This is because i precipitates and causes self-decomposition of the bath and the like, which is not preferable.

On the other hand, hypophosphite as a reducing agent contained in the electroless nickel plating solution includes hypophosphorous acid,
Sodium hypophosphite, potassium hypophosphite, etc. can be used, and the concentration is a molar ratio with respect to the Ni content.
The range may be 0.7 to 3 times. This is because if the molar ratio of hypophosphite to Ni is less than 0.7 times, Ni
It is not practical to add a reducing agent frequently because the deposition efficiency of the solution becomes low, and it is not practical. On the other hand, if it exceeds 3 times, the reducing power becomes too strong and Ni precipitates in the bath and self-decomposes. And both are not preferred.

Ammonia and pyrophosphate added to the electroless nickel plating solution form a weak complex with nickel to stabilize nickel and form a dense film with good adhesion on a zinc-based alloy. It is for doing.
Here, the preferred ranges of the concentrations of ammonia and pyrophosphate are in the range of 0.05 to 0.3 mol / l, respectively, and at least equal to the number of moles of the nickel salt. If the amount of ammonia or pyrophosphate is less than this range, bath stability is low and bath decomposition is likely to occur, and the adhesion of the deposited film is not good, which is not preferable. On the other hand, if the amount is more than the above range, the environment becomes worse because ammonia is easily vaporized and released during bath heating, and the amount of zinc eluted from the zinc-based alloy also increases,
It shortens the life of the bath and is not preferred.

Further, phosphoric acid is added to the electroless plating solution together with ammonia and pyrophosphate. This phosphoric acid works to make the precipitated Ni crystals finer, and serves to increase the density of the plating film, increase the hardness, and further improve the wear resistance and corrosion resistance. Further, since phosphoric acid binds to Zn eluted in the neutral region and precipitates as insoluble zinc phosphate, the effect of zinc eluted in the bath can be significantly reduced. The addition amount of phosphoric acid may be as small as 0.01 to 0.1 mol / l. 0.01mol / l
If it is less than 1, the ability to respond to the eluted zinc is small, while it is less than 0.1.
If it exceeds mol / l, the action as an acid becomes strong, and both are not preferred.

Further, sodium benzenesulfinate, sodium saccharin or sodium allylsulfonate used for preventing cracking in the present invention is thought to reduce the stress in the film to prevent cracking.
It is good to use in the range of 10 to 10 g / l. This is 0.1g
If it is less than / l, the effect of preventing cracking of the film is not remarkable,
Further, even if it is used in excess of 10 g / l, no remarkable improvement in the crack preventing effect is observed, which is economically disadvantageous. These additives may be used as a mixture of two or more kinds.

The optimum conditions for treating the magne-based alloy in the electroless nickel plating bath composed of the elements described above are a pH of 8.0 to 10 and a temperature of 55 to 65 ° C. The pH may be adjusted with potassium hydroxide or sodium hydroxide, but if the pH is less than 8, nickel hydroxide precipitates from the bath, whereas if the pH exceeds 10, the alkalinity is high and the solubility of zinc increases rapidly. Both are not preferred. When the bath temperature is lower than 55 ° C., the reducing power of hypophosphite is weak, so that the plating speed is too slow, which is not preferable. When the bath temperature is 65 ° C. or higher, the amount of ammonia scattered in the bath increases, and the bath balance is maintained. It is not preferable because it becomes difficult to do so.

By performing the treatment in the electroless nickel plating bath described above, it is possible to directly form a nickel coating having high density, good adhesion, no cracks, and excellent durability and corrosion resistance on the magne-based alloy. it can. The nickel coating formed by such a method has Hv ≧ 500 and has a hardness higher than that of a normal acidic electroless Ni plating coating. When this nickel coating is subjected to a salt spray test, it has a thickness of 10 μm. No generation of white rust was observed even after 24 hours.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. Examples 1-4 Plating was carried out on a JIS-MC2 (AZ-91C) mold casting by the methods shown in Tables 1 and 2 below. The evaluation results of the plating films are also shown in Tables 1 and 2. The corrosion resistance was evaluated by a salt spray test. Adhesion is J
According to the IS Gobanme test, a 5 × 5 square was cut with a knife, a tape was applied from above, and the tape was peeled off. Example 5 Plating was carried out on a JIS-MC3 (AZ-92A) sand mold product by the method shown in the following "Table 2", and the evaluation results of the film properties are also shown in "Table 2". Examples 6 and 7 Plating was performed on a JIS-MC6 (ZK51A) sand-cast article by the method shown in Table 3 and the evaluation results of the film properties are also shown in Table 3. Comparative Example 1 Plating was carried out on a JIS-MC2 mold casting using "S-770" (trade name) manufactured by Nippon Kanzen Co., Ltd. as shown in the following "Table 3", and the film evaluation results were similarly determined in "Table 3". " Examples 8 to 11 A JIS-MC2 mold casting was subjected to Ni plating using various plating bath compositions shown in Tables 4 and 5 below.
Similarly, the film evaluation is shown in "Table 4" and "Table 5". "Table 1"
As shown in Table 5 below, better Ni plating could be performed in each case than in Comparative Example 1 shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

[Table 6]

[0030]

As described in connection with the following embodiments, in the present invention, a pre-treatment of a magnesium alloy with an alkali solution without using a fluoride can provide a film having very good adhesion in zincate treatment. Furthermore, by using the electroless nickel plating bath developed by the present inventors, a dense and crack-free plating film can be directly formed on a magnesium alloy without using cyan copper plating. . An effect of the present invention is that a coating having good adhesion and good corrosion resistance can be plated with good dimensional accuracy and without pollution and safety and health problems by directly performing electroless nickel plating on a magnesium alloy.

[Brief description of the drawings]

FIG. 1 is a process chart of a plating process of a magne-based alloy.

Claims (2)

(57) [Claims] 1. An electroless nickel plating method for applying electroless nickel plating to the surface of a magne-based alloy, comprising: an organic acid nickel salt, hypophosphite,
A magne-based alloy characterized by being immersed in an electroless nickel plating solution containing at least one selected from the group consisting of sodium benzenesulfinate, sodium saccharin and sodium allylsulfonate, in addition to pyrophosphate, phosphoric acid and ammonia. Plating method. 2. The method of plating a magne-based alloy according to claim 1, wherein the pre-treatment is performed in a bath containing pyrophosphoric acid as a main component.