JP3192003B2 - High corrosion resistance coating method for magne-based alloy - 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 coating a magnesium alloy (magne-base alloy) with high corrosion resistance, and more particularly, to a coating film having good corrosion resistance and good adhesion.

[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., and then paint.

[0003]

In the prior art,
When a cross-cut was made on the coating film in the salt spray test (SST) of the corrosion resistance test, the magnesium of the base material came into direct contact with the salt water, extremely large pitting occurred, and the soundness of the coating film portion was maintained. Even the crosscut part had problems. Further, in order to ensure corrosion resistance, the coating system also needs a total film thickness close to 100 μm for the primer treatment, the undercoat, and the overcoat.

[0004] In view of the circumstances described above, an object of the present invention is to provide a highly corrosion-resistant coating method for a magne-based alloy having good corrosion resistance and good adhesion even when a cross cut is made.

[0005]

According to the present invention, there is provided a method for plating a magne-based alloy, wherein the surface of the magne-based alloy is coated with high corrosion resistance . Thereafter, degreasing and weak alkali treatment were performed, followed by an alkaline solution having a concentration of 10 to 100 g / L at 30 to 80C.
An alkali treatment at a temperature of, a water washing after the alkali treatment, a zinc coating treatment as a base of the magne-based alloy, and a water washing after the zinc coating treatment, the organic acid nickel salt,
Dipped 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 hypophosphite, pyrophosphate, phosphoric acid, and ammonia; The method includes a step of applying electroless nickel plating to the surface of the alloy, and a step of subsequently coating.

That is, according to the present invention, the hardness and fineness of the base electroless Ni plating film are reduced by providing the coating as an overcoat with the film obtained by directly applying the electroless Ni plating to the magne-based alloy as the base. It becomes a two-layer coating film of the top coat, so that a very high synergistic effect can be obtained, and a high corrosion resistance can be obtained with a thinner film thickness than before.

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, the subsequent plating method, and the coating 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 washed with a weak alkali with a pretreatment liquid mainly composed of pyrophosphate .
Etching process) . 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, and then a painting is performed to obtain a magne-based alloy highly corrosion-resistant painted product.

Hereinafter, the processing steps will be described in order. 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 the degreasing treatment, chemical etching which is a weak alkaline cleaning is performed. At the time of 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 preferably 10 to 50 g / L, more preferably 30 g / L. This is because pyrophosphate has the action of preferentially dissolving magnesium in the magnesium alloy and the magnesium oxide on the surface. If less than 10 g / L , the action is not exhibited, and if it exceeds 50 g / L, the amount of dissolution is large. This is because the surface becomes rough, and both are not preferred. As the surfactant, a commercially available surfactant that operates in an alkali can be used. Further, the amount of addition is preferably about 0.01 to 0.1% by weight. Processing temperature is 25-60
C, more preferably 40 to 50C, and the treatment time is 1 to 5 minutes, more preferably 2 to 3 minutes. The above temperature range is set below 25 ° C
Its control increases the amount of dissolution when exceeding 60 ° C. lower dissolving power of that becomes difficult, because not both preferably. 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,
When the alkali concentration is less than 10 g / L, the reaction to the zinc aluminum component is not sufficient, and the alkali concentration exceeds 100 g / L.
In such cases , the reaction is not accelerated and handling problems increase, which is not preferable. The treatment temperature is 30 to 80 ° C, preferably 40 to 6 ° C.
The temperature is preferably set to 0 ° C. This is because if the temperature is lower than 30 ° C., the alkali reaction is weak, and if the temperature is higher than 80 ° C., the reaction becomes excessive, which is not preferable. Processing time is 1 to 1
The time is more preferably 0 minute, and 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, it has been confirmed by ESCA analysis that magnesium is kept in the state of most metals. In addition, zinc aluminum oxide hydroxide is formed in a mesh shape corresponding to the form of existence in the alloy.

After alkali treatment, washing with water and zinc coating treatment are performed. 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 ).

After the zincate treatment, the substrate is washed sufficiently with water and then nickel-plated. This nickel plating process was developed by the present inventors, and was previously described in Japanese Patent Application No. Hei.
87537 (Japanese Patent Application Laid-Open No. 3-287776). 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 described in JP-A-3-287776 (the details will be described later). The plating time can be adjusted according to the desired film thickness.

It is sufficient that the thickness of the electroless Ni plating directly applied to the magnesium alloy is 1 to 15 μm. This electroless Ni plating treatment can directly provide a thin, fine and high hardness Ni plating film on the magnesium alloy, has good corrosion resistance, and sufficiently satisfies the conditions of the undercoat film. is there. Further, when performing electrodeposition coating in a later step, an anionic system is difficult to use when Mg is bare, but can be sufficiently used with Ni plating.

The coating applied thereafter is 10 to 30 μm in various commonly used coating systems (epoxy coating, acrylic coating, polyurethane coating, anionic electrodeposition, cationic electrodeposition).
By providing a coating film of m, performance equal to or higher than that of the conventional method can be secured. As a coating method, any of commonly used methods such as dipping, coating, electrostatic coating, powder electrostatic, cationic electrodeposition, and anion electrodeposition can be used. In the baking process after coating, by heating at 170 to 200 ° C., the adhesion of the underlying electroless Ni plating film can be further improved, and the increase in film hardness can improve the blocking performance of external corrosion factors. .

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. (Example 1) Die-cast magnesium alloy (JIS-MC-2)
Was treated with potassium pyrophosphate 30 g / L at 50 ° C. for 1 minute, washed with water, treated with NaOH 30 g / L at 60 ° C. for 2 minutes, washed with zincate (WCM method) for 3 minutes, and shown in Table 1. Plating was performed in an electroless Ni plating bath using a plating bath composition at 60 ° C. for 30 minutes to obtain a 5 μm electroless Ni plating film. After washing with water, drying was performed quickly, followed by electrodeposition under a normal condition using a cationic electrodeposition paint (N-50, manufactured by Nippon Paint Co., Ltd.), and baking at 175 ° C. for 30 minutes to obtain a coating film having a thickness of 20 μm. When a salt water spray test was carried out with a cross cut, corrosion of the cross cut portion did not occur even after 2,000 hours, and the secondary adhesion was good.

[0016]

[Table 1]

(Embodiment 2) Electroless Ni plating on a (JIS-MC-6) alloy was performed in the same manner as in Embodiment 1, the plating time was 60 minutes, and the plating film thickness was 11 μm. After washing with water and drying, an electrostatic coating was performed using a urethane-modified acrylic resin paint, and after baking at 150 ° C. for 15 minutes, a film thickness of 15 μm was obtained. When a cross cut was made and the SST test was performed, no corrosion occurred in the cross cut portion even after 2000 hours, and the secondary adhesion was good.

(Embodiment 3) After (Dow7) treatment of (JIS-MC-2) alloy, 30 urethane-modified acrylic resin paint was applied to the undercoat.
μm, and overcoating was similarly performed at 20 μm. After that, a cross cut was performed and the SST test was performed. After 2000 hours, blisters were generated on both sides of the cross cut portion at 3 mm, and pitting corrosion of 200 μm occurred in the material.

[0019]

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 is directly formed on the magnesium alloy without using cyan copper plating, and then the coating is applied to cross-cut. , A coated article having good corrosion resistance and good adhesion can be obtained.

[Brief description of the drawings]

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

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Susumu Takahashi 1333-2, Ojiwara-shi, Ageo-shi, Saitama Mitsui Kinzoku Mining Co., Ltd. Research Laboratory (56) References JP-A-3-287776 (JP, A) 62-7873 (JP, A) Takehiko Fujino, Haruo Inagaki "Practical Handbook for Plating" (March 5, 1978), Engineering Books, pp. 70-71 (58) Fields surveyed (Int. Cl. ⁷ , DB Name) C23C 18/00-18/54 C23C 28/00 C25D 13/20

Claims (1)

(57) [Claims] 1. A method for applying a highly corrosion-resistant coating to the surface of a magne-based alloy, wherein the surface of the magne-based alloy is polished, then degreased and treated with a weak alkali.
Followed by an alkaline solution having a concentration of 10 to 100 g / L.
A step of performing an alkali treatment at a temperature of 0 to 80 ° C., a step of washing with water after the alkali treatment, and a step of coating with zinc as an underlayer of a magne-based alloy; 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 salt, pyrophosphate, phosphoric acid and ammonia,
A highly corrosion-resistant coating method for a magne-based alloy, comprising a step of applying electroless nickel plating to a surface of the magne-based alloy, and a subsequent coating step.