JPH08134662A - Treatment of magnesium or magnesium alloy before coating - Google Patents

Abstract

PURPOSE: To stably impart the adhesiveness and corrosion resistance of a coating film to Mg and Mg alloy by adding a simple fluoride to a zinc-phosphating soln. contg. a complex fluoride. CONSTITUTION: A simple fluoride is added to a zinc-phosphating soln. contg. a complex fluoride (including complex hydrofluoric acid). The Mg or Mg alloy before coating is treated with the soln. The simple fluoride is added to control the equivalent ratio of the Mg ion eluted into the soln. to the complex fluoride to <=1, and the Mg ion is precipitated outside the soln. system. The content of the complex fluoride in the soln. is preferably controlled to 0.05-3g/l, expressed in terms of HF, and the concrete concn. of the Mg ion to <=0.5g/l. A liq. to be measured is sampled from the soln., a simple fluoride is added to the liq., and the Mg ion content is measured to determine the amt. of the simple fluoride to be added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for pretreatment of coating of magnesium or magnesium alloy material, and particularly pretreatment of coating capable of imparting better coating adhesion and coating corrosion resistance than chromate treatment. It is about the method.

[0002]

2. Description of the Related Art Magnesium and magnesium alloy materials are extremely reactive materials, and therefore various pretreatments for coating are applied for the purpose of improving coating adhesion and coating corrosion resistance. Methods are being considered.

As a coating pretreatment method, an electrochemical treatment (anodizing treatment) for the purpose of improving the corrosion resistance of a coating film and a chemical conversion treatment for chemically forming an anticorrosion coating have been put into practical use.

As anodizing treatment, for example, Dow17
The anodizing method is standardized by MIL. Dow1
The 7th method uses a treated magnesium-based metal as an anode
Ammonium fluoride (NH_FourHF₂), Sodium dichromate
Mu (Na₂Cr₂O₇・ 2H ₂O), and phosphoric acid, etc.
Electrolyzes in a treatment solution to remove magnesium-based metal on the surface
This is a method of forming an oxide film. Various magnesium alloys
Adhesion of coating film to materials to a certain extent
And coating film corrosion resistance can be imparted by this method
Contains a chromium compound in the treatment liquid, and
The energy cost is a problem.

As the chemical conversion treatment method, a chromate method (for example, Dow22 method) and a stannate treatment method (for example, Dow23 method) are used.
Method) and manganese phosphate treatment method have been put to practical use. Although the Dow22 method can form a coating base film which is sufficiently satisfactory for practical use, it has a problem from the viewpoint of environmental protection that the treatment liquid contains a chromium compound.
Further, the Dow23 method requires high temperature treatment, and has a problem that the coating film corrosion resistance is inferior to that of the chromate-treated Dow22 method. Further, the manganese phosphate treatment method has a problem that it contains a chromium compound, requires high temperature treatment, and is inferior to the chromate method in coating film corrosion resistance.

An object of the present invention is to solve the above-mentioned conventional problems and to treat magnesium or magnesium alloy material with a conventional anodic oxidation method or chromate treatment method with a treatment liquid containing no chromium compound. It is an object of the present invention to provide a pretreatment method for coating capable of stably imparting coating film adhesion and coating film corrosion resistance equal to or higher than the above.

[0007]

In order to solve the above-mentioned conventional problems, the inventors of the present invention used a treatment liquid containing no chromium compound to achieve coating film adhesion equal to or higher than that of anodizing or chromic acid treatment. As a result of extensive studies on a coating pretreatment method capable of imparting coating film corrosion resistance, a zinc phosphate treatment liquid containing a complex fluoride (including complex hydrofluoric acid) was used.
Pretreatment of magnesium or magnesium alloy material while controlling the amount of magnesium ions eluted in the treatment liquid to a predetermined amount or less stabilizes coating adhesion and coating corrosion resistance equal to or better than conventional ones. The present invention has been completed and the present invention has been completed.

That is, the pretreatment method for coating according to the present invention is a method for treating magnesium or magnesium alloy material before coating with a zinc phosphate treatment solution containing a complex fluoride (including complex hydrofluoric acid). , The zinc phosphate treatment is carried out by adding simple fluoride to the zinc phosphate treatment liquid so that the magnesium ions eluted in the zinc phosphate treatment liquid by the treatment become equal to or less than 1 with respect to the complex fluoride. It is characterized by managing the liquid.

For the magnesium ions in the zinc phosphate treatment liquid of the present invention, the measurement liquid is sampled from the zinc phosphate treatment liquid, a simple fluoride is added to the measurement liquid, and then the HF concentration in the measurement liquid is measured. Therefore, it can be measured. This measuring method will be described in detail later. The amount of simple fluoride to be added to the zinc phosphate treatment liquid is determined according to the amount of magnesium ions in the zinc phosphate treatment liquid thus measured. By adding such a simple fluoride, magnesium ion forms an insoluble salt and precipitates out of the system of the zinc phosphate treatment liquid, and the magnesium ion in the zinc phosphate treatment liquid can be controlled to a predetermined amount.

The content of complex fluoride in the zinc phosphate treatment liquid used in the present invention is preferably 0.0 in terms of HF.
It is 5 to 3 g / liter. If it is less than 0.05 g / liter, the fluctuation of the bath composition becomes large, and it may not be possible to stably form a good film. Even if it exceeds 3 g / liter, there is a case where it is economically disadvantageous because there is no further improvement in the special effect. The complex fluoride in the present invention includes complex hydrofluoric acid such as hydrosilicofluoric acid, borofluoric acid, zirconium hydrofluoric acid and titanium hydrofluoric acid, and further includes these alkali metal salts or ammonium salts. Be done. The more preferable content of the complex fluoride is 0.3 to 1.5 g / liter in terms of HF.

The zinc phosphate treatment liquid used in the preferred embodiment according to the present invention contains 0.5 to 25 g of zinc ions.
/ Liter, manganese ion 0.1 to 3 g / liter,
It contains phosphate ions of 5 to 40 g / liter, complex fluoride (including complex hydrofluoric acid) of 0.05 to 3 g / liter (converted to HF), and a film formation accelerator. In such a zinc phosphate treatment liquid, the magnesium ion is controlled so that the equivalent ratio to the complex fluoride is 1 or less as described above, but the specific concentration is 0.5 g / liter. It is preferable to manage as follows.

The preferable zinc ion content in the zinc phosphate treatment liquid used in the present invention is 0.5 to 2.5 g / liter. If it is less than 0.5 g / liter, the coated magnesium material has salt spray resistance (SST) (JIS
-Measurement according to Z-2371). Also 2.
If it exceeds 5 g / liter, the corrosion resistance performance of the coated magnesium material in the complex corrosion cycle test (CCT) decreases. The more preferable content of zinc ion is 0.8 to
It is 1.5 g / liter.

The preferred content of manganese ion in the zinc phosphate treatment liquid used in the present invention is 0.1 to 3 g.
Within the range of / liter. When it is less than 0.1 g / liter, the corrosion resistance performance of the coated magnesium material in the complex corrosion cycle test (CCT) is deteriorated. 3g /
If it exceeds liter, the salt spray resistance (SST) of the coated magnesium deteriorates. In the present invention, the more preferable content of manganese ion is 0.8 to 2 g / liter.

The ratio of manganese ion / zinc ion content in the zinc phosphate treatment liquid used in the present invention is preferably 1/4 to 4. This ratio is 1 /
If it is less than 4, the effect of improving the corrosion resistance of the coated magnesium material in the complex corrosion cycle test (CCT) may be reduced. If this ratio exceeds 4, the effect of improving the salt spray resistance (SST) performance of the coated magnesium material may be reduced. Further, in the present invention, the more preferable content ratio of manganese ion / zinc ion is 0.5 to 2.

The preferred content of phosphate ions in the zinc phosphate treatment liquid used in the present invention is 5 to 40 g / liter. If the content of phosphate ions is less than 5 g / liter, the bath composition varies greatly, and it becomes impossible to stably form a good film. Further, the effect of improving salt spray resistance (SST) performance is reduced. Further, even if the content of phosphate ion exceeds 40 g / liter, no further particular improvement in the effect is achieved, which is economically disadvantageous. The more preferable content of phosphate ion is 10 to 20 g / liter.

As the film formation accelerator in the zinc phosphate treatment liquid used in the present invention, for example, at least one selected from nitrite, hydrogen peroxide, m-nitrobenzene sulfonate, hydroxylamine and the like is used. it can. When nitrite is used alone, 0.01 to
It is preferable to contain 0.5 g / liter. When hydrogen peroxide is used alone, it is preferably contained in an amount of 0.5 to 10 g / liter. When m-nitrobenzene sulfonate is used alone, 0.05 to 5 g /
It is preferable to contain liter. The concentration of hydroxylamine is preferably 0.5 to 2.5 g / liter, more preferably 1.0 to 2.0 g / liter. When the amount of these film formation accelerators is less than the above range, the salt spray resistance (SST) is reduced. Further, even if the content exceeds the above range, it is not economically disadvantageous because the special effect more than that obtained in the above range cannot be obtained.

In addition to the complex fluoride, the treatment liquid of the present invention may contain a simple fluoride such as hydrofluoric acid and an alkali metal salt or ammonium salt thereof within a range that does not impair the effects of the present invention.

In the zinc phosphate treatment liquid used in the present invention, it is preferable that all of nickel ions, cobalt ions and copper ions are less than 0.01 g / liter. When these ions are contained in an amount of 0.01 g / liter or more, the salt spray resistance (SSC) and the corrosion resistance performance in the complex corrosion cycle test (CCT) may deteriorate.

The zinc phosphate treatment liquid used in the present invention preferably contains less than 0.01 g / liter of iron ions. When iron ions are contained in an amount of 0.01 g / liter or more, similarly, the salt spray resistance (SST) and the corrosion resistance performance of the complex corrosion cycle test (CCT) may decrease.

The zinc phosphate treatment liquid used in the present invention may contain nitrate ions of 2 to 20 g / liter in addition to the above main components. Chlorate ion is 0.0
It may contain 5 to 2 g / liter.

The total acidity of the zinc phosphate treatment liquid used in the present invention is preferably 10 to 40 points. The total acidity can be determined by collecting 10 ml of the treatment liquid and titrating with 0.1N caustic soda using phenolphthalein as an indicator. If it is less than 10 points, the salt spray resistance (SST) is lowered, and if it exceeds 40 points, no particular effect can be obtained, which is economically disadvantageous.

The free acidity of the zinc phosphate treatment liquid used in the present invention is preferably 0.5 to 2.0 points. The free acidity of the treatment liquid was obtained by collecting 10 ml of the treatment liquid,
It can be determined by titrating with 0.1N caustic soda using bromphenol blue as an indicator. 0.
If it is less than 4 points, the stability of the treatment liquid is lowered and sludge may be generated. If it exceeds 2.0 points, the salt spray resistance (SST) may decrease.

[0023]

When magnesium or magnesium alloy material is treated with the zinc phosphate treatment solution of the present invention, complex hydrofluoric acid etches the surface of the magnesium-based material.
For example, when H ₂ SiF ₆ is used as the complex hydrofluoric acid, the following reaction occurs. Mg + H ₂ SiF ₆ → MgSiF ₆ + H ₂ ………… (I)

As in the above chemical formula, H ₂ SiF ₆ reacts with magnesium during the zinc phosphate film treatment to form a magnesium salt, and magnesium ions are eluted in the zinc phosphate treatment solution. As a result, the free H ₂ SiF ₆ concentration is reduced by the treatment, and the activity with respect to the magnesium-based material is reduced.

As a method of returning the activity of the zinc phosphate-treated solution having the lowered activity to the original activity, a method of supplying a replenishing solution containing complex hydrofluoric acid is conceivable. The activity is restored by adding simple fluoride instead of supplementing hydrofluoric acid. That is, complex hydrofluoric acid is produced by adding a simple fluoride to the magnesium salt produced by the reaction of complex hydrofluoric acid and magnesium as described above. For example, when HF is added as a simple fluoride, a reaction represented by the following formula occurs. MgSiF ₆ + 2HF → MgF ₂ + H ₂ SiF ₆ (II)

As shown in the above chemical formula, the reaction between the magnesium salt of complex hydrofluoric acid and the simple fluoride causes
Complex hydrofluoric acid is produced. Since MgF ₂ is poorly soluble, it precipitates out of the system. In addition, if an excess amount of simple fluoride is added to the magnesium salt, unreacted simple fluoride will remain, so measure the residual amount and subtract the residual amount from the added amount to obtain the amount of magnesium salt. You can

Also, when acidic sodium fluoride (NaHF ₂ ) is used as the simple fluoride, complex hydrofluoric acid is similarly produced by the reaction represented by the following formula. MgSiF ₆ + NaHF ₂ + H ⁺ → MgF ₂ + H ₂ SiF ₆ + Na ⁺ (III)

The magnesium ions in the zinc phosphate treatment liquid are dissolved in the zinc phosphate treatment liquid in the form of magnesium salt of complex hydrofluoric acid produced by the reaction of complex hydrofluoric acid and magnesium as described above. . Therefore, according to the present invention, by adding a simple fluoride to the zinc phosphate treatment liquid, magnesium ions can be removed to the outside of the system as a precipitate, so that the magnesium ion in the zinc phosphate treatment liquid is adjusted to a predetermined amount. Can be managed.

In the present invention, the magnesium ion in the zinc phosphate treatment liquid is controlled so that the equivalent ratio to the complex fluoride is 1 or less, preferably 0.5 or less.
If the amount of magnesium ions in the zinc phosphate treatment liquid is higher than this, the amount of complex hydrofluoric acid as an active substance in the zinc phosphate treatment liquid will be insufficient, resulting in a chemical conversion film with excellent coating adhesion and corrosion resistance. Can no longer be formed.

[0030] Since at 1 or less in equivalent ratio, if complex fluorides of divalent as SiF ₆ ^2-, are managed so as to be 1 or less in molar ratio, BF ₄ ^- if monovalent as , And the molar ratio is controlled to be 0.5 or less.

In the present invention, the amount of simple fluoride added is
The magnesium ion may be added in a predetermined amount with respect to the complex fluoride. If the amount of the simple fluoride added is too large, the simple fluoride may directly react with the magnesium surface to form a sparingly soluble magnesium fluoride, so do not add a large amount of the simple fluoride. preferable. Therefore, the addition amount of the simple fluoride is preferably 1 or less in an equivalent ratio with respect to the magnesium ions eluted in the treatment liquid.

The amount of the simple fluoride added is, as described above, that the sample liquid to be measured is sampled from the zinc phosphate treatment liquid, and after adding an excess amount of the simple fluoride from the magnesium salt,
Since the amount of magnesium ions in the measured liquid can be measured by measuring the HF concentration of the residual simple fluoride in the measured liquid, the amount of simple fluoride added to the treatment liquid can be determined accordingly. You can decide.

The HF concentration in the liquid to be measured after adding the simple fluoride can be easily measured by, for example, a silicon electrode meter. As the silicon electrode meter, for example, a silicon electrode meter disclosed in Japanese Patent Publication No. 42-17632 can be used. As an apparatus for measuring HF concentration using such a silicon electrode meter, there is, for example, Surf Proguard 101N (trade name: manufactured by Nippon Paint Co., Ltd.). When such a silicon electrode meter is used, it is preferable that the pH is adjusted to 2 or less so that the HF concentration becomes high in the equilibrium formula shown below, that is, the equilibrium proceeds to the right. H ^{+ +} F ^- → HF

PH for controlling the pH of the solution to be measured to 2 or less
As the adjusting agent, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid, and organic acids such as acetic acid, citric acid and tartaric acid can be used. When returning the measured liquid after the measurement to the zinc phosphate treatment liquid in the treatment tank, it is preferable to use phosphoric acid or nitric acid, which is a component of the treatment liquid, as a pH adjuster.

The simple fluorides added to the zinc phosphate treatment solution and the solution to be measured include HF, NaF, NaHF ₂ and K.
F, and the like KHF _2, NH ₄ F and NH ₄ HF _2. Such simple fluorides may be used alone or in combination.

The residual simple fluoride can be easily measured with a silicon electrode meter or the like as described above. For the measurement of the HF concentration by the silicon electrode meter, it is preferable to select a concentration range having a small measurement error and measure the HF concentration.
When N is used, the residual simple fluoride concentration is H
It is preferable to add a predetermined amount of simple fluoride to the liquid to be measured so as to be 200 to 500 ppm in terms of F.

Further, since the simple fluoride which reacts with the magnesium salt of complex hydrofluoric acid in the solution to be measured has twice the equivalent of the magnesium salt in terms of HF, the concentration of complex hydrofluoric acid in the treatment liquid is Also, the concentration of the magnesium salt existing in the treatment liquid after the treatment is roughly estimated from the treatment conditions and the like, and the simple fluoride concentration corresponding to this can be obtained. Therefore, by adding to this concentration the simple fluoride concentration in the range that can be measured by the silicon electrode meter, it is possible to determine the predetermined amount of the simple fluoride added to the liquid to be measured.

The pH of the liquid to be measured when measuring the HF concentration as described above is preferably adjusted to 2 or less. By adjusting the pH to 2 or less, the free HF concentration can be increased as described above, and the measurement error can be reduced. In addition, it is desirable to keep the temperature at the time of measuring the HF concentration constant, for example, 20 to 60 ° C
The measurement temperature can be appropriately set within the range.

In the above, H is used as the complex hydrofluoric acid.
₂ SiF ₆ and HBF ₄ have been described as an example, but the activity in the treatment liquid can be similarly measured for other complex hydrofluoric acid.

The present invention can also be applied to a zinc phosphate treatment liquid containing a small amount of simple fluoride together with complex hydrofluoric acid. That is, a minute amount that cannot be measured by a silicon electrode meter, for example, 50 pp in HF conversion.
The present invention can be applied to a zinc phosphate treatment liquid containing m or less simple fluoride, and the activity of the treatment liquid, that is, the concentrations of simple fluoride and complex hydrofluoric acid can be measured.

According to a preferred embodiment of the present invention, a solution to be measured is sampled from the zinc phosphate processing solution in the zinc phosphate processing solution tank, and the activity in the solution to be measured is determined as described above for the simple fluoride. Is added, and a simple fluoride is added to the zinc phosphate treatment liquid in the zinc phosphate treatment liquid tank based on the evaluation of the activity. By adding a simple fluoride, the magnesium salt of complex hydrofluoric acid in the zinc phosphate treatment liquid is converted into complex hydrofluoric acid, and the activity of the zinc phosphate treatment liquid can be kept within the control standard range.

In the present invention, the simple fluoride added to the zinc phosphate treatment liquid may be added as a replenishing liquid containing only simple fluoride, or as a replenishing liquid mixed with other treatment bath components. May be.

In the present invention, in order to maintain the activity of the treatment liquid, simple fluoride is added instead of supplementing complex hydrofluoric acid. Complex hydrofluoric acid is generated in the system by adding a simple fluoride, and the concentration thereof is set within a predetermined range to maintain the activity. Therefore, the treatment liquid can be economically used for a long period of time without complicating the composition of the treatment liquid. However, the present invention does not prevent replenishment of a replenisher containing complex hydrofluoric acid, and if the magnesium ion concentration is controlled by the addition of simple fluoride, the complex hydrogen fluoride is added. Acid may be replenished as a replenisher.

In the present invention, the treatment temperature for treatment with the zinc phosphate treatment liquid can be appropriately selected within the range of room temperature (20 ° C.) to 70 ° C. In the present invention, the treatment time with the zinc phosphate treatment liquid is not particularly limited, and is, for example, 10 seconds to 10 minutes, preferably 1 to 2 minutes.

In the present invention, as the method of treating with the zinc phosphate treating solution, treatment methods such as dipping treatment and spraying treatment can be adopted. The magnesium and magnesium alloy materials to be pretreated by coating in the present invention preferably have a low content of iron, nickel, and copper, and have an iron content of 0.004%.
Less, less than 0.001% nickel, and less than 0.015% copper.

[0046]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. (1) Metal to be treated: Magnesium material AZ91D (AS
TM standard, Fe content less than 0.004%, Ni content less than 0.001%, Cu content less than 0.015%; shot blast material using glass beads) was used.

(2) Zinc phosphate treatment liquid: shown in Tables 1 and 2.
The composition used was Other ingredients other than those shown in Table 1
As a PO_Four ³-= 15.0 g / liter, NO₃ ^-
= 5.0 g / liter, NO ₂ ^-= 0.07 g / lit
The total acidity is 21 and the free acidity is 1.0
It is a point. However, in Comparative Example 3, processing by the Dow22 method
The liquid was used. The treatment liquid composition is K⁺1.23 g / lit
Le, Cr₂O₇ ²-130.48 g / l, MnO_Four
^-3.77 g / liter, SO_Four ²-1.00 g / lit
It's Tor.

In Comparative Example 2, a treatment liquid containing no complex fluoride was used. (3) Treatment process: Degreasing → Washing → Surface adjustment → Chemical conversion → Washing →
It was treated according to the steps of washing with pure water, drying, and painting.

(4) Each treatment condition: (a) Degreasing; using an alkaline degreasing agent ("Surf Cleaner 53" 2% by weight aqueous solution manufactured by Nippon Paint Co., Ltd.),
Immersion treatment is performed at 40 to 45 ° C. for 2 minutes. The bath control at this time was performed using alkalinity (0.1 ml of 0.1 N-HCl required for neutralization of 10 ml of the bath using bromphenol blue as an indicator).
1) was kept at the initial value. The surf cleaner 53 was used as a replenishing agent.

(B) Washing with water; using tap water, at room temperature for 15
Rinse with spray water for 2 seconds. (C) Surface conditioning: A surface conditioning agent ("Surffine 5N-8" manufactured by Nippon Paint Co., Ltd., 0.1% by weight concentration aqueous solution) is used, and immersion treatment is performed at room temperature for 20 seconds. The bath control at this time was performed by supplementing with Surffine 5N-8 to maintain the alkalinity.

(D) Chemical conversion: Using the zinc phosphate treatment solutions having the compositions shown in Tables 1 and 2, immersion treatment is performed at 40 ° C. for 2 minutes. The bath was controlled by the concentration of each ionic composition and the free acidity in the zinc phosphate treatment solution (10 ml of the bath had a pH of 3.6.
It was carried out by maintaining the initial value of 0.1N-NaOH (ml number) required until. As a replenishing agent, Zn ion, PO ₄ ion, Mn ion and NO ₃
Replenishing the concentrated treatment liquid A for supplementation containing zinc white, phosphoric acid, manganese carbonate and nitric acid to maintain each concentration of ions, and supplementation containing sodium nitrite for maintaining the NO ₂ ion concentration The concentrated treatment liquid B was replenished.

The magnesium ions eluted in the zinc phosphate treatment solution were analyzed as follows. Example 1 Control was carried out so that the equivalent ratio of magnesium ion to SiF ₆ ²⁻ ion in the treatment liquid was about 0.3. A processing load of 0.1 for measuring magnesium ions in the processing liquid.
A sample solution to be measured is collected every m ² / liter, and 400 ppm of HF equivalent of sodium acid fluoride is added to the sample solution to be measured.
Then, 2 ml of 50% sulfuric acid was added per 100 ml, and the electrolytic current value was measured by Surf Proguard 101N. The electrolytic current value was converted into the HF concentration by the calibration curve of the electrolytic current value and the HF concentration measured in advance shown in FIG. Since the magnesium ion concentration dissolved in the treatment liquid is measured from the obtained HF concentration conversion value, Mg ²⁺ / SiF
_The replenisher C containing sodium acid fluoride (NaHF ₂ ) was added to the treatment liquid so that the equivalent ratio of ₆ ²⁻ would be the above set value.

Regarding the control of magnesium ion concentration,
A specific description will be given with an example after 0.1 m ² / liter treatment. The current electrolysis value by SurfProguard is 90μ when 400 ppm of HF equivalent of sodium acid fluoride is added to the measured liquid collected before processing the magnesium material.
It was A. This current electrolysis value corresponds to an HF-converted concentration of 400 ppm, as is clear from the calibration curve shown in FIG. The current electrolysis value after adding 400 ppm of sodium acid fluoride in terms of HF to the liquid to be measured collected after the treatment with 0.1 m ² / liter was 20 μA. From the calibration curve shown in FIG. 1, it can be seen that the HF-converted concentration of the simple fluoride remaining in the measured liquid is 250 ppm. Therefore, the amount of simple fluoride consumed by the reaction with magnesium ions is 150 ppm. Mg = 24.3
Since HF = 20, Mg is divalent, and HF is monovalent, the magnesium ion concentration in the treatment liquid is 15
It can be seen that 0 ppm × 24.3 / (20 × 2) = 91 ppm, that is, about 0.09 g / liter.

SiF ₆ of magnesium ion in the treatment liquid
^{In order} to make the equivalence ratio (Mg ²⁺ / SiF ₆ ²⁻ ) to ^{2 -} ions approximately 0.3, SiF ₆ = 142
Since F ₆ is divalent, 1.00 × 24.3 / 142 ×
It is necessary to control the magnesium ion so that the concentration becomes 0.3 = 0.05 (g / liter). Therefore, the magnesium ion concentration is 0.09-0.05 = 0.04.
It is necessary to add simple fluoride so as to reduce (g / l). Therefore, 0.04 x (20 x 2) /
It can be seen that it is necessary to add the simple fluoride corresponding to the HF equivalent concentration of 24.3 = 0.066 (g / liter). Therefore, sodium HF is added to the treatment liquid to remove HF.
The amount added was 0.066 g / liter.

The treatment liquid composition shown in Table 1 is the value after the replenisher C is added in this way. As described above,
Even after the treatment of 0.2 m ² / l and after the treatment of 0.3 m ² / l, the magnesium ion in the treatment liquid was measured and the replenisher C was added to the treatment liquid to control the magnesium ion concentration in the treatment liquid. did.

Example 2 The procedure of Example 1 was repeated, except that the equivalent ratio of Mg ²⁺ / SiF ₆ ²⁻ was controlled to be about 0.8.

Comparative Example 1 Using the same treatment liquid as in Examples 1 and 2, the treatment was carried out without adding the replenisher C for sodium acid fluoride, that is, without controlling the magnesium ion.

(E) Washing with water; using tap water, at room temperature for 15
Rinse with spray water for 2 seconds. (F) Rinse with pure water: Using ion-exchanged water, wash with spray water for 15 seconds at room temperature. (G) Drying: Dry with hot air at 80 ° C. for 10 minutes. (H) Coating; a cationic electrodeposition coating (“Power Top U-1000 Dark Gray” manufactured by Nippon Paint Co., Ltd.) with a film thickness of 2
Electrodeposition coating is performed so as to have a thickness of 5 μm, and baking is performed at 175 ° C. for 25 minutes. The following performance tests were carried out on the obtained electrodeposition coating film.

(5) Performance test: (a) Adhesion test; the coated plate was immersed in deionized water at 50 ° C. for 10
After soaking for a day, it was rubbed with 2 mm intervals (100 mm).
Individual pieces) were formed with a sharp cutter, and an adhesive tape was attached to each surface thereof, and then these pieces were peeled off to count the number of scoring films remaining on the coated plate. (B) Salt spray test (JIS-Z-2371): A cross cut was put on a coated plate, and 5% salt water was continuously sprayed for 500 hours, and then the maximum corrosion width (one side) from the cut portion was measured. (C) Composite corrosion test: A cross cut was put on a coated plate, and salt spray (JIS-Z-2371, 24 hours) → wetting test (temperature 40 ° C., relative humidity 85% in atmosphere for 120 hours) → indoors ( For 24 hours, one cycle was repeated four times, and the maximum corrosion width (one side) from the cut portion was measured.

(6) Test results As shown in Tables 1 and 2.

[0061]

[Table 1]

[0062]

[Table 2]

As is clear from Tables 1 and 2, according to the present invention, by controlling the magnesium ions eluted in the treatment liquid so that the equivalent ratio to the complex fluoride is 1 or less, the Dow22 It is possible to impart excellent coating film adhesion and coating film corrosion resistance equal to or higher than those of the method (chromate method).

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a simple fluoride concentration and an electrolytic current value of a silicon electrode meter.

Claims (9)

[Claims] 1. A method of treating magnesium or magnesium alloy material before coating with a zinc phosphate treatment liquid containing complex fluoride (including complex hydrofluoric acid), wherein the zinc phosphate is treated. A simple fluoride is added to the zinc phosphate treatment liquid so that the magnesium ions eluted into the treatment liquid become 1 or less in an equivalent ratio to the complex fluoride, and magnesium ions are added to the system of the zinc phosphate treatment liquid. A pretreatment method for coating a magnesium or magnesium alloy material, which comprises controlling the zinc phosphate treatment solution by precipitating it outside. 2. The pretreatment method for coating magnesium or magnesium alloy material according to claim 1, wherein the content of complex fluoride in the zinc phosphate treatment liquid is 0.05 to 3 g / liter in terms of HF. 3. The zinc phosphate treatment liquid is zinc ion.
The composition according to claim 1, which contains 5 to 25 g / liter, manganese ion 0.1 to 3 / liter, phosphate ion 5 to 40 g / liter, complex fluoride 0.05 to 3 g / liter (converted to HF), and a film formation accelerator. Pretreatment method for coating magnesium or magnesium alloy material. 4. The pretreatment method for coating a magnesium or magnesium alloy material according to claim 1, wherein the zinc phosphate treatment liquid contains 0.5 g / liter or less of magnesium. 5. The magnesium ion in the measured liquid is obtained by collecting the measured liquid from the zinc phosphate treatment liquid, adding simple fluoride to the measured liquid, and measuring the HF concentration in the measured liquid. The method for pre-coating magnesium or magnesium alloy material according to any one of claims 1 to 4, wherein the amount of simple fluoride to be added to the zinc phosphate treatment liquid is determined. 6. The pretreatment method for coating magnesium or magnesium alloy material according to claim 5, wherein the HF concentration in the liquid to be measured is measured with a silicon electrode meter. 7. The zinc phosphate treatment liquid contains 0.05% of any of nickel ions, cobalt ions and copper ions.
The pretreatment method for coating magnesium or magnesium alloy material according to any one of claims 1 to 6, which is a zinc phosphate treatment liquid having a concentration of less than 1 g / liter. 8. The film formation accelerator is nitrite ion 0.0.
1 to 0.5 g / liter, hydrogen peroxide 0.5 to 10 g /
Liter, m-nitrobenzene sulfonate ion 0.0
5-5 g / liter, and hydroxylamine 0.5-
The pretreatment method for coating magnesium or magnesium alloy material according to any one of claims 3 to 7, which is at least one selected from 2.5 g / liter. 9. The iron content of the magnesium or magnesium alloy material is less than 0.004%, the nickel content is less than 0.001%, and the copper content is less than 0.015%. 2. A method of pretreatment for coating magnesium or a magnesium alloy material according to item 1.