JPH06330341A - Pretreatment of magnesium or magnesium alloy material before coating - Google Patents

Abstract

PURPOSE:To impart adhesion and corrosion resistance of a coating film comparable to or higher than those of a film formed by conventional anodic oxidation or chromating while adopting an easy treating method such as dipping or spraying without containing a Cr compd. CONSTITUTION:An Mg or Mg alloy material is pretreated before coating with a zinc phosphate treating soln. contg. 0.5-2.5g/l Zn ions, 0.1-3g/l Mn ions, 5-40g/l phosphate ions, 0.05-3g/l (expressed in terms of HF) fluorine compd. and a film formation accelerator. In the treating soln., Ni ions, Co ions and Cu ions are contained at <0.01g/l concn. each.

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
Method 7 uses a magnesium-based metal-treated product as an anode in a treatment liquid containing acidic ammonium fluoride (NH ₄ HF ₂ ), sodium dichromate (Na ₂ Cr ₂ O ₇ , 2H ₂ O), phosphoric acid, etc. Is used to form an oxide film on the surface of the magnesium-based metal-treated product. By such a method, it is possible to impart a certain degree of coating film adhesion and coating film corrosion resistance to various magnesium alloy materials and the like, but in this method, the treatment liquid contains a chromium compound, and the electric 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 coating pretreatment method capable of imparting coating coating adhesion and coating corrosion resistance that are 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, as a result of pretreatment of a magnesium or magnesium alloy material with a zinc phosphate treatment liquid having a specific composition, a coating equal to or more than the conventional coating can be obtained. The inventors have found that it is possible to obtain film adhesion and coating corrosion resistance, and have completed the present invention.

That is, according to the pretreatment method for coating of the present invention, zinc ion is 0.5 to 2.5 g / liter, manganese ion is 0.1 to 3 g / liter, phosphate ion is 5 to 40 g / liter, and fluorine compound is 0.05 to. A magnesium or magnesium alloy material is treated with a zinc phosphate treatment liquid containing 3 g / liter (converted to HF) and a film formation accelerator, and each of nickel ions, cobalt ions and copper ions is less than 0.01 g / liter. It is characterized by that.

The zinc ion content in the zinc phosphate treatment liquid used in the present invention is 0.5 to 2.5 g / liter. When the amount is less than 0.5 g / liter, the coated magnesium material has salt spray resistance (SST) (JIS-Z-23).
71). On the other hand, if it exceeds 2.5 g / liter, the corrosion resistance performance of the coated magnesium material in the complex corrosion cycle test (CCT) deteriorates. The more preferable content of zinc ion is 0.8 to 1.5 g /
It is a liter.

The content of manganese ion in the zinc phosphate treatment liquid used in the present invention is in the range of 0.1 to 3 g / liter. When it is less than 0.1 g / liter,
Composite corrosion cycle test of painted magnesium material (CC
Corrosion resistance performance in T) decreases. If it exceeds 3 g / liter, the coated magnesium has salt spray resistance (S
ST) decreases. 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 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. Also, the content of phosphate ion is 40 g /
Even if it exceeds the liter, it is economically disadvantageous because there is no further improvement in the effect. The more preferable content of phosphate ion is 10 to 20 g / liter.

The content of the fluorine compound in the zinc phosphate treatment liquid used in the present invention is 0.05 to 3 g / liter in terms of HF. If it is less than 0.05 g / liter, the fluctuation of the bath composition becomes large, and it becomes impossible to stably form a good film. Even if it exceeds 3 g / liter, there is no further improvement in the particular effect, which is economically disadvantageous. As the fluorine compound, for example, hydrofluoric acid, hydrofluoric acid, borohydrofluoric acid, zirconium hydrofluoric acid, titanium hydrofluoric acid, and alkali metal salts or ammonium salts thereof can be used. The more preferable content of the fluorine compound is H
It is 0.3 to 1.5 g / liter in terms of F.

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 and the like can be used. When nitrite is used alone, it is preferably contained in an amount of 0.01 to 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-nitrobenzenesulfonate is used alone, it is preferably contained in an amount of 0.05 to 5 g / liter. When the amount of these film formation accelerators is less than the above range, 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 the zinc phosphate treatment liquid used in the present invention, it is necessary that the nickel ion, cobalt ion and copper ion are all 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) are deteriorated. Further, 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.

In the present invention, the treatment temperature for the 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.

[0021]

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.

However, in Comparative Example 6, magnesium to be treated
As a material, ASTM standard AZ91A (Fe content not specified
However, Ni content is less than 0.01%, Cu content is 0.08%
Less than) shot blast material was used. (2) Acidic phosphate aqueous solution: Use the composition shown in Table 1.
It was In addition, as ingredients other than those shown in Table 1, PO _Four ^3-=
15.0 g / liter, NO₃ ^-= 5.0 g / lit
Le, NO₂ ^-= 0.07 g / liter, total acidity
21 is a point and the free acidity is 1.0 point.

However, in Comparative Example 5, the treatment liquid of the Dow22 method was used. Treatment liquid composition is K ⁺ 1.23 g / liter, C
r ^₂ O ₇ ^2- 130.48g / l, MnO ₄ ^- 3.7
It is 7 g / liter and SO ₄ ^2- 1.00 g / liter. (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.

(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.

(D) Chemical conversion: Using the zinc phosphate treatment solution having the composition shown in Table 1, immersion treatment is carried out at 40 ° C. for 2 minutes. However, Example 3 is immersed at 35 ° C., and Example 4 is immersed for 1 minute.

(E) Rinse with water; use 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: Drying 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 that the thickness becomes 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-237
1); Put a cross cut on the coated plate and add 5% salt water to 500.
After continuing spraying for a time, 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% for 120 hours) → The chamber was left indoors (24 hours) as one cycle and repeated for 4 cycles to measure the maximum corrosion width (one side) from the cut portion. (6) Test results As shown in Tables 1 to 3.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

As can be seen from Tables 1 to 3, the magnesium and magnesium alloy materials pre-treated according to the present invention have excellent coating film adhesion and excellent coating properties in the salt spray test and the complex corrosion test. Shows film corrosion resistance.

[0034]

EFFECTS OF THE INVENTION According to the present invention, the adhesion of the coating film which is equal to or higher than that of the conventional anodizing method or chromate treatment can be obtained by a simple treatment method such as dipping or spraying without containing a chromium compound. And coating film corrosion resistance can be imparted.

According to the present invention, the pretreatment for coating can be performed in a short time without using electric energy and without heating to a high temperature.

Claims (3)

[Claims] 1. A pretreatment method for coating magnesium or magnesium alloy material, which comprises: zinc ion 0.5 to 2.5 g / liter, manganese ion 0.1 to 3 g / liter, phosphate ion 5 to 40 g / liter, fluorine. Compounds 0.05 to 3 g / liter (converted to HF) and a film formation accelerator, and each of nickel ion, cobalt ion and copper ion is 0.01 g /
A method for pretreatment of magnesium or magnesium alloy material, which comprises treating the magnesium or magnesium alloy material before coating with a zinc phosphate treatment liquid of less than 1 liter. 2. The film formation accelerator is nitrite ion 0.0.
1 to 0.5 g / liter, hydrogen peroxide 0.5 to 10 g /
The pretreatment method for coating magnesium or magnesium alloy material according to claim 1, which is at least one selected from liter and m-nitrobenzenesulfonate ion of 0.05 to 5 g / liter. 3. The magnesium or magnesium alloy material according to claim 1, wherein the iron content is less than 0.004%, the nickel content is less than 0.001%, and the copper content is less than 0.015%. Pretreatment method for coating magnesium or magnesium alloy material.