JPH08337882A - Zinc substituting bath for aluminum alloy - Google Patents

Abstract

PURPOSE: To provide a zinc substituting bath used for plating surface preparation at the time of aluminum alloy plating. CONSTITUTION: The zinc substituting bath for aluminum alloy, which contains zinc ion, iron ion, a hydroxide of an alkali metal and an organic phosphonic acid or the salt, is used for surface preparation. As a result, practically sufficient plating adhesion is attained only by a single substituting treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc substitution treatment bath applied in the field of plating aluminum alloy materials such as aluminum-magnesium type, aluminum-silicon type and aluminum-copper type. More specifically, the present invention relates to a zinc substitution treatment bath used as a plating base treatment when plating an aluminum alloy.

[0002]

2. Description of the Related Art Generally, when plating is performed on aluminum alloys, the surface of these alloys is covered with a thick oxide film, and since these alloys have a base surface potential, they are easily oxidized and the surface potential is Since direct plating cannot be performed because of nonuniformity and instability, it is necessary to provide a pretreatment process such as removal of an oxide film and formation of an intermediate layer.

Usually, in order to remove the oxide film and compounds segregated on the surface of the alloy, etching treatment using an alkaline solution and pickling with hydrofluoric acid are carried out, and then zinc or its alloy layer is replaced by an aluminum alloy by a substitution reaction. A zinc substitution treatment for depositing on the surface is performed.

As a zinc substitution treatment bath, a zincate treatment bath in which zinc or zinc white is dissolved in caustic soda is used as a basic composition, and copper, cobalt, iron, nickel, etc. are used as alloy components for eutectoid in the film. Various improved zinc substitution baths (bondal baths) in which one or more of the above metal components are added have been proposed, and considerable ones have been put to practical use.

However, since aluminum alloys are used for various purposes such as high strength, high workability, weight reduction, and wear resistance, the composition thereof is such that silicon, copper, and Nickel, magnesium, zinc,
Many metals are added, and their contents are also different. For this reason, the aluminum alloy greatly differs in crystal structure, uniformity, and chemical reactivity depending on the type of material.

Since the zinc substitution treatment is a technique for forming a film by utilizing the chemical reaction between the material and the bath, it is possible to obtain the same good adhesion to various alloy materials under different conditions. Obtaining a zinc-substituted coating is rather difficult.

For this reason, it is difficult to obtain sufficient plating adhesion by a single treatment even if an improved zinc displacement bath containing alloy components is used. Especially when applied to an aluminum alloy containing a large amount of silicon. In practice, the double zincate treatment (two-step treatment method) in which the formed substitution treatment film was once dissolved and peeled with nitric acid, and then zinc substitution treatment was performed again was essential in practice.

Therefore, the number of steps of the aluminum alloy plating line becomes very large, resulting in a decrease in productivity and an increase in processing cost, which has been a major problem in the aluminum alloy plating technology.

Further, in the case of performing the zinc substitution treatment by the conventional technique, a treatment bath having a composition suitable for the alloy raw material type must be specially prepared, and materials having greatly different compositions are treated in the same bath. It is extremely difficult to do so, and in a general-purpose plating site where various materials are often processed on the same plating line, it has been a cause of impairing productivity and plating quality.

As a means for solving this problem, an improvement of the substitution treatment bath has been proposed, for example, JP-A-63-63.
Japanese Patent No. 317692 discloses a zinc substitution treatment liquid composition for a magnesium alloy containing a pyrophosphate and an acetate, but exhibits a sufficient effect when an aluminum alloy casting material containing a large amount of silicon or an oxide film is thick. It has not been obtained yet that can be applied to the zinc replacement bath for aluminum alloy.

[0011]

DISCLOSURE OF THE INVENTION In the present invention, the zinc substitution treatment of an aluminum alloy, which is a problem of the prior art, requires repeated substitution treatments such as when there are many oxide films and when there are many alloy components. It is an object of the present invention to provide a zinc displacement bath composition that can obtain sufficient plating adhesion even with a single substitution treatment even for aluminum alloy materials, and has a wide range of application to various materials. Is.

[0012]

Means for Solving the Problems Regarding the means for solving the above problems, the present inventor first describes the corrosion potential of a substitution film formed when various alloy components are added to an alkaline zinc substitution bath and the alloy component content. As a result of examining the rate and the plating adhesion, it was found that the substitution film mainly composed of zinc and containing iron was most stable in the plating bath and had excellent plating adhesion.

Further, as a result of detailed examination of the composition of the zinc / iron-based alloy displacement bath, when the aluminum alloy surface is treated with the conventional zincate treatment bath, the oxide film on the surface is not sufficiently removed by the treatment only once. It was also found that this is a cause of a decrease in the adhesion of the zinc substitution coating to the alloy substrate.

Further, by leaching and exfoliating only the zinc displacement plating film from various aluminum alloy materials with 40% nitric acid and observing the morphology of the aluminum alloy surface with an electron microscope, the degree of etching during the formation of the displacement film and the uniformity can be obtained. I also confirmed the sex.

As a result, in the aluminum alloy, the uniformity of the material on the order of micron is not sufficient, and between the corrosion potential of aluminum as the main component in the treatment liquid and the corrosion potential of the alloy components such as silicon and nickel. Due to the large difference, the etching reaction is localized, the oxide film is only partially removed, and the deposited zinc alloy becomes non-uniform, which causes insufficient adhesion. Found out.

Based on these findings, the present inventor has mainly investigated the composition of a replacement liquid for uniformly etching a surface of an aluminum alloy having a non-uniform surface and at the same time obtaining a dense and highly adhesive substitution film. Al-Si alloy material (AC having large potential non-uniformity and uniform etching difficult)
Materials) and other alloy materials.

As a result, by adding an organic phosphonic acid such as 1-hydroxyethylidene-1,1-diphosphonic acid or a salt thereof as an etching agent or a chelating agent to the substitution liquid, oxides or intermetallics on the surface of these aluminum alloys are added. It was newly found that compounds and the like can be rapidly removed, and even if the surface potential of the material is non-uniform, etching can be performed uniformly, and the adhesion of the substitution film and the plating film is greatly improved.

It was also confirmed that when this bath was used for various other alloy materials, the same improvement effect was obtained as compared with the case where the organic phosphonic acid or its salt was not added.

Further, the present inventors have found that the adhesion is further improved by adding an organic carboxylic acid such as gluconic acid or citric acid or a salt thereof as a chelating auxiliary agent for iron ions in the bath, and completed the present invention. It came to do.

That is, according to the present invention, zinc ion, iron ion,
The present invention provides a zinc substitution treatment bath for an aluminum alloy, which comprises an alkali metal hydroxide and an organic phosphonic acid or a salt thereof, which preferably further contains an organic carboxylic acid or a salt thereof. .

The structure of the present invention will be described in detail below. The aluminum alloy of the present invention is an alloy material such as an aluminum-magnesium system, an aluminum-silicon system, and an aluminum-copper system, and is intended for an aluminum alloy plate and an aluminum alloy casting.

In the present invention, zinc ions in the displacement bath are preferably added by mixing and dissolving metallic zinc or zinc oxide together with a caustic solution, an organic phosphonic acid or a salt thereof, but a soluble salt such as zinc sulfate. It is also possible to add in the form of.

The concentration of zinc ions in the displacement bath is 0.3-8.
The concentration range is preferably 0 g / L, more preferably 3 to 30 g / L.

If the concentration is less than 0.3 g / L, the rate of film formation is slow, which is not practical, and if it exceeds 80 g / L, the viscosity of the treatment bath increases and the rinsability deteriorates.

Iron ions in the displacement bath are added as soluble iron salts such as iron sulfate. When an organic carboxylic acid is further added as a chelating auxiliary, iron gluconate, iron citrate, It can also be added in the form of iron tartrate or the like.
These iron salts are preferably added as divalent or trivalent iron salts.

The concentration of iron ion in the treatment bath is 0.1 to 30.
It is preferably in the range of g / L, and 0.5 to 10 g /
The range of L is more preferable, but if this concentration is less than 0.1 g / L, the adhesion of plating is not sufficient, and if it exceeds 30 g / L, iron hydroxide precipitates easily, which is not preferable.

The zinc substitution bath of the present invention must contain an organic phosphonic acid, and the preferred range is 0.02
It is 50 g / L.

As the type of organic phosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid and the like can be used, and particularly 1-hydroxy Ethylidene-1,1-diphosphonic acid is preferable in terms of cost.

By adding these to the bath used in the form of sodium salt or potassium salt, the heat generation during the preparation of the zinc substitution bath can be suppressed.

When the concentration of the organic phosphonic acid is less than 0.02 g / L, the plating adhesion is not sufficient, and when it exceeds 50 g / L, there is a problem in rinsability and economical efficiency, which is not preferable, and a more preferable range is 0. 2 to 20 g / L.

It is necessary that the bath contains an alkali metal hydroxide, and the concentration thereof is preferably 5 to 200 g / L. When these components are in the preferred range, the pH of the bath will be 11-14. Alkali metal hydroxides such as sodium hydroxide and potassium hydroxide are suitable for adjusting the pH to an appropriate range, but of these, sodium hydroxide is the most economical. When the pH is 10 or less, the dissolution effect of the oxide film is not sufficient and the etching becomes nonuniform, so that the adhesiveness is deteriorated, which is not preferable.

Suitable organic carboxylic acids are gluconic acid, tartaric acid, citric acid, succinic acid, and malic acid, or their sodium salts and potassium salts. Among these, gluconic acid, tartaric acid, and sodium salts of citric acid, The potassium salt is particularly suitable. The concentration of organic carboxylic acid is 0.5
~ 50 g / L is preferred.

In addition to the above essential components, depending on the type of aluminum alloy material, the zinc displacement bath of the present invention may further contain metal salts of cobalt, nickel and copper, soluble fluorides such as sodium fluoride as a complexing agent, and polyphosphorus. Acid salt, EDTA
It is also possible to improve the effect by adding such as.

Further, as the treatment condition, it is suitable to immerse in a preferable temperature range of 20 to 40 ° C. for a treatment time of 10 seconds to 2 minutes.

[0035]

The organic phosphonic acid or its salt contained in the zinc displacement treatment bath for aluminum alloys of the present invention stabilizes iron ions and zinc ions in the alkaline region even at a low concentration of less than equimolar to metal ions due to the threshold effect. In addition to being capable of holding, it has a unique property not found in other compounds that rapidly dissolves metal oxides such as aluminum and densifies the precipitated crystals.

Therefore, when the zinc substitution bath of the present invention is used for treatment, the oxide film on the surface of the aluminum alloy material is sufficiently removed and uniform etching is performed, and thereafter a dense zinc alloy film is deposited. Sufficient adhesion can be obtained even by the substitution treatment of. This is the effect achieved only by using the organic phosphonic acid or its salt.

Even if an organic carboxylic acid is used alone, such an effect of improving the adhesiveness cannot be obtained, but due to the chelating effect of iron ions, the adhesiveness is further improved only when it is added together with the organic phosphonic acid. It is thought that.

[0038]

EXAMPLES The contents of the present invention will be described more specifically below with reference to some examples together with comparative examples.

[Sample Aluminum Alloy Material] Table 1 shows the types of aluminum alloys used in the test. Also, vertical 5
An aluminum alloy plate having a thickness of 0 mm, a width of 30 mm, and a thickness of 2 to 5 mm was used.

[Zinc Ion Used] The zinc ion used in the displacement bath is zinc oxide (first-grade reagent). [Iron ion used] The iron ion used in the displacement bath is ferric sulfate (first-grade reagent). [Used alkali metal hydroxide] The alkali metal hydroxide used in the displacement bath is sodium hydroxide (reagent 1
Grade, purity 93%).

[Organic Phosphonic Acid Used] Table 2 shows the kinds of organic phosphonic acid used in the displacement bath. In addition, the organic phosphonic acids shown in Table 2 are (a) to (d) registered trademarks Dequest 2010 and 2 manufactured by Nippon Monsanto Co., Ltd., respectively.
000, 2041 and 2066.

[Organic carboxylic acid used] Table 3 shows the types of organic carboxylic acid used in the displacement bath. As the chemical, a first-grade reagent manufactured by Wako Pure Chemical Industries, Ltd. was used.

[Evaluation Method of Etching Property after Zinc Substitution Treatment] After the coating of the test piece after the zinc substitution treatment was dissolved with 40% nitric acid, the material surface was uniformly etched using an electron microscope. It was confirmed whether or not there was a non-etched portion remained, and that where the entire surface was etched was determined to be uniform.

[Evaluation Method of Film Adhesion After Plating] The film adhesion after plating is determined by shearing the test piece from the center, then inserting the blade of a cutter knife between the film and the material, and forcibly peeling it. The following criteria were used to judge the ease of peeling. Rating Good adhesion ↑ 5: Peeling off with aluminum base when strong force is applied 4: Part is peeled off from plating-base interface when force is applied 3: Peeling from plating-base interface when force is applied 2: Base-plating film interface Easy to peel off from poor ↓ 1: Natural peeling by cutting

Examples 1 to 12 The above-mentioned aluminum test materials were immersed and degreased in an alkaline degreasing liquid for aluminum (registered trademark: Fine Cleaner 315, manufactured by Nippon Parkerizing Co., Ltd.) at 70 ° C. for 2 minutes and then washed with water, and further 30 % Immersion in nitric acid for 30 seconds and then washed with water for 30 seconds were subjected to zinc replacement treatment by immersion in a zinc replacement bath. The zinc substitution treatment in the zinc substitution bath is carried out by using the above-mentioned zinc ions, iron ions, alkali metal hydroxides, organic phosphonic acids and organic carboxylic acids (no organic carboxylic acid is used in Examples 1 and 2). , At a bath temperature of 30 ° C,
The processing time was 30 seconds. Table 4 shows the kinds of materials in the bath, the zinc ion in the bath, the iron ion in the bath, the organic phosphonic acid, the organic carboxylic acid, and the sodium hydroxide in each example. The etching property of the test piece subjected to the zinc substitution treatment was evaluated.

The plating adhesion test sample was subjected to zinc substitution treatment, immediately washed with water, and then subjected to nickel / phosphorus alloy electroplating. The reason why nickel / phosphorus alloy plating is selected as the type of plating film is that this plating has less malleability than nickel plating and adhesion cannot be secured unless a good surface treatment is performed. For nickel / phosphorus alloy electroplating, a bath in which hypophosphorous acid is added to a nickel sulfamate bath is used, and the bath temperature is 57
Plating was performed for 14 minutes at a temperature of 10 ° C. and a current density of 10 A / dm ² . The coating adhesion of the test pieces after plating was evaluated. Table 4 shows the evaluation test results of etching property and film adhesion.
It was shown to.

Comparative Example 1 Treatment was carried out in the same manner as in Example 1 except that iron ions were not used and the raw material species, the amount of zinc ions in the bath, the amount of organic phosphonic acid and the concentration of sodium hydroxide shown in Table 5 were used. I went. The evaluation test results of the etching property and the film adhesion are also shown in Table 5.

Comparative Example 2 Except that the amount of zinc ions in the bath was 0.2 g / L and the amount of iron ions in the bath was 0.05 g / L, which was extremely small, and the amount of organic phosphonic acid was the amount shown in Table 5. The treatment was carried out as in Example 1. The evaluation test results of the etching property and the film adhesion are also shown in Table 5.

Comparative Example 3 Except that the organic carboxylic acid was used and the organic carboxylic acid was used, the material types shown in Table 5, zinc ion content in the bath, iron ion content in the bath, and organic carboxylic acid content were used. The same treatment as in Example 1 was carried out. The evaluation test results of the etching property and the film adhesion are also shown in Table 5.

The following can be said from Examples 1 to 12 and Comparative Examples 1 to 3. In Examples 1 to 12, the etching property is uniform and the film adhesion is good. Examples 1-2 use only organic phosphonic acid,
Further, in Examples 3 to 12, both organic phosphonic acid and organic carboxylic acid are used, but the film adhesion is
Examples 3 to 12 are slightly better than Example 2. It is speculated that this is due to the combined effect of the organic carboxylic acids. In Comparative Example 1 in which iron ions were not used, the etching property was non-uniform and the film adhesion was poor. Comparative Example 2 in which the amount of zinc ions in the bath is extremely small also has non-uniform etching properties and poor film adhesion. Comparative Example 3, which does not use the organic phosphonic acid but uses only the organic carboxylic acid, has non-uniform etching properties and poor film adhesion. This indicates that the use of the organic carboxylic acid alone without the use of the organic phosphonic acid has no effect.

[0051]

As described above, by using the zinc substitution treatment bath for aluminum alloy of the present invention, even in the case of heterogeneous aluminum alloy material containing alloy components such as Si,
It is possible to obtain practically sufficient plating adhesion by a replacement treatment only once, and it is possible to support a wide range of aluminum alloy species. Therefore, it is possible to exert the effect of shortening the process, improving the plating quality and stabilizing the plating at the site of plating the aluminum alloy material.

[0052]

[Table 1]

[0053]

[Table 2]

[0054]

[Table 3]

[0055]

[Table 4]

[0056]

[Table 5]

Claims (2)

[Claims] 1. A zinc substitution treatment bath for an aluminum alloy, which contains zinc ions, iron ions, a hydroxide of an alkali metal, and an organic phosphonic acid or a salt thereof. 2. The zinc replacement treatment bath for an aluminum alloy according to claim 1, wherein the treatment bath further contains an organic carboxylic acid or a salt thereof.