JP2771889B2 - Surface treatment method for aluminum alloy material - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface treatment method for an aluminum alloy material that imparts a surface excellent in zinc phosphate treatment property, and in particular, a zinc phosphate treatment as a pretreatment for coating. In applications (eg, automotive panel materials), excellent zinc phosphate treatability is obtained,
The present invention relates to a surface treatment method for an aluminum alloy material capable of significantly improving coating film performance.

(Prior art) In recent years, aluminum alloys are being used in automobile parts for the purpose of weight reduction. However, in applications where anti-yarn rust resistance is required, such as panel materials, a base material of a normal automobile painting line is used. Although a zinc phosphate treatment, which is a treatment, is performed, a sufficient effect in terms of yarn rust resistance has not been obtained at present with such a base treatment.

That is, Al-Mg-Cu-based alloys are mainly used as aluminum alloy materials for automobile panels. This is because the alloys of the present invention have a higher zinc phosphate content than Al-Si-Mg-based alloys. This is because precipitation is easy to occur and the yarn rust resistance is excellent.

On the other hand, Al-Si-Mg-based alloys have high strength after baking and have excellent properties as automotive panel materials. In fact, they are hardly used in automotive panel applications using zinc phosphate as a base treatment.

For this reason, conventionally, as a surface treatment for accelerating the deposition of zinc phosphate, a method of applying Zn plating to the surface has already been proposed in Japanese Patent Application Laid-Open No. 61-155763, etc. Plating and hot-dip plating are mentioned as examples. In addition, as a method of forming a Zn plating layer on an aluminum alloy surface, for example, chemical displacement plating (zincate) which is usually performed as a base treatment for plating
Is well known. However, since the zincate treatment is performed as a base treatment for plating, the following steps are indispensable to ensure the adhesion of the zincate film.

Alkaline etching → Neutralizing nitric acid → First stage zincate →
Nitric acid peeling → second stage zincate (Washing is required between each step) In addition, since it is performed for the purpose of plating underlayer, the surface activity is high, and corrosion such as discoloration powder blowing easily occurs in the atmosphere. Therefore, for example, when used as a surface treatment of an automobile panel material, the treatment cost increases, and the corrosion resistance of the treated film is hardly sufficient.

(Problems to be Solved by the Invention) Thus, by forming a Zn-based metal film on the surface of an aluminum alloy, the zinc phosphate treatment property can be improved, but the adhesion of the film is insufficient and the corrosion resistance is poor. Is also inadequate. Further, if the two-stage zincate treatment is performed, the adhesion of the film can be improved, but the growth rate of the film is slow, and the treatment process is complicated as described above. Was difficult.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and provides a method for obtaining a surface-treated aluminum alloy material having excellent zinc phosphate treatability and excellent film adhesion, corrosion resistance, etc. at a low cost. It is intended to provide.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have conducted intensive studies on a surface treatment method which is low in cost and has excellent zinc phosphate treatment properties. In a method of precipitating a Zn-based metal having a good quality, a conventional one-stage treatment is performed by adding SiO ₂ to a zincate bath and further adding a specific metal, thereby achieving a same or better than the conventional two-stage treatment. The present inventors have found that a film excellent in film adhesion and film corrosion resistance can be formed, and the present invention has been made here.

That is, the present invention provides 5-25% NaOH and 0.3-2.5%
Contains Zn and 0.3 to 3% of SiO ₂ as essential components.
And a method for surface-treating an aluminum alloy material, characterized by immersing an aluminum alloy in a bath containing 0.05 to 1% of one or two metals of Mn or spraying the bath. is there.

 Hereinafter, the present invention will be described in more detail.

(Operation) As described above, the present invention uses a treatment bath in which a specific amount of SiO ₂ is added to a conventional zincate bath and further a specific metal is added. 2
A film adhesion equal to or higher than that of the step treatment can be obtained, and a film excellent in film corrosion resistance can be formed.

In addition, since a film with excellent adhesion can be obtained without the need for a nitric acid stripping step between the first and second zincates, it is easy to make a multilayer coating of Zn-based metals with different coating compositions. And a film most suitable for the purpose can be formed.
The film forming speed can be significantly improved as compared with the conventional two-step processing.

As the pretreatment of the surface treatment according to the present invention, a method similar to the conventional method can be applied. However, since the adhesion is excellent, sufficient adhesion can be ensured only by washing with an alkaline cleaning agent or nitric acid. Therefore, the productivity of the surface treatment is significantly improved, and the production cost can be significantly reduced.

Next, the reasons for limiting the treatment bath used in the present invention will be described.

[NaOH: 5 to 25%, Zn: 0.3 to 2.5%] NaOH and Zn are indispensable for reacting with aluminum and reducing and depositing Zn on the surface of aluminum. Precipitate
The adhesion of Zn to the aluminum surface is better as the concentration of NaOH is higher. However, on the other hand, the viscosity of the bath is increased, and the amount of the bath to be taken out is increased when performing continuous treatment. Good adhesion is obtained when the concentration of Zn is in the range of 1/5 to 1/20 of the NaOH concentration. The ranges satisfying these were regulated to the ranges of NaOH: 5 to 25% and Zn: 0.3 to 2.5%, respectively.

[SiO ₂ : 0.3 to 3%] SiO ₂ is indispensable for improving the adhesion of Zn deposited on the aluminum surface. When the addition of SiO ₂ is not performed, sufficient adhesion cannot be ensured by the one-step treatment as in the conventional zincate treatment, and two-step treatment is required. Further, since SiO ₂ was simultaneously deposited on the surface layer of the Zn-based metal deposited on the surface and proved to be effective in improving the corrosion resistance of the film, a predetermined amount of SiO ₂ was added.

However, if the added amount of SiO ₂ is less than 0.3%, the improvement of the adhesion of the Zn-based coating becomes insufficient, and if it is added more than 3%, the bad treatment property of phosphoric acid in the next step is undesirably reduced.

As described above, the addition amount of SiO ₂ is specified in the range of 0.3 to 3%, which is effective for improving the adhesion of the Zn-based metal film and the corrosion resistance of the film, and which does not inhibit the zinc phosphate treatment property. .

[One or two of Ni and Mn: 0.05% to 1%] Ni and Mn are precipitated at the same time as Zn, and are effective for improving the adhesion of the film and the performance of the zinc phosphate treated film. But,
If the amount of each addition is less than 0.05%, the effect is insufficient,
On the other hand, if it exceeds 1%, the effect is saturated and the corrosion resistance of the film is lowered, which is not preferable. Therefore, the contents of Ni and Mn are specified in the range of 0.05 to 1%. However, Ni and Mn may be added alone or in combination of two types. In addition, as a method of adding Ni and Mn to the bath, it can be added as a safe chelate in an alkali.

As the surface treatment mode of the present invention, the aluminum alloy material may be immersed in a bath, may be treated by spraying, and may be one-sided treatment or two-sided treatment.

 Other zincate treatment conditions are not particularly limited.

The component system and composition of the aluminum alloy targeted by the present invention are not particularly limited, and Al-Mg-Cu system (5000 system) and Al-Si-Mg system (6000 system) are also possible. Needless to say.

 Hereinafter, examples of the present invention will be described.

(Example) First, a treatment bath having the composition shown in Table 1 was prepared. Also,
A6009 and A5182 aluminum alloy plates were prepared as workpieces.

Example 1 Each aluminum alloy plate was treated at 25 ° C. in a treatment bath shown in Table 1.
After treating for 20 seconds, the weight and adhesion of the film deposited on the surface were evaluated. The result is shown in FIG.

Example 2 For each surface-treated material subjected to the same treatment as in Example 1,
The corrosion resistance in a humid atmosphere was evaluated. Corrosion resistance is 50 ℃ x
After exposure in 85% RH for 10 days, the surface condition was evaluated. Table 2 shows the results.

Example 3 Using each aluminum alloy plate treated in Example 1, zinc phosphate treatment was carried out in a commercially available zinc phosphate bath, and the form and amount of precipitation were investigated. Table 2 shows the results.

Table 2 shows that all of the examples of the present invention are excellent in adhesion and corrosion resistance of the surface film and also excellent in zinc phosphate treatment.

(Effects of the Invention) As described in detail above, according to the present invention, since the coating film has excellent adhesion, good corrosion resistance, and excellent zinc phosphate treatment properties, it can be used for automobile panel materials and the like. When used in the above-mentioned applications, an excellent zinc phosphate coating can be obtained even with the current surface treatment line, a good coating can be expected, and the cost is low, so the effect is remarkable.

Claims (2)

(57) [Claims] (1) 5 to 25% of NaOH and 0.3 to 2.5% of Zn and 0.3%
An aluminum alloy is immersed in a bath containing 浴 3% of SiO ₂ as an essential component and further containing 0.05 to 1% of one or two metals of Ni and Mn, or the bath is sprayed. Surface treatment method for aluminum alloy material. 2. The method according to claim 1, wherein the aluminum alloy is Al-Mg-Cu or Al-Mg-Cu.
The method according to claim 1, wherein the method is a Si-Mg system.