JPS6196074A - Chemical conversion treatment of product consisting of combined aluminum material and steel material - Google Patents

Abstract

PURPOSE:To improve the adhesion of a paint film to an Al material by chromating the Al material, combining the chromated Al material with a steel material, and subjecting them to chemical conversion treatment. CONSTITUTION:When a film is formed on the body of an automobile or the like before coating, an Al material work is washed and chromated with a treating soln. contg. chromic acid. The chromated Al material work is combined with a steel material work and subjected to chemical conversion treatment with a soln. for chemical conversion treatment to form a zinc phosphate film. A paint film having high adhesion can be formed on the Al material.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for chemical conversion treatment of a product made of a combination of aluminum and steel.

[Prior art]

Conventionally, when a workpiece made of a steel plate is subjected to electrodeposition coating, the workpiece is first chemically treated with a fluorine-containing chemical treatment liquid, and then the above-mentioned coating is applied. This is because the above chemical conversion treatment forms a zinc phosphate coating on the surface of the steel sheet to improve the antirust effect and the adhesion of the coating.

On the other hand, when painting workpieces made of aluminum, the workpiece is immersed in a treatment solution containing chromic acid for chromate treatment, which forms a chromate film on the surface of the workpiece and This is to improve the adhesion of the coating film as in the case of .

By the way, some workpieces, such as car bodies, are made by combining a steel layer with an aluminum layer, and when painting a product made of such a combination, conventionally, the steel plate workpiece and the aluminum material workpiece are separately coated. A coating was formed on the surface of the material, and then the two were combined and painted.

However, among the above-mentioned combined products, it is difficult to combine both workpieces after the above-mentioned film formation treatment due to the painting process.In such cases, both workpieces are first combined and then chromate treatment is performed. It is conceivable to sequentially perform chemical conversion treatment to form a film, but doing so would not only be uneconomical as unnecessary chromate treatment would also be applied to the steel plate workpiece, but would also reduce the size of the combined product. A chromate treatment device is required depending on the situation, and the problem arises that the entire device becomes large-scale. Also,
On the other hand, in order to avoid this problem with the chromate treatment equipment, it may be possible to chemically treat the above combination product without chromate treatment, but if this is done, the adhesion of the coating film to the aluminum workpiece will decrease. A problem arises.

[Purpose of the invention]

The present invention has been made in the above-mentioned conventional situation, and is a chemical treatment method for products combining aluminum and steel materials that can improve the adhesion of coatings on aluminum workpieces and steel workpieces without increasing the size of the equipment. The purpose is to provide a processing method.

[Structure of the invention]

The inventor has discovered that when aluminum material is subjected to chemical conversion treatment, ZnF
e (PO4) A film such as 24H20 is formed, and this film inhibits the adhesion of the paint film, but if the ANO-MI material is chromate treated, the above film will remain even after chemical conversion treatment. The present invention has been made by discovering the point that the aluminum material is not formed.That is, the present invention is a chemical conversion treatment method for a product in which aluminum and steel are combined, in which the aluminum material is combined with the steel material after being subjected to chromate treatment, and then the aluminum material is combined with the steel material, and then the This allows the combination product to undergo chemical conversion treatment without forming a film on the aluminum material that inhibits the adhesion of the coating film.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a process diagram for explaining one embodiment of the present invention, in which 1 is a first press step for press-forming, for example, a car body using a steel plate, and 2 is a process diagram for press-forming, for example, a bonnet using an aluminum plate. 3 is a chromate treatment process for chromate-treating the bonnet; 4 is an aluminum plate in which the steel plate car body from the first press process 1 has been subjected to the chromate treatment; 5 is an assembly process for assembling the bonnet; 5 is a chemical conversion treatment process for applying a chemical conversion treatment to the car body to which the bonnet has been assembled; 6 is a painting process for painting the car body and bonnet that have been subjected to the 6 chemical conversion treatments. It is.

FIG. 2 shows details of the chromate treatment step 3. In the chromate treatment, first, degreasing 3a is performed with a 1-3% solution of sodium phosphate and sodium silicate at 50°C, followed by water washing 3b. Neutralization 3C is carried out with deoxydine,
Further, after water washing 3d, chromic acid treatment 3e is performed. This chromic acid treatment 3e includes chromic acid (Cr03) and hydrogen fluoride (HF).

and potassium ferricyanide (K5 Fe (CN) 6
) in tHtH. After this chromic acid treatment 3e, water washing 3f, hot water washing 3g, and drying 3h are performed, thereby completing the chromate treatment step 3.

FIG. 3 shows details of the chemical conversion treatment step 5. In the chemical conversion treatment, after hot water washing 5a, degreasing step 3 of the chromate treatment step 3 is performed.
Degreasing 5b is performed using the same treatment solution as in a, followed by water washing 5c, surface conditioning 5d in the same manner as in neutralization 3C, and further fluorine-based zinc phosphate solution (fluoric acid, nitrate, chloric acid, etc.). Zinc phosphate treatment 5 immersed in
After the zinc phosphate treatment 5e, washing with water 5f and drying 5g are performed, thereby completing the chemical conversion treatment step 5.

FIG. 4 shows the details of the above-mentioned painting process 6. In this painting, first, an undercoat 6a is applied mainly for the purpose of rust prevention by cationic electrodeposition using an epoxy resin paint with the product as a cathode. Next, an intermediate coat 6b is applied by electrostatic painting using a melamine alkyd resin paint, mainly to fill in the pinholes and unevenness of the undercoat.Furthermore, in almost the same manner as this intermediate coat, the main coating is to give a beautiful appearance and to improve durability against the environment. A top coat 6C is applied to improve the quality.

In this way, in the method of this embodiment, the bonnet, which is an aluminum workpiece, is first subjected to chromate treatment, and then this bonnet is attached to the car body, which is a steel workpiece, and the chemical conversion treatment is applied to both, so that the surface of the bonnet is Chromic acid film (C) Fe (CN) 6 ・Cr(OH) 3 ・H
2CrO4・4A1202・8H20) is formed,
This film prevents the formation of a film (Zn
The formation of Fe (PO4) 2 .4H20) can be prevented, and the adhesion of the coating film to the bonnet can be prevented from decreasing. Also, since only the bonnet was treated with chromate, the size of the chromate treatment equipment was not increased (Also, since the car body and bonnet were assembled before the chemical treatment, this assembly work was difficult). It will never happen.

Next, an adhesion test of the coating film formed by the method of the above example will be explained.

This adhesion test shows that the adhesion of a paint film applied to aluminum after chromate treatment and then chemical conversion treatment is greater than the adhesion force when applied only to chemical conversion treatment without chromate treatment. This is a test to confirm.

(I) Pre-treatment and coating conditions (1) Pre-treatment ■Degreasing...PHII~1 consisting of silicate and phosphate
2.2 in a silicate type alkaline degreaser bath at 45°C.
Soaked for minutes.

■Chemical conversion treatment: The fluorine thread was immersed in a zinc sulfate solution bath at 45°C for 3 minutes.

■Chromate treatment: chromic acid, hydrogen fluoride.

Is chromium 100■/d or 80■/n in the potassium ferricyanide solution bath? Soaked for adhesion time.

(2) Painting ■Undercoat...Cationic electrodeposition, film thickness 2oμm ■Intermediate coating...
Spray melamine paint, film thickness 35μm ■Top coat...
Solid paint spray, film thickness 35 μm (II) Test method: Those subjected to only the above chemical conversion treatment, those subjected to chemical conversion treatment after chromate treatment (chromium amount 100 / rrr),
Test specimens A and B were subjected to chemical conversion treatment after chromate treatment (chromium content: 80 μ/rrf).

C, and each test piece A, B, C was soaked in 50"C (7) hot water 2
After immersion for 40 hours, a second eye test was conducted, and the adhesion of the coating film was evaluated based on the coating film residual rate in this case.

Here, in the cross-cut test, 100 cross-cuts are made by making knife scratches in the vertical and horizontal directions at 2-fi intervals on the above test piece, and Ceb tape is pasted on this, and when this is peeled off, This is a test to see how many of the 100 squares remain on the test piece, and of course the greater the number of the remaining squares, the higher the adhesion.

(III) Test Results Table 1 As is clear from Table 1 above, when only chemical conversion treatment was performed, the coating film survival rate was 50%, whereas when chemical conversion treatment was performed after chromate treatment, The coating film survival rate was 100% even for the test piece with a chromium content of 100%, and it can be seen that the adhesion of the coating film was greatly improved when the chemical conversion treatment was performed after the chromate treatment.

〔Effect of the invention〕

As described above, according to the chemical conversion treatment method for a product in which aluminum and steel materials are combined according to the present invention, the aluminum material is chromate-treated and then combined with the steel material, and then both are subjected to chemical conversion treatment. This has the effect of preventing the formation of a film on aluminum material that is harmful to the adhesion of the paint film, and greatly improving the adhesion of the paint film to the aluminum material.

[Brief explanation of the drawing]

Figure 1 is a process diagram of a chemical conversion treatment method for a product combining aluminum and steel materials according to an embodiment of the present invention, Figure 2 is a detailed process diagram of the chromate treatment part, and Figure 3 is a process diagram of the chemical conversion treatment part. Detailed process diagram, Figure 4 is a detailed process diagram of the painted part. 3... Chromate treatment process, 4... Assembly process, 5...
...Chemical conversion treatment process. Patent applicant: Mazda Motor Corporation agent, patent attorney Ken Hayase - Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] (1) A method of coating a product made of aluminum and steel before painting, in which the aluminum is degreased, washed with water, and then chromated with a treatment solution containing chromic acid, and the chromate-treated aluminum is A method for chemical conversion treatment of a product in which aluminum and steel are combined, characterized in that the combined product is chemically treated with a chemical conversion treatment liquid so that a zinc phosphate film is formed on the steel.