JPH07188956A - Surface treatment of mg-containing aluminum alloy sheet for automobile body - Google Patents

Abstract

PURPOSE:To maintain excellent formability and to improve the uniformity of a zinc phosphate film. CONSTITUTION:The Mg-contg. aluminum alloy sheet for an automobile body is cleaned in an alkali soln. kept at <=pH 12 and having a weak etching property in the surface treatment of the sheet before coating. An alkali degreasing agent kept at pH 9-12 is preferably used. The sheet is most preferably cleaned for 10-120sec. in a weak etching alkali soln. with the etching amt. controlled to <=4g/m<2> when dipped for 300sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a magnesium-containing aluminum alloy sheet for automobile bodies, more specifically, a surface treatment before applying a low-viscosity oil for press molding, and a formability when a low-viscosity oil is applied. The present invention relates to a surface treatment method for a Mg-containing aluminum alloy sheet for automobile bodies, which improves the uniformity of a zinc phosphate coating after press molding without reducing the above.

[0002]

2. Description of the Related Art In recent years, the use of aluminum alloy sheets for automobile body panels has been promoted from the viewpoint of saving resources and energy. When using aluminum alloy sheets as automobile body panels, as with steel sheets that have been conventionally used as automobile body panels, it is necessary to perform coating treatment, so various pretreatment methods suitable for aluminum alloy sheets have been studied. Has been done.

With respect to a body panel made of steel plate, after press molding, a pre-coating process and a coating process such as degreasing treatment-zinc phosphate treatment (chemical conversion coating treatment) -electrodeposition coating-medium / top coating are established. As an aluminum alloy sheet for automobile body panels, 5000 series or 60 series alloys containing, for example, 0.5 to 5.5 mass% of Mg as an alloy component are required in view of characteristics.
A 00 series aluminum alloy plate is used, but its surface is M produced in the annealing treatment at the final stage of the manufacturing process.
Since this aluminum alloy sheet is directly passed through the treatment process of the steel sheet for car body panels because it is covered with a heated oxide film layer mainly composed of gO, the heated oxide film layer interferes with the formation of a uniform zinc phosphate film, resulting in coating. The subsequent coating film performance tends to be insufficient. Therefore, the pretreatment for painting is a problem especially for the body panel made of the aluminum alloy sheet, and the establishment of the treatment process remains to be studied.

For example, after press forming, only a member made of an aluminum alloy plate is subjected to a chromate treatment in a separate step in advance,
Then, a method has been proposed in which it is combined with a steel sheet and passed through a zinc phosphate treatment step. (JP-A-61-96074) According to this method, the chromate film preformed on the aluminum alloy plate fulfills the function of the coating base, so there is no problem in coating film performance, but chromate is used in a separate process. Since the treatment is performed, a great deal of cost is required and there is a drawback that the treatment of chromium-containing wastewater is required. Further, a method of press-molding after preliminarily washing and removing the heated oxide film of the aluminum alloy plate with an acidic solution, and treating with zinc phosphate has also been proposed (JP-A 1-240675, JP-A 3-140498).
However, although this method enables the formation of a uniform zinc phosphate coating, it reduces sliding lubricity when a low-viscosity oil for press molding, which is generally used as rust prevention in press molding, is applied. However, there is a problem that the formability of the material is reduced.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems in the surface treatment of an aluminum alloy plate for an automobile body containing Mg as an alloy component, the present invention applies a cleaning method and a low-viscosity oil. This was made as a result of a multi-faceted study of the relationship between the formability and zinc phosphate treatability, and the purpose was to form a low-viscosity oil in the surface treatment of aluminum alloy sheets for automobile bodies. It is an object of the present invention to provide a surface treatment method for a magnesium-containing aluminum alloy sheet for automobile bodies, which improves the zinc phosphate treatment after press molding without deteriorating the property.

[0006]

The surface treatment method for a Mg-containing aluminum alloy sheet for an automobile body of the present invention to achieve the above object is a low-viscosity oil coating for press-forming a Mg-containing aluminum alloy sheet for an automobile body. In the previous surface treatment, the basic feature of the present invention is to wash the aluminum alloy plate in a weakly etching alkaline solution having a pH of 12 or less, and the pH of the alkaline solution is 9 to 12, and Etching amount when immersed in 300s is 4g
10 / m ² or less using a weakly etching alkaline solution
The second and third features of the configuration of the present invention are that the cleaning treatment is performed for 120 seconds.

The surface treatment method for an aluminum alloy sheet for an automobile body of the present invention comprises a step of cleaning in a weakly etching alkaline solution before applying a low viscosity oil for press forming which is also used for rust prevention during press forming. Processing is an essential requirement. As the alkaline solution, for example, an alkaline degreasing agent containing sodium silicate, sodium phosphate, sodium borate or the like is pH 12 or less, preferably pH 9 to 12
Adjust to use. When the pH is less than 9, the removal of the MgO-containing heated oxide film layer formed on the surface of the Mg-containing aluminum alloy plate becomes insufficient and the uniformity of the zinc phosphate film is deteriorated. When the pH exceeds 12, the etching property becomes strong and the aluminum alloy plate is excessively and non-uniformly etched, and as a result, the uniformity of the zinc phosphate coating is deteriorated.

As the cleaning treatment with the alkaline solution in the present invention, a weak etching property such that the etching amount of the aluminum alloy plate when immersed in the alkaline solution for 300 s is 4 g / m ² or less is obtained. It is most preferable to perform a cleaning treatment for 10 to 120 s using an alkaline solution, and under these limited cleaning conditions, the uniformity of the zinc phosphate film can be reliably ensured without lowering the moldability when a low viscosity oil is applied. Can be improved.

The washed aluminum alloy plate according to the present invention is coated with a low-viscosity oil and press-formed into a predetermined shape,
Perform zinc phosphate treatment. For the aluminum alloy plate molded article after the zinc phosphate treatment, by a further known method,
Electro-deposition coating, intermediate coating, and top coating are applied to form automobile body panels.

[0010]

According to the constitution of the present invention, Mg for automobile bodies is used in a weakly etching alkaline solution having a pH in a specific range.
By cleaning the contained aluminum alloy plate, the oxide film layer mainly composed of MgO formed on the surface of the aluminum alloy plate is removed, and sliding lubricity is maintained even when low viscosity oil is applied during press forming. Maintains the excellent formability of aluminum alloy sheet by imparting surface properties that do not deteriorate, improves the uniformity of zinc phosphate coating, and gives a uniform coating appearance and good coating corrosion resistance in the subsequent coating process .

[0011]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 containing Mg4.5 mass% (hereinafter the same) and Cu0.3%,
A test material was taken from an annealed plate material (thickness 1.0 mm) of 5000 series aluminum alloy consisting of the balance Al and unavoidable impurities,
Each test material was washed in a commercially available alkaline degreaser solution whose pH was adjusted. Table 1 shows the type of alkaline degreasing agent used for cleaning each test material, the pH of the solution, the etching amount when the test material was immersed in the solution for 300 s, and the treatment time.

Then, the test material after the washing treatment was washed with water and dried, and then 1 g / m ² of commercially available rust preventive oil (R303P manufactured by Sugimura Chemical Co., Ltd.) was applied to the surface of the test material as a low-viscosity oil. A drawability test and a bulging test were conducted, and the molding height until cracking was measured to evaluate the moldability. Further, with respect to the test material washed with water and dried, 0.5% of the rust preventive oil was used.
After applying g / m ^2, zinc phosphate treatment is performed under standard conditions using a commercially available degreasing agent, surface conditioner, and zinc phosphate treatment agent (Fine Cleaner L4460, Preparene 4040 and Palbond L3020 manufactured by Nippon Parkerizing Co., Ltd.) hand
A 0.8 g / m ² zinc phosphate film was formed and the uniformity of the film was visually observed and evaluated. Table 2 shows the evaluation results of formability and the observation results of the zinc phosphate coating.

For the deep drawability test, using the apparatus shown in FIG. 1, a test material made of a disk having a diameter of 112.5 mm was set in the die 1, and the test material was pressed by the plate pressing member 2 with a plate pressing force of 34 kN.
A cylindrical punch 3 having a shoulder R of 5 mm and a diameter of 50 mm was used for molding at a molding speed of 2.0 mm / s, and the molding height until cracking was measured. For the bulging test, using the device shown in FIG. 2, a test material made of a disk having a diameter of 120.0 mm was set in the die 4, and the test material was pressed by the plate pressing member 5 with a plate pressing force of 40 kN.
With a spherical punch 6 with a tip R of 25 mm, the molding speed is 2.0 mm
/ S was molded, and the molding height before cracking was measured.

[0014]

[Table 1] << Table Note >> A: Sodium silicate included B: Sodium phosphate, sodium silicate included C: Sodium phosphate,
Sodium borate included D: Sodium phosphate included

[0015]

[Table 2] <Table Note> Formability: Better than untreated material (No. 0) ◎ Same as untreated material ○ Zinc phosphate film: No treatment unevenness ◎ Uniformity with slight treatment unevenness ○ With treatment unevenness ×

As shown in Table 2, each of the test materials that had been subjected to the washing treatment according to the examples of the present invention had a moldability as excellent as or higher than that of the untreated aluminum alloy material. As for the uniformity of the zinc phosphate coating, there are some in which slight processing unevenness is observed, but all are within the allowable range, and a good balance between moldability and conversion coating treatment is shown.

Comparative Example 1 A test material was sampled from an annealed plate material (thickness 1.0 mm) of 5000 series aluminum alloy having the same composition as in Example 1, and among the test materials No. 1 to 3, acid cleaning solution A ( (Containing phosphoric acid)
Among them, No. 4 to 5 were washed in the acidic cleaning liquid B (containing sulfuric acid), and No. 6 to 7 were washed with the alkaline degreasing agent as in Example 1. Nos. 8 to 9 were washed in a commercially available alkaline degreasing agent containing sodium phosphate. The type of solution used to wash the test material,
Table 3 shows the pH, the etching amount when the test material was immersed in the solution for 300 s, and the treatment time.

[0018]

[Table 3]

Then, the washed test material was washed with water and dried, and then a deep drawability test and a bulging test were conducted under the same conditions as in Example 1 to evaluate the formability. Further, the washed and dried test material was subjected to a zinc phosphate film treatment under the same conditions as in Example 1 to form a 0.8 g / m ² zinc phosphate film in the same manner as in Example 1 to improve the uniformity of the film. I observed. Table 4 shows the evaluation results of the formability and the observation results of the uniformity of the zinc phosphate coating.

[0020]

[Table 4] <Table Note> Formability: Better than untreated material (No. 0) ◎ Equal to untreated material ○ Inferior to untreated material × Zinc phosphate coating: No treatment unevenness ◎ Uniformity with slight treatment unevenness ○ Treatment unevenness Yes ×

As shown in Table 4, the test materials Nos. 1 to 5 according to the comparative examples are test materials subjected to acid cleaning with an acid cleaning agent, and all of them are caused by the deterioration of sliding lubricity. Moldability is particularly poor in deep drawability. No. 6 to 7 are test materials that were washed with the alkaline degreasing agent of the present invention, but the treatment time was too short to remove the oxide film layer sufficiently and the zinc phosphate film was not even. It was inferior. No.8 ~ 9 is pH
As a result of the cleaning treatment using an alkaline degreasing agent having a large value and a high etching property, the etching during cleaning was non-uniform and smut was generated, so that the uniformity of the zinc phosphate coating was deteriorated.

[0022]

As described above, according to the present invention, in the surface treatment before applying the low-viscosity oil for press forming of the aluminum alloy plate containing Mg for automobile bodies, the formability when the low-viscosity oil is applied There is provided a cleaning method for improving the uniformity of a zinc phosphate film without reducing the above.

[Brief description of drawings]

FIG. 1 is a sectional view of a deep drawability test apparatus.

FIG. 2 is a cross-sectional view of an overhang tester.

[Explanation of symbols]

 1 Die 2 Plate retainer 3 Punch 4 Die 5 Plate retainer 6 Punch

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Takahiro Koyama 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries, Ltd. (72) Inventor Makoto Yonemitsu 5-11-3 Shimbashi, Minato-ku, Tokyo No. Sumitomo Light Metal Industry Co., Ltd.

Claims (3)

[Claims] 1. A surface treatment before applying a low-viscosity oil for press forming of a Mg-containing aluminum alloy plate for an automobile body,
A surface treatment method for a magnesium-containing aluminum alloy sheet for automobile bodies, comprising: washing the aluminum alloy sheet in a weakly etching alkaline solution having a pH of 12 or less. 2. The surface treatment method for a magnesium-containing aluminum alloy plate for automobile bodies according to claim 1, wherein the alkaline solution has a pH of 9 to 12. 3. The automobile according to claim 1, wherein the aluminum alloy plate is immersed in 300 s for an etching amount of 4 g / m ² or less in a weakly etching alkaline solution and washed for 10 to 120 s. A surface treatment method for a Mg-containing aluminum alloy plate for a vehicle body.