JPH0892773A - Production of alloy material excellent in zinc phosphate processability and formability - Google Patents

Abstract

PURPOSE: To obtain a magnesium-contg. aluminum alloy material excellent in zinc phosphate processability and formability by treating the oxide film layer or surface layer so that a specified mass of the oxide film is dissolved off. CONSTITUTION: An Al alloy material contg. >=0.4 mass% Mg and with the oxide film consisting essentially of MgO formed on its surface is treated to dissolve off the surface layer directly below the oxide film. In this case, the material is treated in an inorg. acid or in an acidic soln. consisting essentially of the inorg. acid, and the mass of the formed oxide film is measured. The oxide film layer or surface layer is treated based on the dissolution rate of the oxide film in the acidic soln. in the previously obtained respective treating conditions so that a specified mass of the oxide film is dissolved off. The treatment is carried out under conditions where the oxide film or Al alloy material having a mass of 0.8 to 1.5 times that of the oxide film is dissolved off. Consequently, a material appropriate as the Al alloy sheet for an automobile with press forming and zinc phosphate processing as the process before coating is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum alloy material which is excellent in zinc phosphate treatment and moldability, and more particularly to applications such as coating after surface treatment by zinc phosphate treatment, especially automobile body. TECHNICAL FIELD The present invention relates to a method for producing a magnesium-containing aluminum alloy material having excellent zinc phosphate processability and moldability, which is suitable as a working material.

[0002]

2. Description of the Related Art In recent years, aluminum alloy sheets have been increasingly used for automobile bodies instead of conventional steel sheets and galvanized steel sheets for the purpose of reducing the weight of automobile bodies. Generally, in the manufacture of automobile bodies, after press forming and joining materials,
It is carried out by a process of applying zinc phosphate treatment as a coating base treatment and coating.

As an aluminum alloy sheet for automobile bodies, 0.4% is required because of its characteristics such as strength, corrosion resistance and formability.
Plate materials of 5000 series or 6000 series aluminum alloys containing about 6.5% Mg are often used. However, the aluminum alloy plate containing these Mg does not have Mg on the surface during the annealing treatment performed at the final stage of the manufacturing process.
There is a problem that an oxide film mainly containing O is formed, and when the above zinc phosphate treatment is applied, the oxide film layer hinders the formation of a uniform zinc phosphate film and deteriorates the film performance after coating. .

As a means for eliminating this problem and improving the uniformity of the zinc phosphate coating, the aluminum alloy plate having the oxide coating is treated with an inorganic acid or an acidic solution based on the inorganic acid before press forming. A method of removing the oxide film on the surface has been proposed. (Japanese Patent Laid-Open No. 3-140498)

However, when an aluminum alloy plate is treated under the usual treatment conditions of etching a considerable amount of the base metal in an acidic solution, the zinc phosphate coating formation uniformity is improved, but the press formability is reduced. However, there is a problem that cracking occurs under severe molding conditions.

It is possible to dissolve and remove the surface oxide film with an alkaline solution instead of the acidic solution.
When an aluminum alloy plate having an oxide film containing is treated with an alkaline solution, the press formability is reduced less than when treated with an acidic solution, but the uniformity of zinc phosphate film formation tends to fluctuate depending on the processing conditions, resulting in a uniform There is a problem that it is difficult to obtain a stable zinc phosphate film stably.

In order to find a treatment method which improves the zinc phosphate treatability of an Mg-containing aluminum alloy sheet having a heat-oxidized film mainly composed of MgO on the surface in the annealing step and does not lower the formability, In addition, paying attention to the treatment with an acidic solution that easily forms a uniform zinc phosphate film,
A basic study was carried out on the etching characteristics when an aluminum alloy plate containing an O-based oxide film and various amounts of magnesium was treated in an acidic solution.

As a result, it was found that in the acidic solution, the oxide film rich in MgO was preferentially dissolved more quickly than the aluminum alloy base material, and then the aluminum alloy of the base material was slowly dissolved. It has been found that the zinc phosphate processability is improved when the predetermined amount or more is dissolved and removed, and the zinc phosphate film is most uniformly formed when the etching amount becomes equal to the mass of the oxide film.

On the other hand, the formability gradually decreases as the etching amount increases, and it has been found that the MgO-containing oxide film is useful for improving the lubricity in the press forming. It was also found that the press formability was significantly deteriorated when the etching amount exceeded a certain amount.

[0010]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention The present invention has a conventional problem in a method for removing an oxide film from a magnesium-containing aluminum alloy sheet having a heated oxide film mainly containing MgO formed in an annealing process at the final stage of a manufacturing process. In order to solve the problem, it was made on the basis of the findings obtained by the inventors based on the above-mentioned basic examination, and the purpose thereof is excellent in zinc phosphate treatment and having good moldability. It is to provide a method for manufacturing an aluminum alloy material.

[0011]

In order to achieve the above object, a method for producing an aluminum alloy material excellent in zinc phosphate treatment and formability according to the present invention is to form an oxide film mainly containing MgO on the surface. The treated aluminum alloy material containing 0.4% or more of magnesium in an acidic solution consisting of an inorganic acid or an acidic solution containing an inorganic acid as a main component prior to the zinc phosphate treatment to form an oxide film layer,
Or when dissolving and removing the oxide film and the surface layer made of an aluminum alloy material located directly below the oxide film,
Measure the mass of the oxide film formed, and based on the dissolution rate of the oxide film in the acidic solution under each treatment condition obtained in advance, the oxide film layer or surface under the condition that the predetermined oxide film mass is dissolved and removed. The first feature is to treat the layer, and to treat the oxide layer or the surface layer under the condition that the oxide layer having a mass of 0.8 to 1.5 times the mass of the formed oxide layer is dissolved and removed. This is the second feature.

The present invention is applied to aluminum alloys containing 0.4% (mass%) or more of magnesium, for example, 5000 series alloys such as 5182 or 6000 series alloys such as 6009 and 6010. The acidic solution used in the present invention, hydrochloric acid, sulfuric acid, inorganic acids such as phosphoric acid or a single solution of inorganic acids obtained by mixing these, or containing these inorganic acids as the main component, various accelerators, An acidic solution prepared by adding a surfactant or the like can be applied. A solution containing chromic acid forms a passivation film on the surface of the aluminum alloy material and hinders the formation of a zinc phosphate film, so it is preferable to avoid using it.

In the present invention, an oxide film layer mainly composed of MgO formed on the surface of the aluminum alloy material in the above acidic solution, or an oxide film and a surface layer made of an aluminum alloy material located immediately below the oxide film. Is dissolved and removed, the oxide film layer or the surface layer is treated under the condition that a predetermined mass of the oxide film is dissolved and removed. For that purpose, first, the mass of the formed oxide film is measured. The mass of the oxide film is measured, for example, when a sample is taken from an aluminum alloy plate having an oxide film, and the sample is immersed in a mixed solution of phosphoric acid and chromic acid (JIS H 8680, film stripping solution) to remove the oxide film by dissolution. It is carried out by measuring the mass reduction amount of.

Further, each treatment condition in the acidic solution,
For example, the dissolution rate of the oxide film is obtained in advance for each processing condition such as the type of acidic solution, mixing ratio, concentration, processing temperature, and the like. Based on the dissolution rate determined in advance, under the processing conditions used, the etching treatment time is adjusted so that the oxide film having a predetermined mass of the measured and determined mass of the oxide film is dissolved and removed.

It is most ideal to give the aluminum alloy sheet excellent zinc phosphate treatment and formability by making the etching amount equal to the mass of the oxide film and dissolving and removing only the heated oxide film from the aluminum alloy sheet. Target,
In practical use, the dissolution and removal range of the oxide film that can provide good phosphoric acid treatment and moldability is (oxide film mass x 0.8)
~ (Mass of oxide film x 1.5), that is, 0 of the mass of oxide film.
It is in the range of 8 to 1.5 times. If the oxide film is removed in excess of (oxide film mass x 1), that is, after the mass of the oxide film that has been formed has been completely dissolved and removed, the base material will dissolve, but in this case , (Mass of oxide film + mass of dissolved base material) is (mass of oxide film x 1.5) or less, which means that the aluminum alloy material is etched.

When the amount of oxide film removed by etching in an acidic solution is less than (mass of oxide film × 0.8), the moldability is good, but since MgO is too much, uneven treatment is likely to occur in the zinc phosphate treatment. Even if the amount of oxide film removed exceeds (oxide film mass x 1), if the oxide film removal amount exceeds (oxide film mass x 1.5) or less, the MgO-containing oxide film is removed from the surface. Good moldability is maintained because the surface of the material has not been roughened by etching. When the surface oxide film is treated so that it exceeds ((oxide film mass x 1.5)) and is dissolved, the zinc phosphate processability is good, but the formability is poor. It is more preferable to treat under the condition of dissolving and removing the oxide film in the range of (oxide film mass × 0.9) to (oxide film mass × 1.3), and further excellent zinc phosphate treatability under the oxide film removing condition in this range and Moldability is obtained.

[0017]

In the present invention, when a magnesium-containing aluminum alloy material having an oxide film mainly composed of MgO formed on its surface is treated in an acidic solution to dissolve and remove the oxide film, the mass of the oxide film is measured in advance. Since the control is performed so that a predetermined amount of oxide film is dissolved and removed based on the dissolution rate of the oxide film in the acidic solution, the surface layer of the aluminum alloy material containing the oxide film is removed in an appropriate range, and zinc phosphate treatment is performed. It is possible to obtain an aluminum alloy material having excellent properties and formability.

[0018]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Example 1 Annealed plate material (thickness 1.0 mm) of 5000 series aluminum alloy containing Mg: 4.5%, Cu: 0.3% and the balance Al and unavoidable impurities was used as a test material, and a sulfuric acid-based cleaning agent was used. The etching treatment was carried out under conditions corresponding to the dissolution and removal of 0.8 to 1.5 times the mass of the oxide film (80 to 150 mg / m ² ). In addition,
The mass of the oxide film formed by annealing the test material was 100 mg / m ² as a result of measurement from the mass reduction amount when immersed in a phosphoric acid / chromic acid mixed liquid (JIS H 8680). Table 1 shows the processing conditions and the etching amount.

[0019]

[Table 1] << Table Note >> Sulfuric acid A: 2% sulfuric acid + surfactant + accelerator Sulfuric acid B: 2% sulfuric acid alone Etching amount: Etching amount corresponding to the mass of oxide film

After the test material after the etching treatment was washed with water and dried, 1 g / m ² of a commercially available anticorrosion oil (R303P manufactured by Sugimura Chemical Co., Ltd.) was applied to the surface as a low viscosity oil, and a deep drawing test was performed. Then, a bulging test was conducted, and the molding height until cracking was measured to evaluate the moldability. In addition, after applying 0.5 g / m ² of the above-mentioned rust preventive oil to the test material that has been washed with water and dried, a commercially available degreasing agent, surface modifier and zinc phosphate treatment agent (Fine Cleaner manufactured by Nippon Parkerizing Co., Ltd.) L4460,
Preparene 4040 and Palbond L3020) were used, and zinc phosphate treatment was performed under standard conditions to form a 0.8 g / m ² zinc phosphate film, and the uniformity of the film was visually observed and evaluated. Table 2 shows the evaluation results. As shown in Table 2, when treated according to the conditions of the present invention, excellent zinc phosphate treatment and moldability were exhibited. The details of the deep drawing test and the overhanging property test are as follows.

Deep drawing test: Using the apparatus shown in FIG.
A disc with a diameter of 2.5 mm is set as a test material in the die 1, and the test material is pressed by the plate pressing 2 with a plate pressing force of 34 kN, and the shoulder R5
mm, 50 mm diameter cylindrical punch 3, molding speed 2.0 mm / s
And the molding height until cracking is measured. Overhang test: Using the device shown in Fig. 2, set a 120 mm diameter disc as a test material in the die 4, press the test material with the plate pressing 5 with a plate pressing force of 40 kN, and use the spherical punch 6 with the tip R25 mm to Molding was performed at a molding speed of 2.0 mm / s, and the molding height until cracking was measured.

[0022]

[Table 2] 《Table Note》 Deep drawability: ◎ for 11.7 mm or more, ○ for 11.5 mm or more and less than 11.7 mm, × for less than 11.5 mm × Overhanging ability: ◎ for 17.5 mm or more, × for less than 17.5 mm Zinc phosphate coating uniformity: No unevenness is ◎, slightly unevenness is ○, remarkable unevenness is × Overall evaluation: ◎ is very good, ○ is good, and × is bad

Comparative Example 1 5000 series aluminum alloy annealed plate material used in Example 1
A test material was sampled from (thickness 1.0 mm, oxide film mass 100 mg / m ² ) and subjected to etching treatment under the conditions shown in Table 3. The test materials No. 5 and No. 6 were treated with a commercially available alkaline degreasing agent, and the test material No. 7 was not treated at all. Then, each treated 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. Also, wash with water,
The dried test material was treated with zinc phosphate under the same conditions as in Example 1 to form a 0.8 g / m ² zinc phosphate film, and the uniformity of the film was visually observed as in Example 1. . Table 4 shows the evaluation results of the moldability and the zinc phosphate processability.

[0024]

[Table 3] << Table Note >> Etching amount: Etching amount corresponding to the mass of oxide film

[0025]

[Table 4]

As shown in Table 4, test materials No. 1 and No. 2
Since the etching amount was too small, the oxide film was not sufficiently removed by dissolution, and uneven treatment occurred in the zinc phosphate treatment. In the test materials No. 3 and No. 4, the formability was deteriorated because the etching amount was excessive and the aluminum alloy material was removed by dissolution in excess of the predetermined amount. Test material No.5, No.6
Since the sample was treated in an alkaline solution, uneven treatment occurred in the zinc phosphate treatment.

[0027]

As described above, according to the present invention, a magnesium-containing aluminum alloy material excellent in zinc phosphate treatment and moldability can be obtained, and an automobile body using press molding and zinc phosphate treatment as pre-coating steps. It is particularly preferably used as an aluminum alloy plate for use.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing an outline of an apparatus for a deep drawability test for evaluating formability in the present invention.

FIG. 2 is a partial cross-sectional view showing an outline of an apparatus for an overhanging test for evaluating moldability in the present invention.

[Explanation of symbols]

 1 Die 2 Plate holder 3 Cylindrical punch 4 Die 5 Plate holder 6 Spherical punch

Claims (2)

[Claims] 1. An aluminum alloy material containing 0.4% (mass%, the same applies hereinafter) of magnesium having an oxide film mainly composed of MgO formed on the surface thereof is treated with an acid consisting of an inorganic acid prior to zinc phosphate treatment. It is formed when a solution or an acidic solution containing an inorganic acid as a main component is treated to dissolve and remove the oxide film layer or the oxide film and the surface layer made of an aluminum alloy material located immediately below the oxide film. The mass of the oxide film is measured, and the oxide film layer or the surface layer is treated under the condition that the predetermined mass of the oxide film is dissolved and removed based on the dissolution rate of the oxide film in the acidic solution under each treatment condition determined in advance. A method for producing an aluminum alloy material having excellent zinc phosphate treatment property and formability, which is characterized by the above. 2. The mass of the formed oxide film is 0.8 to
The zinc phosphate treatment property and moldability according to claim 1, wherein the oxide film layer or the surface layer is treated under the condition that an oxide film or an aluminum alloy material having a mass of 1.5 times is removed by dissolution. Aluminum alloy material manufacturing method.