JPH0413894A - Aluminum alloy material to be coated for automobile and its production - Google Patents

Abstract

PURPOSE:To produce an Al alloy material to be coated for an automobile having superior adhesion to a resin coating film by forming an oxide film of a specified thickness on an Al alloy material by AC electrolysis in an alkaline aq. soln. under specified conditions. CONSTITUTION:An Al alloy material is subjected to AC electrolysis in an alkaline aq. soln. of pH 9-13 contg. sodium phosphate, sodium pyrophosphate, etc., at 35-85 deg.C under the conditions of 4-50 A/dm<2> current density and 80 C/dm<2> quantity of electricity to form an oxide film of 500-5,000Angstrom thickness on the surface of the Al alloy material. This oxide film has a very porous structure and a clean surface and an Al alloy material to be coated for an automobile having remarkably improved adhesion to a resin coating film is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an aluminum alloy coating material, and in particular, when an aluminum alloy material is used as an aluminum alloy coating material for automobiles, the treatment bath is contaminated during zinc phosphate treatment. Aluminum alloy coating materials and their manufacture that have been treated with a surface that does not cause damage or fatigue, have excellent adhesion between the aluminum alloy material and the resin coating after baking, and can withstand use in harsh corrosive environments. Regarding the method.

[Prior art] In the past, steel plates were normally used for automobile podiums5. Steel plates for this type of automobile podium include ordinary steel plates, high-strength steel plates, as well as galvanized steel plates and alloyed steel plates. Surface-treated steel sheets such as galvanized steel sheets are used.

On the other hand, surface-treated steel sheets such as galvanized steel sheets and alloyed galvanized steel sheets have excellent corrosion resistance, and have therefore been used in parts or car models that particularly require corrosion resistance.

By the way, in an assembly production line for automobile podiums using such steel plates, the podium steel plates are formed into predetermined shapes by press working etc. to form each podium part, and then each podium part is assembled and spot welded.
After that, the assembled podium is degreased and then subjected to zinc phosphate treatment, which is a type of chemical conversion treatment, with the aim of improving the adhesion between the steel plate and the coating film and corrosion resistance. Spray painting is common.

On the other hand, recently, aluminum plates have been increasingly used for the exterior panels of automobile pods, with the main purpose of reducing the weight of automobile bodies in order to improve fuel efficiency. In this case, it is still rare to make the entire car body aluminum,
-M usually uses a steel plate and an aluminum plate together.

In order to assemble and manufacture automobile pods using both such steel plates and aluminum plates, it is desired to use the same line as in the case of using only steel plates as described above.

That is, after assembling and welding a Pode part made of a formed steel plate and a Pode part made of a formed aluminum plate to create a Pode, the entire Pode is degreased and then treated with zinc phosphate, and then electroplated. Painting or spray painting is recommended. In this way, even if steel plates and aluminum plates are used together, there is no need to establish a new assembly line or painting line, and process continuity is maintained, which is advantageous in terms of manufacturing costs. However, in this case, since the aluminum plate is also subjected to zinc phosphate treatment at the same time as the steel plate, the following problem arises.

In other words, when zinc phosphate treatment is applied to an aluminum plate, not only is a sufficient zinc phosphate film not formed on the surface of the aluminum plate, but the aluminum is dissolved and aluminum ions are generated in the zinc phosphate treatment. Therefore, when zinc phosphate treatment is applied to a podium made of a steel plate and an aluminum plate integrated into an automobile podium as mentioned above, the formation of a zinc phosphate film on the surface of the steel plate is inhibited by the eluted aluminum ions. A problem arises in that sufficient corrosion resistance and sufficient adhesion of the coating film cannot be obtained.

A method to solve such problems has already been proposed in Japanese Unexamined Patent Application Publication No. 6
No. 1-96074 proposes a chemical conversion treatment method for products made of a combination of aluminum and steel.

In this method, a chromate layer is formed on the surface of aluminum in advance, and by forming the chromate layer in this way, aluminum will not be eluted from the aluminum plate during the subsequent zinc phosphate treatment. Even when applying zinc phosphate treatment to a podium made of both aluminum and steel plates, a sufficient zinc phosphate film can be formed on the steel plate without interference from aluminum ions, and the surface of the aluminum plate itself can be treated with zinc phosphate. It is said that a chromate layer exists even after treatment with zinc phosphate.

However, in the chromate-1 treatment method proposed in JP-A No. 61-96074, the treatment liquid mainly consists of chromate, phosphate, hydrofluoric acid, etc., which are extremely harmful to the human body. Therefore, not only does it require large-scale investment in wastewater treatment equipment, but chromium-free treatment is desired from the perspective of environmental conservation.

In addition, when applying chromate treatment to an aluminum alloy plate, the line configuration is long: degreasing -> water washing -> dismat - water washing -> chemical treatment - water washing.In addition, the process takes a long time and requires expensive equipment.

[Problems to be Solved by the Invention] The present invention provides an aluminum alloy coating material for automobiles that ■ has excellent adhesion without cracking or peeling of the base due to processing such as pressing ■ Zinc phosphate treatment The aluminum material must not contaminate the treatment bath with aluminum ions, cause fatigue, or interfere with the zinc phosphate treatment of the steel sheet.■ The aluminum material must have high paint film adhesion even after zinc phosphate treatment.■ The goal was to have a high degree of freedom in choosing the paint (resin).

In addition, the manufacturing method for this aluminum alloy coating material is as follows: ■ The raw materials used must not pollute the environment. ■ The method requires short processing time and the number of steps, and is highly productive. ■ A method with low equipment costs and running costs. With this goal in mind, we have completed the present invention by providing an extremely high-performance aluminum alloy material that is different from conventional surface-treated aluminum alloy materials, and by researching methods for manufacturing it.

"Means for Solving the Problems" The present invention provides an aluminum alloy coating material for automobiles, which is characterized by forming an oxide film obtained by alternating current electrolytic treatment in an alkaline aqueous solution with a film thickness of 500 to 5,000. It is about providing.

Further, the aluminum alloy coating material for automobiles is prepared by coating the aluminum alloy material with a current density of 4-50 A/d m in an alkaline aqueous solution with a pH of 9 to 13 and a bath temperature of 35 to 85°C.
It can be obtained by a manufacturing method in which alternating current electrolytic treatment is performed for a period of time such that the electrical π exceeds 80 c/d m 2 and the thickness of the oxide film becomes 5000 Å or less.

The oxide film obtained by alkaline AC electrolysis according to the present invention is
It has a large bore diameter (approximately 200 holes in diameter, about 50 holes for normal sulfuric acid anodized coating) and has a large number of branched structures. Therefore, when paint or the like is applied, it easily penetrates into the bore, resulting in a high anchoring effect and strong adhesion between the paint film and the aluminum plate.

Aluminum alloys to which the present invention is applied are not particularly limited, but 5000 series and 6000 series are mainly used.

In the present invention, the thickness of the oxide film is 500 to 5,000 times thinner, and as a result of the pore structure with branching, the oxide film is highly flexible, even when processed by pressing etc. There are almost no cracks or peeling in the oxide film,
As a result, coating film adhesion is excellent.

However, if the diameter is less than 500 Å, the length of the bore is short, so a sufficient anchoring effect cannot be expected and the adhesion deteriorates.

On the other hand, 5,000 people can enjoy the effects of the present invention by increasing the thickness of the oxide film, and there are no particular problems, but this is the upper limit of the thickness that can be obtained under normal processing conditions. This is the limit, and there is no particular advantage to making it thicker than this.

The alkaline aqueous solution used in the present invention is not particularly limited, but those containing phosphates such as sodium phosphate, potassium cum phosphate, sodium birophosphate, potassium birophosphate, and phosphoric acid + sodium hydroxide are preferred. In the case of a liquid containing phosphate, particularly high adhesion can be obtained because the bore diameter tends to be large. In addition, it is desirable to use an aqueous solution of sodium carbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, etc., or a mixed solution of two or more thereof, and even if it contains a surfactant to improve the degreasing property. good.

In addition, the desirable hydrogen ion index (p I-
1) is pH 9-13, preferably pH 1O-12.

If the pH is less than 9, the degreasing properties will be poor and rolling oil and oxide film on the surface of the aluminum alloy plate cannot be dissolved and removed. Moreover, it is undesirable because the bath voltage increases and non-uniform electrolysis is likely to occur.On the other hand, if the pH exceeds 13, the solubility is too strong, and the removal of the dissolved residue by bubbles is not only insufficient, but also the adhesion is poor. This should be avoided as it will prevent the formation of a porous oxide film.

The bath temperature of the alkaline solution during electrolytic treatment is usually 35~
It is within the range of 85°C. At low temperatures below 35°C, the degreasing and cleaning effects tend to be insufficient, and at temperatures above -85°C, the solubility is too strong and it becomes difficult to obtain an anodic oxide film of the required thickness. In addition, even within the range of 35 to 85 °C, especially 60 to 80 °C
It is preferably within the range of °C.

The current density during AC electrolysis is 4 to 50 A/dm2, preferably 5 to 30 A/dm2.

If it is less than 4 A/d m2, the amount of bubbles generated during electrolysis will be insufficient, the surface cleaning effect will be poor, and the porous surface with excellent adhesion and 4 properties will be undesirable because the formation of a bio-intoxication film will be insufficient. .

If it exceeds 50 A/dm2, the electrolytic voltage becomes too high, which not only tends to cause electrical leakage but also tends to cause uneven appearance such as "burning" due to reaction heat, which is not preferable.

AC electrolysis must be carried out for a period of time such that the total amount of electricity exceeds 80 c/dm2. Total electricity amount is 80
If it is less than c / d m2, a porous oxide film will not be formed to the specified thickness, and the adhesion to the coating film formed thereon will not be sufficient1. Although it is possible to obtain good film adhesion, a large power source is required due to the high voltage.

The polarity must be an AC waveform.

When treating materials with a thick natural oxide film on the surface, such as 5182 alloy, it is recommended to first dissolve and remove the natural oxide film with an acidic aqueous solution before electrolytic treatment to extend the life of the electrolyte and prevent the oxide film from forming. It is effective for uniformity.

Cleaning treatment before electrolysis may be performed as necessary.

[Function] In this invention, electrolytic treatment is performed using alternating current in an alkaline solution at a high temperature of 35 to 85°C.

By such electrolytic treatment, as described in detail below, the surface of the aluminum material is strongly degreased and cleaned, and at the same time, a porous oxide film with excellent coating film adhesion is generated.

That is, first of all, speaking of the degreasing and cleaning effects, the alkaline solution has degreasing properties by itself, and because of the high temperature, the degreasing properties are stronger. Moreover, in electrolysis using alternating current, oxygen gas is generated during the anode reaction, while hydrogen gas is generated during the cathode reaction. Therefore, during the anode reaction, the degreasing and cleaning effects are activated by the oxidation of organic matter attached to the surface of the aluminum alloy material, and the cathode During the reaction, a mechanical cleaning action occurs due to the expansion of hydrogen bubbles on the plate surface. Therefore, when AC electrolytic treatment is performed in a high-temperature alkaline solution, the above-mentioned effects function synergistically to produce a strong degreasing and cleaning effect, and in an extremely short period of time, there is no adverse effect on paint film adhesion. It completely removes the rolling oil and thermal oxidation film formed in lumps on the surface of the aluminum alloy plate, and at the same time creates a film with a thickness of 500 to 5000 with a clean surface.
It forms a porous oxide film with excellent paint film adhesion.

Furthermore, in the present invention, electrolytic treatment is performed using alternating current in a high-temperature alkaline aqueous solution, so electrolysis can be performed at high current density, and chemical reactions occur at high speed.

That is, the dissolution reaction of the oxide film by the high-temperature alkaline aqueous solution and the formation reaction of the oxide film at the anode polarity occur at high speed. The oxide film produced by the dissolution reaction on the surface of the oxide film and the intermittent growth of the oxide film due to alternating current is extremely porous compared to the oxide film anodized by direct current electrolysis in an acidic aqueous solution. becomes.

The formation of this porous oxide film can only be realized by alternating current electrolytic treatment in an alkaline aqueous solution.

That is, in general electrolytic treatment using direct current, the bath voltage rises rapidly, making it impossible to conduct electrolysis at the high current density necessary for forming an oxide film. In addition, in oxidizing aqueous solutions such as phosphoric acid and sulfuric acid that are generally used to form anodized films,
Because a barrier-type acidic film is likely to form, industrialization is extremely difficult because a voltage five times higher than that for alkaline aqueous solutions is required for short-time treatment with high current density electrolysis. This is because

The oxide film formed by alternating current electrolysis treatment in an alkaline aqueous solution has a clean surface and a very porous structure, which can significantly improve adhesion to resin coatings. Therefore, corrosion resistance is significantly improved.

In addition, the formation of this oxide film prevents aluminum from leaching from the aluminum plate into the bath when a steel plate and an aluminum plate are combined and subjected to zinc phosphate treatment, which is a chemical conversion treatment. This improves the processability of bending lead with phosphate.

Furthermore, since degreasing and cleaning and the generation of a porous oxide film are carried out in the same tank through the same electrolytic treatment, and the electrolytic time is short, the overall working time is significantly shortened compared to conventional methods, improving productivity. Equipment costs are also significantly lower. In addition, since it does not use substances harmful to the human body such as chlorine, it has great advantages in terms of operation and environmental protection.

Further, this AC electrolytic degreasing treatment may be carried out after molding and assembling the material 1, and it is also possible to use the aluminum material 1 as a base for painting.

[Example] The component composition is Mg 0.85wt;%, Sin.

98 wt%, C110, 27wt%, MnO
.

38wt%, the rest is essentially A! Using a plate of an aluminum alloy (alloy equivalent to AA 6010), the coating surface treatment shown in Examples and Comparative Examples was performed. Here, the current density, quantity of electricity, pH of the electrolytic solution, temperature, and thickness of the produced oxide film in AC electrolytic degreasing J3 are also shown in Table 1.

In addition, after treating the base for painting, it was washed with water and dried, and after being treated with a zinc phosphate bath (commercially available Granosyn 2500),
Electrodeposition coating (epoxy resin: 20 um), intermediate coating (melamine alkyd resin, 35ILm), and top coating (melamine alkyd resin: 35 ft m ) were performed.

In addition, the "chemical conversion treatment properties" of each film performance shown in Table 2 are based on the results obtained by applying zinc phosphate treatment together with the steel sheet -C, the formation state of the zinc phosphate treatment film on the surface of the steel sheet, and the zinc phosphate treatment. The deterioration state of the bath was evaluated.

[Coating film adhesion J was made by cutting the coating film at mm intervals], OX 10 base grid-shaped cuts were made,
A peeling test was conducted using cellophane tape, and evaluation was made based on the percentage of peeling that did not occur.

"Thread rust resistance" is based on the method of ASTM D2083.
X: over 3 mm).

"Efficiency" was evaluated based on the time required to process the base.

(Example J) 7 Troughs In an aqueous solution of 2% Na4P2O7 with a pH of 105 at 70°C, an alternating current density of 9 A/dm2 (sine waveform of 50
Hz) for 26.2 seconds. (Total amount of electricity 150c/dm2) (Example 2) Electrolytic treatment for 17.4 seconds (total amount of electricity], 00C/dm2)
The same treatment as in Example 1 was performed except for the following.

(Example 3) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed at an alternating current density of 26 A/dm'' for 9.1 seconds (total electricity amount 150 c/dm2).

(Example 4) The same process as in Example 1 was performed except that the electrolytic process was performed at an alternating current density of 7 A/d m2 for 22.4 seconds (total amount of electricity LOOc/d m2).

(Example 5) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed in an aqueous solution of 2% Na2CO3 with pH and H of 12 at a bath temperature of 40°C.

(Comparative Example 1) The same treatment as in Example 1 was performed except that the electrolytic treatment was carried out for 15.7 seconds (total electricity amount 80 c/dm2).

(Comparative Example 2) The same treatment as in Example 1 was performed except that the electrolytic treatment was performed in an aqueous solution at a bath temperature of 90°C.

(Comparative Example 3) The same treatment as in Example 1 was carried out except that the electrolytic treatment was carried out in an aqueous solution of 2% Na Ot [pH 14] at a bath temperature of 40''C.

(Comparative Example 4) After degreasing with an alkaline degreasing solution, washing with water, dematting, and washing with water, chromate treatment was performed so that the amount of chromium in the film was 50 mg/m2.

(Comparative Example 5) After degreasing with an alkaline degreasing solution and washing with water, Daymat,
I washed it with water.

(Example 6) The same process as in Example 5 was performed except that 5182 was used as the aluminum alloy.

(Example 7) The same process as in Example 5 was performed except that 1100 was used as the aluminum alloy.

Regarding Examples 1 to 7 and Comparative Examples 1 to 5, the manufacturing conditions and the performance of each film are shown in Tables 1 and 2.

(Left below) As is clear from Table 1 and Table 2, Examples 1 to 7 have excellent chemical conversion treatment properties, excellent paint film adhesion, and excellent thread rust resistance. Processing efficiency is also excellent.

[Effect of the invention 1] As is clear from the above examples, the aluminum alloy coating material having an oxide film on the aluminum surface by the AC electrolytic treatment of the present invention has the following effects when treated with zinc phosphate:
Since the aluminum from the aluminum plate is reliably prevented from leaching out during the treatment and does not contaminate the treatment bath, the zinc phosphate treatment properties are excellent, and even when aluminum and steel plates are treated with zinc phosphate at the same time, the surface of the steel plate is reliably treated. A zinc phosphate treatment film can be formed on.

Further, since the oxide film on the aluminum surface is thin and porous, it does not cause cracks or peeling during processing, and has excellent coating film adhesion and good thread rust resistance.

In addition, this method for producing aluminum material is efficient because it does not pollute the environment and can be processed in a very short time, making it possible to reduce costs.

In particular, it has the advantage of being easy to industrialize because it does not use romic acid, which is extremely harmful to the human body like chromate treatment.

Claims (2)

[Claims] (1) An aluminum alloy coating material for automobiles, characterized by having an oxide film obtained by alternating current electrolysis treatment in an alkaline aqueous solution with a film thickness of 500 to 5000 Å. (2) Aluminum alloy material, pH 9 to 13, bath temperature 35
In alkaline aqueous solution at ~85°C, current density 4~50A/
A method for producing an aluminum alloy coating material for automobiles, characterized in that alternating current electrolytic treatment is performed at dm^2 for a time such that the amount of electricity exceeds 80 c/dm^2 and the thickness of the oxide film is 5000 Å or less.