JPH05156413A - Aluminum alloy sheet for automobile body and production thereof - Google Patents

Abstract

PURPOSE:To provide the aluminum alloy sheet for automobile bodies having excellent quality in all of weldability, adhesiveness, coating film adhesion and corrosion resistance. CONSTITUTION:This aluminum alloy sheet for automobile bodies is formed to 10 to 200 angstrom thickness of surface oxide films and has 0.1 to 2.5mum average surface roughness (Ra) and 0.5 to 40mum max. surface roughness (Rmax) as surface roughness. The process for production consists on washing the surface of the sheet >=1 times and etching the surface to >=5mg/m<2> in the stage after hot rolling for producing the aluminum alloy sheet or in the final production stage or further subjecting the sheet to a stabilizing treatment after this etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy plate used for automobile bodies and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, there has been a call for a reduction in vehicle body weight for the purpose of improving the fuel efficiency and performance of automobiles. As a result, the specific gravity is about one-third that of iron instead of the conventionally used steel materials.
The use of aluminum materials is increasing. Not only is this aluminum lightweight, it is also excellent in corrosion resistance, workability, surface treatment properties, etc., and is easily regenerated, so it has attracted the most attention as a material for automobiles. It is currently used in bodies, wheels, bumpers, heat exchangers, engines, etc., and its range of applications is increasing.

When an aluminum material is used as an automobile body, its manufacturing method and process are basically the same as those when using conventional iron and steel materials. Formability, weldability, adhesiveness, and after coating are used. Corrosion resistance and aesthetics are required.

The manufacturing process of the above body will be described below. Forming: A coil or a plate cut into a predetermined size from a coil is formed into a predetermined shape. ↓ Joining: Joining with peripheral parts by welding and / or bonding. At that time, it is combined with the conventional iron and steel materials and flowed to the next step. ↓ Surface treatment i) Degreasing: Using alkaline cleaner ↓ ii) Washing with water ↓ iii) Surface preparation: Colloidal titanate treatment, etc. ↓ iv) Chemical conversion treatment: Zinc phosphate treatment ↓ v) Washing with water ↓ ───── Case In some cases, "post-treatment" with a chromic acid solution is performed in the middle vi) Dry ↓ Coating i) Undercoat (electrodeposition coating) ↓ ii) Intermediate coating ↓ iii) Top coating ↓ Outfitting

An automobile body is manufactured by the above steps (1) to (3). Then, the aluminum plate material as a raw material is manufactured through a normal process of casting → soaking → hot rolling → cold rolling → finish annealing (may be performed during cold rolling), and the coil state as described above. Alternatively, after being cut to a predetermined size, it is subjected to a molding process in a state of a cut plate.

[0006]

The aluminum material conventionally used for such an automobile body has the following problems. Poor adhesion: When an accelerated durability test is performed in a harsh environment, peeling occurs from the joint, or the adhesive strength of the joint falls below a desired value, which impairs safety and reliability. Poor weldability: In spot welding, the number of spots that can be welded continuously is low, and the number of electrode maintenances is high, resulting in low productivity. Poor coating adhesion: When an accelerated durability test is performed in a harsh environment after coating, the coating peels off or swells, impairing the appearance. Poor corrosion resistance: Filiform corrosion is likely to occur when an accelerated durability test is performed in a harsh environment after painting, which not only impairs the aesthetic appearance but also causes a functional problem when it further progresses.

Among the above problems, in particular and when the aluminum material alone is used in combination with the steel material, rather than when it is used alone as an automobile body (when the chemical conversion treatment which is the base treatment of the coating is zinc phosphate treatment) ) Was more frequent, and its severity was a serious problem.

[0008]

As a result of various investigations in view of the above, the present invention has been found to be largely related to the oxide film on the aluminum surface as a cause of such poor adhesion, poor weldability, poor coating adhesion and poor corrosion resistance. That is, the relationship between this oxide film and the above characteristics was examined in more detail, and the following findings were obtained.

Adhesiveness: If the oxide film is thick, the oxide film itself acts as a brittle layer (peeling portion), and the adhesive strength is reduced.

Weldability: Since the oxide film is basically an electrical non-conductor, if the oxide film is thick, the electrical resistance increases and the electrode is damaged. If this is repeated continuously, the welded part called a nugget becomes small and desired strength cannot be obtained.

Coating adhesion: If a large amount of oxide film remains after deoiling during surface treatment, zinc phosphate precipitation nucleation will not be satisfactorily formed in the surface adjustment in the next step, so zinc phosphate during chemical conversion treatment. The amount of coating film adhered is small, and / or zinc phosphate crystals become coarse, and the adhesion after coating is reduced. The reason why a large amount of the oxide film remains after degreasing is greatly influenced not only by the thickness of the oxide film but also by the film quality. That is, magnesium oxide that forms the oxide film or /
It was also found that the less oxide hydroxide film after degreasing, the less magnesium hydroxide and less aluminum oxide and / or aluminum oxide crystalline oxide and / or hydroxide.

Corrosion resistance: Basically, the cause is that the thickness and quality of the oxide film, like the adhesion of the coating film, deteriorates the zinc phosphate treatment property.

Next, the oxide film of aluminum material will be described. That is, aluminum is a very active metal and forms oxides and / or hydroxides depending on temperature (heat) and moisture (humidity) in the atmosphere. The structure of the oxide film of the aluminum material formed in this way is greatly influenced by the alloy composition and
In a material containing 0.3 to 8% by weight, not only aluminum oxide and / or hydroxide but also magnesium oxide and / or hydroxide coexist. This magnesium oxide and / or hydroxide is an alkali-insoluble substance, and if a large amount remains before degreasing during surface treatment (alkaline), it remains even after degreasing, resulting in surface conditioning and chemical conversion treatability in the next step. Is to reduce.

With respect to the aluminum oxide, there are roughly two types of aluminum oxide.
One is an amorphous oxide film (Al ₂ O ₃ ), and the other is a crystalline oxide film. This crystalline oxide film has various phases depending on the formation atmosphere, but the typical one is Gibbsi.
te (γ-Al (OH) ₃ ), Bayerlite (α-Al (O
H) ₃ ), Boehmite (γ-AlOOH) and the like. The following has been found regarding such an oxide film. That is, these oxide films have different chemical behaviors, and the amorphous oxide film has higher solubility in acid and alkali than the crystalline oxide film.

Such two kinds of oxide films are mixed on the surface of the aluminum plate, and the crystalline oxide film occurs when exposed to high temperature in a wet atmosphere. Then, in the manufacturing process of the aluminum plate, it was found that the process causing such a crystalline oxide film was hot rolling. This is because in the hot rolling process, generally, an aqueous rolling oil is used and rolling is performed at 200 ° C or higher. As a result, the crystalline oxide film is crushed and expanded by the subsequent rolling, but remains in the form of being embedded in the aluminum matrix until the end.

In the case of an aluminum material for coating, if there are many such crystalline oxide films, they cannot be completely removed during degreasing and remain, and a desired amount of chemical conversion film can be obtained by subsequent chemical conversion treatment. It was found that the fragile chemical conversion film was formed because the crystal of the chemical conversion film was coarse. In other words, a crystalline oxide film is formed during hot rolling, and the film remains on the final plate, so even if degreasing is performed during surface treatment, it cannot be completely removed and remains. It was found that the coating adhesion and the corrosion resistance after the coating treatment were deteriorated because of the decrease in the coating strength.

In view of the above, the present invention provides an excellent automobile body that solves poor weldability, poor adhesion, poor coating adhesion, and poor corrosion resistance by using an aluminum material whose oxide film thickness and quality are controlled. It is to provide materials for use.

That is, in the aluminum alloy sheet of the present invention, the thickness of the surface oxide film is 10 to 200 angstrom, and the average surface roughness (Ra) is 0.1 to 2.5 μm and the maximum surface roughness (Rmax) is 0.5 to. It is characterized by being 40 μm.

Further, one of the methods for producing an aluminum alloy sheet of the present invention is to wash the surface one or more times during the steps after the hot rolling for producing the aluminum alloy sheet or in the final production step to give the surface of 5 mg / min. m ² or more is characterized by etching, further one of the other manufacturing method of the present invention,
During the process after hot rolling to produce an aluminum alloy plate,
Or, in the final manufacturing process, wash the surface more than once and
It is characterized by performing a stabilization treatment after etching at mg / m ² or more.

[0020]

[Function] First, the reason why the thickness of the surface oxide film is limited to 10 to 200 Å will be described. Oxide film thickness is 10
If it is less than angstrom, electric resistance is too small during spot welding and sufficient heat cannot be obtained, so that no nugget is formed. If it exceeds 200 angstroms, the oxide film itself will act as a fragile layer during bonding, reducing the adhesive strength, and during spot welding, the electrical resistance will be too large, causing electrode damage and a decrease in continuous spotting. Since it is not completely removed during degreasing during processing, the amount of oxide film remaining after degreasing increases, which reduces the surface conditioning and chemical conversion processability and reduces the amount of chemical conversion film, or / and zinc phosphate crystals become coarse and painted. This is because the subsequent adhesion and corrosion resistance are reduced.

The surface roughness of the plate material is Ra (average roughness)
The limits of 0.1 to 2.5 μm and Rmax (maximum roughness) 0.5 to 40 μm are that Ra is less than 0.1 μm and Rmax is 0.5 μm.
If it is less than the above range, the retaining property of the lubricating oil obtained at the time of molding is poor and the moldability is lowered, and further, the adhesion area is reduced at the time of bonding and the adhesiveness is also decreased. On the other hand, Ra is 2.5
If it exceeds .mu.m and Rmax exceeds 40 .mu.m, the smoothness (vividness) of the coating film surface after coating is deteriorated and the commercial value of appearance is deteriorated.

Next, the etching applied to the aluminum alloy plate material is intended to remove the oxide film formed during hot rolling and to reduce the oxide film thickness grown to 200 angstroms or more. The position of etching in the process is effective at any position after hot rolling, but it is most effective particularly at the final process. In this case, the etching amount of 5 mg / m ² or more is
This is because if the amount is less than 5 mg / m ² , the crystalline oxide film cannot be completely removed.

The stabilization treatment after the above washing is
This is because, as described above, the aluminum material is an active metal, and therefore the oxide film has a small thickness immediately after the etching, but increases in film thickness if left to stand. For example, as shown in the following examples, even if the stabilization treatment is not carried out, there is no problem if welding or the like is performed in the next step immediately after etching, but the oxide film becomes thicker with the passage of time. 200 specified as oxide film thickness of aluminum alloy plate
The film may be thicker than angstrom. Especially Mg
Since a material having a large amount has a high film-forming rate, it is desirable to perform a stabilization treatment for the purpose of suppressing the film-forming after etching. Examples of the stabilizing treatment method include a method of applying oil (antirust oil), a method of treating in a solution containing phosphate ion or phosphate, and a method of combining them. Here, the solution containing phosphate ion or phosphate means a solution containing 1 ppm or more of one or more of sodium phosphate, sodium hypophosphite, sodium pyrophosphate and the like. When oil is applied, it is sufficiently effective to apply lubricating oil for molding or the like in addition to rust preventive oil.

The cleaning agent used for cleaning is not particularly limited as long as it etches aluminum, but any reagent or commercially available liquid may be used as long as it has a pH of 5 or less for an acidic detergent and a pH of 10 or more for an alkaline detergent. Absent.
For example, acid detergents include nitric acid-based, sulfuric acid-based, phosphoric acid-based, hydrofluoric acid-based, etc., and composites thereof, and alkaline detergents include sodium hydroxide-based, sodium phosphate-based, sodium carbonate-based, etc., and composites thereof. There is no problem in using either one.

Further, it is preferable to remove the smut after these washings. The smut means an insoluble residue, which is not dissolved during etching and remains on the surface. If the etching amount is small, there will be no problem, but if the etching amount is large, smut will increase, which may affect the adhesiveness, weldability, coating adhesion, and corrosion resistance. It is better to remove the smut when

The manufacturing method of the present invention as described above may be carried out by using a plate obtained by cutting a material into a predetermined size from a coil.
It is more efficient to carry out continuously in the state of the coil, and it also contributes to the improvement of productivity.

Further, when an ordinary aluminum material is used in combination with a steel material as a vehicle body structural material, there is a problem that the chemical conversion processability of the steel material is deteriorated by the dissolved aluminum dissolved in each surface treatment liquid. The use of the aluminum alloy sheet of the present invention is advantageous because the rate of formation of the chemical conversion film during the chemical conversion treatment is high and the elution of aluminum ions into the liquid is suppressed.

[0028]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples, and the present invention is not limited to the following examples, and further, the above-mentioned examples. It goes without saying that various changes, modifications, improvements and the like can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention, other than the specific description.

JIS A5182 (Al-0.3wt% Mn-
4.5wt% Mg), melting, casting, homogenization treatment, hot rolling,
By cold rolling and finish annealing, a plate material with a thickness of 1.0 mm was finished by continuous coil treatment. As shown in Table 1, this plate material was subjected to etching treatment, then smut removal treatment, and then stabilization treatment, or with respect to each plate material that was not performed, the following tests were conducted to evaluate each characteristic. The results are shown in Table 2. The material No. 7 of the present invention which had not been subjected to the stabilization treatment was subjected to the following test immediately after removing the smut and without leaving the test plate material for a long time.

(1) Adhesion test: 2 cut into 25 × 100 mm
The plate materials were laminated with a commercially available epoxy adhesive with a wrap width of 13 mm and baked at 170 ° C. for 30 minutes. After that, a JIS Z2371 salt spray test was conducted for 90 days, the tensile shear strength before and after the salt spray test was measured, and the residual ratio of the strength determined by the following formula was shown.

(2) Weldability test: the number of continuous spots by spot welding (the number of spots until the electrode is damaged and no nugget is formed)

(3) Coating film adhesion test: A 70 × 150 mm plate was cut out from the above aluminum coil, degreased with a weak alkaline degreasing agent at 45 ° C. for 30 seconds and washed with water, and then colloidal titanium. The surface of the system is adjusted for 30 seconds at room temperature with a system solution, and then, as it is, with a commercially available zinc phosphate treatment solution at 45 ° C.
× 2 minutes of chemical conversion treatment. Then, after washing with water and drying, an undercoat by cationic electrodeposition coating, an intermediate coating by spraying, and an overcoat were performed to prepare a test sample. Soak the above sample in warm water at 50 ℃ for 20 days, then
Adhesion is shown by indicating the number of the left-eye stitches that have not been peeled off by the eye-eye test specified in D0202 (100 pieces of 2mm x 2mm eyes made by peeling test with tape) as follows. Was evaluated. Remaining number / test number (100)

(4) Corrosion resistance test: A coated sample was prepared in the same manner as in the coating film adhesion test of (3) above, and then a cross-cut (marked with X) reaching the substrate was put on the sample surface, and JIS was used.
The salt spray test with Z2371 was carried out for 24 hours and then at 50 ° C.
After leaving it in a 95% wet atmosphere for 2000 hours, the maximum length of thread rust (filament corrosion) generated from the cross cut portion was measured and evaluated.

[0034]

[Table 1]

[0035]

[Table 2]

It can be seen from Table 1 that the aluminum alloy plate produced by the method of the present invention is excellent in all properties. On the other hand, it is apparent that the comparative alloy sheet having the oxide film thickness and the surface roughness out of the ranges defined by the present invention is inferior in at least one characteristic.

[0037]

As described above, according to the present invention, it is possible to obtain an aluminum alloy sheet material for an automobile body which is excellent in adhesion, weldability, coating adhesion and corrosion resistance.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Motohiro Namba Motohiro 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Inventor Yoji Ishida 2--6, Marunouchi, Chiyoda-ku, Tokyo No. 1 in Furukawa Aluminum Co., Ltd. (72) Inventor Masaaki Kurihara 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd.

Claims (3)

[Claims] 1. The surface oxide film has a thickness of 10 to 200 angstroms, and the average surface roughness (R
a) 0.1 to 2.5 μm and maximum surface roughness (Rmax) 0.5 to 40 μm
An aluminum alloy plate for an automobile body, which is characterized by being m. 2. An automobile body characterized by cleaning the surface one or more times and etching the surface by 5 mg / m ² or more in a step after hot rolling for manufacturing an aluminum alloy plate or in a final manufacturing step. Aluminum alloy sheet manufacturing method. 3. Stabilizing treatment is performed after the surface is washed once or more and the surface is etched by 5 mg / m ² or more in a step after hot rolling for manufacturing an aluminum alloy plate or in a final manufacturing step. A method for manufacturing an aluminum alloy plate for a car body, which is characterized.