JPH05271955A - Aluminum sheet excellent in formability, weldability and corrosion resistance - Google Patents

Abstract

PURPOSE:To improve the formability, weldability and corrosion resistance of an Al sheet by forming a film contg. specified amounts of Mn and Mo as the shape of metallic salts on the surface of Al. CONSTITUTION:On the surface of an Al or Al alloy sheet, a film contg. one or two kinds of Mn and Mo as the shape of metallic salts is formed by 5 to 200mg/m<2> expressed in terms of metals. By the incorporation of Mn or Mo, its corrosion resistance after coating is made excellent. At the time of joining the Al sheets on which the films have been formed by spot welding with each other, preferably, the content of the metallic elements in the film on the side of the joined face is regulated to >=1.5 times that of the metallic elements in the film on the side of the face to be contacted with an electrode of the spot welding.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum or aluminum alloy plate used for automobile structural members, especially for bodies, and is excellent in formability, weldability and corrosion resistance.

[0002]

2. Description of the Related Art In order to improve the fuel efficiency of automobiles and to reduce the weight of vehicle bodies for the purpose of improving performance, the use of aluminum materials, whose specific gravity is about 1/3 that of iron, replaces the steel materials used conventionally. The use is increasing. Aluminum is not only lightweight, but also has excellent corrosion resistance, workability, surface treatment properties, etc., and is easily regenerated, so it has attracted the most attention as an automatic material. Currently, it is used as a body, wheel, bumper, heat exchanger. It is used in engines, etc., and the range of other applications is also increasing.

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

The manufacturing process of the 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 conventional iron and steel materials and flows to the next step. ↓ Surface treatment i) Degreasing: Using alkaline detergent ↓ ii) Washing with water ↓ iii) Surface preparation: Colloidal titanate treatment ↓ iv) Chemical conversion treatment: Zinc phosphate treatment ↓ v) Washing ↓ → In some cases chromic acid treatment The "post-treatment" with the solution is performed in the middle. vi) Drying ↓ Painting i) Undercoating (Electrodeposition coating) ↓ ii) Intermediate coating ↓ iii) Topcoating ↓ Outfitting

[0005]

The aluminum material conventionally used for such an automobile body has the following problems.

Poor formability: Compared with steel materials that are currently the mainstream for automobile bodies, aluminum materials are soft and have a small elongation, so they easily cause mold galling, cracking, rough skin, etc., resulting in poor moldability.

Poor weldability: At the time of spot welding, the electrode life of an aluminum material is extremely inferior to that of steel, so that the production efficiency of the vehicle body is significantly reduced. That is, in the spot welding of aluminum material, the welding phenomenon is likely to occur, and because the number of welding points that can obtain an appropriate nugget with the same electrode is extremely short, the electrode can be formed before welding occurs or before an appropriate nugget cannot be formed. The shape is frequently adjusted by dressing or replaced with a new electrode, which has a great influence on the welding efficiency and hence the production efficiency of the automobile body.

Poor corrosion resistance: Filiform corrosion (filiform corrosion: Filifo) when an accelerated durability test is performed in a harsh environment after coating.
rm corrosion) is likely to occur, which not only impairs the aesthetic appearance but also causes a functional problem when it progresses further.

In particular, the above is the case where the aluminum material alone is used in combination with the steel material (when the chemical conversion treatment which is the base treatment of the coating is zinc phosphate treatment), rather than the case where the aluminum material is used alone as an automobile body. Occurs frequently and its severity is also severe.

In order to solve such problems, the present inventors have already proposed a method for improving the above characteristics by etching the surface of an aluminum material (Japanese Patent Application No. 3-253).
No. 126). However, although this method has some effects, it was not always at a satisfactory level.

[0011]

Therefore, as a result of various investigations on the above problems, the present inventors have obtained the following findings regarding the characteristics in question.

Formability Aluminum material has a large friction coefficient as compared with steel sheet and has a property of being easily adhered to a press die, resulting in poor formability. In order to improve this, aluminum surface has high hardness and lubricity. Is effective. Although resin treatment has already been found as a method of imparting high hardness and lubricity, the resin treatment is expensive in cost and lacks versatility. or,
Since the method of coating different metals such as plating has problems in corrosion resistance and recyclability, various studies have revealed that it is effective to form a chemical film on the aluminum surface. This is because the chemical film itself has a small friction coefficient and has a good affinity with the molding oil.

Weldability When spot welding of aluminum material is continuously repeated using the same copper-based electrode, the current-carrying diameter at the tip of the electrode increases together with the hitting point, and the current density in the plate decreases due to this, and the nugget diameter also increases. Although it will decrease and finally the life of the electrode will be reached, the characteristic feature of aluminum material is that the expansion rate of the electrode tip diameter is significantly higher than that of a steel sheet.

Therefore, as a result of paying attention to such a phenomenon and carefully studying the cause thereof, in the case of continuous spot welding of an aluminum material, molten aluminum adheres to the current-carrying portion of the electrode tip and its oxide deposits together with the spot. , I found that this formed an insulating layer and finally sparked between the electrode and this insulating layer, at which time the electrode was eroded. Then, it was found that such a peculiar phenomenon of the aluminum material promotes the enlargement of the electrode tip diameter and the electrode life is extremely deteriorated. Therefore, it is important to remove the non-uniform oxides that cause sparks so that a uniform and appropriate electric resistance can be obtained. It was

Corrosion resistance after coating Normally, the thread rust that occurs in a coating material of an aluminum body originates from a coating film defect such as a scratch on the surface, and is corrosive in a corrosive environment such as chlorine. It was found that the main cause is that it reaches the aluminum substrate and corrodes the aluminum substrate. Therefore, it was found that forming a film capable of obtaining a strong anticorrosion effect on an aluminum substrate is an important point of solution, and that the film quality and film thickness of the chemical film have a great influence.

On the basis of the above findings, the present invention provides a moldability,
We have developed an aluminum plate for automobile bodies of excellent quality with improved weldability and corrosion resistance after painting.

That is, according to the present invention, a film containing one or two of Mn and Mo in the form of a metal salt in an amount of 5 to 200 mg / m ^{2 in} terms of metal is formed on the surface of an aluminum or aluminum alloy plate. It is characterized by.

Another aspect of the present invention is an aluminum or aluminum alloy plate joined to each other by spot welding, wherein Mn and Mo in the form of a metal salt are formed on the surface of the plate.
1 or 2 of the above is formed into a film containing 5 to 200 mg / m ^{2 in} terms of metal, and the content of the above metal element in the film on the joint surface side at the time of spot welding is applied to the electrode for spot welding. It is characterized in that the content of the above metal element in the film on the surface side is 1.5 times or more.

[0019]

As described above, one or more of Mn and Mo are contained in the amount of 5 to 200 mg / m ^{2 in} terms of metal of at least one of Mn and Mo as the metal salt constituting the film formed on the surface of the aluminum plate. If the above content is included in this range, the corrosion resistance after coating is excellent. More specifically, if the content is less than 5 mg / m ² , not only the anticorrosion effect on the aluminum substrate is insufficient, but also the desired electric resistance is not obtained and the weldability is deteriorated. m ²
If it exceeds, the electric resistance becomes too large and welding becomes impossible.

The aluminum plate in the present invention includes an aluminum alloy, and is not limited to a plate material, but an extruded material,
There is no particular limitation on the method of manufacturing a casting or the like.

The pretreatment of the chemical treatment for forming the above-mentioned coating does not have to be carried out in particular, and it may be directly treated after rolling, but it is usually produced during the aluminum material manufacturing step before the chemical treatment. For the purpose of removing the uneven coating,
Etching in an acid or alkali and smut (insoluble residue) removal in an acid solution are appropriately selected and performed.

In the present invention, Mn in the chemical coating on the electrode contact surface side and the joint surface side of the aluminum plate during spot welding is also used.
And / or the content of Mo is changed, that is, the content on the electrode contact surface side is set to 2/3 or less of the bonding surface side. This is effective in preventing sparks on the electrode surface side and preventing aluminum from adhering to the electrode surface. Further, so-called single-sided treatment in which such a chemical film is formed only on the joint surface side and no chemical film is formed on the electrode contact surface side is also effective in improving the weldability.

The process for obtaining the inventive aluminum plate may be carried out using a plate cut out from the coil to a predetermined size. However, continuous processing with a coil is more efficient and contributes to productivity.

[0024]

EXAMPLES Examples of the present invention will be shown below, but it goes without saying that the present invention is not limited by the description of such examples. In addition to the embodiments described below, the invention is not limited to the specific description above, and various changes, modifications, and improvements are made based on the knowledge of those skilled in the art without departing from the spirit of the invention. It should be understood that, etc. can be added.

JIS A5182 (Al-0.3Mn-
4.5 Mg) was melted, cast, homogenized, hot-rolled, cold-rolled and finish-annealed to a plate thickness of 1.0 mm by continuous coil processing. After that, etching with a commercially available alkaline detergent, washing with water, removal of smut with nitric acid, and washing with water were performed, and chemical treatment with a treatment liquid having the composition shown in Table 1 was performed to form a film having the properties shown in Table 1 on the surface. Then, the following tests were performed on these aluminum alloy plates.

(1) Formability test: After applying 0.5 g / m ² of cleaning oil on the surface, a sample punched to 70 mmφ was subjected to high speed cylindrical drawing with a diameter of 33 mmφ (processing speed 500 mm / se.
c) was performed, and those in which galling and / or cracking occurred on the side surface of the cylinder were shown as bad (x), and those in which these defects did not occur were shown as good (◯) in Table 1.

(2) Weldability test: The electrode life was evaluated under the following conditions. The evaluation was determined by the number of dots until welding or the number of dots until the nugget diameter fell below 4 × t ^1/2 (t: plate thickness), whichever was smaller. As criteria for judgment, the number of hit points is less than 500 (poor), 500 to 1000 is normal (Δ), 1000 to 2000 is good (∘), and 2000 or more is the best (⊚).

Welding machine: Inverter type DC welding machine Welding condition: Pressurization 150kgf Electrode: Shape Cone head (CF) type Initial pressing time 20/50 seconds Tip diameter 5.0mmφ Energization time 6/50 seconds Material Cr-Cu Hold time 5/50 seconds Welding current 15kA

(3) Corrosion resistance test after coating: After chemical treatment, a 70 × 150 mm plate was cut out from the coil, degreased at 43 ° C. for 2 minutes with a weak alkaline degreasing agent, washed with water, and then colloidal titanium. The surface of the system was adjusted at room temperature for 30 seconds, and as it was, a commercially available zinc phosphate treatment solution was subjected to chemical conversion treatment at 43 ° C. for 2 minutes. Then, after washing with water and drying, an undercoat by cationic electrodeposition coating, an intermediate coat by spraying, and an overcoat were prepared to prepare test samples. The total coating film thickness is 100 μm.

A cross-cut (marked with X) reaching the aluminum substrate was put on the surface of the sample, and a salt spray test according to JISZ 2371 was performed for 24 hours, and then left for 2000 hours in a humid atmosphere of 50 ° C. and 95%, and then cross-cut. The maximum length of thread rust (filament corrosion) generated from the part was measured. Judgment is shown in Table 1 with a thread rust length of 4 mm or more as poor (x), 2 to 4 mm as normal (Δ), and 2 mm or less as good (◯).

[0031]

[Table 1] Note) Alodine 401-45 is a commercially available liquid (made by Nippon Parkerizing): Chromate phosphate system

According to Table 1, each of the sheets of the present invention is superior to the conventional aluminum alloy sheet in terms of formability, weldability, and corrosion resistance after painting. On the other hand, a comparative plate N containing less than 5 mg / m ² of Mn in the coating in terms of metal
o.5, Mo content in the coating in terms of metal is 200 mg / m ²
And the film thickness on the joint surface side is 1.
Comparative plate No. 6 less than 5 times and Mn or Mo in the film
It can be seen that the comparative plate No. 7, which does not contain any of the above, is inferior in any of the properties.

[0033]

As described above, according to the present invention, the poor formability, poor weldability, and poor corrosion resistance after painting, which have been problems in the aluminum plate conventionally used for automobile bodies, are improved. It has the remarkable effects of reducing the vehicle body weight and improving fuel efficiency.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yoji Ishida 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Toshio Tani 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Inventor Masaaki Kurihara 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Osamu Kato 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd.

Claims (2)

[Claims] 1. A surface of an aluminum or aluminum alloy plate is provided with one or two of Mn and Mo in the form of a metal salt.
An aluminum plate excellent in formability, weldability, and corrosion resistance, characterized by forming a film containing 5 to 200 mg / m ^{2 in} terms of metal. 2. An aluminum or aluminum alloy plate to be joined to each other by spot welding, containing 5 to 200 mg / m ^{2 in} terms of metal of one or two of Mn and Mo in the form of a metal salt on the surface of the plate. The content of the metal element in the coating on the joint surface side during spot welding is 1.5 times or more the content of the metal element in the coating on the electrode contact surface side of spot welding. An aluminum plate with excellent formability, weldability, and corrosion resistance.