JPH05271961A - Al sheet having excellent formability, weldability and corrosion resistance - Google Patents

Abstract

PURPOSE:To obtain an Al sheet having excellent formability, weldability and corrosion resistance by forming a film contg. specified amounts of the 4 and 2 group metallic elements in a periodic table on the surface of an aluminum sheet. CONSTITUTION:On the surface of an aluminum or aluminum alloy sheet, a film contg. one or more kinds among the 4 and 2 metallic elements in an elemental periodic table by 5 to 200mg/m<2> expressed in terms of metal is formed. On the surface of the aluminum or aluminum alloy sheets to be joined with each other by spot welding, this film is formed, and the content of the metallic elements in the film on the side of the joined face at the time of the spot welding is regulated to >=2.5times that of the metallic elements in the film on the side of the face to be contacted with an electrode at the time of the spot welding. In this way, the lightening of an automobile body can be realized.

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 structural members, especially for bodies, which has excellent formability, weldability and corrosion resistance.

[0002]

2. Description of the Related Art In order to improve the fuel efficiency of automobiles and 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 the 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-mentioned various characteristics by etching the surface of an aluminum material (Japanese Patent Application No.
253126). However, although this method has some effects, it was not always at a satisfactory level.

[0011]

The inventors of the present invention have made various studies on the above problems, and have obtained the following findings on their respective characteristics.

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. Resin treatment has already been found as a method of imparting high hardness and lubricity, but the resin treatment is costly and lacks versatility. Further, the method of coating different metals such as plating has problems in corrosion resistance and recyclability, and as a result of various studies, it has been found that forming a chemical film on the surface of aluminum is effective. 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. It was also 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 painting The thread rust that usually occurs in coating materials of aluminum bodies originates from coating film defects such as surface scratches. It was found that the main cause is that it reaches the 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.

Based on the above findings, the present invention is an Al for automobile bodies having improved formability, weldability and corrosion resistance after painting.
It is a developed board.

That is, according to one aspect of the present invention, on the surface of an aluminum or aluminum alloy plate, one or more kinds of metal elements of Groups 4 and 2 of the periodic table of the elements are added in an amount of 5 to 200 mg in terms of metal.
It is characterized in that a coating film containing / m ² is formed.

According to another aspect of the present invention, in an aluminum or aluminum alloy plate joined to each other by spot welding, one or more metal elements of Group 4 and 2 of the periodic table of elements are provided on the surface of the plate. 5 to 200 mg in terms of metal
/ M ² contained in the coating, and the content of the above metal element in the coating on the joint surface side during spot welding is 1% of the content of the above metal element in the coating on the electrode contact surface side of spot welding. It is characterized by being set to 5 times or more.

[0019]

As described above, as the metal salt constituting the film formed on the surface of the Al or Al alloy plate, at least one metal selected from metals belonging to Groups 4 and 2 of the Periodic Table of Elements is 5 to 200 mg / metal in terms of metal.
The reason for m ² is that if at least 5 mg / m ^{2 of at} least one metal of Group 4 and Group 2 of the periodic table of the element is contained, corrosion resistance after coating is excellent. More specifically, 5 mg
/ M is less than ^2, not only is insufficient corrosion protection for aluminum matrix, the desired electrical resistance to reduce the obtained without weldability obtained, for exceeds other 200 mg / m ² the electric resistance too great, welding not It is because

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 film is not particularly required to be carried out, and it may be directly treated after rolling, but normally, it is not generated before the chemical treatment during the aluminum material manufacturing process. For the purpose of removing the uniform film, acid,
Etching in alkali and removal of smut (insoluble residue) in acid solution are appropriately selected and performed.

Further, as the metals of the groups 4 and 2 of the periodic table in the present invention, there can be particularly mentioned the group 4: Si, Ti, Zr, Hf group 2: Ca, Zn, Ba.

Further, in the present invention, the content of the above metal elements in the chemical coating on the electrode contact surface side and the joint surface side of the aluminum plate used for spot welding is changed, that is, the content on the electrode contact surface side is changed. It is less than 2/3 of the joint 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.

In order to obtain the Al plate of the present invention, the plate cut out to a predetermined size from the coil may be used for treatment. However, continuous treatment with a coil is more efficient and contributes to productivity. To do.

[0025]

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 following embodiments, the invention is not limited to the specific description above, and various modifications and improvements can be made based on the knowledge of those skilled in the art without departing from the spirit of the invention. It should be understood that it 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 mast with nitric acid, washing with water, and chemical treatment with a treatment liquid having the composition shown in Table 1 were carried out to form a film having the properties shown in Table 1 on the surface. After that, the following tests were performed on these Al alloy plates.

(1) Formability test: After applying 0.5 g / m ² of cleaning oil on the surface, a sample punched out 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 or / and cracking occurred on the side surface of the cylinder were marked as bad (x), and those in which these defects did not occur were marked as good (◯).

(2) Weldability test: The electrode life was evaluated under the following conditions. In the evaluation, the effect was judged by either the number of hitting points until welding or the number of hitting points until the nugget diameter fell below 4 × t ^1/2 (t: plate thickness), whichever was smaller. As a judgment standard, the number of RBIs is less than 500 points is bad (x), 500 to 10
00 is normal (△), 1000 to 2000 is good (○),
A score of 2000 points or more is also shown in Table 1 as the best (double circle). 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 Energizing time 6/50 seconds Material Cr-Cu Holding 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. Surface conditioning was performed at room temperature for 30 seconds with the system liquid, and chemical conversion treatment was performed as it was with a commercially available zinc phosphate treatment liquid at 43 ° C. for 2 minutes. Then wash with water,
After drying, an undercoat by cationic electrodeposition coating, an intermediate coat and a top coat by spraying were performed to prepare a test sample. The total coating film thickness is 100 μm.

A cross-cut (marked with X) reaching the aluminum substrate was put on the surface of this sample, a salt spray test according to JIS Z 2371 was conducted for 24 hours, and after that, it was left in a humid atmosphere of 50 ° C. and 95% for 2000 hours, and then cross-cut. The maximum length of thread rust (filament corrosion) generated from the part was measured. Judgment was made 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) Palbond L3020 is a commercial liquid (manufactured by Nippon Parkerizing): zinc phosphate type Allodine 401-45 is a commercial liquid (manufactured by Nippon Parkerizing): chromate phosphate type

From Table 1, it can be seen that the Al plates of the present invention are all conventional A
It is superior in formability, weldability, and corrosion resistance after painting compared to l. On the other hand, the content of metal elements in the film is 5 mg /
Comparative Al plate No.7 less than m ^2, does not include a Group 4 or Group 2 metal elements content in comparison Al plate No. 8 and film in excess of 200 mg / m ² of metallic elements in the film Comparison A
It can be seen that 1-plate No. 9 is inferior in any of the above characteristics.

As described above, according to the present invention, since an Al plate having excellent formability, weldability and corrosion resistance can be obtained, it is possible to reduce the weight of an automobile body by using it as an automobile structural member. Play.

 ─────────────────────────────────────────────────── ─── 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 of metal elements of Groups 4 and 2 of the Periodic Table of Elements.
Excellent formability, weldability, characterized by forming a film containing 5 to 200 mg / m ^{2 of} metal or more in terms of metal.
Al plate with corrosion resistance. 2. An aluminum or aluminum alloy plate which is joined to each other by spot welding, and the surface of the plate is provided with at least one metal element of Groups 4 and 2 of the Periodic Table of Elements in an amount of 5 to 200 mg in terms of metal. / M ² contained in the coating, and the content of the above metal element in the coating on the joint surface side during spot welding is 1% of the content of the above metal element in the coating on the electrode contact surface side of spot welding. An Al plate having excellent formability, weldability, and corrosion resistance, which is characterized by being made 5 times or more.