JPH083672A - Aluminum sheet excellent in weldability and corrosion resistance - Google Patents

Abstract

PURPOSE:To prepare the Al sheet by specifying the thickness and Mg oxide content of an Al oxide film on the surface of an Al sheet, forming an oil layer on this film, and regulating contact resistance so that it is higher in one surface of the Al sheet than in the other surface. CONSTITUTION:This Al sheet can be obtained by forming an Al oxide film, having <=20wt.% Mg oxide content, on each surface of an Al sheet to 10-200Angstrom film thickness, applying an oil by >=0.1g/m<2> to the each Al oxide film, and further regulating the contact resistance of one surface of the Al sheet to >=1.1 times that of the other surface. For example, the thickness of the Al oxide film on the joining side surface at the time of spot welding is regulated to >=1.1 times the thickness of the Al oxide film on the electrode contact side surface, and the oil is applied to the oxide films by >=0.1g/m<2>, respectively, so that the amount of oil on the joining side surface at the time of spot welding becomes >=1.1 times the amount of oil on the electrode contact side surface.

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.

[0002]

2. Description of the Related Art With the call for reduction of vehicle body weight for the purpose of improving fuel efficiency and performance of automobiles, the use of aluminum materials, whose specific gravity is 1/3 that of iron, replaces the steel materials used conventionally. It is increasing. Aluminum is not only lightweight, but also has excellent corrosion resistance, workability, surface treatment properties, etc., and is easily regenerated.
It is used in heat exchangers, engines, etc., but 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, and are as follows.

Molding A coil-shaped aluminum plate material or a plate material cut into a predetermined size from a coil body is molded into a predetermined shape.

Joining Joining and / or adhering to a member installed on the body. At that time, the material is fed to the next step in combination with a member made of a conventional steel material.

Surface treatment 1) Degreasing with an alkaline detergent 2) Washing with water 3) Surface adjustment by colloidal titanate treatment 4) Chemical conversion treatment with zinc phosphate treatment 5) Washing with water (where necessary, chromium) Perform "post-treatment" with acid solution) 6) Drying

Coating 1) Undercoating by electrodeposition coating 2) Intermediate coating 3) Topcoating

Outfitting Each part is attached to the skeleton member.

That is, the automobile body is manufactured through the above steps (1) to (3), but the aluminum alloy sheet as a material is cast → soaking → hot rolling → cold rolling → finish annealing (annealing is performed during cold rolling. In some cases), it is manufactured in a usual process, and is used for molding in a state of a coil-shaped body or a plate material after being cut into a predetermined size.

[0010]

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

Poor Weldability During spot welding, the electrode life of aluminum material is extremely inferior to that of steel sheet, 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 since the number of welding spots that can obtain an appropriate nugget with the same electrode is extremely short, the electrode shape can be changed before welding occurs or before an appropriate nugget cannot be formed. The frequency of dressing or replacement with a new electrode increases. This has a great influence on the welding efficiency and hence the production efficiency of the entire automobile body.

Poor Corrosion Resistance After Painting When an accelerated durability test is conducted after painting in a harsh environment, filiform corrosion is likely to occur, which not only impairs the appearance but also causes a functional problem as the corrosion progresses.

As means for improving these problems, Japanese Patent Application No. 3-253126, Japanese Patent Application No. 3-253127, and Japanese Patent Application Laid-Open No. 2-57692 are disclosed. However, in JP-A-2-57692 mentioned above, only the corrosion resistance after coating is improved, and in Japanese Patent Application Nos. 3-253126 and 3-253127, the moldability, weldability, and corrosion resistance after coating are improved. We are making improvements, but we have not reached a satisfactory level.

[0014]

In view of the above, the present invention has been intensively studied, and as a result, the ratio of magnesium oxide contained in the aluminum oxide film on the surface of an aluminum plate and the film thickness of the aluminum oxide film were controlled, We have developed an aluminum plate that not only forms an oil layer on the coating, but also has a higher contact resistance on one side of the aluminum plate than the other, with excellent weldability and corrosion resistance.

That is, according to one aspect of the present invention, an aluminum oxide film having a magnesium oxide content of 20 wt% or less is formed on both surfaces of an aluminum plate to a film thickness of 10 to 200 angstroms, and oil is formed on the oxide film. Apply 0.1 g / m ² or more,
Further, the contact resistance of one surface of the aluminum plate is 1.1 times or more the contact resistance of the other surface.

Another aspect of the present invention is to provide an aluminum oxide film having a magnesium-based oxide content of 20 wt% or less on both surfaces of an aluminum plate, each having a film thickness of 10 to 200 angstroms and spot welding. By forming the relevant coating thickness on the joining side surface to be 1.1 times the relevant coating thickness on the electrode contact side surface, the contact resistance of the joining side surface during spot welding shall be 1.1 times or more the contact resistance of the electrode contact side surface. Moreover, 0.1 g / m ² or more of oil is applied onto the oxide film.

Still another aspect of the present invention is that the content of the magnesium oxide is 20 wt% on both sides of the aluminum plate.
The following aluminum oxide film is formed with a film thickness of 10 to 200 angstroms, and oil is applied on the oxide film respectively.
The amount of oil on the joining side surface at the time of spot welding is 0.1 g / m ² or more, and 1.1 times or more of the oil amount on the electrode contacting side surface is applied, so that the contact resistance of the above joining side surface contacts the electrode. The feature is that the contact resistance of the side surface is 1.1 times or more.

In the above, as a method of adjusting the oxide film, a method of adjusting only the magnesium oxide in the initial oxide film by acid or alkali to adjust the composition and film thickness, or removing all the initial oxides After that, the method of adjusting the composition and the film thickness by controlling the growth of the natural oxide film is effective.

[0019]

Next, the present invention will be described in detail.

Weldability When the spot welding of aluminum material is continuously repeated using the same copper-based electrode as in the case of steel sheet, the current-carrying diameter at the tip of the electrode expands along with the hit point, and the current density in the plate decreases accordingly. As a result, the nugget diameter also decreases and eventually the life of the electrode is reached. However, in the case of an aluminum material, the expansion speed 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 investigating the cause thereof, in the case of continuous spot welding of aluminum material, molten aluminum adheres to the current-carrying portion of the electrode tip and its oxide is deposited together with the spot, We found that magnesium oxide on the aluminum surface was welded to form an insulating layer, which eventually caused a spark between the electrode and this insulating layer, at which time the electrode was worm-eating. It was 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 control the oxide film on the surface of the aluminum material, and the present inventors have filed Japanese Patent Application No. 3-253126,
Japanese Patent Application No. 3-253127 describes that the weldability is improved by adjusting the ratio of magnesium oxide contained in the surface oxide film and the aluminum oxide film thickness.

However, as a result of various studies by the present inventors to further improve the weldability, a significant improvement effect can be obtained by making the contact resistance of the electrode contact side material surface during spot welding lower than that of the joining side material surface. What you get. We have found that the ratio is effective when the contact resistance of the material surface on the bonding side is 1.1 times or more the contact resistance of the material surface on the electrode contact side.

As a result of earnestly studying such a method for controlling the contact resistance value in consideration of cost and productivity,
There is a positive correlation between the oxide film thickness and the contact resistance value, that is, one oxide film thickness on the aluminum plate surface is
It was found that the contact resistance value becomes 1.1 times or more by increasing the value more than twice.

Further, it was also found that oil having a viscosity of 10 cst or more or wax type oil can similarly adjust the contact resistance value on both sides of the aluminum plate by the coating amount.

Further, even if the oxide film thickness is the same, it is possible to control the contact resistance value by controlling the film quality, but this is inferior in cost and productivity.
We also found that it was not practical.

Corrosion resistance after painting Usually, the thread rust that occurs in the coating material of the aluminum body originates from the defective portion of the coating film such as scratches on the surface,
The main cause is that a corrosive substance reaches the aluminum base material in a corrosive environment where chlorine or the like exists and corrodes the aluminum base material. Therefore, it is important to form a film capable of obtaining a strong anticorrosion effect on the aluminum substrate, and the present inventors have made various examination results, the ratio of magnesium oxide contained in the surface oxide film, and aluminum. It was found that it is possible to obtain sufficient corrosion resistance by adjusting the oxide film thickness.

Based on the above knowledge, the present inventors
The present invention has led to the development of an aluminum plate as in the present invention as an aluminum material that improves corrosion resistance. Hereinafter, the present invention will be described in more detail.

As a method for adjusting the thickness of magnesium oxide contained in the above-mentioned initial oxide film or controlling the growth of the natural oxide film after removing the initial oxide film, the method of adjusting the thickness of acid or alkali is used. A chemical etching method using a solution is simple and effective. As the etching solution, nitric acid, sulfuric acid and the like can be considered in the acid system, and sodium hydroxide, sodium phosphate, sodium carbonate and the like in the alkaline system, and as the etching treatment method, immersion treatment and spray treatment can be considered. However, of course, these solutions, methods, etc. are not particularly limited. Further, when etching is performed with an alkaline solution, an alkaline insoluble residue may remain on the surface, so it is desirable to remove the insoluble residue with an acid-based solution in a timely manner.

The content of magnesium oxide in the surface coating is adjusted as described above to make it 20 wt% or less.
This is to prevent welding to the electrode during spot welding and to improve the corrosion resistance after coating.

Further, the reason why the oxide film thickness after adjusting the magnesium oxide is set to 10 to 200 angstroms is that if the thickness is less than 10 angstroms, desired electric resistance cannot be obtained during spot welding and the weldability is deteriorated. Also, if it exceeds 200 angstroms, the electric resistance becomes too large, the heat generation amount on both the electrode contact surface side and the material bonding surface side becomes excessive, and the weldability also deteriorates.

Since the main purpose of the oil coating on the aluminum oxide film is to prevent the oxide film from changing over time, commonly used oils such as cleaning rust preventive oil, molding oil, and solid lubricating oil are used. Then, there is no problem and it is not particularly limited. However, considering the handling property and degreasing property in the manufacturing process of automobile parts and the like, it can be expected that further effects can be exhibited by using a low-viscosity (20 cst or less) cleaning rust preventive oil or molding oil. Also, the coating amount is 0.1 g / m
^The reason for setting it to ² or more is that if it is less than this, a sufficient effect of preventing a change with time of the oxide film and a rust preventive effect cannot be obtained.

In the present invention, the aluminum plate may be treated with a plate cut out from the coil to a predetermined size, but it is needless to say that continuous treatment with a coil is more efficient and contributes to productivity. .

At present, aluminum alloys for automobile bodies are mainly 2XXX series, 5XXX series and 6XXX series, and 2XXX series are Cu, Mg, M represented by 2036.
An alloy with n added is used, and the 5XXX series has M
g: 2 to 10 wt%, 6XXX system Mg: 0.1 to 2.0 wt%,
Si: 0.5 to 2.5 wt% is used as a main additive element, and Cu, Mn, Cr, etc. are added as required. The aluminum alloy used in the material of the present invention is not particularly limited, and any one may be used.

Further, the aluminum alloy surface shape is a "mill" shape in which the usual rolling grain remains as it is, a "shot dull" shape in which various patterns are formed on the surface of the rolling roll and transferred to the aluminum alloy surface. ,
There are "laser dull" shapes, but like the alloy components above,
It is not particularly limited, and any one may be used.

Further, the aluminum plate of the present invention is not particularly limited to automobile structural members as long as it is used for one or more processes of welding and painting.

[0037]

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 the examples. Further, in addition to the following embodiments, the present invention further includes various changes, modifications, improvements, etc. based on the knowledge of those skilled in the art without departing from the spirit of the present invention other than the above specific description. Can be added.

JIS A5182 (Al-0.3wt% Mn
-4.5 wt% Mg) was melted, cast, homogenized, hot-rolled, cold-rolled and finish-annealed to a plate thickness of 1.0 mm by continuous coil treatment. After this material was subjected to oxide film adjustment under the conditions shown in Tables 1 and 2, Tables 1 and 2
A predetermined amount of oil as shown in FIG. After that, the temperature 40 ℃,
It is left for 90 days in a constant temperature and humidity chamber with a relative humidity of 95%, the oxide film thickness before and after leaving, the weight ratio of magnesium oxide in the oxide film,
The surface resistance and ratio, weldability, and corrosion resistance after coating were investigated and tested by the methods shown below. The results are shown in Table 1 and Table 2.
It was also described in.

The oxide film thickness and the weight ratio of magnesium oxide in the oxide film were determined by ESCA (X-ray photoelectron spectroscopy analyzer).

Surface Resistance Value and Ratio The resistance values on both sides of the aluminum material were measured with a Yamazaki SQ meter (manufactured by Yamazaki Seiki Co., Ltd.). For the measurement, the electrode was slid on the aluminum surface for 10 mm, and the average value was obtained. The surface resistance ratio was obtained by dividing the value on the joint surface side during spot welding by the value on the electrode contact surface side.

Weldability test The electrode life was evaluated under the conditions shown below. The evaluation is that the number of spots until the electrode is welded or the nugget diameter is 4 t ^1/2 (t:
The effect was judged by the smaller number of RBIs, whichever is less than the number of RBIs below the sheet thickness).

[0042]

Corrosion resistance test after coating A test piece of 70 × 150 mm was cut out from the coil after treatment, degreased with a weak alkaline degreasing material at 43 ° C. for 2 minutes, and washed with water, and then a colloidal titanium-based solution. Room temperature ×
The surface was adjusted for 30 seconds, and a chemical conversion treatment was carried out with a commercially available zinc phosphate treatment solution at 43 ° C. for 2 minutes as it was. Then, after washing with water and drying, an undercoat by cationic electrodeposition coating, an intermediate coat by spraying, and an overcoat were carried out to prepare a sample. The total coating thickness at this time is about 1
It is 00 μm.

A cross-cut reaching the aluminum substrate was put on the surface of this sample, a salt spray test according to JIS-Z-2371 was performed for 24 hours, and after that, the sample was left in a humid atmosphere of 50 ° C. × 95% RH for 2000 hours, and then cross-cut. The maximum length of thread rust (filament corrosion) generated from the part was measured.
Judgment was made such that the thread rust length of 4 mm or more was defective (x), 2 to 4 mm was normal (◯), and 2 mm or less was good (⊚).

[0045]

[Table 1]

[0046]

[Table 2]

As is clear from Table 1, the present invention No. 1
No. 4 shows good weldability immediately after treatment and after 90 days of standing, and good corrosion resistance after painting. In the case of No. 5 of the present invention, when the oxide film thickness exceeds 200 Å and the magnesium oxide exceeds 20% after being left for 90 days, the weldability and the corrosion resistance after coating deteriorate, but if it is in the state immediately after the treatment. It can be seen that it shows good performance.

[0048]

As described above, according to the present invention, it becomes possible to inexpensively and stably supply an aluminum material for an automobile body which is excellent in weldability and corrosion resistance, and has a remarkable industrial effect. .

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Masaaki Kurihara 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd. (72) Naoki Nishiyama 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Inside Steel Engineering Co., Ltd.

Claims (3)

[Claims] 1. An aluminum oxide film having a magnesium oxide content of 20 wt% or less is formed on both surfaces of an aluminum plate to a film thickness of 10 to 200 angstroms, and 0.1 g / m ^{2 of} oil is formed on the oxide film. An aluminum plate excellent in weldability and corrosion resistance, which is characterized in that the contact resistance on one surface of the aluminum plate is 1.1 times or more the contact resistance on the other surface of the aluminum plate after the above coating. 2. An aluminum oxide film having a magnesium oxide content of 20 wt% or less is formed on both surfaces of the aluminum plate and has a thickness of 10 to 200 angstroms, respectively, and the thickness of the film on the joining side surface during spot welding. By forming 1.1 times the relevant film thickness on the electrode contact side surface,
Weldability, characterized in that the contact resistance of the joining side surface during spot welding is 1.1 times or more of the contact resistance of the electrode contact side surface, and further 0.1 g / m ² or more of oil is applied on the oxide film,
Aluminum plate with excellent corrosion resistance. 3. An aluminum oxide film having a magnesium oxide content of 20 wt% or less is formed on both surfaces of the aluminum plate to a film thickness of 10 to 200 angstroms, and 0.1 g / m of oil is formed on each oxide film. ^If the amount of oil is ² or more and 1.1 times or more the amount of oil on the joint side surface during spot welding is applied to the amount of oil on the electrode contact side surface, the contact resistance of the joint side surface will be An aluminum plate with excellent weldability and corrosion resistance, characterized by having a resistance of 1.1 times or more.