JPH0790606A - Organic coated aluminum alloy sheet with excellent spot resistance weldability and corrosion resistance and spot resistance welding method using the same - Google Patents

Abstract

(57) [Summary] (Corrected) [Purpose] An aluminum alloy sheet that improves the continuous spotting property during spot resistance welding, has excellent corrosion resistance, and can be manufactured industrially easily and economically. [Structure] As a pretreatment, the alumina layer on the surface is removed by an alkali etching treatment, or the magnesia layer is mainly removed in an acidic aqueous solution containing a mineral acid, or the above two treatments are sequentially performed to etch the oxide film. The amount of chromium adhered to the welded joint surface during spot resistance welding on the formed aluminum alloy plate is 5 to 200 mg / m in terms of metallic chromium.
^{The second} chromate film is formed on the surface contacting the electrode tip as a first layer with a chromium adhesion amount of 5 to 100 mg / m ² in terms of metallic chromium and 75% or less of the chromium adhesion amount on the welded surface. An organic coated aluminum alloy plate excellent in spot weldability and corrosion resistance, which is further coated with an organic resin as a second layer having a dry film thickness of 0.01 to 3.0 μm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a lightweight material for automobiles, and more particularly to an aluminum alloy plate used as a vehicle body panel.

[0002]

2. Description of the Related Art Conventionally, steel sheets have been widely used as a body panel material for automobiles, but in recent years, in order to improve the fuel efficiency of automobiles from the viewpoint of global environmental problems, in particular, measures against global warming due to CO _2. The weight reduction of the vehicle body is actively promoted, and aluminum alloys have come to be used as inner and outer plates for automobiles because they are lightweight and have excellent corrosion resistance.

Most of these automobile body panel materials are assembled and joined by spot resistance welding. However, aluminum alloy sheets have extremely poor spot resistance weldability, especially electrode life, compared to steel sheets. The current situation is that it has caused a significant decrease in production efficiency.

That is, in spot resistance welding of an aluminum alloy plate, a welding phenomenon between an electrode tip and an aluminum alloy plate is likely to occur, and welding is performed because the number of welding spots at which an appropriate nugget can be obtained with the same electrode is extremely short. Before or before proper nugget cannot be formed, the electrode shape is often dressed or replaced with a new electrode. These have a great influence on the welding efficiency and thus the production efficiency of the automobile body.

As a proposal of means for solving the above problems, for example, JP-A-57-4389 discloses an improvement method by plating with Cr, Ni, Cu and Ag. No. 1874843 discloses an improvement method by controlling the oxide film thickness on the aluminum plate joint surface by anodic oxidation, and Japanese Patent Laid-Open No. 3-146693 discloses Ni plating on the aluminum plate surface and Zn plating on the upper layer. A method of improving by applying is disclosed.

[0006]

However, JP-A-57-57
Cr, Ni, on the aluminum alloy plate of Japanese Patent No. 4389
Cu and Ag plating method and JP-A-3-1466
The improving method of Ni plating on the surface of the aluminum alloy plate and Zn plating on the upper layer of JP-A No. 93 have problems in adhesion of these platings to the aluminum alloy plate,
Plating of a metal nobler than aluminum is not preferable because it significantly reduces corrosion resistance. Also, JP-A-60-18748
The improvement method by controlling only the anodized film of Japanese Patent No. 3 has insufficient corrosion resistance and has a problem that thread rust is likely to occur.

The present invention overcomes the drawbacks of the surface treatment of the aluminum alloy plate described above, significantly improves the electrode life during spot resistance welding, that is, the continuous spotting property, as compared with conventional aluminum materials, and at the same time has excellent corrosion resistance. It is an object of the present invention to provide an aluminum alloy plate that can be manufactured easily and economically and a spot resistance welding method using the same.

[0008]

First, the improvement of spot resistance weldability is based on the following knowledge. That is, when spot resistance welding is repeatedly performed on the aluminum alloy plate using the same copper-based electrode continuously, the current-carrying diameter at the electrode tip expands along with the dot, and the nugget diameter also decreases due to the decrease in the current density in the plate accompanying this. Although it will decrease and eventually become the life of the electrode, the characteristic feature of the aluminum alloy plate is that the expansion speed of the electrode tip diameter is significantly higher than that of the steel plate.

As a result of paying attention to such a phenomenon and carefully studying the cause, as a result of the fact that the electric conductivity of aluminum is about four times as large as that of steel sheet, the heat generated during welding is generated by the surface oxide having a small electric conductivity. Is dominated. Therefore, when current is applied to an aluminum alloy plate having a non-uniform oxide film that is present on the surface of the aluminum alloy plate during welding and that contains a large amount of insulative MgO generated during hot rolling, in addition to the bonding surface, the tip of the electrode surface and the aluminum alloy plate Since heat is also concentrated on the contact portion, the aluminum alloy in the portion in contact with the electrode easily melts and adheres to the tip of the electrode. The aluminum alloy adhering to the tip of the electrode is deposited as an oxide together with the hitting point to form an insulating layer, which eventually causes a spark between the electrode and this insulating layer, and the electrode is damaged like a worm. Therefore, it was found that the diameter of the tip of the electrode is increased and the life of the electrode is extremely deteriorated.

From the above findings, the oxide on the surface of the aluminum alloy plate is removed by the etching treatment, and the amount of chromate on the contact surface of the electrode tip of the aluminum alloy plate is reduced by 25% or more than that of the welded surface. It was found that controlling the adhesion of the molten aluminum alloy to the electrode tip by concentrating it on the surface reduces the wear of the electrode tip and significantly improves the number of continuous dots.

The etching treatment referred to here is a treatment for removing the alumina layer on the surface by an alkali etching treatment,
Alternatively, it is a treatment for removing a part or almost all of the oxide layer on the surface by a pickling treatment for mainly removing the magnesia layer in an acidic aqueous solution containing a mineral acid, or a treatment for performing a pickling treatment after an alkali etching treatment. By the treatment, stable spot resistance weldability is obtained which is not affected by the difference in the surface oxide film due to the composition and history of the aluminum alloy plate.

That is, according to the present invention, the amount of chromium adhered to the spot-welded joint surface of the etched aluminum alloy plate is 5 to 200 mg / m ^{2 in} terms of metallic chromium.
Chromate film is formed as the first layer, and the amount of chromium deposited on the contact surface of the electrode tip is 5 to 1 in terms of metallic chromium.
00 mg / m ² and the amount of chromium deposited on the welded surface is 75
% Or less of the chromate film as the first layer, and the organic resin is further coated on each of the chromate films as a second layer of 0.01 to 3.0 μm in dry film thickness. An organic coated aluminum alloy plate having excellent corrosion resistance is provided.

The organic resin is preferably an epoxy resin, an alkyd resin, an acrylic resin, a urethane resin, a phenol resin, a melamine resin, a polyvinyl butyral resin, a polyester resin, or a mixture of two or more thereof, and a base resin. It is preferable to add general additives such as a reaction accelerator and a stabilizer to the extent that the gist of the present invention is not impaired, but rather preferable.

When spot welding is performed using this aluminum alloy plate, the surface having the larger amount of chromium adhesion is used as the bonding surface between the plates and the other surface is used as the electrode bonding surface.

[0015]

The present invention will be described in more detail below. In the present invention, the nonuniform oxide layer formed in the manufacturing process on the surface of the aluminum alloy plate is removed by etching and then chromate treatment is performed to form a uniform chromate layer. The oxide layer can be removed by an etching treatment by a commonly used method. A treatment for removing the alumina layer on the surface by an alkali etching treatment with caustic potash, caustic soda, or a mineral acid such as sulfuric acid, hydrochloric acid or hydrofluoric acid. In order to remove a part or almost all of the oxide layer on the surface by a pickling treatment for mainly removing the magnesia layer in an acidic aqueous solution containing, or a treatment for carrying out a pickling treatment after an alkali etching treatment, the aluminum is treated by this treatment. Stable spot resistance weldability that is not affected by the difference in surface oxide film due to the composition and history of the alloy plate can be obtained.

The chromate treatment method may be any of the conventional treatment methods such as reaction type chromate treatment, coating type chromate treatment and electrolytic chromate treatment.
A reactive chromate treatment or a coating chromate treatment is desirable because it forms a uniform chromate film.

Next, in order to prevent thread rust, the amount of adhesion of chromate at the joint surface between plates during welding should be at least 5 mg / m ² or more in terms of metallic chromium.
If the amount is more than m ² , the resistance becomes too large, which rather reduces the spot weldability.
It was set to m ² .

Further, in order to reduce heat generation on the electrode contact surface side and remove the aluminum oxide layer on the surface in order to prevent aluminum from adhering to the electrode, a uniform chromate film is applied to the welded surface with a chromium adhesion amount of 75% or less of the welded surface. Need to be formed.

When the adhesion amount exceeds 75% and 100 mg / m ² , welding of the aluminum alloy to the electrode occurs and the weldability is deteriorated, and when the adhesion amount is 5 mg / m ² or less, thread rust occurs. Chromate adhesion amount on the surface is 5-10
The range was limited to 0 mg / m ² .

In the present invention, the second layer film on the chromate film is an organic resin, for example, one of epoxy resin, alkyd resin, acrylic resin, urethane resin, phenol resin, melamine resin, polyvinyl butyral resin, polyester resin. Alternatively, two or more resins are typically used.

If the film thickness of these resins is less than 0.01 μm, the resin cannot completely cover the surface, so that chromium is eluted from the chromate film during zinc phosphate treatment and the zinc phosphate treatment solution is contaminated. , 3.0 μm, the weldability deteriorates, so the range was made 0.01 to 3.0 μm.

[0022]

EXAMPLES The present invention will be specifically described below based on examples.

(Example) A 1 mm thick J which is a typical aluminum alloy plate used as an automobile body material
Using IS A5182 alloy, the aluminum alloy surface was first steam-degreased with trichlorethylene, and then the following etching treatments (a), (b) and (c) were performed, and Table 1 was used.
The surface treatment shown in FIG. (A) 5% NaOH, 50 ° C., 30 sec (b) 30% HNO ₃ , room temperature, 30 sec (c) (a) + (b)

The chromate solution and organic resin used are as follows. (Chromate solution) Coating type: Nippon Parkerizing 4513H Reactive type: Nippon Parkerizing Alchrome 713 (organic resin) Epoxy resin Yuka Shell Epoxy Co., Ltd. Epicoat 1007 Alkyd resin Mitsui Toatsu Kagaku Co., Ltd. Urics acrylic resin Mitsui Toatsu Chemicals Altemax 749-7 Urethane resin manufactured by Mitsui Toatsu Chemical Co., Ltd. Olester phenol resin Dainippon Ink and Chemicals Co., Ltd. Super Beckasite Melamine resin Mitsui Toatsu Chemical Co., Ltd. U-ban Polyvinyl butyral resin Denki Kagaku Co., Ltd. Denka Butyral polyester resin Mitsui Toatsu Chemicals, Inc., Artemax P645

(Welding Property Test) The electrode life of the aluminum alloy plate after the surface treatment was evaluated using an inverter DC welding machine under the following electrodes and welding 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 falls below 4√t (t: plate thickness), whichever is smaller. As for the evaluation criteria, the number of hit points is less than 500 (poor), 500 to 1000 is normal (◯), 10
A score of 00 or more was rated as excellent (⊚).

(Electrode) -Shape: Cone head (CF) type-Tip diameter: 5.0 mmφ-Material: Cr-Cu (welding condition) -Pressure: 150 kgf-Initial pressurization time: 20/50 seconds- Energization time: 6/50 seconds ・ Holding time: 5/50 seconds ・ Welding current: 15 kA

(Chromium elution test in chemical conversion liquid) The amount of chromium dissolved in the surface treated aluminum alloy plate treated with zinc phosphate was measured by fluorescent X-ray analysis, and the amount dissolved per unit area was 1 mg / m ² or less is good (○), 1 mg / m
^The case of exceeding ² was regarded as defective (x).

(Post-painting corrosion resistance test) The surface-treated aluminum alloy plate is treated with zinc phosphate (manufactured by Nippon Parkerizing Co., Ltd., PB-L3080 1.6 mg / m ² ), cationic electrodeposition coating (manufactured by Kansai Paint Co., EL-). No. 2000
20 μm), intermediate coating by spraying (Kansai Paint Co., TP37 35 μm), top coating (Kansai Paint Co., TM13RC 35 μm), cross-cut reaching aluminum base, and spraying with salt water according to JIS Z2371 for 24 hours. After standing for 2000 hours in a humid atmosphere of 50 ° C. and 95% RH, the maximum length of thread rust generated from the cross cut portion was measured. Judgment was judged as good (∘) when the thread rust length was 2 mm or less and bad (x) when it exceeded 2 mm.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Effects of the Invention] Table 1 shows the examples and comparative examples of the present invention. As is clear from Table 1, the present invention is extremely effective in improving spot weldability and corrosion resistance of aluminum alloy sheets.

As described above, according to the present invention, the oxide film on the surface of the aluminum alloy plate is removed, the chromate treatment of the thickness difference is performed, and the organic resin coating treatment is performed, whereby the weldability and the corrosion resistance can be remarkably improved. The frequency of shaping the tip shape by exchanging electrodes or dressing during spot welding at the production site is significantly reduced, which leads to a marked improvement in productivity.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuo Totsuka, Inventor 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Masanori Ikeda Chuo-ku, Chiba-shi, Chiba Kawasaki-cho No. 1 Technical Research Division, Kawasaki Steel Co., Ltd. (72) Inventor Koichi Hashiguchi No. 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Motohiro Nambae 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Industry Co., Ltd.

Claims (3)

[Claims] 1. Alkaline etching treatment as pretreatment
Treatment to remove the alumina layer on the surface or to contain mineral acid
Pickling to remove magnesia layer mainly in acidic aqueous solution
Pickling treatment after treatment or alkali etching treatment
The aluminum film whose oxide film has been etched by
Um alloy plate, on the welding joint surface when spot resistance welding
Chromium adhesion amount is 5 to 200 mg / m in terms of metallic chromium²
Chromate coating on the surface that the electrode tip contacts with chrome
5 to 100 mg / m in terms of metal chromium conversion ²And
Chromate skin with 75% or less of chromium adhesion on welded surface
Each film is formed as the first layer, and the organic layer is formed on the first layer.
The dry film thickness of the resin is 0.01 to 3.0 μm as the second layer.
Spot weldability and corrosion resistance characterized by being covered
Organic coated aluminum alloy plate with excellent properties. 2. The organic resin is an epoxy resin, an alkyd resin, an acrylic resin, a urethane resin, a phenol resin,
The organic coated aluminum alloy plate according to claim 1, which is one kind or a mixture of two or more kinds of a melamine resin, a polyvinyl butyral resin, and a polyester resin. 3. An excellent continuous spotting property, characterized in that the aluminum alloy plate according to claim 1 or 2 is spot-welded with a surface having a large amount of chromium as a joining surface and another surface as an electrode joining surface. Resistance welding method for welded aluminum plate.