JPH0790609A - Surface-treated aluminum material with excellent workability, spot resistance weldability and corrosion resistance - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a surface-treated aluminum material excellent in workability, spot resistance weldability and corrosion resistance. [Structure] On an aluminum alloy substrate whose surface oxide film thickness has been adjusted to 150 Å or less, 5 to 50 mg / mol in terms of metal Cr
m ² chromate layer with a specific surface area of 800
1 to 40% by weight of m ² / g or more of carbon black, and 0.1 g / m ² or more of a rust preventive oil layer containing 1 to 30% by weight of a powdered lubricant. Surface-treated aluminum material with excellent resistance weldability and corrosion resistance. Alkali-soluble C in chromate layer
The amount of r (3% NaOH aqueous solution, 60 ° C., 5 minutes immersion) was 3
It is mg / m ² or less. The powdered lubricant has an average particle size of 2
It is a wax and / or a fluororesin having a size of 0 μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly processes aluminum and aluminum alloy plates (hereinafter referred to as aluminum alloy plates) for automobiles, home appliances, building materials, members for can materials, etc. which are processed by press forming and spot resistance welding. The present invention relates to an aluminum material such as a surface-treated aluminum plate having excellent heat resistance, spot resistance weldability and corrosion resistance.

[0002]

2. Description of the Related Art Aluminum alloy sheets are used for automobiles, home appliances, O
It is widely used in the fields of A equipment, building materials, can materials, etc., and is often subjected to various press workings and spot resistance welding in the manufacturing process of these products.

As a method for improving the formability of such an aluminum alloy plate, for example, a conventional technique developed for can materials, in which only a wax is applied to the surface (for example, JP-A-2-310036 and JP-A-3-180218). No.), the workability is not sufficient when the coating amount of wax is small, and the mold is contaminated when the coating amount is large, so it cannot be used in a wide range of fields and, after pressing, the metal surface of an aluminum alloy plate Since it is exposed, it may cause a problem in corrosion resistance when used as it is. Further, the application of these solid lubricants has a drawback that the spot resistance weldability is deteriorated.

[0004]

In the conventional method for improving workability by applying only these waxes, it is difficult to obtain a stable effect under various molding conditions.
In addition, depending on the environment of use, there is a risk of rusting unless painting or other anticorrosion treatment is applied after processing.

Therefore, in order to overcome these drawbacks of the prior art, it is an object of the present invention to provide a surface-treated aluminum material capable of ensuring higher workability and having both sufficient corrosion resistance and spot resistance welding. And

[0006]

The present invention has been completed on the basis of earnest studies on the above problems of the prior art and the following findings.

First, the improvement of formability is based on the following findings. That is, it is essentially important to improve the formability of the aluminum alloy plate, but it was found that the formability can be improved by improving the slidability of the surface even with the same material, In addition, it has been found that applying rust preventive oil containing organic lubricating fine particles to the surface of the aluminum alloy material is effective for improving the slidability.

The improvement of spot weldability is based on the following knowledge. That is, when spot resistance welding is repeatedly performed on an aluminum alloy plate using the same copper-based electrode, the energization diameter at the electrode tip expands along with the dot, and the nugget is formed due to the decrease in the current density in the plate. It will not be done, and the life of the electrode will finally be reached.

As a result of diligent study on the cause, the electric conductivity of aluminum is large, and the heat generated during welding is dominated by the surface oxide having a small electric conductivity. Therefore, the insulating property generated during hot rolling or annealing is not uniform. When electricity is applied to the aluminum alloy plate having the oxide film, heat is concentrated on the contact portion between the joint, the tip of the electrode surface and the aluminum alloy plate.

Therefore, the aluminum alloy in the portion in contact with the electrode is easily melted and adhered to the tip of the electrode, and the aluminum alloy adhered to the tip of the electrode is deposited as an oxide together with the spot to form an insulating layer. Therefore, it was found that a spark is generated between the electrode and the formed insulating layer, the electrode is damaged in a worm-eating manner, and the electrode tip diameter is enlarged, so that the electrode life is extremely deteriorated.

From the above knowledge, by forming a chromate layer on the aluminum alloy plate, it is possible to prevent the electrode tip from directly contacting the aluminum alloy plate, and to prevent the molten aluminum alloy from adhering to the electrode tip to a proper degree. It has been found that the application of electric resistance reduces the wear of the electrode tip and significantly improves the number of continuous dots. It was also found that the spot resistance weldability was further improved by removing a part or most of the insulating nonuniform oxide film formed during hot rolling and annealing on the aluminum surface by the etching treatment.

On the other hand, it was found that the deterioration of spot resistance weldability due to the application of rust preventive oil containing an organic powder lubricant can be avoided by adding an appropriate amount of carbon black to the rust preventive oil. did.

Further, the improvement of corrosion resistance is based on the following knowledge. That is, the thread rust corrosion, which is the most problematic in the corrosion resistance of the aluminum alloy plate, is caused by the poor formation of zinc phosphate chemical conversion treatment, which promotes the electrochemical dissolution of aluminum at the defective portion of the chemical conversion crystal. And rust corrosion progresses. However, it has been found that by performing chromate treatment on the surface of the aluminum alloy plate, it is possible to significantly suppress thread rust corrosion.

Further, the adhesion of the powder lubricant is improved by subjecting the chromate stabilization treatment after the chromate treatment to a problem caused by the elution of hexavalent chromium in the unpainted use or in the pretreatment process when painting. It was found that the above can be suppressed.

That is, in order to achieve the above-mentioned object, the present invention provides an aluminum alloy substrate whose surface oxide film thickness is adjusted to 150 Å or less, in an amount of 5 to 50 mg / m in terms of metal Cr.
Has ² chromate layers with a specific surface area of 800 m
¹ /40% by weight of carbon black of ² / g or more, and 0.1 g / m ² or more of a rust preventive oil layer containing 1 to 30% by weight of a powdered lubricant, workability and spot resistance. Provided is a surface-treated aluminum material having excellent weldability and corrosion resistance.

Here, the chromate treatment may be any commonly used method such as coating type, reactive type or electrolytic type, but the alkali-soluble Cr (3%) in the chromate film is used.
Aqueous solution of NaOH, dipping at 60 ° C for 5 minutes) 3mg / m
It is preferably ² or less, and a stabilizing treatment is applied for this purpose.

The powdered lubricant is preferably wax and / or fluororesin having an average particle size of 20 μm or less.

[0018]

The present invention will be described in more detail below. The aluminum alloy plate in the present invention may be any aluminum or aluminum plate alloy plate and is not particularly limited. For example, various aluminum alloy plates defined by JIS H4000 may be used.

Further, the aluminum material in the present invention broadly includes aluminum materials such as aluminum and aluminum alloys, and its form is arbitrary such as plate material, bar material, and pipe material.

In the present invention, in order to reduce the surface resistance to improve the spot resistance weldability and to form a uniform chromate layer, it is generated in the manufacturing process formed on the surface of the aluminum alloy plate by etching. Remove some or most of the non-uniform oxide layer.

As the alkali etching treatment and the pickling treatment, a method generally used as a treatment method for an aluminum material may be used, and a commercially available treatment liquid may be used. For example, caustic soda, caustic potash solution and the like can be used for the alkali etching treatment, and sulfuric acid, nitric acid, hydrofluoric acid, nitric acid + hydrofluoric acid mixed solution and the like can be used for the pickling treatment.

As the etching treatment, either an alkali etching treatment for removing the alumina layer on the surface with an alkali aqueous solution, a pickling treatment for mainly removing the magnesia layer in an acidic aqueous solution, or a treatment for carrying out a pickling treatment after the alkali etching treatment is carried out. Is used.

By these treatments, the surface oxide film thickness is 150
Å Less than or equal to If the oxide film thickness exceeds 150Å, the weldability deteriorates, which is not preferable.

In the present invention, a chromate treatment is performed after the etching treatment for the purpose of improving weldability and corrosion resistance.
The method of chromate treatment may be a commonly used treatment method, for example, reactive chromate treatment, coating-type chromate treatment, electrolytic chromate treatment or any other method, but since a chromate film can be easily formed, reactive chromate treatment or coating Type chromate treatment is preferred.

The amount of chromate needs to be at least 5 mg / m ^{2 in} terms of metallic chromium in order to prevent thread rust, and if the amount of adhesion exceeds 50 mg / m ² , there is no further significant improvement in corrosion resistance, Not only is it uneconomical, but the spot resistance weldability is also reduced, so it was set to 5 to 50 mg / m ² .

Further, in the present invention, in order to prevent the elution of hexavalent chromium and improve the adhesion of the powdered lubricant on the chromate upper layer, the chromate stabilization treatment is performed using a solution such as ethanol washing or hot water washing. Is desirable. By this treatment, the amount of alkali-soluble Cr in the chromate film was 3 mg / mm when immersed in a 3% NaOH aqueous solution for 5 minutes at 60 ° C.
m ² or less. This alkali-soluble Cr is 3 mg / m
^If it exceeds ² , chromium is excessively eluted in various treatment liquids used in the pretreatment process before coating or when coating, and the adhesion of the powdery lubricant is deteriorated, which is not preferable.

In the present invention, a rust preventive oil containing a powdered lubricant and carbon black is applied on the chromate layer in order to significantly improve the workability without impairing the spot resistance weldability.

Here, it is preferable to use a polyolefin wax, a fluororesin, or a mixture thereof as the powder lubricant. Examples of the polyolefin wax include polyethylene wax, polypropylene wax, polybutene wax and the like.

Examples of the fluorinated resin include polytetrafluoroethylene resin, polyvinyl fluoride resin, and polyvinylidene fluoride resin.

It is preferable that these lubricants have an average particle size of 20 μm or less and an addition amount of 1 to 30% by weight. If the average particle size of the lubricant exceeds 20 μm, the lubricant is likely to come off during processing, which impairs workability, which is not preferable. Further, if the content is less than 1% by weight, the workability improving effect cannot be obtained, and if it exceeds 30% by weight, the workability improving effect is saturated and spot resistance welding is deteriorated, which is not preferable.

In the present invention, in order not to impair the spot resistance weldability, 1 to 40 carbon black having a specific surface area of 800 m ² / g or more is added to the rust preventive oil.
It is extremely important that the content is wt%. When the specific surface area of this carbon black is less than 800 m ² / g,
The effect of imparting conductivity to rust preventive oil is small, and the effect of improving spot resistance weldability is small. Further, if the content is less than 1% by weight, the effect of improving spot resistance weldability is small and 4
If it is added in an amount of more than 0% by weight, the carbon black is likely to be peeled off during processing and the processability is impaired, which is not preferable.

The rust preventive oil which is the base of the rust preventive oil containing the powdered lubricant and carbon black may be a commonly used one and is not particularly limited, but its coating amount is 0.1 g / m ² is required. This application amount is 0.1g
If it is less than / m ² , coating on the surface is incomplete and the workability is adversely affected.

[0033]

EXAMPLES The present invention will be specifically described below based on examples. (Example 1) A typical aluminum alloy for processing,
Using a JIS A5182 alloy plate having a thickness of 1 mm, first the surface was vapor-degreased with trichloroethane, and then the surface oxide film was adjusted by the treatment shown in Table 1. Here, the oxide film thickness of the sample is A
Obtained from ES analysis.

Then, chromate was applied with a roll coater, and rust preventive oil was applied with a spray. The conditions of the chromate treatment and rust preventive oil at this time are as follows.

[0035] 1) chromate treatment - Type: application type chromate Nippon Parkerizing Co. 4513H-deposition amount: 23~28mg / m ² · chromate stabilization: 10% ethanol, 60 ° C. immersion treatment-soluble Cr: 0.1 mg / m ² or less 2) Anti-rust oil conditions Anti-rust oil-Type: Idemitsu Kosan Co., Ltd. Daphni Oil Coat Z-5-Coating amount: 1.5 g / m ² powdered lubricant-Type: San Nopco SL530 (polyolefin wax) : Average particle size 6 μm) -Content: 15% by weight carbon black-Type: Ketjenblack EC600D (specific surface area: 1270 m ² / g) -Content: 20% by weight

Here, the amount of chromate attached is C before and after the treatment.
According to the fluorescent X-ray analysis of the amount of r, the amount of soluble Cr was immersed in 3% NaOH aqueous solution at 60 ° C. for 5 minutes after the stabilization treatment, and the amount of eluted Cr was determined by atomic absorption spectrometry.

After that, various characteristics of the manufactured sample were measured and evaluated in the following manner. The results are also shown in Table 1.

(Cr dissolution test and evaluation method) Ten samples were used.
After cutting to 0 × 200 mm, the end face was sealed, immersed in 3% saline solution at 60 ° C. for 2 minutes, and Cr eluted from the sample surface
The amount of ions was measured by atomic absorption spectrometry and evaluated according to the following criteria. X: Cr elution amount is 0.5 mg / m ² or more O: Cr elution amount is less than 0.5 mg / m ^2.

(Workability test and evaluation method) 70 mm sample
Punching to φ, 33 mmφ high-speed cylindrical drawing (processing speed 5
00 mm / sec) test was performed and evaluated according to the following criteria. ×: Sample has galling and / or cracking ○: Sample has no galling and can be drawn through

(Welding Test and Evaluation Method) An inverter DC welding machine was used to perform a test under the following electrode and welding conditions. The evaluation was made by either the number of hitting points until welding or the number of hitting points until the nugget diameter fell below 4√t (t: plate thickness), whichever was smaller, and the judgment was made according to the following criteria. (Electrode) ・ Shape: Cone frusto-conical (CF) type ・ Tip diameter: 5.0 mmφ ・
Material: Cr-Cu (welding conditions) -Pressure: 150 kgf-Initial pressurization time: 20/50 seconds-Electrification time: 6/50 seconds-Holding time: 5/50 seconds-Welding current: 15 kA (evaluation standard) : 1000 or more continuous dots x: Less than 1000 continuous dots

(Corrosion resistance test and evaluation method) Corrosion resistance of each sample was 20 μm by cutting a 75 × 150 mm plate from each sample.
Cationic electrodeposition coating (U-600 manufactured by Nippon Paint Co., Ltd.),
Each is coated with a 35 μm intermediate coat (Kansai Paint Co., Ltd. Sheila White KPX50) and top coat coat (Kansai Paint Co., Ltd., Rugabake B531), and reaches the base on the coated surface according to the thread rust test method specified in ASTM D2803. Cross-cut scratches were given, and the test was performed for 6 weeks and evaluated according to the following criteria. ◯: The length of thread rust from the cross-cut scratch is less than 2 mm ×: The length of thread rust from the cross-cut scratch is 2 mm or more

As is clear from the results shown in Table 1, all the samples within the scope of the present invention have excellent workability, corrosion resistance and weldability.

On the other hand, sample No. which is a comparative example. 1,
Since Nos. 2, 6 and 13 have thick oxide films, their weldability is poor.

(Example 2) A5182 as in Example 1
The same evaluation test as in Example 1 was carried out using an aluminum alloy plate and changing the chromate treatment conditions shown in Table 2.
Here, the oxide film adjusting conditions, the chromate species and the rust preventive oil conditions are as follows.

1) Oxide film adjustment treatment-Method: 30% nitric acid, 25 ° C immersion treatment-Oxide film thickness: 105Å 2) Chromate treatment-Treatment method A: coating type chromate manufactured by Nippon Parkerizing 4513H-Treatment method B: coating Type Chromate Kansai Paint Cosmer 150 ・ Processing method C: Reactive Chromate Nippon Parkerizing Alchrom 713 ・ Chromate stabilization treatment: 10% ethanol, 60 ° C immersion treatment 3) Antirust oil conditions Antirust oil ・ Types: Idemitsu Kosan Daphuni Oil Coat Z-5 ・ Coating amount: 1.5 g / m ² powdered lubricant ・ Type: San Nopco SL530 (Polyolefin wax: average particle size 6 µm) ・ Content: 15% by weight carbon black ・Type: EC600D manufactured by Ketjen Black (specific surface area: 1270 m ² / g) ・ Content: 20% by weight

The evaluation test results are also shown in Table 2. As is clear from the results in Table 2, it is understood that all the samples within the scope of the present invention have excellent workability, corrosion resistance and weldability. On the other hand, comparative examples 1, 2, 7,
Sample No. 12 has poor corrosion resistance because it has little or no amount of chromate adhered, and sample No. Sample Nos. 5, 10 and 15 were inferior in weldability due to excessive chromate adhesion. In Nos. 6 and 11, since the amount of soluble Cr in chromate is excessive, the Cr elution property is poor.

(Example 3) A5182 as in Example 1
Using an aluminum alloy plate, the powdery lubricant treatment conditions shown in Table 3 were changed and applied, and the same evaluation test as in Example 1 was performed. Here, the conditions for adjusting the oxide film, the chromate treatment method, and the antirust oil (antirust oil type, powdered lubricant type, carbon black type) are as follows.

1) Oxide film adjustment treatment-Method: 30% nitric acid, 25 ° C immersion treatment-Oxide film thickness: 105Å

[0049] 2) chromate treatment - Type: application type chromate Nippon Parkerizing Co. 4513H-deposition amount: 23~26mg / m ² · chromate stabilization: 10% ethanol, 60 ° C. immersion treatment-soluble Cr: 0.1 mg / m ² or less

3) Anti-rust oil conditions Anti-rust oil type-A: Idemitsu Kosan Co., Ltd. Daphni oil coat Z-5-B: Sugimura Chemical Co., Ltd. Preton R303P powder lubricant type-A: San Nopco SL530 (polyolefin wax) , Average particle size 6 μm) B: Asahi Glass Co., Ltd. AD1 (fluorine resin, average particle size 8)
μm) C: A 100 parts by weight + B 100 parts by weight D: San Nopco SL417 (polyolefin wax, average particle size 14 μm) E: San Nopco SL92 (polyolefin wax, average particle size 27 μm) carbon black type A: Ket EC600D (specific surface area: 1270 m ² / g) manufactured by Cheng Black Co., Ltd. B: EC (specific surface area: 80) manufactured by Ketjen Black Co., Ltd.
0m ² / g) ・ C: Homemade acetylene black (specific surface area: 56
0m ² / g) ・ D: Mitsubishi Kasei Co. # 1000 (specific surface area: 20
0 m ² / g)

The evaluation test results are also shown in Table 3. As is clear from the results shown in Table 3, all the samples within the scope of the present invention are also excellent in workability, corrosion resistance and weldability.

On the other hand, sample No. 1,
No. 3 has poor workability because the amount of rust preventive oil applied is too small. In addition, sample No. Sample Nos. 5, 9 and 13 were inferior in workability because the content of the powdered lubricant in the rust preventive oil was small. 8, 1
Nos. 2 and 16 are inferior in weldability due to excessive content, and sample No. Since No. 18 has an excessively large average particle size, it has poor workability and weldability. Sample No. Nos. 20 and 21 had poor weldability because the specific surface area of carbon black in the rust preventive oil was too small. No. 22 has an insufficient content and is poor in weldability. On the contrary, No. 25 is too large and the workability is poor.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

[Table 3]

[0056]

[Table 4]

[0057]

According to the present invention, after adjusting the thickness of the surface oxide film, the chromate treatment and the formation of the rust preventive oil layer containing the powdered lubricant and carbon black,
The press formability and corrosion resistance are significantly improved without impairing the spot resistance weldability. This can significantly improve the productivity of aluminum members for automobiles, home appliances, building materials, can materials, and the like.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuo Totsuka, Inventor No. 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Masaki Mabuchi, Chuo-ku, Chiba, Chiba Prefecture Kawasaki-cho No. 1 Inside the Technical Research Division, Kawasaki Steel Co., Ltd. (72) Inventor Naoki Nishiyama No. 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Technical Research Division, Kawasaki Steel Co., Ltd. (72) Inventor Koichi Hashiguchi 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Inside Kawasaki Steel Corporation Technical Research Headquarters (72) Inventor, Motohiro Namba 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Aluminum Co., Ltd.

Claims (3)

[Claims] 1. An aluminum alloy substrate having a surface oxide film thickness adjusted to 150 Å or less, and 5 to 50 m in terms of metal Cr.
It has a chromate layer of g / m ² and a specific surface area of 8
1 to 40% by weight of carbon black of 00 m ² / g or more
A surface-treated aluminum material having excellent workability, spot resistance weldability, and corrosion resistance, which further comprises 0.1 g / m ² or more of a rust preventive oil layer containing 1 to 30% by weight of a powdered lubricant. 2. An alkali-soluble Cr in the chromate layer
(3% NaOH aqueous solution, dipping at 60 ° C for 5 minutes) Volume is 3m
The surface-treated aluminum material having excellent workability, spot resistance weldability and corrosion resistance according to claim 1, which has a g / m ² or less. 3. The powdery lubricant has an average particle size of 20 μm.
The surface-treated aluminum material excellent in workability, spot resistance weldability and corrosion resistance according to claim 1 or 2, which is the following wax and / or fluororesin.