JP3588723B2

JP3588723B2 - Solid lubricant coated aluminum alloy sheet excellent in weldability and method for producing the same

Info

Publication number: JP3588723B2
Application number: JP29385592A
Authority: JP
Inventors: 杉田知之; 松井邦昭; 向井良和
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 1992-10-06
Filing date: 1992-10-06
Publication date: 2004-11-17
Anticipated expiration: 2019-11-17
Also published as: JPH06116670A

Description

【０００１】
【産業上の利用分野】
本発明は溶接性に優れたアルミニウム合金板の製造に関し、特に自動車用部品のプレス成形加工用アルミニウム合金板材で、プレス加工後に抵抗スポット溶接して用いられる場合に適している。
【０００２】
【従来の技術及び発明が解決しようとする課題】
アルミニウム合金は、その軽量性のほかに耐食性、成形性に優れているため、鉄鋼材料に次ぐ汎用金属材料として、自動車を始め、様々な産業分野で多用されている。
【０００３】
最近、自動車の軽量化を図るため、アルミニウム合金板の使用が次第に増えつつあるが、アルミニウム合金板は、鋼板に比較して成形性に劣るため、成形時の割れの発生や、設計時に形状が制限されるなど問題が大きい。
【０００４】
また、従来の鋼用のプレスラインを兼用して使用されているので、潤滑油などはアルミニウム材に対して必ずしも適正なものではなく、成形性において不利になっている。
【０００５】
そのため、固形潤滑剤を予めアルミニウム板表面に塗布しておき、プレス時の成形性を向上させる試みがなされているが、その際、自動車メーカー側では工程の簡略化のためプレス加工後に脱脂工程を入れず、固形潤滑剤を塗布した状態でスポット溶接が行われている。しかし、材料表面に潤滑皮膜を付けたままで溶接すると、電極材の消耗が著しい、接合時にちりが発生して接合強度を低下させるなどの問題が発生する。これらの問題に対して、現在のところ、電極材の交換を頻繁に行うことが必要となり、生産性を著しく劣化させている。
【０００６】
本発明は、かゝる事情のもとで、成形性を上げるため固形潤滑剤を塗布することにより生じる接合強度の劣化、溶接電極材の消耗、或いは頻繁に溶接電極を交換することによる生産性の悪さ等の問題がなく、溶接性に優れたアルミニウム合金板を提供し、またその製造方法を提供することを目的とするものである。
【０００７】
【課題を解決するための手段】
本発明者は、前記課題を解決するために鋭意研究を重ねた結果、ここに本発明を完成したものである。
【０００８】
すなわち、本発明は、アルミニウム合金板の表面酸化皮膜が厚さ５０Å以下に調整されており、かつ、その上に固形潤滑剤と更に液体潤滑油が塗布されていることを特徴とする溶接性に優れたアルミニウム合金板を要旨としている。
【０００９】
また、その製造方法は、アルミニウム合金板の酸化皮膜をアルカリ及び／又は酸で溶解除去することによって厚さ５０Å以下に調整した後、固形潤滑剤を塗布し、更に液体潤滑油を塗布することを特徴としている。
【００１０】
以下に本発明を更に詳細に説明する。
【００１１】
【作用】
【００１２】
本発明における条件の限定理由は以下のとおりである。
【００１３】
アルミニウム合金には、空気中の酸素と化合して、表面に強固な酸化皮膜を形成する性質があり、それが溶接電流の通電状態を不安定にし、散りなどの原因になっている。そのため、本発明では、表面酸化皮膜を、アルカリ洗浄（リン酸ソーダ、炭酸ソーダ、苛性ソーダ等）や、酸類（硝酸、硫酸等）によって溶解除去し、従来７０Å程度であった皮膜厚さを５０Å以下に調整することにより、溶接性を向上させることができる。
【００１４】
表面酸化皮膜の厚さを調整した後、固形潤滑剤を塗布する。これにより成形性を向上させることができる。
【００１５】
固形潤滑剤の塗布量は特に制限されるものではないが、０．１〜２．０ｇ／ｍ^２の範囲が好ましい。塗布量が２．０ｇ／ｍ^２を超えると固形潤滑剤皮膜が厚すぎ、溶接電流の通電状態が不安定となり、上述の表面酸化皮膜の調整効果による特性を発揮できない。また、塗布量が０．１ｇ／ｍ^２より少ないと加工時に皮膜の剥離が起こり、成形時のかじりや、割れなどの原因となる。
【００１６】
更に、固形潤滑剤の上に液体潤滑油を塗布する。塗布した潤滑油は、スポット溶接時に炭化蒸発し、それが溶接電極に付着して電極を保護し、寿命を向上する働きを示す。
【００１７】
液体潤滑油の性状及び塗布量等も特に制限されるものではないが、粘度を１０ｃｓｔ／４０℃以下に、塗布量を０．５〜５．０ｇ／ｍ^２に調整するのが好ましい。液体潤滑油の塗布量が０．５〜５．０ｇ／ｍｍ^２の範囲を逸脱して、洗浄油量が多すぎたり、少なすぎたりすると炭化蒸発が起こりにくくなり、電極が保護されなくなる。また、潤滑油の粘度が１０ｃｓｔ／４０℃以上になると、強固な潤滑油膜が形成されるため、同じように炭化蒸発を起こしにくくなる。
【００１８】
なお、本発明で対象とするアルミニウム合金は加工に供し得る成分系及び成分組成のものであれば制限がないことは云うまでもない。
【００１９】
次に本発明の実施例を示す。
【００２０】
【実施例】
【００２１】
Ａｌ−４．５％Ｍｇ合金板（調質：Ｔ４、厚さ：１ｍｍ）を供試材とし、このアルミニウム板の酸化皮膜量を調整した後、その表面に固形潤滑剤を付着させ、潤滑油を塗布して、成形性及び抵抗スポット溶接性を評価した。その結果を表１に示す。なお、酸化皮膜量の調整法、固形潤滑剤の付着法、潤滑油の塗布法は以下の要領にて実施した。
【００２２】
▲１▼酸化皮膜量の調整法：下記のとおり素材表面の洗浄方法により皮膜量を調整した。皮膜量は静電溶量法により測定した。

【００２３】
▲２▼固形潤滑剤の付着法：ワックス系固形潤滑剤を塗布後、乾燥（恒温槽で８０℃×５分）した。塗布量はバーコーダーにて調整し、標準を０．５ｇ／ｍ^２とした。
【００２４】
▲３▼潤滑油の塗布法：ミネラル油系洗浄油（標準として４ｃｓｔ／４０℃、２ｇ／ｍ^２）を使用し、塗布量は、はけ塗り後、電子天秤で測定して調整した。
【００２５】
▲４▼成形性評価方法：以下の条件で絞り試験を実施し、割れが生じる絞り高さにより評価した。
試験片形状：１．０×１００×１００（ｍｍ）
ポンチ径：□４０ｍｍ（ポンチＲ：４．５ｍｍ、ダイＲ：３．０ｍｍ）
ポンチ速度：〜２０ｍｍ／ｍｉｎ
しわ押さえ力：３９２００Ｎ
【００２６】
▲５▼抵抗スポット溶接性評価方法：以下の溶接条件で連続打点性を調査し、接合強度が１．５ｋＮを始めて下回るまでの打点数により評価した。
加圧力：一段一定加圧３００ｋｇｆ
電極：クロム−銅合金、先端半径４０ｍｍのＤＲ型
溶接電流：２０〜３０ｋＡ（ナゲット径が５ｍｍとなるよう調整）
溶接機：単層低周波抵抗スポット溶接機
【００２７】
表１より明らかなように、本発明例はいずれも、固形潤滑剤の付着により成形性を向上させても、良好な溶接性が得られている。
【００２８】
なお、酸化皮膜量の影響については、比較例Ｎｏ．９のように多いと溶接性が劣化するのに対し、本発明範囲（５０Å以下）のように少なくすると（本発明例Ｎｏ．２、Ｎｏ．６、７）、溶接性を改善することができる。固形潤滑剤の塗布量の影響については、無塗布乃至少量の塗布（比較例Ｎｏ．１０、１１）では成形性が得られず、適当量の塗布（本発明例Ｎｏ．１〜３）により成形性を向上させることができるが、多すぎると（比較例Ｎｏ．１２）かえって溶接性が悪くなる。液体潤滑油の粘度及び塗布量の影響については、固形潤滑剤の塗布による加工性の低下を防止するには適当な粘度及び塗布量が望ましく（本発明例Ｎｏ．２、４、５）、粘度が高すぎたり塗布量が多すぎるのは望ましくない（比較例Ｎｏ．１３、１４）。
【００２９】
【表１】

【００３０】
【発明の効果】
以上詳述したように、本発明によれば、▲１▼固形潤滑剤を塗布することによりアルミニウム合金のプレス成形性が向上し、かつ、スポット溶接が可能になることにより、複雑な形状でも無理なく成形組立加工ができる、▲２▼成形性、溶接性の向上によりアルミニウム合金板を鋼板用のラインで加工することができる、▲３▼その結果、アルミニウム合金板の適用範囲が広くなり、アルミ化による自動車の軽量化が達成でき、省エネルギーや排気ガスの低減に効果がある。[0001]
[Industrial applications]
The present invention relates to the production of an aluminum alloy sheet having excellent weldability, and is particularly suitable for an aluminum alloy sheet material for press forming of automotive parts, which is used by resistance spot welding after press working.
[0002]
Problems to be solved by the prior art and the invention
BACKGROUND ART Aluminum alloys are excellent in corrosion resistance and formability in addition to their light weight, and therefore are widely used as general-purpose metallic materials next to steel materials in various industrial fields such as automobiles.
[0003]
Recently, the use of aluminum alloy sheets has been gradually increasing in order to reduce the weight of automobiles.However, aluminum alloy sheets are inferior in formability compared to steel sheets, so cracks occur during forming and the shape during design is reduced. There are serious problems such as being restricted.
[0004]
In addition, since the conventional press line for steel is also used, lubricating oil and the like are not always appropriate for aluminum materials, which is disadvantageous in formability.
[0005]
Therefore, an attempt has been made to apply a solid lubricant to the surface of the aluminum plate in advance to improve the formability at the time of pressing. However, at this time, the automobile manufacturer has performed a degreasing step after pressing to simplify the process. The spot welding is performed in a state where the solid lubricant is applied without inserting. However, if welding is performed with a lubricating film attached to the surface of the material, problems such as remarkable wear of the electrode material and generation of dust at the time of joining to lower the joining strength occur. At present, it is necessary to frequently replace the electrode material with respect to these problems, which significantly lowers productivity.
[0006]
Under such circumstances, the present invention provides a method for improving the formability by applying a solid lubricant to deteriorate the joining strength, exhausting the welding electrode material, or productivity by frequently replacing the welding electrode. It is an object of the present invention to provide an aluminum alloy plate excellent in weldability without problems such as poor quality and a method for producing the same.
[0007]
[Means for Solving the Problems]
The present inventor has made intensive studies to solve the above problems, and as a result, completed the present invention.
[0008]
That is, the present invention provides a weldability characterized in that the surface oxide film of the aluminum alloy plate is adjusted to a thickness of 50 ° or less, and a solid lubricant and further a liquid lubricant are applied thereon. The gist is an excellent aluminum alloy plate.
[0009]
Further, the manufacturing method is to adjust the thickness of the aluminum alloy plate to 50 mm or less by dissolving and removing the oxide film with an alkali and / or an acid, apply a solid lubricant, and further apply a liquid lubricant. Features.
[0010]
Hereinafter, the present invention will be described in more detail.
[0011]
[Action]
[0012]
The reasons for limiting the conditions in the present invention are as follows.
[0013]
Aluminum alloys have the property of forming a strong oxide film on the surface when they combine with oxygen in the air, which makes the current state of welding current unstable and causes scattering. Therefore, in the present invention, the surface oxide film is dissolved and removed with an alkali washing (sodium phosphate, sodium carbonate, caustic soda, etc.) or acids (nitric acid, sulfuric acid, etc.), and the film thickness, which was about 70 mm in the past, is reduced to 50 mm or less. By adjusting to, the weldability can be improved.
[0014]
After adjusting the thickness of the surface oxide film, a solid lubricant is applied. Thereby, moldability can be improved.
[0015]
The application amount of the solid lubricant is not particularly limited, but is preferably in the range of 0.1 to 2.0 g / m ² . If the coating amount is more than 2.0 g / m ² , the solid lubricant film is too thick, the state of current supply of the welding current becomes unstable, and the above-mentioned characteristics due to the effect of adjusting the surface oxide film cannot be exhibited. On the other hand, if the coating amount is less than 0.1 g / m ² , the coating will peel off during processing, causing galling and cracking during molding.
[0016]
Further, a liquid lubricating oil is applied on the solid lubricant. The applied lubricating oil is carbonized and evaporated at the time of spot welding, and adheres to the welding electrode to protect the electrode and improve the service life.
[0017]
There are no particular restrictions on the properties and application amount of the liquid lubricating oil, but it is preferable to adjust the viscosity to 10 cst / 40 ° C. or lower and the application amount to 0.5 to 5.0 g / m ² . If the applied amount of the liquid lubricating oil deviates from the range of 0.5 to 5.0 g / mm ^{2 and} the amount of the cleaning oil is too large or too small, carbonization and evaporation hardly occurs, and the electrode is not protected. Further, when the viscosity of the lubricating oil is 10 cst / 40 ° C. or higher, a strong lubricating oil film is formed, and similarly, it is difficult to cause carbonization and evaporation.
[0018]
It goes without saying that the aluminum alloy targeted in the present invention is not limited as long as it has a component system and a component composition that can be used for processing.
[0019]
Next, examples of the present invention will be described.
[0020]
【Example】
[0021]
An Al-4.5% Mg alloy plate (Temperature: T4, thickness: 1 mm) was used as a test material. After adjusting the amount of oxide film on this aluminum plate, a solid lubricant was adhered to the surface of the aluminum plate, and lubricating oil was applied. Was applied, and the moldability and the resistance spot weldability were evaluated. Table 1 shows the results. The method of adjusting the amount of the oxide film, the method of attaching the solid lubricant, and the method of applying the lubricating oil were performed in the following manner.
[0022]
{Circle around (1)} Method for adjusting the amount of oxide film: The amount of film was adjusted by the method of cleaning the surface of the material as described below. The amount of the coating was measured by the electrostatic dissolution method.

[0023]
{Circle around (2)} Method of attaching solid lubricant: After applying a wax-based solid lubricant, drying was performed (80 ° C. × 5 minutes in a constant temperature bath). The coating amount was adjusted with a bar coder, and the standard was 0.5 g / m ² .
[0024]
{Circle around (3)} Coating method of lubricating oil: A mineral oil-based cleaning oil (standard: 4 cst / 40 ° C., 2 g / m ² ) was used, and the application amount was measured and adjusted by an electronic balance after brushing.
[0025]
{Circle around (4)} Formability evaluation method: A drawing test was performed under the following conditions, and evaluation was made based on the drawing height at which cracks occurred.
Test specimen shape: 1.0 × 100 × 100 (mm)
Punch diameter: 40 mm (Punch R: 4.5 mm, Die R: 3.0 mm)
Punch speed: ~ 20mm / min
Wrinkle holding force: 39200N
[0026]
{Circle around (5)} Resistance spot weldability evaluation method: Continuous spotting properties were investigated under the following welding conditions, and evaluation was made based on the number of spots at which the joining strength was reduced from 1.5 kN to the first time.
Pressing force: One-stage constant pressurization 300kgf
Electrode: chrome-copper alloy, DR type welding current with a tip radius of 40 mm: 20-30 kA (adjusted so that the nugget diameter becomes 5 mm)
Welder: Single layer low frequency resistance spot welder [0027]
As is clear from Table 1, in all of the examples of the present invention, good weldability is obtained even if the formability is improved by the adhesion of the solid lubricant.
[0028]
The effect of the amount of the oxide film is described in Comparative Example No. When the amount is as large as 9, the weldability is deteriorated, whereas when the amount is as small as the range of the present invention (50 ° or less) (Examples Nos. 2, 6, and 7 of the present invention), the weldability can be improved. . Regarding the effect of the amount of the solid lubricant applied, no moldability was obtained with no application or a small amount of application (Comparative Examples Nos. 10 and 11), and molding was performed with an appropriate amount of application (Examples Nos. 1 to 3). The weldability can be improved, but if it is too large (Comparative Example No. 12), the weldability will worsen. Regarding the influence of the viscosity and the amount of the liquid lubricating oil, an appropriate viscosity and the amount of the liquid are desirable to prevent a decrease in workability due to the application of the solid lubricant (Examples Nos. 2, 4, and 5 of the present invention). Is too high or the coating amount is too large (Comparative Examples Nos. 13 and 14).
[0029]
[Table 1]

[0030]
【The invention's effect】
As described above in detail, according to the present invention, (1) the press formability of an aluminum alloy is improved by applying a solid lubricant, and spot welding is enabled, so that even a complicated shape is impossible. (2) Aluminum alloy plate can be processed in a steel sheet line by improving formability and weldability. (3) As a result, the applicable range of aluminum alloy plate is widened, It is possible to achieve a reduction in the weight of automobiles due to energy savings, which is effective in energy saving and reduction of exhaust gas.

Claims

The surface oxide film of the aluminum alloy plate is adjusted to a thickness of 50 ° or less, and a solid lubricant and a liquid lubricating oil are applied thereon , and the applied amount of the solid lubricant is 0.1 to 2 g / m. ^2, the viscosity of the liquid lubricating oil is not more than 10 cst / 40 ° C., the aluminum alloy plate to which the coating amount is excellent in weldability, which is a 0.5 to 5 g / ^{m 2.}

After adjusting the thickness to 50 ° or less by dissolving and removing the oxide film of the aluminum alloy plate with an alkali and / or an acid, a solid lubricant is applied at an application amount of 0.1 to ² g / m ² , and the viscosity is further reduced to 10 cst. A method for producing an aluminum alloy sheet excellent in weldability, characterized by applying a liquid lubricating oil at a temperature of / 40 ° C or lower at an application amount of 0.5 to 5 g / m ² .