JP3704396B2

JP3704396B2 - Aluminum body parts made of aluminum alloy with excellent shock absorption performance

Info

Publication number: JP3704396B2
Application number: JP13761196A
Authority: JP
Inventors: 俊之細川; 夕貴夫吉田
Original assignee: Furukawa Sky Aluminum Corp; Kanto Auto Works Ltd
Current assignee: Furukawa Sky Aluminum Corp; Toyota Motor East Japan Inc
Priority date: 1996-05-08
Filing date: 1996-05-08
Publication date: 2005-10-12
Anticipated expiration: 2016-05-08
Also published as: JPH09296244A

Description

【０００１】
【発明が属する技術分野】
本発明は、衝突時の衝撃を吸収するのに好適な性能を有するアルミニウム合金製自動車ボディー部材に関するものである。
【０００２】
【従来の技術】
近年、自動車の分野において軽量化の要求が強く、従来から使われている素材である鉄をより軽量なアルミニウムに置換して使用する例が多くなっている。
その一方で、近年高まっている衝突時の安全性の要求から、特に車室を保護する各部材に対して高い衝撃吸収性能が求められている。これに対して従来は鋼板を加工して高い衝撃吸収性能を持つ部材を作製、使用していたが、これら部材に対しても軽量化の要求は例外ではなく、アルミニウムの使用が検討されている。
【０００３】
このような要求に対して、現在は押出し性、加工性、耐食性、及び機械的性質等のバランスの良いＡｌ−Ｍｇ−Ｓｉ系即ち６０００系合金からなる押出し材が使用される場合が多い。
【０００４】
【発明が解決しようとする課題】
しかし、このような６０００系の合金は時効後の強度は高いものの、伸びは十分ではなく衝撃に対して割れが発生しやすく、一旦割れが発生するとそれ以降の衝撃は吸収されないので、衝撃吸収特性は非常に低いものとなる。このような特性は衝撃を吸収しなければならない部材にとっては好ましくないものである。
本発明はかかる問題点に鑑みてなされたもので、自動車のセンターピラーやロッカ等、車室内を衝突による衝撃から保護する役割を持つ、衝撃吸収性能に優れるアルミニウム合金製自動車ボディー部材とその製造方法を提供するものである。
【０００５】
【課題を解決するための手段】
即ち本発明のボディー部材は、少なくとも、Ｍｇ：０．４０〜０．８０wt％、Ｓｉ：０．４０〜０．９０wt％、Ｍｎ：０．０５〜０．５０wt％を含有するＡｌ合金材であって、該合金材の表面方向から観察した時に長さ１０ｎｍ以上の大きさのＭｇ₂Ｓｉ析出物の分布密度が１００個／μｍ²以下であることを特徴とする、歪速度１０²／ｓｅｃ以上の衝撃変形を受ける部位に使用される衝撃吸収性能に優れるアルミニウム合金製自動車ボディー部材である。
【０００６】
また本発明の製造方法は、少なくとも、Ｍｇ：０．４０〜０．８０wt％、Ｓｉ：０．４０〜０．９０wt％、Ｍｎ：０．０５〜０．５０wt％を含有するＡｌ合金を熱間押出しした後必要に応じて溶体化及び焼入れ処理を施し、その後の工程で熱を全く加えないか、又は１９０℃以下の温度で１時間未満の熱を加えることを特徴とする、歪速度１０²／ｓｅｃ以上の衝撃変形を受ける部位に使用される衝撃吸収性能に優れるアルミニウム合金製自動車ボディー部材の製造方法である。
【０００７】
本発明において、自動車ボディー部材としてのアルミニウム合金の組成を上記のように限定した理由について、先ず説明する。
【０００８】
Ｍｇはアルミニウム合金の強度を向上させる元素である。しかしその含有量が０．４wt％未満では強度向上の効果がなく、０．８wt％を超えると押出し性が低下し、極端に押出し速度が低くなり、薄肉形材の製造が困難になる他、伸びが低下して加工性が悪くなる。
【０００９】
Ｓｉも強度を高める効果のある元素である。しかしその含有量が０．４wt％未満ではその効果は十分ではなく、０．９wt％を超えると押出し性の低下、伸びの低下に伴う加工性の低下を招く。
【００１０】
Ｍｎは押出し形材の、特に表層付近の再結晶防止に効果があって結晶粒の微細化に有効な元素である。しかしその含有量が０．０５wt％未満では上記効果が不十分であり、０．５wt％を超えると上記効果が限界に達するうえに、粗大な晶出物を生じて曲げ加工等で割れの原因となる。
【００１１】
次に本発明の製造方法について説明する。
本発明では、上記アルミニウム合金の素材の押出し加工後、又はその後必要に応じて施す溶体化及び焼入れ後における工程、即ちその後の該素材の加工工程及び車体組み立て工程において、熱を全く加えないか、又は熱を加える場合は１９０℃以下の温度で１時間未満の処理をするものである。
このように熱を全く加えないか、又は熱を加える場合は１９０℃以下の温度で１時間未満の処理をするのは、Ｍｇ₂Ｓｉを析出させないためである。Ｍｇ₂Ｓｉが析出しない状態での押出し形材は歪速度依存性が高く、歪速度が大きい時の強度及び伸びの増加分が大きい。このような性質は、衝突時の変形で衝撃を吸収する必要のある自動車ボディー部材には好適である。
【００１２】
そして問題となるＭｇ₂Ｓｉ析出物の大きさは１０ｎｍ以上であり、さらにその析出物の分布密度を材料の表面方向からの観察で１００個／μｍ²以下に規制する。このようにＭｇ₂Ｓｉ析出物の大きさを１０ｎｍ以上としたのはこれより小さい析出物は、歪速度依存性にほとんど影響を与えないためであり、またその分布密度を１００個／μｍ²以下としたのは、分布密度が１００個／μｍ²を超えると歪速度依存性にほとんど影響を与えないためである。
【００１３】
自動車ボディー構造における衝撃吸収に関しては、一般に部材の強度が大きいほど変形に要するエネルギーは大きく、衝撃吸収量も大きいといえる。そこで従来は強度増加の目的で１８０℃で２〜３時間程度の人工時効処理が行われる場合があるが、このような処理によれば強度は大きくなるものの伸びは低下して破断し易くなる。そして破断後の衝撃吸収性能はほとんどないため全体として衝撃吸収性能は小さいことになる。
また通常１８０℃程度の温度で行われる塗装焼付け工程も１時間以上の長時間にわたって行われると、人工時効処理と同じくＭｇ₂Ｓｉの析出を促進させることから、本発明ではこのように塗装焼付けを実施する場合には１時間未満の時間で行う必要がある。
【００１４】
本発明のような加熱条件で材料を作製すると、歪速度が低速の場合は強度も小さく伸びもそれほど大きくはない部材でも、衝突のような歪速度が大きい場合、即ち歪速度１０²/sec以上での変形では強度及び伸びの大きい材料として衝撃の吸収に好適な材料となる。さらに、通常低速で行われることの多い曲げ加工等の成形において、本発明の材料及び本発明製造法による押出し形材は、低強度材料として取り扱えるので成形加工が容易であるという利点もある。
【００１５】
【実施例】
以下に本発明を実施例に基づきさらに詳細に説明する。
【００１６】
表１に示す組成の各種Ａｌ合金鋳塊を連続鋳造法により製造した。これらを５１０℃に加熱したのち熱間押出しを行った。その後５３０℃に加熱、溶体化して２０℃／sec の冷却速度で冷却した。しかる後表１に示す加熱条件で加熱し、もしくは加熱せずに、図１に示すような外寸法６０×６０ｍｍで断面田の字形状の中空形材を得た。
【００１７】
【表１】

【００１８】
得られた中空形材よりＪＩＳ５号試験片を採取し、これを低歪速度１０^-1/secで引張試験を行った結果を表２に示す。
また該中空形材より図２に示す試験片を採取し、これを高速引張試験機を用いて高歪速度での耐力を測定してその結果を表２に併記した。なおこの試験では実際の自動車の衝突を想定して歪速度を１０³/sec とした。
【００１９】
また図３に示す衝突試験装置を用いて該中空形材の動的曲げ試験を行い、その時の形材の割れ発生の有無から、高歪速度における材料の伸びの評価を行った。
さらにこの試験の変位−荷重曲線から１００ｍｍまで変位する時のエネルギー吸収量を求めた。これらの結果も表２に併記した。なおこの動的曲げ試験は、重量５００ｋｇの車体（１）前部に供試材である形材（２）を取り付けて速度１５ｋｍ／ｈｒで壁の押し治具（３）に衝突させ、３点曲げの状態で形材を変形させるもので、最も変形を受ける部位の歪速度は１０³/sec のオーダーと考えられる。図中（４）はステー、（５）はダンパー、（６）はレーザー変位計、（７）はロードセルを示す。
また該中空形材からサンプルを採取し、形材表面方向から透過型電子顕微鏡で（１００）面のＭｇ₂Ｓｉ析出物の観察を行い、〔１００〕〔０１０〕方向の長さ１０ｎｍ以上のＭｇ₂Ｓｉ析出物の分布密度を測定した。この結果も表２に示した。
【００２０】
以上の採取試験片を用いた表２の評価結果及び押出し時の限界速度から、各材料の衝撃吸収性と押出し性を評価してこれらを表３に示した。そして各性能のバランスを考慮して、衝撃吸収性能が必要とされる部位に使用される自動車ボディー部材としての総合評価を行いその結果を表３に併記した。
【００２１】
【表２】

【００２２】
【表３】

【００２３】
表２から明らかなように、本発明による形材は高歪速度において高い強度を発揮しており、且つ伸びも大きいといえる。また本発明例のものは１００ｍｍまで変形する時のエネルギー吸収量も大きく、衝突時にも破断することなく有効にエネルギーを吸収していることが判る。さらに本発明例では表３から明らかなように、押出し性も良好なので量産における製造コストも優れているといえる。
これに対して比較例Ｎｏ．４、６、８及び９のものは低速引張試験、高速引張試験又は衝突試験の何れかにおいて本発明例のものより劣っている。また比較例Ｎｏ．５と７のものは低速引張試験、高速引張試験又は衝突試験に関しては、本発明例に近い特性を有するが、表３における押出し性において劣っていることが明らかである。このように比較例ではいずれも衝撃吸収性と押出し性の両者のバランスが共に良好なものはなかった。
【００２４】
【発明の効果】
このように本発明によれば、高歪速度での強度と伸びが共に大きいアルミニウム合金材料の製造が可能で、衝突時の衝撃をその変形によって吸収しなければならない自動車ボディー部材のセンターピラーやロッカ等に好適な材料を提供できる。また本発明の部材は、低歪速度では強度は小さいが伸びが大きいので曲げ加工等の成形加工が容易であるという利点も合わせ持つ。しかも押出し性も良好であるので量産性も良い。
【図面の簡単な説明】
【図１】実施例で製造した中空形材を示す断面図である。
【図２】高速引張試験片の形状を示す平面図である。
【図３】衝突試験装置を示すもので、（ａ）は正面図、（ｂ）は平面図である。
【符号の説明】
１車体
２形材
３押し治具
４ステー
５ダンパー
６レーザー変位計[0001]
[Technical field to which the invention belongs]
The present invention relates to an aluminum alloy automobile body member having a performance suitable for absorbing an impact at the time of a collision.
[0002]
[Prior art]
In recent years, there has been a strong demand for weight reduction in the field of automobiles, and there are many examples of replacing iron, which is a conventionally used material, with lighter aluminum.
On the other hand, high shock absorbing performance is demanded for each member that protects the passenger compartment, in particular, due to the increasing safety requirements at the time of collision. On the other hand, in the past, steel plates were processed and members with high shock absorption performance were produced and used, but the demand for weight reduction is no exception for these members, and the use of aluminum is being studied. .
[0003]
In response to such demands, an extruded material made of an Al—Mg—Si based alloy having a good balance of extrudability, workability, corrosion resistance, and mechanical properties, that is, a 6000 based alloy is often used at present.
[0004]
[Problems to be solved by the invention]
However, although such a 6000 series alloy has high strength after aging, its elongation is not sufficient and cracking is likely to occur with respect to impact. Once cracking occurs, the subsequent impact is not absorbed. Is very low. Such characteristics are undesirable for members that must absorb impact.
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has a role of protecting the interior of a vehicle from an impact caused by a collision, such as an automobile center pillar and a rocker, and an automobile body member made of an aluminum alloy excellent in shock absorbing performance and a method for manufacturing the same. Is to provide.
[0005]
[Means for Solving the Problems]
That is, the body member of the present invention is an Al alloy material containing at least Mg: 0.40 to 0.80 wt%, Si: 0.40 to 0.90 wt%, and Mn: 0.05 to 0.50 wt%. The strain density is 10 ² / sec or more, characterized in that the distribution density of Mg ₂ Si precipitates having a length of 10 nm or more when observed from the surface direction of the alloy material is 100 pieces / μm ² or less. It is an automobile body member made of an aluminum alloy that is excellent in shock absorbing performance and is used in a portion that undergoes impact deformation.
[0006]
Further, the production method of the present invention is a method of hot-working an Al alloy containing at least Mg: 0.40 to 0.80 wt%, Si: 0.40 to 0.90 wt%, and Mn: 0.05 to 0.50 wt%. A solution rate and a quenching treatment are applied as necessary after extrusion, and heat is not applied at all in the subsequent steps, or heat is applied at a temperature of 190 ° C. or lower for less than 1 hour, and a strain rate of 10 ² This is a method for manufacturing an aluminum body member made of an aluminum alloy having excellent shock absorption performance used for a portion subjected to impact deformation of at least / sec.
[0007]
The reason why the composition of the aluminum alloy as the automobile body member in the present invention is limited as described above will be described first.
[0008]
Mg is an element that improves the strength of the aluminum alloy. However, if the content is less than 0.4 wt%, there is no effect of improving the strength, and if it exceeds 0.8 wt%, the extrudability decreases, the extrusion speed becomes extremely low, and the production of the thin-walled material becomes difficult. Elongation decreases and processability deteriorates.
[0009]
Si is also an element having an effect of increasing the strength. However, if the content is less than 0.4 wt%, the effect is not sufficient, and if it exceeds 0.9 wt%, the extrudability is lowered and the workability is lowered due to the elongation.
[0010]
Mn is an element that is effective in preventing recrystallization of the extruded shape, particularly in the vicinity of the surface layer, and is effective in refining crystal grains. However, if the content is less than 0.05 wt%, the above effect is insufficient, and if it exceeds 0.5 wt%, the above effect reaches the limit, and a coarse crystallized product is generated, causing cracks in bending work, etc. It becomes.
[0011]
Next, the manufacturing method of this invention is demonstrated.
In the present invention, after the extrusion process of the aluminum alloy material, or after the solution treatment and quenching performed as necessary thereafter, that is, in the subsequent processing process and body assembly process of the material, heat is not applied at all. Alternatively, when heat is applied, the treatment is performed at a temperature of 190 ° C. or less for less than 1 hour.
In this way, heat is not applied at all, or when heat is applied, the treatment is performed at a temperature of 190 ° C. or lower for less than 1 hour because Mg ₂ Si is not precipitated. Extruded shapes in a state where Mg ₂ Si does not precipitate have a high strain rate dependency, and increase in strength and elongation when the strain rate is large. Such a property is suitable for an automobile body member that needs to absorb an impact by deformation at the time of collision.
[0012]
The size of the Mg ₂ Si precipitates in question is 10 nm or more, and the distribution density of the precipitates is restricted to 100 / μm ² or less by observation from the surface direction of the material. The reason why the size of the Mg ₂ Si precipitates is set to 10 nm or more is that precipitates smaller than this have almost no influence on the strain rate dependence, and the distribution density is 100 / μm ² or less. This is because when the distribution density exceeds 100 / μm ² , the strain rate dependency is hardly affected.
[0013]
Regarding shock absorption in an automobile body structure, it can be said that in general, the greater the strength of a member, the greater the energy required for deformation and the greater the amount of shock absorption. Therefore, conventionally, an artificial aging treatment at 180 ° C. for about 2 to 3 hours may be performed for the purpose of increasing the strength. However, such treatment increases strength but decreases elongation and easily breaks. And since there is almost no shock absorption performance after a fracture | rupture, the impact absorption performance is small as a whole.
In addition, if the paint baking process, which is usually performed at a temperature of about 180 ° C., is performed for a long time of 1 hour or more, it accelerates the precipitation of Mg ₂ Si as in the case of artificial aging treatment. When implemented, it is necessary to carry out in less than 1 hour.
[0014]
When a material is produced under the heating conditions as in the present invention, when the strain rate is low, even when the strength is small and the elongation is not so great, even when the strain rate is high such as a collision, that is, the strain rate is 10 ² / sec or more. In the deformation at, the material having a high strength and elongation becomes a material suitable for absorbing the impact. Furthermore, in molding such as bending, which is often performed at a low speed, the material of the present invention and the extruded shape produced by the production method of the present invention can be handled as a low-strength material, so that there is an advantage that the molding process is easy.
[0015]
【Example】
Hereinafter, the present invention will be described in more detail based on examples.
[0016]
Various Al alloy ingots having the compositions shown in Table 1 were produced by a continuous casting method. These were heated to 510 ° C. and then subjected to hot extrusion. Thereafter, the mixture was heated to 530 ° C., solutionized, and cooled at a cooling rate of 20 ° C./sec. Thereafter, heating was performed under the heating conditions shown in Table 1, or without heating, a hollow material having an outer dimension of 60 × 60 mm and a cross-sectional shape was obtained as shown in FIG.
[0017]
[Table 1]

[0018]
Table 2 shows the results of a JIS No. 5 test piece taken from the obtained hollow profile and subjected to a tensile test at a low strain rate of 10 ^-1 / sec.
Also, a test piece shown in FIG. 2 was collected from the hollow profile, and the yield strength at a high strain rate was measured using a high-speed tensile tester. The results are also shown in Table 2. In this test, the strain rate was set to 10 ³ / sec assuming an actual automobile collision.
[0019]
Further, a dynamic bending test of the hollow profile was performed using the collision test apparatus shown in FIG. 3, and the elongation of the material at a high strain rate was evaluated from the presence or absence of cracking of the profile.
Furthermore, the amount of energy absorbed when displacing from the displacement-load curve of this test to 100 mm was determined. These results are also shown in Table 2. In this dynamic bending test, a specimen (2), which is a specimen, is attached to the front of a car body (1) weighing 500 kg, and is made to collide with a wall pressing jig (3) at a speed of 15 km / hr. The shape is deformed in a bent state, and the strain rate at the most deformed portion is considered to be on the order of 10 ³ / sec. In the figure, (4) is a stay, (5) is a damper, (6) is a laser displacement meter, and (7) is a load cell.
A sample was taken from the hollow shape, and (100) face Mg ₂ Si precipitates were observed with a transmission electron microscope from the shape surface direction, and a length of 10 nm or more in the [100] [010] direction. ₂ Distribution density of Si precipitates was measured. The results are also shown in Table 2.
[0020]
From the evaluation results in Table 2 using the above collected test pieces and the limit speed at the time of extrusion, the impact absorbability and extrudability of each material were evaluated and these are shown in Table 3. Then, considering the balance of each performance, a comprehensive evaluation as an automobile body member used for a portion where shock absorbing performance is required was performed, and the results are also shown in Table 3.
[0021]
[Table 2]

[0022]
[Table 3]

[0023]
As is apparent from Table 2, it can be said that the profile according to the present invention exhibits high strength at a high strain rate and has a large elongation. In addition, it can be seen that the example of the present invention has a large energy absorption amount when deformed to 100 mm and effectively absorbs energy without breaking even at the time of collision. Further, as apparent from Table 3, in the examples of the present invention, since the extrudability is good, it can be said that the production cost in mass production is also excellent.
In contrast, Comparative Example No. Those of 4, 6, 8, and 9 are inferior to those of the examples of the present invention in any of the low-speed tensile test, high-speed tensile test, and impact test. Comparative Example No. 5 and 7 have characteristics close to those of the examples of the present invention with respect to the low-speed tensile test, the high-speed tensile test, or the collision test, but it is apparent that the extrudability in Table 3 is inferior. Thus, none of the comparative examples had a good balance between both impact absorption and extrudability.
[0024]
【The invention's effect】
As described above, according to the present invention, it is possible to manufacture an aluminum alloy material having both high strength and elongation at a high strain rate, and a center pillar or rocker of an automobile body member that must absorb the impact at the time of collision by deformation. A material suitable for the above can be provided. The member of the present invention also has the advantage that it is easy to be formed such as bending because it has low strength but high elongation at a low strain rate. Moreover, since the extrudability is also good, the mass productivity is good.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a hollow profile produced in an example.
FIG. 2 is a plan view showing the shape of a high-speed tensile test piece.
3A and 3B show a collision test apparatus, in which FIG. 3A is a front view and FIG. 3B is a plan view.
[Explanation of symbols]
1 Car body 2 Shape 3 Pushing jig 4 Stay 5 Damper 6 Laser displacement meter

Claims

An Al alloy material containing at least Mg: 0.40 to 0.80 wt%, Si: 0.40 to 0.90 wt%, Mn: 0.05 to 0.50 wt%, and the surface direction of the alloy material Used for a part subjected to impact deformation at a strain rate of 10 ² / sec or more, characterized in that the distribution density of Mg ₂ Si precipitates having a length of 10 nm or more when observed from above is 100 pieces / μm ² or less Aluminum body parts made of aluminum alloy with excellent shock absorption performance.

A solution as needed after hot extrusion of an Al alloy containing at least Mg: 0.40 to 0.80 wt%, Si: 0.40 to 0.90 wt%, Mn: 0.05 to 0.50 wt% And subjected to impact deformation at a strain rate of 10 ² / sec or more, characterized in that heat treatment is performed at a temperature of 190 ° C. or less for less than 1 hour. A method of manufacturing an aluminum body member made of aluminum alloy having excellent shock absorbing performance used for a part.