JPH11241137A - Door beam material made of aluminum alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a door beam material capable of preventing the stress concentration at the time of bending deformation and the resultant occurrence of fracture in an early stage and increased in the amount of energy absorption as well as in the maximum load. SOLUTION: This material is an extruded material of an Al-Zn-Mg type aluminum alloy containing, by weight, 0.8-1.5% Mg and 4-7% Zn or an Al-Si-Mg type aluminum alloy containing 0.5-1.5% Si and 0.5-1.3% Mg. In this material, the thickness of a recrystallized layer in the surface is made to <=50 μm. A fibrous structure is present under the recrystallized layer. Further, the fibrous structure can be present in the surface without the presence of the recrystallized layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy door beam used as a member for reinforcing a door of an automobile.

[0002]

2. Description of the Related Art A door beam of a passenger car is required to have a function of absorbing a load at the time of a collision. For example, FMVSS
(U.S. Federal Safety Standards) provides a fixed reference value for the bending load value when the load is applied from the side of the actual vehicle and for the energy absorption represented by the area of the load-deformation relationship. At the laboratory level, however, they generally assume a collision with a vehicle, and as shown in FIG. 2 (a), support the both ends of a door beam material and press the center with a load jig. It is evaluated by the bending performance of bending.

FIG. 2 (b) is a schematic diagram of a load (P) -displacement (δ) curve obtained by the bending test of FIG. 2 (a). This shows that the load decreases due to buckling deformation due to inability to withstand the load, but in general, in this load (P) -displacement (δ) curve, the maximum load is large, and the displacement until buckling or fracture occurs. It is considered that a larger energy absorption (area) is more desirable.

[0004] Conventional door beams are typically 150k
gf / mm ² class high tensile steel is used,
The use of extruded aluminum bars has been studied from the viewpoint of weight reduction. For example, Japanese Patent Application Laid-Open No. Hei 5-31309 discloses that an extruded aluminum-Zn-Mg-based aluminum alloy
6 describes a processed door beam.
No. 47575 describes a door beam in which a recrystallized layer having a thickness of 70 μm or more is formed on the outer surface of an extruded material of an Al—Zn—Mg-based aluminum alloy or an extruded material of an Al—Si—Mg-based aluminum alloy. .

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Laid-Open No. 5-247 is disclosed.
In Japanese Patent No. 575, a recrystallized layer having a thickness of 70 μm or more is formed on the outer surface of an extruded material of an Al—Zn—Mg-based aluminum alloy or an extruded material of an Al—Si—Mg-based aluminum alloy. The grains are larger in elongation than the fibrous structure, and therefore, when this recrystallized layer is applied to the outer surface of the extruded material having a tensile force of 70 μm or more in which a tensile force is generated by a bending load, the grains are hardly broken and the energy absorption is improved. It is based on the idea that you can.

[0006] On the other hand, the demands on the performance of door beams have become increasingly severe, and it has become necessary to further increase the maximum load and energy absorption without increasing the weight. As an example, in Japanese Patent Application Laid-Open No. Hei 5-247575, the maximum load level in a bending test of an Al-Zn-Mg-based aluminum alloy extruded material is 1100 kg class under a certain vehicle type and a certain bending condition. At present, a 1300 kg class is required under the same bending conditions for the shape.

However, it has been found that when a high σ design (components, extrusion conditions, heat treatment, etc.) is performed in response to the requirement of such a high level of maximum load, the recrystallized layer rather reduces the energy absorption. . This is because if the recrystallized layer is formed thick on the surface, surface roughness occurs in the bending deformation process, and the surface roughness becomes a notch where stress is concentrated, which causes early breakage of the door beam. In particular, recently, door-beam-applied vehicles have spread to small vehicles with short door lengths, and because of the short span, the bending curvature increases even with a small bending stroke (δ).
It is easier to break earlier. The stress concentration caused by the recrystallized layer is not a problem in a door beam having a low-σ design of a conventional level. When a high σ design is used in the present invention, the Al—Zn—Mg system has a proof stress of approximately 40 k.
gf / mm ² or more, approximately 32k for Al-Si-Mg system
gf / mm ² or more falls within the range.

The present inventors have made an aluminum alloy extruded material having a composition described in JP-A-5-247575 to obtain a door beam material having a large maximum load and a large energy absorption without increasing the weight. For the purpose, various studies were made on the component composition and the form of the outer surface texture. As a result, it has been found that, when the level of the maximum load is increased, by reducing or eliminating the thickness of the recrystallized layer, stress concentration during bending deformation can be prevented, and the amount of energy absorption can be improved. . The present invention has been made based on this finding.

[0009]

The door beam material according to the present invention is an Al-Zn-Mg-based aluminum alloy containing 0.8 to 1.5% of Mg and 4 to 7% of Zn, or Si:
An extruded material of an Al-Si-Mg-based aluminum alloy containing 0.5 to 1.5% and Mg: 0.5 to 1.3%, wherein the thickness of a recrystallized layer on the surface is 50 µm or less. It is characterized by the following.

An Al—Zn—Mg based aluminum alloy is
In addition to containing 0.8 to 1.5% of Mg and 4 to 7% of Zn, other components may be included as appropriate.
Mg: 0.8-1.5%, Zn: 4-7%, Ti: 0.
005 to 0.3%, Cu: 0.05 to 0.6%, M
n: 0.2-0.7%, Cr: 0.05-0.3%, Z
r: One or two or more selected from 0.05 to 0.25%, the balance being Al and unavoidable impurities. Al-Si-Mg based aluminum alloy is S
i: 0.5 to 1.5%, Mg: 0.5 to 1.3%, and may contain other components as appropriate, but preferred compositions are Si: 0.5 to 1.5%, Mg: 0.5 to 1.3
%, Ti: 0.005 to 0.2%, and Cu: 0.1 to
0.7%, Mn: 0.05 to 0.6%, Cr: 0.05
０．２0.2%, Zr: One or more selected from 0.05 to 0.2%, with the balance being Al and unavoidable impurities.

In the present invention, there is a fibrous structure particularly under the surface recrystallized layer. However, the surface recrystallization layer may not be present. The fibrous structure is a hot worked structure found in the extruded material, and is a crystal grain structure elongated in the extrusion direction.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The composition of a door beam material according to the present invention will be described below with reference to Al-Zn-Mg type and Al-Si-M
This will be described in detail separately for g-system. (In the case of Al-Zn-Mg system) Mg, Zn Mg and Zn are elements necessary for maintaining the strength of the aluminum alloy. If Mg is less than 0.8% and Zn is less than 4% by weight, desired strength cannot be obtained. In addition, when Mg is 1.
If the content exceeds 5% and the content of Zn exceeds 7%, the extrudability of the aluminum alloy decreases and the elongation also decreases, so that the required characteristic values cannot be obtained. Therefore, Mg: 0.8-1.5%, Zn:
4 to 7%. It should be noted that this is disclosed in
No. 75 corresponds to the Mg-rich side.

Ti Ti is an essential element for refining the ingot structure.
If the Ti content is less than 0.005%, the effect of miniaturization is not sufficient, and if the Ti content is more than 0.3%, saturation occurs and a giant compound is generated. Therefore, the content of Ti is 0.005 to 0.5.
3%.

Cu, Mn, Cr, Zr These elements increase the strength of the aluminum alloy. Further, Cu improves the stress corrosion cracking resistance of the aluminum alloy, and Mn, Cr, and Zr have a function of forming a fibrous structure in the extruded material to strengthen the alloy.
Seeds or more are added as appropriate. The preferred range is Cu: 0.0
5 to 0.6%, Mn: 0.2 to 0.7%, Cr: 0.0
5 to 0.3%, Zr: 0.05 to 0.25%. If each is less than the lower limit, the above action is insufficient, and
Exceeding the upper limit will result in poor extrudability and Cu will result in poor general corrosion resistance.

Inevitable impurities Fe is the most inevitable impurity contained in aluminum ingots. If it exceeds 0.35% in the alloy, coarse intermetallic compounds are crystallized during casting, and the mechanical properties of the alloy are reduced. Impair the nature. Therefore, the content of Fe is 0.35
% Or less. Further, when casting an aluminum alloy, impurities are mixed from various routes such as a base metal and an intermediate alloy of an additive element. There are various elements to be mixed, but impurities other than Fe alone have 0.05% or less, and if the total amount is 0.15% or less, it hardly affects the properties of the alloy. Therefore, these impurities are set to 0.05% or less in a simple substance, and 0.15% or less in total.

(In the case of Al-Si-Mg type) Si, Mg Si and Mg are elements necessary for maintaining the strength of the aluminum alloy. Si is less than 0.5%, Mg is 0.5
If the amount is less than the weight percentage, the desired strength cannot be obtained. On the other hand, if the content of Si exceeds 1.5% and the content of Mg exceeds 1.3%, the extrudability of the aluminum alloy decreases and the elongation also decreases, so that the required characteristic values cannot be obtained. Therefore, Si: 0.5 to 1.5
%, Mg: 0.5 to 1.3%. On the other hand, Ti, C
For u, Mn, Cr, Zr, and unavoidable impurities,
For the same reason as for the Al-Zn-Mg system, it is limited to the above range.

Next, the structure of the extruded material will be described. If the recrystallized layer is formed thick on the surface, rough surface occurs in the bending deformation process, and this rough surface becomes a notch of stress concentration,
Premature breakage of the door beam, resulting in reduced energy absorption. However, when the recrystallized layer is as thin as 50 μm or less as in the present invention, or when the recrystallized layer is not present, the fibrous structure exists under or on the thin recrystallized layer. With a certain degree of bending deformation, surface roughness does not occur on the surface in the process, so that the roughened portion does not become a notch for stress concentration.
Among the recrystallized layers formed on the surface of the extruded material, the one that leads to breakage of the door beam is the recrystallized layer formed on the surface on the side outside the bend. Therefore, the thickness of the recrystallized layer referred to in the present invention is the thickness of the recrystallized layer measured on the surface on the side outside the bending of the door beam.

The recrystallized layer on the surface of the extruded material is formed by causing the surface layer which undergoes particularly large deformation at the time of extrusion to undergo recrystallization by the heat of the extruded material itself during the extrusion process. Therefore, the formation or growth of the recrystallized layer can be prevented by setting the extrusion temperature and the extrusion rate low or adopting a multi-hole extrusion method to make the extrusion ratio relatively small. Furthermore, by rapidly cooling only the surface layer of the extruded material in the vicinity of the die outlet position on the downstream side of the extrusion die, there is an effect of preventing generation of a recrystallized layer or subsequent growth.

In the Al—Zn—Mg-based aluminum alloy having the above-mentioned composition, the method for producing an extruded material having the above-mentioned structure specified in the present invention includes, for example, soaking conditions; 450 ° C. to 500 ° C., extrusion temperature; 400-500
C, extrusion speed; 6 to 10 m / min, extrusion ratio: 35 to 70,
Aging conditions: 130 to 170 ° C. × 6 to 12 hours. Cooling nitrogen gas is blown onto the surface of the extruded material near the exit of the extrusion die to prevent a rise in product temperature immediately after opening from the extrusion die. No. In addition, in the Al—Si—Mg-based aluminum alloy having the above component composition, the method for producing an extruded material having the above structure specified in the present invention includes, for example, soaking conditions;
0 ° C to 550 ° C, extrusion temperature; 480 to 550 ° C, extrusion speed; 6 to 12 m / min, extrusion ratio; 35 to 70, aging conditions;
150 to 200 [deg.] C. for 4 to 16 hours. In addition, a cooled nitrogen gas is sprayed on the surface of the extruded material near the exit position of the extrusion die to prevent a rise in product temperature immediately after opening from the extrusion die.

[0020]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. (Example 1) The aluminum alloy of the component 1 was melted by a conventional method and cast into an ingot having a diameter of 200 mm. This ingot was soaked at 470 ° C. for 8 hours, extruded in two pieces at an extrusion temperature of 470 ° C. and an extrusion speed of 4 m / min (extrusion ratio: 42), and cooled at the position immediately after extrusion by blowing nitrogen gas onto the surface of the extruded material. did. The cross-sectional shape of the extruded material is as shown in FIG. This extruded material was subjected to an aging treatment at 130 ° C. for 12 hours to obtain a test material of Example 1. On the other hand, as Comparative Example 1, 470 ° C. × 8 h
r soaking, extrusion temperature 500 ° C, extrusion speed 12m /
In one minute, the pieces were extruded into the same cross-sectional shape by one piece (extrusion ratio 83). Cooling with the cooled nitrogen gas at the position immediately after extrusion was not performed. 130 ° C × 12 for this extruded material
After the aging treatment for hr, the test material of Comparative Example 1 was obtained.

[0021]

[Table 1]

In the measurement of the surface recrystallized layer thickness of this test material, in the cross section perpendicular to the extrusion direction, the outer side of the bend (the lower flange in FIG. 1A) is divided into four equal parts on the left and right sides, and the dividing position The microstructure of the metal structure at three places (indicated by arrows) was taken as a micrograph, the thickness of the recrystallized layer from the surface was measured, and the average value at three places was determined. Table 2 shows the results. In Example 1, the thickness of the surface recrystallized layer was within the specified range of the present invention, and the lower part of the surface recrystallized layer had a fibrous structure. On the other hand, in Comparative Example 1, the thickness of the surface recrystallized layer exceeded the specified range of the present invention, and a fibrous structure was formed below the surface recrystallized layer. In addition, 3 of bending span 950mm
Table 2 shows the results of the point bending test. As shown in Table 2, in Example 1 in which the surface recrystallized layer thickness is within the specified range of the present invention, the breaking displacement is longer as compared with Comparative Example 1 in which the surface recrystallized layer thickness is large. The breaking displacement is a stroke until a crack occurs on the outside of the bending of the test material (the inner side of the door).

[0023]

[Table 2]

(Embodiment 2) The aluminum alloy of the component 1 is melted by a conventional method, and the diameter is 200 m.
m. The ingot was soaked at 470 ° C. for 8 hours, and extruded at 460 ° C. at an extrusion speed of 5 m / min.
Extrusion (extrusion ratio 35) was performed in the main sampling, and nitrogen gas cooled at a position immediately after extrusion was blown onto the surface of the extruded material to be cooled. The cross-sectional shape of the extruded material is as shown in FIG. This extruded material was subjected to an aging treatment at 130 ° C. for 12 hours to obtain a test material of Example 2. On the other hand, N shown in Table 1
o. An extruded material having the same cross-sectional shape was obtained by the same process using the aluminum alloy of the second component, and the same aging treatment was performed.

Table 3 shows the results of a three-point bending test of the extruded material having a surface recrystallization thickness and a bending span of 700 mm.
The method for measuring the surface recrystallization thickness is the same as in Example 1. Table 3
As shown in Table 2, in both Example 2 and Comparative Example 2, the surface recrystallized layer thickness was within the specified range of the present invention, and the fibrous structure was formed under the surface recrystallized layer. Example 2, which is within the specified range of the invention, is Comparative Example 2 in which the main component is insufficient.
In comparison with, the maximum bending load is large, and the energy absorption up to a displacement of 6 inches is large.

[0026]

[Table 3]

Example 3 An aluminum alloy having the components shown in Table 4 was melted by a conventional method and cast into an ingot having a diameter of 200 mm. The ingot was soaked at 530 ° C. for 12 hours, extruded in two pieces at an extrusion temperature of 530 ° C. and an extrusion speed of 8 m / min (extrusion ratio: 42), and cooled at the position immediately after extrusion by blowing nitrogen gas onto the surface of the extruded material. did. The cross-sectional shape of the extruded material is as shown in FIG. This extruded material was subjected to aging treatment at 190 ° C. for 8 hours to obtain a test material of Example 3. On the other hand, the same aluminum alloy was used, the extrusion speed was set to 15 m / min, and extruded materials of the same shape manufactured under the same conditions as in Example 3 except that cooling with a cooled nitrogen gas was not performed immediately after the extrusion. The test material of Example 3 was used.

[0028]

[Table 4]

Table 5 shows the results of a three-point bending test (implemented up to a displacement of 300 mm) of the extruded material having a surface recrystallization thickness and a bending span of 900 mm. The method for measuring the surface recrystallization thickness is the same as in Example 1.

[0030]

[Table 5]

In both Example 3 and Comparative Example 3, a fibrous structure was present under the surface recrystallized layer.
Example 3 having a surface recrystallized layer thickness within the specified range of the present invention has a longer breaking displacement, a larger maximum bending load, and energy absorption up to a displacement amount of 300 mm, as compared with Comparative Example 3 having a larger surface recrystallized layer thickness. The amount is growing.

[0032]

According to the present invention, it is possible to prevent stress concentration at the time of bending deformation and to prevent premature breakage based on the stress concentration, and to obtain a door beam material having a large maximum load and a large energy absorption.

[Brief description of the drawings]

FIG. 1 is a cross-sectional shape of an extruded material of an example.

FIG. 2 is a diagram showing a bending test method and a load-displacement curve of a door beam material.

Claims (7)

[Claims] 1. An extruded material of an Al—Zn—Mg-based aluminum alloy containing 0.8 to 1.5% (wt%, the same applies hereinafter) of Mg and 4 to 7% of Zn. An aluminum alloy door beam material, wherein the thickness of the crystal layer is 50 μm or less. 2. The Al—Zn—Mg based aluminum alloy contains 0.8 to 1.5% of Mg, 4 to 7% of Zn,
i: 0.005 to 0.3%, Cu: 0.05 to 0.6
%, Mn: 0.2-0.7%, Cr: 0.05-0.3
%, Zr: An aluminum alloy containing one or more selected from 0.05 to 0.25%, and the balance being Al and unavoidable impurities.
A door beam material made of an aluminum alloy described in 1. 3. Si: 0.5 to 1.5%, Mg: 0.5
An extruded material of an Al-Si-Mg-based aluminum alloy containing up to 1.3%, wherein the thickness of the recrystallized layer on the surface is 50 µm.
m or less, wherein the door beam is made of an aluminum alloy. 4. The Al—Si—Mg-based aluminum alloy contains 0.5% to 1.5% of Si and 0.5% to 1.3% of Mg.
%, Ti: 0.005 to 0.2%, and Cu: 0.1 to
0.7%, Mn: 0.05 to 0.6%, Cr: 0.05
4. An aluminum alloy containing at least one selected from the group consisting of Al and unavoidable impurities, wherein one or more selected from 0.05 to 0.2% and Zr: 0.05 to 0.2% are contained. A door beam material made of an aluminum alloy described in 1. 5. The aluminum alloy door beam material according to claim 1, wherein a fibrous structure exists under the recrystallized layer. 6. An aluminum alloy door beam material according to claim 1, wherein no recrystallized layer is present. 7. The aluminum alloy door beam material according to claim 6, wherein a fibrous structure exists on the surface.