JP2003268473A - Al-Mg-Si ALUMINUM ALLOY EXTRUDED-MATERIAL SUPERIOR IN COLLAPSE CRACKING RESISTANCE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an Al-Mg-Si aluminum alloy extruded-material, which has excellent collapse cracking resistance and energy absorptive properties in the axial direction, and excellent collapse cracking resistance in the transverse direction as well at the same time. <P>SOLUTION: The Al-Mg-Si aluminum alloy extruded-material consists of an Al-Mg-Si alloy containing 0.3-0.8% Mg (by mass%, hereafter) and 0.5-1.1% Si, and has 25% or more of a wall thickness reduction rate in the fracture surface after a tensile test using the specimens specified as JIS No.5. The material preferably includes one or more elements of Mn, Cr, and Zr in the amount of 0.1-0.4%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a function of absorbing an impact load of compression when it receives a compressive impact load, and is used as an impact absorbing member such as a side member, a bumper stay and a side frame in a frame structure of an automobile. The present invention relates to a suitable Al-Mg-Si-based aluminum alloy extruded material having excellent resistance to pressure cracking.

[0002]

2. Description of the Related Art In an automobile frame structure, application of an aluminum alloy hollow extruded material having, for example, a rectangular cross section as a shock absorbing member such as a side member or a bumper stay has been studied for weight reduction. These shock-absorbing members that receive a compressive shock load in the axial direction do not cause Euler buckling of the entire extruded material (buckling in which the entire profile bends in a dogleg shape) when a load is applied in the axial direction of the extrusion, and It is required to contract and deform in a bellows shape without causing crush cracking to obtain stable high energy absorption and to have strength (proof strength) required as a vehicle frame structural material.

As an aluminum alloy extruded material which can be used as a shock absorbing member, Al--Mg-- which is relatively superior in corrosion resistance among high strength aluminum alloys and superior in recyclability to other types of aluminum alloys.
Many Si-based aluminum alloy extruded materials have been studied (for example, JP-A-6-25783 and JP-A-7-54).
090, JP-A-7-118782, JP-A-9-256096, etc.).

In order to use the extruded aluminum alloy material for a frame structure of an automobile, etc., it is required to have a proof stress of at least 150 MPa or more, preferably 200 MPa or more. In order to obtain this strength in an Al-Mg-Si-based aluminum alloy extruded material, as described in the above-mentioned publication, in general, online press quenching or offline solution heat treatment / hardening treatment is performed, followed by aging treatment. ing. The aging treatment is performed here to improve the strength of the extruded material and to stabilize the structure and prevent the natural aging from progressing during use to change the strength.

[0005]

The Al-Mg-Si type aluminum alloy extruded material may be exposed to high temperature during use as a side member or the like, and natural aging may progress to deteriorate the pressure crack resistance. To prevent this, aging treatment is an essential requirement when using a heat-treating type Al-Mg-Si-based aluminum alloy extruded material as a shock absorbing member, but T5 and T6 treatments were performed to increase the strength. In this case, there is a problem that a crush crack occurs when it is compressed and deformed in the axial direction. When crush cracking occurs, the bellows-like contraction deformation is hindered and stable energy absorption cannot be obtained. In addition, if the crushing crack is severe, there is a risk that the fragments may scatter. Further, recently, from the viewpoint of recyclability, the same Al-Mg-Si based aluminum alloy extruded material can be used at the same time as other automobile structural members such as side frames subjected to a lateral impact load. Has come to be required. Therefore, the present invention provides Al-Mg with high strength (proof stress).
An object is to give the Si-based aluminum alloy extruded material excellent pressure-resistant cracking resistance and excellent energy absorption in the axial direction and at the same time excellent lateral pressure-resistant cracking resistance.

[0006]

[Means for Solving the Problems] In the course of conducting various experimental studies to develop an aluminum alloy extruded material having excellent resistance to crush cracking, the present inventors have taken JIS No. 5 tensile test pieces taken from the extruded material having a hollow cross section. It was found that the thickness reduction rate of the fractured surface of the test piece in the tensile test was closely related to the pressure crack resistance of the extruded material, and the present invention could be obtained based on it.

That is, the Al-Mg-Si type aluminum alloy extruded material according to the present invention, which is excellent in the resistance to pressure cracking, is
It is characterized in that the thickness reduction rate of the fracture surface when the tensile test is carried out on the IS5 tensile test piece is 25% or more.
Here, the thickness reduction rate of the fracture surface (hereinafter referred to as drawing) means the thickness of the central portion of the fracture surface when the fracture surface of the tensile test piece is viewed from the front (perpendicular to the plate surface of the test piece. When the measured wall thickness) is a (see FIG. 1) and the original wall thickness of the tensile test piece is a ₀ , it is represented by (1-a / a ₀ ) × 100. According to the present invention, Al- which has excellent resistance to pressure cracking
For the Mg-Si based aluminum alloy extruded material, Mg: 0.
Al containing 3 to 0.8% and Si: 0.5 to 1.1%
A -Mg-Si based aluminum alloy is suitable.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The Al-Mg-Si-based aluminum alloy is used as an additive element other than those described above, if necessary.
Includes one or more of Cu, Ti, Mn, Cr and Zr (to be used alone or two sets of these (+
, +, +) Or a combination of three pairs (++)), and Fe as an unavoidable impurity, and other elements. Hereinafter, the composition and the like of the extruded material forming the impact absorbing member of the present invention will be described.

Mg, Si Mg and Si combine to form Mg ₂ Si and improve alloy strength. In order to obtain the strength required as an automobile frame structural material, it is necessary to add 0.3% or more of Mg. However, if it is added in excess of 0.8%, the amount of precipitates will be too large, and it will be difficult to obtain a drawing of 25% or more, and excellent pressure crush resistance will not be obtained. Therefore, M
The g content is 0.3 to 0.8%. A more desirable range is 0.4 to 0.7%, and a further desirable range is 0.45 to 0.
60%. On the other hand, if the Si content is less than 0.5%, the required strength cannot be obtained. If the Si content exceeds 1.1%,
Similarly, grain boundary precipitates increase, and it is difficult to obtain a reduction of 25% or more, and excellent pressure crush cracking resistance cannot be obtained.
Therefore, the Si content is 0.5 to 1.1%. A more desirable range is 0.5 to 1.0%, and a further desirable range is 0.
5 to 0.7%. In order to prevent the quenching sensitivity from becoming sharp and to obtain the required strength even with press quenching by air cooling, Mg: 0.7% or less,
Si: 1.0% or less, excess Si (Si in excess of the balance composition of Mg ₂ Si, “total Si amount−0.578 × Mg
Amount)): 0.1 to 0.5%.

Cu Cu has the effects of improving the alloy strength by precipitation hardening, refining the Mg ₂ Si precipitates in the matrix, increasing the size of the drawing, and improving the resistance to pressure cracking. However, if it is less than 0.1%, it is not effective, while if it exceeds 0.7%, the corrosion resistance and weldability are deteriorated. Therefore, the Cu content is 0.1 to 0.7%, preferably 0.1 to 0.6%,
More preferably, it is 0.1 to 0.4%. Ti Ti improves the alloy strength by refining the crystal grains during casting. To exert this effect, Ti
It is necessary that the addition amount be 0.005% or more. On the other hand, if it is less than 0.005%, the crystal grains become coarse and the drawing becomes small, so that excellent pressure rupture cracking resistance cannot be obtained. On the other hand, when the amount of Ti added exceeds 0.2%, the above-mentioned effect is saturated, and coarse intermetallic compounds are crystallized, so that a predetermined alloy strength cannot be obtained. Further, it becomes difficult to obtain a diaphragm of 25% or more. Therefore, the Ti content is 0.005
To 0.2%, more preferably 0.01 to 0.1%,
More preferably, it is 0.01 to 0.05%.

Mn, Cr, and Zr Mn, Cr, and Zr respectively precipitate as fine intermetallic compounds during homogenization treatment of the billet to refine the crystal grains of the extruded material and improve the strength and the resistance to pressure cracking. But,
If the total amount of these elements added is less than 0.05%, the above effect cannot be exhibited. On the other hand, if the total amount added exceeds 0.6%, the above-mentioned effect will be saturated. Individually, the above effects cannot be exhibited at less than 0.05%, 0.001% and 0.05% respectively, and 0.4%, 0.2% and 0.2%, respectively.
If it exceeds%, the effect will be saturated. Therefore, M
The total content of n, Cr and Zr is 0.05 to 0.6%,
Individually, Mn: 0.05 to 0.4%, Cr: 0.001
To 0.2%, Zr: 0.05 to 0.2%, and one or more of these are appropriately added. More preferably,
Mn: 0.1-0.2%, Cr: 0.001-0.1
%, Zr: 0.1 to 0.15%, or two or more.

By the way, in the Al-Mg-Si-based aluminum alloy extruded material, if a fibrous structure is formed in the extruded material, the strength and the pressure crush resistance are improved. It is desirable that this fibrous structure is formed on the entire cross section of the extruded material, and even if the surface recrystallized layer is formed, it is 1 / th of the thickness of the extruded material cross section.
It is desirable to be formed with a thickness of about 2 or more. The fibrous structure is a structure in which the fibrous structure by extrusion remains without being recrystallized during the heat treatment process after the extrusion process. In order to obtain this fibrous structure, it is necessary to contain Mn, Cr, and Zr in a total amount of 0.1% or more. On the other hand, in order to reduce the manufacturing cost and improve the dimensional accuracy after quenching, it is desired to obtain necessary strength and excellent pressure crush cracking resistance by press quenching by air cooling.
However, the cooling rate is relatively slow (usually 100-400
(° C / min) In the case of air cooling, when Mn, Cr, and Zr are added, these elements sharpen the quenching sensitivity of the Al-Mg-Si-based aluminum alloy, so the total content is 0.4.
If it exceeds%, the steel cannot be sufficiently baked and high strength (especially yield strength) cannot be obtained. Therefore, when Mn, Cr, and Zr are added to obtain a fibrous structure, especially when press quenching by air cooling is performed, the total content of Mn, Cr, and Zr is 0.1.
~ 0.4%. However, normal fan air cooling (200
In order to obtain a fibrous structure at (.degree. C./min),
A content of 18% or more is desirable.

Inevitable Impurities Among the inevitable impurities, Fe is the most contained impurity in the aluminum base metal, and if more than 0.35% is present in the alloy, coarse intermetallic compounds crystallize during casting, and mechanical Spoil the nature. Therefore, the Fe content is 0.35
% Or less. It is preferably 0.30% or less,
Furthermore, 0.25% or less is desirable. Further, when casting an aluminum alloy, impurities are mixed in through various routes such as a base metal, an intermediate alloy of additional elements, and a compound. Although various elements are mixed in, if the impurities other than Fe alone are 0.05% or less and the total amount is 0.15% or less, the characteristics of the alloy are hardly affected. Therefore, these impurities should be 0.05% or less as a simple substance and 0.15% or less as a total amount. In addition,
Among the impurities, B is added to the T
It is mixed in an amount of about 1/5 of the i content, but a more desirable range is 0.02% or less, and further 0.01% or less.

Further, in the extruded material of Al-Mg-Si type aluminum alloy, the value of the drawing defined in the present invention is 25.
%, The reason why the resistance to crush cracking is excellent is that the value of the squeeze is one index showing the local deformability of the material, while when the extruded material is crushed and deformed into a bellows shape, the surface of the material is very small. The elongation that occurs in the area reaches about 30%, and it is considered that the material is locally deformed like a drawing in such an area. Therefore, when the value of the drawing is equal to or larger than a predetermined value, cracking occurs. It is speculated that it was suppressed. The Al-Mg-Si-based aluminum alloy extruded material according to the present invention is excellent in crush resistance in the axial direction of extrusion, but is also excellent in crush resistance in the transverse direction at the same time. It can also be used as a structural member for ships and the like.

[0015]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples that deviate from the scope of the claims of the present invention. First, Al-Mg-Si having the composition shown in Table 1 below.
A system aluminum alloy billet (diameter: 155 mm) was melted by a usual method, and homogenized at about 540 ° C. for 4 hours. After that, each billet is extruded under the conditions of an extrusion temperature of 500 ° C. and an extrusion speed of 5 m / min, and immediately after extrusion, press quenching is performed by air cooling or water cooling, and an extruded material having a hollow rectangular cross section as shown in FIG. (A square pipe having an outer shape of 70 × 54 mm and a wall thickness of 2 mm) was manufactured. In addition, No. Only 9 was water-cooled and the others were air-cooled. This square pipe was subjected to artificial aging treatment under the conditions shown in Table 1 to obtain a test material.

[0016]

[Table 1]

JIS No. 5 test pieces were taken from each of these test materials parallel to the extrusion axis direction, and the tensile strength σB, proof stress σ0.2, and elongation at break (breaking strain) δ were measured according to JISZ2.
Measured according to the metal material tensile test method specified in 241.
On the other hand, the thickness of the central portion of the fracture surface was measured by the method described above, and the value of the aperture defined above was obtained. Original wall thickness is 2mm
Is. The results are shown in Table 2. In addition, longitudinal and lateral crush tests were performed on each test material (length 200 mm). In the longitudinal crush test, a static compression load is applied in the axial direction by an Amsler tester as shown in FIG. 3, and this is compressed to 100 mm to obtain a load-displacement curve, and the maximum load and absorbed energy up to 100 mm are obtained. It was The crackability is evaluated visually,
The case where no opening crack (crack penetrating the wall thickness) was evaluated as ◯, and the case where opening crack occurred was evaluated as x. As a comprehensive evaluation of the vertical crushing test, there was no cracking in the opening and the proof stress was 200.
Absorbed energy of 2500 J or more at 150 MPa or more (150 M
If it is Pa or more, 1500 J or more is almost equivalent to this), and it is determined to be acceptable. In the lateral crush test, a static compressive load was applied to the test material in a horizontal direction so that the long sides were up and down, the static compression load was compressed to 20 mm, and the cracking property was visually evaluated. The evaluation of crackability is the same as the vertical crush test. The results are also shown in Table 2.

[0018]

[Table 2]

As is clear from Table 2, No. No. Nos. 1 to 7 are all excellent in cracking property in longitudinal and lateral compression, and the drawing is less than 25%. 8 and 9 are inferior in crackability. Moreover, No. Nos. 1 and 3 have proof stress. Although it is almost the same as No. 8, Compared with No. 8, the absorbed energy is about 20% higher and the yield strength is No. 8. No. 8 lower than 8 Even in Nos. 2, 4 and 6, the maximum load is slightly low, but the absorbed energy is no. It is higher than 8. The proof stress value is No. No. higher than 8 In No. 7, the absorbed energy is no. It is considerably higher than No. 8, and Higher than 9 In addition, No. The fibrous structure was formed in each of Nos. 1 to 7 and 9 with a thickness of half or more of the cross section. 8
No fibrous tissue was formed in the.

[0020]

According to the present invention, in an Al-Mg-Si type aluminum alloy extruded material, the extruded material has a drawing rate of 25%.
As a result of the above, it has excellent resistance to crush and cracking against longitudinal compression and lateral compression, and has a high absorbed energy. For example, automobile frames (side members, cross members, bumper stays, side frames, pillars, etc.)
- ), An aluminum alloy extruded material suitable as a structural member for automobiles such as bumpers and door beams, a structural member for railway vehicles and ships, and the like.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a diaphragm according to the present invention (a side view,
(Front view)

FIG. 2 is a diagram showing a cross-sectional shape of an extruded material used in Examples.

FIG. 3 is a diagram illustrating a vertical crush test of an example (before crush,
After crushing).

FIG. 4 is a diagram illustrating a lateral crush test of an example (before crush,
After crushing).

Continued front page    (72) Inventor Masakazu Hirano             14-1 Chofu Minatomachi, Shimonoseki City, Yamaguchi Prefecture Co., Ltd.             Kobe Steel Chofu Factory

Claims (3)

[Claims] 1. An Al-Mg-Si having excellent resistance to pressure cracking, characterized in that a thickness reduction rate of a fracture surface when a tensile test is carried out on a JIS No. 5 tensile test piece is 25% or more.
Aluminum alloy extruded material. 2. Al-Mg containing Mg: 0.3 to 0.8% (mass%, the same hereinafter) and Si: 0.5 to 1.1%.
An Al-Mg-Si-based aluminum alloy extruded material having excellent resistance to pressure cracking as set forth in claim 1, which is made of a -Si-based alloy. 3. The pressure crush resistance according to claim 2, wherein the content of any one or more of Mn, Cr and Zr is 0.1 to 0.4%. Excellent Al
-Mg-Si based aluminum alloy extruded material.