JP5288671B2 - Al-Mg-Si-based aluminum alloy extruded material with excellent press workability - Google Patents

Description

  The present invention relates to an aluminum alloy extruded material excellent in press workability suitable for molding a frame of an automobile, a railway vehicle, or a building member.

In recent years, from the viewpoint of environmental problems such as global warming and ozone layer destruction, in order to suppress the increase of carbon dioxide gas in the atmosphere, the weight reduction of automobiles and the introduction of electric cars have been studied in earnest. .
As part of this weight reduction, the replacement of materials, that is, the use of aluminum alloy materials instead of steel plates that have been used mainly in conventional automotive structural materials is increasing. Further, there is a strong demand for reducing the weight of an electric vehicle in order to compensate for an increase in weight for mounting a battery. Furthermore, the use of aluminum alloy materials has attracted attention, such as extrudates that can have a constant cross-sectional shape in the longitudinal direction, but have a wider design freedom and can improve formability by obtaining a cross-sectional shape close to the final shape. Has been.

  As an aluminum alloy extruded material that can be used as a frame material for automobiles, it is required to have a proof stress of at least 150 MPa, desirably 200 MPa or more. Among high-strength aluminum alloys, it is relatively excellent in corrosion resistance. Many Al-Mg-Si-based aluminum alloy extruded materials that are superior to aluminum alloys have been studied. In order to obtain this strength in an Al—Mg—Si-based aluminum alloy extruded material, generally, an on-line press quenching or off-line solution hardening / quenching treatment is performed, followed by an artificial aging treatment. Here, the artificial aging treatment is performed in order to improve the strength of the extruded material, stabilize the structure, and prevent the natural aging from progressing with time and preventing the strength from changing.

Problems to be solved by the invention

  On the other hand, when using an aluminum alloy extruded material as a frame material for automobiles, it is possible to reduce the width and height by crushing part of the length of the hollow extruded material in order to meet the limited space, When mounting with bolts and nuts, it is conceivable to crush the end of the hollow extruded material into a plate shape. In addition, embossing is performed for the purpose of forming ribs that control the bellows pitch of axial crushing on the plate surface of hollow extruded materials used for side members and bumper stays, and forming reinforcing ribs on the plate surface of extruded materials. Is also possible. In addition, since residual stress is generated at the site when such press working is performed, an Al—Mg—Si based aluminum alloy extruded material with less fear of occurrence of SCC (stress corrosion cracking) is suitable for these applications. Yes.

  This press working is preferably performed after the aging treatment described above from the viewpoint of cost, but the Al-Mg-Si-based aluminum alloy extruded material that has been strengthened by the aging treatment has relatively poor formability, and during the press working. It is easy to cause defects such as cracks. If cracks occur, the fatigue strength of the frame material will decrease, or the side members will exhibit the desired performance, such as cracking starting from the cracked part at the time of collision and preventing bellows-like buckling. I can't.

  The present invention has been made in view of such problems of the prior art, and is excellent in press workability such as crushing and embossing after quenching and artificial aging treatment, such as a frame of an automobile, a railway vehicle, or a building member. The present invention was made for the purpose of providing an Al—Mg—Si-based aluminum alloy extruded material suitable for molding.

Means for solving the problem

  In the process of conducting various experimental studies to develop an Al-Mg-Si-based aluminum alloy extrudate that is excellent in press workability after quenching and artificial aging treatment, the inventors of the fracture surface when conducting a tensile test It was found that the thickness reduction rate is closely related to the press workability of the extruded material, and based on this, the present invention could be obtained.

That is, the present invention relates to an Al—Mg—Si-based aluminum alloy extruded material containing Mg: 0.4 to 1.2% and Si: 0.3 to 1.2% and subjected to quenching and artificial aging treatment. The thickness reduction rate of the fracture surface when the tensile test is carried out is 20% or more, and it is excellent in press workability such as crushing and embossing.
Here, the thickness reduction rate of the fracture surface (hereinafter referred to as “squeezing”) is the thickness at the center of the fracture surface when the fracture surface of the tensile specimen is viewed from the front (perpendicular to the plate surface of the specimen). The measured thickness is represented by (1-a / a ₀ ) × 100, where a (see FIG. 1) is a and the original thickness of the tensile test piece is a ₀ . The tensile test piece is collected from the extruded material in accordance with JIS regulations. It should be noted that the drawing value does not change even if different types of tensile test pieces (JIS compliant) are sampled from the extruded material and tested.

The Al-Mg-Si-based aluminum alloy contains, for example, (1) Cu, (2) one or more of Mn, Cr and Zr, and (3) Ti as an additional element other than the above as necessary. (▲ 1 ▼ to ▲ 3) alone or two sets of these (▲ 1 ▼ + ▲ 2 ▼, ▲ 1 ▼ + ▲ 3 ▼, ▲ 2 ▼ + ▲ 3 ▼) or 3 sets (▲ 1 ▼ + ▲ 2 ▼ + ▲ 3 ▼)), and Fe and other elements can be included as inevitable impurities.
Hereinafter, the reason for addition of each component in the aluminum alloy extruded material according to the present invention will be described.

Mg, Si
Mg and Si combine to form Mg ₂ Si, improving the alloy strength. In order to obtain strength required as a structural member such as a frame material for automobiles, Mg needs to be added in an amount of 0.4% or more. However, if it is added in excess of 1.2%, the amount of grain boundary precipitates becomes excessive, making it difficult to obtain a drawing of 20% or more, and excellent press workability cannot be obtained. Therefore, the Mg content is 0.4 to 1.2%. A more desirable range is 0.4 to 0.7%, and further desirably 0.45 to 0.6%.

On the other hand, if the amount of Si is less than 0.3%, the required strength cannot be obtained, and if added over 1.2%, grain boundary precipitates increase, and a drawing of 20% or more can be obtained. Difficult to obtain excellent press workability. Therefore, the Si content is set to 0.3 to 1.2%. A more desirable range is 0.3 to 1.0%, and further desirably 0.5 to 0.7%.
In order to suppress sharpening of quenching sensitivity and to obtain the necessary strength by press quenching by air cooling, Mg: 0.7% or less, Si: 1.0% or less, excess Si ( It is desirable that the amount of Si is more than the balance composition of Mg ₂ Si, defined by “total Si amount−0.578 × Mg amount”: 0.1 to 0.5%.

Cu
Cu precipitates as a fine intermetallic compound and has the effect of refining the microstructure of the Al—Mg—Si-based aluminum alloy extruded material, increasing the strength and enlarging the aperture. However, if it is less than 0.05%, the effect is not sufficient. On the other hand, if it exceeds 0.7%, the corrosion resistance and weldability are deteriorated. Therefore, the Cu content is 0.05 to 0.7%, preferably 0.1 to 0.6%, and more preferably 0.1 to 0.4%.

Mn, Cr, Zr
The transition elements of Mn, Cr, and Zr are each precipitated as a fine intermetallic compound during the soaking process of the billet, and have the effect of refining the crystal grains of the extruded material to increase the strength and increase the aperture. However, if the amount is less than 0.05%, 0.001%, and 0.05%, respectively, the effect is not exhibited. On the other hand, if the amount exceeds 0.6%, 0.2%, and 0.2%, the effect is saturated. Resulting in. Therefore, the contents of Mn, Cr, and Zr are Mn: 0.05 to 0.6%, Cr: 0.001 to 0.2%, Zr: 0.05 to 0.2%, and one of these Or 2 or more types are added suitably. More desirably, it is 1 type or 2 types or more of Mn: 0.1-0.2%, Cr: 0.001-0.1%, Zr: 0.1-0.15%.

  By the way, in the Al—Mg—Si-based aluminum alloy extruded material, when a fibrous structure is formed in the extruded material, strength and drawing are improved. This fibrous structure is desirably formed over the entire cross section of the extruded material, and even when the surface recrystallized layer is formed, it may be formed with a thickness of about 1/2 or more of the cross section thickness of the extruded material. desirable. In addition, this fibrous structure is a structure | tissue of the state which the fibrous structure by hot extrusion remained without recrystallizing also between the heat processing processes after an extrusion process. In order to obtain this fibrous structure, it is necessary to contain 0.1% or more of Mn, Cr, and Zr in total.

  On the other hand, in order to reduce manufacturing costs and improve dimensional accuracy after quenching, it is desired to obtain the necessary strength by press quenching by air cooling. However, in the case of air cooling with a relatively slow cooling rate (usually 100 to 400 ° C./min), when Mn, Cr and Zr are added, these elements sharpen the quenching sensitivity of the Al—Mg—Si based aluminum alloy. When the total content exceeds 0.4%, it is difficult to obtain high strength due to insufficient baking. In particular, if the target is a yield strength of 200 MPa or more, the total content should not exceed 0.4%. Accordingly, when a fibrous structure is obtained by adding Mn, Cr, and Zr, particularly when performing press quenching by air cooling, the total content of Mn, Cr, and Zr is 0.1 to 0.4%. However, a content of 0.18% or more is desirable to obtain a fibrous structure in normal fan air cooling (about 200 ° C./min).

Ti
Ti improves alloy strength by refining crystal grains during casting. In order to exert this effect, the Ti addition amount needs to be 0.005% or more. On the other hand, if it is less than 0.005%, the crystal grains become coarse and the aperture becomes small. On the other hand, if the amount of Ti added exceeds 0.2%, the effect is saturated, and a coarse intermetallic compound is crystallized and a predetermined alloy strength cannot be obtained. In addition, it becomes difficult to obtain an aperture of 20% or more. Therefore, the Ti content is 0.005 to 0.2%, more preferably 0.01 to 0.1%, and still more preferably 0.01 to 0.05%.

Inevitable Impurities Among the inevitable impurities, Fe is the most abundant impurity in aluminum ingots. If it exceeds 0.35% in the alloy, coarse intermetallic compounds are crystallized during casting, which impairs the mechanical properties of the alloy. . Therefore, the Fe content is restricted to 0.35% or less. Desirably, it is 0.30% or less, and further 0.25% or less is desirable. Further, when casting an aluminum alloy, impurities are mixed from various paths such as a metal base and an intermediate alloy of an additive element. The elements to be mixed are various, but impurities other than Fe alone are 0.05% or less, and if the total amount is 0.15% or less, the characteristics of the alloy are hardly affected. Accordingly, these impurities are 0.05% or less as a single substance, and the total amount is 0.15% or less. Of the impurities, B is mixed in the alloy in an amount of about 1/5 of the Ti content with the addition of Ti, but the more desirable range is 0.02% or less, and further preferably 0.01% or less.

  In addition, in the Al—Mg—Si-based aluminum alloy extruded material having the above composition, when the drawing value defined in the present invention is 20% or more, the reason why it is excellent in press workability such as crushing and embossing is shown in FIG. The value of is an index indicating the local deformability of the material. On the other hand, when the extruded material undergoes crushing or embossing, the elongation generated on the surface of the processed part reaches about 20%. In such a region, since the material is considered to be locally deformed like a diaphragm, it is presumed that the occurrence of cracking was suppressed when the diaphragm value was a predetermined value or more. The aperture value is preferably 25% or more.

In order to increase the value of the squeeze, the proportion of the fibrous structure is increased, and the grain boundary precipitates are decreased (for example, quenching is water cooling rather than air cooling, and excess Si is less than the stoichiometric amount of Mg ₂ Si). It is effective to make the aging more advanced (aging temperature, aging time), and by appropriately combining these, a 20% or more aperture can be obtained as shown in the examples.
It should be noted that, as shown in examples described later, a certain relationship cannot be found between the magnitude of elongation at break (total elongation) and the value of the drawing.

Examples of the present invention will be described below.
First, an aluminum alloy ingot having the composition shown in Table 1 below is melted by a usual method, and these ingots are subjected to a homogenization treatment of 500 ° C. × 4 hr. Thereafter, the extrusion temperature is 500 ° C., and the extrusion speed is 4 m. Extrusion was performed under the conditions of / min to obtain a 40 × 40 × 2 t mouth-shaped hollow extruded material (see FIG. 2). Immediately after extrusion, the material was cooled and quenched by forced fan air cooling (cooling rate of about 200 ° C./min) or water cooling (cooling rate of 10,000 ° C./min or more). This is shown in the column of quenching method in Table 1. Subsequently, artificial aging treatment was performed under the conditions shown in Table 1 to obtain test materials.

The following measurements were performed using this sample material. The results are shown in Table 2.
Fibrous tissue;
The thickness of the recrystallized layer from the outer surface and the inner surface was measured with an optical microscope, and the ratio of the thickness was determined with the remainder as the fibrous tissue layer.
Mechanical properties;
A JIS No. 5 test piece was taken in a direction parallel to the extrusion direction, and the tensile strength σ B, the yield strength σ 0.2, and the breaking elongation δ were measured in accordance with the metal material tensile test method specified in JIS Z2241.

Aperture;
About the test piece after a tensile test, the thickness of the center part of a torn surface was measured by the method demonstrated previously, and the value of the aperture | phragm defined previously was calculated | required. The original wall thickness is 2 mm.
Press workability;
The specimen is cut into a length of 200 mm, and a 30 Ton universal testing machine is used. As shown in FIG. 3, the specimen is placed so that the left and right sides are vertical and the upper and lower sides are horizontal. A 50 mm square jig 1 is pushed 20 mm vertically to perform a crushing test, and the surface condition of the specimen and the presence or absence of cracks are visually observed. ◎: No crack, rough skin, ○: No crack, rough skin X: Evaluated as occurrence of cracks.

Invention Example No. in which the component composition and the value of the drawing satisfy the requirements of the present invention. Nos. 1 to 5 have good crushing workability, especially No. 1 with a drawing value of 25% or more. Nos. 1, 2, 4, and 5 did not cause cracks or rough surface in the processed part. In addition, a suitable amount of one or more of Mn, Cr and Zr was added to obtain a fibrous structure. Nos. 1, 4, and 5 have large aperture values. Although 1 is air-cooled, it can be seen from the proof stress that baking is included.
On the other hand, Comparative Example No. 6-9, 11 and 12 have open cracks and are inferior in crushing workability. Comparative Example No. No. 10 has a large squeezing value and relatively good crushing workability, but has a low Si and Mg content and a low proof stress.

Effect of the invention

  As described above, in an Al—Mg—Si-based aluminum alloy extruded material, excellent press working is achieved by setting the thickness reduction rate (drawing) value of the fracture surface after quenching and artificial aging treatment to 20% or more. Sex is obtained. This Al-Mg-Si-based aluminum alloy extruded material is used for automobile frames (side members, cross members, bumper stays, side frames, pillars) with crushing and embossing, bumpers, door beams, impact beams (front-rear direction in the door) It is suitable as a structural member such as a structural member for automobiles such as a safety member for receiving an impact load in the axial direction and a frame of a railway vehicle, a ship or a building member.

  It is a figure explaining the measuring method of the thickness reduction rate (drawing) of a torn surface.   It is a figure which shows the cross-sectional shape of the test material of an Example.   It is a figure explaining a crushing test method.

Claims (5)

Mg: 0.4-1.2% (mass%, the same shall apply hereinafter), Si: 0.3-1.2%, and Ti: 0.005-0.2%, the balance from Al and inevitable impurities In the Al-Mg-Si-based aluminum alloy hollow extruded material that has been subjected to quenching and artificial aging treatment, the thickness of the fracture surface when a tensile test was carried out using a JIS No. 5 test piece taken in the direction parallel to the extrusion direction An Al-Mg-Si-based aluminum alloy extruded material for crushing, which is excellent in press workability and has a reduction rate of 20% or more.
Furthermore, Cu: 0.05-0.7% is contained, The Al-Mg-Si type aluminum alloy extrusion material for crushing process excellent in press workability described in Claim 1 characterized by the above-mentioned.
Further, it contains one or more of Mn: 0.05 to 0.6%, Cr: 0.001 to 0.2%, Zr: 0.05 to 0.2%, and a structural member for an automobile (door beam). 3. An extruding material of Al—Mg—Si-based aluminum alloy for crushing excellent in press workability according to claim 1 or 2, which is used for
The total content of one or more of Mn, Cr and Zr is 0.10 to 0.40%, has a fibrous structure, and has been subjected to artificial aging treatment after press quenching by air cooling The Al-Mg-Si-based aluminum alloy extruded material for crushing excellent in press workability according to claim 3.
  An automotive structural member comprising the Al-Mg-Si-based aluminum alloy extruded material according to any one of claims 1 to 4 and having been crushed in a part in a length direction.

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