KR20010087232A - Aℓ-Mg-Si BASED ALUMINUM ALLOY EXTRUSION FOR DOOR BEAM AND DOOR BEAM - Google Patents

Abstract

PURPOSE: To obtain excellent upset workability and high strength by performing aging treatment after press quenching by air cooling in an Al-Mg-Si based aluminum alloy extruded material for a door beam. CONSTITUTION: This extruded material has a composition in which the content of Mg is, by mass, 0.30 to 0.80%, the content of Si is 0.4 to 0.8%, the content of Si more surplus than the balance composition of Mg2Si is 0.10 to 0.50%, the content of Cu is 0.1 to 0.4%, the content of Ti is 0.005 to 0.2%, the total content of one or more kinds among Mn, Cr and Zr is 0.10 to 0.40%, and the balance Al with inevitable impurities, has a fibrous microstructure and has proof stress of >= 200 MPa.

Description

AL-Mg-Si-based aluminum alloy extrusion material for door beam and door beam {Aℓ-Mg-Si BASED ALUMINUM ALLOY EXTRUSION FOR DOOR BEAM AND DOOR BEAM}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a door beam comprising an Al-Mg-Si-based aluminum alloy extrusion material for a door beam of an automobile and an Al-Mg-Si-based aluminum alloy extrusion material.

As door beams for automobiles, aluminum alloy hollow extrusion materials tend to be applied to reduce weight. Since the door beam requires high energy absorption, the extruded material is required to have a strength of medium to high strength (≥ 200 MPa), and so far, the Al-Mg-Si system (6000 series), which has a high strength by heat treatment as a door beam. And Al-Mg-Zn-based (7000 series) aluminum alloy extrusion materials have been proposed (for example, Japanese Patent Laid-Open No. 11-71624, Japanese Patent Laid-Open No. 5-247575, etc.).

In order to secure the safety of passengers, the application model of the door beam tends to be expanded to a compact car, and in this case, it is necessary to simultaneously store parts such as a door beam, a window glass, and a motor in a relatively thin door thickness. For this reason, the squeeze process is given to a part of the longitudinal direction of an aluminum alloy extrusion material, and it is examined to secure a storage space. However, if squeeze processing is performed, residual stresses are generated at the site, and in the case of Aℓ-Mg-Zn system, SCC (stress corrosion cracking) may be generated. .

In the Al-Mg-Si-based aluminum alloy extruded material, in order to attain the above-mentioned strength, generally, an quenching treatment is performed after online quenching or offline quenching and quenching. This aging treatment improves the strength of the extruded material, at the same time stabilizes the structure, and prevents the change in strength due to the progress of natural aging during use. The squeeze processing is preferably carried out after the aging treatment in terms of cost. However, when the strength of the Al-Mg-Si-based aluminum alloy extruded material is improved in this way, unsatisfactory conditions such as cracks are likely to occur during squeeze processing. If a crack has occurred, it is buckled from the crack part at the time of a collision, and the desired performance required as a door beam cannot be exhibited.

In order to improve the cracking property during squeeze processing, it is considered that it is effective to make the microstructure into a fibrous structure (the structure in which the fibrous structure by extrusion does not recrystallize even during the heat treatment step after the extrusion step), but the above publications As also shown, in order to obtain this fibrous structure, it is necessary to add transition elements such as Mn, Cr, and Zr. And these transition elements are sensitive to the quenching sensitivity of the Al-Mg-Si-based aluminum alloy, thereby lowering the hardenability.

For this reason, quenching is basically performed by water cooling, but when water cooling is performed during press quenching or solution quenching reheating after extrusion, a difference in cooling rate occurs at the cross section due to a difference in cross-sectional shape or thickness of the extruded material, and thus the temperature during cooling. Uneven distribution causes deformation and poor dimensional accuracy. This is particularly noticeable in thin hollow hollow extruded materials such as door beams. Therefore, it is difficult to thin the cross-sectional shape of the door beams, and there is a problem that the degree of freedom of the cross-sectional shapes decreases when trying to prevent the occurrence of such deformation.

On the other hand, when quenching is performed by air cooling, there is little deformation, and in particular, when press quenching is performed by air cooling, there is an advantage of low cost, but the cooling rate is limited (usually up to about 200 ° C / min). One Al-Mg-Si-based aluminum alloy extruded material has a problem that high strength is hardly obtained and energy absorption is also lowered.

Herein, the present inventors have a medium to high strength (bearing force ≥ 200 MPa), and are excellent in energy absorption, in consideration of press hardening by air cooling, which is advantageous in terms of dimensional accuracy and cost, with respect to the Al-Mg-Si-based aluminum alloy extruded material. In addition, as a result of repeated studies for the purpose of obtaining an extruded material for a door beam exhibiting good squeeze workability (crack resistance), an optimum alloy composition was found for press quenching by air cooling.

Means to solve the problem

The Al-Mg-Si-based aluminum alloy extruded material for door beams according to the present invention has a Mg content of 0.30 to 0.80% and a Si content of 0.4 to 0.8%. Excess Si content is 0.10 to 0.50%, Cu content is 0.1 to 0.4%, Ti content is 0.005 to 0.2%, and the content of any one or two or more of Mn, Cr, and Zr is higher than the balance composition of Mg ₂ Si. Furnace consisting of 0.10 to 0.40% of the remaining Al and inevitable impurities, characterized in that the microstructure has a strength of 200Mpa or more into the fibrous tissue. Further, the Al-Mg-Si-based alloy contains Fe and other elements as unavoidable impurities.

Moreover, the door beam which concerns on this invention consists of said Al-Mg-Si type aluminum alloy extrusion material, It is characterized by the squeeze process being given to a part of longitudinal direction.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the cross-sectional shape of the test material of an Example.

It is a figure explaining the squeeze test method.

3 is a view for explaining a three-point bending test method.

In the squeeze processing, in order to prevent the occurrence of cracking and to increase the strength of the alloy at the same time, the extruded material is preferably made of a fibrous structure. Therefore, transition elements such as Mn, Cr, and Zr are added to the Al-Mg-Si-based aluminum alloy. Although added, these transition elements make the quenching sensitivity of the alloy sensitive. In addition, when the amount of Mg and excess Si increases, the strength of the alloy is improved, but the quenching sensitivity is also sensitive.

In the case of press quenching by quenching of water, or solution treatment and quenching, even if the quenching sensitivity is somewhat sensitive, the quenching is fed without problems, and high strength can be obtained by subsequent aging treatment. However, as press hardening by air cooling, if the hardenability becomes sensitive, high strength cannot be obtained even after subsequent aging treatment. That is, even if an alloying element is added for the purpose of strength improvement, it will reverse strength.

In the present invention, the Al-Mg-Si-based aluminum alloy extruded material is formed into a fibrous structure and press quenched by air cooling, and then, in order to obtain high strength by aging treatment, the positive effect is required by adding the above elements. At the same time, the optimum alloy composition is determined in view of the necessity of suppressing the above negative action. Moreover, when press hardening by water cooling is performed with respect to the A-Mg-Si type aluminum alloy extruded material which concerns on this invention, hardening can be fed more reliably and a required strength can be obtained.

Hereinafter, the composition etc. of the Al-Mg-Si type aluminum alloy extrusion material for door beams which concern on this invention are demonstrated.

Mg, Si

Mg and Si combine to form Mg ₂ Si, improving alloy strength. To obtain the strength required as the door beam material, Mg needs to be added at least 0.30%. However, when added in excess of 0.80%, the quenching sensitivity is sensitive, the quenching is not eaten into the press quenching by air cooling, and the required strength does not come out. Therefore, Mg content is made into 0.30 to 0.80%. More preferred range is 0.3 to 0.7%, even more 0.40 to 0.60%, even more preferably 0.45 to 0.55%.

On the other hand, if the amount of excess Si (excess Si is more than the balance composition of Mg ₂ Si and defined as "excess Si amount (%) = total Si amount-Mg amount / 1.73") is less than 0.10%, the required strength cannot be obtained. When this exceeds 0.50%, the quenching sensitivity is sensitive, and the quenching is not fed into the press quenching by air cooling and the required strength is not obtained. Therefore, content of excess Si is made into 0.10 to 0.50%. The more preferable range is 0.22 to 0.40% because the yield strength is further improved to 0.22% or more, the grain boundary precipitates are reduced below 0.40% and the squeeze workability is further improved.

Within the range of the Mg amount and the excess Si, a high strength is obtained and the quenching sensitivity is not so sensitive. The total Si amount is made 0.4 to 0.8%. More preferred range is 0.5 to 0.8%, even more preferably 0.5 to 0.7%.

Mn, Cr, Zr,

Transition elements of Mn, Cr, and Zr precipitate finely in the case of billet cracking, inhibit the growth of grains by pinning the grain boundaries, and form fibrous structures in the extruded material to prevent cracking during bending. There is an effect of improving, and one or two or more of them are added in a range of 0.10 to 0.40% in total. When the addition amount of these transition elements is less than 0.10%, the fibrous structure or the surface recrystallization layer is thick and the crack resistance at the time of squeeze deteriorates and the weldability is further deteriorated. Moreover, when it exceeds 0.40%, hardening will not take in by press hardening by air cooling, and the intensity | strength required as a door beam material will not appear.

Therefore, the content of any one or two or more of Mn, Cr and Zr is 0.10 to 0.40% in total. In Mn, Cr, and Zr, Zr suppresses the quenching sensitivity relatively relatively, so that the quenching is easily absorbed, and Zr is first added, and Mn and Cr may be added if necessary. The preferred ranges of Mn, Cr, and Zr are Mn: 0.001 to 0.35%, Cr: 0.001 to 0.20%, and Zr: 0.001 to 0.20%.

Moreover, the more preferable range of the total addition amount of these transition elements is 0.20 to 0.30%, wherein the preferred range of each element is Mn: 0.05 to 0.25%, Cr: 0.001 to 0.15%, Zr: 0.05 to 0.18%, the sum of transition elements The more preferable range of addition amount is 0.22 to 0.28%, wherein the preferred range of each element is Mn: 0.10 to 0.20%, Cr: 0.001 to 0.10%, Zr: 0.07 to 0.14%.

In the alloy of the present invention, in order not to sensitize the quenching sensitivity, the addition amount of these transition elements is an amount of the limit point at which the fibrous structure can be maintained in the extruded material by press quenching by air cooling. For this reason, if the solution is quenched and quenched off-line rather than press hardening, the possibility of recrystallization advances by heating at the time of solution treatment. Furthermore, the cooling rate of air cooling is preferably 150 to 300 ° C / min.

The fibrous structure is preferably formed in the whole cross section of the extruded material, and even when the surface recrystallization layer is formed, the thickness of the fibrous structure needs to be about 1/2 or more of the total thickness. If it is an extrusion material with a thickness of 1-5 mm like a door beam material, it is preferable to make surface recrystallization layer about 500 micrometers deep (preferably 300 micrometers) or less in the surface of an extrusion material. This means that the recrystallized grain has a larger grain size than the fibrous structure, and in particular, in the case of press quenching by air cooling, the cooling rate is smaller than that of water cooling, and more precipitates precipitate at the grain boundary during the cooling process. This is because cracking tends to occur. Furthermore, if the amount of transition elements such as Mn is less than the above range, it is difficult to regulate the formation of the surface recrystallization layer as described above in press quenching by air cooling.

Cu,

Cu has the effect of increasing the strength of the Al-Mg-Si-based aluminum alloy and improving stress corrosion cracking resistance. However, if the content is less than 0.10%, the action is insufficient. If the content exceeds 0.40%, the hardenability is lowered and the strength does not come out, so the content is preferably 0.10 to 0.40%. More preferred range is 0.15 to 0.35%, still more preferably 0.18 to 0.30%.

Ti

Ti has a function to refine the ingot tissue. However, if it is less than 0.005%, the effect of miniaturization is not sufficient, and if it is more than 0.2%, a large compound is generated. Therefore, content of Ti is made into 0.005 to 0.2%. The more preferable range is 0.01 to 0.10%, and still more preferable range is 0.015 to 0.050%.

Inevitable impurities

Among the unavoidable impurities, Fe is the most included impurity in the aluminum substrate metal, and when present in the alloy in excess of 0.35%, coarse intermetallic compounds are crystallized during casting and impair the mechanical properties of the alloy. Therefore, the Fe content is regulated to 0.35% or less. Preferably it is 0.30% or less, and still more preferably 0.25% or less. In the case of casting an aluminum alloy, impurities are mixed from various paths such as substrate metal and intermediate alloy of additional elements. Although there are various elements to be mixed, impurities other than Fe alone have 0.05% or less, and total amounts of 0.15% or less have little effect on the properties of the alloy. Therefore, these impurities are individually 0.05% or less and 0.15% or less in total amount. In addition, the impurity B is mixed with the addition of Ti in an amount of about 1/5 of the Ti content in the alloy, but more preferably in the range of 0.02% or less, even more preferably 0.01% or less.

In the case of the extruded material having the above-mentioned composition, it is possible to exhibit 200 MPa or more, which is the strength (bearing capacity) required as the door beam material by performing aging treatment after press quenching by air cooling. However, if it deviates from the said composition, the strength cannot be exhibited or squeeze processability will fall even if fibrous structure is not formed or formed. The preferable range of the yield strength is 220 MPa or more.

Furthermore, the cross-sectional shape of the Al-Mg-Si-based aluminum alloy extruded material for door beams according to the present invention is hollow, and typically consists of both parallel flanges facing perpendicular to the load direction and both webs connecting them vertically. In addition, although squeeze processing is normally performed in the load direction (the thickness direction of a door) after an aging process, it can also be performed before an aging process.

Example

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described.

By DC casting, the Al-Mg-Si type aluminum alloy billet of the component composition shown in Table 1 was melted, and the crack process of 4hr was performed at 470 degreeC. Subsequently, extrusion processing is performed under the conditions of an extrusion temperature of 500 ° C. and a compression rate of 5 m / min, and press quenching (fan air cooling (cooling rate: about 200 ° C./min)) is performed by air cooling at a position immediately after extrusion, and is shown in FIG. 1. The extruded material (left and right symmetrical shape) of the hollow cross section was obtained. Subsequently, this hollow extruded material was subjected to an aging treatment at 190 ° C. for 3 hours to obtain a test material. The thickness of the recrystallized layer from the outer surface and inner surface of the center part of both parallel flanges A and B of the cross section of this specimen was measured, and the average value of 8 places was calculated | required. The results are shown in Table 1.

The following test is done using a test material, and the result is shown in Table 2.

Tensile Test: A JIS 13B test piece was taken from the center of the flange portion A of the specimen in the extrusion direction, and subjected to a tensile test in accordance with JIS Z 2241.

Squeeze test: When the specimen was cut to 200 mm in length, and pressed with a 20 mm jig (1) of 50 × 50 mm angle on the flange A side as shown in Fig. 2 using a 30 Ton universal testing machine, the surface state of the specimen and The presence of cracks was observed.

Three-point bend test: The specimen was supported at a span of 600 mm as shown in FIG. 3, and the energy absorption amount up to a displacement amount of δ = 300 mm was measured with a pressing tool 2 having a radius of 6 inches (152.4 mm).

As shown in Table 2, the alloys (Nos. 1 to 7) within the composition range specified in the present invention exhibit high squeeze resistance (crack resistance) and energy absorbency even with press hardening by air cooling.

On the other hand, alloys whose compositions do not satisfy the requirements of the present invention (Nos. 8 to 16) have reached (200 at the same time inferior in energy absorption) or have reached a strength of 200 MPa, which is required as a door beam material. 14 and 15) are inferior in crack resistance at the time of squeeze processing.

According to the present invention, a door beam material exhibiting excellent squeeze workability and energy absorption property with high strength (bearing strength) can be obtained even when the Al-Mg-Si-based aluminum alloy extruded material is subjected to aging treatment after press quenching by air cooling. Moreover, when press hardening by air cooling is performed, the door beam material which is advantageous in terms of dimensional accuracy and cost compared with water cooling can be obtained.

Claims (3)

Mg content is 0.30 to 0.80% (mass% or less is the same), and Si content is 0.4 to 0.8%. Excess Si content is 0.10 to 0.50%, Cu content is 0.1 to 0.4%, Ti content is 0.005 to 0.2%, and the content of any one or two or more of Mn, Cr, and Zr is higher than the balance composition of Mg ₂ Si. Al-Mg-Si-based aluminum alloy extruded material for a door beam consisting of 0.10 to 0.40%, the remaining AL and inevitable impurities, the microstructure has a strength of 200MPa or more as a fibrous structure. The Al-Mg-Si-based aluminum alloy extruded material for a door beam according to claim 1, wherein at least Zr of Mn, Cr, and Zr is included, and the content thereof is 0.001 to 0.20%. A door beam comprising the Al-Mg-Si-based aluminum alloy extruded material according to claim 1 or 2, wherein a part of the longitudinal direction is squeezed.