JP3077974B2 - Al-Mg-Si based aluminum alloy extruded material with excellent axial crushing properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aluminum alloy extruded profile, and more particularly, to an impact load and a static load when subjected to a compression impact load or a static addition of compression in the extrusion direction of the profile. The present invention relates to an extruded aluminum alloy material having an action of absorbing aluminum and particularly suitably applied to structural members for automobiles, for example, side members and bumper stays.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of environmental protection, fuel-efficient vehicles,
Although attention has been focused on the development of electric vehicles, reducing the weight of the body is essential for achieving that goal. On the other hand, vehicle weight tends to increase in order to meet safety standards and improve vehicle performance. Under such circumstances, the extruded aluminum alloy has a specific gravity of about 1/3 that of iron, has excellent energy absorption, and has a high degree of freedom in cross-sectional shape. Adopted for bumper reinforcements, frames, etc., demand for automotive components is growing.
Among automobile structural members, especially for automobile frames,
In order to absorb impact energy at the time of collision, high strength and pressure-resistant cracking resistance that does not cause cracking during bellows deformation, that is, excellent axial crushing properties are required. As a material for an automobile frame such as a side member or a bumper stay which is required to have such a shaft crushing property, for example, Japanese Unexamined Patent Publication No. 9-256
No. 096 proposes the use of an extruded Al-Mg-Si-based aluminum alloy which is relatively excellent in corrosion resistance among high-strength aluminum alloys and superior in recycling to other aluminum alloys. I have.

[0003]

However, Al-
When the strength of an Mg-Si-based aluminum alloy is increased by the addition of an alloy component or heat treatment, the higher the strength, the lower the pressure cracking resistance tends to be. For this reason, there has been a strong demand for the development of an aluminum alloy having high strength and excellent axial crushing characteristics without crushing cracks. The present invention has been made in view of such a problem, and is suitable for an automobile structural member having excellent shaft crushing characteristics (high strength and excellent pressure crush cracking resistance).
An object of the present invention is to provide an extruded 1-Mg-Si-based aluminum alloy.

[0004]

Means for Solving the Problems The present inventors have proposed Al-M
Various experimental studies were conducted on g-Si-based aluminum alloys in order to develop extruded members having excellent axial crushing properties. As a result, when the inside of crystal grains of the alloy was observed, Mg _{2 having a} specific orientation on the (100) plane was observed. It has been found that when the size and distribution of the Si precipitate and the size of the precipitate such as Mg ₂ Si on the crystal grain boundary are within a certain range, excellent axial crushing characteristics can be obtained. The present invention has been made based on this finding. That is, the shaft crushing characteristics according to the present invention are excellent.
In the Al-Mg-Si-based aluminum alloy extruded shape, the average value of the size of the Mg ₂ Si precipitate in the [100] and [010] directions of the (100) plane in the crystal grain is 20 nm or more, and , Mg ₂ S in the [001] direction of the (100) plane
i The distribution density of precipitates is 100 particles / μm ² or more, and the size of precipitates such as Mg ₂ Si on the grain boundaries is 100
0 nm or less. This Al-Mg-
Since extruded Si-based aluminum alloy material has excellent axial crushing properties, it is crushable in the crushable member (when subjected to the impact load of compression in the axial direction or the static application of compression), it is crushed in the axial direction to reduce the impact load and static load. It is suitable for use as a member having an absorbing function).

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the range of the size and distribution density of intragranular precipitates and the size of grain boundary precipitates in the extruded aluminum alloy material according to the present invention are as follows. (Size of Intragranular Precipitate) The intragranular Mg ₂ Si precipitates precipitate in the form of rods in the <100> direction during the artificial aging treatment and increase the strength by disturbing the movement of dislocations. When the average of the size of the precipitates in the [100] and [010] directions of the (100) plane in the crystal grain is less than 20 nm, the dislocations shear the precipitated particles during compression deformation. In this case, the subsequent dislocations can move very easily on the slip plane ((111) plane), so that a linear coarse slip band structure is formed. For this reason, stress concentration occurs at the grain boundary and the grain boundary is broken, so that the pressure cracking resistance is poor. More preferably, the size of the precipitate is 30 nm or more on average. However, if the precipitates become too large, the strength is reduced. Therefore, it is desirable that the average value does not exceed 1000 nm. (Distribution Density) The distribution density of the Mg ₂ Si precipitate affects the strength similarly to the size of the precipitate. (10
When the distribution density of precipitates in the [001] direction of the 0) plane is 100 or less / μm ² or less, the strength is low and the energy absorption during compression deformation is low. Therefore, the distribution density is 100 pieces /
μm ² or more. This distribution density is desirably 400 / μm ² or more in the sense that higher strength is obtained. However, since the crushing cracking the distribution density becomes too large easily bring, it is desirable to 2,000 / [mu] m ² or less. The size and distribution density of the Mg ₂ Si precipitate are measured by a measuring method described later. (Grain Boundary Precipitates) Mg ₂ Si precipitates, Si alone, etc. on the grain boundaries are formed during cooling after extrusion or after solution treatment, and affect the fracture mode. 1000n size of grain boundary precipitate
m, the precipitate becomes a crack initiation point and breaks at the grain boundary,
Poor crush resistance. Desirably, it is 500 nm or less.

In the Al-Mg-Si-based aluminum alloy extruded material according to the present invention, it is desirable that the crystal structure be a fibrous structure (fiber structure). Here, the fiber structure is a hot-worked structure found in the extruded material, and is a crystal grain structure elongated in the extrusion direction. The strain in the material when the material is deformed is induced by the movement of dislocations. However, since the dislocations disappear in a portion where the arrangement of metal crystals such as crystal grain boundaries is irregular, the metal crystals such as crystal grain boundaries and the like are lost. Is irregular, lattice displacement due to dislocations accumulates, and distortion concentrates. Therefore, the distribution of dislocations in the material, that is, the distribution of strain, tends to be uniform throughout the material as the crystal grain size is smaller. Then, in order to suppress the occurrence of cracks at the time of crushing, it is necessary to make the deformation strain uniform in the material. By suppressing the recrystallization and keeping the fiber structure, that is, the grain boundaries in a fine state, the deformation strain can be evenly distributed in the material, and the high pressure resistance and cracking resistance can be improved.

The Al—Mg—Si based alloy according to the present invention comprises:
It is a precipitation hardening type alloy containing Mg and Si as main components. As a preferable composition, Mg: 0.2 to 1.6%, Si: 0.1%.
2 to 1.8%, if necessary, contains Cu: 1.0% or less, and further, Mn: 0.05 to 0.5%, or T
i: 0.01 to 0.1%, Cr: 0.01 to 0.2%,
One or more of Zr: 0.05 to 0.2% is included as necessary, and a composition comprising the balance of Al and impurities can be given. If the content of Fe is 0.7% or less and the other impurities are 0.05% or less, that is, 0.15% or less in total, the characteristics of the alloy are not affected. The reasons for limiting each component are as follows.

(Mg, Si) Mg and Si are elements that form Mg ₂ Si precipitates and impart strength to the alloy. M
If g: less than 0.2% and Si: less than 0.2%, the strength required as a structural member or energy absorbing member to which an impact load or a static load is applied in the axial direction cannot be obtained. On the other hand, Mg:
If the content exceeds 1.6% and the content of Si exceeds 1.8%, the deformability of the extruded shape material is reduced and secondary processing becomes difficult, and crushing cracks are easily generated due to deformation in the extrusion axis direction. Therefore, Mg:
0.2 to 1.6%, Si: 0.2 to 1.8%. Particularly preferred ranges are 0.4 to 0.8% and 0.7, respectively.
~ 1.1%. (Cu) Cu has the effect of improving the matrix strength of the alloy according to the amount of Cu added, and is appropriately added. To obtain this effect, it is preferable to add 0.1% or more. However, when the addition amount exceeds 1%, corrosion resistance, stress corrosion cracking resistance and weldability are reduced, and crush cracking due to deformation in the direction of the extrusion axis is likely to occur. Therefore, when adding Cu, the upper limit is desirably 1.0%. A particularly desirable range for the addition is 0.45 to 0.55%.

(Mn) Mn is added as appropriate because it suppresses recrystallization of the alloy structure and is effective in refining the structure. Further, from this property, it has a function of stabilizing the fiber structure of the extruded shape. These effects become apparent with the addition of 0.05% or more.
And suppresses the diffusion of, degrades the heat treatment property and generates a coarse compound, which causes deterioration of the crush cracking property. Therefore, the addition amount is desirably 0.05 to 0.5%. (Ti, Cr, Zr) Ti has the effect of generating nuclei during melt casting and making the cast structure fine, and is added as appropriate. The effect becomes remarkable when added in an amount of 0.01% or more, and when it exceeds 0.1%, a coarse compound is formed, which causes deterioration of crush cracking property. Therefore, the addition amount is desirably 0.01 to 0.1%. Cr has the effect of pinning the grain boundaries and has the function of stabilizing the fiber structure of the extruded material.
It is added as appropriate. The effect becomes apparent with the addition of 0.01% or more. However, if the addition exceeds 0.2%, the initial pressure at the time of extrusion processing is remarkably increased, which is not practical. 0.01 to 0.2% is preferred. Z
r has an effect of pinning the grain boundaries similarly to Cr and has a function of stabilizing the fiber structure of the extruded material, so that r is appropriately added. The effect becomes apparent with the addition of 0.01% or more. However, the effect of stabilizing the fiber structure is not further increased even if the addition exceeds 0.2%. 0.2% is preferred.

In order to manufacture the extruded material of the present invention using the above-mentioned Al-Mg-Si-based aluminum alloy, the ingot is formed by melting and casting according to a conventional method, and then homogenized to obtain a desired cross section. Either quenching (press quenching) immediately after hot extrusion to a shape or solution quenching after hot extrusion. In hot extrusion-press quenching, the solution temperature is also used by using the processing temperature of the extrusion process, and it is important that the extrusion temperature be the solution temperature. At this time, in order to obtain the fiber structure, the extrusion temperature is set to an appropriate temperature so that the fiber structure after extrusion does not recrystallize and change to coarse recrystallized grains, or when solution extrusion and quenching after hot extrusion. Also, the fiber structure may be recrystallized after hot extrusion or during the solution treatment so as not to change into coarse recrystallized grains. In order to prevent coarsening of the grain boundary precipitates and to keep the size within the above range, it is necessary to immediately quench the steel after the solution (after extrusion in the former case). Subsequently, aging treatment is performed, and Mg
₂ Precipitate Si.

In the case where the Al-Mg-Si-based aluminum alloy extruded material according to the present invention is used as a structural member for automobiles such as a side member or a bumper stay, in order to obtain a high energy absorption, aging treatment is performed. Later, tensile strength of 200 N / mm ² or more, 150 N / mm
It is desirable to have at least ^two proof stresses.

[0012]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples. Several aluminum alloys containing Mg and Si as main addition elements were melted by a usual method to obtain an ingot having a diameter of 155 mm. Next, these ingots were subjected to a homogenization treatment at 550 ° C. × 8 hours, and then each billet was extruded under the conditions of an extrusion temperature of 500 ° C. and an extrusion speed of 5 m / min. Speed about 12000 ℃ /
min) or air cooling (also about 190 ° C./min) to obtain a square pipe having a long piece of 60 mm, a short piece of 40 mm and a wall thickness of 2 mm. The cross section is shown in FIG. Next, these square pipes were subjected to artificial aging treatment to obtain test materials. Table 1 shows the alloy composition of each test material, and Table 2 shows the processing conditions.

[0013]

[Table 1]

[0014]

[Table 2]

A JIS No. 5 test piece was sampled from these test materials, and the tensile strength σ _B , proof stress σ _0.2 , and elongation at break δ were measured using the test piece according to the metal material tensile test specified in JIS Z2241. It was measured. In addition, a crush test was performed on each test material (length: 200 mm). FIG. 2 is a schematic diagram showing a crush test method. A load was applied to the specimen 1 in the axial direction by the universal testing machine 2. Then, a displacement-load diagram was created based on the test results, and the amount of energy absorption up to a displacement amount of 100 mm was determined from the displacement-load diagram. In addition, the crack characteristics were evaluated in the state of the crack generated by the crush test. However, those in which cracks did not occur were evaluated as ○, and those in which cracks occurred were evaluated as x. Further, a sample was collected from the test material, and the transmission electron microscope was used to obtain (10
0) plane was set as the observation plane, and the magnification was 200,000.
Of the Mg ₂ Si precipitates precipitated in the [0] and [010] directions, only the length of the precipitate having a length of 5 nm or more in the direction was measured. On the same observation surface, the number of Mg ₂ Si precipitates having a diameter of 1 nm or more precipitated in the [001] direction was measured, and the distribution density was obtained. Each measurement was performed on the same test material in four visual fields (total observation area of 0.16
μm ² ), and the average value was determined. In addition, the size (maximum value) of a precipitate such as Mg ₂ Si and elemental Si on the grain boundary was determined using the same test material. Table 3 shows the above results. In addition, the suitability as a material for structural members for automobiles such as side members was comprehensively evaluated, and the results are also shown in Table 3. However, the case where it is suitable as an automobile structural member such as a side member is indicated by ○, and the case where it is not suitable is indicated by ×.

[0016]

[Table 3]

As is clear from Table 3, the test material No. corresponding to the present invention example. All of Examples 1 to 4 had good axial crushing characteristics (energy absorption and cracking properties). On the other hand, No.
In all of Nos. 4 to 6, the axial crushing characteristics were not satisfactory.

[0018]

According to the present invention, the size of intragranular precipitates,
By regulating the distribution density and the size of the grain boundary precipitates within a predetermined range, an extruded aluminum alloy material having excellent axial crushing characteristics and suitable as a material for automobile structural members such as side members can be obtained. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a hollow member manufactured in an example.

FIG. 2 is a schematic view showing a crush test method.

[Explanation of symbols]

 1 Test material 2 Universal testing machine

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-9-296244 (JP, A) JP-A-9-263869 (JP, A) JP-A-8-325663 (JP, A) JP-A-9-296 256096 (JP, a) Yamashita, plain "aluminum extrusions of the 3-point bending characteristics" Light Metals Society Conference Overview Vol90th, P233-234 (1996) (58 ) investigated the field (Int.Cl. ^7, DB name) C22C 21/00-21/18

Claims (9)

(57) [Claims] 1. The average value of the size of the Mg ₂ Si precipitate in the [100] and [010] directions of the (100) plane in the crystal grain is 20 nm or more, and the [00] plane of the (100) plane
The distribution density of Mg ₂ Si precipitates in the 1] direction is 100 particles / μ.
m ² or more, and the size of the precipitate on the grain boundary is 1
Excellent axial crushing characteristics characterized by being less than 000 nm
Al-Mg-Si aluminum alloy extruded profile that is. 2. The average value of the size of the Mg ₂ Si precipitate in the [100] and [010] directions of the (100) plane in the crystal grain is 20 nm or more, and the [00] plane of the (100) plane
The distribution density of Mg ₂ Si precipitates in the 1] direction is 100 particles / μ.
m ² or more, and the size of the precipitate on the grain boundary is 1
An extruded Al-Mg-Si-based aluminum alloy material for crushable members, having a thickness of 000 nm or less. 3. Al-Mg-S containing 0.2 to 1.6% of Mg (wt%, the same applies hereinafter) and 0.2 to 1.8% of Si.
The Al-Mg-Si based aluminum alloy extruded shape according to claim 1 or 2, which is made of an i-based aluminum alloy. 4. The extruded Al-Mg-Si aluminum alloy according to claim 3, wherein the Al-Mg-Si aluminum alloy contains Cu: 1.0% or less. 5. The extruded Al—Mg—Si aluminum alloy according to claim 4, wherein the Al—Mg—Si aluminum alloy contains Mn: 0.05 to 0.5%. Wood. 6. The Al-Mg-Si-based aluminum alloy, wherein Ti: 0.01-0.1%, Cr: 0.01-
The Al-Mg-Si-based aluminum alloy extruded shape according to claim 4 or 5, wherein the Al-Mg-Si-based aluminum alloy contains 0.2%, Zr: 0.01 to 0.2%, or one or more of them. Wood. 7. The Al—Mg according to claim 1, wherein the crystal structure is a fibrous structure.
-Extruded Si-based aluminum alloy. 8. The extruded Al-Mg-Si-based aluminum alloy according to claim 1, wherein the tensile strength is 200 N / mm ² or more and the proof stress is 150 N / mm ² or more. 9. A structural member for an automobile, wherein the aluminum alloy extruded member according to any one of claims 1 to 8 is used.