JP4203393B2 - Aluminum alloy extruded hollow shape with excellent bending workability and pressure cracking resistance - Google Patents

Description

  The present invention relates to an Al-Mg-Si-based (hereinafter also referred to as 6000) aluminum alloy extruded hollow shape (hereinafter, aluminum is also simply referred to as Al) having excellent bending workability and pressure cracking resistance.

  Conventionally, 6000 series aluminum alloy extruded hollow members have been used for transportation devices such as automobiles, ships or vehicles, household electrical appliances, buildings, and structural members and parts. In particular, structural materials for transportation vehicles are not only reduced in weight from energy saving measures, but also have a need for recyclability and recyclability, and the positioning of 6000 series aluminum alloy materials is increasing.

  The 6000 series aluminum alloy has age hardening ability, and has the advantage that the yield strength is improved by age hardening by heating at a relatively low temperature artificial aging treatment, and the required strength can be secured. In addition, the amount of alloying elements is relatively small as compared to other 5000 series aluminum alloys having a large amount of alloy such as Mg. Therefore, when reusing these 6000 series aluminum alloy alloy scrap as aluminum alloy melting material (melting raw material), it is easy to obtain the original 6000 series aluminum alloy alloy ingot, and it is also excellent in recyclability and recyclability. There are advantages.

  In addition, the aluminum alloy extruded material can form a complex hollow shape material by processing the billet as a raw material at once, and has a large degree of freedom in cross-sectional shape and designability for each of the above applications. Has advantages.

These aluminum alloy extruded hollow shapes are often subjected to bending work in the longitudinal direction according to the applied member and product shape.
However, when bending is performed on an extruded aluminum alloy hollow shape, there are processing defects such as cracks on the outer surface of the curved portion, dents on the outer surface of the curved portion, and wrinkles on the inner surface of the curved portion. Easy to get up. Such processing defects greatly hinder shape accuracy, strength, bondability with other members, aesthetics, and the like required for members and products after bending.

  For this reason, conventionally, improvement of bending workability has been achieved mainly by improvement of a bending apparatus or bending method, or by devising the cross-sectional shape of the extruded hollow profile. However, the improvement of the bending apparatus and the bending method has a limit for improving the bending workability. Further, the device of the cross-sectional shape of the extruded hollow shape material also leads to restrictions on the cross-sectional shape and the degree of freedom in design, thereby eliminating the advantages of the extruded hollow shape material.

  On the other hand, if the bendability is improved on the side of the aluminum alloy extruded hollow shape, which is a material for bending, the improvement on the side of the bending apparatus or the bending method, or the cross-sectional shape side of the extruded hollow shape Can greatly reduce the load of constraints.

  Up to now, the improvement of the bending workability of Al-Mg-Si-based aluminum alloy extruded hollow shapes, which are bending materials, has mainly been achieved by reducing the strength, the longitudinal direction of aluminum extruded shapes or the shape of extruded shapes. This has been dealt with by minimizing variations in mechanical properties such as between rods.

  For example, when producing an aluminum alloy extruded shape by homogenizing a 6000 series aluminum alloy billet such as 6063, extruding it, cooling and aging treatment, at least one from the extruded material cooled after extrusion Obtain the above sample, age the sample in advance, and evaluate the mechanical properties. Based on this, the mechanical properties are 0.2% proof stress 120-140 MPa and the elongation is 12% or more. It has been proposed to set aging treatment conditions. And by such a method, an aluminum extruded profile that has 0.2% proof stress and elongation optimal for bending, has little variation in bending accuracy and proof stress, and does not buckle even in bending such as push-through. We are trying to obtain it (see Patent Document 1).

It has also been proposed to improve bending workability by making the metal structure a structure composed of granular crystal grains (equal axis grain structure). More specifically, the average crystal grain size is 100 μm or less, and the aspect ratio of the crystal grains, that is, the ratio of the length in the extrusion direction to the length in the thickness direction of the crystal grains constituting the aluminum alloy extruded profile is Bending workability is improved as an equiaxed grain structure such as 2 or less crystal grains (see Patent Document 2).
Furthermore, in order to improve the crushing characteristics in the axial (longitudinal) direction of the extruded hollow profile (hereinafter also referred to as longitudinal crushing) and the crushing characteristics in the cross-sectional direction of the extruded hollow profile (hereinafter also referred to as lateral crushing). It is also known that the metal structure is not the equiaxed grain structure but a fibrous structure elongated in the extrusion direction (see Patent Document 3).
JP 2001-316788 (page 2-3) JP 2002-241880 A (page 2-3) JP2003-183757 (page 2-3)

  However, even if the variation in the mechanical properties of the aluminum alloy extruded hollow member is minimized as in the conventional case, the limit of the bending workability of the original aluminum alloy extruded hollow member is not raised. In other words, among the hollow shapes that are originally difficult to bend, only the hollow shapes that are significantly inferior in bending are eliminated.

  Moreover, in order to prevent springback during bending, Patent Document 1 defines a 0.2% proof stress as 120 to 140 MPa. As a result, the low proof strength is a conventional means for improving bending workability. It's just a change. Therefore, it cannot be applied to a high-strength aluminum alloy extruded hollow member having a 0.2% proof stress of, for example, 200 MPa or more. In other words, the increase in strength as a structural material and the reduction in thickness and weight are thereby sacrificed.

  Moreover, when considering application as a frame structure material (impact absorbing member = collision energy absorbing member) of an automobile, the energy absorbing characteristic is deteriorated if the strength is less than 200 MPa.

  Furthermore, when the metal structure is an equiaxed grain structure, the pressure cracking characteristics are low. Therefore, even if bending by U-shaped bending with a relatively low pressure is possible, the bending workability in bending where pressure is applied and pressure cracking is a problem is low. As these processing methods, there are, for example, tensile bending, compression bending, and rotational pulling bending in which an extended force is applied. Furthermore, because of its low pressure cracking characteristics, it can be used as an impact absorbing member in the axial direction of the extruded profile, or in the cross-sectional direction of the extruded profile, in any direction of energy absorption. Will also be inferior. That is, when the metal structure is an equiaxed grain structure, both the bending workability and the pressure cracking characteristic cannot be satisfied or both are reduced.

Furthermore, even if the metal structure of the extruded shape is not the above equiaxed grain structure but a fibrous structure elongated in the extrusion direction, the bending workability is not necessarily improved.
For this reason, it is quite possible to improve the bending workability from the material side and to achieve both the bending workability and the pressure cracking characteristics for high-strength aluminum alloy extruded hollow shapes with 0.2% proof stress of 200 MPa or more. This is a difficult technical issue, and it has been virtually impossible, or if so, it can be said that there were significant limitations as described above.

  The present invention has been made paying attention to such circumstances, and its purpose is to improve the bending workability and achieve both the bending workability and the pressure cracking characteristics, and is a hollow type extruded with a 6000 series aluminum alloy. The material is to be provided.

In order to achieve this object, the gist of the extruded Al-Mg-Si-based aluminum alloy of the present invention is that the extruded hollow profile is divided into a length L ₁ in the extrusion direction of the crystal grains and a length L in the thickness direction. with an aspect ratio of ₂ L ₁ / L ₂ is a fibrous tissue, such as more than 5, the elongation [delta] ₁ of 45 degree direction to the extrusion direction, parallel elongation [delta] ₂ and the extrusion to the extrusion direction greater than a right angle direction of elongation [delta] ₃ with respect to the direction, [delta] ₁ and the ratio [delta] ₁ / [delta] ₂ and [delta] _2, such that the ratio δ ₁ / δ ₃ of the [delta] ₁ and [delta] ₃ is in each 1.1 or higher This is a structure having anisotropy.

According to the knowledge of the present inventors, an Al-Mg-Si-based aluminum alloy extruded hollow material (hereinafter also simply referred to as an extruded material) is not a conventional isotropic structure, but particularly in the direction of extrusion. By forming a structure with an anisotropy where the elongation δ _{1 in the} 45-degree direction is greater than the elongation in the other direction, bending workability, and also the crushability in the profile section direction and profile axis (longitudinal) direction (Deformability) is improved.

  Normally, the structure of the extruded material is a structure in which crystal grains called fibers (fibrous) are elongated in the extrusion direction depending on the cooling conditions and tempering (heat treatment) conditions after extrusion, or the length of the crystal grains in the extrusion direction. And an equiaxed grain structure in which the ratio of the length in the thickness direction is 2 or less. However, in any case, the mechanical properties usually do not greatly differ in any of the parallel direction, the perpendicular direction, and the 45 degree direction with respect to the extrusion direction of the extruded material. It becomes a material that is uniform and uniform. For this reason, when referring to the mechanical properties such as elongation and yield strength of the extruded material, it is usual to represent the mechanical properties in either the parallel direction or the perpendicular direction to the extrusion direction of the extruded material.

However, even in the case of an extruded material having normal isotropic properties, it is inevitable that some anisotropy occurs depending on the manufacturing conditions described above. That is, the elongation δ _{1 in the} direction of 45 degrees with respect to the extrusion direction may be lower than the elongation δ _{2 in the} direction parallel to the extrusion direction and the elongation δ _{3 in the} direction perpendicular to the extrusion direction. Arise. This can also be said to be a structure having anisotropy, but in the case of such an anisotropic structure, the bending workability and the crushability (deformability) in the cross-section direction of the profile are significantly reduced.

In contrast, as in the present invention, if the elongation [delta] ₁ of 45 degree direction to the extrusion direction, and a tissue having anisotropy is larger than the elongation of the other directions, reasons unclear Although not a tissue or with the isotropic for tissues with anisotropic as elongation [delta] ₁ is smaller than the elongation of the other direction, the bending workability and profile cross-section and axially The crushability (deformability) of is improved.

  Moreover, this effect is particularly exhibited when the extruded material has a high strength such that the 0.2% proof stress is 200 MPa or more. Therefore, it is not necessary to reduce the strength of the extruded material and improve the bending workability and the crushability in the cross-sectional direction as in the conventional case.

(Extruded hollow shape)
The Al-Mg-Si-based aluminum alloy extruded hollow shape referred to in the present invention refers to a shape obtained by subjecting an Al-Mg-Si-based aluminum alloy to normal tempering after extrusion. The normal tempering treatment refers to artificial aging treatment, solution treatment and quenching treatment, a combination of these heat treatments, and the like.

  In addition, the cross-sectional shape of the hollow shape member can be appropriately selected from a rectangular shape, a substantially rectangular shape, a circular shape (tube), a substantially circular shape, etc. Furthermore, in addition to the case where the normal extrusion (longitudinal) has a uniform cross section, the case where it has a non-uniform cross section is included.

(Extruded hollow shape)
The requirements for the anisotropic structure of the extruded hollow profile of the present invention will be described below.
The requirements for the anisotropic structure of the extruded hollow profile of the present invention will be described in the direction of sampling the tensile test piece of the extruded hollow profile 1 shown in a perspective view in FIG. In the extrusion hollow profile 1, to the extrusion direction A indicated by an arrow, the elongation value of the tensile test taken specimen X ₁ oriented in 45 degrees direction, the 45-degree direction to the extrusion direction in the present invention extends it is a δ _1. Further, elongation of the tensile test taken test piece X ₂ oriented in parallel (L direction) to the extrusion direction A is the elongation [delta] ₂ in the parallel direction to the extrusion direction. Further, elongation of the tensile test taken specimens X ₃ oriented in a direction perpendicular (LT direction) with respect to the extrusion direction, is elongation [delta] ₃ of the direction perpendicular to the extrusion direction. In FIG. 1, two specimens in each direction are collected in parallel, and the average of these two elongation values is taken as the elongation value of the specimen. The same applies to the tensile strength and 0.2% proof stress in the measurement of mechanical properties of the collected specimen.

In the present invention, the elongation δ _{1 in the} direction of 45 degrees with respect to the extrusion direction is larger than the elongation δ _{2 in the} direction parallel to the extrusion direction and the elongation δ _{3 in the} direction perpendicular to the extrusion direction, δ ₁ and δ ₂ the ratio [delta] ₁ / [delta] ₂ of, the ratio δ ₁ / δ ₃ of the [delta] ₁ and [delta] ₃ is assumed at each 1.1 or more.

On the other hand, the isotropic structure is a structure in which these δ ₁ , δ ₂ , and δ ₃ are approximately equal or δ ₁ is smaller than δ ₂ and δ ₃ . If the structure has an isotropy such that the elongation δ _{1 in the} direction of 45 ° with respect to the extrusion direction is substantially equal to or smaller than δ ₂ or δ ₃ , bending workability In addition, the crushability (deformability) in the cross-section direction of the profile is reduced.

Then, if the [delta] ₁ and the ratio [delta] ₁ / [delta] ₂ and [delta] _2, [delta] ₁ and [delta] ₃ and the ratio δ ₁ / δ ₃ and are each less than 1.1, [delta] ₁ is, the [delta] ₂ and [delta] ₃ Therefore, the bending workability of the profile and the crushability (deformability) in the cross-section direction of the profile are reduced.

It should be noted that δ ₁ , δ ₂ , δ ₃ itself, δ ₁ / δ ₂ and δ ₁ / δ ₃ are better as they are higher or larger, from the view of the bending workability of the profile and the crushing effect in the profile section direction There is no upper limit. However, the improvement in δ itself is limited by the required strength of the profile (0.2% proof stress), the chemical composition of the 6000 series Al alloy sheet, and the metallurgical conditions of the manufacturing process. Also, due to this same constraint, the numerical values that can be made high for both δ ₁ / δ ₂ and δ ₁ / δ ₃ naturally have metallurgical limitations.

(Bending workability)
The extruded hollow profile having anisotropy of the present invention is improved in bending workability when it is bent in the direction indicated by arrow B in FIG. 1 (up and down in the three-dimensional sense of FIG. 1). . In this case, of the profile surfaces of the hollow profile 1 to be bent, the profile surface 1a is the inside of the bend and the profile surface 1b is the outside of the bend. When the bending process is performed in the direction indicated by the arrow B over the longitudinal direction, if the δ ₁ is larger than δ ₂ or δ _3, wrinkles or In addition, it is possible to perform bending without causing cracks due to a tensile force load on the shape surface 1b which is the outer side of the bending.

(Crush resistance)
Further, correlating with this bending workability is the pressure-proof fracture resistance of the hollow member 1 in the cross-sectional direction. Now, when a collision load is applied to the front surface of the profile surface 1a from the direction indicated by the arrow C in FIG. 1, the absorption performance of the collision load is improved. That is, when a large collision load indicated by an arrow C is applied to the front of the profile surface 1a, if the δ ₁ of the hollow profile 1 is larger than δ ₂ or δ ₃ , Similar to the bending process, wrinkles due to compressive force loading on the profile surface 1a which is the inner side of bending and cracks due to tensile force load are less likely to occur on the profile surface 1b which is the outer side of bending. Therefore, at the initial stage of the collision load, the hollow shape member 1 is bent in the longitudinal direction in the direction indicated by the arrow B 1 to absorb the collision load, as in the bending process.

When the collision load is large, the bending load cannot be absorbed even by bending deformation in the longitudinal direction of the hollow profile 1, and the deformation in the cross-sectional direction of the hollow profile 1 starts. However, even in this case, when the [delta] ₁ of the hollow profile 1 is greater than [delta] ₂ and [delta] _3, the vertical wall profile surfaces 1a as (flange), 1b and the transverse wall profile surface 1c as (web), 1d or the corners (four corners) that are the connection between the vertical and horizontal walls are not crushed (damaged), but are deformed in the cross-section direction of the section (in the direction of arrow C) to further absorb the collision load. . Therefore, the impact load absorption characteristic (deformability) in the cross-section direction of the profile is improved. For this reason, it is suitable for uses such as bumpers and door beams in automobile materials that require impact load absorption characteristics in the cross-section direction of the profile.

It should be noted that the anisotropy of the hollow member 1 in which Δ ₁ is larger than Δ ₂ or Δ ₃ also contributes to the crushing characteristics of the hollow member 1 in the axial (longitudinal) direction. That is, when the hollow profile 1 is subjected to a collision load in the axial (longitudinal) direction (A direction in FIG. 1), the hollow profile 1 does not collapse and deforms in a bellows shape in the axial (longitudinal) direction. It also contributes to crushing properties that absorb impact loads. If the δ ₁ of the hollow profile 1 is larger than δ ₂ or δ ₃ , when the hollow profile 1 receives a collision load in the axial (longitudinal) direction, the profile surfaces 1a, 1b as the vertical walls and The shape surfaces 1c and 1d as the horizontal wall, or the corners (four corners) that are the joints between the vertical wall and the horizontal wall are not crushed (damaged), but are deformed in the axial direction of the material, causing a collision load. Absorb. Therefore, the collision load absorption characteristic (deformability) in the shape axis direction is improved. For this reason, it is suitable for uses, such as a side member, a bumper stay, and a side frame in an automobile material, which require a collision load absorption characteristic in the shape axis direction.

(Fibrous structure)
In order to obtain an anisotropic structure in which the δ ₁ is larger than δ ₂ or δ ₃ as in the present invention, the aspect ratio of the crystal grains (the length L ₁ in the extrusion direction of the crystal grains and the length in the thickness direction) the aspect ratio of the L ₂ L ₁ / L ₂₎ is greater than 2 such fibrous crystal grains (be extended grain) tissue is a prerequisite. The more the fine fibrous structure is formed, the more easily the anisotropic structure of the present invention is formed. In addition, strength and pressure cracking resistance are improved.

However, even in the case of a fibrous structure, as a mechanical property, an isotropic structure (a structure in which the mechanical properties are almost equal in any of the parallel direction, the perpendicular direction, and the 45 degree direction with respect to the extrusion direction) or the δ _In the case of a structure in which 1 has an anisotropy smaller than δ ₂ or δ ₃ , bending workability and crushability (deformability) in the cross-section direction of the profile are inferior to the anisotropic structure of the present invention.

In addition, in an equiaxed grain structure having an aspect ratio of 2 or less, an anisotropic structure in which the δ ₁ is larger than δ ₂ or δ ₃ as in the present invention cannot be obtained, and as in the prior art described above, bending is not possible. Either the workability and the pressure cracking characteristics cannot be made compatible, or both are lowered.

  The fibrous structure is preferably formed on the entire wall constituting the cross section of the extruded hollow profile. In general, an equiaxed granular recrystallized layer is likely to be formed on the surface of an extruded hollow profile, but even in this case, the fibrous structure has a cross-sectional thickness (wall thickness) of the wall constituting the hollow profile. It is desirable that it is formed with a thickness of 70% or more. In other words, the surface recrystallized layer should be as thin as possible, less than 30% of the total wall thickness. Furthermore, it is desirable that the recrystallized grains in the equiaxed granular recrystallized layer to be formed have a fine average recrystallized grain size of 500 μm or less at least on the surface of the extruded hollow profile (the part from the outer surface to 500 μm). .

  For example, the adverse effect of the recrystallized layer increases as the extruded hollow shape becomes thinner 1 to 5 mm. This is because the crystal grains of the recrystallized layer have a larger crystal grain size than the fibrous structure, and when there are many precipitates precipitated at the crystal grain boundaries of the recrystallized layer, This is because strain is concentrated and cracks are likely to occur.

In order to obtain such a fibrous structure, it is preferable to contain transition elements such as Mn, Cr, and Zr as described later. When these transition elements are not contained, when the cooling rate is relatively low during direct quenching by water cooling immediately after extrusion, it is difficult to obtain the fibrous structure. This 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. Therefore, in the tempering treatment after the extrusion step, for example, when solution treatment and quenching treatment are performed, this fibrous structure is damaged, and the fibrous structure and the equiaxed grain structure are mixed, or the equiaxed grain It becomes an organization close to. In such a structure, a fibrous structure in which the aspect ratio of the crystal grains of the present invention exceeds 2 is not obtained, and furthermore, the anisotropy in which the δ ₁ is larger than δ ₂ and δ ₃ as in the present invention. There is no organization. Therefore, the bending workability and the pressure cracking characteristics cannot be made compatible or both are lowered.

  Below, the preferable component composition and manufacturing conditions of an Al—Mg—Si-based aluminum alloy extruded hollow shape for obtaining such a structure of the present invention will be described. However, there is no guarantee that all of the hollow shapes manufactured under such conditions will surely have a structure having the elongation anisotropy. If the component composition is different, the resulting structure is different even if the production conditions are the same. Moreover, if the production conditions are different, the resulting structure is different even if the component composition is the same. Further, even if the above-mentioned Patent Document 1 is not used, the more the aluminum extruded profile is, the more likely it is that the actual manufacturing conditions are affected by fluctuations (swaying) and variations, such as in the longitudinal direction or between the rods of the extruded profile. There are large variations in organization. Therefore, it is necessary to select the above-described chemical component composition and production conditions with careful consideration each time, and to confirm the conditions (component composition and production conditions) for reliably obtaining the anisotropic structure of the present invention.

(Aluminum alloy composition)
In the present invention, the structure of the present invention such as high strength of 200 MPa or higher, 0.2% proof stress in the direction of 45 degrees with respect to the fibrous structure or the extrusion direction and high elongation anisotropy, and further satisfy the required characteristics as the structural material. The preferred component composition of the Al-Mg-Si-based aluminum alloy extruded hollow shape material for achieving this is described below.

  From this viewpoint, the Al-Mg-Si-based aluminum alloy composition contains Mg: 0.4 to 1.0%, Si: 0.4 to 1.0%, Cu: 0.001 to 1.0%, and Mn: 0.05 to 0.40% in mass%. , Cr 0.05 to 0.20%, Zr: 0.05 to 0.20%, or one or more of them, and the balance is preferably Al and inevitable impurities. In the present invention, “%” in the chemical component composition means “% by mass”.

(Mg: 0.4-1.0%)
Mg and Si combine to form Mg ₂ Si, improving the alloy strength. In order to obtain a strength of 200 MPa or more with a 0.2% proof stress as a necessary structural material such as the impact absorbing member, it is necessary that Mg is contained in an amount of 0.4% or more. However, if added over 1.0%, the quenching sensitivity becomes sharp, and when the quenching speed is lowered due to water cooling after extrusion, etc., quenching does not occur, and a strength of 200 MPa or more cannot be obtained with 0.2% proof stress. Therefore, the Mg content is preferably set to 0.4 to 1.0%.

(Si: 0.4-1.0%)
On the other hand, if the Si content is less than 0.4%, the required strength cannot be obtained, and if it exceeds 1.0%, the quenching sensitivity becomes sharp, and direct quenching by water cooling immediately after extrusion processing, etc. The required strength is not obtained. Therefore, the range of Si content is preferably 0.4 to 1.0%.

  Preferably, Mg and Si have a Si-rich composition with a mass ratio Si / Mg of Si / Mg of more than 1. When the Si-rich composition is used, the strength can be further increased, and the fibrous structure and anisotropic structure of the present invention can be easily formed.

(Mn, Cr, Zr)
Transition elements such as Mn, Cr, and Zr form a fibrous structure in the extruded material to facilitate the anisotropic structure of the present invention. Moreover, there exists an effect | action which raises an intensity | strength and improves the pressure | voltage resistant cracking property as said shock-absorbing member. Moreover, the anisotropic structure of the present invention is easily formed. Accordingly, one or more of these are contained in the ranges of Mn: 0.05 to 0.40%, Cr 0.05 to 0.20%, Zr: 0.05 to 0.20%. If the content of these transition elements is less than the lower limit, this effect is not achieved, and it becomes difficult to form a fibrous structure or to form the anisotropic structure of the present invention depending on manufacturing conditions. In addition, if the content of these transition elements exceeds the upper limit, coarse intermetallic compounds and crystal precipitates are likely to be generated during melting and casting, which tends to be the starting point of fracture, thus reducing the mechanical properties of the Al alloy sheet. Cause it.

(Cu: 0.001 to 1.0%)
Cu has the effect of increasing the strength by promoting the precipitation of a compound phase such as a GP zone in the crystal grains of an aluminum alloy structure under the conditions of artificial aging treatment at a relatively low temperature for a short time. This effect is not obtained when the Cu content is less than 0.001%. On the other hand, if it exceeds 1.0%, the stress corrosion cracking resistance and weldability are significantly deteriorated. Therefore, the range of Cu content is 0.001 to 1.0%.

In the following, elements that are selectively contained as required or elements that are impurities but have an effect of inclusion will be described.
(Ti, B)
When Ti and B are contained in amounts exceeding Ti: 0.1% and B: 300 ppm, coarse crystals are formed. However, Ti and B are contained in a small amount and have the effect of refining the crystal grains of the ingot. Therefore, the content of Ti: 0.1% or less and B: 300ppm or less is allowed.

(Fe)
Fe mixed in from the melting raw material and contained as impurities produces crystallized products such as Al ₇ Cu ₂ Fe, Al ₁₂ (Fe, Mn) ₃ Cu ₂ , and (Fe, Mn) Al ₆ . These crystallized substances serve as nuclei of recrystallized grains, and when Fe is contained in an amount of 0.08% or more, the crystal grains are prevented from coarsening and the crystal grains are reduced to a fine grain of 50 μm or less. However, on the other hand, these crystallized materials significantly deteriorate the fracture toughness and fatigue characteristics, and further, the flat hem workability and press formability in which the processing conditions are severe. These deterioration characteristics become significant when the Fe content exceeds 0.50%. For this reason, the content of Fe when contained is preferably 0.08 to 0.50%.

  In addition to the above alloy elements, other alloy elements such as Zn, Ni, and V are basically impurity elements. However, from the viewpoint of recycling, not only high-purity Al ingots but also 6000 series alloys and other aluminum alloy scrap materials, low-purity aluminum ingots, etc. are used as melting raw materials as melting materials. When the composition is melted, these other alloy elements are necessarily included. Therefore, in the present invention, it is allowed to contain these other alloy elements as long as the intended effect is not hindered.

(Production method)
Next, a preferable manufacturing method and manufacturing conditions will be described below.
The aluminum alloy extruded hollow section of the present invention is subjected to hot extrusion by subjecting a cast billet of an aluminum alloy having the above composition to homogenization heat treatment, or after being cooled and then reheated. At this time, hot extrusion may be performed by direct heating without performing homogenization heat treatment.

  The homogenization heat treatment is preferably selected from the range of 400 to 530 ° C. and is preferably performed for 1 to 20 hours. When the homogenization treatment temperature exceeds 530 ° C., the dispersed particles due to the transition elements such as Mn, Cr, Zr are coarsened, and the dispersed particles themselves that promote the fine fibrous structure and the anisotropic structure of the present invention are promoted. Insufficient number. On the other hand, if the homogenization heat treatment temperature is too low, less than 400 ° C., coarse crystallized material remains, and it becomes difficult to increase the strength of the extruded hollow profile.

Hot extrusion is also preferably performed in a temperature range of 400 ° C. or higher and lower than 500 ° C. When the extrusion temperature is less than 400 ° C., the solid solution amount of Mg and Si in the matrix is small, and sufficient strength cannot be obtained by the above direct quenching or artificial aging treatment. On the other hand, when the extrusion temperature is 500 ° C. or higher, the dispersed particles by the transition elements such as Mn, Cr, and Zr are coarsened, and the dispersed particles themselves that promote the fine fibrous structure and the anisotropic structure of the present invention are promoted. The number is likely to be insufficient, and there is a high possibility that these organizations will not be obtained. In addition, the artificial aging treatment is likely to reduce the amount of Mg ₂ Si precipitates.

  The extrusion ratio of hot extrusion is as high as possible exceeding 90% (extrusion ratio of 10 or more) in order to obtain a structure having the elongation anisotropy. When this extrusion ratio is low, there is a high possibility that the fibrous structure and a structure having anisotropy in elongation cannot be obtained.

  Immediately after this hot extrusion, it is preferable to carry out direct quenching online by quenching from the high temperature during extrusion by water cooling or air cooling. However, when the cooling rate is relatively slow due to air cooling or cooling, it is difficult to obtain the fibrous structure.

  The extruded and directly quenched aluminum alloy hollow profile is subjected to a tempering treatment such as an artificial aging treatment of 160 to 230 ° C. × 1 to 10 hours. In addition, it is preferable not to perform solution treatment and quenching treatment because a fibrous structure cannot be obtained as described above.

 Next, examples of the present invention will be described. Various extrusion production conditions were changed to obtain extruded hollow profiles 1 having a rectangular cross section as shown in FIG. 1, and the collapse anisotropy (longitudinal) , Side) and bending workability were evaluated.

  That is, the composition, the homogenization heat treatment temperature, the extrusion temperature, the extrusion ratio, and the on-line direct quenching speed after the extrusion, which affect the anisotropy of the elongation of the structure, were varied, and the structure of the extruded hollow shape 1 The anisotropy of elongation was controlled and changed by changing the texture, the equiaxed texture, and the like, and the aspect ratio of the crystal grains of these textures.

  Specifically, aluminum alloy billets having respective 6000-based component compositions shown in Table 1 were melted by DC casting and subjected to 4 hours of homogenization heat treatment at each temperature shown in Table 2. Subsequently, each extrusion temperature extrusion process shown in Table 2 was performed, and immediately after extrusion, each was directly quenched by water cooling. Next, these extruded materials were commonly subjected to an aging treatment of 190 ° C. × 3 hours to obtain test materials. In common with each example, the extrusion speed was 5 m / min, the extrusion ratio was 61, and the cooling rate during direct quenching was 350 ° C./second, making it easy to obtain the fibrous structure and anisotropic structure of the present invention. .

  The test material was an extruded hollow shape 1 having a rectangular cross section shown in FIG. 1 in common with each example, and had a long side of 100 mm, a short side of 70 mm, and a wall thickness of 1.5 mm.

A specimen is collected from the specimen, and the structure is observed with a 200 × optical microscope. The aspect ratio L ₁ between the length L ₁ in the extrusion direction and the length L ₂ in the thickness direction of a plurality of crystal grains in the field of view. / L ₂ was calculated to obtain an average aspect ratio. Whether the fibrous structure extends long in the direction parallel to the extrusion direction or the equiaxed structure in which the difference between the length L ₁ in the extrusion direction and the length L ₂ in the thickness direction is not significant. Determined. These results are shown in Table 3. In both the inventive example and the comparative example, the length L ₂ in the thickness direction of the crystal grains is fine crystal grains of 20 μm or less, the grain size of the recrystallized layer on the surface of the extruded material is 50 μm or less, and the thickness is 300 μm or less. there were.

A JIS No. 5 test piece was collected from the test material, and a tensile test was performed in accordance with JISZ2241. The crosshead speed was 5 mm / min, and the test piece was run at a constant speed until the test piece broke. However, in the case of the present invention, the tensile strength (σ _B : MPa) and the proof stress (σ _0.2 : MPa) in the direction of 45 degrees with respect to the extrusion direction of the specimens of each example were measured. Further, as described above with reference to FIG. 1, the elongation (%) is the elongation δ _{1 in} the direction of 45 ° with respect to the extrusion direction A indicated by the arrow, the elongation δ _{2 in the} direction parallel to the extrusion direction A (L direction), The elongation δ ₃ in the direction perpendicular to the extrusion direction A was measured. Then, in order to observe the anisotropy of elongation in the 45 degree direction, δ ₁ / δ ₂ and δ ₁ / δ ₃ were obtained. These results are shown in Table 3.

  Using a 200 mm long specimen, a static compressive load was applied in the axial direction as shown in FIG. 2 using an Amsler tester, and this was compressed to 100 mm to evaluate the longitudinal crushing characteristics. The longitudinal crush characteristic evaluation was performed based on the presence or absence of cracks in the axial bellows-shaped deformed portion due to compression. Evaluation of this cracking property is carried out by visual inspection. If the sample has no cracks at the bellows-shaped deformed part of the sample after compression deformation, including opening cracks and minute cracks, A case where an open crack was generated was evaluated as Δ, and a case where an open crack was generated was evaluated as × because the longitudinal crushing property was inferior. Note that the opening crack means a case where any wall of the hollow shape member 1 having a closed cross section in FIG. 1 is cracked so as to form an opening.

  Similarly, using a specimen with a length of 200 mm, as shown in Fig. 3, place the specimen sideways so that the long sides 1a and 1b of the specimen are up and down, and apply a static compressive load. The lateral crushing characteristics were evaluated by compressing to a low pressure. The lateral crushing property evaluation is based on the presence of cracks in the shape surface 1d, 1c bent part and each shape face joint when deforming to the outside of the shape surface (wall) 1d, 1c in the width direction due to compression Went by. This evaluation of cracking was performed visually. In the sample after compression, if the crack is not generated at all, the lateral crushing characteristics are excellent as ○, if the minute crack is generated as Δ, if the large crack is generated as crushing characteristics are inferior as × Each was evaluated.

  Using a specimen with a length of 2000 mm, a bending test using a draw bender shown in Fig. 4 was performed. The bending inner radius R was 300 mm. The mechanical clearance during bending was set to 0.1 mm. The appearance of cracks on the profile surface 1a in FIG. 1 that is the outer side of the sample after bending and wrinkles on the profile surface 1b that is the inner side of the bend was visually evaluated. Bending samples with no cracks or wrinkles are considered to be excellent in bending workability, △ are those with minute cracks or wrinkles, and those with opening cracks are inferior in bending workability As x, each was evaluated.

As shown in Tables 1 to 3, in the examples of the present invention, the aluminum alloy extruded hollow profile has a component composition within the range of the present invention, and the homogenization heat treatment temperature and the extrusion temperature are manufactured within preferable conditions. As a result, the aspect ratio L ₁ / L ₂ between the length L ₁ in the extrusion direction of the crystal grains and the length L ₂ in the thickness direction exceeds 10 (> 10). On the other hand, the elongation δ _{1 in the} direction of 45 degrees is larger than the elongation δ _{2 in the} direction parallel to the extrusion direction and the elongation δ _{3 in the} direction perpendicular to the extrusion direction, and the ratio δ ₁ / δ of δ ₁ and δ _{2 2} and a ratio δ ₁ / δ _{3 of} δ ₁ and δ ₃ are each an anisotropy having an anisotropy of 1.1 or more. For this reason, it is excellent in bending workability and vertical and horizontal pressure cracking resistance. Moreover, this effect is particularly exhibited when the extruded material has a high strength such that the 0.2% proof stress is 200 MPa or more.

In contrast, in Comparative Examples 8 and 9, the aluminum alloy extruded hollow profile has a component composition within the range of the present invention, but the homogenization heat treatment temperature or the extrusion temperature is out of the preferable condition range. It is manufactured under high conditions. As a result, a fibrous structure cannot be obtained, and only an equiaxed structure with a small aspect ratio is obtained. As a result, only a structure having no anisotropy as in the invention example and anisotropy such that the elongation δ ₁ is smaller than the elongation in the other direction is obtained. For this reason, bending workability and the vertical and horizontal pressure cracking resistance are inferior.

The ratio Comparative Examples 11 to 13, aluminum alloy extruded hollow shape member is a component composition outside the scope the present invention, production conditions are produced within preferred conditions ranges homogenization heat treatment temperature and the extrusion temperature. As a result, a fibrous structure cannot be obtained, and only an equiaxed structure with a small aspect ratio is obtained. As a result, only the structure having the anisotropy such that the elongation δ ₁ is smaller than the elongation in the other direction is obtained, which does not have the anisotropy as in the invention example. For this reason, bending workability and the vertical and horizontal pressure cracking resistance are inferior.

Therefore, the results of these examples support the critical significance of the component composition and organization requirements of the present invention.

  As described above, according to the present invention, it is possible to provide a 6000 series aluminum alloy extruded hollow member that improves bending workability and achieves both bending workability and pressure cracking characteristics. Therefore, it is possible to expand the application of aluminum alloy to automobile frame materials that require bending workability and pressure cracking resistance, such as side members, side frames, bumper reinforcements, bumper stays, and door beams.

It is a perspective view which shows this invention aluminum alloy extrusion hollow shape material. It is a figure (before a deformation | transformation and after a deformation | transformation) explaining the vertical crushing test in an Example. It is a figure (before a deformation | transformation and after a deformation | transformation) explaining the lateral crush test in an Example. It is a figure explaining the bending process test in an Example.

Explanation of symbols

1: Aluminum alloy hollow shape, A: extrusion direction, B: bending direction,
X ₁ : Tensile specimen in 45 ° direction, X ₂ : Tensile specimen in parallel direction,
X ₃ perpendicular tensile test specimen,

Claims (3)

In an Al-Mg-Si-based aluminum alloy extruded hollow profile, a fiber shape in which the aspect ratio L ₁ / L ₂ between the length L ₁ in the extrusion direction and the length L ₂ in the thickness direction exceeds 5 The elongation δ _{1 in the} direction of 45 ° with respect to the extrusion direction is larger than the elongation δ _{2 in the} direction parallel to the extrusion direction and the elongation δ _{3 in the} direction perpendicular to the extrusion direction, and δ ₁ and δ ₂ the ratio [delta] ₁ / [delta] ₂ and is characterized in that a tissue having anisotropy such as a ratio [delta] ₁ / [delta] ₃ of the [delta] ₁ and [delta] ₃ is in each 1.1 or more, the bending property Aluminum alloy extruded hollow shape with excellent pressure cracking resistance.   2. The aluminum alloy extruded hollow member having excellent bending workability and pressure cracking resistance according to claim 1, wherein a 0.2% proof stress in a direction at 45 degrees with respect to the extrusion direction of the extruded hollow member is 200 MPa or more. The Al-Mg-Si-based aluminum alloy contains Mg: 0.4 to 1.0%, Si: 0.4 to 1.0%, Cu: 0.001 to 1.0%, and Mn: 0.05 to 0.40%, Cr 0.05 in mass%. Aluminum alloy extrusion excellent in bending workability and pressure cracking resistance according to claim 1 or 2, comprising at least one of ˜0.20% and Zr: 0.05 to 0.20%, the balance being Al and inevitable impurities Hollow profile.

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