JP7714922B2 - Aluminum alloy extrusions - Google Patents

Description

The present invention relates to an aluminum alloy extrusion material.

Aluminum alloys are lightweight and strong, and in recent years their applications have expanded to include transportation equipment such as automobiles and railway vehicles, civil engineering and construction, as well as household items such as furniture and everyday items, and home appliances. There is a demand for aluminum alloy materials to be further lightened by thinning them, which requires further improvements in their strength as materials.

Patent Document 1 describes a method for manufacturing an aluminum-magnesium-silicon aluminum alloy extrusion material, which contains, by mass, 0.5-0.9% magnesium, 0.9-1.3% silicon, 0.3-0.5% iron, and 0.005-0.1% titanium, with copper limited to 0.4% or less, manganese limited to 0.30% or less, chromium limited to 0.10% or less, and zirconium limited to 0.10% or less, with the remainder being aluminum and unavoidable impurities. The extrusion is then quenched by air cooling, after which a further processing strain of 2-5% is introduced, and then artificial aging is performed.

Patent Document 2 describes an aluminum alloy extrusion material containing Si: 0.70 to 1.3% (mass %, the same applies below), Mg: 0.45 to 1.2%, Cu: 0.15 to less than 0.40%, Mn: 0.10 to 0.40%, Cr: 0.06% or less (excluding 0%), Zr: 0.05 to 0.20%, Ti: 0.005 to 0.15%, Fe: 0.30% or less, V: 0.01% or less, the balance being Al and unavoidable impurities, with a yield strength of 350 MPa or more, the grain size of crystallized particles being regulated to 5 μm or less, and the area ratio of fibrous structures in a cross section parallel to the hot extrusion direction being 95% or more.

Patent Document 3 describes an aluminum alloy extrusion material for cutting, which has a component composition consisting of 0.8-2.0 mass% Si, 0.7-1.0 mass% Mg, 0.3-1.0 mass% Cu, ≦0.20 mass% Fe, 0.2-0.8 mass% Mn, 0.1-0.4 mass% Cr, 0.3-0.9 mass% Mn + Cr, with the balance being Al and unavoidable impurities, with the amounts of Mg and Si satisfying the relationship Mg/1.73 + 0.2≦Si≦Mg/1.73 + 1.6, and which has a fibrous metal structure.

Japanese Patent Application Laid-Open No. 2007-254809 JP 2014-074213 A JP 2017-110238 A

Patent Document 1 incorporates a process of introducing processing strain after hardening, which involves more steps than normal and is likely to result in higher costs.

Patent Document 2 has a fibrous structure in the extrusion direction, which can result in inferior mechanical properties in the direction perpendicular to the extrusion direction compared to the direction parallel to the extrusion direction.

In Patent Document 3, the extrusion moldability is insufficient, and in order to mold at a sufficient extrusion speed, the extrusion pressure must be increased, and distortion of the extruded product is likely to increase. As a result, maintaining the quality of the extruded material tends to be expensive.

The object of the present invention is to provide an aluminum alloy extrusion material that is low cost and has high tensile strength and yield strength.

The present invention's configuration for solving the above problems is as follows.

[1] An aluminum alloy extrusion material,
Si: 0.90% by mass or more and 2.00% by mass or less,
Mg: 0.65% by mass or more and 0.90% by mass or less,
Cu: 0.25% by mass or more and 0.50% by mass or less,
Fe: 0.050% by mass or more and 0.49% by mass or less,
Zr: 0.10% by mass or more and 0.25% by mass or less,
Ti: 0.010% by mass or more and 0.10% by mass or less,
B: 0.050 times or more and 1.0 times or less of Ti on a mass basis,
and the balance is Al and unavoidable impurities,
In a cross section perpendicular to the extrusion direction, the area ratio of crystal grains having an aspect ratio of 5.0 or less and a length in the major axis direction of 50 μm or more and 1000 μm or less is 90.0% or more,
An aluminum alloy extrusion material in which the density of Al-Fe-Si particles having a length of 0.10 μm or more and 30 μm or less is 8.5×10 ³ particles/mm ² or more and 20×10 ³ particles/mm ² or less in a cross section perpendicular to the extrusion direction.

[2] In a cross section perpendicular to the extrusion direction, the density of Zr-containing fine particles having a particle size of 0.010 μm or more and 1.0 μm or less is 0.30 pieces/μm ² or more and 3.0 pieces/μm ² or less. The aluminum alloy extrusion material according to [1].

[3] The aluminum alloy extrusion material according to the preceding paragraph [2], wherein the Zr-containing fine particles further contain Si.

[4] An aluminum alloy extrusion material according to any one of the preceding paragraphs [1] to [3], wherein, in a cross section perpendicular to the extrusion direction, the number-based 25% aspect ratio, which is the value that represents the 25% aspect ratio counted from the largest, for Al-Fe-Si particles having a length of 0.10 μm or more and 30 μm or less, is 3.00 or more and 6.50 or less.

[5] In a cross section perpendicular to the extrusion direction, the density of Al—Fe—Si particles having a length of 0.10 μm or more and 30 μm or less is 15 × 10 ³ particles / mm ² or less. [4] The aluminum alloy extrusion material according to any one of [1] to [4].

[6] An aluminum alloy extrusion material according to any one of the preceding paragraphs [1] to [5], in which the compressive deformation initiation stress at 500°C is 25 MPa or less and the 0.2% yield strength is 285 MPa or more.

Aluminum alloy material having the composition described in the preceding paragraph [1] is easily deformed when heated, making it possible to lower the extrusion pressure, improving the productivity of aluminum alloy extrusion material and reducing manufacturing costs.

When the aluminum alloy extrusion has the composition and crystal grains described in the previous paragraph [1] and has a density of Al-Fe-Si particles within the specified range, the yield strength and strength are significantly improved.

Therefore, the present invention makes it possible to provide aluminum alloy extrusions with high tensile strength and yield strength at low cost.

FIG. 1 is a diagram showing an example (Example 1) of a photograph of a polarized texture taken by an optical microscope in a cross section perpendicular to the extrusion direction of an aluminum alloy extrusion according to one embodiment of the present invention. FIG. 2 is a diagram showing an example (Example 1) of a scanning electron microscope (SEM) photograph of a cross section perpendicular to the extrusion direction of an aluminum alloy extrusion according to one embodiment of the present invention. FIG. 3 shows an image obtained by binarizing the photograph of FIG. 2 and then inverting the black and white. FIG. 4 is a diagram showing an example (Example 1) of a scanning electron microscope (SEM) photograph of the microstructure in a cross section perpendicular to the extrusion direction of an aluminum alloy extrusion according to one embodiment of the present invention. FIG. 5 is a diagram showing an example of an EDX line analysis diagram (Example 1) of an aluminum alloy extrusion material according to one embodiment of the present invention. FIG. 6 shows an image obtained by binarizing the photograph of FIG. 4 and then inverting the black and white. FIG. 7 is a flow chart showing an example of a method for producing an aluminum alloy extrusion according to one embodiment of the present invention. FIG. 8 is a diagram showing the extrusion cross section of the die used in each example and each comparative example. FIG. 9 is a diagram showing the aluminum alloy extrusions produced in each of the examples and comparative examples. FIG. 10 is a diagram showing the amount of deformation of the cross section of the extruded material from the designed shape.

The following describes an embodiment of the present invention.

In the following description, unless otherwise specified, the terms "extruded material" and "aluminum alloy extruded material" refer to aluminum alloy extruded material.
<1. Aluminum alloy extrusion material>
The chemical composition of the aluminum alloy extrusion material according to this embodiment is composed of Si, Mg, Cu, Fe, Zr, Ti, B, and a balance of Al and unavoidable impurities, each of which is contained in an amount described below. As will be described later, the extrusion material according to this embodiment does not necessarily contain B. That is, the extrusion material according to this embodiment may have a chemical composition consisting of Si, Mg, Cu, Fe, Zr, Ti, B, and a balance (consisting of Al and unavoidable impurities), or may have a chemical composition consisting of Si, Mg, Cu, Fe, Zr, Ti, and a balance (consisting of Al and unavoidable impurities).

The aluminum alloy extrusion according to this embodiment contains crystal grains having an aspect ratio of 5.0 or less and a length in the major axis direction of 50 μm to 1000 μm in a cross section perpendicular to the extrusion direction. The details of these crystal grains will be described later.
The aluminum alloy extrusion according to this embodiment has Al—Fe—Si particles with lengths of 0.10 μm to 30 μm in a cross section perpendicular to the extrusion direction. The Al—Fe—Si particles will be described in detail later.

The aluminum alloy extrusion material according to this embodiment preferably contains fine particles containing Zr. Here, the fine particles containing Zr are sometimes referred to as Zr-containing fine particles. The Zr-containing fine particles will be described in detail later.
[1-1. Components of aluminum alloy extrusion material]
[1-1-1. Si]
The Si content in the extruded material is 0.90% by mass or more, preferably 1.03% by mass or more, and more preferably 1.05% by mass or more. This is because Si easily forms compounds through interaction with Mg, and the formation of Mg ₂ Si precipitates contributes to improving the strength of the extruded material. Also, by adding Si in excess of the amount of Mg added that exceeds the amount required to generate Mg ₂ Si, the properties such as strength of the extruded material after artificial aging treatment (the aging process described below) can be further improved.

The Si content in the extruded material may be 1.30% by mass or more, or 1.50% by mass or more.

The Si content in the extruded material is 2.00% by mass or less, and preferably 1.78% by mass or less. This is to suppress grain boundary precipitation of elemental Si and further increase the toughness of the extruded material. It also reduces the extrusion pressure, improving productivity and yield.

The Si content in the extruded material may be 1.50 mass % or less, or may be 1.25 mass % or less.
[1-1-2. Mg]
The Mg content in the extruded material is 0.65% by mass or more, preferably 0.70% by mass or more, more preferably 0.72% by mass or more, and even more preferably 0.74% by mass or more, because Mg easily forms compounds through interaction with Si, and the formation of Mg ₂ Si precipitates contributes to improving the strength of the extruded material.

The Mg content in the extruded material is 0.90% by mass or less, preferably 0.88% by mass or less, and more preferably 0.83% by mass or less. The reason for this is that by setting the amount of precipitates within an appropriate range, quench sensitivity is improved and an increase in pressure during extrusion is suppressed. Also, the generated Mg ₂ Si precipitates are easily dissolved at low temperatures, further improving the accuracy of the shape of the product (extruded material).
[1-1-3. Cu]
The Cu content in the extruded material is 0.25% by mass or more, preferably 0.28% by mass or more, more preferably 0.32% by mass or more, and even more preferably 0.36% by mass or more. This is because the inclusion of Cu increases the apparent supersaturation amount of _Mg2Si precipitates, increasing the precipitation amount of _Mg2Si precipitates, thereby improving the age hardenability of the extruded material. Furthermore, the fine precipitation of Cu-containing compounds within crystal grains contributes to improving strength.

The Cu content in the extruded material is 0.50% by mass or less, preferably 0.45% by mass or less, and more preferably 0.42% by mass or less, because this improves extrusion processability and enables extrusion molding at low extrusion pressures, and also improves the corrosion resistance of the extruded material.
[1-1-4. Fe]
The content of Fe in the extruded material is 0.050% by mass or more, preferably 0.080% by mass or more, more preferably 0.10% by mass or more, and even more preferably 0.13% by mass or more, because Fe combines with Al and Si to crystallize during casting and has the effect of suppressing coarsening of crystal grains.

The Fe content in the extruded material is 0.49% by mass or less, preferably 0.45% by mass or less, more preferably 0.35% by mass or less, even more preferably 0.30% by mass or less, still more preferably 0.27% by mass or less, and particularly preferably 0.24% by mass or less, in order to suppress crystallization of acicular Al-Fe-Si compounds and further improve extrusion moldability and toughness of the extruded product.
[1-1-5. Zr]
Zr precipitates as Zr-containing fine particles (details of which will be described later) during homogenization and serves as the nuclei of crystal grains (details of which will be described later) generated during extrusion. The Zr content in the extruded material is 0.10% by mass or more, preferably 0.11% by mass or more, and more preferably 0.13% by mass or more. The reason for this is to increase the number of Zr-containing fine particles, i.e., recrystallization nuclei, and suppress the coarsening of crystal grains (described later).

The Zr content in the extruded material is 0.25% by mass or less, preferably 0.20% by mass or less, and more preferably 0.17% by mass or less, because this improves the fluidity of the molten alloy during casting, facilitating the formation of the extrusion material by casting, and as a result, improves the productivity of the extruded material.
[1-1-6. Ti]
Ti has the effect of refining crystal grains during casting and also has the effect of suppressing cracking of the ingot during casting. The Ti content in the extruded material is 0.010% by mass or more, preferably 0.020% by mass or more, and more preferably 0.025% by mass or more.

The Ti content in the extruded material is 0.10% by mass or less, preferably 0.085% by mass or less, and more preferably 0.060% by mass or less, because this improves the fluidity of the molten alloy during casting, making it easier to form the extrusion material by casting, and as a result, improving the productivity of the extruded material.
[1-1-7. B]
Like Ti, B is also effective in refining crystal grains, and it is believed that adding it generates and disperses _TiB2 particles. Furthermore, it is believed that _TiB2 particles become solidification nuclei of crystals, resulting in the refinement of crystal grains, as described below. B may or may not be included. Here, "not containing B" means that B other than unavoidable impurities is not included, and B as an unavoidable impurity may be included. When B is included, the content of B in the extruded material is preferably 0.050 times or more, more preferably 0.10 times or more, and even more preferably 0.15 times or more of Ti by mass. The reason for this is to suppress the coarsening of crystal grains, as described below.

The B content in the extruded material is 1.0 times or less, preferably 0.50 times or less, and more preferably 0.25 times or less, that of Ti on a mass basis, in order to prevent excess B from bonding with Mg and thereby prevent Mg that should be bonded with Si from being consumed.
[1-1-8. Other elements]
As unavoidable impurities in the extruded material, for example, the contents of Mn and Cr are preferably kept as low as possible, because this reduces the quench sensitivity, reduces the effect of variations in cooling rate on strength, and makes the quality of the extruded material more stable.
[1-2. Crystal grains]
1 shows an example of a polarized light texture photograph taken by an optical microscope (Example 1, described later) of a cross section perpendicular to the extrusion direction of an aluminum alloy extrusion according to one embodiment of the present invention. As shown in the figure, in the cross section perpendicular to the extrusion direction of the extruded material (hereinafter simply referred to as the cross section), the area ratio of crystal grains having an aspect ratio of 5.0 or less and a long-axis length of 50 μm to 1000 μm is 90.0% or more, preferably 95.0% or more, more preferably 98.0% or more, and particularly preferably 99.0% or more. The reason for this is to suppress cleavage fracture between crystal grains and improve the strength of the extruded material against shear stress.

The area ratio is a value measured in two fields of view in a 1.95 mm × 2.60 mm area in a cross section perpendicular to the extrusion direction, i.e., the area ratio of crystal grains to the two fields of view. Also, particles that are at the edge of the image and are only partially visible are not included in either the area of each field of view or the area of the crystal grains (i.e., the area of each field of view used to calculate the area ratio is smaller than 1.95 mm × 2.60 mm). The area ratio of the crystal grains is a value expressed as a percentage of the total area of the two fields of view of crystal grains that satisfy the above conditions relative to the total area of the two fields of view.
[1-3. Al-Fe-Si particles]
Figure 2 shows an example (Example 1) of a scanning electron microscope (SEM) photograph of a cross section perpendicular to the extrusion direction of an aluminum alloy extrusion according to one embodiment of the present invention. Here, Al-Fe-Si particles are particles identified based on semi-quantitative analysis of the amount of each element in EDX mapping analysis of the same field of view. Specifically, Al-Fe-Si particles are particles having an Fe content of 5.0 mass% to 40 mass% and an Si content of 5.0 mass% to 40 mass% in this analysis, with the remainder being Al (which may contain unavoidable impurities). The white dots or rod-shaped portions in the photograph of Figure 2 are Al-Fe-Si particles.

Figure 3 shows an image of the photograph in Figure 2 after it has been binarized and then inverted. The length of the Al-Fe-Si particles is 0.010 μm or more and 30 μm or less (particles with sizes outside this range are not Al-Fe-Si particles as defined in this invention). The length of the Al-Fe-Si particles is determined based on the binarized SEM image. The length of the Al-Fe-Si particles is the distance between the longest two points in the black parts of the binarized image. Note that if the binarized image is not inverted, the length of the Al-Fe-Si particles is the distance between the longest two points in the white parts.

The density of Al—Fe—Si particles in a cross section perpendicular to the extrusion direction of the extruded material is 8.5×10 ³ particles/mm ² or more, and preferably 8.7×10 ³ particles/mm ² or more. This is to improve the yield strength and tensile strength of the extruded material while maintaining good extrudability.

The density of Al—Fe—Si particles in a cross section perpendicular to the extrusion direction of the extruded material is 20×10 ³ particles/mm ² or less, preferably 15×10 ³ particles/mm ² or less, and more preferably 13×10 ³ particles/mm ² or less. This is because by suppressing the size of the Al—Fe—Si particles, the toughness of the extruded material is improved, and the mechanical properties are also improved.

The number of Al-Fe-Si particles was counted using a JEOL JSM-7000F field emission scanning electron microscope at 1,000x magnification in four fields of view with a field of view of 121 μm × 90.9 μm = 10,998.9 ^μm² . The density of Al-Fe-Si particles was calculated by dividing the total number N _F of Al-Fe-Si particles in the four fields of view by the area of the four fields of view. In other words, the density of Al-Fe-Si particles is N _F /(4 × 10,998.9) [particles/ ^μm² ] = 10 ⁶ × N _F /(4 × 10,998.9) [particles/ ^mm² ].

The number-based 25% aspect ratio of Al-Fe-Si particles is the value (rounded to the nearest whole number) of Al-Fe-Si particles with a length of 0.10 μm or more and 30 μm or less, counting from the largest aspect ratio, in a cross section perpendicular to the extrusion direction. The aspect ratio of Al-Fe-Si particles is measured based on a binarized image.

For example, if there are 100 Al-Fe-Si particles that satisfy the above conditions within the four fields of view, the number-based 25% aspect ratio of the Al-Fe-Si particles will be the 25th largest aspect ratio, and if there are 123 particles, it will be the 31st largest aspect ratio (rounded up from 30.3).

In a cross section perpendicular to the extrusion direction, the number-based 25% aspect ratio of Al-Fe-Si particles is preferably 3.00 or greater, more preferably 3.70 or greater, and even more preferably 4.50 or greater. This is to prevent excessive recrystallization through the pinning effect.

In a cross section perpendicular to the extrusion direction, the number-based 25% aspect ratio of the Al—Fe—Si particles is preferably 6.50 or less, more preferably 6.00 or less, and even more preferably 5.65 or less.
[1-4. Zr-containing fine particles]
FIG. 4 is a diagram showing an example (Example 1) of a scanning electron microscope (SEM) photograph of the microstructure of a cross section perpendicular to the extrusion direction of an aluminum alloy extrusion according to one embodiment of the present invention. The white parts in the photograph in FIG. 4 are Zr-containing fine particles. The particle size of the Zr-containing fine particles is 0.010 μm or more and 1.0 μm or less (particles with sizes outside this range are not Zr-containing fine particles according to the present invention), and whether or not the particle size is within this range is determined based on a binarized image, as described below. The aluminum alloy extrusion according to this embodiment preferably contains Zr-containing fine particles. This is because using the Zr-containing fine particles as nuclei makes it easier to form crystal grains. The Zr-containing fine particles are preferably Al ₃ Zr _a Si _1-a (0<a≦1).

Figure 5 shows an example (Example 1) of an EDX line analysis diagram for an aluminum alloy extrusion according to one embodiment of the present invention. The vertical axis of the EDX line analysis diagram is in units of cps, counts per second. The EDX line analysis diagram at the bottom of Figure 5 was taken along the straight line in the SEM photograph at the top of Figure 5. Zr-containing microparticles are particles that satisfy the above size conditions and in which, in the EDX line analysis, a Zr peak is observed at a location corresponding to the particle in the SEM photograph (the white area in Figure 4).

The Zr-containing microparticles may also contain Si. In EDX line analysis, it is preferable that, among elements other than Al, the Zr peak intensity be the highest or second highest after the Si peak intensity in the Zr-containing microparticles, and it is even more preferable that, among elements other than Al, the Zr peak intensity be the highest.

Figure 6 shows an image of the photograph in Figure 4 that has been binarized and then inverted. The particle size of the Zr-containing microparticles is determined based on the binarized SEM image. Since the image in Figure 6 is inverted, the particle size of the Zr-containing microparticles is calculated from the area of the black parts, which are considered to be circles. If the binarized image is not inverted, the particle size of the Zr-containing microparticles is calculated by considering the white parts as circles.

The density of the Zr-containing fine particles in a cross section perpendicular to the extrusion direction of the extruded material is preferably 0.30 particles/μm ² or more, more preferably 0.40 particles/μm ² or more, and even more preferably 0.50 particles/μm ² or more, in order to suppress the coarsening of the crystal grains.

The density of the Zr-containing fine particles in a cross section perpendicular to the extrusion direction of the extruded material is preferably 3.0 particles/μm ² or less, more preferably 2.0 particles/μm ² or less, and even more preferably 1.0 particles/μm ² or less, in order to more reliably generate the crystal grains.

The number of Zr-containing microparticles was counted using a JEOL JSM-7000F field emission scanning electron microscope at a magnification of 10,000x, with a visual field of 12.1 μm × 9.09 μm = 109.989 ^μm² , in four visual fields. The density of Zr-containing microparticles was calculated by dividing the total number _NZ of Zr microparticles in the four visual fields by the area of the four visual fields. In other words, the density of Zr-containing microparticles was _NZ /(4 × 109.989) [particles/ ^μm² ].
1-5. Mechanical properties of aluminum alloy extrusions
The compressive deformation initiation stress of the aluminum extrusion material according to this embodiment at 500°C is preferably 25 MPa or less, more preferably 20 MPa or less, and even more preferably 19 MPa or less, where the compressive deformation initiation stress at 500°C is a value measured by the method in the examples described later.

The tensile strength of the aluminum extrusion material according to this embodiment is preferably 300 MPa or more, more preferably 320 MPa or more, and even more preferably 330 MPa or more. Here, the tensile strength is a value measured using the method described in the Examples below (a value obtained using a No. 5 test piece (dimensions described below) in accordance with JIS Z2241).

The 0.2% yield strength of the aluminum extrusion according to this embodiment is preferably 285 MPa or more, more preferably 290 MPa or more, and even more preferably 300 MPa or more. Here, the 0.2% yield strength is a value measured by the method described in the Examples below (a value obtained using a No. 5 test piece (dimensions of which will be described later) in accordance with JIS Z2241).
<2. Manufacturing method of aluminum alloy extrusion material>
7 is a flow diagram showing an example of a method for manufacturing an aluminum alloy extrusion material according to one embodiment of the present invention. Hereinafter, an example of a method for manufacturing an aluminum alloy extrusion material according to one embodiment of the present invention will be described, but the method for manufacturing an extrusion material according to the present invention is not limited to this.

7, a manufacturing method of an aluminum alloy extrusion material according to an example of this embodiment includes a melting step, a casting step, a homogenizing step, a heating step, an extrusion step, a die-quenching step, and an aging step. Note that not all of these steps are necessarily required. For example, if a cast material is available, the melting step and the casting step are unnecessary, and if a homogenized material is available, the steps up to the homogenizing step are unnecessary.
2-1. Melting process
In the melting step, a molten aluminum alloy is prepared. The chemical composition of the molten aluminum alloy is preferably the same as that of the aluminum alloy extrusion material to be obtained, and the elements contained in the aluminum alloy extrusion material are as described above.
[2-2. Casting process]
In the casting step, the molten metal obtained in the melting step is cast to obtain a billet (extrusion material). The casting method is not particularly limited, but examples thereof include vertical float continuous casting, vertical hot top continuous casting, and horizontal continuous casting.
[2-3. Homogenization process]
In the homogenization step, a homogenization treatment is performed to homogenize the metal structure of the billet obtained in the casting step and to sufficiently dissolve the atoms contained in the aluminum alloy. The homogenization step produces an extruded material with high strength. The chemical composition of the aluminum alloy (billet) used in the homogenization step is preferably the same as the chemical composition of the aluminum alloy extruded material to be obtained, and the elements contained in the aluminum alloy extruded material are as described above.

The homogenization temperature is preferably 500°C or higher, more preferably 530°C or higher, and even more preferably 550°C or higher. The reason for this is to sufficiently homogenize the metal structure of the billet and to sufficiently dissolve the atoms contained in the aluminum alloy. The homogenization temperature is preferably 600°C or lower, and more preferably 570°C or lower. By suppressing the melting of the intermetallic compounds in this way, coarsening of the intermetallic compound particles is suppressed, improving the mechanical properties of the extruded material.

The homogenization treatment time is preferably 3 hours or more, more preferably 8 hours or more, and even more preferably 12 hours or more. This is to ensure that the metal structure of the billet is sufficiently homogenized and that the atoms contained in the aluminum alloy are sufficiently solid-dissolved. The homogenization treatment time is preferably 24 hours or less, more preferably 20 hours or less, and even more preferably 18 hours or less. This is to prevent the particles of the intermetallic compounds from coarsening and improve the mechanical properties of the extruded material.

After the homogenization treatment, it is preferable to cool the billet. The temperature of the billet after cooling is preferably 150°C or less, more preferably 100°C or less. The billet may be cooled to 50°C or less and stored. The cooling method may include, but is not limited to, water cooling, mist cooling, air cooling, fan cooling, natural cooling, etc. The cooling rate is preferably 100°C/h or more, more preferably 150°C/h or more.
[2-4. Heating process]
In the heating step, the billet homogenized in the homogenizing step is heated to reduce the deformation resistance of the billet. The components constituting the billet are also dissolved by the heating step. The elements and their contents contained in the aluminum alloy material constituting the billet used in the heating step are as described above in the description of the aluminum alloy extrusion material.

The heating temperature is 350°C or higher, preferably 400°C or higher, and more preferably 450°C or higher. The reason for this is to reduce the deformation resistance of the billet and lower the extrusion pressure.

The heating temperature preferably does not exceed the solidus temperature of the aluminum alloy constituting the billet. The reason for this is to suppress melting of intermetallic compounds in the aluminum alloy. In the extrusion step described below, taking into consideration the heat generated by processing of the billet itself and heating of the material due to friction with the die, the specific heating temperature is 600°C or less, preferably 550°C or less, more preferably 530°C or less, and even more preferably 510°C or less.
2-5. Extrusion process
In the extrusion process, the billet heated in the heating process is extruded to obtain an extruded material. Specifically, for example, the billet heated in the heating process is loaded into a container and pressed against an extrusion mold (hereinafter referred to as a die) having a predetermined opening shape to obtain an extruded material having a desired cross-sectional shape. The extruded material according to this embodiment preferably has a hollow shape. The extrusion speed is preferably 5.0 mm/min or more, and more preferably 6.5 mm/min or more. This is because strain is applied to the material, making it easier to form a metal structure having the above-mentioned crystal grains. Also, this improves the productivity of the extruded material.
2-6. Die-quenching process
In the die-quenching process, the extruded material obtained by extrusion processing (extrusion process) is cooled. The cooling method is not particularly limited, but examples include water cooling, mist cooling, fan cooling, and natural cooling. A supersaturated solid solution is formed by the die-quenching process. The cooling rate is 7.0°C/sec or more, preferably 10°C/sec or more, and more preferably 12°C/sec or more. This is because precipitation of dissolved components is suppressed and the supersaturated solid solution is easily maintained. In addition, the productivity of the extruded material is improved.

The cooling rate is 80°C/sec or less, preferably 40°C/sec or less, and more preferably 20°C/sec or less. The reason for this is to prevent deformation of the extruded material due to thermal contraction during cooling.

The target temperature for the die-quenching step is 150° C. or less, preferably 100° C. or less, and more preferably 50° C. or less. After the die-quenching step, the extruded material may be stored at room temperature, for example, 30° C. or less, until the aging step described below.
[2-7. Aging process]
In the aging step, the extruded material cooled in the die quenching step is subjected to artificial aging treatment. The aging step causes Mg ₂ Si-based precipitates to grow in the extruded material, thereby improving the strength of the extruded material.

The aging temperature is 120°C or higher, preferably 140°C or higher, and more preferably 160°C or higher. This is because _Mg2Si -based precipitates are more likely to precipitate in the extruded material. The aging temperature is 240°C or lower, preferably 220°C or lower, and more preferably 200°C or lower. This is because excessive growth of _Mg2Si -based precipitates in the extruded material is suppressed, and the strength of the extruded material is improved.

The aging treatment time is 2 hours or more, preferably 4 hours or more, and more preferably 5 hours or more. The reason for this is to allow sufficient precipitation of Mg ₂ Si-based precipitates. The aging treatment time is 48 hours or less, preferably 16 hours or less, and more preferably 8 hours or less. The reason for this is to suppress excessive growth of Mg ₂ Si-based precipitates in the extruded material and improve the strength of the extruded material. Also, this is to improve the productivity of the extruded material.

The aluminum alloy extrusion material and the manufacturing method thereof according to the present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these.
<1. Preparation of aluminum alloy extrusion material>
An aluminum alloy containing the elements, Al, and inevitable impurities shown in Table 1 was used to produce a billet having a circular cross section and a diameter of 156 mm by continuous casting. The resulting billet was subjected to a homogenization treatment at 560°C for 14 hours. The billet was then cooled to 30°C at a rate of 180°C/h. The cooled billet was then heated to 500°C. For reference, the parts with a gray background in Table 1 deviate from the gist of the present invention.

Figure 8 shows the extrusion cross section (extrusion hole) of the die used in each example and comparative example. In each example and comparative example, this die D1 is used to form the extrusion material 1 shown in Figures 9 and 10. This extrusion material 1 is a hollow extrusion material with an outer wall 11 having a rectangular cross section and an inner partition wall 12 integrally formed with the outer wall 11, dividing the interior (hollow portion) into two.

The die D1 shown in Figure 8 has an extrusion hole D10 having an outer wall forming hole D11 for forming the outer wall 11 of the extrusion material 1 and an inner partition wall forming hole D12 for forming the inner partition wall 12. Furthermore, in this die D1, the outer wall forming hole D11 has a horizontal dimension L1 of 50 mm and a vertical dimension L2 of 50 mm. Furthermore, the width T1 of the outer wall forming hole D11 and the inner partition wall 12 is 2.5 mm, and the inner radius of curvature Ri of the outer wall forming hole D11 is 2.5 mm and the outer radius of curvature Ro is 5 mm.

In each example and comparative example, a billet heated to 500°C was extruded in an 8-inch direct extruder using die D1 shown in Figure 8 (extrusion process). The extrusion speeds for this extrusion process in each example and comparative example are shown in Table 1.

A die-quenching step was carried out immediately after the extrusion step, and the temperature of the extruded material was set to 30°C. The cooling rates in the die-quenching step for each Example and Comparative Example are shown in Table 1. The extruded material after the die-quenching step was subjected to artificial aging treatment (aging step) at 180°C for 6 hours to obtain an aluminum alloy extrusion material. In the following description, unless otherwise specified, the extrusion material refers to the aluminum alloy extrusion material obtained after the aging step. Furthermore, the aluminum alloy extrusion material after the aging treatment is the aluminum alloy extrusion material according to the present invention.
<2. Various measurements of aluminum alloys>
[2-1. Measurement of compressive deformation initiation stress of aluminum alloy at 500°C]
After homogenization, a cooled billet was cut from its center into a φ8 mm × 12 mm test piece. The longitudinal direction of the φ8 mm × 12 mm specimen was the longitudinal direction of the billet (extrusion direction). The cut test piece was heated to 500°C at a rate of 50°C/sec, held at 500°C for 10 minutes, and compressed at 500°C at a strain rate of 0.10/sec (increase in compression rate per second) to a compression rate of 0.75 ({dimension reduced by compression (0 mm before the test)}/dimension before compression (12 mm)). A stress-strain (compression rate) diagram was obtained. Compression was performed in a vacuum atmosphere. A Thermec Master Z tester manufactured by Fuji Electric Industrial Co., Ltd. was used.

Here, the compressive deformation initiation stress was defined as the maximum value of stress in the stress-strain diagram between compression ratios of 0 and 0.30. The maximum value is the value at which the load at that compression ratio is the maximum within a range of ±0.050 from that compression ratio.

The compressive deformation initiation stress measured for the aluminum alloys of each example and each comparative example is shown in Table 1.
2-2. Extrudability
The extrudability in the extrusion step (extrusion processing using a billet heated to 500° C.) was evaluated based on the following criteria.
"Good": The extrusion pressure is less than 25 MPa and the extruded material has no cracks or visible cracks.
"Poor": When at least one of the following occurs: the extrusion pressure is 25 MPa or more, the extruded material has cracks, or the extruded material has visible cracks.

The results of evaluation of extrudability for the aluminum alloys of the examples and comparative examples are shown in Table 1.
<3. Various measurements of aluminum alloy extrusions>
9 and 10 are diagrams showing the aluminum alloy extrusions produced in each example and comparative example, as described above. In the following description, the directions indicated by L, LT, and ST refer to the directions indicated by the arrow symbols "L,""LT," and "ST" in FIGS.
[3-1. Area ratio of crystal grains in the cross section of extruded material]
For each extrusion, test pieces with thicknesses of L: 10 mm, LT: 10 mm, and ST: 2 mm were cut from the portion (side wall) with a thickness in the ST direction (the L-LT surface was removed by 0.5 mm to give a thickness of 2 mm). These test pieces were embedded in resin, and the cross section perpendicular to the L direction was buffed to a mirror finish, followed by etching with Barker's electrolyte. Images of the polarized texture in the processed cross section taken with an optical microscope were analyzed using the image processing software Image J. The observation area was 1.95 mm x 2.60 mm, and two images were taken for each example and comparative example. An example of a photograph for observing crystal grains is shown in Figure 1, which is a cross-sectional photograph of the extrusion of Example 1.

For each image, the area percentage occupied by crystal grains with an aspect ratio of 5.0 or less and a length in the major axis direction of 50 μm or more and 1000 μm or less was calculated. Note that particles located at the edge of the image and partially outside the image were not included in the area of each field of view or the area of the crystal grains. The area percentage occupied by the above crystal grains is the total area of the two fields of view of crystal grains that meet the above conditions, expressed as a percentage, relative to the total area of the two fields of view.

The area ratios occupied by crystal grains measured for the extruded materials of each Example and Comparative Example are shown in Table 1.
3-2. Measurements on Al-Fe-Si particles
(Density of Al—Fe—Si particles)
For each extruded material, test pieces were cut out from the part (side wall) having a thickness in the LT direction with a thickness of L: 10 mm, ST: 10 mm, and LT: 2 mm (the L-ST surface was shaved off by 0.5 mm to make the thickness 2 mm). The cut-out test pieces were cut perpendicular to the L direction (extrusion direction), and a cross section for observation was formed using a JEOL cross-section polisher. Using a JEOL field emission scanning electron microscope JSM-7000F, four images were acquired at a magnification of 1,000 times, with a field of view of 121 μm × 90.9 μm = 10998.9 μm ² , and EDX mapping analysis was performed.

Using the obtained mapping analysis results and the binarized image (e.g., FIG. 3), the number N of Al—Fe— _Si particles having a length of 0.10 μm or more and 30 μm or less was counted for four visual fields. The number _N of counted Al—Fe—Si particles was divided by the area of the four visual fields to calculate the density of the Al—Fe—Si particles. The definition of the counted Al—Fe—Si particles is as described above.

The density of Al—Fe—Si particles measured for the extruded materials of each example and each comparative example is shown in Table 1.
(25% aspect ratio by number of Al-Fe-Si particles)
For each extruded material, the aspect ratio of the Al—Fe—Si particles counted was determined to be the value that was 25% (rounded to the nearest whole number) counting from the largest (numerical 25% aspect ratio).

The number-based 25% aspect ratios of the Al—Fe—Si particles measured for the extruded materials of each Example and Comparative Example are shown in Table 1.
[3-3. Density of Zr-containing fine particles in the cross section of the extruded material]
For each extrusion, test pieces with thicknesses of L: 10 mm, LT: 10 mm, and ST: 2 mm were cut from the portion (sidewall) with a thickness in the ST direction (the L-LT surface was removed by 0.5 mm to obtain a thickness of 2 mm). The cut test pieces were cut perpendicular to the L direction (extrusion direction), and a cross section for observation was formed using a JEOL cross-section polisher. Using a JEOL JSM-7000F field emission scanning electron microscope, ^four images were acquired at 10,000x magnification, covering a field of view of 12.1 μm × 9.09 μm = 109.989 μm². Zr-containing particles with a particle size of 0.010 μm to 1.0 μm were counted by EDX line analysis (e.g., Figure 5) and binarized images (e.g., Figure 6). The number of Zr-containing particles in four fields of view, _NZ , was divided by the area of the four fields of view to calculate the density of Zr-containing particles.

The density of the Zr-containing fine particles measured for the extruded materials of each Example and Comparative Example is shown in Table 1.
[3-4. Tensile strength and 0.2% yield strength]
Measurements were performed using the method specified in JIS Z2241 from the aluminum alloy extrusions obtained in each Example and Comparative Example. No. 5 test pieces were cut out for measurement. Specifically, they were cut out along the extrusion direction (L direction) with a gauge length of 50 mm, a parallel portion length of 60 mm, a width of 25 mm, a thickness of 2 mm, and a shoulder radius of 30 mm. A tensile test (in accordance with JIS Z2241) was performed on the tensile test pieces at room temperature (24°C) at a crosshead speed of 2 mm/min to calculate the tensile strength, and the 0.2% proof stress was measured using the offset method.

The tensile strength and 0.2% yield strength measured for the extruded materials of each Example and Comparative Example are shown in Table 1.
3-5. Deformation of extruded material
The extruded material after the aging process was cut on a plane perpendicular to the extrusion direction. The angles of two adjacent sides in the outline of the cut cross section of the extruded material were measured, and the absolute value θ [°] of the difference from 90° was calculated as the deformation amount, as shown in Figure 10. The measured deformation amount θ for the extruded materials of each Example and Comparative Example is shown in Table 1.
4. Evaluation
The aluminum alloys according to the respective examples all have excellent extrudability. Therefore, the productivity of the aluminum alloy extrusions according to the respective examples can be improved, and as a result, the manufacturing costs of the extrusions can be reduced. Furthermore, the aluminum alloy extrusions according to the respective examples all have high tensile strength and yield strength.

In a cross section perpendicular to the extrusion direction, the extruded material of Comparative Example 1, which had a low density of Al-Fe-Si particles, had low tensile strength and yield strength.

The aluminum alloys in Comparative Examples 2 and 3 have the same composition, but contain no Zr and instead contain Mn and Cr. The aluminum alloys in Comparative Examples 2 and 3 have a high compressive deformation initiation stress at 500°C, which leads to reduced productivity. With this composition, increasing the extrusion speed as in Comparative Example 3 resulted in cracks in the extruded material (poor extrudability). On the other hand, decreasing the extrusion speed as in Comparative Example 2 allows for the production of an extruded material, but this results in low productivity and increased manufacturing costs.

The aluminum alloy of Comparative Example 4 contains a small amount of Zr and also contains Mn and Cr. The aluminum alloy of Comparative Example 4 has a high compressive deformation initiation stress at 500°C, which leads to reduced productivity. Although it was possible to produce an extruded material in Comparative Example 4, the desired crystal grains could not be formed in the extruded material. Furthermore, the extruded material of Comparative Example 4 had a low density of Al-Fe-Si particles in a cross section perpendicular to the extrusion direction. This extruded material had low tensile strength and yield strength.

The aluminum alloy of Comparative Example 5 has a lower Mn and Cr content than the aluminum alloy of Comparative Example 4. Furthermore, the extruded material of Comparative Example 5 has a low density of Al-Fe-Si particles in a cross section perpendicular to the extrusion direction. The extruded material of Comparative Example 5 also had low tensile strength and yield strength.

The extruded material of Comparative Example 6, which had a low Si content and a low density of Al-Fe-Si particles, had low tensile strength and yield strength.

The extruded material of Comparative Example 7, which had a low Cu content and a low density of Al-Fe-Si particles, had low tensile strength and yield strength.

The aluminum alloy of Comparative Example 8 had a high Cu content. The aluminum alloy of Comparative Example 8 had a high compressive deformation initiation stress at 500°C, and cracks occurred in the extruded material (poor extrudability).

The extruded material of Comparative Example 9, which had a low Mg content, had low tensile strength and yield strength.

The aluminum alloy of Comparative Example 10 has a high Mg content. The aluminum alloy of Comparative Example 10 had a high compressive deformation initiation stress at 500°C, and cracks occurred in the extruded material (poor extrudability).

The extruded material of Comparative Example 11, which did not contain Zr and had a low density of Al-Fe-Si particles, had low yield strength.

From the above, it can be seen that the aluminum alloy extrusion material of the present invention is low-cost and has high tensile strength and yield strength. Furthermore, it can be seen that the manufacturing method for aluminum alloy extrusion material of the present invention makes it possible to obtain aluminum alloy extrusion material with high tensile strength and yield strength at low cost.

The aluminum alloy extrusion material of this invention can be used as a high-strength structural material.

1: Aluminum alloy extrusion material

Claims (5)

An aluminum alloy extrusion material,
Si: 0.90% by mass or more and 2.00% by mass or less,
Mg: 0.65% by mass or more and 0.90% by mass or less,
Cu: 0.25% by mass or more and 0.50% by mass or less,
Fe: 0.050% by mass or more and 0.49% by mass or less,
Zr: 0.10% by mass or more and 0.25% by mass or less,
Ti: 0.010% by mass or more and 0.10% by mass or less,
B: 1.0 times or less of Ti by mass,
and the balance is Al and unavoidable impurities,
In a cross section perpendicular to the extrusion direction, the area ratio of crystal grains having an aspect ratio of 5.0 or less and a length in the major axis direction of 50 μm or more and 1000 μm or less is 90.0% or more,
In a cross section perpendicular to the extrusion direction, the density of Al—Fe—Si particles having a length of 0.10 μm or more and 30 μm or less is 8.5×10 ³ particles/mm ² or more and 20×10 ³ particles/mm ² or less ,
An aluminum alloy extrusion material having a compressive deformation initiation stress of 25 MPa or less and a 0.2% yield strength of 285 MPa or more at 500°C . 2. The aluminum alloy extrusion material according to claim 1, wherein the density of Zr-containing fine particles having a particle size of 0.010 μm or more and 1.0 μm or less is 0.30 particles/μm ² or more and 3.0 particles/μm ² or less in a cross section perpendicular to the extrusion direction. The aluminum alloy extrusion material according to claim 2, wherein the Zr-containing fine particles further contain Si. An aluminum alloy extrusion material according to any one of claims 1 to 3, wherein the number-based 25% aspect ratio, which is the value that represents the 25% aspect ratio counted from the largest, for Al-Fe-Si particles having a length of 0.10 μm or more and 30 μm or less in a cross section perpendicular to the extrusion direction is 3.00 or more and 6.50 or less. The aluminum alloy extrusion material according to any one of claims 1 to 4, wherein the density of Al-Fe-Si particles having a length of 0.10 μm or more and 30 μm or less in a cross section perpendicular to the extrusion direction is 15 × 10 ³ particles/mm ² or less.