Aluminum alloy extruded material

Abstract

To provide an aluminum alloy extruded material having high tensile strength and durability at a low cost.SOLUTION: There is provided an aluminum alloy extruded material which comprises 0.90 mass% or more and 2.00 mass% or less of Si, 0.65 mass% or more and 0.90 mass% or less of Mg, 0.25 mass% or more and 0.50 mass% or less of Cu, 0.050 mass% or more and 0.49 mass% or less of Fe, 0.10 mass% or more and 0.25 mass% or less of Zr, 0.010 mass% or more and 0.10 mass% or less of Ti, B of 0.050 times or more and 1.0 times or less Ti on a mass basis and the remainder of Al and unavoidable impurities, wherein in the cross-section perpendicular to the extrusion direction, the area ratio occupied by crystal particles having an aspect ratio of 5.0 or less and a long axis direction length of 50 μm or more and 1000 μm or less is 90.0% or more and in the cross-section perpendicular to the extrusion direction, the density of Si particles having a particle diameter of 0.010 μm or more and 1.0 μm or less is 50×103 pcs / mm2 or more and 150×103 pcs / mm2 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an aluminum alloy extruded material.

Background Art

[0002] Aluminum alloys are lightweight and have high strength. In recent years, their applications have expanded to transportation equipment such as automobiles and railway vehicles, civil engineering and construction fields, and further to daily necessities such as furniture and household goods, and household electrical appliances. There is a demand for further weight reduction of aluminum alloy materials due to thinning, etc., and for this purpose, further improvement in strength as a material is required.

[0003] Patent Document 1 describes a method for manufacturing an aluminum-magnesium-silicon-based aluminum alloy extruded material, which contains magnesium in an amount of 0.5 to 0.9% by mass, silicon in an amount of 0.9 to 1.3% by mass, iron in an amount of 0.3 to 0.5% by mass, titanium in an amount of 0.005 to 0.1% by mass, and further limits copper to 0.4% or less, manganese to 0.30% or less, chromium to 0.10% or less, and zirconium to 0.10% or less. The balance is composed of aluminum and inevitable impurities. The aluminum alloy is extruded and quenched by air cooling, and then a processing strain of 2 to 5% is further introduced, and then artificial aging is performed.

[0004] Patent Document 2 describes an aluminum alloy extruded material having a chemical composition containing Si: 0.70 to 1.3% (mass%, the same hereinafter), Mg: 0.45 to 1.2%, Cu: 0.15 to less than 0.40%, Mn: 0.10 to 0.40%, Cr: less than 0.06% (excluding 0%), Zr: 0.05 to 0.20%, Ti: 0.005 to 0.15%, regulated Fe to 0.30% or less, V to 0.01% or less, and the balance being Al and inevitable impurities, having a yield strength of 350 MPa or more, the crystal grain size of the precipitates being regulated to 5 μm or less, and the area ratio of the fibrous structure in the cross section parallel to the hot extrusion direction being 95% or more.

[0005] Patent Document 3 describes an extruded material of an aluminum alloy for cutting, having a component composition consisting of Si: 0.8 to 2.0% by mass, Mg: 0.7 to 1.0% by mass, Cu: 0.3 to 1.0% by mass, Fe: ≤0.20% by mass, Mn: 0.2 to 0.8% by mass, Cr: 0.1 to 0.4% by mass, Mn + Cr: 0.3 to 0.9% by mass, with the balance being Al and inevitable impurities, and further satisfying the relational expression of Mg / 1.73 + 0.2 ≤ Si ≤ Mg / 1.73 + 1.6, and having a fibrous metal structure.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] In Patent Document 1, a process of introducing processing strain after quenching is incorporated, and due to the larger number of processes than the normal process, it is likely to result in high costs.

[0008] In Patent Document 2, it has a fibrous structure in the extrusion direction, and the mechanical properties in the direction perpendicular to the extrusion direction may be inferior to those in the direction parallel to the extrusion direction.

[0009] In Patent Document 3, the extrusion formability is insufficient, and to form at a sufficient extrusion speed, it is necessary to increase the extrusion pressure, and also the distortion of the extruded product is likely to increase. Therefore, it is likely to result in high costs in order to maintain the quality as an extruded material.

[0010] Therefore, an object of the present invention is to provide an extruded material of an aluminum alloy that is low - cost and has high tensile strength and yield strength.

Means for Solving the Problem

[0011] The configuration of the present invention for solving the above problems is as follows.

[0012] [1] An aluminum alloy extruded material, Si: 0.90 mass% or more and 2.00 mass% or less, Mg: 0.65 mass% or more and 0.90 mass% or less, Cu: 0.25 mass% or more and 0.50 mass% or less, Fe: 0.050 mass% or more and 0.49 mass% or less, Zr: 0.10 mass% or more and 0.25 mass% or less, Ti: 0.010 mass% or more and 0.10 mass% or less, B: 0.050 times or more and 1.0 times or less of Ti based on mass, and the balance consists of Al and inevitable impurities, in a cross-section perpendicular to the extrusion direction, the area ratio 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 is 90.0% or more, in a cross-section perpendicular to the extrusion direction, the existence density of Si particles with a particle size of 0.010 μm or more and 1.0 μm or less is 50×10 3 pieces / mm 2 or more and 150×10 3 pieces / mm 2 or less An aluminum alloy extruded material.

[0013] [2] In a cross-section perpendicular to the extrusion direction, the existence density of Zr-containing fine particles with 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, and the aluminum alloy extruded material according to the above item [1].

[0014] [3] The aluminum alloy extruded material according to the above item [2], wherein the Zr-containing fine particles further contain Si.

[0015] [4] In a cross-section perpendicular to the extrusion direction, the density of Si particles with a particle size of 0.010 μm or more and 1.0 μm or less is 53×10 3 particles / mm 2 or more, and the aluminum alloy extruded material according to any one of the preceding items [1] to [3].

[0016] [5] In a cross-section perpendicular to the extrusion direction, the density of Si particles with a particle size of 0.010 μm or more and 1.0 μm or less is 120×10 3 particles / mm 2 or less, and the aluminum alloy extruded material according to any one of the preceding items [1] to [4].

[0017] [6] The aluminum alloy extruded material according to any one of the preceding items [1] to [5], wherein the compression deformation start stress at 500 °C is 25 MPa or less and the 0.2% proof stress is 285 MPa or more.

Advantages of the Invention

[0018] The aluminum alloy material having the composition described in the preceding item [1] is easily deformed by heating, so that the extrusion pressure can be reduced, the productivity of the aluminum alloy extruded material is improved, and the manufacturing cost can be reduced.

[0019] The aluminum alloy extruded material has the composition and crystal grains described in the preceding item [1] and the density of Si particles within the specified range, so that the proof stress and strength are greatly improved. Therefore, according to the present invention, it is possible to provide an aluminum alloy extruded material with low cost, high tensile strength and high proof stress.

Brief Description of the Drawings

[0020]

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MODE FOR CARRYING OUT THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described.

[0022] In the following description, when "extruded material" or "aluminum alloy extruded material" is mentioned, unless otherwise specified, it means an aluminum alloy extruded material. <1. Aluminum Alloy Extruded Material> The chemical composition of the aluminum alloy extruded material according to this embodiment consists of Si, Mg, Cu, Fe, Zr, Ti, B, and the balance, with the balance consisting of Al and unavoidable impurities, as described below. As will be described later, the extruded material according to this embodiment may not contain B. That is, the extruded material according to this embodiment may have a chemical composition consisting of Si, Mg, Cu, Fe, Zr, Ti, B, and the balance (consisting of Al and unavoidable impurities), or a chemical composition consisting of Si, Mg, Cu, Fe, Zr, Ti, and the balance (consisting of Al and unavoidable impurities).

[0023] The aluminum alloy extruded material 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 or more and 1000 μm or less in a cross section perpendicular to the extrusion direction. Details of these crystal grains will be described later.

[0024] The aluminum alloy extruded material according to this embodiment contains Si particles having a particle size of 0.010 μm or more and 1.0 μm or less in a cross section perpendicular to the extrusion direction. Details of the Si particles will be described later. It is preferable that fine particles containing Zr are present in the aluminum alloy extruded material according to this embodiment. Here, the fine particles containing Zr may also be referred to as Zr-containing fine particles. Details of the Zr-containing fine particles will be described later. [1-1. Each Component of the Aluminum Alloy Extruded Material] [1-1-1. Si] The content rate of Si 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 a compound through interaction with Mg, and when Mg2Si precipitates are formed, it contributes to improving the strength of the extruded material. Also, by adding an excessive amount exceeding the addition amount for generating Mg2Si with respect to the addition amount of Mg described later, the properties such as the strength of the extruded material after artificial aging treatment (the aging process described later) can be further enhanced.

[0025] The content rate of Si in the extruded material may be 1.30% by mass or more, or may be 1.50% by mass or more.

[0026] The Si content in the extruded material is 2.00% by mass or less, preferably 1.78% by mass or less. This is because it suppresses the grain boundary precipitation of elemental Si and further enhances the toughness of the extruded material. Also, it is to reduce the extrusion pressure and improve productivity and yield.

[0027] The Si content in the extruded material may be 1.50% by mass or less, or may be 1.25% by 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. This is because Mg easily forms a compound through interaction with Si, and when Mg2Si precipitates are formed, it contributes to the improvement of the strength of the extruded material.

[0028] 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. This is because by setting the amount of precipitates within an appropriate range, the hardenability is improved and the increase in pressure during extrusion is suppressed. Also, it is to make it easier to dissolve the formed Mg2Si precipitates at a low temperature and further improve the shape accuracy 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. The inclusion of Cu increases the apparent supersaturation amount of Mg2Si precipitates, and by increasing the precipitation amount of Mg2Si precipitates, the age hardenability of the extruded material is improved. Also, when a Cu-containing compound precipitates finely within the crystal grains, it contributes to the improvement of strength.

[0029] 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. This is because it improves the extrusion processability and enables extrusion molding at a low extrusion pressure. Also, it improves the corrosion resistance of the extruded material. [1-1-4.Fe] The Fe content 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. This is because Fe combines with Al and Si and crystallizes during casting, and it has the effect of suppressing the coarsening of crystal grains.

[0030] 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, even more preferably 0.27% by mass or less, and particularly preferably 0.24% by mass or less. This is because it suppresses the crystallization of acicular Al-Fe-Si-based compounds and further improves the extrusion moldability and the toughness of the extruded product. [1-1-5.Zr] Zr precipitates as Zr-containing fine particles (details will be described later) during the homogenization treatment and serves as nuclei for crystal grains (details will be described later) generated during the extrusion process. 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. This is because it increases the number of Zr-containing fine particles, i.e., the number of recrystallization nuclei, and suppresses the coarsening of crystal grains described later.

[0031] 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. This is because it improves the fluidity of the alloy melt during casting, facilitates 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 function of refining crystal grains during casting, and in addition, it has the effect of suppressing ingot cracking during casting. The content of Ti 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.

[0032] The content of Ti 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. The reason is that the fluidity of the molten alloy is improved during casting, the formation of the material for extrusion by casting becomes easy, and as a result, the productivity of the extruded material is improved. [1-1-7.B] Similar to Ti, B is also effective in refining crystal grains. By adding B, it is considered that TiB2 particles are generated and dispersed. Furthermore, it is considered that the TiB2 particles serve as crystal solidification nuclei, resulting in the refinement of crystal grains described later. B may or may not be contained. Here, "not containing B" means not containing B other than inevitable impurities, and B as an inevitable impurity may be contained. When B is contained, 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 based on mass. The reason is to suppress the coarsening of crystal grains described later.

[0033] The content of B in the extruded material is 1.0 times or less, preferably 0.50 times or less, and more preferably 0.25 times or less of Ti based on mass. The reason is to suppress the combination of excess B with Mg and to suppress the consumption of Mg that should combine with Si. [1-1-8. Other elements] As inevitable impurities in the extruded material, for example, it is preferable to minimize the contents of Mn and Cr as much as possible. The reason is that it can blunt the hardening sensitivity, reduce the influence of the variation in cooling rate on the strength, and make the quality of the extruded material more stable. [1-2. Crystal grains] FIG. 1 is a view showing an example of a photograph of a polarized structure by an optical microscope in a cross section perpendicular to the extrusion direction of an aluminum alloy extruded material according to an embodiment of the present invention (Example 1 described later). As shown in the figure, in the cross section perpendicular to the extrusion direction of the extruded material (hereinafter, simply referred to as a cross section in this section), the area ratio occupied by 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, preferably 95.0% or more, more preferably 98.0% or more, and particularly preferably 99.0% or more. This is because it suppresses cleavage fracture between crystal grains and improves the strength of the extruded material against shear stress.

[0034] Here, the above area ratio is a value measured in two fields in a range of 1.95 mm × 2.60 mm in a cross section perpendicular to the extrusion direction, that is, the area ratio of crystal grains for two fields. Also, for particles at the end of the image and only partially shown, they are not included in either the area of each field or the area of crystal grains (that is, the area of each field used for calculating the area ratio is smaller than 1.95 mm × 2.60 mm). The area ratio occupied by the above crystal grains is a value expressed as a percentage of the total area of two fields of crystal grains satisfying the above conditions with respect to the total area of two fields. 〔1-3. Si particles〕 FIG. 2 is a view showing an example of a photograph by a scanning electron microscope (SEM) in a cross section perpendicular to the extrusion direction of an aluminum alloy extruded material according to an embodiment of the present invention (Example 1). Here, Si particles are particles confirmed based on quantitative analysis of the amount of each element in EDX mapping of the same field of view. Specifically, Si particles are particles having a Si content of 90 mass% or more and the balance being Al (which may include inevitable impurities. Also, Si may be 100 mass% (no balance)) in this analysis. The black dots in the photograph of FIG. 2 are Si particles.

[0035] Figure 3 is a binarized image of the photograph in Figure 2. The particle size of the Si particles is 0.010 μm or more and 1.0 μm or less (particles with a size outside this range are not the Si particles in the present invention). The particle size of the Si particles is determined based on the binarized SEM image. The particle size of the Si particles is the diameter calculated from the area after binarizing the image and regarding the black part of the image as a circle.

[0036] The density of Si particles present in a cross-section perpendicular to the extrusion direction of the extruded material is 50×10 3 particles / mm 2 or more, preferably 53×10 3 particles / mm 2 or more, and more preferably 54×10 3 particles / mm 2 or more. This is to achieve both high productivity of the extruded material and high tensile strength and high yield strength.

[0037] The density of Si particles present in a cross-section perpendicular to the extrusion direction of the extruded material is 150×10 3 particles / mm 2 or less, preferably 120×10 3 particles / mm 2 or less, and more preferably 85×10 3 particles / mm 2 or less. This is to suppress embrittlement at the grain boundaries and improve the mechanical properties of the extruded material.

[0038] Note that the number of Si particles is counted in 4 fields of view at a magnification of 10,000 times using a field emission scanning electron microscope JSM-7000F manufactured by JEOL Ltd., with a field of view of 12.1 μm × 9.09 μm = 109.989 μm 2 The total number N Si of Si particles in 4 fields of view is divided by the area of 4 fields of view to calculate the density of Si particles present. That is, the density of Si particles present is N Si / (4×109.989) [particles / μm 2 = 10 6 ×N Si / (4×109.989) [particles / mm 2 . [1 - 4. Zr-containing fine particles] Figure 4 is a diagram showing an example (Example 1) of a photograph taken by a scanning electron microscope (SEM) of the microstructure in a cross-section perpendicular to the extrusion direction of an aluminum alloy extruded material according to an embodiment of the present invention. The white portions in the photograph of Figure 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 in the present invention), and whether the particle size is within this range is determined based on the binarized image described later. The aluminum alloy extruded material according to the present embodiment preferably contains Zr-containing fine particles. This is because by using the Zr-containing fine particles as nuclei, crystal grains are more likely to form. The Zr-containing fine particles are Al3Zr a Si 1-a (0 < a ≤ 1) is preferable.

[0039] Figure 5 is a diagram showing an example (Example 1) of an EDX line analysis diagram in an aluminum alloy extruded material according to an embodiment of the present invention. Note that the unit cps on the vertical axis of the EDX line analysis diagram is counts per second. The lower EDX line analysis diagram in Figure 5 is performed along the straight line in the SEM photograph above Figure 5. The Zr-containing fine particles are particles that satisfy the above size conditions and in which a Zr peak is observed at a location corresponding to the particles (the white portions in Figure 4) in the SEM photograph in the EDX line analysis.

[0040] The Zr-containing fine particles may contain Si. Regarding the EDX line analysis, in the Zr-containing fine particles, among the elements other than Al, it is preferable that the peak intensity of Zr is the highest or the second highest after the peak intensity of Si, and it is more preferable that the peak intensity of Zr is the highest among the elements other than Al.

[0041] FIG. 6 is a diagram showing an image obtained by binarizing the photograph of FIG. 4 and then inverting black and white. The particle size of the Zr-containing fine particles is determined based on the image obtained by binarizing the SEM image. In FIG. 6, since black and white are inverted, the particle size of the Zr-containing fine particles is the diameter calculated from the area after regarding the black portion as a circle. Note that when black and white are not inverted in the binarized image, the particle size of the Zr-containing fine particles is calculated by regarding the white portion as a circle.

[0042] The density of the Zr-containing fine particles in the 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. This is for suppressing the coarsening of the above-described crystal grains.

[0043] The density of the Zr-containing fine particles in the 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. This is for more surely generating the above-described crystal grains.

[0044] The number of the Zr-containing fine particles is counted in four fields of view at a magnification of 10,000 times using a field emission type scanning electron microscope JSM-7000F manufactured by JEOL Ltd., with a field of view of 12.1 μm × 9.09 μm = 109.989 μm 2 The total number N of Zr fine particles in four fields of view Z is divided by the area of four fields of view to calculate the density of the Zr-containing fine particles. That is, the density of the Zr-containing fine particles is N Z / (4 × 109.989) [particles / μm 2 . [1-5. Mechanical Properties of Aluminum Alloy Extruded Material] The compression deformation start stress of the aluminum extruded 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. Here, the compression deformation start stress at 500 °C is a value measured by the method of the examples described later.

[0045] The tensile strength of the aluminum extruded 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 by the method of the examples described later (a value obtained using a No. 5 test piece (dimensions will be described later) in JIS Z2241).

[0046] The 0.2% proof stress of the aluminum extruded material 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% proof stress is a value measured by the method of the examples described later (a value obtained using a No. 5 test piece (dimensions will be described later) in JIS Z2241). <2. Manufacturing method of aluminum alloy extruded material> FIG. 7 is a flowchart showing an example of a manufacturing method of an aluminum alloy extruded material according to an embodiment of the present invention. Hereinafter, an example of a manufacturing method of an aluminum alloy extruded material according to an embodiment of the present invention will be described, but the manufacturing method of the extruded material according to the present invention is not limited thereto.

[0047] As shown in FIG. 7, the manufacturing method of the aluminum alloy extruded material according to an example of this embodiment includes a melting step, a casting step, a homogenization step, a heating step, an extrusion step, a die quenching step, and an aging step. Note that not all of these steps are necessary. For example, if the material after casting is available, the melting step and the casting step are not required. If the material after homogenization is available, the steps up to the homogenization step are not required. 〔2-1. Melting step〕 In the melting process, a molten aluminum alloy is prepared. The chemical composition of the molten metal is preferably the same as that of the aluminum alloy extrusion material to be obtained, and for each element contained in the aluminum alloy extrusion material, it is as described above. [2-2. Casting process] In the casting process, a billet (material for extrusion) is obtained by casting the molten metal obtained in the melting process. The casting method is not particularly limited, and examples include a vertical type float continuous casting method, a vertical type hot top continuous casting method, a horizontal type continuous casting method, and the like. [2-3. Homogenization process] In the homogenization process, a homogenization treatment is performed to homogenize the metal structure of the billet obtained in the casting process and to sufficiently dissolve the atoms contained in the aluminum alloy. A high-strength extrusion material can be obtained by the homogenization process. The chemical composition of the aluminum alloy (billet) used in the homogenization process is preferably the same as that of the aluminum alloy extrusion material to be obtained, and for each element contained in the aluminum alloy extrusion material, it is as described above.

[0048] The temperature of the homogenization treatment is preferably 500 °C or higher, more preferably 530 °C or higher, and even more preferably 550 °C or higher. This is because in order to sufficiently homogenize the metal structure of the billet and to sufficiently dissolve the atoms contained in the aluminum alloy. The temperature of the homogenization treatment is preferably 600 °C or lower, more preferably 570 °C or lower. By suppressing the melting of the intermetallic compound in this way, coarsening of the particles of the intermetallic compound is suppressed, and the mechanical properties of the extrusion material are improved.

[0049] 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 because in order to sufficiently homogenize the metal structure of the billet and to sufficiently dissolve the atoms contained in the aluminum alloy. 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 because in order to suppress the coarsening of the intermetallic compound particles and improve the mechanical properties of the extruded material.

[0050] 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. Examples of the cooling method include water cooling, mist cooling, air cooling, fan cooling, natural cooling, etc., but it is not particularly limited. The cooling rate is preferably 100°C / h or more, more preferably 150°C / h or more. 〔2-4. Heating process〕 In the heating process, the billet homogenized in the homogenization process is heated to reduce the deformation resistance of the billet. Also, the components constituting the billet are dissolved by the heating process. The elements contained in the aluminum alloy material constituting the billet used in the heating process and their contents are as described above in the description of the aluminum alloy extruded material.

[0051] The heating temperature is 350°C or more, preferably 400°C or more, and more preferably 450°C or more. This is because in order to reduce the deformation resistance of the billet and lower the extrusion pressure.

[0052] The heating temperature preferably does not exceed the solidus temperature of the aluminum alloy constituting the billet. This is to suppress the melting of intermetallic compounds in the aluminum alloy. Considering the heat generation during processing of the billet itself and the heating of the material due to friction with the die in the extrusion process described later, the specific heating temperature is 600 °C or lower, preferably 550 °C or lower, more preferably 530 °C or lower, and even more preferably 510 °C or lower. [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 die (hereinafter referred to as a die) having a predetermined opening shape, whereby an extruded material having a desired cross-sectional shape is obtained. 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, it is because the productivity of the extruded material is improved. [2-6. Die quenching process] In the die quenching process, the extruded material obtained by extrusion (extrusion process) is cooled. The cooling method is not particularly limited, and examples include water cooling, mist cooling, fan air cooling, and natural cooling. The die quenching process forms a supersaturated solid solution. 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 it suppresses the precipitation of the dissolved components and makes it easier to maintain the supersaturated solid solution. Also, it is because the productivity of the extruded material is improved.

[0053] The cooling rate is 80 °C / sec or lower, preferably 40 °C / sec or lower, and more preferably 20 °C / sec or lower. This is to suppress the deformation of the extruded material due to thermal contraction during cooling.

[0054] The target temperature in the die quenching process is 150°C or lower, preferably 100°C or lower, and more preferably 50°C or lower. After the die quenching process, the extruded material may be stored at room temperature, for example, 30°C or lower, until the aging process described later. [2-7. Aging process] In the aging process, artificial aging treatment is performed on the extruded material cooled in the die quenching process. By the aging process, Mg2Si-based precipitates grow in the extruded material, and the strength of the extruded material is improved.

[0055] The aging treatment temperature is 120°C or higher, preferably 140°C or higher, and more preferably 160°C or higher. This is because it becomes easier to precipitate Mg2Si-based precipitates in the extruded material. The aging treatment temperature is 240°C or lower, preferably 220°C or lower, and more preferably 200°C or lower. This is to suppress excessive growth of Mg2Si-based precipitates in the extruded material and improve the strength of the extruded material.

[0056] The aging treatment time is 2 hours or longer, preferably 4 hours or longer, and more preferably 5 hours or longer. This is to sufficiently precipitate Mg2Si-based precipitates. The aging treatment time is 48 hours or shorter, preferably 16 hours or shorter, and more preferably 8 hours or shorter. This is to suppress excessive growth of Mg2Si-based precipitates in the extruded material and improve the strength of the extruded material. Also, it is to improve the productivity of the extruded material.

Examples

[0057] Hereinafter, the aluminum alloy extruded material and its manufacturing method according to the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited thereto. [1. Production of aluminum alloy extruded material] An aluminum alloy composed of the elements shown in Table 1, Al, and inevitable impurities was used to produce a billet having a circular cross-section with a diameter of 156 mm by continuous casting. The obtained billet was subjected to a homogenization treatment at 560 °C for 14 hours. Then, the billet was cooled to 30 °C at a rate of 180 °C / h. Next, the cooled billet was heated to 500 °C. For reference, the portions with a gray background color in Table 1 are parts that deviate from the gist of the present invention.

[0058] [Table 1]

[0059] FIG. 8 is a view showing the extrusion cross-section (extrusion hole) of the die used in each example and each comparative example. In each example and comparative example, the extruded material 1 shown in FIGS. 9 and 10 is formed by this die D1. This extruded material 1 is a hollow extrusion profile in which an inner partition wall 12 that divides its interior (hollow portion) into two is integrally formed on the outer peripheral wall 11 having a rectangular cross-section.

[0060] And the die D1 shown in FIG. 8 includes an extrusion hole D10 having an outer peripheral wall forming hole D11 for forming the outer peripheral wall 11 of the extruded material 1 and an inner partition wall forming hole D12 for forming the inner partition wall 12. Further, in this die D1, the horizontal dimension L1 of the outer peripheral wall forming hole D11 is 50 mm, and the vertical dimension L2 is 50 mm. Furthermore, the width T1 of the outer peripheral wall forming hole D11 and the inner partition wall 12 is 2.5 mm, the inner curvature radius Ri in the outer peripheral wall forming hole D11 is 2.5 mm, and the outer curvature radius Ro is 5 mm.

[0061] In each of the examples and comparative examples, extrusion processing was performed on the billet heated to 500 °C using the die D1 of FIG. 8 above with an 8-inch direct extrusion machine (extrusion step). The extrusion speeds in each example and each comparative example in this extrusion step are shown in Table 1.

[0062] Immediately after the extrusion process, a die quenching process was performed, and the temperature of the extruded material was set to 30°C. The cooling rates in the die quenching processes of each example and each comparative example are shown in Table 1. An artificial aging treatment (aging process) at 180°C for 6 hours was performed on the extruded material after the die quenching process to obtain an aluminum alloy extruded material. In the following description, unless otherwise specified, the extruded material refers to the aluminum alloy extruded material obtained after the aging process. Further, the aluminum alloy extruded material after the aging treatment becomes the aluminum alloy extruded material according to the present invention. <2. Various Measurements of Aluminum Alloys> [2-1. Measurement of the Compression Deformation Initiation Stress of Aluminum Alloy at 500°C] Homogenization treatment was performed, and a test piece with a shape of φ8 mm × 12 mm was cut out from the center of the cooled billet. The longitudinal direction of the φ8 mm × 12 mm is the longitudinal direction (extrusion direction) of the billet. The cut test piece was heated to 500°C at a rate of 50°C / sec, held at 500°C for 10 min, compressed at 500°C at a strain rate of 0.10 / sec (the increase amount of the compression ratio per second), and compressed until the compression ratio ({the dimension reduced by compression (0 mm before the test start)} / the dimension before compression (12 mm)) reached 0.75 to obtain a stress-strain (compression ratio) diagram. The compression was carried out in a vacuum atmosphere. A Thermecmaster Z manufactured by Fuji Denpa Kikai Co., Ltd. was used as the testing machine.

[0063] Here, in the stress-strain diagram, the value that is the maximum value and the maximum value of the stress between a compression ratio of 0 and 0.30 was defined as the compression deformation initiation stress. Here, the maximum value is the value at which the load at that compression ratio is maximum within a range of ±0.050 from the value of that compression ratio.

[0064] The compression deformation initiation stresses measured for the aluminum alloys according to each example and each comparative example are shown in Table 1. [2-2. Extrudability] The extrudability in the above extrusion process (extrusion using a billet heated to 500°C) was determined based on the following criteria. "Good" ··· When the extrusion pressure is less than 25 MPa and there are no cracks and visually observable cracks in the extruded material. "Defective" refers to the case where at least one of the following conditions is met: the extrusion pressure is 25 MPa or more, cracks have occurred in the extruded material, and there are visible cracks in the extruded material.

[0065] Table 1 shows the evaluation results of the extrudability of the aluminum alloys according to each example and each comparative example. <3. Various Measurements of Aluminum Alloy Extruded Materials> Figures 9 and 10 are diagrams showing the aluminum alloy extruded materials produced in each example and each comparative example as described. In the following description, the directions indicated by L, LT, and ST are the directions indicated by the arrow symbols "L", "LT", and "ST" in Figures 9 and 10. 〔3-1. Area Ratio Occupied by Crystal Grains in the Cross-Section of the Extruded Material〕 For each extruded material, test pieces were cut out from the portion (side wall) having a thickness in the LT direction to a thickness of L: 10 mm, ST: 10 mm, and LT: 2 mm (the L-ST surface was shaved by 0.5 mm to a thickness of 2 mm). This test piece was resin-embedded, and after mirror-finishing the cross-section perpendicular to the L direction by buff polishing, etching treatment was performed with Barker electrolyte. The following analysis was performed on the polarized light micrograph of the treated cross-section using the image processing software ImageJ. The observation range was 1.95 mm × 2.60 mm, and the number of images was 2 for each example and each comparative example. An example of a photograph for observing crystal grains is as shown in Figure 1, which is a cross-sectional photograph of the extruded material of Example 1.

[0066] In each image, the area ratio occupied by crystal grains with an aspect ratio of 5.0 or less and a major axis length of 50 μm or more and 1000 μm or less was calculated. For particles at the edge of the image and partially outside the image, they were not included in either the area of each field of view or the area of the crystal grains. The area ratio occupied by the above crystal grains is a value expressed as a percentage of the total area of the two fields of view of the crystal grains satisfying the above conditions with respect to the total area of the two fields of view.

[0067] Table 1 shows the area ratio occupied by crystal grains measured for the extruded materials according to each example and each comparative example. 〔3-2. Presence Density of Si Particles〕 For each extruded material, test pieces were cut out from the portion (side wall) having a thickness in the LT direction to a thickness of L: 10 mm, ST: 10 mm, and LT: 2 mm (the L-ST surface was shaved by 0.5 mm to a thickness of 2 mm). The cut test pieces were cut perpendicular to the L direction (extrusion direction), and an observation cross-section was formed using a cross-section polisher manufactured by JEOL Ltd. Using a field emission scanning electron microscope JSM-7000F manufactured by JEOL Ltd., at a magnification of 10,000 times, an image of a field of 12.1 μm × 9.09 μm = 109.989 μm 2 Four images of the field were acquired, and EDX mapping analysis was performed.

[0068] Using the obtained mapping analysis results and the binarized images (e.g., Figure 3), the number N of Si particles having a particle size of 0.10 μm or more and 1.0 μm or less Si was counted for four fields. The number N of the counted Si particles Si was divided by the area of four fields to calculate the existence density of Si particles. The definition of the Si particles to be counted is as described above.

[0069] The existence densities of Si particles measured for the extruded materials according to each example and each comparative example are shown in Table 1. [3-3. Existence density of Zr-containing fine particles in the cross-section of the extruded material] For each extruded material, test pieces were cut out from the portion (side wall) having a thickness in the LT direction to a thickness of L: 10 mm, ST: 10 mm, and LT: 2 mm (the L-ST surface was shaved by 0.5 mm to a thickness of 2 mm). The cut test pieces were cut perpendicular to the L direction (extrusion direction), and an observation cross-section was formed using a cross-section polisher manufactured by JEOL Ltd. Using a field emission scanning electron microscope JSM-7000F manufactured by JEOL Ltd., at a magnification of 10,000 times, an image of a field of 12.1 μm × 9.09 μm = 109.989 μm 2 Four images of the field were acquired, and Zr-containing fine particles having a particle size of 0.010 μm or more and 1.0 μm or less were counted with reference to EDX line analysis (e.g., Figure 5) and the binarized images (e.g., Figure 6). The number N of Zr-containing fine particles for four fields Z was divided by the area of four fields to calculate the existence density of Zr-containing fine particles.

[0070] Table 1 shows the density of Zr-containing fine particles measured for the extruded materials according to each example and each comparative example. [3-4. Tensile strength and 0.2% proof stress] Measured from the aluminum alloy extruded materials obtained in each example and each comparative example by the method specified in JIS Z2241. The measurement was performed by cutting out No. 5 test pieces. Specifically, they were cut out 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 R of 30 mm along the extrusion direction (L direction). The tensile strength was calculated by performing a tensile test (conforming to JIS Z2241) at room temperature (24°C) of the tensile test piece at a crosshead speed of 2 mm / min, and the 0.2% proof stress was measured by the offset method.

[0071] Table 1 shows the tensile strength and 0.2% proof stress measured for the extruded materials according to each example and each comparative example. [3-5. Amount of deformation of the extruded material] The extruded material after the aging process was cut with a plane perpendicular to the extrusion direction. The angle between two adjacent sides of the outer shape of the cut cross-section of the extruded material was measured, and the absolute value θ [°] of the difference from 90° as shown in Fig. 10 was determined as the amount of deformation. Table 1 shows the measured amount of deformation θ for the extruded materials according to each example and each comparative example. [4. Evaluation] All of the aluminum alloys according to the examples are excellent in extrudability. Therefore, the productivity of the aluminum alloy extruded materials according to the examples can be improved, and as a result, the manufacturing cost of the extruded materials can be reduced. In addition, all of the aluminum alloy extruded materials according to the examples have high tensile strength and proof stress.

[0072] In the cross-section perpendicular to the extrusion direction, the extruded material according to Comparative Example 1 with a low density of Si particles had low tensile strength and proof stress.

[0073] The aluminum alloys according to Comparative Examples 2 and 3 have the same composition, do not contain Zr, and contain Mn and Cr. The aluminum alloys according to Comparative Examples 2 and 3 have a high compression deformation start stress at 500 °C, leading to a decrease in productivity. With this composition, when the extrusion speed was increased as in Comparative Example 3, cracks occurred in the extruded material (poor extrudability). On the other hand, if the extrusion speed was decreased as in Comparative Example 2, an extruded material could be obtained, but the productivity was low and the manufacturing cost increased.

[0074] The aluminum alloy according to Comparative Example 4 contains a small amount of Zr and contains Mn and Cr. The aluminum alloy according to Comparative Example 4 has a high compression deformation start stress at 500 °C, leading to a decrease in productivity. In Comparative Example 4, it was possible to produce an extruded material, but desired crystal grains could not be formed in the extruded material. This extruded material had low tensile strength and yield strength.

[0075] The aluminum alloy according to Comparative Example 5 has lower contents of Mn and Cr than the aluminum alloy of Comparative Example 4. The extruded material according to Comparative Example 5 had low tensile strength and yield strength.

[0076] The extruded material according to Comparative Example 6 with a low Si content had low tensile strength and yield strength.

[0077] The extruded material according to Comparative Example 7 with a low Cu content had low tensile strength and yield strength.

[0078] The aluminum alloy according to Comparative Example 8 has a high Cu content. The aluminum alloy according to Comparative Example 8 has a high compression deformation start stress at 500 °C and cracks occurred in the extruded material (poor extrudability).

[0079] The extruded material according to Comparative Example 9 with a low Mg content had low tensile strength and yield strength.

[0080] The aluminum alloy according to Comparative Example 10 has a high Mg content. The aluminum alloy according to Comparative Example 10 has a high compression deformation start stress at 500 °C and cracks occurred in the extruded material (poor extrudability).

[0081] The extruded material according to Comparative Example 11 that does not contain Zr had low yield strength.

[0082] Furthermore, consider Comparative Examples 1, 2, 6, 10, and 11 where the density of Si particles in the extruded material is low. The extruded materials according to Comparative Examples 1, 6, and 11 all have low tensile strength and yield strength. On the other hand, in Comparative Example 2, the tensile strength and yield strength are high, and it can be seen that by adjusting the composition of the aluminum alloy, these properties are improved, but the compression deformation start stress at 500 °C has increased, leading to a decrease in productivity (an increase in cost). Also, in Comparative Example 10, cracks occurred in the extruded material.

[0083] From this, it can be seen that an extruded material with a low density of Si particles cannot achieve both high productivity (low cost) and high tensile strength and high yield strength.

[0084] From the above, it can be seen that the aluminum alloy extruded material according to the present invention has low cost, high tensile strength, and high yield strength. Also, according to the manufacturing method of the aluminum alloy extruded material according to the present invention, it can be seen that an aluminum alloy extruded material with low cost, high tensile strength, and high yield strength can be obtained.

Industrial Applicability

[0085] The aluminum alloy extruded material of this invention can be used as a high-strength structural material.

Explanation of Symbols

[0086] 1: Aluminum alloy extruded material

Claims

1. An aluminum alloy extruded 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 on a mass basis, and the balance consists of Al and inevitable impurities, in a cross-section perpendicular to the extrusion direction, the area ratio 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 is 90.0% or more, In a cross-section perpendicular to the extrusion direction, the density of Si particles with a particle size of 0.010 μm or more and 1.0 μm or less is 50×10 ３ pieces / mm ２ or more and 150×10 ３ pieces / mm ２ or less, and an aluminum alloy extruded material having a compression deformation start stress at 500 °C of 25 MPa or less and a 0.2% proof stress of 285 MPa or more.

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 particles / μm ２ or more and 3.0 particles / μm ２ The aluminum alloy extruded material according to claim 1, wherein the density is as described above

3. The aluminum alloy extruded material according to claim 2, wherein the Zr-containing fine particles further contain Si.

4. In a cross-section perpendicular to the extrusion direction, the density of Si particles having a particle size of 0.010 μm or more and 1.0 μm or less is 53 × 10 ３ particles / mm ２ or more. The aluminum alloy extruded material according to any one of claims 1 to 3.

5. In a cross-section perpendicular to the extrusion direction, the density of Si particles having a particle size of 0.010 µm or more and 1.0 µm or less is 120 × 10 ３ pieces / mm ２ The aluminum alloy extruded material according to any one of claims 1 to 4, wherein the density is 120 × 10

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