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 Al-Fe-Si particles having a length of 0.10 μm or more and 30 μm or less is 8.5×103 pcs / mm2 or more and 20×103 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 sundries, 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, and titanium in an amount of 0.005 to 0.1% by mass. Further, copper is limited to 0.4% or less, manganese is limited to 0.30% or less, chromium is limited to 0.10% or less, and zirconium is limited to 0.10% or less. The balance is an aluminum alloy composed of aluminum and inevitable impurities, which is extruded and then quenched by air cooling. After that, 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: less than 0.15 to 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, with the balance being Al and inevitable impurities, having a yield strength of 350 MPa or more, the grain size of precipitates being regulated to 5 μm or less, and the area ratio of the fibrous structure in a cross section parallel to the hot extrusion direction being 95% or more.

[0005] Patent Document 3 describes an aluminum alloy extrusion material for cutting work, which has a component composition consisting of 0.8 to 2.0 mass% Si, 0.7 to 1.0 mass% Mg, 0.3 to 1.0 mass% Cu, Fe: ≦0.20 mass%, Mn: 0.2 to 0.8 mass%, Cr: 0.1 to 0.4 mass%, Mn + Cr: 0.3 to 0.9 mass%, and the balance being Al and unavoidable impurities, and further the amounts of Mg and Si satisfy the relational expression Mg / 1.73 + 0.2≦Si≦Mg / 1.73 + 1.6, and which has a fibrous metal structure. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-254809 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-074213 [Patent Document 3] Japanese Patent Application Publication No. 2017-110238 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, a process of introducing processing strain is incorporated after quenching, which requires more steps than normal processes and is likely to result in high costs.

[0008] In Patent Document 2, the material 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 moldability is insufficient, and in order to mold at a sufficient extrusion speed, the extrusion pressure needs to be increased, and distortion of the extruded product tends to increase. Therefore, maintaining the quality of the extruded material tends to result in high costs.

[0010] SUMMARY OF THE INVENTION An object of the present invention is to provide an aluminum alloy extrusion material that is low in cost and has high tensile strength and yield strength.

Means for Solving the Problems

[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 unavoidable 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 Al-Fe-Si particles with a length of 0.10 μm or more and 30 μm or less is 8.5×10 3 pieces / mm 2 or more and 20×10 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, for Al-Fe-Si particles with a length of 0.10 μm or more and 30 μm or less, the number-based 25% aspect ratio, which is the value at which it becomes 25% when counted from the one with the larger aspect ratio, is 3.00 or more and 6.50 or less. 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 Al-Fe-Si particles with a length of 0.10 μm or more and 30 μm or less is 15 × 10 3 particles / mm 2 or less. The aluminum alloy extruded material according to any one of the preceding items [1] to [4].

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

Advantages of the Invention

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

[0019] Since the aluminum alloy extruded material has the composition and crystal grains described in the preceding item [1] and has the density of Al-Fe-Si particles within the specified range, the proof stress and strength are greatly improved.

[0020] 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

[0021]

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[0022] Hereinafter, an embodiment of the present invention will be described.

[0023] 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 extrusions> 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 as described below, and the balance consists of Al and unavoidable impurities. 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 may have a chemical composition consisting of Si, Mg, Cu, Fe, Zr, Ti, and the balance (consisting of Al and unavoidable impurities).

[0024] 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. The aluminum alloy extruded material according to this embodiment has 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. Details of the Al-Fe-Si particles will be described later.

[0025] 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 mass% or more, preferably 1.03 mass% or more, and more preferably 1.05 mass% or more. Si easily forms a compound by interacting with Mg. 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.

[0026] The Si content in the extruded material may be 1.30 mass % or more, or 1.50 mass % or more.

[0027] The Si content in the extruded material is 2.00% by mass or less, and preferably 1.78% by mass or less. This is because it suppresses grain boundary precipitation of simple Si and further enhances the toughness of the extruded material. It is also because it reduces the extrusion pressure and improves productivity and yield.

[0028] The Si content in the extruded material may be 1.50 mass % or less, or 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 MgSi precipitates contributes to improving the strength of the extruded material.

[0029] 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, the quenching sensitivity is improved and the increase in pressure during extrusion is suppressed. Also, the generated MgSi precipitates are easily dissolved at low temperatures, which further improves the shape precision 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 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 improved strength.

[0030] The Cu content in the extruded material is 0.50 mass% or less, preferably 0.45 mass% or less, and more preferably 0.42 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 mass% or more, preferably 0.080 mass% or more, more preferably 0.10 mass% or more, and even more preferably 0.13 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.

[0031] The Fe content in the extruded material is 0.49 mass% or less, preferably 0.45 mass% or less, more preferably 0.35 mass% or less, even more preferably 0.30 mass% or less, even more preferably 0.27 mass% or less, and particularly preferably 0.24 mass% or less. This is because it suppresses the crystallization of acicular Al-Fe-Si-based compounds and further improves the extrusion moldability and 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 becomes the nuclei of crystal grains (details will be described later) generated during the extrusion process. The Zr content in the extruded material is 0.10 mass% or more, preferably 0.11 mass% or more, and more preferably 0.13 mass% or more. This is because it increases the number of Zr-containing fine particles, that is, the number of recrystallization nuclei, and suppresses the coarsening of crystal grains described later.

[0032] The Zr content in the extruded material is 0.25 mass% or less, preferably 0.20 mass% or less, and more preferably 0.17 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. ​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.

[0033] 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, facilitating the formation of the extrusion material by casting, and as a result, improves the productivity of the extruded material. [1-1-7.B] Like Ti, B is also effective in refining crystal grains, and its addition is thought to generate and disperse TiB2 particles. Furthermore, it is thought that the TiB2 particles act as solidification nuclei for 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.

[0034] 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] 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. The reason for this is to suppress cleavage fracture between crystal grains and improve the strength of the extruded material against shear stress.

[0035] Here, the above area ratio is a value measured in a range of 1.95 mm × 2.60 mm in two fields of view in a cross section perpendicular to the extrusion direction, that is, the area ratio of crystal grains for two fields of view. Also, for particles located at the end of the image and only partially imaged, they are not included in either the area of each field of view or the area of the crystal grains (that is, the area of each field of view 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 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. 〔1-3. Al-Fe-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, the Al-Fe-Si particles are particles confirmed based on the semi-quantitative analysis of the amount of each element in the EDX mapping analysis of the same field of view. Specifically, the Al-Fe-Si particles are particles having a Fe content of 5.0 mass% or more and 40 mass% or less, a Si content of 5.0 mass% or more and 40 mass% or less, and the balance being Al (which may include inevitable impurities) in this analysis. The white dots or rod-shaped portions in the photograph of FIG. 2 are Al-Fe-Si particles.

[0036] Figure 3 shows an image obtained by binarizing the photograph of Figure 2 and then inverting the black and white. The length of the Al-Fe-Si particles is 0.010 μm or more and 30 μm or less (particles with a size outside this range are not the Al-Fe-Si particles in the present 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 two longest points in the black portion of the binarized image. When the black and white are not inverted in the binarized image, the length of the Al-Fe-Si particles is the distance between the two longest points in the white portion.

[0037] The density of Al-Fe-Si particles present 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.

[0038] The density of Al-Fe-Si particles present 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 enhanced.

[0039] The number of Al-Fe-Si particles is counted in 4 fields of view at a magnification of 1,000 times using a field emission scanning electron microscope JSM-7000F manufactured by JEOL Ltd., with a field of view of 121 μm × 90.9 μm = 10998.9 μm 2 . The density of Al-Fe-Si particles present is calculated by dividing the total number N F of Al-Fe-Si particles in the 4 fields of view by the area of the 4 fields of view. That is, the density of Al-Fe-Si particles present is N F / (4 × 10998.9) [particles / μm 2 = 106 ×N F / (4 × 10998.9) [particles / mm 2 results in

[0040] The number-based 25% aspect ratio of Al-Fe-Si particles is the value obtained by rounding off the decimal part, which is 25% when counting from the Al-Fe-Si particles with aspect ratios greater than 0.10 μm and less than 30 μm in length in a cross-section perpendicular to the extrusion direction. The aspect ratio of Al-Fe-Si particles is measured based on a binarized image.

[0041] For example, in the above four fields of view, if there are 100 Al-Fe-Si particles that meet the above conditions, the number-based 25% aspect ratio of Al-Fe-Si particles is the 25th value when counting from the particles with larger aspect ratios. If there are 123 particles, it is the 31st value (rounded off from 30.3).

[0042] 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 more, more preferably 3.70 or more, and even more preferably 4.50 or more. This is to suppress recrystallization more than necessary due to the pinning effect.

[0043] In a cross-section perpendicular to the extrusion direction, the number-based 25% aspect ratio of 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〕 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 a size 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.

[0044] Figure 5 is a diagram showing an example (Example 1) of a line analysis diagram of EDX 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 upper SEM photograph in 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.

[0045] 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.

[0046] Figure 6 is a diagram showing an image obtained by binarizing the photograph in Figure 4 and then inverting the black and white. The particle size of the Zr-containing fine particles is determined based on the binarized SEM image. In Figure 6, since the 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 the 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.

[0047] The density of Zr-containing fine particles in a cross-section perpendicular to the extrusion direction of the extruded material is 0.30 particles / μm 2 or more, preferably 0.40 particles / μm 2 or more, more preferably 0.50 particles / μm 2 or more is even more preferable. This is to suppress the coarsening of the above-mentioned crystal grains.

[0048] The density of Zr-containing fine particles in a cross-section perpendicular to the extrusion direction of the extruded material is 3.0 particles / μm 2 or less, preferably 2.0 particles / μm 2 or less, more preferably 1.0 particles / μm 2 or less is even more preferable. This is to more surely generate the above-mentioned crystal grains.

[0049] The number of Zr-containing fine particles is counted in 4 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 4 fields of view Z is divided by the area of 4 fields of view to calculate the density of Zr-containing fine particles. That is, the density of Zr-containing fine particles is N Z / (4 × 109.989) [particles / μm 2 . [1-5. Mechanical properties of aluminum alloy extruded materials] The compression deformation start stress at 500 °C of the aluminum extruded material according to this embodiment 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.

[0050] 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).

[0051] 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 method for manufacturing an aluminum alloy extruded material according to an embodiment of the present invention. Hereinafter, an example of a method for manufacturing 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.

[0052] 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 necessary. If the material after homogenization is available, the steps up to the homogenization step are not necessary. [2-1. Melting Step] In the melting step, a molten metal of an aluminum alloy is prepared. The chemical composition of the molten metal is preferably the same as the chemical composition of the aluminum alloy extruded material to be obtained, and for each element contained in the aluminum alloy extruded material, it is as described above. [2-2. Casting Step] 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 thereof 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. By the homogenization process, an extruded material with high strength can be obtained. The chemical composition of the aluminum alloy (billet) used in the homogenization process is preferably the same as the chemical composition of the aluminum alloy extruded material to be obtained, and each element contained in the aluminum alloy extruded material is as described above.

[0053] 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. 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 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, the coarsening of the particles of the intermetallic compound is suppressed, and the mechanical properties of the extruded material are improved.

[0054] The time of the homogenization treatment is preferably 3 hours or more, more preferably 8 hours or more, and even more preferably 12 hours or more. 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 time of the homogenization treatment is preferably 24 hours or less, more preferably 20 hours or less, and even more preferably 18 hours or less. The reason for this is to suppress the coarsening of the particles of the intermetallic compound and to improve the mechanical properties of the extruded material.

[0055] After homogenization treatment, it is preferable to cool the billet. The temperature of the billet after cooling is preferably 150 °C or lower, more preferably 100 °C or lower. The billet may be cooled to 50 °C or lower 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 higher, more preferably 150 °C / h or higher. 〔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.

[0056] The heating temperature is 350 °C or higher, preferably 400 °C or higher, more preferably 450 °C or higher. The reason for this is to reduce the deformation resistance of the billet and lower the extrusion pressure.

[0057] The heating temperature preferably does not exceed the solidus temperature of the aluminum alloy constituting the billet. The reason for 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, etc. 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 the present 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 the metal structure having the above-mentioned crystal grains. Also, this 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 the extrusion process (extrusion process) is cooled. The cooling method is not particularly limited, and examples include water cooling, mist cooling, fan air cooling, and natural cooling. By the die quenching process, a supersaturated solid solution is formed. 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, this is because the productivity of the extruded material is improved.

[0058] The cooling rate is 80 °C / sec or less, preferably 40 °C / sec or less, and more preferably 20 °C / sec or less. This is to suppress the deformation of the extruded material due to thermal shrinkage during cooling.

[0059] The target temperature of the die quenching process is 150 °C or less, preferably 100 °C or less, and more preferably 50 °C or less. After the die quenching process, the extruded material may be stored at room temperature, for example, 30 °C or less, 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.

[0060] 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.

[0061] 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

[0062] 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. Preparation of Aluminum Alloy Extruded Material> Using an aluminum alloy composed of the elements shown in Table 1, Al and inevitable impurities, a billet having a circular cross-section with a diameter of 156 mm was produced 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 parts with a gray background color in Table 1 deviate from the gist of the present invention.

[0063]

Table 1

[0064] FIG. 8 is a diagram showing an extruded 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-shaped extruded 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.

[0065] 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. Also, 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. Further, the width T1 of the outer peripheral wall forming hole D11 and the inner partition wall 12 is 2.5 mm, the inner radius of curvature Ri in the outer peripheral wall forming hole D11 is 2.5 mm, and the outer radius of curvature Ro is 5 mm.

[0066] In each of the Examples and Comparative Examples, extrusion was performed using the die D1 of FIG. 8 on a billet heated to 500° C. 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.

[0067] Immediately after the extrusion step, a die quench step was performed to set the temperature of the extruded material to 30° C. The cooling rates in the die quench steps of each Example and each Comparative Example are shown in Table 1. An artificial aging treatment (aging step) was performed on the extruded material after the die quench step at 180° C. for 6 hours to obtain an aluminum alloy extruded material. In the following description, unless otherwise specified, the extruded material is the aluminum alloy extruded material obtained after the aging step. Also, 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 Compressive Deformation Initiation Stress of Aluminum Alloy at 500° C.〕 Homogenization treatment was performed, and specimens with a size of φ8 mm × 12 mm were cut out from the center of the cooled billet. Note that the longitudinal direction of the φ8 mm × 12 mm specimen is the longitudinal direction (extrusion direction) of the billet. The cut specimens were heated to 500°C at a rate of 50°C / sec, held at 500°C for 10 minutes, compressed at 500°C with a strain rate of 0.10 / sec (the increase in the compression ratio per second), and a compression ratio of ({the dimension reduced by compression (0 mm before the start of the test)} / the dimension before compression (12 mm)) of 0.75 was reached to obtain a stress-strain (compression ratio) diagram. The compression was carried out in a vacuum atmosphere. A Servomech Master Z manufactured by Fuji Denpa Koki Co., Ltd. was used as the testing machine.

[0068] Here, in the stress-strain diagram, the value that is the maximum and the largest value of the stress between a compression ratio of 0 and 0.30 was defined as the starting stress of compression deformation. Here, the maximum value is the value at which the load at that compression ratio is maximized within a range of ±0.050 from that compression ratio value.

[0069] Table 1 shows the starting stress of compression deformation measured for the aluminum alloys according to each example and each comparative example. [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 or visible cracks in the extruded material. "Poor" ··· When at least one of the following conditions is met: the extrusion pressure is 25 MPa or more, cracks have occurred in the extruded material, or there are visible cracks in the extruded material.

[0070] Table 1 shows the evaluation results of the extrudability for 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 of crystal grains in the cross section of extruded material] For each extrusion, test specimens with thicknesses of L: 10 mm, LT: 10 mm, and ST: 2 mm were cut from the thick portion (sidewall) in the ST direction (the L-LT plane was removed by 0.5 mm to obtain a thickness of 2 mm). These test specimens 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 of 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 × 2.60 mm, and two images were taken for each example and comparative example. An example of a photograph for observing the crystal grains is shown in Figure 1, which is a cross-sectional photograph of the extrusion of Example 1.

[0071] In each image, the area percentage of crystal grains with an aspect ratio of 5.0 or less and a length in the major axis direction of 50 μm to 1000 μm was calculated. Note that particles at the edge of the image, with some outside the image, were not included in either the area of each field or the area of the crystal grains. The area percentage of the crystal grains is the percentage of the total area of the two fields of view of crystal grains that meet the above conditions relative to the total area of the two fields of view.

[0072] Table 1 shows the area ratios occupied by crystal grains measured for the extruded materials of each example and each comparative example. [3-2. Measurements on Al-Fe-Si particles] (Density of Al-Fe-Si particles) For each extrusion, test pieces were cut out from the part (side wall) with thickness in the LT direction to thicknesses 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. A JEOL field emission scanning electron microscope JSM-7000F was used to measure the area of 121 μm × 90.9 μm = 10998.9 μm at a magnification of 1,000 times. 2 Four images of the field of view were acquired and subjected to EDX mapping analysis.

[0073] Using the obtained mapping analysis results and the binarized image (e.g., Figure 3), the number N of Al-Fe-Si particles with a length of 0.10 μm or more and 30 μm or less F was counted for four fields of view. The counted number N of Al-Fe-Si particles F was divided by the area of four fields of view to calculate the density of Al-Fe-Si particle presence. Note that the definition of the Al-Fe-Si particles to be counted is as described above.

[0074] Table 1 shows the density of Al-Fe-Si particle presence measured for the extruded materials according to each example and each comparative example. (Number-based 25% aspect ratio of Al-Fe-Si particles) For each extruded material, for the aspect ratio of the Al-Fe-Si particles targeted for counting, the value (number-based 25% aspect ratio) that becomes 25% (rounded off at the decimal point) when counted from the larger one was determined.

[0075] Table 1 shows the number-based 25% aspect ratio of Al-Fe-Si particles measured for the extruded materials according to each example and each comparative example. [3-3. 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 ST direction to a thickness of L: 10 mm, LT: 10 mm, and ST: 2 mm (the L-LT 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, four images of a field of view of 12.1 μm × 9.09 μm = 109.989 μm 2 were obtained, and Zr-containing fine particles with a particle size of 0.01 μm or more and 1.0 μm or less were counted while referring to EDX line analysis (e.g., Figure 5) and the binarized image (e.g., Figure 6). The number N of Zr-containing fine particles for four fields of view Z was divided by the area of four fields of view to calculate the density of Zr-containing fine particle presence.

[0076] 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 carried out by cutting out No. 5 test pieces. Specifically, it was 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 (in accordance with 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.

[0077] 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 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.

[0078] In the cross-section perpendicular to the extrusion direction, the extruded material according to Comparative Example 1 with a low density of Al-Fe-Si particles had low tensile strength and proof stress.

[0079] 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 initiation 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.

[0080] 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 initiation 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. Further, the extruded material according to Comparative Example 4 has 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.

[0081] The aluminum alloy according to Comparative Example 5 has lower contents of Mn and Cr than the aluminum alloy of Comparative Example 4. Further, the extruded material according to Comparative Example 5 has a low density of Al-Fe-Si particles in a cross section perpendicular to the extrusion direction. The extruded material according to Comparative Example 5 had low tensile strength and yield strength.

[0082] The extruded material according to Comparative Example 6, which has a low Si content and a low density of Al-Fe-Si particles, had low tensile strength and yield strength.

[0083] The extruded material according to Comparative Example 7, which has a low Cu content and a low density of Al-Fe-Si particles, had low tensile strength and yield strength.

[0084] 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 initiation stress at 500 °C and cracks occurred in the extruded material (poor extrudability).

[0085] The extruded material according to Comparative Example 9, which has a low Mg content, had low tensile strength and yield strength.

[0086] 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).

[0087] The extruded material according to Comparative Example 11, which did not contain Zr and had a low density of Al-Fe-Si particles, had low yield strength.

[0088] From the above, it is clear that the aluminum alloy extrusion material according to the present invention has high tensile strength and proof stress at low cost. Furthermore, it is clear that the manufacturing method of the aluminum alloy extrusion material according to the present invention makes it possible to obtain an aluminum alloy extrusion material having high tensile strength and proof stress at low cost. [Industrial Applicability]

[0089] The aluminum alloy extrusion material of the present invention can be used as a high-strength structural material. [Explanation of symbols]

[0090] 1: Aluminum alloy extrusion

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 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, 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, for Al—Fe—Si particles having a length of 0.10 μm or more and 30 μm or less, the number-based 25% aspect ratio, which is the value at which it becomes 25% when counted from the larger aspect ratio, is 3.00 or more and 6.50 or less. 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 Al—Fe—Si particles having a length of 0.10 μm or more and 30 μm or less is 15×10 ３ pieces / mm ２ or less. The aluminum alloy extruded material according to any one of claims 1 to 4.

Images