Aluminum alloy extruded material

Abstract

To provide an aluminum alloy extruded material whose strength deterioration can be sufficiently suppressed even when the contents of Fe and Si are increased by reusing aluminum scrap.SOLUTION: Any one or more selected from the group consisting of Zn:5.70 mass% or more and 6.80 mass% or less, Mg: 1.10 mass% or more and 1.55 mass% or less, Cu: 0.10 mass% or more and 0.40 mass% or less, Ti: 0.05 mass% or less (excluding 0 mass%), and B: 0.02 mass% or less (excluding 0 mass%), Zr: 0.10 mass% or more and 0.20 mass% or less, Cr: 0.10 mass% or less (including 0 mass%), Fe: more than 0.15 mass% and 1.05 mass% or less, and Si: 0.05 mass% or more and 0.45 mass% or less, with the balance being Al and inevitable impurities, An aluminum alloy extruded material comprising Al-Fe-based crystallized products, wherein arithmetic average circle equivalent diameters of the Al-Fe-based crystallized products are 1.30 μm or more and 1.60 μm or less, and number densities of the Al-Fe-based crystallized products are 3.0 * 10 - 3 pieces / μ m2 or more and 1.7 * 10 - 2 pieces / μ m2 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to aluminum alloy extrusions, and in particular to Al-Zn-Mg-based alloy extrusions (i.e., 7000-series aluminum alloy extrusions). [Background technology]

[0002] 7000 series aluminum alloy extrusions have excellent strength and are therefore used for automotive frame components such as bumpers, etc. Patent documents 1 to 3 include prior art documents relating to 7000 series aluminum alloy extrusions. Patent Documents 1 and 2 describe that strength is improved mainly by Zn and Mg (MgZn2 precipitates). Patent Document 3 describes that in addition to adding components such as Zn and Mg that improve strength, Al3Zr dispersoids are precipitated to improve strength. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 2927445 [Patent Document 2] Patent No. 5204793 [Patent Document 3] Patent No. 6971151 Summary of the Invention [Problem to be solved by the invention]

[0004] Currently, in light of resource depletion, recycling of various things is progressing, and recycling of metals, which are consumed in large quantities, has also been carried out for some time. In response to the global trend toward promoting carbon neutrality, the reuse of aluminum scrap containing large amounts of Fe and Si in 7000 series aluminum alloy extrusions has been considered. However, as a result of studies by the present inventors, it was found that increasing the blending amount of aluminum scrap inevitably increases the Fe and Si contents, which in turn reduces strength (tensile strength and yield strength).

[0005] The present disclosure has been made in view of the above circumstances, and one of its objectives is to provide an aluminum alloy extrusion material that can sufficiently suppress a decrease in strength even when the Fe and Si contents are increased by reusing aluminum scrap. [Means for solving the problem]

[0006] Aspect 1 of the present invention is Zn: 5.70 mass% or more and 6.80 mass% or less, Mg: 1.10% by mass or more and 1.55% by mass or less, Cu: 0.10 mass% or more and 0.40 mass% or less, one or more selected from the group consisting of Ti: 0.05% by mass or less (excluding 0% by mass) and B: 0.02% by mass or less (excluding 0% by mass); Zr: 0.10% by mass or more and 0.20% by mass or less, Cr: 0.10% by mass or less (including 0% by mass), Fe: more than 0.15 mass% and not more than 1.05 mass%; and Si: 0.05% by mass or more and 0.45% by mass or less, and the balance being Al and inevitable impurities, Contains Al-Fe crystallized substances, The Al-Fe-based crystallized particles have an arithmetic mean equivalent circle diameter of 1.30 μm or more and 1.60 μm or less, The number density of the Al-Fe crystallized particles is 3.0 × 10 -3 pieces / μm 2 Over 1.7 x 10 -2 pieces / μm 2 The following is an aluminum alloy extrusion material.

[0007] Aspect 2 of the present invention is Aspect 1 is the aluminum alloy extrusion material according to aspect 1, wherein the Fe content is more than 0.15 mass % and not more than 0.60 mass %, and the Si content is 0.05 mass % or more and 0.20 mass % or less. [Effects of the Invention]

[0008] According to an embodiment of the present invention, it is possible to provide an aluminum alloy extrusion material that can sufficiently suppress a decrease in strength even if the Fe and Si contents increase due to the reuse of aluminum scrap. [Brief explanation of the drawings]

[0009] [Figure 1] Figure 1 shows a backscattered electron image taken by SEM of the aluminum alloy extrusion material of Test No. 1-2. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors have conducted research from various angles in order to realize an aluminum alloy extrusion material that can sufficiently suppress a decrease in strength even when the Fe and Si contents are increased by reusing aluminum scrap.

[0011] It is known that the strength of 7000 series aluminum alloys is improved by forming MgZn2 (precipitates). However, the inventors' studies have revealed that even if a predetermined amount of Mg and Zn is contained so that MgZn2 is formed, the strength decreases as the Fe and Si contents increase. The inventors believe that the reason for this is that, particularly with an increase in the Si content, a large amount of Mg2Si (crystallized precipitates) may be formed during casting, reducing the amount of solute Mg and preventing the sufficient formation of MgZn2, which is effective for precipitation strengthening.

[0012] Therefore, the present inventors focused on Al-Fe-based crystallized products (crystallized products containing Al and Fe and / or crystallized products containing Al, Fe, and Si). The present inventors considered that, since Al-Fe-based crystallized products may also contain Si, the formation of Mg2Si (crystallized product) can be effectively suppressed by the Al-Fe-based crystallized products, and the shortage of MgZn2 can be suppressed. The inventors have also realized an aluminum alloy extrusion material that can sufficiently suppress a decrease in strength even when the Fe and Si contents increase due to the reuse of aluminum scrap, by appropriately controlling the size and number density of Al-Fe-based crystallized particles. The details of each requirement stipulated in this embodiment are shown below.

[0013] <Component composition> The aluminum alloy extrusion material according to this embodiment is Zn: 5.70 mass% or more and 6.80 mass% or less, Mg: 1.10% by mass or more and 1.55% by mass or less, Cu: 0.10 mass% or more and 0.40 mass% or less, one or more selected from the group consisting of Ti: 0.05% by mass or less (excluding 0% by mass) and B: 0.02% by mass or less (excluding 0% by mass); Zr: 0.10% by mass or more and 0.20% by mass or less, Cr: 0.10% by mass or less (including 0% by mass), Fe: more than 0.15 mass% and not more than 1.05 mass%; and Si: 0.05 mass% or more and 0.45 mass% or less and the remainder is Al and inevitable impurities. Each component will be described in detail below.

[0014] (Zn: 5.70 mass% or more and 6.80 mass% or less) Zn, together with Mg, is an element that improves the strength of an aluminum alloy extrusion material. If the Zn content is less than 5.70% by mass, the strength cannot be sufficiently improved. On the other hand, if the Zn content exceeds 6.80% by mass, the elongation decreases and the workability becomes insufficient. Therefore, the Zn content is set to 5.70 to 6.80% by mass.

[0015] (Mg: 1.10 mass% or more and 1.55 mass% or less) Mg, together with Zn, is an element that improves the strength of aluminum alloy extrusions. If the Mg content is less than 1.10% by mass, the strength cannot be sufficiently improved. On the other hand, if the Mg content exceeds 1.55% by mass, the elongation decreases and the weldability becomes insufficient. Therefore, the Mg content is set to 1.10 to 1.55% by mass.

[0016] (Cu: 0.10 mass% or more and 0.40 mass% or less) Cu has the effect of improving the strength and stress corrosion cracking resistance of aluminum alloy extrusions. If the Cu content is less than 0.10 mass%, these effects cannot be sufficiently obtained. On the other hand, if the Cu content exceeds 0.40 mass%, the quenching sensitivity increases, resulting in a decrease in strength. Therefore, the Cu content is set to 0.10 to 0.40 mass%. More preferably, the Cu content is 0.10 mass% or more and 0.35 mass% or less.

[0017] (one or more selected from the group consisting of Ti: 0.05% by mass or less (excluding 0% by mass), and B: 0.02% by mass or less (excluding 0% by mass)) Ti and B are elements added to refine the ingot. Therefore, the aluminum alloy extrusion material of this embodiment contains more than 0% by mass of any one or more elements selected from the group consisting of Ti and B. The Ti content is preferably 0.01% by mass or more. The B content is preferably 0.002% by mass or more. On the other hand, if the Ti content exceeds 0.05% by mass and / or the B content exceeds 0.02% by mass, the grain refinement effect saturates, and further addition of these elements does not provide any further refinement effect. Therefore, the aluminum alloy extrusion material of this embodiment contains one or more elements selected from the group consisting of Ti: 0.05% by mass or less (excluding 0% by mass) and B: 0.02% by mass or less (excluding 0% by mass).

[0018] (Zr: 0.10 mass% or more and 0.20 mass% or less) Zr has the effect of suppressing recrystallization of aluminum alloy extrusions and improving stress corrosion cracking resistance. If the Zr content is less than 0.10% by mass, this effect cannot be fully achieved. On the other hand, if the Zr content exceeds 0.20% by mass, extrusion properties decrease and quench sensitivity increases, resulting in a decrease in strength. Therefore, the Zr content is set to 0.10 to 0.20% by mass.

[0019] (Cr: 0.10% by mass or less (including 0% by mass)) Cr is an optional additive element. Cr has the effect of suppressing recrystallization of the aluminum alloy extrusion material and improving stress corrosion cracking resistance. Therefore, when Cr is added, its content is preferably 0.02% by mass or more. On the other hand, if the Cr content exceeds 0.10% by mass, the above effect saturates. Therefore, when Cr is added, its content is set to 0.10% by mass or less. In this specification, "including 0% by mass" means that it includes embodiments in which it is not intentionally added, i.e., the content is below the unavoidable impurity level (it does not exclude cases in which it is intentionally added).

[0020] (Fe: more than 0.15 mass% and 1.05 mass% or less) Fe, along with Si, is a major impurity in aluminum alloys. In this embodiment, the Fe content is set to more than 0.15% by mass to enable reuse of aluminum scrap. From the viewpoint of enabling reuse of a larger amount of aluminum scrap, the Fe content is preferably set to more than 0.50% by mass, and more preferably to 0.60% by mass or more. On the other hand, in order to prevent a significant deterioration in the properties of the aluminum alloy extrusion material, the Fe content needs to be 1.05% by mass or less. From the viewpoint of further preventing the deterioration in the properties of the aluminum alloy extrusion material, the Fe content is preferably 1.00% by mass or less, more preferably 0.80% by mass or less, even more preferably 0.60% by mass or less, and even more preferably 0.50% by mass or less.

[0021] (Si: 0.05 mass% or more and 0.45 mass% or less) Si, along with Fe, is a major impurity in aluminum alloys. In this embodiment, the Si content is set to 0.05% by mass or more to enable recycling of aluminum scrap. From the viewpoint of recycling as much aluminum scrap as possible, the Si content is preferably set to more than 0.30% by mass, and more preferably set to 0.35% by mass or more. On the other hand, if the Si content is increased, coarse MgSi crystallizes during casting, which may significantly deteriorate the mechanical properties of the aluminum alloy extrusion material. Therefore, the Si content is set to 0.45% by mass or less. From the viewpoint of further suppressing deterioration of the mechanical properties of the aluminum alloy extrusion material, the Si content is preferably set to 0.20% by mass or less, and more preferably set to 0.15% by mass or less.

[0022] The aluminum alloy extruded material according to this embodiment contains the above component composition. In one embodiment of the present invention, the balance is preferably Al and inevitable impurities. As inevitable impurities, the inclusion of elements brought in depending on the situation of raw materials, materials, manufacturing equipment, etc. is allowed. For example, elements such as Fe and Si are usually preferably contained in smaller amounts. Therefore, although they are inevitable impurities, there are elements whose composition ranges are separately defined as described above. For this reason, in this specification, the term "inevitable impurities" is a concept excluding elements whose composition ranges are separately defined. As inevitable impurities, for example, Mn, Pb, Bi, Sn, etc. may each be contained at 0.01 mass% or less. The total amount of inevitable impurities may be, for example, 0.10 mass% or less.

[0023] <Al-Fe-based precipitate> The aluminum alloy extruded material according to this embodiment contains Al-Fe-based precipitates (precipitates containing Al and Fe and / or precipitates containing Al, Fe, and Si). In this embodiment, the arithmetic mean circle equivalent diameter of the Al-Fe-based precipitates is 1.30 μm or more and 1.60 μm or less, and the number density of the Al-Fe-based precipitates is 3.0×10 -3 pieces / μm 2 or more and 1.7×10 -2 pieces / μm 2 or less. By setting it within this range, the formation of Mg2Si (precipitates) can be effectively suppressed, and the decrease in the strength of the aluminum alloy extruded material can be suppressed. Also, it becomes possible to suppress the decrease in the elongation of the aluminum alloy extruded material. If the arithmetic mean circle equivalent diameter of the Al-Fe-based precipitates is less than 1.30 μm and / or the number density of the Al-Fe-based precipitates is less than 3.0×10 -3 pieces / μm 2 the formation of Mg2Si (precipitates) cannot be sufficiently suppressed. The arithmetic mean circle equivalent diameter of the Al-Fe-based precipitates is preferably 1.40 μm or more. The number density of the Al-Fe-based precipitates is preferably 4.0×10 -3 pieces / μm 2 or more. On the other hand, the arithmetic mean circle equivalent diameter of the Al-Fe crystallized particles is more than 1.60 μm and / or the number density of the Al-Fe crystallized particles is 1.7 × 10 -2 pieces / μm 2 If the content exceeds 1.50 μm, the Al-Fe crystals will be excessively abundant, which may significantly reduce the mechanical properties. The arithmetic mean equivalent circle diameter of the Al-Fe crystals is preferably 1.50 μm or less. The number density of the Al-Fe crystals is preferably 1.5×10 -2 pieces / μm 2 The following is the result. The arithmetic mean equivalent circle diameter and number density of the Al-Fe crystallized particles can be measured by the method described in the Examples below.

[0024] <Manufacturing method> The method for manufacturing an aluminum alloy extrusion material according to this embodiment includes the steps of: (a) a step of heating and melting an aluminum alloy having a predetermined component composition to 700°C or higher and performing DC casting to obtain a billet, wherein, after the heating and melting, the average cooling rate from 660°C to 560°C is 2 to 6°C / sec, and the cooling rate from 559°C to 200°C is more than 6°C / sec; (b) After step (a), the billet is heated to 450 to 500°C and extruded at an extrusion ratio (cross-sectional area after extrusion / cross-sectional area before extrusion) of 30 to 70% and an extrusion speed of 1 to 5 m / min. Each step will be described below.

[0025] [(a) DC casting process] An aluminum alloy having the predetermined component composition is prepared. This aluminum alloy is heated to 700°C or higher, melted, and DC cast. The upper limit of the temperature during melting can be, for example, 750°C or lower. After melting, the alloy is cooled slowly from 660°C to 560°C at an average cooling rate of 2°C / sec to 6°C / sec, and then rapidly cooled from 559°C to 200°C at a rate of more than 6°C / sec. By performing this slow cooling from 660°C to 560°C, Al-Fe-based crystals can be sufficiently crystallized. Because crystallization of Al-Fe-based crystals and Mg2Si occurs simultaneously below 559°C (up to 200°C), Mg can be solid-dissolved by performing this rapid cooling in a manner that prevents Mg2Si from crystallizing.

[0026] After DC casting and before extrusion, as described below, the billet may be subjected to a homogenization treatment step in which it is heated to 450 to 550°C, if necessary. The heating time is not particularly limited, but may be, for example, 1 hour or more. After heating, the billet may be appropriately cooled, for example, by air cooling.

[0027] [(b) Extrusion processing process] After step (a), the billet is heated to 450 to 500°C and extruded at an extrusion ratio (cross-sectional area after extrusion / cross-sectional area before extrusion) of 30 to 70% and an extrusion speed of 1 to 5 m / min. This produces an aluminum alloy extrusion material having Al-Fe crystallized particles of a desired size and number density. There are no particular limitations on the shape of the extruded material after extrusion.

[0028] After step (b), the steel may be appropriately quenched by a known method, for example, by air cooling, water cooling, mist, etc. Furthermore, an aging treatment step may be carried out after the quenching step.

[0029] The method for manufacturing an aluminum alloy extrusion material according to an embodiment of the present invention may include other steps without departing from the scope of the present disclosure. [Example]

[0030] Hereinafter, embodiments of the present invention will be described more specifically with reference to examples. The embodiments of the present invention are not limited by the following examples, and can be implemented with appropriate modifications within the scope that can conform to the foregoing and following gists, and all of them are included in the technical scope of the embodiments of the present invention.

Example

[0031] As shown in Table 1, five aluminum alloys having the same component composition except for Fe and Si were each heated and melted at 700°C or higher and 750°C or lower, and then DC casting was performed to obtain billets. The casting speed during DC casting was 80 mm / min, the average cooling rate from 660°C to 560°C after heating and melting was 2 - 6°C / sec, and the cooling rate from 559°C to 200°C was more than 6°C / sec. Then, the billets were heated to 470°C for homogenization treatment. The heating time was 6 hours. After the homogenization treatment, they were air-cooled with a fan. Thereafter, the billets were heated to 470°C to obtain square pipes having a rectangular hollow cross-section with a length (H) of 54 mm × width (W) of 70 mm and a wall thickness of 2 mm. The extrusion ratio (cross-sectional area after extrusion / cross-sectional area before extrusion) was 41.9%, and the extrusion speed was 4 m / min. After the extrusion process, quenching was performed by air-cooling at an average cooling rate of 200°C / min. Thereafter, as the aging treatment, heat treatment of 90°C × 3 hours + 155°C × 8 hours was performed to obtain aluminum alloy extruded materials of Test Nos. 1-1 to 1-5. In Table 1, "Tr." is an abbreviation for Trace, meaning a trace amount, and it is not an intentionally added element and can be less than 0.01 mass%, for example.

[0032]

Table 1

[0033] Observation of Al-Fe-based precipitates and tensile tests were performed on the obtained aluminum alloy extruded materials.

[0034] <Observation of Al-Fe-based precipitates> Rectangular measurement samples (2 mm in height (H) × 15 mm in width (W) × 15 mm in length in the extrusion direction) were taken from the center of the transverse and extrusion directions of the aluminum alloy extrusions of Test Nos. 1-1 to 1-5. Backscattered electron images of the center of the longitudinal and extrusion directions of the measurement samples were obtained using an SEM (JEOL Ltd., JSM-IT100) at an acceleration voltage of 20.0 kV and a magnification of 300x. As an example, a backscattered electron image of the aluminum alloy extrusion material of Test No. 1-2 is shown in Figure 1. In this example, the white areas in the backscattered electron image were Al-Fe-based crystallized products (crystallized products containing Al and Fe and / or crystallized products containing Al, Fe, and Si). From the SEM images, the arithmetic mean equivalent circular diameter and the number per unit area of ​​the white areas in the backscattered electron images were calculated using an image measuring device (Winroof 2018 ver4.7.0). The measurement area was 1.2 × 10 5 μm 2 The smallest circle-equivalent diameter of the white area actually observed was 0.67 μm. In this embodiment, even if Al-Fe-based crystallized particles having an equivalent circle diameter of less than 0.67 μm are present, such small Al-Fe-based crystallized particles are considered not to contribute to the effects of this embodiment. Therefore, the arithmetic mean equivalent circle diameter and number density of the Al-Fe-based crystallized particles according to this embodiment are calculated using Al-Fe-based crystallized particles having an equivalent circle diameter of 0.67 μm or more.

[0035] <Tensile test> Two JIS No. 5 test pieces were cut from the aluminum alloy extrusion so that the tensile direction was parallel to the extrusion direction (L direction), and tensile tests were conducted in accordance with the metallic material tensile test method specified in JIS Z2241:2022 to measure tensile strength, yield strength, and elongation. Elongation was measured using the butt joint method. The results are shown in Table 2.

[0036] [Table 2]

[0037] The following can be seen from Table 2. Test No. 1-1 is a reference example, and the Fe content and Si content are at the normal impurity level (i.e., it is not intended to reuse aluminum scrap), and it has high tensile strength and yield strength. Compared with Test No. 1-1, Test Nos. 1-2 to 1-4 met all the requirements defined in this embodiment, and despite the increased Fe and Si contents, the strength degradation was sufficiently suppressed (i.e., the degradation of tensile strength and yield strength was suppressed to within 20% compared with Test No. 1-1). Furthermore, Test Nos. 1-2 to 1-4 also suppressed the degradation of elongation to within 20% compared with Test No. 1-1. On the other hand, Test No. 1-5 did not satisfy the requirements (Fe content, Si content, and arithmetic mean circle equivalent diameter of Al-Fe based crystallized particles) defined in this embodiment, and the tensile strength and yield strength were significantly reduced. [Example]

[0038] Aluminum alloy extrusion materials of Test Nos. 2-1 to 2-5 were obtained in the same manner as in Example 1, except that aluminum alloys having the composition shown in Table 3 (i.e., five types of aluminum alloys having the same composition except for Fe and Si) were melted. In Table 3, "Tr." is an abbreviation for Trace, meaning a trace amount, which is not an intentionally added element and may be, for example, less than 0.01 mass %.

[0039] [Table 3]

[0040] The obtained aluminum alloy extrusions were subjected to a tensile test in the same manner as in Example 1. Note that the values ​​(arithmetic mean circle equivalent diameter, number density) of the Al-Fe-based crystallized products in Test Nos. 2-1 to 2-5 may depend on the Fe and Si contents if the same manufacturing method is used, and therefore are considered to be equivalent to those in Test Nos. 1-1 to 1-5, respectively. The results are shown in Table 4.

[0041] [Table 4]

[0042] The following can be seen from Table 4. Test No. 2-1 is a reference example, and the Fe content and Si content are at the normal impurity level (i.e., it is not intended to reuse aluminum scrap), and it has high tensile strength and yield strength. Compared to Test No. 2-1, Test Nos. 2-2 to 2-4 showed a sufficient reduction in strength despite the increased Fe and Si contents (i.e., the reduction in tensile strength and yield strength was reduced to within 20% compared to Test No. 2-1). Furthermore, Test Nos. 2-2 to 2-4 also showed a reduction in elongation to within 20% compared to Test No. 2-1. On the other hand, Test No. 2-5 did not satisfy the requirements (Fe content, Si content, etc.) defined in this embodiment, and the tensile strength and yield strength were significantly reduced.

Claims

1. Zn: 5.70% by mass or more and 6.80% by mass or less, Mg: 1.10% by mass or more and 1.55% by mass or less, Cu: 0.10% by mass or more and 0.40% by mass or less, one or more selected from the group consisting of Ti: 0.05% by mass or less (excluding 0% by mass) and B: 0.02% by mass or less (excluding 0% by mass); Zr: 0.10% by mass or more and 0.20% by mass or less, Cr: 0.10% by mass or less (including 0% by mass), Fe: more than 0.15 mass% and not more than 1.05 mass%; and Si: 0.05% by mass or more and 0.45% by mass or less, and the balance being Al and inevitable impurities, Contains Al-Fe crystallized substances, the arithmetic mean equivalent circle diameter of the Al—Fe crystallized product is 1.30 μm or more and 1.60 μm or less; The number density of the Al-Fe crystallized particles is 3.0 × 10 －３ pieces / μm ２ 1.7 x 10 －２ pieces / μm ２ The following is an aluminum alloy extrusion material.

2. 2. The aluminum alloy extrusion material according to claim 1, wherein the Fe content is more than 0.15 mass% and not more than 0.60 mass%, and the Si content is 0.05 mass% or more and 0.20 mass% or less.

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