Aluminum alloy extrusion material

Abstract

This aluminum alloy extrusion material contains: one or more elements selected from the group consisting of Zn: 5.70 mass% to 6.80 mass% inclusive, Mg: 1.10 mass% to 1.55 mass% inclusive, Cu: 0.10 mass% to 0.40 mass% inclusive, Ti: 0.05 mass% or less (excluding 0 mass%) and B: 0.02 mass% or less (excluding 0 mass%); Zr: 0.10 mass% to 0.20 mass% inclusive, 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% to 0.45 mass% inclusive with the balance being Al and inevitable impurities, and contains an Al-Fe crystallized product, the Al-Fe crystallized product has an arithmetic average circle-equivalent diameter of 1.30 μm to 1.60 μm inclusive, and the Al-Fe crystallized product has a number density of 3.0×10-3 / μm2 to 1.7×10-2 / μm2 inclusive.

Description

Aluminum alloy extrusions

[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).

[0002] 7000 series aluminum alloy extrusions are used for automotive frame and bumper structural members due to their excellent strength. Prior documents on 7000 series aluminum alloy extrusions include Patent Documents 1 to 3. Patent Documents 1 and 2 describe aluminum alloys containing mainly Zn and Mg (MgZn ２ Patent Document 3 describes that the strength is improved by the addition of elements such as Zn and Mg that improve the strength, and also by the addition of Al ３ It is described that Zr dispersoids are precipitated to improve strength.

[0003] Patent No. 2927445 Patent No. 5204793 Patent No. 6971151

[0004] Currently, in view of resource depletion, recycling of various materials is progressing, and recycling of metals that are consumed in large quantities has also been carried out for some time. Furthermore, in response to the global trend toward promoting carbon neutrality, reuse of aluminum scrap containing large amounts of Fe and Si has also been considered for 7000 series aluminum alloy extrusions. 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, resulting in a decrease in 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.

[0006] Aspect 1 of the present invention is a steel sheet comprising: 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; Ti: 0.05% by mass or less (inclusive of 0% by mass) and B: 0.02% by mass or less (inclusive of 0% by mass); Zr: 0.10% by mass or more and 0.20% by mass or less; Cr: 0.10% by mass or less (inclusive of 0% by mass); Fe: more than 0.15% by mass and 1.05% by mass or less; and Si: 0.05% by mass or more and 0.45% by mass or less, the balance being Al and inevitable impurities; and the steel sheet contains Al-Fe based crystallized products, and the arithmetic mean equivalent circle diameter of the Al-Fe based crystallized products 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.

[0007] A second aspect of the present invention is the aluminum alloy extrusion material according to the first aspect, 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 not more than 0.20 mass %.

[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.

[0009] FIG. 1 is a backscattered electron image of the aluminum alloy extrusion material of Test No. 1-2 taken by SEM.

[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 increase due to the reuse of aluminum scrap.

[0011] 7000 series aluminum alloys are MgZn ２ However, the inventors have found that the formation of MgZn (precipitates) improves the strength. ２It was found that even if a predetermined amount of Mg and Zn is contained so that the strength is formed, the strength decreases as the content of Fe and Si increases. The inventors have found that the reason for this is that the increase in the content of Si, in particular, causes the formation of Mg during casting. ２ A large amount of Si (crystallized product) can be formed, the amount of dissolved Mg decreases, and MgZn, which is effective for precipitation strengthening, is ２ It was thought that this would prevent sufficient formation.

[0012] Therefore, the present inventors have focused on Al-Fe-based crystallized products (crystallized products containing Al and Fe and / or crystallized products containing Al, Fe and Si). Since the Al-Fe-based crystallized products may also contain Si, the present inventors have found that the Al-Fe-based crystallized products can also contain Si, and therefore, Mg ２ The formation of Si (crystallized matter) can be effectively suppressed, and MgZn ２ The inventors have realized an aluminum alloy extrusion material capable of sufficiently suppressing a decrease in strength even when the Fe and Si contents are increased by reusing aluminum scrap, by appropriately controlling the size and number density of Al-Fe crystallized particles. Details of each requirement specified in this embodiment are shown below.

[0013] <Component Composition> The aluminum alloy extrusion material according to this embodiment preferably contains: Zn: 5.70% by mass to 6.80% by mass, Mg: 1.10% by mass to 1.55% by mass, Cu: 0.10% by mass to 0.40% by mass, 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 to 0.20% by mass, Cr: 0.10% by mass or less (including 0% by mass), Fe: more than 0.15% by mass to 1.05% by mass, and Si: 0.05% by mass to 0.45% by mass, with the balance being Al and inevitable impurities. Each component will be described in detail below.

[0014] (Zn: 5.70% by mass or more and 6.80% by mass or less) Zn is an element that, together with Mg, 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% by mass or more and 1.55% by mass or less) Mg, together with Zn, is an element that improves the strength of an aluminum alloy extrusion material. 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% by mass or more and 0.40% by mass or less) Cu has the effect of improving the strength of an aluminum alloy extrusion material and the effect of improving stress corrosion cracking resistance. If the Cu content is less than 0.10% by mass, these effects cannot be sufficiently obtained. On the other hand, if the Cu content exceeds 0.40% by mass, the quenching sensitivity increases, leading to a decrease in strength. Therefore, the Cu content is set to 0.10 to 0.40% by mass. More preferably, the Cu content is 0.10% by mass or more and 0.35% by mass or less.

[0017] (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)) 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 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 a 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% by mass or more and 0.20% by mass or less) Zr has the effect of suppressing recrystallization of an aluminum alloy extrusion material and improving stress corrosion cracking resistance. If the Zr content is less than 0.10% by mass, this effect cannot be sufficiently obtained. On the other hand, if the Zr content exceeds 0.20% by mass, extrudability decreases, and further, quenching sensitivity increases, leading to 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 added 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 0.10% by mass or less. Note that in this specification, "including 0% by mass" means that it includes embodiments in which Cr is not intentionally added, that is, cases in which the content is below the unavoidable impurity level (it does not exclude cases in which Cr is intentionally added).

[0020] (Fe: more than 0.15 mass% and not more than 1.05 mass%) Fe, along with Si, is a major impurity in aluminum alloys. In this embodiment, the Fe content is more than 0.15 mass% to enable reuse of aluminum scrap. From the viewpoint of enabling reuse of as much aluminum scrap as possible, the Fe content is preferably more than 0.50 mass%, and more preferably 0.60 mass% or more. On the other hand, in order to suppress a significant deterioration in the properties of the aluminum alloy extrusion material, the Fe content needs to be 1.05 mass% or less. From the viewpoint of further suppressing a deterioration in the properties of the aluminum alloy extrusion material, the Fe content is preferably 1.00 mass% or less, more preferably 0.80 mass% or less, even more preferably 0.60 mass% or less, and even more preferably 0.50 mass% or less.

[0021] (Si: 0.05% by mass or more and 0.45% by mass or less) Si, together with Fe, is a major impurity in aluminum alloys. In this embodiment, the Si content is set to 0.05% by mass or more in order to enable reuse of aluminum scrap. From the viewpoint of being able to reuse 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 Mg particles are generated during casting. ２ Silicon may crystallize, significantly deteriorating 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 the 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 extrusion material according to this embodiment preferably includes the above-described component composition, with the balance being Al and unavoidable impurities. Elements introduced due to the conditions of raw materials, materials, manufacturing equipment, etc. are permitted as unavoidable impurities. Note that, for example, Fe and Si, the lower the content, the better, and therefore these elements are unavoidable impurities, but their composition ranges are separately specified as described above. Therefore, in this specification, the term "unavoidable impurities" excludes elements whose composition ranges are separately specified. Examples of unavoidable impurities include Mn, Pb, Bi, Sn, and the like, each of which may be contained in an amount of 0.01% by mass or less. The total amount of unavoidable impurities may be, for example, 0.10% by mass or less.

[0023] <Al-Fe-based crystallized products> The aluminum alloy extrusion material according to this embodiment contains Al-Fe-based crystallized products (crystallized products containing Al and Fe and / or crystallized products containing Al, Fe, and Si). In this embodiment, the arithmetic mean circle equivalent diameter of the Al-Fe-based crystallized products is 1.30 μm or more and 1.60 μm or less, and the number density of the Al-Fe-based crystallized products is 3.0 × 10 －３ pieces / μm ２ 1.7 x 10 －２ pieces / μm ２ By setting the content in this range, Mg ２ The formation of Si (crystallized particles) can be effectively suppressed, and a decrease in the strength of the aluminum alloy extrusion material can be suppressed. It is also possible to suppress a decrease in the elongation of the aluminum alloy extrusion material. When the arithmetic mean equivalent circle diameter of the Al-Fe crystallized particles is less than 1.30 μm and / or the number density of the Al-Fe crystallized particles is 3.0 × 10 －３ pieces / μm ２ If it is less than that, Mg ２ The arithmetic mean equivalent circle diameter of the Al—Fe based crystallized particles is preferably 1.40 μm or more. The number density of the Al—Fe based crystallized particles is preferably 4.0×10 －３ pieces / μm ２ On the other hand, the arithmetic mean equivalent circle 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 or more.－２ pieces / μm ２ If the content exceeds 1.50 μm, the Al—Fe crystals will be excessive, and the mechanical properties may be significantly reduced. 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 arithmetic mean equivalent circle diameter and number density of Al-Fe crystallized particles can be measured by the methods described in Examples below.

[0024] <Manufacturing Method> The method for manufacturing an aluminum alloy extrusion material according to this embodiment includes: (a) a step of heating and melting an aluminum alloy having a predetermined chemical 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; and (b) after step (a), a step of heating the billet to 450 to 500°C, and performing extrusion processing 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 Step] An aluminum alloy having the above-described predetermined component composition is prepared. This aluminum alloy is heated to 700°C or higher and melted, followed by DC casting. The upper limit of the temperature during heating and melting can be, for example, 750°C or lower. After heating and 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 cooling rate of more than 6°C / sec. By performing the slow cooling from 660°C to 560°C, Al-Fe-based crystals can be sufficiently crystallized. At temperatures below 559°C (up to 200°C), Al-Fe-based crystals and Mg ２ Since crystallization of Si occurs simultaneously, Mg ２ By carrying out the rapid cooling in a manner that does not cause crystallization of Si, Mg can be dissolved.

[0026] After DC casting, and before the extrusion process described below, a homogenization treatment step may be performed, as necessary, in which the billet is heated to 450 to 550°C. 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 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.

[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 the embodiment of the present invention may include other steps without departing from the scope of the present disclosure.

[0030] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0031] As shown in Table 1, five aluminum alloys with identical composition except for Fe and Si were heated to 700°C or higher and 750°C or lower, melted, and DC cast to obtain billets. The casting speed during DC casting was 80 mm / min. After heating and melting, the average cooling rate from 660°C to 560°C was 2-6°C / sec, and the cooling rate from 559°C to 200°C was over 6°C / sec. The billets were then heated to 470°C and homogenized. The heating time was 6 hours. After homogenization, the billets were air-cooled with a fan. The billets were then heated to 470°C to obtain square pipes with a rectangular hollow cross section measuring 54 mm in length (H) x 70 mm in width (W) and 2 mm in wall thickness. 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 extrusion, the pipes were quenched by air-cooling at an average cooling rate of 200°C / min. Thereafter, heat treatment was performed as aging treatment at 90°C for 3 hours and then at 155°C for 8 hours to obtain aluminum alloy extrusion materials of Test Nos. 1-1 to 1-5. In Table 1, "Tr." is an abbreviation for Trace, which means a trace amount, is not an intentionally added element, and may be, for example, less than 0.01 mass%.

[0032]

[0033] The resulting aluminum alloy extrusions were observed for Al-Fe crystallized particles and subjected to a tensile test.

[0034] <Observation of Al-Fe-based crystallized products> Rectangular parallelepiped measurement samples (length (H) 2 mm × width (W) 15 mm × length (L) in the extrusion direction 15 mm) were taken from the center in the transverse direction and the extrusion direction of the aluminum alloy extrusions of Test Nos. 1-1 to 1-5. Backscattered electron images of the center in the longitudinal direction and the extrusion direction of the measurement samples were obtained using an SEM (JSM-IT100, manufactured by JEOL Ltd.) 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 of Test No. 1-2 is shown in FIG. 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 captured SEM image, the arithmetic mean equivalent circular diameter and the number per unit area of ​​the white part of the backscattered electron image 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 portions actually observed was 0.67 μm. In this embodiment, even if Al—Fe-based crystallized particles having a circle-equivalent 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 circle-equivalent diameter and number density of the Al—Fe-based crystallized particles according to this embodiment are calculated using Al—Fe-based crystallized particles having a circle-equivalent diameter of 0.67 μm or more.

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

[0036]

[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., not intended to reuse aluminum scrap), and it has high tensile strength and yield strength. Compared to Test No. 1-1, Test Nos. 1-2 to 1-4 fulfill all the requirements specified 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 to Test No. 1-1). Furthermore, Test Nos. 1-2 to 1-4 also fulfilled the elongation degradation to within 20% compared to Test No. 1-1. On the other hand, Test No. 1-5 did not fulfill the requirements specified in this embodiment (Fe content, Si content, and arithmetic mean circle equivalent diameter of Al—Fe-based crystallized particles), and the tensile strength and yield strength were significantly reduced.

[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, which means a trace amount, is not an intentionally added element, and may be, for example, less than 0.01 mass%.

[0039]

[0040] The obtained aluminum alloy extrusions were subjected to tensile tests 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]

[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 had increased Fe and Si contents, but the strength reduction was sufficiently suppressed (i.e., the reduction in tensile strength and yield strength was suppressed to within 20% compared to Test No. 2-1). Furthermore, Test Nos. 2-2 to 2-4 also had a reduction in elongation that was suppressed to within 20% compared to Test No. 2-1. On the other hand, Test No. 2-5 did not meet the requirements (Fe content, Si content, etc.) defined in this embodiment, and the tensile strength and yield strength were significantly reduced.

[0043] This application claims priority from Japanese Patent Application No. 2024-100753, filed June 21, 2024. Japanese Patent Application No. 2024-100753 is incorporated herein by reference.

Claims

1. A steel sheet comprising: 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; Ti: 0.05% by mass or less (inclusive of 0% by mass) and B: 0.02% by mass or less (inclusive of 0% by mass); Zr: 0.10% by mass or more and 0.20% by mass or less; Cr: 0.10% by mass or less (inclusive of 0% by mass); Fe: more than 0.15% by mass and 1.05% by mass or less; and Si: 0.05% by mass or more and 0.45% by mass or less, with the balance being Al and inevitable impurities; and containing Al-Fe-based crystallized products, the arithmetic mean equivalent circle diameter of the Al-Fe-based crystallized products being 1.30 μm or more and 1.60 μm or less; The number density of the Al-Fe crystals 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. 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 not more than 0.20 mass%.

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