Aluminum alloy, hot-worked aluminum alloy material, and method for producing the same

Abstract

To provide an aluminum alloy that can achieve both excellent hot workability and high strength, both when Mg is not contained and when a relatively small amount of Mg is contained, an aluminum alloy hot-worked material that comprises the aluminum alloy, and a method for manufacturing the same.SOLUTION: The aluminum alloy has a chemical composition containing Sc: 0.01 mass% or more and 0.40 mass% or less, Mg: 0 mass% or more and 2.5 mass% or less, Zr: 0 mass% or more and 0.4 mass% or less, and the balance being Al and unavoidable impurities. The compressive deformation resistance calculated based on the true stress when the aluminum alloy is compressed and deformed at a strain rate of 1 s-1 at a temperature of 450°C is 62 MPa or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an aluminum alloy, a hot-worked aluminum alloy material, and a method for manufacturing the same.

Background Art

[0002] Aluminum materials (including pure aluminum and aluminum alloys) utilize the characteristics of high specific strength and excellent workability, and are used in various fields such as materials for transportation equipment such as vehicles, aircraft, and ships, building materials, and general machine parts. Among these applications, for example, in materials for vehicles, high strength is required for vehicle weight reduction. In addition, materials for vehicles and the like may be subjected to forming processing into a cross-sectional shape having a complex cross-sectional shape or a fine structure. To meet these requirements, aluminum materials used in vehicles are required to have a 0.2% proof stress of 140 MPa or more and excellent hot workability. Aluminum alloys that satisfy such requirements include 6000 series alloys containing Al (aluminum), Mg (magnesium), and Si (silicon), and 7000 series alloys containing Al, Mg, and Zn (zinc).

[0003] However, 6000 series alloys are not suitable for applications that require welding because of their low welding joint efficiency. In addition, 7000 series alloys have a problem of low corrosion resistance.

[0004] On the other hand, as aluminum materials having excellent welding joint efficiency and corrosion resistance, 1000 series aluminum and 5000 series alloys containing Al (aluminum) and Mg (magnesium) (for example, Patent Document 1) are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, since the 1000 series aluminum has a low content of alloying elements, it has a problem of low strength. Also, in order to increase the strength in the 5000 series alloy, a method of simply increasing the content of Mg can be considered. However, when the content of Mg increases, for example, the deformation resistance increases during hot working such as hot rolling or hot extrusion, and there is a risk that it becomes difficult to form the 5000 series alloy into a desired shape.

[0007] The present invention has been made in view of such a background, and provides an aluminum alloy capable of achieving both excellent hot workability and high strength even when it does not contain Mg or when the content of Mg is relatively small, an aluminum alloy hot-worked material made of this aluminum alloy, and a method for manufacturing the same.

Means for Solving the Problems

[0008] One aspect of the present invention is An aluminum alloy used for port hole extrusion, Sc: 0.01% by mass or more and 0.40% by mass or less, Mg: 0 .4 % by mass or more and 2.5% by mass or less, Zr: 0 .01 % by mass or more and 0.4% by mass or less, having a chemical composition consisting of the balance being Al and unavoidable impurities, When compressed and deformed at a strain rate of 1 s -1 at a temperature of 450°C, the aluminum alloy has a compressive deformation resistance calculated based on the true stress during deformation of 62 MPa or less.

[0009] Another aspect of the present invention is having at least one hollow portion surrounded by a wall portion made of an aluminum alloy, and the wall portion being formed with at least one welded surface where the aluminum alloys are welded together, the aluminum alloy hot working material, Sc: 0.01% by mass or more and 0.40% by mass or less, Mg: 0 .4 % by mass or more and 2.5% by mass or less, Zr: 0 .01 % by mass or more and 0.4% by mass or less, having a chemical composition consisting of the balance being Al and unavoidable impurities, having Al-Sc-based second-phase particles dispersed in the Al matrix phase, and the number density of the Al-Sc-based second-phase particles being 3000 particles / μm 3The above is an aluminum alloy hot-worked material.

[0010] Still another aspect of the present invention is that hot working is performed on the aluminum alloy of the above aspect in a state where the temperature is in the range of 350°C or higher and 550°C or lower. Port hole extrusion as such A hot working step of performing hot working, and a heat treatment step of holding the aluminum alloy at a holding temperature of 250°C or higher and 550°C or lower for a total of 30 minutes or more in at least one of before and after the hot working step. There is a method for manufacturing an aluminum alloy hot-worked material having these steps.

Advantages of the Invention

[0011] The aluminum alloy contains Sc as an essential component, and Mg and Zr as optional components. Sc in the aluminum alloy exists as a solid solution element dissolved in the Al matrix phase or Al-Sc-based second-phase particles dispersed in the Al matrix phase. Sc has little influence on the deformation resistance during hot working in any of these states. Therefore, the aluminum alloy can suppress an increase in deformation resistance and avoid deterioration of hot workability whether it contains no Mg or contains Mg within the specific range.

[0012] In addition, Sc as a solid solution element precipitates in the Al matrix phase as Al-Sc-based second-phase particles by performing the specific heat treatment step. By the precipitation strengthening of these Al-Sc-based second-phase particles, the strength of the aluminum alloy can be improved.

[0013] As described above, the aluminum alloy can achieve both excellent hot workability and high strength whether it contains no Mg or contains a relatively small amount of Mg.

[0014] Further, the hot-worked aluminum alloy material has the specific chemical composition and the number density of Al-Sc-based second-phase particles dispersed in the Al matrix phase is within the specific range. By setting the number density of the Al-Sc-based second-phase particles in the hot-worked aluminum alloy material within the specific range, high strength can be easily achieved.

[0015] In addition, the method for manufacturing the hot-worked aluminum alloy material includes a hot working step of subjecting the aluminum alloy of the above-described embodiment to hot working, and a heat treatment step of heating the aluminum alloy under the specific conditions. In the heat treatment step, by heating the aluminum alloy under the specific conditions, Sc dissolved in the aluminum alloy can be precipitated as Al-Sc-based second-phase particles. Thereby, the strength of the finally obtained hot-worked aluminum alloy material can be easily improved.

Mode for Carrying Out the Invention

[0016] (Aluminum alloy) The chemical composition of the aluminum alloy and the reasons for its limitation will be described.

[0017] ·Sc: 0.01% by mass or more and 0.40% by mass or less The aluminum alloy contains 0.01% by mass or more and 0.40% by mass or less of Sc as an essential component. As described above, Sc in the aluminum alloy exists in the form of a solid solution element dissolved in the Al matrix phase or Al-Sc-based second-phase particles. Sc dissolved in the Al matrix phase precipitates as Al-Sc-based second-phase particles in the Al matrix phase when the aluminum alloy is held at a holding temperature of 250°C or higher and 550°C or lower. And the Al-Sc-based second-phase particles dispersed in the Al matrix phase have the effect of improving the strength of the aluminum alloy by precipitation strengthening.

[0018] By setting the content of Sc within the specific range, the aluminum alloy is configured to enable the number density of the Al-Sc based second-phase particles present in the Al matrix phase to be within the specific range. Therefore, the strength of the aluminum alloy can be easily improved. Also, as described above, both Sc dissolved in the Al matrix phase and the Al-Sc based second-phase particles have little influence on the hot workability. Therefore, even when the Al-Sc based second-phase particles are present, the aluminum alloy can suppress an increase in the flow stress during hot working.

[0019] The content of Sc is preferably 0.03 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.07 mass% or more. By increasing the content of Sc in the aluminum alloy, the number density of the Al-Sc based second-phase particles after heat treatment can be made higher. As a result, the strength of the aluminum alloy can be further improved. When the content of Sc is less than 0.01 mass%, it becomes difficult to increase the number density of the Al-Sc based second-phase particles, and there is a possibility that it becomes difficult to increase the strength.

[0020] On the other hand, when the content of Sc becomes excessively high, the content of Sc exceeds the solid solubility limit, and it becomes difficult to dissolve Sc in the aluminum alloy. As a result, there is a possibility that the effect of improving the strength by the Al-Sc based second-phase particles cannot be obtained. From the viewpoint of avoiding such a problem, the content of Sc is set to 0.40 mass% or less. From the same viewpoint, the content of Sc is preferably 0.35 mass% or less, more preferably 0.30 mass% or less, even more preferably 0.25 mass% or less, and particularly preferably 0.15 mass% or less.

[0021] ·Mg: 0.4 0.5 mass% or more and 2.5 mass% or less The aluminum alloy 0.4 mass% or more contains 2.5 mass% or less of Mg ofMg in the aluminum alloy exists as a solid solution element dissolved in the Al matrix phase and has the effect of improving the strength of the aluminum alloy. By setting the content of Mg in the aluminum alloy within the specific range, it is possible to obtain the effect of strength improvement by Mg while suppressing an increase in the flow stress during hot working.

[0022] From the viewpoint of further enhancing the effect of strength improvement by Mg, the content of Mg is preferably 0.4% by mass or more, more preferably 0.8% by mass or more, still more preferably 1.0% by mass or more, and particularly preferably 1.2% by mass or more. On the other hand, from the viewpoint of further enhancing the hot workability, the content of Mg is preferably 2.2% by mass or less, more preferably 2.0% by mass or less, and still more preferably 1.8% by mass or less.

[0023] · Zr: 0.01 mass% or more 0.40% by mass or less The aluminum alloy 0.01 mass% or more contains 0.40% by mass or less of Zr of Zr in the aluminum alloy exists in the form of a solid solution element dissolved in the Al matrix phase or Zr-based precipitates. Zr dissolved in the Al matrix phase precipitates so as to surround the Al-Sc-based second-phase particles when the aluminum alloy is held at a holding temperature of 250°C or higher and 550°C or lower. The Zr-based precipitates thus precipitated have the effect of suppressing the coarsening of the Al-Sc-based second-phase particles. And, since the coarsening of the Al-Sc-based second-phase particles is suppressed by the Zr-based precipitates, finer and more numerous Al-Sc-based second-phase particles can be precipitated in the Al matrix phase. As a result, the effect of strength improvement by the Al-Sc-based second-phase particles can be further enhanced.

[0024] From the viewpoint of further enhancing the above-described action and effect by Zr, the content of Zr is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, still more preferably 0.06% by mass or more, and particularly preferably 0.09% by mass or more.

[0025] On the one hand, when the content of Zr becomes excessively high, the content of Zr exceeds the solid solubility limit, making it difficult to dissolve Zr in the aluminum alloy. As a result, the above-described effects of Zr-based precipitates may not be obtained. From the perspective of avoiding such problems, the content of Zr should be 0.40% by mass or less. From the same perspective, the content of Zr is preferably 0.35% by mass or less, more preferably 0.30% by mass or less, and even more preferably 0.25% by mass or less.

[0026] · Cu (copper): More than 0% by mass and 1.0% by mass or less The aluminum alloy may contain, as an optional component, more than 0% by mass and 1.0% by mass or less of Cu. In this case, the strength of the aluminum alloy can be further increased. From the perspective of enhancing the strength improvement effect of Cu, the content of Cu is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and even more preferably 0.30% by mass or more.

[0027] On the other hand, when the content of Cu becomes excessively high, there is a risk of causing a decrease in corrosion resistance. From the perspective of obtaining the strength improvement effect of Cu while avoiding a decrease in corrosion resistance, the content of Cu is preferably 0.90% by mass or less, more preferably 0.80% by mass or less, and even more preferably 0.70% by mass or less.

[0028] · Mn (manganese): More than 0% by mass and 1.0% by mass or less, Cr (chromium): More than 0% by mass and 0.30% by mass or less The aluminum alloy may contain, as an optional component, one or two elements of more than 0% by mass and 1.0% by mass or less of Mn and more than 0% by mass and 0.30% by mass or less of Cr. By setting the content of these elements within the specific range, the coarsening of the crystal grain structure in the manufacturing process of the aluminum alloy can be more effectively suppressed.

[0029] ·Ti (Titanium): More than 0 mass% and 0.10 mass% or less, B (Boron): More than 0 mass% and 0.010 mass% or less The aluminum alloy may contain, as optional components, one or two elements selected from Ti of more than 0 mass% and 0.10 mass% or less and B of more than 0 mass% and 0.010 mass% or less. These elements have the effect of refining crystal grains when the molten metal is solidified during the production process of the aluminum alloy. By setting the contents of Ti and B within the specific ranges, the crystal grains of the aluminum alloy can be sufficiently refined, and the strength of the finally obtained hot-worked aluminum alloy material can be further improved.

[0030] ·Inevitable impurities Examples of the inevitable impurities contained in the aluminum alloy include elements such as Fe (iron) and Si (silicon). The content of Fe as an inevitable impurity is 0.50 mass% or less, and the content of Si is 0.50 mass% or less. In addition, the inevitable impurities other than Fe and Si are 0.05 mass% or less for each element. If the content of the elements as inevitable impurities is within the aforementioned range, it can be easily avoided that the above-described effects are impaired by the inevitable impurities.

[0031] ·Compressive deformation resistance: 62 MPa or less The aluminum alloy having the chemical composition within the specific range has a compressive deformation resistance of 62 MPa or less. Note that the compressive deformation resistance in this specification is the compressive deformation resistance calculated based on the true stress when compressed and deformed at a strain rate of 1 s -1 at a temperature of 450°C.

[0032] By setting the compressive deformation resistance of the aluminum alloy within the specific range, the hot workability of the aluminum alloy can be improved. In addition, the aluminum alloy having the compressive deformation resistance within the specific range can be applied to a forming method that particularly requires high hot workability, such as porthole extrusion, that is, a forming method in which the aluminum alloy is extruded from a die formed by combining a male die and a female die.

[0033] (Hot-worked aluminum alloy material) By subjecting the aluminum alloy to hot working such as hot rolling or hot extrusion, a hot-worked aluminum alloy material (hereinafter referred to as "hot-worked material") can be obtained. The chemical composition of the hot-worked material is the same as that of the aluminum alloy used as the raw material.

[0034] In the Al matrix phase of the hot-worked material, Al-Sc-based second-phase particles, that is, second-phase particles containing Al and Sc, are dispersed. Specifically, the Al-Sc-based second-phase particles are composed of intermetallic compounds having compositions such as Al3Sc and Al3(Sc x Zr 1-x ). The value of x in Al3(Sc x Zr 1-x ) is 0 < x < 1. The value of x in Al3(Sc x Zr 1-x ) varies depending on the Zr content in the aluminum alloy and the heating conditions in the heat treatment process.

[0035] The number density of the Al-Sc-based second-phase particles in the hot-worked material is preferably 3000 particles / μm 3 or more. The Al-Sc-based second-phase particles have the effect of improving the strength of the hot-worked material by precipitation strengthening. By setting the number density of the Al-Sc-based second-phase particles in the hot-worked material within the specific range, the strength of the hot-worked material can be increased.

[0036] Regarding the effect of precipitation strengthening by the second-phase particles, it can be predicted to some extent based on the following formula (1) described in C. B. Fuller et al., Acta Materialia 51(2003)4803-4814. σ = 2.8 / λ(lnλ + 5.4) + σ0 ··· (1) In the above formula, σ is the 0.2% proof stress [MPa] of the aluminum alloy strengthened by precipitation of the second-phase particles, λ is the average interparticle distance [μm] of the second-phase particles, and σ0 is the 0.2% proof stress [MPa] of the aluminum alloy without the second-phase particles.

[0037] The average interparticle distance λ of the second-phase particles in the formula (1) is the number density N [particles / μm 3 per unit volume of the second-phase particles and can be expressed as in the following formula (2). λ = N -1 / 3 ···(2)

[0038] When using 35 MPa, which is the typical 0.2% proof stress of JIS A1100 aluminum, as σ0, the formula (1) can be written as in the following formula (3). σ = 2.8N 1 / 3 (lnN -1 / 3 + 5.4) + 35 ···(3)

[0039] And when N in the formula (3) is taken as 3000 particles / μm 3 , the 0.2% proof stress σ becomes about 145 MPa. Therefore, by setting the number density of the Al-Sc-based second-phase particles within the specific range, it can be expected that the 0.2% proof stress of the aluminum alloy will be 140 MPa or more even when Mg is not contained.

[0040] From the viewpoint of further increasing the strength of the hot-worked material, the number density of the Al-Sc-based second-phase particles is more preferably 5000 particles / μm 3 or more, and even more preferably 7000 particles / μm 3 or more. The upper limit of the number density of the Al-Sc-based second-phase particles is naturally determined according to the amount of Sc contained in the aluminum alloy hot-worked material.

[0041] The number density of the Al-Sc based second phase particles in the hot-worked material can be calculated based on the results of microstructure observation using a transmission electron microscope (TEM). More specifically, first, after collecting a measurement sample from the hot-worked material, the thickness of the measurement sample is made 0.1 μm by electrolytic polishing. This measurement sample is observed using a TEM, and the number of Al-Sc based second phase particles with an equivalent circle diameter of 0.5 nm or more and less than 10 nm present in the field of view is counted. Then, the value obtained by converting the number of Al-Sc based second phase particles present in the field of view to the number per 1 μm 3 in volume is defined as the number density of the Al-Sc based second phase particles.

[0042] The shape of the aluminum alloy hot-worked material is not particularly limited, and it can take various shapes such as a plate material, a bar material, a pipe material, a strip material, an extruded shape, etc. The aluminum alloy hot-worked material is produced by porthole extrusion of. The hot-extruded material produced by porthole extrusion has at least one hollow part surrounded by a wall part made of an aluminum alloy. Further, at least one welded surface formed by welding the aluminum alloys to each other may be formed on the wall part of the hot-extruded material produced by porthole extrusion.

[0043] As described above, the aluminum alloy has hot workability to such an extent that porthole extrusion is possible. Therefore, by using the aluminum alloy, a hot-extruded material having a complex cross-sectional shape or a cross-sectional shape with a fine structure that can be realized by porthole extrusion can be easily produced.

[0044] (Manufacturing method of aluminum alloy hot-worked material) The manufacturing method of the aluminum alloy hot-worked material includes a hot working step of performing hot working on the aluminum alloy in a state where the temperature is in the range of 350°C or more and 550°C or less, and a heat treatment step of holding the aluminum alloy at a holding temperature of 250°C or more and 550°C or less for a total of 30 minutes or more in at least one of before the hot working step and after the hot working step is completed.

[0045] ·Hot working process As the aluminum alloy to be subjected to the hot working process, those prepared by conventional methods can be used. For example, the aluminum alloy may be an ingot cast by a method such as DC casting or CC casting from a molten metal having the specific chemical composition, or may be a billet.

[0046] The hot working in the hot working process is , po -Tube hole extrusion is carried out. Po By performing tube hole extrusion, a hot extruded material having a cross-sectional shape with a complex cross-sectional shape or a fine structure can be easily obtained.

[0047] The starting temperature of the hot working in the hot working process is set to be 350 °C or higher and 550 °C or lower. When the starting temperature is less than 350 °C, the deformation resistance of the aluminum alloy becomes excessively high, making it difficult to perform hot working. On the other hand, when the starting temperature exceeds 550 °C, there is a risk that the aluminum alloy may be partially melted during hot working due to heat generation during processing.

[0048] ·Heat treatment process In the manufacturing method, a heat treatment process for heating the aluminum alloy is performed. The holding temperature in the heat treatment process is set to be 250 °C or higher and 550 °C or lower. Also, the total holding time in the heat treatment process is set to be 30 minutes or longer. By setting the holding temperature and holding time in the heat treatment process within the specific ranges, fine and numerous Al-Sc-based second-phase particles can be precipitated in the Al matrix phase, and the strength of the hot-worked material can be improved.

[0049] When the holding temperature in the heat treatment process is less than 250 °C, or when the total holding time is less than 30 minutes, the precipitation amount of the Al-Sc-based second-phase particles becomes insufficient, which may lead to a decrease in the strength of the hot-worked material. When the holding temperature in the heat treatment process exceeds 550 °C, there is a risk of partial melting of the aluminum alloy.

[0050] The heat treatment process may be carried out before the hot working process or after the hot working process is completed. Also, the heat treatment process may be carried out both before and after the hot working process. As described above, the Al-Sc based second phase particles have little influence on the hot workability. Therefore, even when the heat treatment process is carried out before the hot working process and hot working is performed on the aluminum alloy in which the Al-Sc based second phase particles are precipitated, hot working can be easily carried out.

Example

[0051] Examples of the aluminum alloy, the hot-worked aluminum alloy material, and the method for manufacturing the same will be described below. Note that the specific embodiments of the aluminum alloy, the hot-worked aluminum alloy material, and the method for manufacturing the same according to the present invention are not limited to the embodiments described in the examples, and the configuration can be appropriately changed without departing from the gist of the present invention.

[0052] In this example, first, a molten aluminum alloy having the chemical composition shown in Table 1 is cast by a conventional method to produce a billet having a cylindrical shape with a diameter of 90 mm and a length of 200 mm. Note that the symbol "Bal." in Table 1 indicates the balance. This billet is held at a holding temperature of 300 °C for 10 hours, and then held at a holding temperature of 400 °C for 10 hours (heat treatment process).

[0053] After the heat treatment process is completed, the billet is heated to 450 °C and hot extrusion is performed (hot working process). In the hot extrusion, the container temperature is 450 °C, the die temperature is 450 °C, and the extrusion speed is 1.0 m / min. Thus, test materials A to F can be obtained. Note that the test materials A to F are strip materials having a width of 35 mm and a thickness of 2 mm.

[0054] Also, by heating the billet to 500 °C and performing hot extrusion under the conditions of a container temperature of 500 °C, a die temperature of 500 °C, and an extrusion speed of 1.4 m / min, a test material G can be obtained. Note that the test material G is a strip material having a width of 35 mm and a thickness of 2.6 mm.

[0055] In addition, test specimens H and I shown in Table 1 are test specimens for comparison with test specimens A - G. The manufacturing methods of test specimens H and I are the same as those of test specimens A - F, except that the chemical compositions of the aluminum alloys are different.

[0056] The physical properties of each test specimen and the aluminum alloy used for manufacturing the test specimen can be evaluated by the following methods.

[0057] · Compressive deformation resistance of aluminum alloy After performing the heat treatment process, a compression test specimen having a cylindrical shape with a diameter of 8 mm and a length of 12 mm is taken from the billet before hot working. Using this test specimen, a compression test is performed under the conditions of a temperature of 450°C and a strain rate of 1 s -1 to obtain a load - displacement curve. Based on this load - displacement curve, assuming that the deformation of the test specimen during the compression test is uniform, true strain and true stress are calculated. Then, the true stress in the range where the true strain is 0.3 or more and less than 0.6 is arithmetically averaged, and this value is taken as the compressive deformation resistance. The compressive deformation resistance of each test specimen is shown in Table 2.

[0058] · Number density of Al - Sc - based second - phase particles present in the test specimen After cutting the test specimen into an appropriate size, a test specimen with a thickness of 0.1 μm is prepared by electrolytic polishing. Three randomly selected locations are observed from this test specimen using TEM, and a dark - field image of a 2 μm × 2 μm field of view is obtained. Then, the number of Al - Sc - based second - phase particles with an equivalent circle diameter of 0.5 nm or more and less than 10 nm present in these three dark - field images is converted to the number per 1 μm 3 in volume to calculate the number density of Al - Sc - based second - phase particles.

[0059] The number density of Al - Sc - based second - phase particles present in test specimen A is 10000 particles / μm 3 . Also, the number density of Al - Sc - based second - phase particles present in test specimens B - G is estimated to be about the same as that of test specimen A.

[0060] · Mechanical properties of the test specimen Specimens No. 5 specified in JIS Z2241:2011 are taken from the test materials. Tensile tests are conducted using these specimens, and the tensile strength and 0.2% proof stress are calculated. The tensile strength and 0.2% proof stress of each test material are shown in Table 2.

[0061] · Extrudability The evaluation of extrudability is carried out by the following method. First, the billet after the heat treatment process is heated to 520 °C. Then, using a die configured to be able to form a square tube with a cross-sectional shape of a square with a side length of 31 mm and a wall thickness of 2.5 mm surrounding the hollow part, porthole extrusion is performed on the billet. In porthole extrusion, the container temperature is 450 °C, the die temperature is 450 °C, and the extrusion speed is 1.0 m / min.

[0062] The symbol "A" described in the "Extrudability" column of Table 2 indicates that a square tube can be produced when porthole extrusion is performed under the aforementioned conditions, and the symbol "B" indicates that a square tube cannot be produced.

[0063] [Table 1]

[0064] [Table 2]

[0065] As shown in Table 1 and Table 2, the aluminum alloys used for test materials A to G have the specific chemical composition, and the compressive deformation resistance of the billet is 62 MPa or less. Therefore, these test materials have excellent hot workability and can be subjected to porthole extrusion. In addition, since test materials A to G have the specific chemical composition, by performing heat treatment, the number density of Al-Sc-based second-phase particles can be made 3000 particles / μm 3 or more. As a result, the 0.2% proof stress of test materials A to G after heat treatment can be made 140 MPa or more.

[0066] On the one hand, since the test material H is composed of an aluminum alloy that does not contain Sc, Al-Sc-based second-phase particles are not formed in the billet after heat treatment. Therefore, the 0.2% proof stress of the test material H is lower than that of the test material A.

[0067] In order to increase the strength of the aluminum alloy constituting the test material I compared to the test material H, a larger amount of Mg is contained in the test material I than in the test material H. However, due to the increase in the Mg content, the compression deformation resistance of the aluminum alloy increases and the hot extrusion property deteriorates. Therefore, it is difficult to perform porthole extrusion on the test material I. Also, although the 0.2% proof stress of the test material I is higher than that of the test material H, it is lower than that of the test materials A to G.

Claims

1. An aluminum alloy used for porthole extrusion, containing Sc: 0.01% by mass or more and 0.40% by mass or less, Mg: 0.4% by mass or more and 2.5% by mass or less, Zr: 0.01% by mass or more and 0.4% by mass or less, and having a chemical composition in which the balance is Al and inevitable impurities, Compressed and deformed at a strain rate of -1 at a temperature of 450°C for 1 s, the aluminum alloy has a compressive deformation resistance calculated based on the true stress of 62 MPa or less. -1 ​

2. The aluminum alloy according to Claim 1, further containing one or more elements selected from the group consisting of Cu: more than 0% by mass and 1.0% by mass or less, Mn: more than 0% by mass and 1.0% by mass or less, Cr: more than 0% by mass and 0.30% by mass or less, Ti: more than 0% by mass and 0.10% by mass or less, B: more than 0% by mass and 0.10% by mass or less.

3. An aluminum alloy hot-worked material having at least one hollow portion surrounded by a wall portion made of an aluminum alloy, and at least one welded surface formed by welding the aluminum alloys to each other on the wall portion, containing Sc: 0.01% by mass or more and 0.40% by mass or less, Mg: 0.4% by mass or more and 2.5% by mass or less, Zr: 0.01% by mass or more and 0.4% by mass or less, and having a chemical composition in which the balance is Al and inevitable impurities, An aluminum alloy hot-worked material having Al-Sc-based second-phase particles dispersed in an Al matrix and having a number density of the Al-Sc-based second-phase particles of 3000 particles / μm 3 or more.

4. The aluminum alloy hot-worked material according to Claim 3, further containing one or more elements selected from the group consisting of Cu: more than 0% by mass and 1.0% by mass or less, Mn: more than 0% by mass and 1.0% by mass or less, Cr: more than 0% by mass and 0.30% by mass or less, Ti: more than 0% by mass and 0.10% by mass or less, B: more than 0% by mass and 0.10% by mass or less.

5. A hot-working process of subjecting the aluminum alloy according to Claim 1 or 2 to porthole extrusion as hot working in a state where the temperature is in the range of 350°C or more and 550°C or less, and a heat treatment process of holding the aluminum alloy at a holding temperature of 250°C or more and 550°C or less for a total of 30 minutes or more in at least one of before and after the hot-working process, a method for manufacturing an aluminum alloy hot-worked material.

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