Aluminum alloy forging material and method for manufacturing the same

Abstract

The present invention provides an aluminum alloy forging material that possesses high yield strength and can further improve creep characteristics. [Solution] The aluminum alloy forged material contains Si: 0.10% to 0.25% by mass, Fe: 0.9% to 1.3% by mass, Cu: 1.9% to 2.7% by mass, Mg: 1.3% to 1.8% by mass, Ni: 0.90% to 1.20% by mass, Ti: 0.01% to 0.10% by mass, and Zn: 0.10% by mass or less, with the remainder being Al and unavoidable impurities. Furthermore, the yield strength in a tensile test at 180°C is 220 MPa or more, and the S' phase formation peak area appearing in the temperature range of 200°C to 400°C in the DSC curve obtained by differential scanning calorimetry is 1.8 J / g or more.

Description

Technical Field

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

Background Art

[0002] Generally, many rotating parts and reciprocating parts such as engines, compressors, and turbocharger impellers are continuously used at high temperatures. Therefore, creep characteristics are particularly required for aluminum alloy forging materials used as materials for these parts.

[0003] For example, Patent Document 1 discloses an aluminum alloy forging material consisting of Si: 0.10 to 0.25% by mass, Fe: 0.9 to 1.3% by mass, Cu: 1.9 to 2.7% by mass, Mg: 1.3 to 1.8% by mass, Zn: 0.10% by mass or less, Ni: 0.9 to 1.2% by mass, Ti: 0.01 to 0.1% by mass, with the balance being Al and unavoidable impurities. Further, the above aluminum alloy forging material defines that the total content of Fe and Ni is 2.2% by mass or less, the total content of Mn, Cr, and Zr is 0.20% by mass or less, the average circle equivalent diameter of the intermetallic compound is 4.5 μm or less, and the variation in the distance between intermetallic compounds in the ST direction is 2.3 or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in rotating parts and reciprocating parts, further improvement in resistance to higher-speed rotation and use at high temperatures is required. Along with this, in the aluminum alloy forging material used as a raw material, it is required to achieve both more excellent creep characteristics and high strength.

[0006] Furthermore, in recent years, achieving carbon neutrality has become a challenge for society as a whole, and there is a demand for reducing CO2 emissions during the manufacturing of forged materials. In other words, by lowering the heat treatment temperature and reducing the heat treatment time under various heat treatment conditions in the manufacturing process of forged materials, it is possible to reduce CO2 emissions.

[0007] The present invention has been made in view of the above problems, and aims to provide an aluminum alloy forging material that has high yield strength and can further improve creep characteristics. Furthermore, the present invention aims to provide a method for manufacturing aluminum alloy forging materials that can reduce manufacturing costs, suppress CO2 emissions, and reduce the impact on global warming in the manufacturing process of aluminum alloy forging materials. [Means for solving the problem]

[0008] The above objective is achieved by the aluminum alloy forged material described in (1) below according to the present invention.

[0009] (1) Si: 0.10% by mass or more and 0.25% by mass or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90 mass% or more and 1.20 mass% or less, It contains Ti: 0.01% by mass or more and 0.10% by mass or less. An aluminum alloy forging material having Zn: 0.10 mass% or less, with the remainder being Al and unavoidable impurities, The yield strength in a tensile test at 180°C is 220 MPa or higher. An aluminum alloy forged material characterized in that, in the DSC curve obtained by differential scanning calorimetry, the S' phase formation peak area appearing in the temperature range of 200°C to 400°C is 1.8 J / g or more.

[0010] Furthermore, the above objective is achieved by the method for manufacturing aluminum alloy forging materials according to the present invention (2) below.

[0011] (2) A method for manufacturing aluminum alloy forgings as described in (1), Si: 0.10 mass% or more and 0.25 mass% or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90 mass% or more and 1.20 mass% or less, It contains Ti: 0.01% by mass or more and 0.10% by mass or less. A casting process for casting an aluminum alloy ingot having Zn: 0.10 mass% or less, with the remainder being Al and unavoidable impurities, A homogenization-quenching process is performed on the aluminum alloy ingot, which involves homogenization heat treatment, hot forging, solution treatment, and quenching. The process includes an artificial aging treatment step in which artificial aging treatment is performed on the quenched material after the aforementioned quenching, A method for manufacturing an aluminum alloy forged material, characterized in that the heating temperature in the artificial aging treatment step is 170°C or higher and 220°C or lower, and the heating time is less than 22 hours. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an aluminum alloy forged material that has high yield strength and can further improve creep characteristics.

[0013] Furthermore, according to the present invention, it is possible to provide a method for manufacturing aluminum alloy forgings that can reduce manufacturing costs in the manufacturing process of aluminum alloy forgings, suppress CO2 emissions, and reduce the impact on global warming. [Brief explanation of the drawing]

[0014] [Figure 1]FIG. 1 is a graph showing a DSC curve when the vertical axis is DSC (mW / mg) and the horizontal axis is temperature T (°C). [Figure 2] FIG. 2 is a schematic diagram showing the position of the sample collected in this embodiment. [Figure 3A] FIG. 3A is a plan view showing the region where a test piece is collected from the obtained aluminum alloy forging. [Figure 3B] FIG. 3B is a side view of the aluminum alloy forging shown in FIG. 3A. [Figure 4] FIG. 4 is a graph showing the relationship between the creep rupture time and the peak area of S' phase formation when the vertical axis is the creep rupture time t and the horizontal axis is the peak area of S' phase formation.

Mode for Carrying Out the Invention

[0015] In order to further improve the creep properties of the aluminum alloy forging, the present inventors have intensively studied the relationship between the aging conditions and the creep properties. As a result, the present inventors have found that the creep properties can be improved by performing sub-aging compared to general peak aging. Further, the present inventors have found that there is a correlation between the area of the peak appearing in a predetermined region in the DSC curve obtained by differential scanning calorimetry and the creep properties of the aluminum alloy forging. The present invention has been made based on the above findings. Hereinafter, the aluminum alloy forging according to the embodiment of the present invention will be described in detail.

[0016] [Aluminum Alloy Forging] The aluminum alloy forging according to the present embodiment contains the following specific elements within a predetermined content range. Specifically, an AA2618 aluminum alloy material having excellent properties at high temperatures can be used as the material of the aluminum alloy forging according to the present embodiment. Hereinafter, the elements contained in the aluminum alloy forging and the reasons for limiting their contents will be described in detail. In the following description, the aluminum alloy forging may be simply referred to as a forging.

[0017] (Si: 0.10 mass% or more and 0.25 mass% or less) Si, together with Mn, precipitates finely dispersed phases such as Al-Mn-Si compounds, enhancing the pinning effect of dislocations and suppressing the coarsening of recrystallized grains during solution treatment, thereby improving the strength of aluminum alloy forgings. If the Si content in the forging is less than 0.10 mass%, the effect of improving strength cannot be sufficiently obtained. Therefore, the Si content in the forging should be 0.10 mass% or more, preferably 0.13 mass% or more, and more preferably 0.15 mass% or more, relative to the total mass of the forging.

[0018] On the other hand, if the Si content in the forged material exceeds 0.25% by mass, compounds of Mg and Si are formed, reducing the heat resistance. Therefore, the Si content in the forged material should be 0.25% by mass or less, preferably 0.23% by mass or less, and more preferably 0.21% by mass or less, relative to the total mass of the forged material.

[0019] (Fe: 0.9 mass% or more and 1.3 mass% or less) Fe, together with Ni, forms Fe-Ni compounds, which have the effect of improving the heat resistance of aluminum alloy forgings. If the Fe content in the forging is less than 0.9% by mass, the effect of improving the heat resistance of the forging cannot be sufficiently obtained. Therefore, the Fe content in the forging should be 0.9% by mass or more, and preferably 1.0% by mass or more, relative to the total mass of the forging.

[0020] On the other hand, if the Fe content in the forged material exceeds 1.3% by mass, Fe-based compounds such as Al-Fe and Al-Fe-Cu are significantly formed in the matrix, reducing the effect of improving heat resistance. Therefore, the Fe content in the forged material should be 1.3% by mass or less, and preferably 1.2% by mass or less, relative to the total mass of the forged material.

[0021] (Cu: 1.9 mass% or more and 2.7 mass% or less) Cu has the effect of improving the strength of aluminum alloy forgings at room temperature and high temperature. Specifically, by including Cu in the forging material in a predetermined amount, both solid solution strengthening and precipitation strengthening effects are obtained, and the high temperature resistance and heat resistance required in this embodiment can be ensured. More specifically, during high-temperature artificial aging treatment, Cu combines with Al and Mg to precipitate GPB zones and S' phases in a fine and high-density manner, thereby improving the strength of the forging material after artificial aging treatment. The S' phase will be described later.

[0022] If the Cu content in the forged material is less than 1.9 mass%, the effect of improving the strength of the forged material cannot be sufficiently obtained. Therefore, the Cu content in the forged material should be 1.9 mass% or more, preferably 2.0 mass% or more, and more preferably 2.1 mass% or more, relative to the total mass of the forged material. On the other hand, if the Cu content in the forged material exceeds 2.7 mass%, the eutectic melting initiation temperature decreases, requiring a lower solution treatment temperature, which reduces the amount of solid solution into the matrix phase, and the effect of improving the strength of the forged material cannot be obtained. Therefore, the Cu content in the forged material should be 2.7 mass% or less, preferably 2.6 mass% or less, and more preferably 2.5 mass% or less, relative to the total mass of the forged material.

[0023] (Mg: 1.3 mass% or more and 1.8 mass% or less) Mg, in coexistence with Cu, has the effect of improving the strength of aluminum alloy forgings at room temperature and high temperatures. Specifically, by including Mg in a predetermined amount in the forging, both solid solution strengthening and precipitation strengthening effects can be obtained, ensuring the high-temperature resistance and heat resistance required in this embodiment. More specifically, during high-temperature artificial aging treatment, Mg combines with Al and Cu to precipitate GPB zones and S' phases in a fine and high-density manner, thereby improving the strength of the forging after artificial aging treatment.

[0024] If the Mg content in the forged material is less than 1.3% by mass, the effect of improving the strength of the forged material cannot be sufficiently obtained. Therefore, the Mg content in the forged material should be 1.3% by mass or more, preferably 1.4% by mass or more, and more preferably 1.5% by mass or more, relative to the total mass of the forged material. On the other hand, if the Mg content in the forged material exceeds 1.8% by mass, the deformation resistance of the material increases during hot working such as forging, and productivity decreases. Therefore, the Mg content in the forged material should be 1.8% by mass or less, preferably 1.7% by mass or less, and more preferably 1.6% by mass or less, relative to the total mass of the forged material.

[0025] (Ni: 0.90 mass% or more and 1.20 mass% or less) Ni, together with Fe, forms Fe-Ni compounds and other structures, which improve the heat resistance of aluminum alloy forgings. If the Ni content in the forging is less than 0.90% by mass, the effect of improving heat resistance cannot be sufficiently obtained. Therefore, the Ni content in the forging should be 0.90% by mass or more, preferably 0.95% by mass or more, and more preferably 1.00% by mass or more, relative to the total mass of the forging.

[0026] On the other hand, if the Ni content in the forged material exceeds 1.20% by mass, Ni-based compounds such as Al-Ni and Al-Ni-Cu are formed dispersed in the matrix, reducing the effect of improving heat resistance. In addition, coarse intermetallic compounds such as Fe-Ni are formed, making the material more prone to cracking during hot working such as forging, thus reducing productivity. Therefore, the Ni content in the forged material should be 1.20% by mass or less, preferably 1.18% by mass or less, and more preferably 1.10% by mass or less, relative to the total mass of the forged material.

[0027] (Ti: 0.01 mass% or more and 0.10 mass% or less) Ti is a component included in the forging material to stably obtain a fine grain structure. If the Ti content in the forging material is less than 0.01% by mass, the effect of stabilizing the fine grain structure cannot be sufficiently obtained. Therefore, the Ti content in the forging material should be 0.01% by mass or more, and preferably 0.04% by mass or more, relative to the total mass of the forging material.

[0028] On the other hand, if the Ti content in the forged material exceeds 0.10 mass%, large Al-Ti compounds and the like are formed during casting, reducing the strength. Therefore, the Ti content in the forged material should be 0.10 mass% or less relative to the total mass of the forged material, and preferably 0.09 mass% or less.

[0029] (Zn: 0.10% by mass or less) Zinc (Zn) is an element that is often present in forged materials as an unavoidable impurity. Furthermore, Zn has the effect of improving the room-temperature and high-temperature strength of aluminum alloy forgings through solid solution strengthening and precipitation strengthening. However, since the effect of improving the room-temperature and high-temperature strength of aluminum alloy forgings can be sufficiently obtained with Cu and Mg, the presence of Zn in the forging material is not necessarily required.

[0030] Furthermore, if the Zn content in the forged material exceeds 0.10% by mass, the corrosion resistance of the forged material decreases. Therefore, the Zn content in the forged material should be 0.10% by mass or less relative to the total mass of the forged material, preferably 0.09% by mass or less, more preferably 0.08% by mass or less, and even more preferably 0.05% by mass or less.

[0031] (Remainder: Al and inevitable impurities) The remainder of the aluminum alloy forged material according to this embodiment consists of Al and unavoidable impurities. Unavoidable impurities are inevitably present due to the raw materials used in actual operation. Examples of unavoidable impurities, in addition to Zn, include Mn, Cr, Zr, and V. Of these unavoidable impurities, the amount of V is preferably 0.05% by mass or less relative to the total mass of the forged material. The total content of Mn, Cr, and Zr is preferably, for example, 0.20% by mass or less, and more preferably 0.15% by mass or less, relative to the total mass of the forged material. Note that the V content and the total content of Mn, Cr, and Zr do not exceed the upper limits described in this embodiment, and the effects of the present invention are not hindered even if they are included intentionally, not just as unavoidable impurities.

[0032] (0.2% yield strength in tensile test at 180°C: 220 MPa or higher) The aluminum alloy forged material according to this embodiment aims to obtain even better creep properties compared to conventional forged materials. For example, in the aluminum alloy forged material described in Patent Document 1, the creep properties (time until the test piece fractures) when the applied stress is 220 MPa at a temperature of 180°C are at most 284.6 hours. Therefore, in this embodiment, the creep properties are set to be better than conventional products, i.e., 290 hours or more. In order to obtain these creep properties, the forged material must have a 0.2% yield strength of 220 MPa or more when a tensile test is performed at a temperature of 180°C. Accordingly, the aluminum alloy forged material has a 0.2% yield strength of 220 MPa or more in a tensile test at 180°C, preferably 250 MPa or more, and more preferably 280 MPa or more. Furthermore, the 0.2% proof stress obtained by tensile testing at 180°C can be measured, for example, using the flanged test specimen described in Annex A, in accordance with the "High-temperature tensile testing method for iron and steel materials and heat-resistant alloys" in JIS G0567:2020.

[0033] (S' phase formation peak area: 1.8 J / g or higher) Generally, when differential scanning calorimetry (DSC) is performed on aluminum alloy materials, an upwardly convex exothermic peak is obtained due to the precipitation of precipitates of several nanometers. Conversely, it is known that a downwardly convex endothermic peak is obtained due to solid solution (annihilation) ((Reference 1) Akikazu Maezono, Light Metals, vol. 51, No. 9, (2001), 464-476., (Reference 2) Taichi Suzuki, Hidekazu Hata, Hideo Yoshida, Light Metals, vol. 68, No. 7, (2018), 333-338.).

[0034] Figure 1 is a graph showing the DSC curve, with the vertical axis representing DSC (mW / mg) and the horizontal axis representing temperature T (°C). The analytical conditions used to show the graph in Figure 1 are as follows: • Equipment used: Therma plus EVO2 High-Sensitivity Differential Scanning Calorimeter DSC8231 (manufactured by Rigaku Corporation) ·Heat flux DSC device (JIS K 0129:2005) Measurement conditions: Temperature was raised from room temperature (approximately 25°C) to 530°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. • Sample: Approximately 20 mg used • Reference sample: Al2O3 powder

[0035] As shown in Figure 1, in the aluminum alloy forged material according to this embodiment, DSC measurements show that an exothermic peak C of S' phase formation appears within the temperature range of 200 to 400°C. The S' phase is an intermediate layer (metastable phase) that is thought to precipitate after the GPB zone. It has a lath-like morphology, an orthorhombic structure with a=4.0 Å, b=9.2 Å, and c=7.1 Å, and its precipitation plane is the {210} plane. <100> This is the direction. The matrix phase is a compound that is partially to semi-coherent and readily nucleates on the transition loop. This S' phase is a precipitated phase that contributes to strength improvement, and although no clear chemical formula has been reported, the stable S phase is considered to be a CuMgAl2 compound. In this embodiment, the area of ​​the S' phase formation peak that appears in the temperature range of 200°C to 400°C in the DSC curve obtained by DSC is defined.

[0036] The S' phase formation peak area will be further explained using Figure 1. The peak that appears in the temperature range of 200°C to 400°C (S' phase formation peak) is defined as the exothermic peak C, and the peak adjacent to the exothermic peak C via the endothermic peak B at temperatures lower than the exothermic peak C is defined as the exothermic peak A. In this specification, the area per unit heating rate (°C / s) of the shaded region enclosed by the exothermic peak C and the auxiliary line drawn parallel to the x-axis, which is formed when an auxiliary line is drawn passing through the vertex of the exothermic peak A, is defined as the "S' phase formation peak area".

[0037] If the S' phase formation peak area in the forged material is less than 1.8 (J / g), the desired creep characteristics cannot be obtained. Therefore, the S' phase formation peak area should be 1.8 (J / g) or higher. On the other hand, there is no particular upper limit to the S' phase formation peak area, but when measuring a sample in the as-quenched state (before the artificial aging treatment described later), where the S' phase formation peak area is likely to be the largest, it is 7.4 (J / g). Therefore, it is preferable that the S' phase formation peak area in the forged material be 7.4 (J / g) or less.

[0038] Next, a method for producing an aluminum alloy forged material according to an embodiment of the present invention will be described.

[0039] [Manufacturing method for aluminum alloy forgings] The method for manufacturing an aluminum alloy forged material according to this embodiment includes a casting step of casting an aluminum alloy ingot having a predetermined composition, a homogenization-quenching step of performing homogenization heat treatment, hot forging, solution treatment and quenching on the obtained aluminum alloy ingot, and an artificial aging treatment step of performing artificial aging treatment on the quenched material after quenching. Each step will be described in more detail below.

[0040] <Casting Process> The casting process involves casting molten metal, which has been melted to a predetermined composition, to produce an aluminum alloy ingot. The aluminum alloy ingot contains Si, Fe, Cu, Mg, Ni, and Ti in predetermined amounts, with a Zn content below a predetermined value, and the remainder consisting of Al and unavoidable impurities. The reasons for the predetermined content and numerical limits of each element in the aluminum alloy ingot are the same as those for each element in the aluminum alloy forging described above, as stated above. There are no particular limitations on the casting method or the shape of the ingot; ordinary methods and shapes can be used.

[0041] <Homogenization-quenching process> Next, the aluminum alloy ingot obtained by the above casting process is subjected to homogenization heat treatment, hot forging, solution treatment, and quenching. The heating rate and holding temperature of the homogenization heat treatment are not particularly limited, and general conditions can be used. The heating rate of the homogenization heat treatment can be, for example, 5°C / min or less, and the holding temperature can be, for example, 450 to 550°C. The starting and ending temperatures of the hot forging are also not particularly limited, and general conditions can be used. The starting temperature of the hot forging can be, for example, 350 to 500°C, and the ending temperature can be, for example, 300 to 500°C. The holding temperature, holding time, and heating rate of the solution treatment are also not particularly limited, and general conditions can be used. The holding temperature of the solution treatment can be, for example, 520 to 570°C, the holding time can be, for example, 20 minutes to 20 hours, and the heating rate can be, for example, 100°C / hour or more. Quenching is a process in which the treated material after solution treatment is cooled by immersion in water or hot water. The cooling rate is not particularly limited, and general conditions can be used. The cooling rate for quenching can be, for example, 40°C / second or higher.

[0042] <Artificial aging process> The artificial aging process is a process in which artificial aging is performed on the quenched material obtained by the above-mentioned quenching process. As described above, in this embodiment, the creep characteristics of the forged material are improved by setting the conditions of the artificial aging process to sub-aged. In other words, it is important to select heat treatment conditions before peak aging occurs. The conditions for sub-aging are determined by appropriately selecting a balance between heating temperature and heating time, but for example, a general range of heating temperatures can be applied and a shorter heating time than the general range can be selected.

[0043] If the heating temperature in the artificial aging process is below 170°C, the effect of hardening the forged material cannot be sufficiently obtained. Therefore, the heating temperature in the artificial aging process should be 170°C or higher, preferably 180°C or higher, and more preferably 190°C or higher. On the other hand, if the heating temperature in the artificial aging process exceeds 220°C, it deviates from the conditions for sub-aging, making it difficult to improve the creep characteristics. Therefore, the heating temperature in the artificial aging process should be 220°C or lower, preferably 210°C or lower, and more preferably 200°C or lower.

[0044] If the heating time in the artificial aging process is set to 22 hours or more, it will deviate from the conditions for sub-aging, making it difficult to improve the creep characteristics. Therefore, the heating time in the artificial aging process should be less than 22 hours. [Examples]

[0045] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples, and can be implemented with modifications within the scope that is consistent with the spirit of the present invention, and all such modifications are included within the technical scope of the present invention.

[0046] <Manufacturing of aluminum alloy forgings> (Casting process) Figure 2 is a schematic diagram showing the location of the sample to be taken in this embodiment. An iron mold 11 having a bottomed cylindrical shape with a smaller diameter at the bottom than at the opening was prepared, and molten aluminum alloy having a predetermined composition was poured into this mold 11 to produce an ingot 12 by die casting. The mass of the obtained ingot 12 was approximately 5.5 kg. Next, the ingot 12 removed from the mold 11 was cut and machined to produce a cylindrical sample 13 from approximately the center of the ingot 12. The size of the sample 13 was set to a diameter of 100 mm and a height of 120 mm. In this embodiment, the mass of the ingot 12 is approximately 5.5 kg, but the ingot is not limited to this size, and for example, aluminum alloy forgings can be manufactured under the same conditions as shown below even with ingots with a mass of 2 tons or more.

[0047] (Homogenization-quenching process) Subsequently, sample 13 was placed in an air furnace and subjected to homogenization heat treatment at a temperature of 520°C for 20 hours, after which it was cooled to room temperature. Then, sample 13 was again placed in the air furnace, heated to 300-340°C, removed from the furnace, and hot forging was performed using a hydraulic forging press. After that, the hot-forged material was placed in an air furnace and subjected to solution treatment at a temperature of 530°C for 6 hours, followed by quenching in boiling water to obtain a quenched material.

[0048] (Artificial aging process) Subsequently, the quenched material after the homogenization-quenching process was placed in an air furnace, and artificial aging treatment was carried out at a temperature of 197°C for the times shown below to obtain T61 treated aluminum alloy forgings. In this embodiment, Invention Example No. 1 had an artificial aging treatment time of 16 hours, resulting in sub-aged treatment conditions. Comparative Example No. 1 had an artificial aging treatment time of 22 hours, resulting in peak aging conditions. Comparative Example No. 2 had an artificial aging treatment time of 36 hours, resulting in over-aged treatment conditions.

[0049] Figure 3A is a plan view showing the area from which test specimens were taken from the obtained aluminum alloy forging, and Figure 3B is a side view of the aluminum alloy forging shown in Figure 3A. The disc-shaped aluminum alloy forging 21 had a diameter of 200 mm in the rolling direction (L direction) and a thickness of 30 mm in the thickness direction (ST direction). In Figures 3A and 3B, the hatched areas indicate the area 22 from which test specimens were taken. Specifically, test specimens for tensile and creep tests were taken from the center of the thickness of the aluminum alloy forging 21 and from the area 22 extending radially from near the center of the disc shape.

[0050] <Evaluation of aluminum alloy forgings> Using test specimens taken from the obtained aluminum alloy forging 21, DSC measurements, tensile tests, and creep tests were performed. The electrical conductivity of the obtained aluminum alloy forging 21 was also measured.

[0051] (Calculation of S' phase formation peak area) Samples for DSC measurement were taken from the chuck portion of tensile test specimens taken from aluminum alloy forging material 21, and DSC measurements were performed. The area of ​​the S' phase formation peak that appeared within the temperature range of 200 to 400°C was then calculated. The measurement conditions were as follows. • Equipment used: Therma plus EVO2 High-Sensitivity Differential Scanning Calorimeter DSC8231 (manufactured by Rigaku Corporation) ·Heat flux DSC device (JIS K 0129:2005) Measurement conditions: Temperature was raised from room temperature (approximately 25°C) to 530°C in a nitrogen gas atmosphere at a heating rate of 10°C / min. • Sample: Approximately 20 mg used • Reference sample: Al2O3 powder

[0052] (Tensile test) In accordance with JIS G 0567:2020, "High-temperature tensile testing method for iron and steel materials and heat-resistant alloys," tensile tests were conducted at 180°C using flanged test specimens as described in Annex A, and the tensile strength, 0.2% proof stress, and elongation after fracture were measured.

[0053] (Creep test) In accordance with JIS Z 2271:2010, "Test Methods for Creep and Creep Rupture of Metallic Materials," the creep rupture time was measured at a temperature of 180°C with a load of 220 MPa. A creep rupture time of 290 hours or more was judged as a good evaluation (○), while a creep rupture time of less than 290 hours was judged as a poor evaluation (×).

[0054] (Measurement of electrical conductivity) The obtained aluminum alloy forged material 21 was cut at an arbitrary position, and the exposed cross-section was mechanically polished to #2000 grit. The conductivity of the resulting surface was then measured. Conductivity was measured at room temperature (approximately 25°C) by pressing the probe tip of the conductivity meter against the sample. Note that any surface that is reasonably smooth can be polished to any desired roughness to measure conductivity. The equipment used for measuring conductivity is shown below. • Equipment used: Conductivity meter SIGMASCOPE SMP350 (manufactured by Fischer Instruments Co., Ltd.) • Applicable standards: ASTM E1004, etc.

[0055] The content of each component in the aluminum alloy forging and the heating conditions in the artificial aging process are shown in Table 1 below, and the measurement results of each test are shown in Table 2 below.

[0056] [Table 1]

[0057] [Table 2]

[0058] Figure 4 is a graph showing the relationship between creep rupture time and S' phase formation peak area, with the vertical axis representing creep rupture time t and the horizontal axis representing S' phase formation peak area. As shown in Tables 1 and 2 and Figure 4, Invention Example No. 1 has components contained in the forged material within the range specified in the present invention, and the heating temperature and time in the artificial aging process are appropriately controlled, resulting in sub-aging. Therefore, the S' phase formation peak area was 1.8 J / g or more, the 0.2% yield strength at a high temperature of 180°C was 220 (MPa), and the creep rupture time was 290 hours or more. In addition, since the heating time in the artificial aging process can be set shorter than conventional methods, manufacturing costs can be reduced, CO2 emissions can be suppressed, and the impact on global warming can be reduced.

[0059] On the other hand, in Comparative Examples No. 1 and 2, the heating conditions in the artificial aging process resulted in either peak aging or over-aging, and therefore the desired creep characteristics could not be obtained. [Explanation of Symbols]

[0060] 11. Mold 12 Ingot 13 samples 21 Aluminum alloy forging

Claims

1. Si: 0.10% by mass or more and 0.25% by mass or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90% by mass or more and 1.20% by mass or less, It contains Ti: 0.01% by mass or more and 0.10% by mass or less. An aluminum alloy forging material having Zn: 0.10% by mass or less, with the remainder being Al and unavoidable impurities, The yield strength in a tensile test at 180°C is 220 MPa or more. An aluminum alloy forged material characterized in that, in the DSC curve obtained by differential scanning calorimetry, the S' phase formation peak area appearing in the temperature range of 200°C to 400°C is 1.8 J / g or more.

2. A method for manufacturing an aluminum alloy forged material as described in claim 1, Si: 0.10% by mass or more and 0.25% by mass or less, Fe: 0.9% by mass or more and 1.3% by mass or less, Cu: 1.9% by mass or more and 2.7% by mass or less, Mg: 1.3% by mass or more and 1.8% by mass or less, Ni: 0.90% by mass or more and 1.20% by mass or less, It contains Ti: 0.01% by mass or more and 0.10% by mass or less. A casting process for casting an aluminum alloy ingot having Zn: 0.10 mass% or less, with the remainder being Al and unavoidable impurities, The aluminum alloy ingot is subjected to a homogenization-quenching process, in which homogenization heat treatment, hot forging, solution treatment, and quenching are carried out. The process includes an artificial aging treatment step in which artificial aging treatment is performed on the quenched material after the aforementioned quenching, A method for manufacturing an aluminum alloy forged material, characterized in that the heating temperature in the artificial aging treatment step is 170°C or higher and 220°C or lower, and the heating time is less than 22 hours.

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