Method for producing aluminum alloy

Abstract

The present invention relates to a method for producing an aluminum alloy, the method comprising: (i) an adjustment step for adjusting the composition of the raw material of the aluminum alloy to a specific composition; (ii) a continuous casting step for casting the raw material of the aluminum alloy, the composition of which has been adjusted in step (i), to produce a cast ingot; and (iii) a hot working step of performing hot working on the ingot manufactured in step (ii) so that the reduction rate is appropriate according to the composition of the aluminum alloy.

Description

Technical Field

[0001] This invention relates to a method for manufacturing aluminum alloys, and more specifically, to a method for manufacturing aluminum alloys for high-pressure gas storage. Background Technology

[0002] In recent years, hydrogen has attracted attention as a clean energy source. Hydrogen has the property of embrittlement of metals such as iron and aluminum, therefore, efforts are underway to develop metal alloys for safe and simple storage, particularly under high pressure.

[0003] For example, Japanese Patent Application Publication No. 2002-348631 discloses an aluminum-zinc-magnesium alloy for casting and forging with excellent castability and forgeability, characterized in that, by mass%, zinc: 3-5%, magnesium: 1-3%, copper: 0.20-1.0%, titanium: 0.15-0.30%, zirconium: 0.10-0.40%, silicon: less than 0.30%, iron: less than 0.50%, and the balance being composed of aluminum and unavoidable impurities.

[0004] Japanese Patent Application Publication No. 2014-101541 discloses an aluminum alloy material for high-pressure hydrogen containers, characterized in that it is composed of an aluminum alloy containing Si: 0.6-1.5 wt%, Mg: 0.6-1.6 wt%, Cu: 0.1-1.0 wt%, and Fe: 0.05-0.4 wt%, and is limited to Mn: 0.9 wt% or less, Cr: 0.3 wt% or less, Zr: 0.15 wt% or less, and V: 0.2 wt%. The content of Mn, Cr, Zr and V is less than 0.05% by mass, Zn is less than 0.25% by mass and Ti is less than 0.1% by mass, the balance is composed of Al and unavoidable impurities, the total content of Mn, Cr, Zr and V is more than 0.05% by mass, and the yield strength S (MPa) and conductivity E (IACS%) satisfy the following formula (1) [S≤-10.46×E+801] and formula (2) [S≥-25×E+1296], the yield strength S is more than 270 MPa and the conductivity E is more than 36IACS%.

[0005] High-pressure gas storage tanks are used in hydrogen refueling stations, transportation, and vehicle-mounted applications, with vehicle-mounted tanks requiring particularly lightweight construction. Therefore, aluminum alloys, lighter than iron, have been investigated as a candidate metal alloy material for manufacturing vehicle-mounted tanks. Aluminum alloys used in such applications not only need to possess resistance to hydrogen embrittlement, intergranular corrosion, and stress corrosion cracking (SCC), but also need to be resistant to stress corrosion cracking (HG - SCC) in atmospheres that can cause hydrogen embrittlement of aluminum alloys, specifically atmospheres where moisture exists as an impurity in hydrogen. Summary of the Invention

[0006] Therefore, the objective of this invention is to provide a method for manufacturing an aluminum alloy that has sufficient resistance to HG-SCC and specifically passes the HG-SCC test (HPISE 103:2018) (hereinafter also referred to as the "HG-SCC test") established by the Japan High Pressure Technology Association in 2018.

[0007] The inventors have conducted various studies on methods for solving the above-mentioned problems. The results showed that, in the method of manufacturing aluminum alloy materials containing copper (Cu) and silicon (Si) by hot working (hot casting), when the Cu content is in the range of 0.15 wt% to 0.40 wt% and the reduction rate based on hot working is 40% or more, when the Si content is in the range of 0.65 wt% to 0.80 wt% and the reduction rate based on hot working is less than 40%, when the Si content is in the range of 0.65 wt% to (0.6002 × Cu content (mass%) + 0.5606) wt% and the reduction rate generated by hot working is less than 40%, and when the Si content is in the range of (0.6002 × Cu content (mass%) + 0.5606) wt% to 0.80 wt% (except for compositions with Cu content of 0.15 wt% and Si content of 0.80 wt%), it is possible to manufacture aluminum alloys that pass the HG-SCC test, thus completing the present invention.

[0008] That is, the main idea of ​​this invention is as follows.

[0009] (1) A method for manufacturing an aluminum alloy for high-pressure gas storage, comprising: (i) an adjustment step, wherein the composition of the raw material of the aluminum alloy is adjusted such that when the raw material of the aluminum alloy is set to 100% by mass, it contains Cu in the range of 0.15% to 0.40% by mass, Si in the range of 0.65% to 0.80% by mass, and Al and unavoidable impurities; (ii) a continuous casting step, wherein the raw material of the aluminum alloy with the adjusted composition in step (i) is cast to produce an ingot; and (iii) a hot working step, wherein the ingot produced in step (ii) is hot-worked to achieve a reduction rate of 40% or more.

[0010] (2) According to the method described in (1), in the adjustment step of (i), when the Cu content and Si content are used to make an xy curve by taking the Cu content on the x-axis and the Si content on the y-axis, the range is enclosed by the three points (x, y) = (0.15, 0.65), (0.15, 0.80) and (0.40, 0.80).

[0011] (3) A method for manufacturing an aluminum alloy for high-pressure gas storage, comprising:

[0012] (i) Adjustment step, adjusting the composition of the aluminum alloy raw material to include 0.15% to 0.40% Cu, 0.65% to (0.6002 × Cu content + 0.5606)% Si, and Al and unavoidable impurities when the total raw material of the aluminum alloy is set to 100% by mass; (ii) Continuous casting step, casting the raw material of the aluminum alloy with the adjusted composition in step (i) to produce an ingot; and (iii) Hot working step, hot working the ingot produced in step (ii) to make the reduction rate less than 40%.

[0013] (4) A method for manufacturing an aluminum alloy for high-pressure gas storage, comprising: (i) an adjustment step, wherein the composition of the raw material of the aluminum alloy is adjusted to include, when the total raw material of the aluminum alloy is set to 100% by mass, 0.15% to 0.40% by mass of Cu, (0.6002 × Cu content + 0.5606)% to 0.80% by mass of Si, and Al and unavoidable impurities, wherein the composition does not include a composition with a Cu content of 0.15% by mass and a Si content of 0.80% by mass.

[0014] (ii) Continuous casting step, in which the raw material of the aluminum alloy whose composition was adjusted in step (i) is cast to produce an ingot; and

[0015] (iii) Hot working step: hot working is performed on the ingot produced in step (ii) so that the reduction rate is less than 40%.

[0016] (5) The method according to any one of (1) to (4), wherein the aluminum alloy passes the humid gas stress corrosion cracking test established by the Japan High Pressure Technology Association in 2018.

[0017] (6) An aluminum alloy for high-pressure gas storage, manufactured by any one of (1) to (5).

[0018] According to the present invention, a method is provided for manufacturing an aluminum alloy having sufficient resistance to HG-SCC, specifically capable of passing the HG-SCC test. Attached Figure Description

[0019] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like symbols denote like elements, and

[0020] Figure 1 It is a diagram schematically illustrating the hot (forging) process performed on a continuous casting bar used to illustrate the reduction rate;

[0021] Figure 2 This is a graph schematically illustrating the relationship between Cu content, Si content, and hot workability in aluminum alloy castings of embodiments and comparative examples of the present invention; and

[0022] Figure 3 This is a schematic diagram of the test piece prepared in the 2.HG-SCC test; the unit is mm. Detailed Implementation

[0023] The preferred embodiments of the present invention will now be described in detail.

[0024] In this specification, the features of the invention will be described with appropriate reference to the accompanying drawings. In the drawings, for clarity, the dimensions and shapes of the parts are exaggerated and the actual dimensions and shapes are not accurately depicted. Therefore, the technical scope of the invention is not limited to the dimensions and shapes of the parts shown in these drawings. It should be noted that the method for manufacturing the aluminum alloy of the present invention is not limited to the following embodiments, and can be implemented in various ways with modifications and improvements that can be made by those skilled in the art without departing from the spirit of the invention.

[0025] Furthermore, in this invention, the expression "the range above the lower limit and below the upper limit" indicates a range that includes both the lower limit and the upper limit.

[0026] The method for manufacturing the aluminum alloy of the present invention includes: (i) an adjustment step, wherein the composition of the raw material of the aluminum alloy is adjusted to a specific composition; (ii) a continuous casting step, wherein the raw material of the aluminum alloy whose composition has been adjusted in step (i) is cast to produce an ingot; and (iii) a hot working step, wherein the ingot produced in step (ii) is hot-worked so that the reduction rate is appropriate according to the composition of the aluminum alloy.

[0027] The steps (i) to (iii) are described below.

[0028] (i) In the adjustment step, the composition of the raw materials for the aluminum alloy is adjusted. Here, raw materials for aluminum alloys can be listed in the form of powder, molten metal, or castings (e.g., aluminum alloy ingots).

[0029] Aluminum ingots can be used as a raw material for aluminum alloys.

[0030] As a raw material for aluminum alloys, commercially available products with known compositions can be used. Even when the composition of the raw material for an aluminum alloy is unknown, it is possible to analyze its composition.

[0031] There are no limitations on the analysis of the composition of aluminum alloy raw materials, especially the content of Cu, Si, Mg, Zn, Fe and Mn. For example, it can be carried out by emission spectroscopy analysis, fluorescence X-ray analysis (XRF) and other methods.

[0032] By analyzing the raw materials of aluminum alloys, it is possible to prepare raw materials for aluminum alloys with the same composition as the aluminum alloy to be manufactured.

[0033] Next, the raw materials of the aluminum alloy are adjusted to include Cu: 0.15% to 0.40% by mass, Si: 0.65% to 0.80% by mass, 0.65% to (0.6002 × Cu content (mass%) + 0.5606)% by mass, or (0.6002 × Cu content (mass%) + 0.5606)% to 0.80% by mass (excluding compositions with Cu content of 0.15% by mass and Si content of 0.80% by mass), as well as Al and unavoidable impurities when the total raw materials of the aluminum alloy are set to 100% by mass.

[0034] When the raw material of the aluminum alloy is set to 100% by mass, the Cu content is 0.15% by mass or more, in one embodiment 0.18% by mass or more, in another embodiment 0.20% by mass or more, in another embodiment 0.22% by mass or more and 0.40% by mass or less, in another embodiment 0.38% by mass or less, in another embodiment 0.36% by mass or less, in another embodiment 0.34% by mass or less, in another embodiment 0.32% by mass or less, in another embodiment 0.30% by mass or less, and in another embodiment 0.28% by mass or less.

[0035] The Cu content can be adjusted by mixing two or more aluminum alloy raw materials with known composition in any proportion, and by adding additives as appropriate, such as adding additives known in the art (pure copper or Cu-containing alloys or compounds (e.g., oxides)) to adjust the Cu content in the aluminum alloy raw materials.

[0036] Here, the Cu content can be determined by emission spectroscopy.

[0037] The Si content can vary depending on the reduction rate during the hot working step in (iii).

[0038] When the reduction rate in the hot working step (iii) is 40% or more, and the total raw material of the aluminum alloy is set to 100% by mass, the Si content is 0.65% by mass or more, in one embodiment 0.67% by mass or more, in another embodiment 0.69% by mass or more, in another embodiment 0.71% by mass or more, in another embodiment 0.73% by mass or more, and 0.80% by mass or less, in another embodiment 0.78% by mass or less, and in another embodiment 0.76% by mass or less. Hereinafter, the Cu content and Si content suitable for the case where the reduction rate in the hot working step (iii) is 40% or more will be referred to as CuSi content A. CuSi content A is the range enclosed by the four points (x, y) = (0.15, 0.65), (0.40, 0.65), (0.40, 0.80), and (0.15, 0.80) when constructing an xy graph with Cu content on the x-axis and Si content on the y-axis.

[0039] On the other hand, when the reduction rate in the hot working step (iii) is less than 40%, and the total raw material of the aluminum alloy is set to 100% by mass, the Si content is 0.65% by mass or more. It should be noted that when the reduction rate is less than 40%, the upper limit of the Si content depends on the Cu content and is (0.6002 × Cu content (mass%) + 0.5606)% by mass. Hereinafter, the Cu content and Si content applicable when the reduction rate in the hot working step (iii) is less than 40% will be referred to as CuSi content B. CuSi content B is the range enclosed by the three points (x, y) = (0.15, 0.65), (0.40, 0.65), and (0.40, 0.80) when constructing an xy graph with Cu content on the x-axis and Si content on the y-axis.

[0040] Alternatively, when the reduction rate in the hot working step (iii) is 40% or less, the lower limit of the Si content depends on the Cu content and is (0.6002 × Cu content (mass%) + 0.5606) mass%. When the total raw material of the aluminum alloy is set to 100 mass%, the Si content is 0.80 mass% or less. However, this range does not include compositions with a Cu content of 0.15 mass% and a Si content of 0.80 mass%. In one embodiment, this range does not include compositions with a Cu content of 0.15 mass% to 0.28 mass% and a Si content of (0.5385 × Cu content (mass%) + 0.6492) mass% to 0.80 mass%. Hereinafter, the Cu and Si contents applicable when the reduction rate in the hot working step (iii) is 40% or less will be referred to as CuSi content B'. The CuSi content B' is the range enclosed by the three points (x, y) = (0.15, 0.65), (0.15, 0.80), and (0.40, 0.80) when creating an xy graph with Cu content on the x-axis and Si content on the y-axis. This excludes the composition with Cu content of 0.15% by mass and Si content of 0.80% by mass. In one embodiment, it excludes the composition within the range enclosed by the three points (x, y) = (0.15, 0.73), (0.15, 0.80), and (0.28, 0.80).

[0041] The Si content can be adjusted by mixing two or more aluminum alloy raw materials with known compositions in any proportion, and by adding additives as appropriate, such as adding additives known in the art (pure silicon or alloys or compounds containing Si (e.g., oxides)) to adjust the Si content in the aluminum alloy raw materials.

[0042] Here, the Si content can be determined by emission spectroscopy.

[0043] In aluminum alloys, reducing the Cu content can improve corrosion resistance, while increasing the Si content can improve strength. As a result, the strength of the obtained aluminum alloy can be improved, and its corrosion resistance can also be enhanced.

[0044] In addition to the elements mentioned above, aluminum alloy raw materials may also contain elements such as magnesium (Mg), zinc (Zn), iron (Fe), manganese (Mn), nickel (Ni), tin (Sn), chromium (Cr), titanium (Ti), calcium (Ca), strontium (Sr), and sodium (Na).

[0045] In this invention, the raw materials of the aluminum alloy with adjusted composition can also be homogenized. As a method for homogenization, for example, a simple mixing method of the aforementioned aluminum alloy raw materials can be employed. This method can be used when the aluminum alloy raw materials are in easily mixable forms, such as powder, granules, etc.

[0046] Alternatively, as a method of homogenization, one could exemplify the method of melting aluminum alloy raw materials to prepare molten aluminum alloy.

[0047] In the continuous casting step (ii), the raw material of the aluminum alloy whose composition was adjusted in step (i) is cast to produce an ingot.

[0048] Here, casting refers to the process of pouring molten metal (including alloys) that has been melted at high temperatures, typically 680°C to 700°C, into the hollow part (cavity) of a mold made of sand or metal, cooling it, and solidifying it at typically 200°C to 350°C to produce an ingot.

[0049] As for casting, examples include continuous casting, continuous casting rolling, semi-continuous casting (direct-chill (DC) casting), hot-top casting, and other common melting casting methods, or die casting.

[0050] Aluminum alloys obtained through casting can be used for homogenization treatment.

[0051] The homogenization process can be carried out using homogenization processes known in the art, such as heat-treating aluminum alloys obtained by casting at a temperature of 400°C to 500°C for 2 to 10 hours.

[0052] In the hot working step (iii), the ingot produced in step (ii) is hot-worked so that the reduction ratio is appropriate according to the composition of the aluminum alloy.

[0053] Hot working refers to a processing method that heat-treats an ingot, such as a continuous casting bar, produced in step (ii) while applying pressure.

[0054] The reduction rate refers to, for example, Figure 1 As shown, when hot working is performed on a continuous casting bar (thickness before forming: a) to manufacture an aluminum alloy (thickness after forming: b), the degree of rolling is calculated as (ab) / a×100 (%).

[0055] When the Cu and Si contents are adjusted to CuSi content A in adjustment step (i), the reduction rate is 40% or more in the hot working step (iii). It should be noted that there is no upper limit to the reduction rate when the Cu and Si contents are adjusted to CuSi content A. The reduction rate is typically less than 100%, and in one embodiment is 99% or less, in another embodiment is 98% or less, in another embodiment is 97% or less, in another embodiment is 96% or less, in another embodiment is 95% or less, in another embodiment is 90% or less, in another embodiment is 85% or less, and in another embodiment is 80% or less.

[0056] On the other hand, when the Cu and Si contents are adjusted to CuSi content B in the adjustment step (i), the reduction rate can be less than 40% in the hot working step (iii), specifically 39% or less in one embodiment, 38% or less in another embodiment, 37% or less in another embodiment, 36% or less in another embodiment, 35% or less in another embodiment, 30% or less in another embodiment, and 25% or less in another embodiment. It should be noted that when the Cu and Si contents are adjusted to CuSi content B, the lower limit of the reduction rate is not limited. The reduction rate is generally greater than 0%, specifically 1% or more in one embodiment, 2% or more in another embodiment, 3% or more in another embodiment, 4% or more in another embodiment, 5% or more in another embodiment, 10% or more in another embodiment, 15% or more in another embodiment, and 20% or more in another embodiment.

[0057] In other words, when the Cu and Si contents adjusted in step (i) are within the range bounded by the three points (x, y) = (0.15, 0.65), (0.15, 0.80), and (0.40, 0.80) when creating an xy graph with Cu content on the x-axis and Si content on the y-axis, the reduction rate is greater than 40%. On the other hand, when the Cu and Si contents adjusted in step (i) are CuSi content B, the reduction rate can be less than 40%.

[0058] Alternatively, if the Cu and Si contents are adjusted to CuSi content B' in the adjustment step (i), the reduction rate can be set to 40% or less in the hot working step (iii), specifically 39% or less in one embodiment, 38% or less in another embodiment, 37% or less in another embodiment, 36% or less in another embodiment, 35% or less in another embodiment, 30% or less in another embodiment, and 25% or less in another embodiment. It should be noted that when the Cu and Si contents are adjusted to CuSi content B', the lower limit of the reduction rate is not limited. The reduction rate is generally greater than 0%, 1% or more in one embodiment, 2% or more in another embodiment, 3% or more in another embodiment, 4% or more in another embodiment, 5% or more in another embodiment, 10% or more in another embodiment, 15% or more in another embodiment, and 20% or more in another embodiment.

[0059] There is no limitation on the heat treatment temperature, but it is generally above 450°C, above 500°C in one embodiment, and generally below 600°C, below 550°C in one embodiment.

[0060] By adjusting step (i) and hot working step (iii), the aluminum alloy is given sufficient resistance to HG-SCC, resulting in the manufacture of an aluminum alloy that can pass the HG-SCC test.

[0061] The resulting aluminum alloy can then be subjected to solution treatment and / or aging treatment.

[0062] Solution treatment can be carried out using solutions known in the art, for example, heat-treating aluminum alloys obtained by casting at a temperature of 500°C to 600°C for 2 to 4 hours.

[0063] Furthermore, by cooling after solution treatment, a supersaturated solid solution of metallic elements that may affect the strength and toughness of aluminum alloys can be formed.

[0064] Aging treatment can be carried out using aging treatments known in the art, such as heat-treating solution-treated aluminum alloys at a temperature of 150°C to 200°C for 2 to 10 hours.

[0065] Aging treatment can stabilize the precipitated metal structure in aluminum alloys and improve their strength.

[0066] It should be noted that in this invention, no change in composition occurs when the aluminum alloy is manufactured from the raw material of the aluminum alloy, so the raw material of the aluminum alloy and the resulting aluminum alloy have the same composition.

[0067] Furthermore, the aluminum alloy manufactured in this invention is an aluminum alloy casting, and a casting refers to a shaped object manufactured by casting. Therefore, castings include shaped objects manufactured by low-pressure casting, gravity casting, die casting, etc.

[0068] The aluminum alloy manufactured in this invention exhibits sufficient resistance to HG-SCC. Specifically, the aluminum alloy of this invention passed the HG-SCC test (HPISE 103:2018) established by the Japan High Pressure Technology Association in 2018, suppressing crack lengths exceeding 0.16 mm. Therefore, by casting the aluminum alloy of this invention, it can be used as a material for high-pressure gas, particularly hydrogen, storage tanks.

[0069] It should be noted that, as mentioned above, although the aluminum alloy manufactured in this invention exhibits resistance to HG-SCC, the structure and properties of the aluminum alloy, which should be altered by the manufacturing method of this invention, have not yet been elucidated. This is because the structure and properties of the aluminum alloy are not only determined by commonly used indicators such as the composition and photographs of a specific part of the aluminum alloy, but also require analysis from multiple perspectives, such as obtaining measurements of the composition and structure of the aluminum alloy from local (microscopic) to overall (macroscopic) dimensions. Such analysis is not easy with current analytical techniques and is time-consuming, labor-intensive, and costly. Therefore, the aluminum alloy manufactured in this invention can only be represented by the manufacturing method under current analytical techniques. In the aluminum alloy of this invention, there are aspects that cannot be represented by methods other than the manufacturing method, which are impossible or unrealistic.

[0070] The following describes several embodiments of the present invention, but it is not intended to limit the present invention to the contents shown in these embodiments.

[0071] 1. Sample preparation

[0072] The raw material containing the aluminum alloy with the chemical composition listed in Table 1 was melted. A continuous casting rod was manufactured by casting the molten metal, and the resulting rod was homogenized at 470°C for 7 hours. Next, the homogenized rod was hot-worked at 520°C to the reduction ratio listed in Table 1. The hot-worked alloy was then solution-treated at 530°C for 3 hours, followed by aging at 180°C for 6 hours to prepare samples.

[0073] 2. HG-SCC test

[0074] For the obtained samples, the HG-SCC test (HPISE 103:2018) established by the Japan High Pressure Technology Association in 2018 was carried out. Specifically, for the prepared samples, the HG-SCC test was carried out in the following order: (1) Preparation of test pieces (based on Figure 3 (2) Fatigue pre-crack introduction, (3) Constant load test (for the 0.2% yield strength (σ) obtained in the tensile test of each substrate beforehand) 0.2 According to the stress expansion factor K of the crack IAPP =0.056×σ 0.2 The load input to the crack tip of the test piece was adjusted. The test environment was: atmospheric atmosphere at 25±5℃, relative humidity above 85%, and the test period was 90 days. (4) Crack initiation and fracture after fatigue, (5) SCC crack length determination, and (6) Material suitability determination (SCC crack length below 0.16mm is considered qualified). The results are shown in Table 1 and Figure 2 .

[0075] (Table 1)

[0076]

[0077]

[0078] From Table 1 and Figure 2 It is evident that in the HG-SCC test, a high Si content, low Cu content, and low reduction rate become disadvantageous. Specifically, it is known that with a reduction rate above 40%, by adjusting the Cu content to the range of 0.15% to 0.40% by mass and the Si content to the range of 0.65% to 0.80% by mass, an aluminum alloy that passes the HG-SCC test can be manufactured. Conversely, with a reduction rate below 40%, by adjusting the Cu content to the range of 0.15% to 0.40% by mass and the Si content to the range of 0.65% to (0.6002 × Cu content (mass%) + 0.5606)% by mass, an aluminum alloy that passes the HG-SCC test can be manufactured. When the content is below 40%, in aluminum alloys, by adjusting the Cu content to the range of 0.15% to 0.40% by mass and the Si content to the range of (0.6002 × Cu content (mass%) + 0.5606)% to 0.80% by mass, but excluding compositions with a Cu content of 0.15% by mass and a Si content of 0.80% by mass, preferably excluding compositions with a Cu content of 0.15% to 0.28% by mass and a Si content of (0.5385 × Cu content (mass%) + 0.6492)% to 0.80% by mass, an aluminum alloy that can pass the HG-SCC test can be manufactured.

Claims

1. A method for manufacturing an aluminum alloy for high-pressure gas storage, comprising: (i) Adjustment steps to adjust the composition of the aluminum alloy raw materials so that, when the total raw materials of the aluminum alloy are set to 100% by mass, they contain Cu ranging from 0.15% to 0.40% by mass, Si ranging from 0.65% to 0.80% by mass, and Al and unavoidable impurities. (ii) Continuous casting step, in which the raw material of the aluminum alloy whose composition was adjusted in step (i) is cast to produce an ingot; and (iii) Hot working step: hot working is performed on the ingot produced in step (ii) so that the reduction rate is more than 40%.

2. A method for manufacturing an aluminum alloy for high-pressure gas storage, comprising: (i) Adjustment steps to adjust the composition of the aluminum alloy raw materials to include 0.15% to 0.40% Cu, 0.65% to (0.6002 × Cu content + 0.5606)% Si, and Al and unavoidable impurities when the total raw material of the aluminum alloy is set to 100% by mass. (ii) Continuous casting step, in which the raw material of the aluminum alloy whose composition was adjusted in step (i) is cast to produce an ingot; and (iii) Hot working step: hot working is performed on the ingot produced in step (ii) so that the reduction rate is less than 40%.

3. A method for manufacturing an aluminum alloy for high-pressure gas storage, comprising: (i) Adjustment step: Adjust the composition of the aluminum alloy raw material to include 0.15% to 0.40% Cu, (0.6002 × Cu content + 0.5606)% to 0.80% Si, and Al and unavoidable impurities when the total raw material of the aluminum alloy is set to 100% by mass. (ii) Continuous casting step, in which the raw material of the aluminum alloy whose composition was adjusted in step (i) is cast to produce an ingot; and (iii) Hot working step: hot working is performed on the ingot produced in step (ii) so that the reduction rate is less than 40%.

4. The method according to any one of claims 1 to 3, wherein, The aluminum alloy passed the moisture stress corrosion cracking test established by the Japan High Pressure Technology Association in 2018.

5. An aluminum alloy for high-pressure gas storage, manufactured by the method described in claim 2.

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