Manufacturing method for aluminum alloys

Abstract

This invention provides a method for manufacturing an aluminum alloy with sufficient resistance to HG-SCC (High-Grade Successful Carbon Deposition). [Solution] The present invention relates to a method for manufacturing an aluminum alloy, comprising: (i) an adjustment step of adjusting the composition of the raw material for the aluminum alloy to a specific composition; (ii) a continuous casting step of casting the raw material for the aluminum alloy whose composition has been adjusted in step (i) to produce an ingot; and (iii) a hot working step of hot working the ingot produced in step (ii) so that the reduction ratio is appropriate according to the composition of the aluminum alloy.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an aluminum alloy, specifically, a method for manufacturing an aluminum alloy for high-pressure gas storage.

Background Art

[0002] In recent years, hydrogen has attracted attention as a clean energy. Since hydrogen has the property of embrittling metals such as iron and aluminum, the development of metal alloy materials for safely and easily storing hydrogen, particularly storing it at high pressure, has been underway.

[0003] For example, Patent Document 1 describes an aluminum-zinc-magnesium-based aluminum alloy for casting and forging, which is excellent in castability and forgeability, and has, in mass%, zinc: 3 to 5%, magnesium: 1 to 3%, copper: 0.20 to 1.0%, titanium: 0.15 to 0.30%, zirconium: 0.10 to 0.40%, silicon: 0.30% or less, iron: 0.50% or less, and the balance being aluminum and unavoidable impurities.

[0004] Patent Document 2 describes an aluminum alloy containing Si: 0.6 to 1.5 mass%, Mg: 0.6 to 1.6 mass%, Cu: 0.1 to 1.0 mass%, and Fe: 0.05 to 0.4 mass%, regulated to Mn: 0.9 mass% or less, Cr: 0.3 mass% or less, Zr: 0.15 mass% or less, V: 0.2 mass% or less, Zn: 0.25 mass% or less, and Ti: 0.1 mass% or less, with the balance being Al and unavoidable impurities, and composed of an aluminum alloy in which the total content of Mn, Cr, Zr, and V is 0.05 mass% or more, satisfying the following formulas (1) [S ≦ -10.46×E + 801] and (2) [S ≧ -25×E + 1296] regarding the yield strength S (MPa) and the conductivity E (IACS%), and having a yield strength S of 270 MPa or more and a conductivity E of 36 IACS% or more, which is a characteristic of an aluminum alloy material for a high-pressure hydrogen gas container.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-348631 [Patent Document 2] Japanese Patent Publication No. 2014-101541 [Overview of the project] [Problems that the invention aims to solve]

[0006] High-pressure gas storage tanks are used for hydrogen stations, transportation, and on vehicles, and vehicle-mounted tanks, in particular, require to be lightweight. Therefore, aluminum alloys, which are lighter than iron, are being considered as candidate metal alloy materials for the manufacture of vehicle-mounted tanks. Aluminum alloys used in such applications must possess not only resistance to hydrogen embrittlement, resistance to intergranular corrosion, and resistance to stress corrosion cracking (SCC), but also resistance to stress corrosion cracking (HG (Humid Gas)-SCC) in atmospheres that can cause hydrogen embrittlement of aluminum alloys, i.e., in atmospheres where water is present as an impurity in a hydrogen atmosphere.

[0007] Therefore, the object of the present invention is to provide a method for manufacturing an aluminum alloy that has sufficient resistance to HG-SCC, specifically, one that can pass the HG-SCC test (HPIS E 103:2018) (hereinafter also simply referred to as the "HG-SCC test") established by the Japan High Pressure Technology Association in 2018. [Means for solving the problem]

[0008] The inventors have investigated various means to solve the above problems. As a result, in a method for producing an aluminum alloy material containing copper (Cu) and silicon (Si) by hot working (hot casting), when the Cu content is in the range of 0.15% by mass or more and the reduction ratio by hot working is 40% or more, the Si content is in the range of 0.65% by mass or more and 0.80% by mass, and when the reduction ratio by hot working is less than 40%, the Si content is 0.65% by mass or more (0.6002 × Cu content) We have discovered that by setting the Si content to a range of (mass%) + 0.5606) mass% or less, and the reduction ratio by hot working to 40% or less, and setting the Si content to a range of (0.6002 × Cu content (mass%) + 0.5606) mass% or more and 0.80 mass% or less (excluding compositions in which the Cu content is 0.15 mass% and the Si content is 0.80 mass%), it is possible to manufacture an aluminum alloy that can pass the HG-SCC test, thus completing the present invention.

[0009] In other words, the gist of this invention is as follows: (1) A method for producing an aluminum alloy for high-pressure gas storage, comprising: (i) an adjustment step of adjusting the composition of the raw materials for the aluminum alloy so that, when the total raw materials for the aluminum alloy are considered as 100% by mass, Cu is in the range of 0.15% by mass or more and 0.40% by mass or less, Si is in the range of 0.65% by mass or more and 0.80% by mass or less, Al and unavoidable impurities; (ii) a continuous casting step of casting the raw materials for the aluminum alloy whose composition has been adjusted in step (i) to produce an ingot; and (iii) a hot working step of hot working the ingot produced in step (ii) so that the reduction ratio is 40% or more. (2) The method according to (1), wherein in the adjustment step of (i), the Cu content and Si content are within the range enclosed by the three points (x,y) = (0.15,0.65), (0.15,0.80), and (0.40,0.80) when an xy graph is created with the Cu content on the x axis and the Si content on the y axis. (3) A method for producing an aluminum alloy for high-pressure gas storage, comprising: (i) an adjustment step of adjusting the composition of the raw materials for the aluminum alloy so that, when the total raw materials for the aluminum alloy are considered as 100% by mass, Cu is in the range of 0.15% by mass or more and 0.40% by mass or less, Si is in the range of 0.65% by mass or more and (0.6002 × Cu content (mass%) + 0.5606)% by mass or less, Al and unavoidable impurities; (ii) a continuous casting step of casting the raw materials for the aluminum alloy whose composition has been adjusted in step (i) to produce an ingot; and (iii) a hot working step of hot working the ingot produced in step (ii) so that the reduction ratio is less than 40%. (4) A method for producing an aluminum alloy for high-pressure gas storage, comprising: (i) an adjustment step of adjusting the composition of the raw materials for the aluminum alloy so that, when the total raw materials for the aluminum alloy are considered as 100% by mass, Cu: in the range of 0.15% by mass or more and 0.40% by mass or less, Si: in the range of (0.6002 × Cu content (mass%) + 0.5606)% by mass or more and 0.80% by mass or less, Al and unavoidable impurities, excluding compositions in which the Cu content is 0.15% by mass and the Si content is 0.80% by mass; (ii) a continuous casting step of casting the raw materials for the aluminum alloy whose composition has been adjusted in step (i) to produce an ingot; and (iii) a hot working step of hot working the ingot produced in step (ii) so that the reduction ratio is 40% or less. (5) A method according to any one of (1) to (4) that allows an aluminum alloy to pass the HG-SCC test established by the Japan High Pressure Technology Association in 2018. (6) An aluminum alloy for high-pressure gas storage manufactured by any one of the methods described in (1) to (5). [Effects of the Invention]

[0010] The present invention provides a method for producing an aluminum alloy that has sufficient resistance to HG-SCC, specifically, one that can pass the HG-SCC test. [Brief explanation of the drawing]

[0011] [Figure 1] This diagram schematically shows the hot working (forging) process applied to a continuous casting rod used to explain the reduction ratio. [Figure 2] This figure schematically shows the relationship between Cu content, Si content, and hot working rate in aluminum alloy castings of the embodiment and comparative example of the present invention. [Figure 3] 2. This diagram schematically shows the test specimens prepared in the HG-SCC test. Units are in mm. [Modes for carrying out the invention]

[0012] Preferred embodiments of the present invention will be described in detail below. This specification will describe the features of the present invention with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of each part are exaggerated for clarity and do not accurately depict the actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of each part shown in these drawings. Furthermore, the method for manufacturing aluminum alloy of the present invention is not limited to the following embodiments and can be implemented in various forms with modifications and improvements that can be made by those skilled in the art, without departing from the spirit of the present invention.

[0013] Furthermore, in this invention, the expression "range of a numerical value (lower limit) or greater than or equal to a numerical value (upper limit)" indicates a range that includes both the lower limit and the upper limit.

[0014] The present invention provides a method for producing an aluminum alloy, comprising: (i) an adjustment step of adjusting the composition of the raw material for the aluminum alloy to a specific composition; (ii) a continuous casting step of casting the raw material for the aluminum alloy whose composition has been adjusted in step (i) to produce an ingot; and (iii) a hot working step of hot working the ingot produced in step (ii) so that the reduction ratio is appropriate according to the composition of the aluminum alloy.

[0015] Steps (i) through (iii) are described below.

[0016] In the adjustment step of (i), the composition of the raw material of the aluminum alloy is adjusted. Here, examples of the raw material of the aluminum alloy include those in the form of powder, molten metal, and castings (e.g., aluminum alloy ingots).

[0017] As the raw material of the aluminum alloy, aluminum ingots or the like can be used.

[0018] As the raw material of the aluminum alloy, commercially available ones with known compositions may be used. When the composition of the raw material of the aluminum alloy is unknown, the composition of the raw material of the aluminum alloy can be analyzed.

[0019] The analysis of the composition of the raw material of the aluminum alloy, particularly the contents of Cu, Si, Mg, Zn, Fe, and Mn, is not limited, but can be carried out by, for example, emission spectroscopy, X-ray fluorescence analysis (XRF), etc.

[0020] By analyzing the raw material of the aluminum alloy, a raw material of the aluminum alloy having the same composition as the aluminum alloy to be manufactured can be prepared.

[0021] Subsequently, the raw material of the aluminum alloy is adjusted to include Cu in the range of 0.15 mass% or more and 0.40 mass% or less, Si in the range of 0.65 mass% or more and 0.80 mass% or less, 0.65 mass% or more and (0.6002 × the content of Cu (mass%) + 0.5606) mass% or less, or (0.6002 × the content of Cu (mass%) + 0.5606) mass% or more and 0.80 mass% or less (excluding the composition where the content of Cu is 0.15 mass% and the content of Si is 0.80 mass%), with the total of the raw material of the aluminum alloy being 100 mass%, as well as Al and inevitable impurities.

[0022] The Cu content is 0.15% by mass or more when the total raw material of the aluminum alloy is considered as 100% by mass, in one embodiment it is 0.18% by mass or more, in one embodiment it is 0.20% by mass or more, in one embodiment it is 0.22% by mass or more and 0.40% by mass or less, in one embodiment it is 0.38% by mass or less, in one embodiment it is 0.36% by mass or less, in one embodiment it is 0.34% by mass or less, in one embodiment it is 0.32% by mass or less, in one embodiment it is 0.30% by mass or less, and in one embodiment it is 0.28% by mass or less.

[0023] The Cu content can be adjusted, for example, by mixing two or more aluminum alloy raw materials of known composition in any proportion, and optionally by adding additives, such as additives known in the art (pure copper or alloys or compounds containing Cu (e.g., oxides)) to adjust the Cu content in the aluminum alloy raw materials.

[0024] Here, the Cu content can be measured by emission spectroscopy.

[0025] The Si content may vary depending on the reduction ratio in the hot working step (iii).

[0026] In the hot working step of (iii), when the reduction ratio is 40% or more, the Si content is 0.65% by mass or more when the total raw material of the aluminum alloy is considered as 100% by mass, in one embodiment it is 0.67% by mass or more, in one embodiment it is 0.69% by mass or more, in one embodiment it is 0.71% by mass or more, in one embodiment it is 0.73% by mass or more and 0.80% by mass or less, in one embodiment it is 0.78% by mass or less, and in one embodiment it is 0.76% by mass or less. Hereinafter, the Cu content and Si content suitable when the reduction ratio is 40% or more in the hot working step of (iii) will be referred to as CuSi content A. The 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 an xy graph is created with the Cu content on the x-axis and the Si content on the y-axis.

[0027] On the other hand, if the reduction ratio in the hot working step (iii) is less than 40%, the Si content is 0.65 mass% or more, when the total mass of the aluminum alloy raw material is considered to be 100 mass%. Note that when the reduction ratio 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) mass%. Hereinafter, the Cu and Si content suitable for when the reduction ratio 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 an xy graph is created with the Cu content on the x axis and the Si content on the y axis.

[0028] Alternatively, if the reduction ratio is 40% or less in the hot working step of (iii), the lower limit of the Si content depends on the Cu content and is (0.6002 × Cu content (mass%) + 0.5606) mass%. The Si content is 0.80 mass% or less when the total raw material of the aluminum alloy is considered as 100 mass%. However, within this range, compositions in which the Cu content is 0.15 mass% and the Si content is 0.80 mass% are excluded. In one embodiment, within this range, compositions in which the Cu content is in the range of 0.15 mass% or more and 0.28 mass% or less and the Si content is in the range of (0.5385 × Cu content (mass%) + 0.6492) mass% or more and 0.80 mass% or less are excluded. Hereinafter, the Cu content and Si content suitable for when the reduction ratio is 40% or less in the hot working step of (iii) is 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 an xy graph is created with the Cu content on the x-axis and the Si content on the y-axis, provided that compositions with a Cu content of 0.15 mass% and a Si content of 0.80 mass% are excluded. In one embodiment, compositions within the range enclosed by the three points (x,y) = (0.15,0.73), (0.15,0.80), and (0.28,0.80) are excluded.

[0029] The Si content can be adjusted, for example, by mixing two or more aluminum alloy raw materials of known composition in any proportion, and optionally by adding additives, such as 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.

[0030] Here, the Si content can be measured by emission spectroscopy.

[0031] In aluminum alloys, reducing the Cu content improves corrosion resistance, and increasing the Si content improves strength. As a result, the strength of the resulting aluminum alloy can be increased, and its corrosion resistance can also be improved.

[0032] In addition to the elements mentioned above, the raw materials for aluminum alloys 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).

[0033] In the present invention, the raw materials for the aluminum alloy whose composition has been adjusted may be made homogeneous. As a method for making them homogeneous, for example, one can simply mix the raw materials for the aluminum alloy. This method can be used when the raw materials for the aluminum alloy are in a form that is easy to mix, such as powder or granules.

[0034] Alternatively, as a method to achieve uniformity, one example is to melt the raw materials of the aluminum alloy to prepare molten aluminum alloy.

[0035] 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.

[0036] In this context, casting refers to the process of pouring molten metal (including alloys), which has been melted at high temperatures—typically 680°C to 700°C in the case of aluminum alloys—into a cavity made of sand or other metal, and then cooling it down to a solidified ingot, typically between 200°C and 350°C.

[0037] Casting methods include conventional melting and casting methods such as continuous casting, continuous casting and rolling, semi-continuous casting (DC casting), and hot-top casting, as well as die-casting methods.

[0038] The aluminum alloy obtained by casting may be subjected to a homogenization treatment.

[0039] Homogenization treatment can be carried out using homogenization treatments known in the art. For example, an aluminum alloy obtained by casting is heat-treated at a temperature of 400°C to 500°C for 2 to 10 hours.

[0040] In the hot working step (iii), the ingot produced in step (ii) is subjected to hot working so that the reduction ratio is appropriate according to the composition of the aluminum alloy.

[0041] Hot working refers to a processing method in which an ingot, such as a continuous casting rod, produced in step (ii), is heat-treated while pressure is applied.

[0042] The reduction ratio, as shown in Figure 1, refers to the degree of rolling reduction calculated as (ab) / a × 100 (%) when a continuous casting rod (thickness before forming: a) is subjected to hot working to produce an aluminum alloy (thickness after forming: b).

[0043] If the Cu content and Si content are adjusted to CuSi content A in adjustment step (i), the reduction ratio in hot working step (iii) shall be 40% or more. Note that when the Cu content and Si content are adjusted to CuSi content A, the upper limit of the reduction ratio is not limited. The reduction ratio is usually less than 100%, and in one embodiment it is 99% or less, in one embodiment it is 98% or less, in one embodiment it is 97% or less, in one embodiment it is 96% or less, in one embodiment it is 95% or less, in one embodiment it is 90% or less, in one embodiment it is 85% or less, and in one embodiment it is 80% or less.

[0044] On the other hand, if the Cu content and Si content are adjusted to CuSi content B in the adjustment step of (i), the reduction ratio in the hot working step of (iii) may be less than 40%, 39% or less in one embodiment, 38% or less in one embodiment, 37% or less in one embodiment, 36% or less in one embodiment, 35% or less in one embodiment, 30% or less in one embodiment, and 25% or less in one embodiment. Note that when the Cu content and Si content are adjusted to CuSi content B, the lower limit of the reduction ratio is not limited. The reduction ratio is usually greater than 0%, 1% or more in one embodiment, 2% or more in one embodiment, 3% or more in one embodiment, 4% or more in one embodiment, 5% or more in one embodiment, 10% or more in one embodiment, 15% or more in one embodiment, and 20% or more in one embodiment.

[0045] In other words, if the Cu and Si content adjusted in adjustment step (i) falls within the range enclosed by the three points (x,y) = (0.15,0.65), (0.15,0.80), and (0.40,0.80) when an xy graph is created with the Cu content on the x-axis and the Si content on the y-axis, the reduction ratio should be 40% or more. On the other hand, if the Cu and Si content adjusted in adjustment step (i) is CuSi content B, the reduction ratio may be less than 40%.

[0046] Alternatively, if the Cu content and Si content are adjusted to CuSi content B' in the adjustment step of (i), the reduction ratio in the hot working step of (iii) may be 40% or less, 39% or less in one embodiment, 38% or less in one embodiment, 37% or less in one embodiment, 36% or less in one embodiment, 35% or less in one embodiment, 30% or less in one embodiment, and 25% or less in one embodiment. Note that when the Cu content and Si content are adjusted to CuSi content B', the lower limit of the reduction ratio is not limited. The reduction ratio is usually greater than 0%, 1% or more in one embodiment, 2% or more in one embodiment, 3% or more in one embodiment, 4% or more in one embodiment, 5% or more in one embodiment, 10% or more in one embodiment, 15% or more in one embodiment, and 20% or more in one embodiment.

[0047] The hot working temperature is not limited, but is usually 450°C or higher, 500°C or higher in one embodiment, and usually 600°C or lower, and 550°C or lower in one embodiment.

[0048] The adjustment step (i) and the hot working step (iii) impart sufficient HG-SCC resistance to the aluminum alloy, and as a result, an aluminum alloy that can pass the HG-SCC test can be manufactured.

[0049] Next, the obtained aluminum alloy may be subjected to solution treatment and / or aging treatment.

[0050] Solution treatment can be carried out using solution treatments known in the art. For example, an aluminum alloy obtained by casting is heat-treated at a temperature of 500°C to 600°C for 2 to 4 hours.

[0051] Furthermore, by cooling after the solution treatment, it is possible to form a supersaturated solid solution of metallic elements that can affect the strength and toughness of the aluminum alloy.

[0052] The aging treatment can be carried out using aging treatments known in the art, for example, by heat-treating a solution-treated aluminum alloy at a temperature of 150°C to 200°C for 2 to 10 hours.

[0053] Aging treatment can stabilize the precipitated metal structure in aluminum alloys and improve their strength.

[0054] Furthermore, in this invention, since no change in composition occurs when manufacturing an aluminum alloy from an aluminum alloy raw material, the aluminum alloy raw material and the resulting aluminum alloy have the same composition.

[0055] Furthermore, the aluminum alloy produced in this invention is an aluminum alloy casting, and a casting refers to a molded product manufactured by casting. Therefore, castings include molded products manufactured by low-pressure casting, gravity casting, die casting, and the like.

[0056] The aluminum alloy produced in this invention has sufficient resistance to high-pressure gas (HG-SCC). Specifically, the aluminum alloy in this invention can pass the HG-SCC test (HPIS E 103:2018), established in 2018 by the Japan High Pressure Technology Association, by suppressing crack lengths exceeding 0.16 mm. Therefore, by forming the aluminum alloy in this invention by casting, it can be used as a material for storage tanks for high-pressure gases, especially hydrogen gas.

[0057] As stated above, although the aluminum alloy produced in this invention has HG-SCC resistance, the structure and properties of the aluminum alloy, which should be altered due to the manufacturing method of this invention, remain unclear. This is because the structure and properties of the aluminum alloy require analysis from multiple perspectives, not only based on measurement results using commonly used indicators such as the composition and photographs of specific parts of the aluminum alloy, but also by obtaining measurement results ranging from the local (micro) structure to the overall (macro) structure of the composition and structure of the aluminum alloy. Such analysis is not easily performed with current analytical techniques and is time-consuming, laborious, and costly. Therefore, the aluminum alloy produced in this invention can only be described by its manufacturing method at the current level of analytical technology, and there are impossible and impractical aspects of the aluminum alloy of this invention that cannot be described by any method other than the manufacturing method. [Examples]

[0058] The following describes some embodiments of the present invention, but the present invention is not intended to be limited to those shown in these embodiments.

[0059] 1. Sample preparation The raw materials for the aluminum alloy containing the chemical components listed in Table 1 were melted. The molten metal was cast to produce continuous casting rods, and the resulting continuous casting rods were homogenized at 470°C for 7 hours. Subsequently, the homogenized continuous casting rods were hot-worked at 520°C to achieve the reduction ratios listed in Table 1. The hot-worked alloy was solution-treated at 530°C for 3 hours, followed by aging at 180°C for 6 hours to prepare samples.

[0060] 2. HG-SCC test The obtained samples were subjected to the HG-SCC test (HPIS E 103:2018), which was established in 2018 by the Japan High Pressure Technology Association. Specifically, the HG-SCC test involved (1) specimen preparation (prepared according to Figure 3), (2) fatigue crack induction, and (3) constant load testing (using the 0.2% yield strength (σ) obtained from tensile tests performed on each substrate beforehand). 0.2 ) for the crack stress intensity factor K IAPP = 0.056 × σ 0.2 The load was adjusted so that it was applied to the crack tip of the test specimen, the test environment was 25±5℃ in an atmospheric environment with a relative humidity of 85% or higher, and the test period was 90 days. The procedure was as follows: (4) post-fatigue crack introduction and fracture, (5) measurement of SCC crack length, and (6) determination of material suitability (SCC crack length of 0.16 mm or less was considered acceptable). The results are shown in Table 1 and Figure 2.

[0061] [Table 1]

[0062] Table 1 and Figure 2 show that the HG-SCC test is unfavorable when the Si content is high, the Cu content is low, and the reduction ratio is small. Specifically, when the reduction ratio is 40% or more, an aluminum alloy that can pass the HG-SCC test can be manufactured by adjusting the Cu content to a range of 0.15 mass% to 0.40 mass% and the Si content to a range of 0.65 mass% to 0.80 mass%. When the reduction ratio is less than 40%, an aluminum alloy that can pass the HG-SCC test can be manufactured by adjusting the Cu content to a range of 0.15 mass% to 0.40 mass% and the Si content to a range of 0.65 mass% to (0.6002 × Cu content (mass%) + 0.5606) mass%. In the case below, it was found that an aluminum alloy that can pass the HG-SCC test can be manufactured by adjusting the Cu content in the aluminum alloy to a range of 0.15 mass% to 0.40 mass%, and the Si content to a range of (0.6002 × Cu content (mass%) + 0.5606) mass% to 0.80 mass%, provided that compositions with a Cu content of 0.15 mass% and a Si content of 0.80 mass% are excluded, and preferably 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% are excluded.

Claims

1. (i) Adjustment step to adjust the composition of the raw materials for the aluminum alloy so that, when the total raw materials for the aluminum alloy are considered as 100% by mass, Cu is in the range of 0.15% by mass or more and 0.40% by mass or less, Si is in the range of 0.65% by mass or more and 0.80% by mass or less, Al and unavoidable impurities, (ii) A continuous casting step in which the raw materials of the aluminum alloy whose composition has been adjusted in step (i) are cast to produce ingots, (iii) A hot working step in which the ingot produced in step (iii) is subjected to hot working so that the reduction ratio is 40% or more. A method for producing aluminum alloy for high-pressure gas storage, including [the specified element].

2. (i) Adjustment step to adjust the composition of the raw materials for the aluminum alloy so that, when the total raw materials for the aluminum alloy are considered as 100% by mass, Cu is in the range of 0.15% by mass or more and 0.40% by mass or less, Si is in the range of 0.65% by mass or more and (0.6002 × Cu content (mass%) + 0.5606)% by mass or less, and Al and unavoidable impurities, (ii) A continuous casting step in which the raw materials of the aluminum alloy whose composition has been adjusted in step (i) are cast to produce ingots, (iii) A hot working step in which the ingot produced in step (iii) is subjected to hot working so that the reduction ratio is less than 40% A method for producing aluminum alloy for high-pressure gas storage, including [the specified element].

3. (i) Adjustment step to adjust the composition of the raw materials for the aluminum alloy so that, when the total raw materials for the aluminum alloy are considered as 100% by mass, Cu: in the range of 0.15% by mass or more and 0.40% by mass or less, Si: in the range of (0.6002 × Cu content (mass%) + 0.5606)% by mass or more and 0.80% by mass or less, and Al and unavoidable impurities, except for compositions in which the Cu content is 0.15% by mass and the Si content is 0.80% by mass, (ii) A continuous casting step in which the raw materials of the aluminum alloy whose composition has been adjusted in step (i) are cast to produce ingots, (iii) A hot working step in which the ingot produced in step (iii) is subjected to hot working so that the reduction ratio is 40% or less. A method for producing aluminum alloy for high-pressure gas storage, including [the specified element].

4. The method according to any one of claims 1 to 3, wherein the aluminum alloy passes the HG-SCC test established in 2018 by the Japan High Pressure Technology Association.

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

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