Manufacturing method of aluminum alloy forging

Abstract

To provide a method for manufacturing an aluminum alloy forging material of high strength and high corrosion resistance while reducing a used amount of aluminum new bullion to reduce a CO2 discharge amount.SOLUTION: A method for manufacturing an aluminum alloy forging material from a mixture containing aluminum scrap, aluminum new bullion, and at least one additive element selected from the group consisting of Si, Fe, Cu, Ti, Mn, Cr, Zn, and Mg, includes a heating and melting step of the mixture, a forging step, and an aging step of a forged material. The mixture is composed of Si: 0.7-1.5 mass%, Fe: at most 0.8 mass%, Cu: 0.20-0.7 mass%, Ti: at most 0.15 mass%, Mn: 0.20-0.80 mass%, Cr: at most 0.1 mass%, Zn: at most 0.30 mass%, Mg: 0.050-1.2 mass% and the balance of Al and inevitable impurities. The content of the aluminum scrap in the mixture is 40 mass% or more and 75 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an aluminum alloy forging. [Background technology]

[0002] In recent years, in the field of automobiles, the application of aluminum alloy forgings to suspension parts such as upper arms and lower arms has been expanding in order to reduce weight as well as to improve steering stability and ride comfort, etc. Examples of aluminum alloy forgings applied to suspension parts of automobiles include Al-Mg-Si aluminum alloys, which are lightweight, high-strength and highly corrosion-resistant.

[0003] For example, Patent Document 1 describes an aluminum alloy forging comprising an aluminum alloy containing 0.70-1.50 mass% Mg, 0.80-1.30 mass% Si, 0.30-0.90 mass% Cu, 0.10-0.40 mass% Fe, 0.005-0.15 mass% Ti, and one or more of 0.10-0.60 mass% Mn, 0.10-0.45 mass% Cr, and 0.05-0.30 mass% Zr, with the balance being Al and unavoidable impurities, wherein the aluminum alloy forging is characterized in that the major axis of the Q phase at the site where maximum stress occurs is 50-500 nm.

[0004] Patent Document 2 discloses a method for producing an aluminum alloy hot forged product from an aluminum alloy material containing 0.7 to 1.5 mass% Si, 0.8 mass% or less Fe, 0.20 to 0.7 mass% Cu, 0.20 to 0.7 mass% Mn, 0.05 to 1.2 mass% Mg, 0.04 to 0.25 mass% Cr, 0.30 mass% or less Zn, 0.15 mass% or less Ti, with the balance being Al and unavoidable impurities. The method includes a material heating step of heating the aluminum alloy material under conditions of a heating temperature of 540°C to 555°C for a heating time of 2 hours or more, and a step of rotating the heated aluminum alloy material from a first direction. a second hot forging step of forging the aluminum alloy material after the first hot forging step from a second direction different from the first direction; a quenching step of quenching the aluminum alloy material after the second hot forging step under conditions where a quenching start temperature is 450°C or higher within 100 seconds after the second hot forging step; and an aging treatment step of aging the aluminum alloy material after the quenching step under conditions where an aging treatment temperature is 180°C or higher and 200°C or lower and an aging treatment time is 1 hour or longer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2015-193903 A [Patent Document 2] JP 2019-123902 A Summary of the Invention [Problem to be solved by the invention]

[0006] Aluminum alloy forgings made of Al-Mg-Si aluminum alloys are often used for automobile suspension parts that require light weight, high strength, and high corrosion resistance. Impurity elements contained in the material of aluminum alloy forgings can have a significant effect not only on mechanical properties but also on corrosion resistance. For this reason, lightweight, high strength, and highly corrosion resistant aluminum alloy forgings are usually produced from virgin aluminum produced by refining bauxite. However, refining bauxite requires a huge amount of electricity. In addition, this electricity is usually supplied by thermal power generation. For this reason, there is a problem that a large amount of CO2 is emitted in conjunction with the production of lightweight, high strength, and highly corrosion resistant aluminum alloy forgings.

[0007] Therefore, an object of the present invention is to provide a means for producing high-strength, highly corrosion-resistant aluminum alloy forgings while reducing the amount of virgin aluminum used and, therefore, reducing CO2 emissions. [Means for solving the problem]

[0008] The inventors have studied various means for solving the above problems. They have found that it is possible to manufacture high-strength and high-corrosion-resistant aluminum alloy forgings by using a predetermined amount of aluminum scrap together with new aluminum metal as a material, adding additive elements to the material mixture to adjust the elemental composition of the material mixture to a predetermined range, heating and melting the material, forging the material, and further performing aging treatment under predetermined conditions. Based on the above findings, the inventors have completed the present invention.

[0009] That is, the present invention includes the following aspects and embodiments. (1) A method for producing an aluminum alloy forging from a mixture containing aluminum scrap, aluminum ingot, and at least one additive element selected from the group consisting of Si, Fe, Cu, Ti, Mn, Cr, Zn, and Mg, comprising the steps of: the mixture contains, relative to a total mass of the mixture, 0.7 to 1.5 mass% Si, 0.8 mass% or less Fe, 0.20 to 0.7 mass% Cu, 0.15 mass% or less Ti, 0.20 to 0.80 mass% Mn, 0.1 mass% or less Cr, 0.30 mass% or less Zn, and 0.050 to 1.1 mass% Mg, with the remainder being Al and unavoidable impurities; The content x of aluminum scrap in the mixture is in the range of 40% by mass or more and 75% by mass or less, based on the total mass of the mixture; The process is as follows: a heating and dissolving step of heating and dissolving the mixture; a forging step for forging the mixture after the heating and melting step; After the forging process, the material is aged at the following temperatures and times: an aging treatment process in which aging treatment is performed under conditions within the range surrounded by (aging temperature, aging time) = (185, 4), (185, 7), (200, 1), and (200, -2 / 25x+8); The method comprising: (2) The method according to the above embodiment (1), wherein the aluminum scrap is an Al-Mg-Mn based alloy having, with respect to a total mass, 0.1-0.5 mass% of Si, 1.0-2.0 mass% of Mg, and 0.10-2.0 mass% of Mn. (3) The method according to the above embodiment (2), wherein the aluminum scrap is an aluminum can. Effect of the Invention

[0010] The present invention makes it possible to provide a means for producing high-strength, highly corrosion-resistant aluminum alloy forgings while reducing the amount of virgin aluminum metal used and reducing CO2 emissions. [Brief description of the drawings]

[0011] [Figure 1]1 is a graph showing the relationship between electrical conductivity and Vickers hardness of the aluminum alloy forgings of Examples 1 to 3 and Comparative Examples 1 to 5. In the graph, the horizontal axis represents relative electrical conductivity (%IACS) when the electrical conductivity of international standard annealed copper (resistivity: 1.7241×10-8 Ωm) is taken as 100%, and the vertical axis represents Vickers hardness (HV). [Diagram 2] 2 is a graph showing the relationship between the aluminum can content and electrical conductivity for the aluminum alloy forgings of Examples 1 to 3 and Comparative Examples 1 to 5, which were aged under the same aging conditions (185°C, 5 hours). In the graph, the horizontal axis represents the aluminum can content (mass%), and the vertical axis represents electrical conductivity (%IACS). [Diagram 3] 3 is a graph showing the relationship between the aging treatment time during production and the electrical conductivity in the aluminum alloy forgings of Examples 2 and 3. A shows the results of Example 2, and B shows the results of Example 3. In the figure, the horizontal axis is the aging treatment time (hours), and the vertical axis is the electrical conductivity (%IACS). The dotted line in the figure shows the electrical conductivity of Comparative Example 5 (41.2%IACS). [Figure 4] 4 is a graph showing the relationship between the aging treatment time during production and the hardness in the aluminum alloy forgings of Examples 2 and 3. A shows the results of Example 2, and B shows the results of Example 3. In the figure, the horizontal axis is the aging treatment time (hours), and the vertical axis is the Vickers hardness (HV). The dotted line in the figure shows the Vickers hardness (140.5 HV) of Comparative Example 5. [Diagram 5] 5 is a graph showing the aging treatment conditions for obtaining high hardness and electrical conductivity, which were determined based on the relationship between the aging treatment conditions during production and the hardness and electrical conductivity in the aluminum alloy forgings of Examples 1 to 3. In the graph, the horizontal axis represents the aging treatment temperature (° C.), and the vertical axis represents the aging treatment time (hours). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Preferred embodiments of the present invention will now be described in detail.

[0013] <1. Manufacturing method of aluminum alloy forgings> Aluminum alloy forgings made of Al-Mg-Si aluminum alloys are often used for automobile suspension parts such as upper and lower arms, which require light weight, high strength and high corrosion resistance. Impurity elements contained in the material of aluminum alloy forgings can have a significant effect not only on mechanical properties but also on corrosion resistance. For this reason, lightweight, high strength and high corrosion resistance aluminum alloy forgings are usually produced from new aluminum ingots produced by a process of refining alumina from bauxite (Bayer process) and a process of refining pure aluminum from alumina (Hall-Heroult process). However, refining bauxite, especially electrolytic refining by the Hall-Heroult process, requires a huge amount of electricity. In addition, the electricity is usually supplied by thermal power generation. For this reason, when manufacturing aluminum alloy forgings from new aluminum ingots, there was a problem that a large amount of CO2 was emitted.

[0014] The present inventors have found that it is possible to produce an aluminum alloy forging having high strength and high corrosion resistance by using a predetermined amount of aluminum scrap together with virgin aluminum as a material, adding additive elements to the material mixture to adjust the elemental composition of the material mixture to a predetermined range, melting the material by heating and forging the material, and then performing aging treatment under predetermined conditions. Therefore, one aspect of the present invention relates to a method for producing an aluminum alloy forging.

[0015] The method of this embodiment is characterized in that an aluminum alloy forging is produced from a mixture containing aluminum scrap, aluminum ingot, and at least one additive element selected from the group consisting of Si, Fe, Cu, Ti, Mn, Cr, Zn, and Mg. The content x of aluminum scrap in the mixture is usually in the range of 40% by mass or more and 75% by mass or less, particularly in the range of 50% by mass or more and 75% by mass or less, based on the total mass of the mixture. For example, in the case of a conventional aluminum alloy such as an AA6110 alloy consisting only of aluminum ingot, about 10 kg of CO2 is emitted to produce 1 kg of aluminum alloy forging. In contrast, in the case of a content of 50% by mass of aluminum scrap, the content of aluminum ingot is 50% by mass, so that the CO2 emission when producing 1 kg of aluminum alloy forging is reduced to about 5 kg. Furthermore, as shown in the following examples, even when a material mixture containing aluminum scrap in the above-mentioned range is used, by carrying out the method of this embodiment, it is possible to obtain an aluminum alloy forging having substantially the same strength and corrosion resistance as when a material mixture consisting of only virgin aluminum metal is used. Therefore, by carrying out the method of this embodiment using a material mixture containing aluminum scrap in the above-mentioned range, it is possible to manufacture an aluminum alloy forging having high strength and high corrosion resistance while reducing CO2 emissions.

[0016] In each embodiment of the present invention, aluminum scrap means a recycled material containing aluminum. The aluminum scrap is preferably an Al-Mg-Mn alloy having Si: 0.1-0.5 mass%, Mg: 1.0-2.0 mass%, and Mn: 0.10-2.0 mass% relative to the total mass, and more preferably an Al-Mg-Mn alloy having Si: 0.1-0.3 mass%, Mg: 1.3-1.6 mass%, and Mn: 0.10-1.5 mass%. The aluminum scrap is preferably an aluminum can or an Al-Mg alloy end material (e.g., end material of a material used for ships, etc.), and more preferably an aluminum can. By carrying out the method of this embodiment using a material mixture containing aluminum scrap having the characteristics exemplified above, it is possible to reduce CO2 emissions compared to the case of using a material mixture consisting only of new aluminum ingots.

[0017] In each embodiment of the present invention, the new aluminum ingot means an aluminum or aluminum alloy material produced by refining bauxite. The new aluminum ingot may be, for example, a 6000 series (Al-Mg-Si) aluminum alloy, which is lightweight, high-strength, and highly corrosion-resistant. The new aluminum ingot is preferably a 6000 series (Al-Mg-Si) aluminum alloy, such as an AA6110 alloy, an AA6061 alloy, or an AA6082 alloy. By carrying out the method of this embodiment using a material mixture containing the new aluminum ingot having the characteristics exemplified above, a high-strength and highly corrosion-resistant aluminum alloy forging can be produced.

[0018] In the method of this embodiment, the material mixture contains, relative to the total mass of the mixture, 0.7 to 1.5 mass% Si, 0.8 mass% or less Fe, 0.20 to 0.7 mass% Cu, 0.15 mass% or less Ti, 0.20 to 0.80 mass% Mn, 0.1 mass% or less Cr, 0.30 mass% or less Zn, and 0.050 to 1.2 mass% Mg, with the remainder being Al and inevitable impurities. The material mixture preferably contains, relative to the total mass of the mixture, 0.9 to 1.3 mass% Si, 0.35 mass% or less Fe, 0.4 to 0.75 mass% Cu, 0.15 mass% or less Ti, 0.40 to 0.80 mass% Mn, 0.1 mass% or less Cr, 0.15 mass% or less Zn, and 0.8 to 1.2 mass% Mg, with the remainder being Al and inevitable impurities. The elemental composition exemplified above is substantially the same as that of a conventional aluminum alloy such as AA6110 alloy consisting only of new aluminum ingots, except for Cr. Therefore, by carrying out the method of this embodiment using a material mixture whose elemental composition is adjusted to the above range by the addition of additional elements, it is possible to obtain an aluminum alloy forging having substantially the same strength and corrosion resistance as when a material mixture consisting only of new aluminum ingots is used.

[0019] In the method of this embodiment, the additive element means an element component added to the material mixture to adjust the elemental composition of the material mixture to a predetermined range. The additive element is usually at least one selected from the group consisting of Si, Fe, Cu, Ti, Mn, Cr, Zn, and Mg. As explained above, aluminum scrap has a lower Si content and a higher Mg content than new aluminum ingots. Therefore, by carrying out the method of this embodiment using a material mixture adjusted to the elemental composition within the above range by the additive elements exemplified above, an aluminum alloy forging material having substantially the same strength and corrosion resistance as when a material mixture consisting of only new aluminum ingots is used can be obtained.

[0020] The method of this embodiment includes a heating and melting step, a forging step, and an aging treatment step. Each step of the method of this embodiment will be described below.

[0021] [1-1. Heating melting process] This process involves heating and melting the material mixture described above.

[0022] This step can be carried out by means commonly used in the art, such as an electric furnace.

[0023] In this process, the heating temperature and heating time of the material mixture are not particularly limited as long as they are within the range of temperatures and times used in the art for heating and melting aluminum alloy material mixtures. If the heating temperature is lower than a commonly used temperature, the elements in the material mixture may not be sufficiently dissolved. If the heating temperature exceeds a commonly used temperature, cracks may occur in the forging process described below. Also, if the heating time is lower than a commonly used temperature, the elements in the material mixture may not be sufficiently dissolved. Therefore, by carrying out this process under conditions used in the art for heating and melting aluminum alloy material mixtures, the elements in the material mixture can be sufficiently dissolved.

[0024] [1-2. Forging process] This process involves forging the mixture after the heating and melting process.

[0025] This process can be carried out using means commonly used in the art such as hydraulic, water or hammer presses.

[0026] In this step, the forging temperature of the mixture is preferably in the range of 520 to 560°C, more preferably in the range of 540 to 555°C. The number of times of forging the mixture is preferably 2 or more, more preferably 3 or more. This step is preferably performed continuously at the forging temperature and the number of times of forging in the above range. If the forging temperature is below the lower limit, the strength of the resulting aluminum alloy forging may be insufficient. If the forging temperature exceeds the upper limit, cracks may occur. If the number of times of forging is below the lower limit, the strength of the resulting aluminum alloy forging may be insufficient. Therefore, by performing this step under the above conditions, a high-strength aluminum alloy forging can be obtained.

[0027] In this process, quenching (forging quenching) may be performed immediately after forging (hot forging) the mixture under the conditions described above. By performing forging quenching, the strength of the aluminum alloy forging can be further improved.

[0028] [1-3. Solution treatment process] The method of this embodiment may optionally include a solution treatment step in which the material is heated and cooled after the forging step.

[0029] This step can be carried out using means commonly used in the art, such as an electric furnace and a cooling water bath.

[0030] In this step, the heating temperature of the solution treatment is preferably in the range of 530 to 560°C, more preferably in the range of 540 to 555°C. The heating time of the solution treatment is preferably 1 hour or more, more preferably 2 hours or more. The quenching water temperature of the solution treatment is preferably in the range of 25 to 60°C, more preferably in the range of 35 to 55°C. If the quenching water temperature exceeds the upper limit, the solution of the elements in the material may be insufficient. If the quenching water temperature does not reach the lower limit, the product dimensions may be significantly affected by quenching distortion. If the heating time is less than the lower limit, the solution of the elements in the material may be insufficient. Therefore, by carrying out this step under the above conditions, the elements in the material can be sufficiently solutionized.

[0031] [1-4. Aging treatment process] This process involves aging the material after the forging process.

[0032] This step can be carried out by means commonly used in the art, such as an electric furnace.

[0033] In this process, the material after the forging process is subjected to the aging temperature and aging time as follows: It has been found that the strength and corrosion resistance of the resulting aluminum alloy forging can be improved by performing the aging treatment under conditions within the range surrounded by (aging temperature, aging time) = (185, 4), (185, 7), (200, 1), (200, -2 / 25x + 8). Here, x is the content (mass%) of aluminum scrap in the material mixture. The reason why each aspect of the present invention has the above-mentioned effects can be explained as follows. Note that each aspect of the present invention is not limited to the following effects and principles. In the aging treatment of an aluminum alloy forging, when the aging treatment temperature is constant, the electrical conductivity of the resulting aluminum alloy forging increases as the aging treatment time increases (Figure 3). In contrast, the hardness of the resulting aluminum alloy forging gradually decreases when the aging treatment time exceeds a certain length (Figure 4). In addition, in the aging treatment of an aluminum alloy forging, when the aging treatment temperature is constant, the diffusion speed of the elements contained in the alloy is the same. Therefore, it can be assumed that the hardness, i.e., strength, of the resulting aluminum alloy forging is rate-determined by the amount of precipitates, which are compounds of Mg and Si. Here, the precipitates precipitate using Mn derived from aluminum scrap (e.g., aluminum cans) as nucleation sites. Therefore, by carrying out the aging treatment under the above conditions defined based on the aluminum scrap content x, an aluminum alloy forging with high strength and high corrosion resistance can be obtained. In this process, for example, when the aluminum scrap content x is 50 mass%, the material after the forging process is subjected to the aging treatment at the following aging temperature and aging time: It is preferable to perform the aging treatment under conditions within the range surrounded by (aging temperature, aging time) = (185, 4), (185, 7), (200, 1), and (200, 4), and it is more preferable to perform the aging treatment under conditions of an aging temperature of 185 ° C. and an aging time in the range of 4 to 7 hours, or an aging temperature of 200 ° C. and an aging time of 1 to 4 hours. For example, when the content x of aluminum scrap is 75 mass %, the material after the forging process is subjected to the aging temperature and aging time as follows: It is preferable to perform the aging treatment under the conditions within the range surrounded by (aging temperature, aging time) = (185, 4), (185, 7), (200, 1), and (200, 2), and more preferably, the aging treatment is performed under the conditions of an aging temperature of 185 ° C and an aging time in the range of 4 to 7 hours, or an aging temperature of 200 ° C and an aging time of 1 to 2 hours. In this process, if the aging treatment time exceeds the above range, the strength of the resulting aluminum alloy forging may be reduced due to so-called overaging. Therefore, by performing this process under the above conditions, an aluminum alloy forging having high strength and high corrosion resistance can be obtained.

[0034] <2. Aluminum alloy forgings> As described above, the manufacturing method according to one aspect of the present invention can provide an aluminum alloy forging having high strength and high corrosion resistance. Therefore, another aspect of the present invention relates to an aluminum alloy forging that can be obtained by the manufacturing method according to one aspect of the present invention, and preferably obtained by the method.

[0035] In each embodiment of the present invention, the strength of the aluminum alloy forging can be evaluated, for example, using the hardness of the aluminum alloy forging as an index, but is not limited thereto. The hardness of the aluminum alloy forging can be measured, for example, as Vickers hardness (HV) using a Vickers hardness tester based on JIS Z 2244:2009. It is known that there is a certain correlation between strength and hardness in aluminum alloy forging. Therefore, the strength of the aluminum alloy forging can be evaluated by measuring the hardness of the aluminum alloy forging.

[0036] In each embodiment of the present invention, the corrosion resistance of the aluminum alloy forging can be evaluated, for example, using the electrical conductivity of the aluminum alloy forging as an index, but is not limited thereto. The electrical conductivity of the aluminum alloy forging can be evaluated, for example, using the electrical conductivity of international standard annealed copper (resistivity: 1.7241×10 -8The relative conductivity (%IACS) can be measured using a high-precision conductivity meter or the like, with the conductivity of Ωm being taken as 100%. It is known that there is a certain correlation between the corrosion resistance and conductivity of aluminum alloy forgings. Therefore, the corrosion resistance of an aluminum alloy forging can be evaluated by measuring the conductivity of the forging.

[0037] The aluminum alloy forging of this embodiment usually has a Vickers hardness of 135 HV or more, for example, 140 HV or more, particularly in the range of 140 to 150 HV. The aluminum alloy forging of this embodiment also usually has an electrical conductivity of 41% IACS or more, for example, 41.5% IACS or more, particularly in the range of 41.5 to 44% IACS. In contrast, an aluminum alloy forging obtained from a conventional aluminum alloy such as the AA6110 alloy has a Vickers hardness of about 140 HV and an electrical conductivity of about 41% IACS. Therefore, the aluminum alloy forging of this embodiment can have high strength and high corrosion resistance that are comparable to or greater than those of an aluminum alloy forging obtained from a conventional aluminum alloy.

[0038] The aluminum alloy forging material of this embodiment is lightweight, high-strength, and highly corrosion-resistant, and can be used as a structural member of an automobile by appropriately performing extrusion and / or forging. Examples of the structural members of an automobile include automobile suspension parts such as upper arms, lower arms, and steering knuckle carriers, as well as energy absorbing members that absorb energy during a collision, such as bumper reinforcements and door impact beams. By using the aluminum alloy forging material of this embodiment as the structural members of an automobile exemplified above, it is possible to reduce the weight of the automobile and improve the steering stability and ride comfort. EXAMPLES

[0039] The present invention will be described in more detail below with reference to examples, although the technical scope of the present invention is not limited to these examples.

[0040] <I:Manufacture of Aluminum Alloy Forgings> [I-1:Material Composition] The material compositions of the aluminum alloy forgings of the examples and comparative examples are shown in Table 1. The element compositions and material compositions in the table are shown in mass% based on the total mass of the material mixture.

[0041]

Table 1

[0042] [I-2:Manufacture] After adjusting the materials of the examples and comparative examples to the compositions shown in Table 1, the material mixture was heated and melted at a temperature of 700 °C or higher and continuously cast. Forging was carried out on the materials of the examples and comparative examples under the condition of 555 °C. Thereafter, the materials of the examples and comparative examples were each subjected to T6 treatment under the various conditions shown below. Solution treatment: The material mixture was heated under the conditions of 555 °C for 2 hours, and then water-cooled. Aging treatment: The material after solution treatment was aged under the conditions of 170 to 200 °C for 1 to 10 hours.

[0043] <II:Performance Evaluation of Aluminum Alloy Forgings> [II-1:Relationship between Conductivity and Hardness] The conductivity and Vickers hardness of the aluminum alloy forgings of the examples and comparative examples were measured. The conductivity of the forgings was measured using a high-precision conductivity measuring instrument. Also, the Vickers hardness of the forgings was measured using a Vickers hardness tester based on JIS Z 2244:2009.

[0044] The relationship between the conductivity and Vickers hardness of the aluminum alloy forgings of Examples 1 to 3 and Comparative Examples 1 to 5 is shown in Fig. 1. In the figure, the horizontal axis is the international standard soft copper (resistivity: 1.7241×10 -8The graph shows the relative electrical conductivity (%IACS) when the electrical conductivity in Ωm is taken as 100%, and the vertical axis shows the Vickers hardness (HV). As shown in FIG. 1, Comparative Examples 1 to 4 have almost the same or higher hardness as Comparative Example 5, which is a conventional aluminum alloy (AA6110 alloy), but the electrical conductivity is lower. Therefore, the aluminum alloy forgings of Comparative Examples 1 to 4 may have low corrosion resistance although they have high strength. In contrast, Examples 1 to 3 have almost the same or higher hardness as Comparative Example 5 and higher electrical conductivity. Therefore, it is presumed that the aluminum alloy forgings of Examples 1 to 3 have high strength and high corrosion resistance.

[0045] [II-2: Relationship between aluminum can content and electrical conductivity] FIG. 2 shows the relationship between the aluminum can content and electrical conductivity in the aluminum alloy forgings of Examples 1 to 3 and Comparative Examples 1 to 5, which were aged under the same aging conditions (185°C, 5 hours). In the figure, the horizontal axis is the aluminum can content (mass%), and the vertical axis is electrical conductivity (%IACS). As shown in FIG. 2, it became clear that in order to obtain electrical conductivity exceeding the electrical conductivity (41.2%IACS) of Comparative Example 5, which is a conventional aluminum alloy (AA6110 alloy), the aluminum can content must be 75 mass% or less (Examples 1 to 3). In this example, in order to ensure the amount of precipitation hardening, after the aluminum can was mixed into the material mixture, elemental components were added so that the elemental composition was the same as that of the AA6110 alloy (excluding the composition of Cr). Therefore, even when the aluminum can content was reduced from that of Example 1, the electrical conductivity hardly changed (results not shown). However, from the viewpoint of reducing CO2 emissions during manufacturing, a high aluminum can content is preferable. For example, in the case of a conventional aluminum alloy such as AA6110 alloy consisting only of virgin aluminum metal, about 10 kg of CO2 is emitted to produce 1 kg of aluminum alloy forging. In contrast, in the case of an aluminum can content of 50 mass%, the content of virgin aluminum metal is 50 mass%, so the CO2 emissions when producing 1 kg of aluminum alloy forging are reduced to about 5 kg. Therefore, in this embodiment, by setting the aluminum can content to 40 mass% or more, it is possible to reduce the CO2 emissions while maintaining high electrical conductivity.

[0046] [II-3: Relationship between aging conditions and electrical conductivity] FIG. 3 shows the relationship between the aging time during production and the electrical conductivity in the aluminum alloy forgings of Examples 2 and 3. A is the result of Example 2, and B is the result of Example 3. In the figure, the horizontal axis is the aging time (hours), and the vertical axis is the electrical conductivity (%IACS). The dotted line in the figure indicates the electrical conductivity (41.2%IACS) of Comparative Example 5. As shown in FIG. 3, the electrical conductivity of the aluminum alloy forgings improved with the aging time during production. In the case of the aluminum alloy forgings of Example 2, in order to obtain an electrical conductivity exceeding that (41.2%IACS) of Comparative Example 5, which is a conventional aluminum alloy (AA6110 alloy), an aging treatment of 4 hours or more was required at an aging temperature of 185°C, and an aging treatment of 1 hour or more was required at an aging temperature of 200°C (FIG. 3A). In contrast, in the case of the aluminum alloy forging of Example 3, in order to obtain a conductivity exceeding that (41.2% IACS) of Comparative Example 5, which is a conventional aluminum alloy (AA6110 alloy), aging treatment for one hour or more was required at both aging treatment temperatures of 185°C and 200°C (FIG. 3B). In the case of the aluminum alloy forging of Example 1, since the aluminum can compounding ratio was almost the same as in Example 2, the results were almost the same as in Example 2 (results not shown).

[0047] [II-4: Relationship between aging conditions and hardness] FIG. 4 shows the relationship between the aging time at the time of manufacture and the hardness in the aluminum alloy forgings of Examples 2 and 3. A is the result of Example 2, and B is the result of Example 3. In the figure, the horizontal axis is the aging time (hours), and the vertical axis is the Vickers hardness (HV). The dotted line in the figure indicates the Vickers hardness (140.5 HV) of Comparative Example 5. As shown in FIG. 4, the hardness of the aluminum alloy forgings of Example 2 decreased with the aging time at the time of manufacture due to so-called overaging. In the case of the aluminum alloy forgings of Example 2, in order to obtain a hardness exceeding the Vickers hardness (140.5 HV) of Comparative Example 5, which is a conventional aluminum alloy (AA6110 alloy), an aging treatment in the range of 4 to 7 hours was required at an aging temperature of 185°C, and an aging treatment in the range of 1 to 4 hours was required at an aging temperature of 200°C (FIG. 4A). In contrast, in the case of the aluminum alloy forging of Example 3, in order to obtain a hardness exceeding the Vickers hardness (140.5 HV) of Comparative Example 5, which is a conventional aluminum alloy (AA6110 alloy), aging treatment was required for 4 to 7 hours at an aging treatment temperature of 185°C and for 1 to 2 hours at an aging treatment temperature of 200°C (FIG. 4B).

[0048] [II-5: Aging treatment conditions for producing high-strength and high-corrosion-resistant aluminum alloy forgings] Fig. 5 shows the aging treatment conditions for obtaining high hardness and electrical conductivity, which were determined based on the relationship between the aging treatment conditions during production and the hardness and electrical conductivity in the aluminum alloy forgings of Examples 1 to 3. In the figure, the horizontal axis represents the aging treatment temperature (°C), and the vertical axis represents the aging treatment time (hours). In the aging treatment of aluminum alloy forgings, when the aging temperature is constant, the electrical conductivity of the resulting aluminum alloy forgings increases with the aging time (Figure 3). In contrast, the hardness of the resulting aluminum alloy forgings gradually decreases when the aging time exceeds a certain length (Figure 4). In addition, in the aging treatment of aluminum alloy forgings, when the aging temperature is constant, the diffusion speed of the elements contained in the alloy is the same. Therefore, it can be assumed that the hardness, i.e., strength, of the resulting aluminum alloy forgings is rate-limited by the amount of precipitates, which are compounds of Mg and Si. Here, the precipitates precipitate using Mn derived from aluminum scrap (aluminum cans) as a nucleation site. Therefore, the following is defined based on the content x (mass%) of aluminum scrap relative to the total mass of the material mixture: By performing aging treatment under conditions within the range surrounded by (aging temperature, aging time) = (185, 4), (185, 7), (200, 1), and (200, -2 / 25x+8) (the shaded area in Figure 5), it is possible to obtain an aluminum alloy forging material with high strength and high corrosion resistance.

[0049] The present invention is not limited to the above-described embodiments, but includes various modified examples. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the configurations described. In addition, it is possible to add, delete, and / or replace part of the configuration of each embodiment with other configurations.

Claims

1. A method for producing an aluminum alloy forging from a mixture containing aluminum scrap, aluminum ingot, and at least one additive element selected from the group consisting of Si, Fe, Cu, Ti, Mn, Cr, Zn, and Mg, comprising: the mixture contains, relative to a total mass of the mixture, 0.7 to 1.5 mass% Si, 0.8 mass% or less Fe, 0.20 to 0.7 mass% Cu, 0.15 mass% or less Ti, 0.20 to 0.80 mass% Mn, 0.1 mass% or less Cr, 0.30 mass% or less Zn, and 0.8 to 1.2 mass% Mg, with the remainder being Al and unavoidable impurities; The content x of aluminum scrap in the mixture is in the range of 40% by mass or more and 75% by mass or less, based on the total mass of the mixture; The process is as follows: a heating and dissolving step of heating and dissolving the mixture; a forging step in which the mixture after the heating and melting step is forged at a temperature in the range of 520 to 560°C; A solution treatment process in which the material after the forging process is heated at a temperature in the range of 530 to 560°C and then water-cooled at a quenching water temperature in the range of 25 to 60°C; The material after the solution treatment process is subjected to the aging temperature and the aging time as follows: An aging treatment process in which aging treatment is performed under conditions within the range surrounded by (aging temperature, aging time) = (185, 4), (185, 7), (200, 1), and (200, -2 / 25x+8); The method comprising:

2. 2. The method according to claim 1, wherein the aluminum scrap is an Al-Mg-Mn based alloy having, relative to the total mass, 0.1-0.5% by mass of Si, 1.0-2.0% by mass of Mg, and 0.10-2.0% by mass of Mn.

3. 3. The method of claim 2, wherein the aluminum scrap is aluminum cans.

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