Aluminum alloy forged member and manufacturing method thereof

Abstract

To provide an aluminum alloy-made forged member which has excellent tensile characteristics and sufficiently secures strength and reliability as the whole member, in which variations in microstructures and tensile characteristics are suppressed and to provide an efficient manufacturing for producing the same.SOLUTION: There is provided a method for manufacturing an aluminum alloy-made forged member by forging an aluminum alloy-made billet, wherein the aluminum alloy-made billet comprises 0.6 to 1.2 mass% of Si, 0.1 to 0.25 mass% of Fe, 0.2 to 1.1 mass% of Cu, 0.7 to 1.2 mass% of Mg, 0.1 to 0.4 mass% of Cr, more than 0 to 0.1 mass% of Ti and the balance Al with inevitable impurities, a content of Mg2Si is 1.1 to 1.8 mass%, an amount of excessive Si not constituting Mg2Si is 0.1 to 0.7 mass% and a temperature-compensated strain rate (Z) in the forging process satisfies a following expression, Z>2×1012 or Z≤2×1010.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an aluminum alloy forged member which is required to have high strength and reliability, and to a method for manufacturing the same. [Background technology]

[0002] Aluminum has a specific gravity of about one-third that of iron, and depending on the type of alloy and manufacturing process, it can achieve extremely high strength. As a result, it has a high specific strength compared to other metals, and is therefore used to reduce the weight of automobiles, aircraft, bicycles, various storage containers, etc.

[0003] In addition, aluminum is easy to process plastically, and extrusion can produce extruded products with complex shapes, while forging can produce even more complex shapes. In other words, by performing plastic processing on high-strength aluminum alloys, it is possible to efficiently manufacture various components that require high reliability.

[0004] However, the demands on the mechanical properties of structural members are getting higher day by day, and it is becoming difficult for existing aluminum alloys to meet these demands. In particular, when an aluminum alloy part has a portion with a large shape change such as a rounded portion or a recessed portion, the portion is subjected to a large stress during use, which may lead to cracks or breakage even if the strength of the other portions is sufficiently ensured.

[0005] In contrast, for example, Patent Document 1 (Japanese Patent No. 5561846) describes an Al-Cu-Mg-Si aluminum alloy material obtained by extrusion and cold working, which contains 1.0 to 3.0% (mass%, the same applies below) of Cu, 0.4 to 1.8% of Mg, 0.2 to 1.6% of Si, and the balance being Al and impurities. In this material, rod-shaped precipitates are formed within the crystal grains of the matrix. <100> The precipitates are aligned in the

[0001] direction, the average length of the precipitates is 10 to 70 nm, the maximum length is 120 nm or less, and the number density of precipitates in the

[0001] direction measured in the observation field from the (001) plane is 500 pieces / μm 2 The proposed high-strength aluminum alloy material is characterized in that the matrix has a structure consisting of equiaxed crystal grains formed by recrystallization, the average aspect ratio (L / ST) is 1.5 to 4.0, where L is the average grain size of the crystal grains in the extrusion direction and ST is the average grain size in the thickness direction, and the tensile strength is 450 MPa or more, the yield strength is 400 MPa or more, and the elongation is 7% or more.

[0006] The high-strength aluminum alloy material described in the above Patent Document 1 is a heat-treated Al-Cu-Mg-Si high-strength aluminum alloy cold-worked material that has excellent extrusion processability, can be produced into hollow extrusion materials by porthole extrusion method, and has high strength, and in particular, the cold-worked pipe material in a pipe shape can be suitably used as a transportation equipment component such as a motorcycle structural material.

[0007] Also, in Patent Document 2 (JP 2017-43802 A), an aluminum alloy extrusion material is described, which contains, by mass%, 2.5 to 3.3% Cu, 1.3 to 2.5% Mg, 0.50 to 1.3% Ni, 0.50 to 1.5% Fe, less than 0.50% Mn, 0.15 to 0.40% Si, 0.06 to 0.20% Zr, less than 0.05% Ti, and the balance being Al and unavoidable impurities, and in a cross section, the grain size of the intermetallic compound is 20 μm or less in terms of circle equivalent diameter, and the density of the intermetallic compound having a grain size of 0.3 to 20 μm in terms of circle equivalent diameter is 5×10 3 pieces / mm 2The aluminum alloy extrusion material is characterized in that the average grain size of the subgrains is 20 μm or less in terms of circle equivalent diameter.

[0008] The aluminum alloy extrusion material of Patent Document 2 can improve the strength and creep resistance at high temperatures, for example, above 200°C, and can improve not only the strength in the extrusion direction (L direction) but also the strength in the direction perpendicular to the extrusion direction (LT direction). It also improves the creep resistance, particularly in the LT direction, and is applicable to parts of internal combustion engines and superchargers of automobiles and the like that are used in high-temperature environments. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5561846 [Patent Document 2] JP 2017-43802 A Summary of the Invention [Problem to be solved by the invention]

[0010] In the high-strength aluminum alloy material of Patent Document 1, the tensile properties at room temperature are improved by the composition, the shape and size of precipitates, etc. In the aluminum alloy extrusion material of Patent Document 2, the strength and creep resistance at high temperatures are improved by the composition, the grain size of intermetallic compounds, and the average grain size of subgrains. However, in these aluminum alloy materials, the variations in microstructure and mechanical properties throughout the aluminum alloy material actually obtained are not taken into consideration at all, and a method for obtaining a homogeneous aluminum alloy material having excellent mechanical properties has not been considered.

[0011] In view of the problems in the prior art as described above, the object of the present invention is to provide an aluminum alloy forged member having excellent tensile properties and sufficient strength and reliability as a whole member, in which the variations in microstructure and tensile properties are suppressed, and an efficient method for manufacturing the same. Another object of the present invention is to reduce stress concentration at grain boundaries when stress is applied by refining and homogenizing the structure of the aluminum alloy forged member, thereby effectively suppressing the occurrence and propagation of fatigue cracks. [Means for solving the problem]

[0012] In order to achieve the above-mentioned object, the inventors have conducted extensive research into aluminum alloy forged members and methods for manufacturing the same, and as a result, have discovered that it is extremely effective to optimize the composition of the aluminum alloy, and to selectively form a fine recrystallized structure or a recovered structure consisting of subcrystals by controlling the forging process, thereby suppressing the generation of coarse recrystallization, thereby arriving at the present invention.

[0013] That is, the present invention provides: A method for producing an aluminum alloy forged member by forging an aluminum alloy billet, comprising the steps of: The aluminum alloy billet is Si:0.6~1.2% by mass, Fe: 0.1~0.25% by mass, Cu: 0.2~1.1% by mass, Mg: 0.7~1.2% by mass, Cr:0.1~0.4% by mass, Ti: more than 0 to 0.1 mass%, The balance is an aluminum alloy containing Al and unavoidable impurities, Mg 2 The Si content is 1.1 to 1.8 mass %, Said Mg 2 The amount of excess Si that does not constitute Si is 0.1 to 0.7 mass %, The temperature compensation strain rate (Z) in the forging process is Z>2×10 12 Or Z≦2×10 10To satisfy the following: The present invention provides a method for producing an aluminum alloy forged member, comprising the steps of: Here, the value of Z can be controlled by strain rate and temperature, and Z>2×10 12 Or Z≦2×10 10 As long as the forging conditions satisfy the above, various conventionally known forging methods can be widely used.

[0014] In the method for producing an aluminum alloy forged member of the present invention, the additive elements are designed to give the aluminum alloy forged member high strength and excellent ductility, and to facilitate the formation of a fine recrystallized structure or a recovered structure after forging. In addition, the aluminum alloy billet having the optimized composition has a temperature compensated strain rate (Z) of Z>2×10 12 By performing the forging process under the condition of Z≦2×10, it is possible to leave distortion during the forging process and form a fine recrystallized structure after the subsequent solution treatment. 10 By performing the forging process under the condition of 3 Since the formation of coarse recrystallization is suppressed by the dispersed particles of Zr, etc., a fine recovery structure can be formed after the subsequent solution treatment. That is, in either case, the formation of coarse recrystallization can be suppressed extremely effectively.

[0015] In the manufacturing method of the aluminum alloy forged member of the present invention, it is preferable that the aluminum alloy billet contains 0.1-0.8 mass% Mn, and the total content of the Cr and the Mn is 0.2-0.9 mass%. By adding Mn and Cr in combination, Al-Fe(Mn, Cr)-Si-based dispersed particles are formed (substituting for Fe), which can suppress grain boundary migration and recrystallization during T6 treatment of high-temperature forged material. In addition, there is an effect of accumulating strain during low-temperature forging and forming a fine recrystallized structure during T6 treatment, and the crystal structure of the forged material can be controlled more effectively. In addition, an effect of trapping hydrogen atoms and suppressing hydrogen embrittlement can be expected.

[0016] By adding 0.1 to 0.8 mass% of Mn to an aluminum alloy billet and setting the total content of Cr and Mn to 0.2 to 1.2 mass%, the range of forging conditions in which a fine recrystallized structure or a recovered structure consisting of subcrystals can be obtained can be expanded. In this case, the temperature compensation strain rate (Z) in the forging process is Z≧1×10 12 Or Z≦1×10 11 It is preferable that the following condition is satisfied.

[0017] In the manufacturing method of the aluminum alloy forged member of the present invention, the aluminum alloy billet preferably contains Zr: 0.1 to 0.3 mass%. Zr is finely crystallized in the metal structure as an Al-Zr intermetallic compound, suppresses grain boundary migration during T6 treatment of the high-temperature forged material, and suppresses recrystallization. In addition, it accumulates strain during low-temperature forging, and can form a fine recrystallized structure.

[0018] Furthermore, in the method for producing an aluminum alloy forged member of the present invention, a homogenization heat treatment step of holding the aluminum alloy billet at 500 to 570°C before the forging process; A solution treatment process in which the forged member obtained by the forging process is maintained at 520 to 575 ° C.; and an artificial aging step of holding the solution-treated member obtained in the solution treatment step at 170 to 200°C for 2 to 15 hours. It is preferable that the time from the solution treatment step to the artificial aging step (natural aging time) is 100 minutes or less.

[0019] By undergoing these heat treatment processes, it is possible to impart high tensile properties to the aluminum alloy forged member obtained by precipitation strengthening. Particularly important is the time from the solution treatment process to the artificial aging process (time of natural aging), and by setting this to 100 minutes or less, it is possible to form favorable clusters composed of Mg and Si that contribute to improving the strength of the aluminum alloy. On the other hand, if the time of natural aging is longer than 100 minutes, Si-rich clusters are formed, making it difficult to improve the strength of the aluminum alloy forged member.

[0020] The present invention also provides a method for producing a semiconductor device comprising the steps of: Si:0.6~1.2% by mass, Fe: 0.1~0.25% by mass, Cu: 0.2~1.1% by mass, Mg: 0.7~1.2% by mass, Cr:0.1~0.4% by mass, Ti: more than 0 to 0.1 mass%, The balance is an aluminum alloy containing Al and unavoidable impurities, Mg 2 The Si content is 1.1 to 1.8 mass %, Said Mg 2 The amount of excess Si that does not constitute Si is 0.1 to 0.7 mass %, A recrystallized or recovered structure having an average grain size of 500 μm or less is formed, Tensile strength: 360 MPa or more, yield strength: 330 MPa or more, and elongation at break: 6% or more. The present invention also provides an aluminum alloy forged member, characterized in that

[0021] In the aluminum alloy forged member of the present invention, the type and content of additive elements are optimized for the purpose of improving tensile properties (tensile strength, 0.2% yield strength, and elongation) and controlling the structure. 2 By controlling the Si content, it is possible to achieve both high strength and excellent ductility, and by specifying the Cr content (the sum of the Cr content and Mn content as necessary), it is designed to make it easier for a fine recrystallized structure or recovery structure to form after forging.

[0022] In addition, the aluminum alloy forged member of the present invention has high strength and reliability due to the effective precipitation strengthening and the formation of a recrystallized or recovered structure having an average grain size of 500 μm or less. More specifically, the aluminum alloy forged member has tensile properties of 360 MPa or more, 330 MPa or more in tensile strength, and 6% or more in yield strength.

[0023] Here, in the aluminum alloy forged member and its manufacturing method of the present invention, "average grain size is 500 μm or less" means that the average grain width is 500 μm or less. Specifically, in the case of a recovered structure (subcrystal), the crystal structure is an extrusion processed structure (fiber structure) or an extrusion material fine recrystallized structure that remains in a state where it has been plastically processed by forging. Since the crystal grains also elongate during forging, the average grain size is evaluated by the width of the crystal grains. Even in the case of a recrystallized structure, it is sufficient to evaluate the grain width of the structure recrystallized by the solution treatment after forging.

[0024] In addition, the aluminum alloy forged member of the present invention preferably further contains 0.1-0.8 mass% Mn, and the total content of the Cr and Mn is 0.2-1.2 mass%. By adding Mn and Cr in combination, Al-Fe(Mn, Cr)-Si-based dispersed particles are formed (substituting for Fe), which can suppress grain boundary migration and recrystallization during T6 treatment of high-temperature forged material. In addition, there is an effect of accumulating strain during low-temperature forging and forming a fine recrystallized structure, and the crystal structure of the forged material can be controlled more effectively.

[0025] The aluminum alloy forged member of the present invention preferably further contains 0.1 to 0.3 mass% Zr. Zr is finely crystallized in the metal structure as an Al-Zr intermetallic compound, suppresses grain boundary migration during T6 treatment of high-temperature forged material, and suppresses recrystallization. In addition, it accumulates strain during low-temperature forging, allowing the formation of a fine recrystallized structure.

[0026] The aluminum alloy forged member of the present invention can be suitably obtained by the method for producing an aluminum alloy forged member of the present invention.

[0027] Furthermore, the present invention provides an aluminum alloy forged part comprising the aluminum alloy forged member of the present invention. In the aluminum alloy forged part of the present invention, a recrystallized structure or a recovered structure having an average grain size of 500 μm or less is formed in all regions, and the aluminum alloy forged part has extremely high reliability and mechanical properties. Effect of the Invention

[0028] According to the present invention, it is possible to provide an aluminum alloy forged component having excellent tensile properties while fully ensuring the strength and reliability of the component as a whole, in which variations in microstructure and tensile properties are suppressed, and an efficient method for manufacturing the same. [Brief description of the drawings]

[0029] [Figure 1] 1 is an example of a process diagram for obtaining an aluminum alloy forged member. [Diagram 2] FIG. 2 is a schematic diagram of a cross-sectional shape of a forged material in an embodiment. [Diagram 3] 1 is a photograph of the structure of the aluminum forged part obtained in Example 12. [Figure 4] 1 is a photograph of the structure of the aluminum forged part obtained in Example 11. [Diagram 5] 2 is a photograph of the structure of the aluminum forged part obtained in Comparative Example 1. [Figure 6] 1 is a graph showing the relationship between the structure and the forging conditions for Examples 1 and 2 and Comparative Example 1. [Figure 7] 1 is a graph showing the relationship between the structure and the forging conditions for Examples 3 to 7 and Comparative Example 2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] Representative embodiments of the aluminum alloy forged member and its manufacturing method according to the present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these. In the following description, the same or equivalent parts are given the same reference numerals, and duplicated descriptions may be omitted. In addition, since the drawings are intended to conceptually explain the present invention, the dimensions of each component shown and their ratios may differ from the actual ones.

[0031] 1. Aluminum alloy forged parts The aluminum alloy forged member of the present invention is a member for obtaining various aluminum alloy forged parts, and is characterized in that the aluminum alloy composition is optimized and a fine recrystallized structure or recovered structure is formed, and the aluminum alloy forged member has homogeneous and extremely excellent tensile properties. The composition, structure, mechanical properties, etc. of the aluminum alloy forged member will be described in detail below.

[0032] (1) Composition The aluminum alloy used for the aluminum alloy member is an aluminum alloy containing Si: 0.6-1.2 mass%, Fe: 0.1-0.25 mass%, Cu: 0.2-1.1 mass%, Mg: 0.7-1.2 mass%, Cr: 0.1-0.4 mass%, Ti: more than 0-0.1 mass%, and the balance being Al and unavoidable impurities. In addition, Mn and Zr can be added as optional additive elements. Each component element will be explained below.

[0033] (1-1) Essential additive elements Si:0.6~1.2% by mass Si forms Mg-Si precipitates together with Mg, and has the effect of enhancing mechanical strength and fatigue strength. If the Si content is less than 0.6 mass%, the solid solution strengthening and age hardening ability are insufficient, and the mechanical strength and fatigue strength required for aluminum alloy members cannot be obtained. On the other hand, if the Si content is more than 1.2 mass%, the corrosion resistance and hydrogen embrittlement resistance are reduced. By imparting high strength and excellent hydrogen embrittlement resistance to aluminum alloy forged members, they can also be suitably used as aluminum alloy forged members for obtaining various hydrogen container members (mouthpieces, valves, etc.). In addition, if the Si content is more than 1.2 mass%, coarse crystallized particles and precipitates are formed, which may reduce ductility and workability.

[0034] Fe:0.1~0.25% by mass Fe is an effective element for forming Al-Fe(Mn, Cr)-Si dispersed particles. It suppresses the recrystallization of Al and contributes to improving strength, but this effect is not fully obtained at less than 0.1 mass%. However, if added in excess, it reduces the precipitates and precipitated Si, Mn, and Cr that contribute to strength, and forms coarse intermetallic compounds, reducing strength, so the upper limit of the amount added is set at 0.25 mass%.

[0035] Cu:0.2~1.1% by mass Cu forms Al-Cu precipitates and has the effect of increasing mechanical strength and fatigue strength. If the Cu content is less than 0.2 mass%, these effects cannot be fully obtained, and the mechanical strength and fatigue strength required for aluminum alloy forged members cannot be obtained. On the other hand, if the Cu content exceeds 1.1 mass%, there is a risk of reducing corrosion resistance.

[0036] Mg:0.7~1.2% by mass Mg forms Mg-Si precipitates together with Si, and has the effect of increasing mechanical strength and fatigue strength. This effect is significant at 0.7 mass% or more, but even if added in excess of 1.2 mass%, little contribution to hardness can be expected, and there is a risk of forming coarse intermetallic compounds that become the starting point of fracture, reducing mechanical strength and ductility.

[0037] Cr:0.1~0.4% by mass Cr crystallizes finely in the metal structure as an Al-Cr intermetallic compound, suppressing grain boundary migration and recrystallization during T6 treatment of high-temperature forged material. It also accumulates strain during low-temperature forging, forming a fine recrystallized structure. It is also expected to trap hydrogen atoms and suppress hydrogen embrittlement. This effect is particularly noticeable at 0.1 mass% or more, but if it is contained in excess of 0.4 mass%, it forms undesirable compounds that impair ductility.

[0038] Ti: more than 0~0.1% by mass Ti refines the cast structure and prevents casting cracks.

[0039] (1-2) Optional additive elements Mn:0.1~0.8% by mass By adding Mn and Cr in combination, dispersed particles of Al-Fe(Mn, Cr)-Si system are formed (substituting for Fe), which suppresses grain boundary migration during T6 treatment of high-temperature forged material and suppresses recrystallization. In addition, there is an effect of accumulating strain during low-temperature forging and forming a fine recrystallized structure, and it is possible to more effectively control the crystal structure of the forged material. In addition, it is expected to have an effect of trapping hydrogen atoms and suppressing hydrogen embrittlement. This effect is particularly remarkable when it is 0.1 mass% or more, but if it is contained in excess of 0.8 mass%, it increases the quenching sensitivity and inhibits the solution treatment property (if quenching is delayed, the strength decreases). For these reasons, the total amount of Cr and Mn is preferably 0.1 to 1.2 weight%.

[0040] Zr:0.1~0.3% by mass Zr crystallizes finely in the metal structure as an Al-Zr intermetallic compound, suppressing grain boundary migration and recrystallization during T6 treatment of high-temperature forged material. It also accumulates strain during low-temperature forging, forming a fine recrystallized structure. This effect is particularly noticeable at 0.1% by mass or more, but if it is contained in excess of 0.3% by mass, it forms a material compound that inhibits ductility, etc.

[0041] (1-3) Other conditions regarding composition Mg 2 Si content: 1.1 to 1.8 mass% Mg 2 By making the Si content 1.1 mass% or more, the strength required for aluminum alloy forged members can be achieved by precipitation strengthening. 2 By setting the Si content to 1.8 mass % or less, it is possible to suppress a decrease in the ductility of the aluminum alloy forged member.

[0042] Excess Si content: 0.1 to 0.7 mass% By setting the amount of excess Si to 0.1 mass % or more, the effect of precipitation strengthening can be sufficiently obtained. Furthermore, by setting the amount of excess Si to 0.7 mass % or less, deterioration of corrosion resistance and hydrogen embrittlement resistance can be suppressed.

[0043] (2) Organization The aluminum alloy forged member of the present invention is characterized in that a recrystallized structure or a recovered structure having an average grain size of 500 μm or less is formed. Here, in the forging process, it is difficult to accurately define the processing conditions in the vicinity of the die contact surface, and there is a difference between the processing conditions obtained by analysis and the actual processing conditions. For example, the friction coefficient of the die surface changes depending on the type and state of the lubricant, and the thermal conductivity of the die also affects the analysis results. Therefore, in the aluminum alloy forged member of the present invention, the vicinity of the extreme surface that is affected by contact with the die is not specified. Here, "near the extreme surface" means a range of about 5 mm from the die contact surface.

[0044] The method for determining the average grain size of crystal grains is not particularly limited as long as it does not impair the effects of the present invention, and various conventionally known methods may be used. For example, the average grain size of the base material crystal grains can be calculated by cutting the aluminum alloy forged member at an arbitrary cross section, observing the obtained cross section sample with an optical microscope or a scanning electron microscope, and calculating the average grain size of the base material crystal grains. In this case, for example, the grain size can be measured by the intersection method. In addition, it may be measured by an electron backscatter diffraction measurement device (SEM-EBSD) attached to a scanning electron microscope. The observation area for determining the average grain size depends on the size and shape of the aluminum alloy forged member, but an accurate value can be obtained by determining the observation area so that at least 20 grains are to be measured. In addition, the cross section sample may be subjected to mechanical polishing, buff polishing, electrolytic polishing, etching, etc. depending on the observation method.

[0045] The aluminum alloy forged member has tensile properties of tensile strength: 360 MPa or more, proof stress: 330 MPa or more, and breaking elongation: 6% or more. Here, the tensile strength is preferably 380 MPa or more, more preferably 400 MPa or more, and most preferably 420 MPa or more. The proof stress is preferably 340 MPa or more, more preferably 350 MPa or more, and most preferably 360 MPa or more. The breaking elongation is preferably 8% or more, more preferably 10% or more, and most preferably 12% or more. Since the aluminum alloy forged member has these tensile properties, it can be suitably used as a member for manufacturing parts for automobiles, aircraft, bicycles, various high-pressure gas storage containers, and the like.

[0046] Furthermore, the forged aluminum alloy member can be efficiently manufactured by forging an extruded member, not only because the forged aluminum alloy member can be given any shape, but also because the microstructure obtained by the forging process can be a fine recrystallized structure or a recovered structure.

[0047] 2.Aluminum alloy forged parts The aluminum alloy forged part of the present invention is an aluminum alloy forged part made of the aluminum alloy forged member of the present invention. In the aluminum alloy forged part of the present invention, a recrystallized structure or a recovered structure having an average grain size of 500 μm or less is formed in all regions, and the aluminum alloy forged part has extremely high reliability and mechanical properties.

[0048] The shape and size of the aluminum alloy forged part of the present invention are not particularly limited as long as the effect of the present invention is not impaired, and may be any of the shapes and sizes of various conventionally known forged parts. Examples of aluminum alloy forged parts include parts for automobiles, aircraft, bicycles, and various high-pressure gas storage containers. The method of obtaining an aluminum alloy forged part from an aluminum alloy forged member is also not particularly limited as long as the effect of the present invention is not impaired, and various conventionally known processing methods such as cutting can be used.

[0049] 3. Manufacturing method of aluminum alloy forged components The method for manufacturing an aluminum alloy forged member of the present invention involves forging an aluminum alloy billet (extruded bar or cast material), and its greatest feature is the combination of the aluminum alloy composition and the temperature compensated strain rate (Z) during the forging process.

[0050] Specifically, the aluminum alloy billet to be forged contains 0.6-1.2% by mass of Si, 0.1-0.25% by mass of Fe, 0.2-1.1% by mass of Cu, 0.7-1.2% by mass of Mg, 0.1-0.4% by mass of Cr, and more than 0.1% by mass of Ti, with the remainder being Al and unavoidable impurities. 2 The Si content is 1.1 to 1.8 mass%, and the Mg 2 The amount of excess Si that does not constitute Si is 0.1 to 0.7 mass %.

[0051] In the manufacturing method of the aluminum alloy forged member of the present invention, the temperature compensation strain rate (Z) in the forging process is set to Z>2×10 12 Or Z≦2×10 10 The value of Z can be easily controlled by the strain rate and temperature, and the value increases with a decrease in forging temperature and / or an increase in strain rate, and decreases with an increase in forging temperature and / or a decrease in strain rate.

[0052] More specifically, the temperature-compensated strain rate (Z) can be calculated by Z = strain rate × exp(Q / RT), where Q is the activation energy of aluminum self-diffusion, and in the present invention, it is set to 142 kJ / mol. R is the gas constant (8.314 J / mol K), and T is temperature (K).

[0053] The strain rate in the forging process can be obtained by using a simulation of the forging process, but in the case of simple processing, it may be calculated using the processing time and strain. As for the temperature during the forging process, in the case of hot forging, the set forging temperature may be used, or a value obtained from a simulation may be used. In the case of cold forging, the effect of processing heat is large, so it is preferable to use a value obtained from a simulation.

[0054] In the method for producing an aluminum alloy forged member of the present invention, the additive elements are designed to give the aluminum alloy forged member high strength and excellent ductility, and to facilitate the formation of a fine recrystallized structure or a recovered structure after forging. In addition, the aluminum alloy billet having the optimized composition has a temperature compensated strain rate (Z) of Z>2×10 12 By performing the forging process under the condition of Z≦2×10, it is possible to leave distortion during the forging process and form a fine recrystallized structure after the subsequent solution treatment. 10 By performing the forging process under the condition of 3 Since the formation of coarse recrystallization is suppressed by the dispersed particles of Zr, etc., a fine recovery structure can be formed after the subsequent solution treatment. That is, in either case, the formation of coarse recrystallization can be suppressed extremely effectively.

[0055] In addition, the strain exists as a parameter of the forging process, and the strain can be appropriately set in consideration of the desired shape of the forged part and the forging process time. Here, Z>2×10 12In the case of forging, a fine recrystallized structure can be formed more reliably by setting the strain to 1.5 or more, while in the case of cold forging, a sufficiently fine recrystallized structure can be obtained by setting the strain to 0.2 or more. 10 In the case of , a fine recovery structure can be formed more reliably by setting the strain to 3 or less, but if the strain is large, the forging conditions should be adjusted appropriately to reduce the Z factor. Note that if the strain is 0.3 or less, the effect of the strain is almost negligible, so the value of Z does not need to be specified.

[0056] The aluminum alloy billet further contains 0.1-0.8 mass% Mn, and the total content of Cr and Mn is preferably 0.2-1.2 mass%. By adding Mn and Cr in combination, Al-Fe(Mn, Cr)-Si-based dispersed particles are formed (substituting for Fe), which can suppress grain boundary migration and recrystallization during T6 treatment of high-temperature forged material. In addition, there is an effect of accumulating strain during low-temperature forging and forming a fine recrystallized structure during T6 treatment, and the crystal structure of the forged material can be controlled more effectively. In addition, the effect of trapping hydrogen atoms and suppressing hydrogen embrittlement can be expected.

[0057] By adding 0.1 to 0.8 mass% of Mn to an aluminum alloy billet and setting the total content of Cr and Mn to 0.2 to 1.2 mass%, the range of forging conditions in which a fine recrystallized structure or a recovered structure consisting of subcrystals can be obtained can be expanded. In this case, the temperature compensation strain rate (Z) in the forging process is Z≧1×10 12 Or Z≦1×10 11 It is preferable that Z≧1×10 12 In this case, it is preferable to set the strain to 1 or more, and Z≦1×10 11 In this case, it is preferable to set the strain to 2.5 or less.

[0058] The aluminum alloy billet preferably further contains Zr: 0.1 to 0.3 mass %. Zr is finely crystallized in the metal structure as an Al-Zr intermetallic compound, suppresses grain boundary migration during T6 treatment of high-temperature forged material, and suppresses recrystallization. In addition, it accumulates strain during low-temperature forging, and can form a fine recrystallized structure.

[0059] An example of a process diagram for obtaining an aluminum alloy forged member using the method for producing an aluminum alloy forged member of the present invention is shown in Figure 1. In addition to a forging process for an aluminum alloy forged material, the manufacturing process includes a homogenization heat treatment process, a solution treatment process for the forged member, and an artificial aging process for the solution treatment member. In addition, a casting process is required to obtain an aluminum alloy billet. Each process other than the forging process will be described below.

[0060] (1) Casting In order to obtain an aluminum alloy billet, a molten aluminum alloy having the above composition is prepared, and then the molten aluminum alloy is subjected to a conventionally known degassing treatment and filtration treatment (such as a filtration method using a ceramic foam filter or a porous tube filter). The effect of the degassing treatment can be measured by a known hydrogen quantification method such as the Lansley method or the LECO method, and the effect of removing inclusions by the filtration treatment can be measured, for example, by a fracture surface observation method.

[0061] Thereafter, a rod hardener (Al-Ti-B alloy) is added before the mold as necessary for the purpose of refining the structure, and a cylindrical ingot (hereinafter referred to as a "billet") is obtained by DC continuous casting or the like. Here, the DC continuous casting method is a casting method in which molten metal is introduced through a launder into a quench casting mold whose inner wall surface is water-cooled, the molten metal is rapidly solidified on the inner wall surface of the quench casting mold, and the billet immediately after solidification is successively drawn downward or to the side, and further cooled by injecting cooling water onto the billet, and is known as a casting method for aluminum alloys with excellent productivity.

[0062] (2) Homogenization heat treatment process The resulting billet is preferably subjected to homogenization treatment, which is preferably performed at a temperature of 500 to 570° C., and more preferably maintained at that temperature for 2 hours or more.

[0063] (3) Solution treatment process The solution treatment is a process in which the forged aluminum alloy member is held at 520 to 575°C. The holding time is preferably 30 minutes or more. This treatment allows the Mg-Si compounds and Al-Cu compounds precipitated during cooling after the homogenization heat treatment and forging to be dissolved in the matrix.

[0064] Next, the solution-treated aluminum alloy forged component is quenched in water or warm water (preferably water at 70°C or less), thereby making it possible to suppress reprecipitation of elements such as Mg, Si, and Cu that have been dissolved in the parent phase during the solution treatment.

[0065] (4) Artificial aging process By subjecting a solution-treated aluminum alloy forged member to artificial aging, elements such as Mg, Si, and Cu dissolved in the matrix can be precipitated as intermetallic compounds that contribute to mechanical strength. Specifically, by holding the solution-treated member at 170 to 200°C for 2 to 15 hours, the intermetallic compounds can be sufficiently precipitated.

[0066] The time from the solution treatment step to the artificial aging step (natural aging time) is preferably 100 minutes or less. By setting the natural aging time to 100 minutes or less, it is possible to form preferable clusters that are mainly composed of Mg and Si and contribute to improving the strength of the aluminum alloy. On the other hand, if the natural aging time is longer than 100 minutes, Si-rich clusters are formed, making it difficult to improve the strength of the aluminum alloy forged member.

[0067] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention. EXAMPLES

[0068] Example An aluminum alloy billet having the composition shown in Table 1 was obtained by DC continuous casting. Table 1 includes the following: "total Mn content and Cr content"; "Mg 2 The "Si content" and "excess Si content" are also listed.

[0069] [Table 1]

[0070] Next, an aluminum alloy billet with a diameter of 325 mm was subjected to homogenization heat treatment, and then extrusion processing was performed, and the obtained extruded material was forged. The extrusion diameter was 70 mm, and the extrusion ratio was 21.6. The extrusion temperature was 320 to 520°C, and the extrusion speed was 4 to 25 m / min. In addition, the forging process was performed with a die temperature of 280 to 350°C, a forging temperature of room temperature to 520°C, and an average forging speed of 30 mm / s, and a forged material with a cross-sectional shape shown in Figure 2 was obtained.

[0071] Next, the obtained forged material was subjected to solution treatment, natural aging and artificial aging under the treatment conditions shown in Table 2 to obtain the aluminum alloy forged member of the present invention.

[0072] [Table 2]

[0073] Each aluminum alloy forged member obtained in Examples 1 to 15 was cut, mirror-polished and etched to prepare a cross-sectional observation sample, and the structure was observed by an optical microscope. The observation area is the area surrounded by a dashed line in FIG. 2. The average grain size (average grain width) was calculated, and the type of microstructure was determined. The results are shown in Table 3. When a fine recrystallized structure or subcrystalline structure with an average grain size of 500 μm or less was formed, it was marked with ○, and when a structure other than these (a coarse recrystallized structure with an average grain size larger than 500 μm) was formed, it was marked with ×. As a representative structure observation result, optical microscope photographs of the aluminum alloy forged members obtained in Examples 12 and 11 are shown in FIGS. 3 and 4, respectively. It can be seen that a fine recrystallized structure was formed in Example 12, and a fine subcrystalline structure (recovered structure) was formed in Example 11, and no coarse grains were present.

[0074] In each forging condition in Examples 1 to 15, the Z factor was calculated from the forging temperature and strain rate in the structure observation region, and the obtained values ​​are shown in Table 3. In addition, the strain in the structure observation region in each forging condition was calculated and shown in Table 3. The strain rate, forging temperature, and strain in the structure observation region were values ​​obtained by simulation. For the simulation, plastic processing simulation software (Forge3) from TRANSVALOR was used. In addition, 142 kJ / mol was used as the activation energy of self-diffusion of aluminum, and 8.314 J / mol·K was used as the gas constant to calculate the Z factor.

[0075] The tensile properties of each of the aluminum alloy forged members obtained in Examples 1 to 15 were evaluated. The tensile test pieces used were No. 14A test pieces specified in JIS Z 2241, and the test pieces were cut out so that the structure observation region was the parallel portion. The tensile speed was in accordance with JIS Z 2241, and was 2 mm / min up to 0.2% yield strength and 5 mm / min after 0.2% yield strength. The tensile properties obtained are shown in Table 3. It can be seen that the aluminum alloy forged members of the present invention have tensile properties of tensile strength: 360 MPa or more, yield strength: 330 MPa or more, and fracture elongation: 6% or more.

[0076] [Table 3]

[0077] Comparative Example Aluminum alloy members were obtained in the same manner as in the Examples, except that the compositions and treatment conditions shown as Comparative Examples in Tables 1 and 2 were used. Furthermore, the Z factor, microstructure, and the like were evaluated in the same manner as in the Examples, and the obtained results are shown in Table 2.

[0078] As a representative result of the microstructural observation, an optical microscope photograph of the aluminum alloy forged member obtained in Comparative Example 1 is shown in Fig. 5. It can be seen that a structure consisting of coarse recrystallized grains is formed in Comparative Example 1. Moreover, as shown in Table 2, in Comparative Examples 1 and 2, the average grain size is larger than 500 μm.

[0079] Moreover, the aluminum alloy forged member of Comparative Example 1 has low tensile strength and does not show a sufficient value for fracture elongation. The aluminum alloy forged member of Comparative Example 2 shows a tensile strength of 401 MPa, but a low fracture elongation of 5.4%.

[0080] [Relationship between structure and forging conditions] For Examples 1 and 2 and Comparative Example 1, which have the same composition, the structure of the aluminum alloy forged member was observed in multiple regions with different strains during forging. The Z factor of the observed region was calculated by the above method, and the formed structure was judged to be either "fine recrystallized grains", "fine unrecrystallized grains (recovered structure)", or "coarse recrystallized grains". Here, when the average grain size was 500 μm or less, it was judged to be "fine", and when it was larger than 500 μm, it was judged to be "coarse". The relationship between the Z factor and strain during forging and the resulting structure is shown in Figure 6.

[0081] As shown in Fig. 6, the obtained structure is highly dependent on the Z factor, with Z>2×10 12 Or Z≦2×10 10 It can be seen that if the above condition is satisfied, a fine recrystallized structure or a fine non-recrystallized structure can be obtained.

[0082] For Examples 3 to 7 and Comparative Example 2 having the same composition, the relationship between the Z factor and strain in the forging process and the resulting structure was evaluated in the same manner as in Examples 1 and 2 and Comparative Example 1. The obtained results are shown in FIG.

[0083] In Examples 3 to 7 and Comparative Example 2, the obtained structure is also largely dependent on the Z factor. In addition, the combined addition of Cr and Mn expands the range of forging conditions in which a fine recrystallized structure or a fine unrecrystallized structure can be obtained, and Z≧1×10 12 Or Z≦1×10 11 It can be seen that if the above condition is satisfied, a fine recrystallized structure or a fine non-recrystallized structure can be obtained.

Claims

[Claim 1] A method for producing an aluminum alloy forged member by forging an aluminum alloy billet, comprising the steps of: The aluminum alloy billet is Si: 0.6 to 1.2% by mass, Fe: 0.1 to 0.25% by mass, Cu: 0.2 to 1.1% by mass, Mg: 0.7 to 1.2% by mass, Cr: 0.1 to 0.4% by mass, Ti: more than 0 to 0.1 mass %, The aluminum alloy further contains Mn: 0.1 to 0.8 mass %, The balance is an aluminum alloy containing Al and unavoidable impurities, The total content of the Cr and the Mn is 0.2 to 1.2 mass %, Mg 2 The Si content is 1.1 to 1.8 mass %, The Mg 2 The amount of excess Si that does not constitute Si is 0.1 to 0.7 mass %, The temperature compensation strain rate (Z) in the forging process is Z>1×10 12 Or Z≦1×10 11 To satisfy the following: A method for manufacturing an aluminum alloy forged member, comprising the steps of:

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