Aluminum alloy forging member and producing method thereof

Abstract

To provide a forged aluminum alloy member that has excellent tensile properties, with the strength and reliability of the entire member sufficiently guaranteed, and provides a forged aluminum alloy member with suppressed variation in microstructure and tensile properties, and its efficient producing method.SOLUTION: Provided is a method for producing aluminum alloy forged members by subjecting aluminum alloy billets to forging processing, wherein the aluminum alloy billets contain Si: 0.6 to 1.2 mass%, Fe: 0.1 to 0.25 mass%, Cu: 0.2 to 1.1 mass%, Mg: 0.7 to 1.2 mass%, Cr: 0.1 to 0.4 mass%, Ti: 0 to 0.1 mass%, with the remainder being aluminum and unavoidable impurities, the content of Mg2Si is 1.1 to 1.8 mass%, the excess Si amount that does not constitute Mg2Si is 0.1 to 0.7 mass%, and the temperature compensation strain rate (Z) in the forging process satisfies Z>2×1012 or Z≤2×1010.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a forged member made of an aluminum alloy that requires high strength and reliability, and a method for manufacturing the same.

Background Art

[0002] In addition to the specific gravity of aluminum being about 1 / 3 that of iron, extremely high strength can be achieved depending on the type of alloy and the manufacturing process. As a result, a high specific strength can be obtained compared to other metal materials, so it is utilized for weight reduction of automobiles, airplanes, bicycles, various storage containers, and the like.

[0003] Moreover, aluminum is easy to plastically process. In extrusion processing, an extruded material with a complex shape can be obtained, and in forging processing, an even more complex shape can be achieved. That is, by plastically processing a high-strength aluminum alloy, various members that require high reliability can also be efficiently manufactured.

[0004] However, the requirements for the mechanical properties of structural members are increasing day by day, and it has become difficult for existing aluminum alloys to satisfy such requirements. In particular, when an aluminum alloy component has a portion with a large shape change such as an R portion or a concave portion, a large stress is applied to this region during use. Therefore, even if the strength outside this region is sufficiently ensured, cracks may occur or breakage may result.

[0005] On the other hand, for example, in Patent Document 1 (Japanese Patent No. 5561846), an Al-Cu-Mg-Si series aluminum alloy material having a composition containing Cu: 1.0 to 3.0% (mass%, the same hereinafter), Mg: 0.4 to 1.8%, Si: 0.2 to 1.6% obtained by extrusion and cold working, with the balance being Al and impurities, in which rod-shaped precipitates are arranged in the <100> direction within the crystal grains of the matrix, the average value of the length of the precipitates is 10 to 70 nm, the maximum value of the length is 120 nm or less, and the number density of the precipitates in the

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

[0006] In the high-strength aluminum alloy material described in the above Patent Document 1, it has excellent extrudability, can be used to produce a hollow extruded material by the porthole extrusion method, and is a heat-treatable Al-Cu-Mg-Si series high-strength aluminum alloy cold-worked material with high strength. In particular, cold-worked pipe-shaped materials can be suitably used as transportation equipment members such as motorcycle structural materials.

[0007] Also, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2017-43802), an aluminum alloy extruded material contains, by mass%, Cu: 2.5 to 3.3%, Mg: 1.3 to 2.5%, Ni: 0.50 to 1.3%, Fe: 0.50 to 1.5%, Mn: less than 0.50%, Si: 0.15 to 0.40%, Zr: 0.06 to 0.20%, Ti: less than 0.05%, with the balance being Al and unavoidable impurities. In the cross-section, the particle diameter of the intermetallic compound is 20 μm or less in terms of the equivalent circle diameter, and the density of the intermetallic compound with a particle diameter of 0.3 to 20 μm in terms of the equivalent circle diameter is 5×10 3 pieces / mm 2An aluminum alloy extruded material has been proposed, which satisfies the above conditions and has an average grain size of sub-grains of 20 μm or less in terms of equivalent circle diameter.

[0008] In the aluminum alloy extruded material of Patent Document 2 above, for example, the strength and creep resistance in a high-temperature range of 200°C or higher can be improved. Regarding the strength, not only the strength in the extrusion direction (L direction) but also the strength in the direction perpendicular to the extrusion direction (LT direction) can be improved. Also, regarding the creep resistance, especially the creep resistance in the LT direction can be improved, and it can be applied to parts such as internal combustion engines and superchargers of automobiles used in high-temperature environments.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] In the high-strength aluminum alloy material of Patent Document 1 above, the tensile properties at room temperature are improved by the composition, shape and size of precipitates, etc. Also, in the aluminum alloy extruded material of Patent Document 2 above, the strength and creep resistance in a high-temperature range are improved by the composition, grain size of intermetallic compounds and average grain size of sub-grains. However, in these aluminum alloy materials, the variation in the microstructure and mechanical properties of the entire actually obtained aluminum alloy material is not considered at all, and a method for obtaining a homogeneous aluminum alloy material having excellent mechanical properties has not been studied.

[0011] In view of the problems in the prior art as described above, an object of the present invention is to provide a forged member made of an aluminum alloy having excellent tensile properties and sufficient strength and reliability as a whole member, a forged member made of an aluminum alloy in which variations in microstructure and tensile properties are suppressed, and an efficient manufacturing method thereof. Another object of the present invention is to reduce stress concentration at grain boundaries during stress application by refining and homogenizing the structure in a forged member made of an aluminum alloy, and effectively suppress the generation and propagation of fatigue cracks.

Means for Solving the Problems

[0012] As a result of intensive research on a forged member made of an aluminum alloy and its manufacturing method in order to achieve the above object, the present inventors have optimized the composition of the aluminum alloy and the like, and selectively formed a recovery structure composed of a fine recrystallized structure or subcrystals by controlling the forging process, and found that suppressing the generation of coarse recrystallization is ultimately effective, and thus reached the present invention.

[0013] That is, the present invention is A method for manufacturing a forged member made of an aluminum alloy by subjecting a billet made of an aluminum alloy to forging, The billet made of the aluminum alloy 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% by mass, and contains The balance is made of an aluminum alloy composed of Al and inevitable impurities, Mg 2 The content of Si is 1.1 to 1.8% by mass, The above Mg 2 The excess Si amount not constituting Si is 0.1 to 0.7% by mass, The temperature compensation strain rate (Z) in the forging is Z > 2×10 12 Or Z ≤ 2×10 10satisfy; A method for manufacturing a forged member made of an aluminum alloy, characterized by: Here, the value of Z can be controlled by the 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 manufacturing a forged member made of an aluminum alloy of the present invention, while imparting high strength and excellent ductility to the forged member made of an aluminum alloy, the additive elements are designed so that a fine recrystallized structure or a recovered structure is likely to be formed after the forging process is performed. In addition, for an aluminum alloy billet with an optimized composition, when the temperature-compensated strain rate (Z) is Z > 2×10 12 by performing a forging process under the condition that, strain can be left during the forging process, and a fine recrystallized structure can be formed after the subsequent solution treatment. Further, when the forging process is performed under the condition that Z ≤ 2×10 10 in addition to promoting the recovery during the forging process, the movement of grain boundaries is suppressed by dispersed particles such as Al-Fe(Mn, Cr)-Si-based and Al 3 Zr, etc., so that a fine recovered structure can be formed after the subsequent solution treatment. That is, in any case, the generation of coarse recrystallization can be extremely effectively suppressed.

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

[0016] By adding Mn: 0.1 to 0.8% by mass to an aluminum alloy billet and setting the total content of Cr and Mn to 0.2 to 1.2% by mass, the range of forging conditions under which a recovery structure composed of a fine recrystallized structure or sub-grains can be obtained can be expanded. In this case, it is preferable that the temperature compensation strain rate (Z) in the forging process satisfies Z ≧ 1×10 12 or Z ≦ 1×10 11 .

[0017] Also, in the method for manufacturing a forged member made of an aluminum alloy of the present invention, it is preferable that the aluminum alloy billet contains Zr: 0.1 to 0.3% by mass. Zr precipitates finely in the metal structure as an Al-Zr based intermetallic compound, suppresses grain boundary movement during the T6 treatment of a high-temperature forged material, and suppresses recrystallization. Also, at the time of low-temperature forging, strain can be accumulated to form a fine recrystallized structure.

[0018] Furthermore, in the method for manufacturing a forged member made of an aluminum alloy 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 step of holding the forged member obtained by the forging process at 520 to 575°C, and an artificial aging step of holding the solution-treated member obtained by the solution treatment step at 170 to 200°C for 2 to 15 hours, and 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 passing through these heat treatment steps, high tensile properties can be imparted to the forged member made of an aluminum alloy obtained by precipitation strengthening. Particularly important is the time from the solution treatment step to the artificial aging step (natural aging time), and by setting this to 100 minutes or less, a preferable cluster composed of Mg and Si and contributing to the strength improvement of the aluminum alloy can be formed. On the other hand, when the natural aging time is longer than 100 minutes, it is difficult to form a Si-rich cluster and improve the strength of the forged member made of an aluminum alloy.

[0020] In addition, the present invention contains 0.6 to 1.2% by mass of Si, 0.1 to 0.25% by mass of Fe, 0.2 to 1.1% by mass of Cu, 0.7 to 1.2% by mass of Mg, 0.1 to 0.4% by mass of Cr, more than 0 to 0.1% by mass of Ti, and consists of an aluminum alloy in which the balance is Al and inevitable impurities, wherein the content of Mg Mg 2 the content of Si is 1.1 to 1.8% by mass, and the excess Si amount that does not constitute Mg 2 Si is 0.1 to 0.7% by mass, a recrystallized structure or a recovered structure with an average grain size of 500 μm or less is formed, and it has tensile properties of a tensile strength of 360 MPa or more, a yield strength of 330 MPa or more, and an elongation at break of 6% or more. The present invention also provides a forged member made of an aluminum alloy, which is characterized by the above.

[0021] In the forged member made of the aluminum alloy of the present invention, the types and contents of additive elements are optimized for the purpose of improving tensile properties (tensile strength, 0.2% proof stress, and elongation) and controlling the structure. Also, by controlling the content of Mg 2 Si, high strength and excellent ductility are made compatible, and by defining the Cr content (the total of the Cr content and the Mn content if necessary), after forging, a fine recrystallized structure or a recovered structure is likely to be formed.

[0022] In addition, in the forged member made of the aluminum alloy of the present invention, in addition to being effectively precipitation-strengthened, a recrystallized structure or a recovered structure with an average grain size of 500 μm or less is formed, so that it has high strength and reliability. More specifically, it has tensile properties of a tensile strength of 360 MPa or more, a yield strength of 330 MPa or more, and an elongation at break of 6% or more.

[0023] Here, in the forged member made of an aluminum alloy of the present invention and the method for manufacturing the same, "the average grain size is 500 μm or less" means that the average width of the crystal grains is 500 μm or less. Specifically, in the case of a recovered structure (subgrain), the crystal structure is the extruded structure (fiber structure) or the fine recrystallized structure of the extruded material remaining in the state plastically processed by forging. Since the crystal grains also elongate in forging forming, the average grain size is evaluated by the width of the crystal grains. Further, even in the case of a recrystallized structure, it may be evaluated by the width of the crystal grains for the structure recrystallized by the solution treatment after forging.

[0024] Further, in the forged member made of an aluminum alloy of the present invention, it is more preferable that Mn: 0.1 to 0.8% by mass is further contained, and the total content of the Cr and the Mn is 0.2 to 1.2% by mass. By adding Mn and Cr in combination, Al-Fe(Mn, Cr)-Si-based dispersed particles are formed (substituting for Fe), the grain boundary movement during the T6 treatment of the high-temperature forged material is suppressed, and recrystallization can be suppressed. Further, during low-temperature forging, strain is accumulated, and there is an effect of forming a fine recrystallized structure, and the crystal structure of the forged material can be controlled more effectively.

[0025] Further, in the forged member made of an aluminum alloy of the present invention, it is more preferable that Zr: 0.1 to 0.3% by mass is further contained. Zr precipitates finely in the metal structure as an Al-Zr-based intermetallic compound, suppresses the grain boundary movement during the T6 treatment of the high-temperature forged material, and suppresses recrystallization. Further, during low-temperature forging, strain can be accumulated and a fine recrystallized structure can be formed.

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

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

Advantages of the Invention

[0028] According to the present invention, there can be provided a forged member made of an aluminum alloy having excellent tensile properties and sufficient strength and reliability as a whole member, a forged member made of an aluminum alloy in which variations in microstructure and tensile properties are suppressed, and an efficient manufacturing method thereof.

Brief Description of the Drawings

[0029]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0030] Hereinafter, representative embodiments of the forged member made of an aluminum alloy of the present invention and its manufacturing method will be described in detail with reference to the drawings, but the present invention is not limited thereto. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions may be omitted. Also, since the drawings are for conceptually explaining the present invention, the dimensions and ratios of the components shown may be different from the actual ones.

[0031] 1. Forged Member Made of Aluminum Alloy The forged member made of an aluminum alloy of the present invention is a member for obtaining various forged parts made of aluminum alloys. The composition of the aluminum alloy and the like are optimized, and a fine recrystallized structure or a recovered structure is formed. The forged member made of an aluminum alloy has homogeneous and extremely excellent tensile properties. Hereinafter, the composition, structure, mechanical properties, etc. of the forged member made of an aluminum alloy will be described in detail.

[0032] (1) Composition The aluminum alloy used for the aluminum alloy member contains 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% by mass, and the balance is an aluminum alloy composed of Al and unavoidable impurities. Further, Mn and Zr can be added as optional additive elements. Hereinafter, each component element will be described respectively.

[0033] (1-1) Essential additive elements Si: 0.6 to 1.2% by mass Si forms Mg-Si-based precipitates together with Mg and has the effect of increasing mechanical strength and fatigue strength. When the Si content is less than 0.6% by mass, solid solution strengthening and age hardening ability are insufficient, and the mechanical strength and fatigue strength required for the aluminum alloy member cannot be obtained. On the other hand, when the Si content exceeds 1.2% by mass, corrosion resistance and hydrogen embrittlement resistance decrease. By imparting high strength and excellent hydrogen embrittlement resistance to the forged member made of an aluminum alloy, it can also be suitably used as a forged member made of an aluminum alloy for obtaining various members for hydrogen containers (such as caps and valves). Also, when the Si content exceeds 1.2% by mass, coarse crystallized products and precipitates may be formed, which may reduce ductility and workability.

[0034] Fe: 0.1 to 0.25% by mass Fe is an element effective in forming dispersed particles in the Al-Fe(Mn, Cr)-Si system. It suppresses the recrystallization of Al and contributes to the improvement of strength. However, if the content is less than 0.1% by mass, the effect cannot be fully obtained. On the other hand, if added excessively, it depletes precipitates, precipitated Si, Mn, and Cr that contribute to strength, and forms coarse intermetallic compounds, resulting in a decrease in strength. Therefore, the upper limit of the addition amount is set at 0.25% by mass.

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

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

[0037] Cr: 0.1 - 0.4% by mass Cr precipitates finely in the metal structure as an Al-Cr system intermetallic compound, suppresses grain boundary migration during the T6 treatment of high-temperature forged materials, and suppresses recrystallization. Also, during low-temperature forging, strain is accumulated to form a fine recrystallized structure. In addition, it can trap hydrogen atoms and is expected to have the effect of suppressing hydrogen embrittlement. This effect becomes particularly significant at 0.1% by mass or more. However, if it contains more than 0.4% by mass, it forms a material compound, inhibiting ductility, etc.

[0038] Ti: More than 0 to 0.1% by mass Ti refines the casting structure and prevents casting cracks.

[0039] (1 - 2) Optional additive element Mn: 0.1 - 0.8 mass% By adding Mn and Cr in combination, dispersed particles of the Al-Fe(Mn, Cr)-Si system are formed (substituting for Fe), grain boundary migration during the T6 treatment of the hot forged material can be suppressed, and recrystallization can be suppressed. Also, during low-temperature forging, strain accumulates, and there is an effect of forming a fine recrystallized structure, and the crystal structure of the forged material can be controlled more effectively. Further, it can be expected to trap hydrogen atoms and suppress hydrogen embrittlement. This effect becomes particularly significant at 0.1 mass% or more, but when the content exceeds 0.8 mass%, the hardenability increases and the solution heat treatment property is inhibited (when hardening is delayed, the strength decreases). For these reasons, the total amount of Cr and Mn is preferably 0.1 - 1.2 wt%.

[0040] Zr: 0.1 - 0.3 mass% Zr precipitates finely in the metal structure as an Al-Zr-based intermetallic compound, suppresses grain boundary migration during the T6 treatment of the hot forged material, and suppresses recrystallization. Also, during low-temperature forging, strain accumulates and a fine recrystallized structure is formed. This effect becomes particularly significant at 0.1 mass% or more, but when the content exceeds 0.3 mass%, a material compound is formed, inhibiting ductility, etc.

[0041] (1 - 3) Other conditions regarding the composition Mg 2 Content of Si: 1.1 - 1.8 mass% Mg 2 By setting Si to 1.1 mass% or more, the strength required for the forged member made of aluminum alloy can be realized by precipitation strengthening. On the other hand, Mg 2 By setting Si to 1.8 mass% or less, a decrease in the ductility of the forged member made of aluminum alloy can be suppressed.

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

[0043] (2) Structure The forged member made of an aluminum alloy 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 very vicinity of the die contact surface, and a difference occurs between the processing conditions obtained by analysis and the actual processing conditions. For example, in addition to the friction coefficient of the die surface changing depending on the type and state of the lubricant, the thermal conductivity of the die also affects the analysis results. Therefore, in the forged member made of an aluminum alloy of the present invention, the vicinity of the extreme surface affected by the contact with the die is excluded from the definition. Here, the "vicinity of the extreme surface" means a range of about 5 mm from the die contact surface.

[0044] The method for obtaining the average grain size of crystal grains is not particularly limited as long as the effects of the present invention are not impaired, and it may be measured by various conventionally known methods. For example, a forged member made of an aluminum alloy is cut at an arbitrary cross section, and the obtained cross-sectional sample is observed with an optical microscope or a scanning electron microscope, and the average value of the grain sizes of the base metal crystal grains can be calculated to obtain it. At that time, for example, the crystal grain size can be measured by the intersection method. In addition, it may be measured by a backscattered electron diffraction measuring device (SEM-EBSD) attached to a scanning electron microscope. The observation area for obtaining the average grain size also depends on the size and shape of the forged member made of an aluminum alloy, but an accurate value can be obtained by determining the observation region so that at least 20 or more crystal grains to be measured are included. Note that depending on the observation method, the cross-sectional sample may be subjected to mechanical polishing, buff polishing, electrolytic polishing, etching, etc.

[0045] The forged member made of aluminum alloy has tensile properties of a tensile strength of 360 MPa or more, a yield strength of 330 MPa or more, and an elongation at break of 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. Also, the yield strength is preferably 340 MPa or more, more preferably 350 MPa or more, and most preferably 360 MPa or more. Further, the elongation at break is preferably 8% or more, more preferably 10% or more, and most preferably 12% or more. By the forged member made of aluminum alloy having these tensile properties, it can be suitably used as a member for manufacturing parts such as automobiles, aircraft, bicycles, and various high-pressure gas storage containers.

[0046] Furthermore, the forged member made of aluminum alloy can not only be given an arbitrary shape to the forged member made of aluminum alloy by forging, but also can have a fine recrystallized structure or a recovered structure with respect to the fine structure obtained by the forging. Here, by subjecting the extrusion member to forging, the forged member made of aluminum alloy can be efficiently manufactured.

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

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

[0049] 3. Method for manufacturing a forged member made of an aluminum alloy The method for manufacturing a forged member made of an aluminum alloy of the present invention is to perform forging on a billet (extruded bar or casting material) made of an aluminum alloy, and is characterized by the combination of the composition of the aluminum alloy and the temperature-compensated strain rate (Z) during forging.

[0050] Specifically, the aluminum alloy billet to be forged contains 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% by mass, and the balance is an aluminum alloy composed of Al and unavoidable impurities. The content of Mg 2 Si is 1.1 to 1.8% by mass, and the excess Si amount that does not constitute the Mg 2 Si is 0.1 to 0.7% by mass.

[0051] Also, in the method for manufacturing a forged member made of an aluminum alloy of the present invention, the temperature-compensated strain rate (Z) in forging is set to a value that satisfies either 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 the forging temperature and / or an increase in the strain rate, and the value decreases with an increase in the forging temperature and / or a decrease in the strain rate.

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

[0053] The strain rate in the forging process can be obtained using a simulation related to the forging process, but in the case of simple processing, it may also be calculated using the processing time and strain. Also, regarding the temperature during the forging process, in the case of hot forging, the set forging temperature may be used, or a value obtained from the simulation may be used. In the case of cold forging, since the influence of heat generation during processing is large, it is preferable to use a value obtained from the simulation.

[0054] In the method for manufacturing a forged member made of an aluminum alloy of the present invention, while imparting high strength and excellent ductility to the forged member made of an aluminum alloy, the additive elements are designed so that a fine recrystallized structure or a recovered structure is likely to be formed after the forging process is performed. In addition, for an aluminum alloy billet with an optimized composition, the temperature-compensated strain rate (Z) satisfies Z > 2×10 12 By performing the forging process under the condition that, strain can be left during the forging process, and a fine recrystallized structure can be formed after the subsequent solution treatment. Also, by performing the forging process under the condition that Z ≦ 2×10 10 In addition to promoting recovery during the forging process, the movement of grain boundaries is suppressed by dispersed particles such as Al-Fe(Mn, Cr)-Si-based and Al 3 Zr, etc., so that a fine recovered structure can be formed after the subsequent solution treatment. That is, in any case, the generation of coarse recrystallization can be extremely effectively suppressed.

[0055] Also, although strain exists as a parameter for the forging process, the strain may be appropriately set in consideration of the desired shape of the forged member, the forging process time, etc. Here, Z > 2×10 12In the case of [[ID=]], by setting the strain to 1.5 or more, a fine recrystallized structure can be more reliably formed. In the case of cold forging, by setting the strain to 0.2 or more, a sufficiently refined recrystallized structure can be obtained. Also, when Z≦2×10 10 In the case of [[ID=]], by setting the strain to 3 or less, a finer recovery structure can be more reliably formed. However, when the strain becomes large, the forging conditions may be appropriately adjusted so that the Z factor becomes small. Note that when the strain is 0.3 or less, since the influence of the strain is almost negligible, it is not necessary to define the value of Z.

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

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

[0058] Further, it is preferable that the aluminum alloy billet further contains Zr: 0.1 to 0.3% by mass. Zr precipitates finely in the metal structure as an Al-Zr based intermetallic compound, suppresses grain boundary migration during the T6 treatment of the hot forged material, and suppresses recrystallization. Further, during cold forging, strain can be accumulated to form a fine recrystallized structure.

[0059] An example of a process diagram for obtaining a forged member made of an aluminum alloy using the method for manufacturing a forged member made of an aluminum alloy of the present invention is shown in FIG. 1. 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-treated member, in addition to the forging process for the aluminum alloy workpiece. Further, a casting process is required to obtain an aluminum alloy billet. Hereinafter, each process other than the forging process will be described.

[0060] (1) Casting In order to obtain an aluminum alloy billet, after preparing a molten aluminum alloy having the above composition, conventional degassing treatment and filtration treatment (filtration methods using filters such as ceramic foam filters and porous tube filters) are performed. The effect of the degassing treatment can be measured by known hydrogen quantification methods such as the Lantzley method and the LECO method, and the effect of inclusion removal by the filtration treatment can be measured by, for example, the fracture surface observation method.

[0061] Thereafter, if necessary, a rod hardener (Al-Ti-B alloy) for the purpose of refining the structure is added in front of the mold, and a cylindrical ingot (hereinafter referred to as "billet") is obtained by the DC continuous casting method or the like. Here, the DC continuous casting method is a casting method in which molten metal led by a trough is poured into a rapid cooling mold with a water-cooled inner wall surface, the molten metal is rapidly solidified on the inner wall surface of the rapid cooling mold, and the billet immediately after solidification is sequentially pulled downward or laterally, and further, cooling water is sprayed onto the billet for rapid cooling. It is a well-known casting method for aluminum alloys with excellent productivity.

[0062] (2) Homogenization heat treatment process It is preferable to perform a homogenization treatment on the obtained billet. The temperature of the homogenization treatment is preferably 500 to 570 °C, and it is more preferable to hold at this temperature for 2 hours or more.

[0063] (3) Solution treatment step The solution treatment is a step of holding a forged aluminum alloy member at 520 to 575 °C. The holding time is preferably 30 minutes or more. By this treatment, Mg-Si-based compounds and Al-Cu-based compounds precipitated during the homogenization heat treatment and cooling after forging can be dissolved in the matrix phase.

[0064] Next, by quenching the solution-treated forged aluminum alloy member with water or warm water (preferably water at 70 °C or lower), it is possible to suppress the re-precipitation of elements such as Mg, Si, and Cu dissolved in the matrix phase during the solution treatment.

[0065] (4) Artificial aging step By performing an artificial aging treatment on the forged aluminum alloy member subjected to the solution treatment, elements such as Mg, Si, and Cu dissolved in the matrix phase 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, intermetallic compounds can be sufficiently precipitated.

[0066] The time (natural aging time) from the solution treatment step to the artificial aging step is preferably 100 minutes or less. By setting the natural aging time to 100 minutes or less, it is possible to form a preferable cluster mainly composed of Mg and Si, which contributes to the improvement of the strength of the aluminum alloy. On the other hand, when the natural aging time is longer than 100 minutes, it is difficult to form a Si-rich cluster and improve the strength of the forged aluminum alloy member.

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

Example

[0068] ≪Example≫ An aluminum alloy billet having the composition shown in Table 1 was obtained by the DC continuous casting method. Here, Table 1 also shows the "total of Mn content and Cr content", "Mg 2 content of Si" and "excess Si amount".

[0069]

Table 1

[0070] Next, after subjecting the aluminum alloy billet with a diameter of 325 mm to homogenization heat treatment, extrusion processing was performed, and the obtained extruded material was subjected to forging processing. 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. Also, for the forging processing, the die temperature was 280 to 350 °C, the forging temperature was room temperature to 520 °C, the forging speed was an average of 30 mm / s, and a forged material having the 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 forged member made of the aluminum alloy of the present invention.

[0072]

Table 2

[0073] The forged members made of each aluminum alloy obtained in Examples 1 to 15 were cut, and cross-sectional observation samples were prepared by mirror polishing and etching, and the microstructure was observed with an optical microscope. The observation region is the region surrounded by the broken line in Fig. 2. The average grain size (average of the widths of the crystal grains) was calculated, and the type of the fine microstructure was discriminated, and the obtained results are shown in Table 3. When a fine recrystallized structure or a subgrain structure with an average grain size of 500 μm or less was formed, it was marked as ○, and when other structures (coarse recrystallized structures with an average grain size larger than 500 μm) were formed, it was marked as ×. As typical microstructure observation results, optical micrographs of the forged members made of the aluminum alloy obtained in Example 12 and Example 11 are shown in Fig. 3 and Fig. 4, respectively. It can be seen that a fine recrystallized structure was formed in Example 12 and a fine subgrain structure (recovery structure) was formed in Example 11, and no coarse crystal grains exist.

[0074] Under each forging condition in Examples 1 to 15, the Z factor was calculated from the forging temperature and the strain rate in the microstructure observation region, and the obtained values are shown in Table 3. Also, the strain in the microstructure observation region under each forging condition was calculated and shown in Table 3. The values of the strain rate, forging temperature, and strain in the microstructure observation region were the values obtained by simulation. The plastic working simulation software (Forge3) of TRANSVALOR was used for the simulation. Also, for the calculation of the Z factor, 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.

[0075] Also, the tensile properties of the forged members made of each aluminum alloy obtained in Examples 1 to 15 were evaluated. As the tensile test piece, a No. 14 A test piece described in JIS Z 2241 was used, and the test piece was cut out so that the microstructure observation region became the parallel part. The tensile speed conformed to JIS Z 2241, 2 mm / min up to the 0.2% proof stress, and 5 mm / min after the 0.2% proof stress. The obtained tensile properties are shown in Table 3. It can be seen that the forged member made of the aluminum alloy of the present invention has tensile properties of a tensile strength of 360 MPa or more, a proof stress of 330 MPa or more, and an elongation at break of 6% or more.

[0076]

Table 3

[0077] ≪Comparative Example≫ An aluminum alloy member was obtained in the same manner as in the examples, except that the compositions and processing conditions shown as comparative examples in Table 1 and Table 2 were used. Also, in the same manner as in the examples, the Z factor, microstructure, and microstructure were evaluated, and the obtained results are shown in Table 2.

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

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

[0080] [Relationship between microstructure and forging conditions] Regarding Examples 1, 2 and Comparative Example 1 having the same composition, the microstructure of the forged aluminum alloy member was observed in a plurality of regions with different strains in the forging process. The Z factor of the observation region was calculated by the above method, and it was determined which of the formed microstructures corresponded to "fine recrystallized grains", "fine unrecrystallized grains (recovery structure)" and "coarse recrystallized grains". Here, when the average grain size was 500 μm or less, it was defined as "fine", and when it was larger than 500 μm, it was defined as "coarse". The relationship between the Z factor and strain in the forging process and the resulting microstructure is shown in Fig. 6.

[0081] From Fig. 6, it can be seen that the resulting microstructure depends greatly on the Z factor, and a fine recrystallized microstructure or a fine unrecrystallized microstructure can be obtained when Z > 2×10 12 or Z ≤ 2×10 10 is satisfied.

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

[0083] For Examples 3 to 7 and Comparative Example 2, the resulting microstructure greatly depends on the Z factor. Also, due to the combined addition of Cr and Mn, the range of forging conditions under which a fine recrystallized structure or a fine non-recrystallized structure can be obtained is expanded, and it can be seen that a fine recrystallized structure or a fine non-recrystallized structure can be obtained if Z ≧ 1×10 12 or Z ≦ 1×10 11 is satisfied.

Claims

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: 0.17 to 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 %, 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>2×10 １２ Or Z≦2×10 １０ To satisfy the following: A method for manufacturing an aluminum alloy forged member, comprising the steps of:

2. The temperature compensation strain rate (Z) is 3×10 ９ ≦Z≦2×10 １０ To satisfy the following:

2. The method for producing an aluminum alloy forged member according to claim 1,

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