Blank for aluminum alloy forging, aluminum alloy forged product, and method for producing same

Abstract

The invention discloses an aluminum alloy forged product. The present invention relates to a copper alloy which contains 0.25 to 0.55% by mass (inclusive) of Cu, 0.60 to 1.25% by mass (inclusive) of Mg, 0.95 to 1.4% by mass (inclusive) of Si, 0.35 to 0.60% by mass (inclusive) of Mn, 0.15 to 0.30% by mass (inclusive) of Fe, 0.25% by mass or less of Zn, 0.050 to 0.30% by mass (inclusive) of Cr, 0.01 to 0.1% by mass (inclusive) of Ti, and the balance of copper and unavoidable impurities. The present invention relates to a high-strength aluminum alloy which comprises, by mass, 0.0010-0.030% of B, 0.0010-0.050% of Zr, an Fe / Mn ratio of less than 1.4, the remainder comprising Al and unavoidable impurities, the number density of Mn-containing precipitates in 2.0 [mu] m < 2 > including grain boundaries being 4 / [mu] m2 or more, the ratio of large-angle grain boundaries having a crystal orientation difference of 15 DEG or more being 27% or less, and the impact value at normal temperature being 10 J / cm2 or more.

Description

Technical Field

[0001] The present invention relates to a blank for forging an aluminum alloy, a forged aluminum alloy product, and a method for manufacturing the same.

[0002] This application claims priority based on Japanese Patent Application No. 2022-210255 filed on December 27, 2022, the content of which is incorporated herein by reference. Background Art

[0003] In recent years, the use of aluminum alloys effectively utilizing their light weight as structural members of various products has been expanding. For example, in the running parts and bumper components of automobiles, high-strength steel has been used so far. On the other hand, in recent years, high-strength aluminum alloy materials have been used.

[0004] In addition, in automotive parts, especially in suspension parts for example, ferrous materials have been specifically used. On the other hand, in recent years, for the main purpose of weight reduction, there have been more cases of replacing them with aluminum materials or aluminum alloy materials.

[0005] These automotive parts are required to have excellent corrosion resistance, high strength, and excellent workability. Therefore, Al-Mg-Si alloys, especially A6061, are frequently used as aluminum alloy materials. Moreover, for such automotive parts, in order to improve strength, an aluminum alloy material is used as a processing blank and forged as one of the plastic working processes.

[0006] In addition, recently, there has been a need to reduce costs. Therefore, suspension parts that are obtained by forging a cast member as a blank without extrusion and then performing a solution treatment and an artificial aging treatment (T6 treatment) have started to be put into practical use, and the development of high-strength alloys that replace the conventional A6061 is being promoted for further weight reduction (for example, refer to Patent Documents 1 to 3).

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Publication No. 5-59477

[0010] Patent Document 2: Japanese Unexamined Patent Publication No. 5-247574

[0011] Patent Document 3: Japanese Unexamined Patent Publication No. 6-256880 Summary of the Invention

[0012] However, the above-mentioned high-strength Al-Mg-Si alloys have the following problems: during the forging and heat treatment processes, the processed structure recrystallizes, resulting in coarse grains, and thus sufficient high strength cannot be obtained. Therefore, in order to prevent the formation of coarse recrystallized grains, there is a solution of adding Zr (zirconium) to prevent recrystallization (for example, refer to the above-mentioned Patent Documents 1 and 2).

[0013] However, although adding Zr has an effect in preventing recrystallization, there are the following problems.

[0014] (1) By adding Zr, the grain refinement effect of the Al-Ti-B alloy is weakened, the grains of the ingot itself become coarser, leading to a decrease in the strength of the processed product (forged product) after plastic working.

[0015] (2) Since the grain refinement effect of the ingot itself is weakened, ingot cracks are likely to occur, internal defects increase, and the yield rate deteriorates.

[0016] (3) Zr forms compounds with the Al-Ti-B alloy, and the compounds accumulate at the bottom of the furnace storing the alloy melt, contaminating the furnace. Moreover, these compounds also crystallize coarsely in the manufactured ingot, reducing the strength.

[0017] Thus, although adding Zr has an effect in preventing recrystallization, it is difficult to maintain the stability of strength.

[0018] The present invention has been completed in view of such a technical background, and its object is to provide a blank for forging aluminum alloy, a forged aluminum alloy product, and a manufacturing method thereof, which have excellent mechanical properties at normal temperature.

[0019] The present invention provides the following means to solve the above problems.

[0020] Embodiment 1 of the present invention is a blank for forging aluminum alloy, which is composed of the following aluminum alloy. The aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio. The balance is composed of Al and inevitable impurities. The conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

[0021] Embodiment 2 of the present invention is a blank for forging aluminum alloy, which is composed of the following aluminum alloy. The aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is 0.3 or more and 1.2 or less in terms of mass ratio. The balance is composed of Al and inevitable impurities. The conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

[0022] In Embodiment 3 of the present invention, an aluminum alloy forged product is made of the following aluminum alloy, which has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio. The balance is composed of Al and unavoidable impurities. The number density of Mn precipitates contained within a 2.0-μm square including grain boundaries is 4 per μm 2 or more, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm 2 or more.

[0023] In Embodiment 4 of the present invention, in the aluminum alloy forged product of Embodiment 3, the size of the precipitates is 0.5 μm or less.

[0024] In Embodiment 5 of the present invention, an aluminum alloy forged product is made of the following aluminum alloy, which has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is 0.3 or more and 1.2 or less in terms of mass ratio. The balance is composed of Al and unavoidable impurities. The number density of Mn precipitates contained within a 2.0-μm square including grain boundaries is 4 per μm 2The ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm 2 or more.

[0025] In the aluminum alloy forging product of Mode 6 of the present invention, the size of the precipitate is 0.5 μm or less.

[0026] Mode 7 of the present invention is a method for manufacturing an aluminum alloy forging product, which is a method for manufacturing the aluminum alloy forging product according to any one of Modes 3 to 6, and has: a melt forming step of obtaining a melt of the aluminum alloy; a casting step of obtaining a casting by casting the obtained melt; a forging step of heating the casting at a temperature of 500 °C to the melting point to perform plastic working to obtain a forging; a solution treatment step of performing solution treatment on the obtained forging by heating at a heating rate of 5.0 °C / min or more from 20 °C to 500 °C and holding at a temperature of 530 to 560 °C for 0.3 to 3 hours; a quenching step of bringing all surfaces of the forging into contact with quenching water within 5 to 60 seconds after the solution treatment and quenching in a water tank for more than 1 minute and within 40 minutes; and an aging treatment step of heating the forging after the quenching treatment step at a temperature of 180 °C to 220 °C for 0.5 hour to 8 hours to perform aging treatment.

[0027] In Mode 8 of the present invention, in the method for manufacturing an aluminum alloy forging product of Mode 4, a homogenization heat treatment step is further provided, and the homogenization heat treatment step is a step of performing homogenization heat treatment by holding the casting of the aluminum alloy in a temperature range of 370 °C or more and 560 °C or less for 2 hours or more and 10 hours or less between the casting step and the forging step.

[0028] According to the present invention, it is possible to provide a billet for aluminum alloy forging having excellent mechanical properties at room temperature.

[0029] According to the present invention, it is possible to provide an aluminum alloy forging product having excellent mechanical properties at room temperature.

[0030] In addition, according to the present invention, since the homogenization treatment step that was conventionally performed to remove segregation after casting the aluminum alloy melt is eliminated, it is possible to provide a method for manufacturing an aluminum alloy forging product with low cost and energy saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a perspective view showing an example of an aluminum alloy forging product according to an embodiment of the present invention.

[0032] Figure 2 is a plan view showing another example of an aluminum alloy forging product according to an embodiment of the present invention.

[0033] Figure 3 It is a perspective view showing another example of an aluminum alloy forged product according to an embodiment of the present invention.

[0034] Figure 4 It is a cross-sectional view showing an example near the mold of a horizontal continuous casting apparatus for manufacturing an aluminum alloy forged product according to an embodiment of the present invention.

[0035] Figure 5 It is Figure 4 A cross-sectional view obtained by magnifying the main part near the cooling water chamber of the horizontal continuous casting apparatus shown.

[0036] Figure 6 It is an explanatory view for explaining the heat flux of the cooling wall portion of the horizontal continuous casting apparatus.

[0037] Figure 7 It is a plan view showing the extraction position of the central portion when extracting a specimen for mechanical property evaluation from the aluminum alloy forged product obtained in this embodiment.

[0038] Figure 8 It is a plan view showing the specimen for mechanical property evaluation fabricated in this embodiment. Detailed Description of the Invention

[0039] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0040] Furthermore, in the accompanying drawings used in the following description, in order to facilitate understanding of the features, sometimes the portions that become the features are enlarged for convenience, and the dimensional ratios of the respective components are not necessarily the same as the actual ones. In addition, the materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not necessarily limited thereto, and can be appropriately changed within the range without changing its effects.

[0041] [Blank for Aluminum Alloy Forging]

[0042] First, a blank for aluminum alloy forging according to an embodiment of the present invention will be described.

[0043] The blank for aluminum alloy forging of this embodiment has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio, the balance is composed of Al and inevitable impurities, the conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

[0044] The blank for aluminum alloy forging of another embodiment of the present invention is composed of the following aluminum alloy, and the aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of the content of Fe to the content of Mn, Fe / Mn, is 0.3 or more and 1.2 or less in terms of mass ratio, the balance is composed of Al and inevitable impurities, the conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

[0045] Fe / Mn can be set to 0.3 or more and 1.0 or less in terms of mass ratio. Additionally, it can be set to 0.4 or more and 0.8 or less. Additionally, it can be set to 0.4 or more and 0.7 or less.

[0046] The blank for aluminum alloy forging of the above embodiment is equivalent to 6000 series aluminum alloy in that it contains Mg and Si.

[0047] (Conductivity: 25% IACS or more and 35% IACS or less)

[0048] The conductivity of the blank for aluminum alloy forging in the above-described embodiment is 25% IACS or more and 35% IACS or less. This conductivity is the conductivity at room temperature, and the room temperature is on the order of 20°C ± 15°C.

[0049] When the conductivity is less than 25% IACS, it is too hard and the workability is reduced. When it exceeds 35% IACS, sometimes the machinability (chip breakability) deteriorates due to softness and the guaranteed strength of the final product cannot be satisfied.

[0050] (Rockwell hardness HRF: 62 or more and 82 or less)

[0051] The Rockwell hardness HRF of the blank for aluminum alloy forging in the above-described embodiment is 62 or more and 82 or less. Here, the Rockwell hardness HRF is a value measured according to "Rockwell hardness test - Test method" of JIS Z2245:2016.

[0052] This is because if the Rockwell hardness HRF is within this range, the workability is good. That is, when the Rockwell hardness HRF is less than 62, sometimes the machinability (chip breakability) deteriorates due to softness and the guaranteed strength of the final product cannot be satisfied. When it exceeds 82, it is too hard and the workability is reduced.

[0053] [Aluminum alloy forging]

[0054] An aluminum alloy forging of an embodiment of the present invention will be described.

[0055] Figure 1 is a perspective view of an aluminum alloy forging of an embodiment of the present invention.

[0056] As Figure 1 shown, the aluminum alloy forging 1a has a long strip portion 2 and connecting portions 4a, 4b respectively connected to both ends in the length direction of the long strip portion 2. The cross section of the long strip portion is a quadrilateral. It is sufficient to provide through holes in these two connecting portions 4 respectively. The aluminum alloy forging 1a of this shape can be used as, for example, an I-type suspension arm.

[0057] The aluminum alloy forged product of this embodiment is composed of the following aluminum alloy, and the aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio. The balance is composed of Al and inevitable impurities. The number density of Mn precipitates contained within a 2.0 μm square including grain boundaries is 4 per μm 2 Above, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less.

[0058] In addition, the impact value of the aluminum alloy forged product of this embodiment at room temperature is 10 J / cm 2 Above.

[0059] If the size of the Mn-containing precipitates contained within a 2.0 μm square including grain boundaries is exemplified, it is 0.5 μm or less.

[0060] The aluminum alloy forged product of this embodiment is equivalent to a forged product of 6000 series aluminum alloy in that it contains Mg and Si.

[0061] (Cu: 0.25% by mass or more and 0.55% by mass or less)

[0062] Cu has the function of finely dispersing Mg-Si compounds in the aluminum alloy and the function of increasing the tensile strength of the aluminum alloy by precipitating Al-Cu-Mg-Si compounds led by the Q phase. By having the Cu content within the above range, the mechanical properties of the aluminum alloy forged product 1a at room temperature can be improved.

[0063] (Mg: 0.60% by mass or more and 1.25% by mass or less)

[0064] Mg has the effect of improving the tensile strength of aluminum alloy. By dissolving Mg in the aluminum matrix phase, or by precipitating as β'' phase or Mg-Si based compounds (Mg2Si) or Al-Cu-Mg-Si based compounds (AlCuMgSi) headed by Q phase, it contributes to the strengthening of aluminum alloy. In addition, Mg2Si has the effect of suppressing the formation of CuAl2 phase in aluminum alloy. By suppressing the formation of CuAl2 phase, the corrosion resistance of the forged aluminum alloy product 1a is improved. By having the Mg content rate within the above range, it is possible to improve the mechanical properties of the forged aluminum alloy product 1a at room temperature and its corrosion resistance at the same time.

[0065] (Si: 0.90 mass% or more and 1.4 mass% or less)

[0066] Si, like Mg, has the effect of improving the mechanical properties and corrosion resistance of the forged aluminum alloy product 1a at room temperature. However, if Si is excessively added to the aluminum alloy, coarse primary Si grains will crystallize, and thus the tensile strength of the aluminum alloy may decrease. By having the Si content rate within the above range, it is possible to suppress the crystallization of primary Si and improve the mechanical properties of the forged aluminum alloy product 1a at room temperature and its corrosion resistance at the same time.

[0067] (Mn: 0.35 mass% or more and 0.60 mass% or less)

[0068] Mn has the effect of improving the tensile strength of aluminum alloy by forming fine granular crystals including intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy. By having the Mn content rate within the above range, it is possible to improve the mechanical properties of the forged aluminum alloy product 1a at room temperature.

[0069] (Fe: 0.15 mass% or more and 0.30 mass% or less)

[0070] Fe has the effect of improving the tensile strength of aluminum alloy by crystallizing as fine crystals including intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe in the aluminum alloy. By having the Fe content rate within the above range, it is possible to improve the mechanical properties of the forged aluminum alloy product 1a at room temperature.

[0071] Furthermore, the relationship of Fe / Mn is less than 1.4. By having the relationship of Fe / Mn less than 1.4, it is possible to suppress the crystallization of AlFeSi-based compounds of 3.0 μm or more, and it is possible to increase the number density of AlMn-based compounds in the crystal grains.

[0072] (Cr: 0.050 mass% or more and 0.30 mass% or less)

[0073] Cr has the effect of increasing the tensile strength of the aluminum alloy by forming fine granular crystals including intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy. By having the Cr content within the above range, the mechanical properties of the aluminum alloy forging 1a at normal temperature can be improved.

[0074] (Ti: 0.01% by mass or more and 0.1% by mass or less)

[0075] Ti has the effect of refining the crystal grains of the aluminum alloy and improving the formability. When the Ti content is less than 0.01% by mass, it may not be possible to fully obtain the effect of refining the crystal grains. On the other hand, if the Ti content exceeds 0.1% by mass, it may form coarse crystals, reducing the formability. In addition, if a large amount of coarse crystals containing Ti are mixed into the aluminum alloy forging 1a, the toughness may sometimes decrease. Therefore, the Ti content can be set to 0.012% by mass or more and 0.035% by mass or less. The Ti content is preferably 0.015% by mass or more and 0.050% by mass or less.

[0076] (B: 0.001% by mass or more and 0.03% by mass or less)

[0077] B has the effect of refining the crystal grains of the aluminum alloy and improving the formability. By adding B together with the above-mentioned Ti to the aluminum alloy, the effect of refining the crystal grains is improved. When the B content is less than 0.0010% by mass, it may not be possible to fully obtain the effect of refining the crystal grains. On the other hand, if the B content exceeds 0.030% by mass, it may form coarse crystals and be mixed into the aluminum alloy forging 1a as inclusions. In addition, if a large amount of coarse crystals containing B are mixed into the final product of the aluminum alloy, the toughness may sometimes decrease. Therefore, the B content is set to 0.0010% by mass or more and 0.030% by mass or less. The B content is preferably 0.0050% by mass or more and 0.025% by mass or less.

[0078] (Zr: 0.0010% by mass or more and 0.05% by mass or less)

[0079] When Zr is 0.05 mass% or less, it precipitates in the form of Al3Zr and Al-(Ti, Zr), thereby contributing to the improvement of the strength of the aluminum alloy forging 1a through the effect of suppressing recrystallization and precipitation strengthening. When the content rate of Zr exceeds 0.050 mass%, it crystallizes as coarse Zr compounds, which may lead to a decrease in the corrosion resistance of the aluminum alloy forging 1a. Therefore, the content rate of Zr is set to 0.050 mass% or less. In addition, in order to obtain the effect of improving the strength of the forging brought about by the above-mentioned effect of suppressing recrystallization and precipitation strengthening, the content rate of Zr is preferably 0.0010 mass% or more.

[0080] (Zn: 0.250 mass% or less)

[0081] It is sufficient that Zn is 0.250 mass% or less. When the content rate of Zn exceeds 0.250 mass%, MgZn2 is generated and precipitates from the Al matrix phase to the grain boundary, thereby causing intergranular corrosion and leading to a decrease in the corrosion resistance of the aluminum alloy forging. Therefore, the content rate of Zn is preferably 0.250 mass% or less or not contained at all.

[0082] (Inevitable impurities)

[0083] Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from the billet or the manufacturing process. Examples of inevitable impurities include Ni, Sn, Be, etc. The content rate of these inevitable impurities is preferably not more than 0.1 mass%.

[0084] The central part 2a in the length direction of the long strip part 2 of the aluminum alloy forging 1a of the present embodiment is, for example, the part where the maximum principal stress acts when the aluminum alloy forging 1a is used as a suspension arm of a vehicle. The central part 2a is, for example, a region within a range of 1% or more and 80% or less with respect to the whole of the long strip part 2 including the center in the length direction of the long strip part 2. The aspect ratio (length in the length direction / length of the short side in the direction perpendicular to the length direction) of the long strip part 2 is, for example, within a range of 2 or more and 100 or less. The cross-section of the central part 2a of the long strip part 2 is the cross-section in the direction along the direction of the applied pressure when manufacturing the aluminum alloy forging 1a by forging (hereinafter sometimes referred to as the central part cross-section).

[0085] (Excluding AlFeSi(Mn)-based compounds with an average particle size of 3.0 μm or more)

[0086] In the alloy structure of the central part cross-section of the aluminum alloy forging 1a, AlFeSi(Mn)-based compounds with an average particle size of 3.0 μm or more are not contained. If AlFeSi(Mn)-based compounds with an average particle size of 3.0 μm or more exist, the mechanical properties (tensile properties / fatigue properties, etc.) may decrease.

[0087] (The impact value is 10 J / cm 2 or more)

[0088] The central cross-section of the forged product 1a made of aluminum alloy has an impact value of 10 J / cm at room temperature (20 °C) 2 or more of mechanical properties. When the impact value is less than 10 J / cm 2 , the durability of the component may be reduced.

[0089] In this specification, the "impact value" means the Charpy impact strength obtained by measuring according to the provisions of the "Charpy impact test method for metallic materials" of JIS Z2242-2005. As the test piece, a cylindrical test piece is used for measurement.

[0090] (The ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less)

[0091] In the central cross-section of the aluminum alloy forged product 1a, the grain boundaries (large-angle grain boundaries) with a crystal orientation difference of 15° or more serve as an index of the progress of recrystallization of the long strip portion 2 of the aluminum alloy forged product 1a. The ratio of this large-angle grain boundary being 27% or less indicates that recrystallization is sufficiently suppressed. By sufficiently suppressing recrystallization, the mechanical properties of the long strip portion 2 are improved. The ratio of the large-angle grain boundary can be obtained from the EBSD image.

[0092] The aluminum alloy forged product 1a of the present embodiment configured as described above has the above alloy composition as its material, so recrystallization hardly occurs during the manufacture of the forged product. Therefore, it is difficult to generate overly coarse grains. In addition, the cross-section of the central portion 2a of the long strip portion 2 of the aluminum alloy forged product 1a of the present embodiment has a number density of precipitates containing Mn of 4 per μm 2 or more and a ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more of 27% or less within a 2.0 μm square including grain boundaries.

[0093] Therefore, the central portion 2a of the long strip portion 2 has high tensile properties, fatigue properties, excellent toughness, and improved impact resistance.

[0094] The aluminum alloy forged product 1a of the present embodiment can be advantageously used as a suspension arm for vehicles such as automobiles because the central portion 2a of the long strip portion 2 has high strength, durability, and is lightweight.

[0095] In Figure 1In the aluminum alloy forging 1a of the present embodiment shown, one connecting portion 4a is in the shape of a cylinder with a relatively small diameter, and one connecting portion 4b is in the shape of a cylinder with a relatively large diameter. The long strip portion 2 is shaped such that the width becomes wider from the end edge on the side of one connecting portion 4a toward the end edge on the side of the other connecting portion 4b. However, the shape of the aluminum alloy forging 1a is not limited thereto. For example, one connecting portion 4a and the other connecting portion 4b of the aluminum alloy forging 1a may also have the same shape. The width of the long strip portion 2 may also be constant. Additionally, the long strip portion 2 may also be in a curved shape. Regarding the connecting portion 4, three or more may also be formed.

[0096] Figure 2 It is a plan view of another example of an aluminum alloy forging according to an embodiment of the present invention.

[0097] Figure 2 The aluminum alloy forging 1b shown has three connecting portions 4c, 4d, and 4e. The connecting portion 4c and the connecting portion 4d are connected by the long strip portion 2, and the connecting portion 4d and the connecting portion 4e are connected by a short strip portion 5 that is relatively shorter in length than the long strip portion 2. A through hole is provided in the connecting portion 4c. This aluminum alloy forging 1b can be used, for example, as an L-shaped suspension arm.

[0098] Figure 3 It is a plan view of yet another example of an aluminum alloy forging according to an embodiment of the present invention.

[0099] Figure 3 The aluminum alloy forging 1c shown has three connecting portions 4f, 4g, and 4h. The connecting portion 4f and the connecting portion 4g, and the connecting portion 4f and the connecting portion 4h are respectively connected by the long strip portion 2. A through hole is provided in the connecting portion 4f. This aluminum alloy forging 1b can be used, for example, as an A-shaped suspension arm.

[0100] An aluminum alloy forging of another embodiment of the present invention is composed of the following aluminum alloy, and the aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is 0.3 or more and 1.2 or less in terms of mass ratio. The balance is composed of Al and inevitable impurities. The number density of the precipitates containing Mn within a 2.0 μm square including the grain boundary is 4 per μm 2 Above, the ratio of the large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less.

[0101] In addition, the impact value of the aluminum alloy forging of the present embodiment at room temperature is 10 J / cm 2 Above.

[0102] Fe / Mn can be set to 0.3 or more and 1.0 or less in terms of mass ratio. In addition, it can be set to 0.4 or more and 0.8 or less. In addition, it can be set to 0.4 or more and 0.7 or less.

[0103] If the size of the Mn-containing precipitates contained within a 2.0 μm square including the grain boundary is exemplified, it is 0.5 μm or less.

[0104] [Manufacturing method of aluminum alloy forging]

[0105] Next, the manufacturing method of the aluminum alloy forging of the present embodiment will be described.

[0106] The manufacturing method of the aluminum alloy forging of the present embodiment includes, for example, a melt formation process, a casting process, a forging process, a solution treatment process, a quenching treatment process, and an aging treatment process.

[0107] (Melt formation process)

[0108] The molten metal forming process is a process of melting raw materials to obtain an aluminum alloy molten metal with an adjusted composition. The composition of the aluminum alloy molten metal is adjusted to be the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio, and the balance is composed of Al and inevitable impurities, thereby obtaining a molten metal of 6000 series aluminum alloy.

[0109] It can also be adjusted so that Fe / Mn is 0.3 or more and 1.2 or less in terms of mass ratio.

[0110] By using the aluminum alloy molten metal with the above composition in the subsequent process, an Al-Mg-Si series aluminum alloy forged product that is difficult to recrystallize and has excellent mechanical properties at room temperature can be obtained. Furthermore, the so-called aluminum ingot is aluminum with a concentration of 99% or more obtained by electrolyzing alumina produced from minerals, which is called electrolytic refining.

[0111] The aluminum alloy molten metal can be obtained by heating the aluminum alloy to melt it. In addition, it can also be formed by melting a mixture of simple substances of elements that contain the raw materials of the aluminum alloy in the ratio to generate the target aluminum alloy or compounds containing two or more elements. For example, for the purpose of controlling the crystal grain size of the aluminum alloy generated in the casting process, Ti and B can be mixed in the form of a grain refinement material such as an Al-Ti-B rod.

[0112] Alternatively, the following raw materials can also be used as the raw materials for the aluminum alloy melt, and they are melted to obtain an aluminum alloy melt with adjusted composition. The raw materials are waste materials of aluminum alloys of the 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and / or 7000 series containing more than 10%, and the remaining part is new aluminum blocks and materials of the above-mentioned additive elements. In this case, an Al-Mg-Si series aluminum alloy forgings that are difficult to recrystallize and have excellent mechanical properties at room temperature can be obtained. Furthermore, the new aluminum block is aluminum with a purity of 99% or more obtained by electrolyzing alumina manufactured from minerals, which is called electrolytic refining.

[0113] (Casting process)

[0114] In the casting process, the melt (liquid phase) of the aluminum alloy is cooled and solidified into a solid (solid phase) to obtain an aluminum alloy casting. The casting process can use, for example, the horizontal continuous casting method.

[0115] Here, Figure 4 and Figure 5 show a horizontal continuous casting device that can be used for the manufacture of aluminum alloy castings of the present embodiment.

[0116] Furthermore, Figure 4 is a cross-sectional view showing an example near the mold 12 of the horizontal continuous casting device 10. Figure 5 is an enlarged cross-sectional view of the main part near the cooling water chamber 24 of the horizontal continuous casting device 10.

[0117] Figure 4 and Figure 5 The horizontal continuous casting device 10 shown has a melt receiving part (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (heat insulation member) 13 disposed between one end side 12a of the mold 12 and the melt receiving part 11.

[0118] The melt receiving part 11 is composed of a melt inflow part 11a that receives the aluminum alloy melt M obtained in the above melt forming process, a melt holding part 11b, and an outflow part 11c that flows out into the hollow part 21 of the mold 12.

[0119] The melt receiving part 11 maintains the height of the upper liquid surface of the aluminum alloy melt M at a position higher than the upper surface of the hollow part 21 of the mold 12, and in the case of multi-strand continuous casting, stably distributes the aluminum alloy melt M to each mold 12.

[0120] The aluminum alloy melt M held by the melt holding part 11b in the melt receiving part 11 is injected into the hollow part 21 of the mold 12 from the injection passage 13a provided in the refractory plate-like body 13. Then, the aluminum alloy melt M supplied into the hollow part 21 is cooled and solidified by a cooling device 23 described later, and is pulled out as an aluminum alloy bar B (a solidified ingot) from the other end side 12b of the mold 12.

[0121] On the other end side 12b of the mold 12, it is sufficient to provide a pulling drive device (not shown) for pulling out the cast aluminum alloy bar B at a constant speed. In addition, it is also preferable to provide a synchronous cutting machine (not shown) for cutting the continuously pulled aluminum alloy bar B into an arbitrary length.

[0122] The refractory plate-like body 13 is a member that blocks heat transfer between the melt receiving part 11 and the mold 12, and can be made of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, and graphite. Such a refractory plate-like body 13 can also be composed of a plurality of layers with different constituent materials.

[0123] The mold 12 is a hollow cylindrical member in the present embodiment, and is formed of a material selected from one or more combinations of aluminum, copper, or their alloys. For the material of such a mold 12, the best combination can be selected from the aspects of thermal conductivity, heat resistance, and mechanical strength.

[0124] The hollow part 21 of the mold 12 is formed in a circular cross-section so that the cast aluminum alloy bar B becomes a cylindrical bar, and the mold 12 is held in such a way that the mold central axis (central axis) C passing through the center of the hollow part 21 is substantially along the horizontal direction.

[0125] [[ID=H15]]The inner peripheral surface 21a of the hollow part 21 of the mold 12 is formed at an elevation angle of 0° to 3° (more preferably 0° to 1°) with respect to the mold central axis C in the casting direction of the aluminum alloy bar B (refer to Figure 1 )). That is, the inner peripheral surface 21a is configured to be conical and open in the casting direction. And the angle of the configuration of this cone is the elevation angle.

[0126] When the elevation angle is less than 0°, when the aluminum alloy bar B is pulled out from the mold 12, resistance is received on the other end side 12b which is the mold outlet, so casting may become difficult. On the other hand, if the elevation angle exceeds 3°, the contact between the inner peripheral surface 21a and the aluminum alloy melt M becomes insufficient, and the heat dissipation effect from the aluminum alloy melt M and its solidified shell to the mold 12 is reduced, and thus solidification may become insufficient. As a result, casting failures such as the generation of a remelted skin on the surface of the aluminum alloy bar B or the ejection of the non-solidified aluminum alloy melt M from the end of the aluminum alloy bar B may occur, so it is not preferable.

[0127] Furthermore, the cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape when observing the hollow portion 21 of the mold 12 from the other end side 21b) can be, for example, a triangle, a rectangular cross-sectional shape, a polygon, a semi-circle, an ellipse, or a special-shaped cross-sectional shape without a symmetry axis and / or a symmetry plane, etc., other than the circular shape of the present embodiment, and it can be selected according to the shape of the aluminum alloy rod to be cast.

[0128] A fluid supply pipe 22 for supplying a lubricating fluid into the hollow portion 21 of the mold 12 is arranged on one end side 12a of the mold 12. As the lubricating fluid supplied by the fluid supply pipe 22, any one or two or more kinds of lubricating fluids selected from gas lubricating materials and liquid lubricating materials can be used. In the case of supplying both a gas lubricating material and a liquid lubricating material, it is preferable to separately provide fluid supply pipes. The lubricating fluid pressurized and supplied by the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricating material supply port 22a.

[0129] In the present embodiment, the pressed lubricating fluid is supplied from the lubricating material supply port 22a to the inner peripheral surface 21a of the mold 12. Furthermore, it can also be configured such that the liquid lubricating material is heated to become a decomposed gas and is supplied to the inner peripheral surface 21a of the mold 12. Additionally, it can also be configured such that a porous material is arranged at the lubricating material supply port 22a, and the lubricating fluid oozes to the inner peripheral surface 21a of the mold 12 through the porous material.

[0130] A cooling mechanism, i.e., a cooling device 23, for cooling and solidifying the aluminum alloy melt M is formed inside the mold 12. The cooling device 23 of the present embodiment has: a cooling water chamber 24 for storing cooling water W for cooling the inner peripheral surface 21a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 for communicating the cooling water chamber 24 and the hollow portion 21 of the mold 12.

[0131] The cooling water chamber 24 is formed in a ring shape inside the mold 12 at a position outside the inner peripheral surface 21a of the hollow portion 21 so as to surround the hollow portion 21, and the cooling water W is supplied through a cooling water supply pipe 26.

[0132] The mold 12 cools the inner peripheral surface 21a by using the cooling water W stored in the cooling water chamber 24, and extracts the heat of the aluminum alloy melt M filled in the hollow portion 21 of the mold 12 from the surface in contact with the inner peripheral surface 21a of the mold 12, thereby forming a solidified shell on the surface of the aluminum alloy melt M.

[0133] In addition, the cooling water injection passage 25 directly sprays the cooling water W from the spray opening 25a facing the hollow portion 21 toward the aluminum alloy rod B on the other end side 12b of the mold 12 to cool the aluminum alloy rod B. The longitudinal sectional shape of such a cooling water injection passage 25 may be, for example, a semicircle, a pear shape, or a horseshoe shape in addition to the circular shape of the present embodiment.

[0134] Furthermore, in the present embodiment, the cooling water W supplied via the cooling water supply pipe 26 is first stored in the cooling water chamber 24 to cool the inner peripheral surface 21a of the hollow portion 21 of the mold 12, and then the cooling water W in the cooling water chamber 24 is sprayed toward the aluminum alloy rod B from the cooling water injection passage 25. However, it may be configured such that these cooling waters are supplied by separate cooling water supply pipes of separate systems.

[0135] The length from the position where the extension line of the central axis of the spray opening 25a of the cooling water injection passage 25 contacts the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate-like body 13 is defined as the effective mold length L. This effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. If the effective mold length L is less than 10 mm, casting becomes impossible due to the failure to form a good film or the like. If it exceeds 40 mm, the effect of forced cooling becomes low, solidification caused by the mold wall becomes dominant, the contact resistance between the mold 12 and the aluminum alloy melt M or the aluminum alloy rod B becomes large, cracks are generated on the surface of the casting, and breakage occurs inside the mold, etc., and casting may become unstable. Therefore, it is not preferable.

[0136] The supply of the cooling water W to the cooling water chamber 24 and the spraying of the cooling water W from the spray opening 25a of the cooling water injection passage 25 are preferably capable of controlling the operations separately by control signals from a control device (not shown).

[0137] The cooling water chamber 24 is formed such that the inner bottom surface 24a close to the hollow portion 21 of the mold 12 is parallel to the inner peripheral surface 21a of the hollow portion 21 of the mold 12.

[0138] Furthermore, the parallelism mentioned here also includes the case where the inner peripheral surface 21a of the hollow portion 21 of the mold 12 forms an elevation angle of 0° to 3° with respect to the inner bottom surface 24a of the cooling water chamber 24, that is, it also includes the case where the inclination angle of the inner bottom surface 24a with respect to the inner peripheral surface 21a exceeds 0° and is 3° or less.

[0139] As Figure 4 shown, as the cooling wall portion 27 of the mold 12 where the inner bottom surface 24a of such a cooling water chamber 24 faces the inner peripheral surface 21a of the hollow portion 21 of the mold 12, the heat flux value per unit area of the cooling water W from the aluminum alloy melt M in the hollow portion 21 toward the cooling water chamber 24 is 10×105 W / m 2 or more and 50×10 5 W / m 2 It is formed in the following range or less.

[0140] It is sufficient to form the mold 12 such that the thickness t of the cooling wall portion 27 of the mold 12, that is, the interval between the inner bottom surface 24a of the cooling water chamber 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12 is, for example, 0.5 mm or more and 3.0 mm or less, preferably 0.5 mm or more and 2.5 mm or less. In addition, it is sufficient to select the forming material of the mold 12 such that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is in the range of 100 W / m·K or more and 400 W / m·K or less.

[0141] In Figure 4 the molten aluminum alloy M in the molten metal receiving portion 11 is supplied from one end side 12a of the mold 12 through the refractory plate-like body 13, and is forcibly cooled on the other end side 12b of the mold 12 to become an aluminum alloy rod B, and the mold 12 is held such that the mold central axis C is substantially horizontal.

[0142] The aluminum alloy rod B is pulled out at a constant speed by a pulling drive device (not shown) provided near the other end side 12b of the mold 12, and thus a long aluminum alloy rod B is continuously cast. The pulled-out aluminum alloy rod B is cut into a desired length by, for example, a synchronous cutting machine (not shown).

[0143] Furthermore, the composition ratio of the cast aluminum alloy rod B can be confirmed by, for example, the method described in "JIS H1305" using a photoelectric photometric emission spectroscopic analysis device (device example: PDA-5500 manufactured by Shimadzu Corporation, Japan).

[0144] The difference in height between the liquid level of the molten aluminum alloy M stored in the molten metal receiving portion 11 and the height of the inner peripheral surface 21a on the upper side of the mold 12 is preferably set to 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting it within such a range, the pressure of the molten aluminum alloy M supplied into the mold 12 and the lubricating oil and the gas formed by the vaporization of the lubricating oil and gas are appropriately balanced, and thus the castability is stable.

[0145] As the liquid lubricant, vegetable oil used as lubricating oil can be used. For example, rapeseed oil, castor oil, and salad oil can be cited. They have little adverse impact on the environment, and thus are preferred.

[0146] The lubricating oil supply amount is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min or more and 1 mL / min or less). If the supply amount is too small, the molten aluminum alloy M of the aluminum alloy rod B may leak from the mold 12 due to insufficient lubrication before solidifying.

[0147] If the supply amount is too large, there is a possibility that the excess part may mix into the aluminum alloy rod B and become an internal defect.

[0148] The speed of pulling out the aluminum alloy rod B from the mold 12, i.e., the casting speed, is preferably 200 mm / min or more and 1500 mm / min or less (more preferably 400 mm / min or more and 1000 mm / min or less). This is because if the casting speed is within this range, the network structure of the crystals formed by casting becomes uniform and fine, the resistance to deformation of the aluminum billet at high temperature increases, and the high-temperature mechanical strength improves.

[0149] The amount of cooling water sprayed from the spray opening 25a of the cooling water spray passage 25 is preferably 10 L / min or more and 50 L / min or less per mold (more preferably 25 L / min or more and 40 L / min or less). If the amount of cooling water is less than this, the molten aluminum alloy M may leak from the mold 12 before solidifying. In addition, there is a possibility that the surface of the cast aluminum alloy rod B may remelt and form a non-uniform structure, which remains as an internal defect. On the other hand, if the amount of cooling water is more than this range, there is a possibility that the heat dissipation of the mold 12 is too large and it solidifies halfway.

[0150] The average temperature of the molten aluminum alloy M flowing into the mold 12 from the molten metal receiving portion 11 is preferably 650 °C or more and 750 °C or less (more preferably 680 °C or more and 720 °C or less), for example. If the temperature of the molten aluminum alloy M is too low, there is a possibility that coarse crystals may form in the mold 12 and its vicinity and enter the interior of the aluminum alloy rod B as internal defects. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen is likely to enter the molten aluminum alloy M, and there is a possibility that it may be incorporated into the aluminum alloy rod B as pores and become internal cavities.

[0151] Moreover, by setting the heat flux value per unit area of the cooling water W from the molten aluminum alloy M in the hollow portion 21 to the cooling water chamber 24 in the cooling wall portion 27 of the mold 12 to be 10×10 5 W / m 2 or more and 50×10 5 W / m 2 or less, the occurrence of thermal adhesion of the aluminum alloy rod B can be prevented.

[0152] The cooling wall portion 27 of the mold 12 is heated by the heat dissipation from the aluminum alloy melt M, and heat exchange is performed by cooling this heat using the cooling water W stored in the cooling water chamber 24. Regarding the state of this heat exchange, as shown in the explanatory diagram Figure 6 shown, the heat flux per unit area is considered. The heat flux per unit area is expressed by the following formula (1) according to Fourier's law.

[0153] Q = -k × (T1 - T2) / L ··· (1)

[0154] Q: Heat flux

[0155] k: Thermal conductivity (W / m·K) of the part through which heat passes (in this embodiment, it is the cooling wall portion 27 of the mold 12)

[0156] T1: Low-temperature side temperature of the part through which heat passes (in this embodiment, it is the inner bottom surface 24a of the cooling water chamber 24)

[0157] T2: High-temperature side temperature of the part through which heat passes (in this embodiment, it is the inner peripheral surface 21a of the hollow portion 21 of the mold 12)

[0158] L: Interval length (mm) of the part through which heat passes (in this embodiment, it is the thickness t of the cooling wall portion 27 of the mold 12)

[0159] By using a mold material, thickness, and temperature measurement data that can obtain good results even when reducing the amount of lubricating oil during casting, the heat flux value per unit area becomes 10×10 5 W / m 2 or more, the cooling wall portion 27 of the mold 12 is configured in this way, and thermal adhesion of the cast aluminum alloy rod B can be prevented. In addition, it is preferable that the heat flux value per unit area is 50×10 5 W / m 2 or less.

[0160] In order to make the cooling wall portion 27 of the mold 12 within such a range of heat flux values, it is sufficient to form the mold 12 such that the thickness t of the cooling wall portion 27 of the mold 12 is, for example, in the range of 0.5 mm or more and 3.0 mm or less. In addition, it is sufficient to set the thermal conductivity of at least the cooling wall portion 27 of the mold 12 in the range of 100 W / m·K or more and 400 W / m·K or less.

[0161] When manufacturing the aluminum alloy rod B of this embodiment, the above horizontal continuous casting device 10 is used, and the aluminum alloy melt M stored in the melt receiving portion 11 is continuously supplied into the hollow portion 21 from one end side 12a of the mold 12. In addition, cooling water W is supplied to the cooling water chamber 24, and a lubricating fluid, such as lubricating oil, is supplied from the fluid supply pipe 22.

[0162] Then, under the condition that the heat flux value per unit area in the cooling wall portion 27 is 10×10 5 W / m 2 or more, the molten aluminum alloy M supplied into the hollow portion 21 is cooled and solidified to cast the aluminum alloy rod B. In addition, when casting the aluminum alloy rod B, it is preferable that the wall surface temperature of the cooling wall portion 27 of the mold 12 cooled by the cooling water W is 100°C or less.

[0163] The aluminum alloy rod B thus obtained, by cooling and solidifying under the condition that the heat flux value per unit area in the cooling wall portion 27 is 10×10 5 W / m 2 or more, can suppress the adhesion of reaction products such as carbides caused by the contact between the gas of the lubricating oil and the molten aluminum alloy M. Therefore, it is not necessary to cut and remove carbides and the like on the surface of the aluminum alloy rod B, and the aluminum alloy rod B can be manufactured with a high yield.

[0164] The casting process for obtaining a casting from the molten aluminum alloy M is not limited to the above horizontal continuous casting method, and known continuous casting methods such as the vertical continuous casting method can be used. The vertical continuous casting method is classified into the floating method and the hot top method according to the supply method of the molten aluminum alloy M to the mold (mold 12). Hereinafter, the case of using the hot top method will be briefly described.

[0165] The casting device for the hot top method includes a mold, a molten metal receiver (manifold), etc. The molten metal supplied to the molten metal receiving portion passes through the liquid outlet and through the manifold, thereby adjusting the flow rate, and enters a substantially horizontally arranged cylindrical mold, where it is forcibly cooled to form a solidified shell on the outer surface of the molten metal.

[0166] Furthermore, cooling water is directly radiated to the casting pulled out from the mold, and the casting is continuously pulled out while the solidification of the metal progresses into the casting. Usually, the mold uses a metal member with good thermal conductivity and has a hollow structure for introducing a cooling medium into the interior.

[0167] The cooling medium used can be appropriately selected from the cooling media that can be industrially utilized, but water is recommended from the viewpoint of ease of use.

[0168] The mold used in the present embodiment is appropriately selected from metals such as copper and aluminum or graphite from the viewpoints of heat transfer performance and durability of the contact portion in contact with the molten metal. The manifold is generally made of a refractory material and is provided on the upper side of the mold. The material and size of the manifold can be appropriately selected according to the composition range of the alloy to be cast and the size of the casting, and there is no particular limitation.

[0169] The average cooling rate during casting can be appropriately selected from the generally recommended range, such as 10 to 300 °C / second. The casting speed can be appropriately selected from the general range in horizontal continuous casting, for example, appropriately selected from the range of 200 to 600 mm / minute.

[0170] According to the casting method described above, even for medium to large-sized castings, it becomes possible to obtain a uniform metal structure. The diameter of the casting object is not particularly limited, and it can be well used for bars with a diameter of 30 mm to 100 mm.

[0171] (Forging process)

[0172] The forging process is a process of cutting the cast aluminum alloy casting after casting into a specified size, heating the obtained forging blank to a specified temperature, and then performing die forming by applying pressure using a press. In the present embodiment, forging is performed without performing the homogenization treatment that was conventionally performed after casting to remove segregation. Therefore, it is necessary to remove segregation that occurs in the homogenization treatment by heating the blank during forging. Therefore, regarding heating, the blank needs to be heated at a temperature of 500 °C or higher and below the melting point. Thereafter, forging is performed to obtain a forging (such as a suspension arm component of an automobile). If the heating temperature of the blank during forging is lower than 500 °C, compounds such as AlFeSi-based and Mg2Si-based in the alloy structure remain in a segregated state, the deformation resistance becomes high, sufficient processing cannot be performed, and cracks are generated. On the other hand, if the temperature exceeds the melting point temperature, defects such as eutectic melting are likely to occur.

[0173] (Solution treatment process)

[0174] The solution treatment process is a process of heating the forging obtained in the forging process to cause it to dissolve, thereby relieving the strain introduced in the forging process and performing the solution of solute elements.

[0175] In the present embodiment, solution treatment is performed by maintaining the forging at a treatment temperature of 530 °C or higher and 560 °C or lower for 0.3 hours or longer and 3 hours or shorter. The heating rate from room temperature to the above treatment temperature is preferably 5.0 °C / minute or higher. If the treatment temperature is lower than 530 °C, the solution of solute elements may be insufficient. On the other hand, if it exceeds 560 °C, although the solution of solute elements is further promoted, eutectic melting and recrystallization are likely to occur. In addition, when the heating rate is lower than 5.0 °C / minute, Mg2Si may precipitate coarsely. On the other hand, when the treatment temperature is lower than 530 °C, the solution is not performed, and it may be difficult to achieve high strength based on age precipitation.

[0176] (Quenching treatment process)

[0177] The quenching treatment process is a process of rapidly cooling the forged product in a solid solution state obtained through the solution treatment process to form a supersaturated solid solution.

[0178] In the present embodiment, the quenching treatment is performed by immersing the forged product in water by putting the forged product into a water tank (quenching water). The water temperature in the water tank is preferably 20°C or higher and 60°C or lower. The input of the forged product into the water tank is preferably performed within 5 seconds or more and 60 seconds or less after the solution treatment in such a manner that the entire surface of the forged product comes into contact with water. The immersion time of the forged product varies depending on the size of the casting product and is, for example, a period exceeding 1 minute and within 30 minutes.

[0179] (Aging treatment process)

[0180] The aging treatment process is a process of heating and holding the forged product at a lower temperature to precipitate the elements supersaturatedly solid-solved and impart an appropriate hardness.

[0181] In the present embodiment, the aging treatment is performed by heating the forged product after the quenching treatment process to a temperature of 170°C or higher and 210°C or lower and holding it at this temperature for 0.5 hours or more and 7 hours or less. If the treatment temperature is lower than 170°C or the holding time is less than 0.5 hours, the Mg2Si-based precipitates that increase the tensile strength may not be able to grow sufficiently. On the other hand, when the treatment temperature exceeds 190°C or the holding time exceeds 7 hours, the Mg2Si-based precipitates become too coarse and may not be able to sufficiently increase the tensile strength.

[0182] The manufacturing method of the aluminum alloy forged product according to another embodiment of the present invention further includes a homogenization heat treatment process, which is a process of performing homogenization heat treatment by holding the aluminum alloy casting product in a temperature range of 370°C or higher and 560°C or lower for 2 hours or more and 10 hours or less between the above-mentioned casting process and the above-mentioned forging process.

[0183] The manufacturing method of the aluminum alloy forged product of this embodiment is different from the manufacturing method of the aluminum alloy forged product of the above embodiment in that it includes a homogenization heat treatment process.

[0184] Examples

[0185] Next, specific examples of the present invention will be described, but the present invention is not particularly limited by these examples.

[0186] [Examples 1 to 8 and Comparative Examples 1 to 3]

[0187] (Production of continuous casting products)

[0188] First, an aluminum alloy having the alloy composition shown in Table 1 below (the balance being aluminum) was prepared. Using the prepared aluminum alloy, a continuously cast product having a circular cross-section with a diameter of 82 mm was produced.

[0189]

[0190] (Manufacture of Aluminum Alloy Forged Product)

[0191] Next, the obtained continuously cast product was successively subjected to a homogenization heat treatment process (only for Comparative Examples 1 to 3), a forging process, a solution treatment process, a quenching process, and an artificial aging treatment process to obtain Figure 1 an aluminum alloy forged product 1a having the shape shown. The conditions of the homogenization heat treatment process (only for Comparative Examples 1 to 3), the forging process, the solution treatment process, the quenching process, and the artificial aging treatment process are shown in Table 2 below.

[0192]

[0193] [Evaluation]

[0194] The central portion 2a in the longitudinal direction of the long strip portion 2 in the aluminum alloy forged products 1a of Examples 1 to 8 and Comparative Examples 1 to 3 obtained as described above was evaluated as follows. The evaluation results of the central portion 2a of the long strip portion 2 are shown in Table 3 below.

[0195] <fe mn>

[0196] The Fe / Mn was adjusted so that the Fe / Mn of the examples was 0.3 or more and 1.2 or less, and the Fe / Mn of the comparative examples exceeded 1.2.

[0197] "○”... is 0.3 or more and 1.2 or less.

[0198] "×”... exceeds 1.2.

[0199] <Electrical conductivity (%IACS)>

[0200] The electrical conductivity was measured at room temperature.

[0201] (Judgment criteria)

[0202] "○”... is 25%IACS or more and 35%IACS or less.

[0203] "×”... is less than 25%IACS or exceeds 35%IACS.

[0204] <Rockwell hardness (HRF)>

[0205] The Rockwell hardness (HRF) was measured in accordance with "Rockwell hardness test - Test method" of JIS Z2245:2016.

[0206] (Judgment criteria)

[0207] "○”... is 62 or more and 82 or less.

[0208] "×”... is less than 0.62 or exceeds 82.

[0209] <Evaluation of mechanical properties (impact properties)>

[0210] The central part 2a of the long strip part 2 of the forged product 1a made of aluminum alloy was cut as Figure 7 shown to produce a prism for making a specimen for evaluating mechanical properties (impact properties). The obtained prism was processed to produce a Figure 8 cylindrical specimen for evaluating mechanical properties as shown. The diameter A of the parallel part of the specimen for evaluating mechanical properties was set to 8.0 mm, and the distance G between the punctuation marks was set to 30.0 mm. For the specimen for evaluating mechanical properties, a Charpy impact test was conducted in accordance with JIS Z2242 at normal temperature (25°C), and the impact value was measured. The obtained impact value was evaluated based on the following judgment criteria.

[0211] (Judgment criteria)

[0212] "○”... The impact value at normal temperature is 10 J / cm 2 or more.

[0213] "×"... The impact value at room temperature is less than 10 J / cm 2 .

[0214] <Micro-refinement evaluation, recrystallization and crystal coarsening evaluation>

[0215] Cut the central part 2a of the long strip part 2 of the aluminum alloy forging 1a in a direction perpendicular to the surface of the central part 2a to obtain a plate-like body (thickness 2 mm) for making a specimen for micro-refinement evaluation. Cut the obtained plate-like body into squares with a side length of 7 mm to obtain a specimen for micro-refinement evaluation with a size of 7 mm × 7 mm × thickness 2 mm. For the surface of the prepared specimen for micro-refinement evaluation (the cross-section of the central part 2a), use SEM-EBSD (scanning electron microscope - electron backscatter diffraction device) to measure the number of AlFeSi-based compounds with a size of 3.0 μm or more and the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more. Based on the following criteria, respectively judge the number of AlFeSi-based compounds with a size of 3.0 μm or more and the ratio of large-angle grain boundaries obtained, and evaluate the micro-refinement of grains and recrystallization and crystal coarsening. Furthermore, regarding the measurement conditions of SEM-EBSD, set the acceleration voltage to 15 kV, set the measurement pitch to 0.5 μm / px, and set the analysis area to 500 × 500 μm 2 , and set the grain boundary definition angle to 15°.

[0216] (Judgment criteria)

[0217] (Judgment criteria for the number of AlFeSi-based compounds with a size of 3.0 μm or more)

[0218] "O"... In the case of none (0 pieces).

[0219] "×"... In the case of having.

[0220] (Judgment criteria for the ratio of large-angle grain boundaries)

[0221] "○"... 27% or less.

[0222] "×"... Exceeding 27%.

[0223] <Method for measuring the number density of Mn-based precipitates in aluminum alloy forgings>

[0224] In addition, for each aluminum alloy forging, a FE-SEM device (field emission scanning electron microscope device) was used to measure the number density of Mn-containing precipitates within a 2.0-μm square including grain boundaries. Furthermore, a sample piece for microstructure observation with a size of approximately 10 mm in length × 10 mm in width × 10 mm in thickness was cut out from the central part 2a of the long strip part 2 of the aluminum alloy forging 1a, and this sample piece was polished using a cross section polisher. Then, a FE-SEM photograph (field emission scanning electron microscope photograph) of the polished sample piece was taken, and within the field-of-view area of 1.5815 mm 2 in this SEM photograph, the number density of Mn-containing precipitates was determined within a 2.0-μm square including grain boundaries, and the number density was evaluated according to the following judgment criteria.

[0225] (Judgment criteria for number density)

[0226] "○”... 4 pieces / μm 2 or more.

[0227] "×”... less than 4 pieces / μm 2 or less.

[0228] [Comprehensive evaluation]

[0229] Based on the following judgment criteria, the evaluation results of 7 items including the Fe / Mn ratio, conductivity, Rockwell hardness, impact characteristics, the number of AlFeSi-based compounds with a size of 3.0 μm or more, the number density of AlMn-based compounds, and the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more were evaluated.

[0230] (Judgment criteria)

[0231] "○”... All 7 evaluations are "O".

[0232] "×”... One or more of the 7 evaluations are "×".

[0233]

[0234] Explanation of reference numerals

[0235] 10... Horizontal continuous casting device

[0236] 11... Molten metal receiving part (tundish)

[0237] 11a... Molten metal inflow part

[0238] 11b... Molten metal holding part

[0239] 11c... Outflow part

[0240] 12... Mold

[0241] 12a…One end side

[0242] 12b…The other end side

[0243] 13…Plate-like body made of refractory material (heat insulation member)

[0244] 13a…Liquid injection passage

[0245] 21…Hollow part

[0246] 21a…Inner peripheral surface

[0247] 21b…The other end side

[0248] 22…Fluid supply pipe

[0249] 22a…Lubricating material supply port

[0250] 23…Cooling device

[0251] 24…Cooling water chamber

[0252] 24a…Inner bottom surface

[0253] 25…Cooling water injection passage

[0254] 25a…Spray opening

[0255] 26…Cooling water supply pipe

[0256] 27…Cooling wall portion

[0257] B…Aluminum alloy rod

[0258] M…Alloy melt

[0259] W…Cooling water

[0260] 100…Aluminum alloy forging< / fe>

Claims

1. A blank for forging an aluminum alloy, having the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio, and the balance is composed of Al and inevitable impurities, the conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

2. A blank for forging an aluminum alloy, having the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of the content of Fe to the content of Mn, Fe / Mn, is 0.3 or more and 1.2 or less in terms of mass ratio, and the balance is composed of Al and inevitable impurities, the conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

3. An aluminum alloy forgings, It is composed of the following aluminum alloy, and the aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is less than 1.4 in terms of mass ratio. The balance is composed of Al and inevitable impurities. The number density of Mn precipitates within a 2.0-μm square containing grain boundaries is 4 per μm 2 or more, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm 2 or more.

4. The aluminum alloy forging according to claim 3, The size of the precipitate is 0.5 μm or less.

5. An aluminum alloy forging, It is composed of the following aluminum alloy, and the aluminum alloy has the following alloy composition: containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.60% by mass or more and 1.25% by mass or less, Si in the range of 0.90% by mass or more and 1.4% by mass or less, Mn in the range of 0.35% by mass or more and 0.60% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less. The ratio of the content of Fe to the content of Mn, Fe / Mn, is 0.3 or more and 1.2 or less in terms of mass ratio. The balance is composed of Al and inevitable impurities. The number density of Mn precipitates within a 2.0-μm square containing grain boundaries is 4 per μm 2 or more, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm 2 or more.

6. The aluminum alloy forging according to claim 5, The size of the precipitate is 0.5 μm or less.

7. A method for manufacturing an aluminum alloy forging, which is a method for manufacturing the aluminum alloy forging according to any one of claims 3 to 6, and has: A melt forming step of obtaining a melt of the aluminum alloy; A casting step of obtaining a casting by performing casting processing on the obtained melt; A forging step of heating the casting at a temperature of 500 °C to the melting point to obtain a forging by performing plastic processing; A solution treatment step of solution-treating the obtained forging under the condition of heating at a heating rate of 5.0 °C / minute or more from 20 °C to 500 °C and holding at a temperature of 530 to 560 °C for 0.3 to 3 hours; A quenching process in which all surfaces of the forged product come into contact with quenching water within 5 to 60 seconds after the solution treatment, and the quenching is carried out in a water tank for more than 1 minute and within 40 minutes; and An aging treatment process in which the forged product that has undergone the quenching treatment process is heated at a temperature of 180°C to 220°C for 0.5 hours to 8 hours for aging treatment.

8. The method for manufacturing an aluminum alloy forged product according to claim 7, further comprising a homogenization heat treatment process, which is a process of performing homogenization heat treatment on the cast product of the aluminum alloy in a temperature range of 370°C or higher and 560°C or lower for 2 hours or more and 10 hours or less between the casting process and the forging process.

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