Aluminum alloy forging material, aluminum alloy forged product, and method for manufacturing the same

Abstract

This aluminum alloy forging billet has the following alloy composition: Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, Zn in the range of 0.25% to 0.050% to 0.30% by mass. The Fe content relative to Mn content is 0.3 to 1.1 by mass, with the balance consisting of Al and unavoidable impurities. The Fe / Mn ratio is 0.3 to 1.1 by mass. The Fe content relative to Mn content is 0.3 to 1.1 by mass. The balance consists of Al and unavoidable impurities. In the thermal analysis curve obtained by differential thermal analysis (DSC), exothermic peaks are generated in the range of 200 to 300 °C and 400 to 500 °C, respectively.

Description

Technical Field

[0001] This invention relates to aluminum alloy forging blanks, aluminum alloy forgings, and manufacturing methods thereof.

[0002] This application claims priority based on Japanese Patent Application No. 2024-022300 filed on February 16, 2024, the contents of which are incorporated herein by reference. Background Technology

[0003] In recent years, aluminum alloys have been increasingly used as structural components in various products due to their lightweight properties. For example, high-strength steel has been used in automotive chassis and bumper parts until now. On the other hand, high-strength aluminum alloys have begun to be used in recent years.

[0004] In addition, iron-based materials are often used in automotive components, such as suspension parts. On the other hand, in recent years, primarily for the purpose of weight reduction, they have been largely replaced by aluminum or aluminum alloy materials.

[0005] These automotive parts require excellent corrosion resistance, high strength, and excellent machinability; therefore, Al-Mg-Si alloys, especially A6061, are mostly used as aluminum alloy materials. Furthermore, to improve strength, these automotive parts are manufactured using aluminum alloy materials as processing blanks and undergoing forging, a type of plastic forming process.

[0006] In addition, recently, due to the need to reduce costs, suspension components that are forged directly from cast parts without extrusion and then subjected to solution treatment and artificial aging treatment (T6 treatment) have begun to be put into practical use. With the aim of further reducing weight, the development of a high-strength alloy to replace the previous A6061 is being promoted (see, for example, Patent Documents 1-3).

[0007] Existing technical documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 5-59477

[0009] Patent Document 2: Japanese Patent Application Publication No. 5-247574

[0010] Patent Document 3: Japanese Patent Application Publication No. 6-256880 Summary of the Invention

[0011] However, the aforementioned Al-Mg-Si high-strength alloys have the following problem: the processed microstructure recrystallizes during forging and heat treatment processes, resulting in coarse grains, which prevents the attainment of sufficient high strength. Therefore, in order to prevent the formation of coarse recrystallized grains, there are methods to prevent recrystallization by adding Zr (zirconium) (for example, see the aforementioned Patent Documents 1 and 2).

[0012] However, while adding Zr is effective in preventing recrystallization, it has the following problems.

[0013] (1) Due to the addition of Zr, the grain refinement effect of Al-Ti-B alloy is weakened, the grains of the ingot itself become coarser, resulting in a decrease in the strength of the processed parts (forgings) after plastic processing.

[0014] (2) Because the grain refinement effect of the ingot itself is weakened, ingot cracks are more likely to occur, internal defects increase, and yield deteriorates.

[0015] (3) Zr forms compounds with Al-Ti-B alloys. These compounds accumulate at the bottom of the furnace where the alloy melt is stored, contaminating the furnace. At the same time, these compounds also coarsely crystallize in the manufactured ingots, reducing their strength.

[0016] Thus, while the addition of Zr is effective in preventing recrystallization, it is difficult to maintain the stability of strength.

[0017] The present invention was made in view of the above-mentioned technical background, and its purpose is to provide aluminum alloy forging blanks with excellent mechanical properties at room temperature, aluminum alloy forgings and their manufacturing methods.

[0018] To address the aforementioned issues, the present invention provides the following means.

[0019] Solution 1 of the present invention is an aluminum alloy forging billet having the following alloy composition: Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, Zn in the range of 0.25% to 0.050% to 0.30% by mass. The Fe / Mn content ratio is 0.3 or more and 1.1 or less, with the balance consisting of Al and unavoidable impurities. The Fe / Mn content ratio is 0.3 or more and 1.1 or less, with the balance consisting of Al and unavoidable impurities. In the thermal analysis curve obtained by differential thermal analysis (DSC), exothermic peaks are generated in the range of 200-300℃ and 400-500℃, respectively.

[0020] Solution 2 of the present invention is an aluminum alloy forging having the following alloy composition: Cu in the range of 0.25% by mass and 0.55% by mass, Mg in the range of 0.85% by mass and 1.25% by mass, Si in the range of 1.02% by mass and 1.4% by mass, Mn in the range of 0.55% by mass and 1.0% by mass, Fe in the range of 0.32% by mass and 0.65% by mass, and Z in the range of 0.25% by mass and 0% by mass. The content of Fe relative to Mn is 0.3% to 0.1% by mass, the content of Cr is 0.050% to 0.30% by mass, the content of Ti is 0.01% to 0.1% by mass, the content of B is 0.0010% to 0.030% by mass, and the content of Zr is 0.0010% to 0.050% by mass. The Fe / Mn ratio is 0.3 to 1.1 by mass, and the balance consists of Al and unavoidable impurities. After corrosion resistance testing based on JIS H8502, 1999, the corrosion rate is 0.045% or less, and the corrosion area is 3% / 1.05E+0.9μm. 2 The corrosion depth is below 300μm.

[0021] Solution 3 of the present invention is an aluminum alloy forging according to Solution 2, which is used for suspension arms.

[0022] Scheme 4 of the present invention is a method for manufacturing aluminum alloy forgings, which is the method for manufacturing aluminum alloy forgings described in Scheme 2 or Scheme 3. It includes a melt formation process, a casting process, a forging process, a solution treatment process, a quenching process, and an aging treatment process. In the melt formation process, an aluminum alloy melt is obtained. In the casting process, a casting is obtained by casting the obtained melt. In the forging process, the casting is heated at a temperature above 500°C and below its melting point to perform plastic processing and obtain a forging. A solution treatment is performed in the solution treatment process. The forging is heated at a rate of 5.0℃ / minute or higher between 20℃ and 500℃ and held at 530℃ for 0.3 to 3 hours. In the quenching process, the entire surface of the forging is brought into contact with quenching water for 5 to 60 seconds after the solution treatment process, and quenching is performed in the water bath for more than 1 minute but less than 40 minutes. In the aging process, the forging is heated at 180℃ to 220℃ for 0.5 to 8 hours to age. The time interval between the quenching process and the aging process is less than 2 hours.

[0023] Scheme 5 of the present invention is a method for manufacturing aluminum alloy forgings, which is the method for manufacturing aluminum alloy forgings described in Scheme 2 or Scheme 3. It includes a melt formation process, a casting process, a forging process, a solution treatment process, a quenching process, and an aging treatment process. In the melt formation process, an aluminum alloy melt is obtained. In the casting process, a casting is obtained by casting the obtained melt. In the forging process, the casting is heated at a temperature above 500°C and below its melting point to perform plastic processing and obtain a forging. In the solution treatment process, a solution treatment is performed to achieve the desired temperature. The forging is heated at a rate of 5.0℃ / minute or higher from 20℃ to 500℃ and held at 530℃ to 560℃ for 0.3 to 3 hours. In the quenching process, the entire surface of the forging is brought into contact with quenching water for 5 to 60 seconds after the solution treatment process, and quenching is performed in the water bath for more than 1 minute but less than 40 minutes. In the aging process, the forging is heated at 180℃ to 220℃ for 0.5 to 8 hours for aging treatment. In the casting process, the solidification time at 650℃ to 600℃ is less than 20 seconds.

[0024] Scheme 6 of the present invention is a method for manufacturing aluminum alloy forging billet, which is the method for manufacturing aluminum alloy forging billet described in Scheme 1. It includes a melt formation process and a casting process. In the melt formation process, an aluminum alloy melt is obtained. In the casting process, a casting is obtained by casting the obtained melt. Furthermore, no homogenization treatment is performed after the casting process.

[0025] According to the present invention, aluminum alloy forging blanks with excellent mechanical properties at room temperature, aluminum alloy forgings, and manufacturing methods thereof can be provided. Attached Figure Description

[0026] Figure 1 This is a perspective view showing an example of an aluminum alloy forging according to an embodiment of the present invention.

[0027] Figure 2 This is a top view showing another example of an aluminum alloy forging according to one embodiment of the present invention.

[0028] Figure 3 This is a perspective view showing yet another example of an aluminum alloy forging according to an embodiment of the present invention.

[0029] Figure 4 This is a cross-sectional view showing an example of the area near the mold in a horizontal continuous casting apparatus used to manufacture aluminum alloy forgings according to an embodiment of the present invention.

[0030] Figure 5 yes Figure 4An enlarged cross-sectional view of the main part near the cooling water chamber of the horizontal continuous casting apparatus shown.

[0031] Figure 6 This is an explanatory diagram illustrating the heat flux of the cooling wall section of a horizontal continuous casting unit.

[0032] Figure 7 This is a top view showing the location where the central portion of the aluminum alloy forging obtained from this embodiment was taken as a test piece for evaluating mechanical properties.

[0033] Figure 8 This is a top view showing the test piece used for evaluating mechanical properties produced in this embodiment. Detailed Implementation

[0034] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0035] Furthermore, to facilitate understanding of its features, the accompanying drawings used in the following description may sometimes be enlarged representations of certain features for convenience, and the dimensions and ratios of the constituent elements may not be the same as in reality. Additionally, the materials, dimensions, etc., illustrated in the following description are examples, and the present invention is not necessarily limited thereto; appropriate modifications can be made without altering its effects.

[0036] [Materials for Aluminum Alloy Forging]

[0037] First, an aluminum alloy forging billet according to one embodiment of the present invention will be described.

[0038] The aluminum alloy forging billet of this embodiment has the following alloy composition: Cu in the range of 0.25% by mass and 0.55% by mass, Mg in the range of 0.85% by mass and 1.25% by mass, Si in the range of 1.02% by mass and 1.4% by mass, Mn in the range of 0.55% by mass and 1.0% by mass, Fe in the range of 0.32% by mass and 0.65% by mass, Zn in the range of 0.25% by mass, and Fe in the range of 0.050% by mass and 0.30% by mass. The Fe content relative to Mn content is 0.3 to 1.1 by mass, with the balance consisting of Al and unavoidable impurities. In the thermal analysis curve obtained by differential thermal analysis (DSC), exothermic (precipitation) peaks are generated in the ranges of 200 to 300 °C and 400 to 500 °C, respectively. The Fe / Mn content is 0.3 to 1.1 by mass, and the balance consists of Al and unavoidable impurities.

[0039] (The heating (precipitation) peak in the thermal analysis curve obtained by differential thermal analysis)

[0040] It is known that the exothermic peak appearing in the thermal analysis curve (DSC curve) obtained by differential thermal analysis of metallic materials corresponds to the formation of the predetermined precipitate.

[0041] In the aluminum alloy forging billet of this embodiment, an exothermic peak is obtained in the DSC curve between 200~300℃ and between 400~500℃. The exothermic peak between 200~300℃ corresponds to the formation of β'-Mg2Si, and the exothermic peak between 400~500℃ corresponds to the formation of β-Mg2Si.

[0042] [Aluminum Alloy Forgings]

[0043] Next, an aluminum alloy forging according to one embodiment of the present invention will be described.

[0044] Figure 1 This is a perspective view of an aluminum alloy forging according to one embodiment of the present invention.

[0045] like Figure 1 As shown, the aluminum alloy forging 1a has an elongated portion 2 and connecting portions 4a and 4b that are respectively connected to the two ends of the elongated portion 2 along its long side. The cross-section of the elongated portion is quadrilateral. Through holes are provided on the two connecting portions 4. This shape of aluminum alloy forging 1a can be used, for example, as an I-type suspension arm.

[0046] The aluminum alloy forging of this embodiment has the following alloy composition: Cu in the range of 0.25% by mass and 0.55% by mass, Mg in the range of 0.85% by mass and 1.25% by mass, Si in the range of 1.02% by mass and 1.4% by mass, Mn in the range of 0.55% by mass and 1.0% by mass, Fe in the range of 0.32% by mass and 0.65% by mass, Zn in the range of 0.25% by mass and O The content of Cr is ≥0.050% by mass and ≤0.30% by mass; Ti is ≥0.01% by mass and ≤0.1% by mass; B is ≥0.0010% by mass and ≤0.030% by mass; and Zr is ≥0.0010% by mass and ≤0.050% by mass. The Fe / Mn content ratio is ≥0.3 by mass and ≤1.1 by mass, with the balance consisting of Al and unavoidable impurities. After corrosion resistance testing based on JIS H8502, 1999, the corrosion rate is ≤0.045%, and the corrosion area is 3 [% / 1.05E+0.9μm]. 2 The corrosion depth is below 300μm.

[0047] The aluminum alloy forging blanks and aluminum alloy forgings described above are equivalent to 6000 series aluminum alloys in that they contain Mg and Si.

[0048] (Cu: ≥0.25% by mass and ≤0.55% by mass)

[0049] Cu has the function of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys by precipitating Al-Cu-Mg-Si compounds, primarily the Q phase. By ensuring the Cu content is within the aforementioned range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0050] (Mg: ≥0.85% by mass and ≤1.25% by mass)

[0051] Mg contributes to the tensile strength of aluminum alloys. It strengthens aluminum alloys by dissolving Mg into the aluminum matrix or by precipitating as a Mg-Si compound (Mg₂Si) or an Al-Cu-Mg-Si compound (AlCuMgSi) dominated by the Q phase. Furthermore, Mg₂Si inhibits the formation of the CuAl₂ phase in aluminum alloys. By suppressing CuAl₂ phase formation, the corrosion resistance of aluminum alloy forging blanks and forgings using these blanks is improved. Maintaining a Mg content within the aforementioned range enhances the mechanical properties and corrosion resistance of aluminum alloy forging blanks and forgings using these blanks at room temperature.

[0052] (Si: ≥1.02% by mass and ≤1.4% by mass)

[0053] Like Mg, Si improves the mechanical properties and corrosion resistance of aluminum alloy forging blanks at room temperature. However, excessive addition of Si to aluminum alloys can lead to the precipitation of coarse primary Si grains, potentially reducing the tensile strength of the alloy. By maintaining the Si content within the aforementioned range, the crystallization of primary Si can be suppressed, thereby improving the mechanical properties and corrosion resistance of both the aluminum alloy forging blank and the aluminum alloy forgings using that blank at room temperature.

[0054] (Mn: ≥0.55% by mass and ≤1.0% by mass)

[0055] Mn can improve the tensile strength of aluminum alloys by forming fine granular crystals containing intermetallic compounds such as Al-Mn-Fe-Si or Al-Mn-Cr-Fe-Si. By maintaining the Mn content within the aforementioned range, the mechanical properties of aluminum alloy forging blanks and aluminum alloy forgings using these blanks at room temperature can be improved.

[0056] (Fe: ≥0.32% by mass and ≤0.65% by mass)

[0057] Fe enhances the tensile strength of aluminum alloys by crystallizing as fine-grained intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe. Maintaining an Fe content within the aforementioned range improves the mechanical properties of aluminum alloy forging blanks and forgings made from these blanks at room temperature.

[0058] Furthermore, the Fe / Mn ratio is 0.3 or higher and 1.1 or lower. By maintaining a Fe / Mn ratio of 0.3 or higher and 1.1 or lower, the crystallization of AlFeSi compounds with a particle size of 2.0 μm or larger can be suppressed, and the number density of AlMn compounds within the grains can be increased.

[0059] (Cr: ≥0.050% by mass and ≤0.30% by mass)

[0060] Cr enhances the tensile strength of aluminum alloys by forming fine granular crystals containing intermetallic compounds such as Al-Mn-Cr-Fe-Si or Al-Fe-Cr. When the Cr content is within the aforementioned range, the mechanical properties of aluminum alloy forging blanks and aluminum alloy forgings using these blanks at room temperature can be improved.

[0061] (Ti: ≥0.01% by mass and ≤0.1% by mass)

[0062] Ti (Ti) has the function of refining the grain size of aluminum alloys and improving their ductility and workability. If the Ti content is below 0.01% by mass, the grain refinement effect may not be sufficiently achieved. On the other hand, if the Ti content exceeds 0.1% by mass, coarse crystals may form, reducing ductility and workability. Furthermore, if a large amount of coarse Ti-containing crystals are incorporated into the aluminum alloy forging billet and the aluminum alloy forging using the billet, the toughness will decrease. Therefore, the Ti content is set to be 0.01% by mass or more and 0.1% by mass or less. The preferred Ti content is 0.015% by mass or more and 0.050% by mass or less.

[0063] (B: 0.0010% by mass or more and 0.030% by mass or less)

[0064] Boron (B) has the function of refining the grain size of aluminum alloys and improving their ductility and workability. Adding B to aluminum alloys together with Ti (Ti) improves the grain refinement effect. When the B content is below 0.0010% by mass, the grain refinement effect may not be sufficiently achieved. On the other hand, if the B content exceeds 0.030% by mass, coarse crystals may form and become inclusions in aluminum alloy forging blanks and aluminum alloy forgings using those blanks. Furthermore, if a large amount of coarse B-containing crystals are incorporated into the final aluminum alloy product, the toughness decreases. Therefore, the B content is set to 0.0010% to 0.030% by mass. The preferred B content is 0.0050% to 0.025% by mass.

[0065] (Zr: ≥0.0010% by mass and ≤0.050% by mass)

[0066] If the Zr content is 0.05% by mass or less, it precipitates as Al3Zr and Al-(Ti,Zr), thereby contributing to the improvement of the strength of aluminum alloy forging blanks and aluminum alloy forgings using these blanks through recrystallization suppression and precipitation strengthening. If the Zr content exceeds 0.050% by mass, it crystallizes as coarse Zr compounds, which may lead to a decrease in the corrosion resistance of aluminum alloy forging blanks and aluminum alloy forgings using these blanks. Therefore, the Zr content is set to 0.050% by mass or less. Furthermore, in order to obtain the aforementioned recrystallization suppression effect and precipitation strengthening effect on the strength improvement of forgings, the Zr content is preferably 0.0010% by mass or more.

[0067] (Zn: less than 0.250% by mass)

[0068] The Zn content should be below 0.250% by mass. If the Zn content exceeds 0.250% by mass, MgZn2 will form and precipitate from the Al matrix towards the grain boundaries, causing grain boundary corrosion and reducing the corrosion resistance of the aluminum alloy forging blank and the aluminum alloy forgings using the blank. Therefore, the Zn content is preferably below 0.250% by mass, or completely absent.

[0069] (Unavoidable impurities)

[0070] Unavoidable impurities are impurities that are unavoidably introduced into the aluminum alloy from the raw materials or manufacturing process. Examples of unavoidable impurities include Ni, Sn, and Be. The content of these unavoidable impurities is preferably no more than 0.1% by mass.

[0071] The central portion 2a of the elongated portion 2 of the aluminum alloy forging 1a in this embodiment, in the direction of its long side, is the portion where the maximum principal stress is applied, for example, when the aluminum alloy forging 1a is used as a suspension arm of a vehicle. The central portion 2a is, for example, a region that is between 1% and 80% of the entire elongated portion 2, including its center in the direction of its long side. The aspect ratio of the elongated portion 2 (length in the direction of the long side / length of the short side in the direction perpendicular to the long side) is, for example, between 2 and 100. The cross-section of the central portion 2a of the elongated portion 2 is the cross-section along the direction of applied pressure when the aluminum alloy forging 1a is manufactured by forging (hereinafter sometimes referred to as the central portion cross-section).

[0072] (After the corrosion resistance test, the corrosion rate was 0.045%, and the corrosion area was 3% / 1.05E+09μm) 2 (The corrosion depth is below 300μm)

[0073] Corrosion resistance tests were conducted according to the method based on JIS H8502, 1999.

[0074] The aluminum alloy forging billet and the aluminum alloy forging using the billet of this embodiment exhibit a corrosion rate of 0.045% or less after a corrosion resistance test conducted according to JISH 8502, 1999. The corrosion rate is preferably 0.040% or less.

[0075] The corrosion rate can be obtained from the following formula.

[0076] Corrosion rate (%) = (W - W') / W × 100

[0077] in,

[0078] W: Weight of the aluminum product before corrosion

[0079] W': Weight of the corroded aluminum product

[0080] If the corrosion rate exceeds 0.045%, it will be difficult to adapt to automotive running parts, such as suspension arms, due to its low corrosion resistance.

[0081] The aluminum alloy forging billet and the aluminum alloy forging using the billet of this embodiment, after corrosion resistance testing according to JIS H8502, 1999, showed a corrosion area ratio of 3 [% / 1.05E+0.9μm]. 2 Below 1.05E+0.9μm. The preferred corrosion area ratio is 2% / 1.05E+0.9μm. 2 Below 1.5%, more preferably 1.05E+09μm 2 ]the following.

[0082] The corrosion area ratio can be determined by any 1.05 × 10⁻⁶ of the corrosion test specimens before and after corrosion resistance testing according to JIS H8502, 1999. 9 μm 2 The proportion of the eroded area is calculated using image analysis.

[0083] If the corrosion area ratio exceeds 3% / 1.05E+09μm 2 Due to its low corrosion resistance, it is difficult to adapt to automobile running parts, such as suspension arms.

[0084] The aluminum alloy forging billet and the aluminum alloy forging using the billet of this embodiment exhibit a corrosion depth of 300 μm or less after a corrosion resistance test conducted according to JISH 8502, 1999. The corrosion depth is preferably 250 μm or less, and more preferably 210 μm or less.

[0085] Corrosion depth can be measured, for example, using a one-button 3D shape measuring machine (KEYENCE, VR6000). In this machine, light with a striped pattern is shone onto the object. The shape of the object is determined by the deformation of the striped pattern according to the object's unevenness, using a CMOS sensor to receive the reflected light and triangulation to measure the deformation of the striped pattern.

[0086] If the corrosion depth exceeds 300 μm, it will be difficult to adapt to automotive running parts, such as suspension arms, due to its low corrosion resistance.

[0087] (The size of Mg2Si compounds is less than 2.5 μm)

[0088] In the aluminum alloy forging blanks and aluminum alloy forgings of this embodiment, the size of the Mg2Si compound is 2.5 μm or less. If the size exceeds 2.5 μm, corrosion pits are easily formed, and the corrosion resistance may be reduced.

[0089] The aluminum alloy forging blank and aluminum alloy forging of this embodiment, constructed as described above, have the aforementioned alloy composition as the aluminum alloy used as the material, and are manufactured using the method described later. Since the size of the Mg2Si compound is controlled to be below 2.5 μm, the corrosion rate is below 0.045% and the corrosion area is 3 [% / 1.05E+09μm] after corrosion resistance testing according to JIS H8502, 1999. 2 Below 300μm, the corrosion resistance becomes good.

[0090] The aluminum alloy forging blanks and aluminum alloy forgings of this embodiment have high strength and durability, good corrosion resistance, and light weight, and can therefore be advantageously used as suspension arms for vehicles such as automobiles.

[0091] exist Figure 1 In the aluminum alloy forging 1a shown in this embodiment, one connecting portion 4a is a cylinder with a relatively small diameter, and the other connecting portion 4b is a cylinder with a relatively large diameter. The elongated portion 2 is made such that its width widens from the end edge of the connecting portion 4a to the end edge of the connecting portion 4b, but the shape of the aluminum alloy forging 1a is not limited to this. For example, the connecting portions 4a and 4b of the aluminum alloy forging 1a may have the same shape. The width of the elongated portion 2 may also be constant. In addition, the elongated portion 2 may also be curved. Three or more connecting portions 4 may also be formed.

[0092] Figure 2 This is a top view of another example of an aluminum alloy forging according to one embodiment of the present invention.

[0093] Figure 2 The aluminum alloy forging 1b shown has three connecting portions 4c, 4d, and 4e. Connecting portions 4c and 4d are connected by a long portion 2, and connecting portions 4d and 4e are connected by a short portion 5, which is shorter than the long portion 2. A through hole is provided in connecting portion 4c. This aluminum alloy forging 1b can be used, for example, as an L-shaped suspension arm.

[0094] Figure 3 This is a top view of yet another example of an aluminum alloy forging according to an embodiment of the present invention.

[0095] Figure 3 The aluminum alloy forging 1c shown has three connecting portions 4f, 4g, and 4h. Connecting portions 4f and 4g, as well as connecting portions 4f and 4h, are connected by elongated portions 2. A through hole is provided in connecting portion 4f. This aluminum alloy forging 1b can be used, for example, as an A-type suspension arm.

[0096] [Manufacturing methods for aluminum alloy forging billets and aluminum alloy forgings]

[0097] Next, a method for manufacturing an aluminum alloy forging billet and a method for manufacturing an aluminum alloy forging according to one embodiment of the present invention will be described.

[0098] The method for manufacturing aluminum alloy forging billets and aluminum alloy forgings in this embodiment includes, for example, a melt formation process, a casting process, a forging process, a solution treatment process, a quenching process, and an aging process.

[0099] (Molten liquid formation process)

[0100] The melt formation process is the process of melting raw materials to obtain a molten aluminum alloy with a modified composition. The composition of the molten aluminum alloy is adjusted to include: Cu at a concentration of 0.25% to 0.55% by mass, Mg at a concentration of 0.85% to 1.25% by mass, Si at a concentration of 1.02% to 1.4% by mass, Mn at a concentration of 0.55% to 1.0% by mass, Fe at a concentration of 0.32% to 0.65% by mass, Zn at a concentration of 0.25% by mass, and 0.050% by mass. A molten 6000 series aluminum alloy is obtained by comprising Cr in the range of 0.30% by mass or less, Ti in the range of 0.01% by mass or more but less than 0.1% by mass, B in the range of 0.0010% by mass or more but less than 0.030% by mass, and Zr in the range of 0.0010% by mass or more but less than 0.050% by mass, wherein the Fe / Mn content ratio is 0.3 or more but less than 1.1 by mass, and the balance consists of Al and unavoidable impurities.

[0101] By using the aluminum alloy molten metal with the above composition for subsequent processes, Al-Mg-Si alloy forgings that are difficult to recrystallize and have excellent mechanical properties at room temperature can be obtained. Furthermore, new aluminum ingots refer to aluminum with a concentration of 99% or higher obtained through electrolysis of alumina produced from minerals, a process known as electrolytic refining.

[0102] Molten aluminum alloy can be obtained by heating an aluminum alloy to melt it. Alternatively, it can be formed by melting a mixture of elemental substances containing the elements that serve as the raw material for the aluminum alloy, or a mixture of compounds containing two or more elements, in proportions that produce the target aluminum alloy. For example, to control the grain size of the aluminum alloy produced in the casting process, Ti and B can be mixed as grain-refining materials such as Al-Ti-B rods.

[0103] Furthermore, as raw materials for molten aluminum alloys, scrap from 1000, 2000, 3000, 4000, 5000, 6000, and 7000 series aluminum alloys (10% or more) can be used, with the remainder being new aluminum ingots and the aforementioned additive elements. These materials can be melted to obtain a molten aluminum alloy with a formulated composition. In this case, Al-Mg-Si series aluminum alloy forgings that are difficult to recrystallize and have excellent mechanical properties at room temperature can be obtained. Moreover, new aluminum ingots refer to aluminum with a purity of, for example, 99% or higher, obtained through electrolysis of alumina produced from minerals, a process known as electrolytic refining.

[0104] (Casting process)

[0105] In the casting process, molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain aluminum alloy castings. Casting processes can use methods such as vertical continuous casting and horizontal continuous casting.

[0106] The solidification process of casting is controlled so that the time between 650 and 600°C is less than 20 seconds.

[0107] Here, Figure 4 and Figure 5 This refers to a horizontal continuous casting apparatus capable of manufacturing aluminum alloy castings for this embodiment.

[0108] Furthermore, Figure 4 This is a cross-sectional view showing an example of the area near the mold 12 of the horizontal continuous casting apparatus 10. Figure 5 This is an enlarged cross-sectional view of the main part near the cooling water chamber 24 of the horizontal continuous casting device 10.

[0109] Figure 4 and Figure 5 The horizontal continuous casting apparatus 10 shown has a molten receiving part (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-shaped body (insulating member) 13 disposed between one end side 12a of the mold 12 and the molten receiving part 11.

[0110] The molten metal receiving section 11 consists of a molten metal inflow section 11a that receives the molten aluminum alloy M obtained in the above-mentioned molten metal forming process, a molten metal holding section 11b, and an outflow section 11c that flows into the hollow section 21 of the mold 12.

[0111] The molten aluminum alloy receiving section 11 maintains the liquid level of the upper surface of the molten aluminum alloy M at a position higher than the upper surface of the hollow section 21 of the mold 12, and in the case of multi-casting, stably distributes the molten aluminum alloy M into each mold 12.

[0112] Molten aluminum alloy M, held in the molten holding section 11b within the molten receiving section 11, is poured from the pouring passage 13a provided on the refractory plate 13 into the hollow section 21 of the mold 12. Then, the molten aluminum alloy M supplied into the hollow section 21 is cooled and solidified by the cooling device 23 (described later), and is drawn out from the other end 12b of the mold 12 as a solidified ingot, i.e., an aluminum alloy rod B.

[0113] A drawing drive device (not shown) that draws the cast aluminum alloy bar B at a certain speed can be provided at the other end 12b of the mold 12. Alternatively, a synchronous cutting machine (not shown) that cuts the continuously drawn aluminum alloy bar B into arbitrary lengths is preferably provided.

[0114] The refractory plate 13 is a component that isolates the thermal movement between the molten metal receiving part 11 and the mold 12. It can be made of materials such as calcium silicate, alumina, silicon dioxide, a mixture of alumina and silicon dioxide, silicon nitride, silicon carbide, graphite, etc. Such a refractory plate 13 can also be composed of multiple layers with different constituent materials.

[0115] In this embodiment, the mold 12 is a hollow cylindrical component, formed, for example, from one or more materials selected from aluminum, copper, or alloys thereof. The material of such a mold 12 can be selected by considering the optimal combination of thermal conductivity, heat resistance, and mechanical strength.

[0116] In order to make the cast aluminum alloy rod B into a cylindrical rod shape, the hollow part 21 of the mold 12 is formed into a circular cross section, and the mold 12 is held such that the central axis (central axis) C of the mold passing through the center of the hollow part 21 is approximately horizontal.

[0117] The inner circumferential surface 21a of the hollow portion 21 of the mold 12 faces the casting direction of the aluminum alloy rod B (see reference). Figure 1 The inner circumferential surface 21a is formed at an angle of 0° to 3° (more preferably 0° to 1°) relative to the central axis C of the mold. That is, the inner circumferential surface 21a is configured as a cone that opens in a conical shape in the casting direction. Moreover, the angle formed by this cone shape is an angle of elevation.

[0118] If the elevation angle is less than 0°, the aluminum alloy bar B will encounter resistance at the mold exit, i.e., the other end 12b, when it is pulled from the mold 12, making casting difficult. On the other hand, if the elevation angle exceeds 3°, the contact between the inner surface 21a and the molten aluminum alloy M becomes insufficient, reducing the heat dissipation effect from the molten aluminum alloy M or its solidified shell after cooling to the mold 12, resulting in incomplete solidification. As a result, a remelted skin may form on the surface of the aluminum alloy bar B, or casting defects such as undone molten aluminum alloy M ejecting from the end of the aluminum alloy bar B may occur, which is therefore undesirable.

[0119] Furthermore, the cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape of the hollow portion 21 of the mold 12 when viewed from the other end side 21b) can be, in addition to the circle in this embodiment, a triangular or rectangular cross-sectional shape, a polygon, a semicircle, an ellipse, or an irregular cross-sectional shape that does not have an axis of symmetry or a plane of symmetry, etc., depending on the shape of the aluminum alloy rod being cast.

[0120] A fluid supply pipe 22 is disposed on one end side 12a of the mold 12 to supply lubricating fluid into the hollow portion 21 of the mold 12. The lubricating fluid supplied from the fluid supply pipe 22 can be any one or more lubricating fluids selected from gaseous lubricating materials and liquid lubricating materials. When gaseous lubricating materials and liquid lubricating materials are supplied simultaneously, it is preferable to provide separate fluid supply pipes for each. The lubricating fluid supplied under pressure from the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricating material supply port 22a.

[0121] In this embodiment, the pressurized lubricating fluid is supplied from the lubricating material supply port 22a to the inner peripheral surface 21a of the mold 12. Alternatively, the liquid lubricating material may be heated to become a decomposition gas and then supplied to the inner peripheral surface 21a of the mold 12. Another option is to place a porous material at the lubricating material supply port 22a, through which the lubricating fluid seeps to the inner peripheral surface 21a of the mold 12.

[0122] A cooling mechanism, namely a cooling device 23, is formed inside the mold 12 to cool and solidify the molten aluminum alloy M. In this embodiment, the cooling device 23 has a cooling water chamber 24 and a cooling water spray passage 25. The cooling water chamber 24 receives cooling water W for cooling the inner peripheral surface 21a of the hollow part 21 of the mold 12, and the cooling water spray passage 25 connects the cooling water chamber 24 and the hollow part 21 of the mold 12.

[0123] The cooling water chamber 24 is located inside the mold 12 and is positioned outside the inner circumferential surface 21a of the hollow portion 21. It is formed in an annular shape to surround the hollow portion 21 and is supplied with cooling water W via the cooling water supply pipe 26.

[0124] The inner surface 21a of the mold 12 is cooled by cooling water W contained in the cooling water chamber 24, thereby taking away heat from the aluminum alloy melt M that fills the hollow part 21 of the mold 12 from the surface in contact with the inner surface 21a of the mold 12, and forming a solidified shell on the surface of the aluminum alloy melt M.

[0125] Furthermore, the cooling water spray passage 25 sprays cooling water W directly onto the aluminum alloy rod B from the spray opening 25a facing the hollow part 21 at the other end 12b of the mold 12, thereby cooling the aluminum alloy rod B. The longitudinal cross-sectional shape of such a cooling water spray passage 25 can be, for example, semi-circular, pear-shaped, or horseshoe-shaped, in addition to the circular shape of this embodiment.

[0126] Furthermore, in this embodiment, the cooling water W supplied via the cooling water supply pipe 26 is first collected in the cooling water chamber 24 to cool the inner peripheral surface 21a of the hollow part 21 of the mold 12, and then the cooling water W in the cooling water chamber 24 is sprayed from the cooling water spray passage 25 to the aluminum alloy rod B. However, it is also possible to have a structure in which the cooling water W is supplied by a separate cooling water supply pipe.

[0127] The effective mold length L is defined as the length from the point where the extension of the central axis of the spray opening 25a of the cooling water spray passage 25 contacts the surface of the aluminum alloy rod B being cast, to the contact surface between the mold 12 and the refractory plate 13. This effective mold length L is preferably 10 mm or more and 40 mm or less. If the effective mold length L is less than 10 mm, casting is impossible due to the inability to form a good coating. If it exceeds 40 mm, the effect of forced cooling decreases, solidification caused by the mold wall becomes dominant, and the contact resistance between the mold 12 and the molten aluminum alloy M or the aluminum alloy rod B increases, potentially causing cracks on the casting surface or inside the mold, making casting unstable and therefore undesirable.

[0128] The supply of cooling water W to these cooling water chambers 24 and the spraying of cooling water W from the spray openings 25a of the cooling water spray passage 25 are preferably controlled by control signals from a control device (not shown).

[0129] The cooling water chamber 24 is formed such that the inner bottom surface 24a of the hollow portion 21 near the mold 12 is parallel to the inner peripheral surface 21a of the hollow portion 21 of the mold 12.

[0130] Furthermore, the parallelism mentioned here also includes the case where the inner circumferential surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° relative to the inner bottom surface 24a of the cooling water chamber 24, that is, the case where the inner bottom surface 24a is inclined at more than 0° relative to the inner circumferential surface 21a up to 3°.

[0131] like Figure 4 As shown, the portion of 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 facing each other constitutes the cooling wall portion 27 of the mold 12, such that the heat flux per unit area from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water chamber 24 is 10 × 10⁻⁶. 5 W / m 2 Above and 50×10 5 W / m 2 The following range of methods are formed.

[0132] The thickness t of the cooling wall portion 27 of such a mold 12, i.e., the distance 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 within the range of 0.5 mm or more and 2.5 mm or less. Furthermore, the forming material of the mold 12 can be selected such that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is within the range of 100 W / m·K or more and 400 W / m·K or less.

[0133] exist Figure 4 In the process, the molten aluminum alloy M in the molten receiving section 11 is supplied from one end 12a of the mold 12, which is held approximately horizontally to the central axis C of the mold, via a refractory plate 13, and is forcibly cooled at the other end 12b of the mold 12 to become an aluminum alloy rod B.

[0134] The aluminum alloy bar B is drawn at a certain speed by a traction drive device (not shown) located near the other end 12b of the mold 12, thus continuously casting to form a long aluminum alloy bar B. The drawn aluminum alloy bar B is cut to the desired length, for example, by a synchronous cutting machine (not shown).

[0135] Furthermore, the composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by using a photoelectric emission spectrometer as described in "JIS H1305" (e.g., Shimadzu PDA-5500).

[0136] The difference between the height of the molten aluminum alloy M stored in the molten aluminum alloy receiving section 11 and the height of the inner circumferential 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 to the mold 12 and the lubricating oil and the gas generated by the vaporization of the lubricating oil are properly balanced, thus ensuring stable casting performance.

[0137] Liquid lubricants can use vegetable oils as lubricants. Examples include rapeseed oil, castor oil, and salad oil.

[0138] The lubricating oil supply rate 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 rate is too low, the molten aluminum alloy M of the aluminum alloy rod B may not solidify and leak out from the mold 12 due to insufficient lubrication.

[0139] If the supply is excessive, the excess may mix into the aluminum alloy rod B and become an internal defect.

[0140] The casting speed, i.e., the speed at which the aluminum alloy bar B is drawn from the mold 12, 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 during casting becomes more uniform and fine, increasing the resistance to deformation of the aluminum billet at high temperatures and improving its high-temperature mechanical strength.

[0141] 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, the molten aluminum alloy M may not solidify and may leak out of the mold 12. In addition, the surface of the cast aluminum alloy bar B may remelt, forming an uneven structure, which may remain as an internal defect. On the other hand, if the amount of cooling water is more than this range, the heat dissipation of the mold 12 is too large, and it may solidify midway.

[0142] The average temperature of the molten aluminum alloy M flowing from the molten receiving section 11 into the mold 12 is preferably, for example, 650°C or higher and 750°C or lower (more preferably 680°C or higher and 720°C or lower). If the temperature of the molten aluminum alloy M is too low, coarse crystals will form in and near the mold 12, which may be introduced into 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 gas will easily be introduced into the molten aluminum alloy M, which may enter the aluminum alloy rod B as pores, forming internal voids.

[0143] Furthermore, in the cooling wall section 27 of the mold 12, the heat flux per unit area from the molten aluminum alloy M in the hollow section 21 to the cooling water W in the cooling water chamber 24 is set to 10×10 5 W / m 2 Above and 50×10 5 W / m 2 Within the following range, thermal sticking of aluminum alloy rod B can be prevented.

[0144] The cooling wall section 27 of the mold 12 receives heat by dissipating heat from the molten aluminum alloy M, and exchanges heat by cooling it with cooling water W contained in the cooling water chamber 24. Regarding the state of this heat exchange, as follows... Figure 6 As shown in the explanatory diagram, we focus on the heat flux per unit area. The heat flux per unit area is expressed by the following equation (1) according to Fourier's law.

[0145] Q = -k×(T1-T2) / L…(1)

[0146] Q: Heat flux

[0147] k: Thermal conductivity (W / m·K) of the portion through which heat passes (in this embodiment, the cooling wall portion 27 of the mold 12).

[0148] 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).

[0149] T2: The high-temperature side temperature of the part through which heat passes (in this embodiment, it is the inner circumferential surface 21a of the hollow part 21 of the mold 12).

[0150] L: Length of the section through which heat passes (mm) (in this embodiment, it is the thickness t of the cooling wall 27 of the mold 12)

[0151] Based on the mold material, thickness, and temperature measurement data, which showed good results even with reduced lubricating oil during casting, the heat flux per unit area was expressed as 10 × 10⁻⁶. 5 W / m 2 The above-described manner constitutes the cooling wall 27 of the mold 12, thereby preventing the cast aluminum alloy rod B from sticking due to heat. Furthermore, a heat flux per unit area of ​​50 × 10⁻⁶ is preferred. 5 W / m 2 the following.

[0152] In order to ensure that the cooling wall portion 27 of the mold 12 is within such a range of heat flux value, the mold 12 can be formed such that the thickness t of the cooling wall portion 27 is, for example, in the range of 0.5 mm or more and 3.0 mm or less. In addition, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 can be set to the range of 100 W / m·K or more and 400 W / m·K or less.

[0153] When manufacturing the aluminum alloy bar B of this embodiment, the horizontal continuous casting apparatus 10 described above is used to continuously supply molten aluminum alloy M stored in the molten metal receiving section 11 from one end side 12a of the mold 12 into the hollow section 21. In addition, cooling water W is supplied to the cooling water chamber 24, and lubricating fluid, such as lubricating oil, is supplied from the fluid supply pipe 22.

[0154] Then, the heat flux per unit area of ​​the molten aluminum alloy M supplied to the hollow section 21 in the cooling wall section 27 is made to be 10 × 10. 5 W / m 2 The aluminum alloy rod B is cast by cooling and solidifying under the above conditions. In addition, during the casting of the aluminum alloy rod B, it is preferable to keep the wall surface temperature of the cooling wall portion 27 of the mold 12, which is cooled by cooling water W, below 100°C.

[0155] The aluminum alloy rod B obtained in this way has a heat flux per unit area of ​​10 × 10⁻⁶ in the cooling wall section 27. 5 W / m 2Cooling and solidification under the above conditions suppress the adhesion of reaction products, such as carbides, caused by the contact between the lubricating oil gas and the molten aluminum alloy M. Therefore, it is possible to manufacture aluminum alloy rod B in high yield without the need for cutting to remove carbides and other contaminants from its surface.

[0156] The casting process for obtaining castings from molten aluminum alloy M is not limited to the horizontal continuous casting method described above; known continuous casting methods such as vertical continuous casting can be used. Vertical continuous casting is classified into float casting and hot-top casting based on the method of supplying molten aluminum alloy M to the mold (mold 12). The following is a brief explanation of the case where the hot-top casting method is used.

[0157] The casting apparatus used in the hot-top method includes a mold, a molten metal container (header), etc. Molten metal supplied to the molten metal receiving section passes through the outlet and through the header, thereby adjusting the flow rate, and enters the cylindrical mold that is set in a roughly horizontal position. Here, it is forced to cool, thereby forming a solidified shell on the outer surface of the molten metal.

[0158] Furthermore, cooling water is directly sprayed onto the casting as it is pulled from the mold, and the casting is continuously pulled while the metal solidifies until it reaches the interior of the casting. Generally, the mold uses a metal component with good thermal conductivity and has a hollow structure for introducing the cooling medium into the interior.

[0159] The cooling medium used can be selected appropriately from those available in industrial applications, but water is recommended from the perspective of ease of use.

[0160] In this embodiment, the mold is appropriately selected from metals such as copper and aluminum, or graphite, considering the heat transfer performance and durability of the contact area with the molten metal. The manifold is generally made of refractory material and is located on the upper side of the mold. The material and size of the manifold can be appropriately selected based on the composition range of the alloy being cast and the size of the casting; there are no particular restrictions.

[0161] The average cooling rate during casting can be appropriately selected from a generally recommended range, such as 10–300°C / second. The casting speed, in horizontal continuous casting, can be appropriately selected from a general range, such as 200–600 mm / min.

[0162] According to the casting method described above, even medium to large-sized castings can achieve a uniform metallic structure. There are no particular limitations on the diameter of the castings; it can be appropriately used for bars with diameters of 30 to 100 mm.

[0163] (Forging process)

[0164] The forging process involves cutting the cast aluminum alloy part into predetermined dimensions, heating the resulting forging billet to a predetermined temperature, and then applying pressure using a press to form it using a die. In this embodiment, the homogenization treatment performed after casting to remove segregation, as is typically done, is not performed during forging. Therefore, the billet heating during forging is used to remove segregation as part of the homogenization treatment; thus, the heating must be performed at a temperature above 500°C and below the melting point. Forging is then performed to obtain a forged part (e.g., a suspension arm component for automobiles). If the billet heating temperature during forging is below 500°C, compounds such as AlFeSi and Mg2Si in the alloy structure remain in a segregated state, resulting in high deformation resistance, insufficient machining, and crack formation. Furthermore, if the melting point temperature is exceeded, defects such as eutectic melting are likely to occur.

[0165] (Solution treatment process)

[0166] Solution treatment is a process in which the forgings obtained during the forging process are heated to dissolve the solute elements, thereby mitigating the strain introduced during the forging process.

[0167] In this embodiment, solution treatment is performed by holding the forging at a processing temperature of 530°C or higher and 560°C or lower for 0.3 to 3 hours. The heating rate from room temperature to the aforementioned processing temperature is preferably 5.0°C / min or higher. If the processing temperature is below 530°C, the solute element dissolution may become insufficient. On the other hand, if the temperature exceeds 560°C, although the solute element dissolution is further promoted, eutectic melting and / or recrystallization may easily occur. Furthermore, if the heating rate is below 5.0°C / min, coarse Mg₂Si may precipitate. On the other hand, if the processing temperature is below 530°C, solution treatment does not occur, and it may be difficult to achieve the high strength resulting from aging precipitation.

[0168] (Quenching process)

[0169] The quenching process is a process that rapidly cools the forgings that have been in a solution-treated state to form a supersaturated solid solution.

[0170] In this embodiment, the forging is placed in a water tank containing water (quenching water), and quenching is performed by submerging the forging in water (water-flooding the forging). The water temperature in the tank is preferably 20°C or higher and 60°C or lower. The forging is preferably placed in the water tank such that the entire surface of the forging is in contact with the water for 5 seconds or more but no more than 60 seconds after solution treatment. The water immersion time of the forging varies depending on the size of the casting, for example, exceeding 1 minute but within 30 minutes.

[0171] The time interval between the quenching process and the subsequent aging process is set to be within 2 hours.

[0172] (Aging process)

[0173] The aging process involves heating and holding the forging at a relatively low temperature to allow supersaturated dissolved elements to precipitate out, thus imparting appropriate hardness.

[0174] In this embodiment, the forging after the quenching process is heated to a temperature of 170°C or higher and 210°C or lower, and held at this temperature for 0.5 hours or more and 7 hours or less, thereby performing an aging treatment. If the treatment temperature is lower than 170°C or the holding time is less than 0.5 hours, the Mg2Si precipitates that increase tensile strength may not grow sufficiently. On the other hand, if the treatment temperature exceeds 190°C or the holding time exceeds 7 hours, the Mg2Si precipitates become too coarse, which may not adequately improve the tensile strength.

[0175] As mentioned above, the time interval between the quenching process and the subsequent aging process is set to be no more than 2 hours. The time interval is the period from after solution treatment and water quenching until before artificial aging.

[0176] By keeping the segmentation time within 2 hours, the size of the Mg2Si compound can be controlled to below 2.5 μm.

[0177] [Manufacturing method of aluminum alloy forging billets]

[0178] A method for manufacturing an aluminum alloy forging billet according to one embodiment of the present invention will be described.

[0179] The method for manufacturing aluminum alloy forging blanks in this embodiment includes a melt formation process for obtaining molten aluminum alloy and a casting process for obtaining castings by casting the obtained molten alloy. Furthermore, no homogenization treatment is performed after the casting process.

[0180] According to the method for manufacturing aluminum alloy forging blanks of this embodiment, it is possible to manufacture aluminum alloy forging blanks with a Rockwell hardness [HRF] of 60 or more and 78 or less, and with more than 200 chips per 1g during machining.

[0181] [Example]

[0182] Next, specific embodiments of the present invention will be described, but the present invention is not particularly limited to these embodiments.

[0183] [Examples 1-8 and Comparative Examples 1-4]

[0184] (Fabrication of continuous castings)

[0185] First, prepare an aluminum alloy with the alloy composition shown in Table 1 below (balance being aluminum). Using the prepared aluminum alloy, fabricate a continuous casting with a circular cross-section of 82 mm in diameter.

[0186] Table 1

[0187]

[0188] (Manufacturing of aluminum alloy forgings)

[0189] Next, the obtained continuous castings were subjected to a homogenization heat treatment process (comparative examples 1-4 only), a forging process, a solution treatment process, a quenching process, and an artificial aging process in sequence to obtain... Figure 1 Aluminum alloy forging 1a of the shape shown. The conditions for the homogenization heat treatment process (Comparative Examples 1-4 only), forging process, solution treatment process, quenching process, and artificial aging process are shown in Table 2 below.

[0190] Table 2

[0191]

[0192] [evaluate]

[0193] The following evaluation was performed on the central portion 2a of the elongated portion 2 in the length direction of the aluminum alloy forgings 1a of Examples 1-8 and Comparative Examples 1-4 obtained above. The evaluation results of the central portion 2a of the elongated portion 2 are shown in Table 3 below.

[0194] <Fe / Mn>

[0195] In the examples, the Fe / Mn ratio was adjusted to be above 0.3 and below 1.1, while in the comparative examples it was adjusted to be below 0.3 or above 1.1.

[0196] (Judgment Criteria)

[0197] "〇"... 0.3 or higher and 1.1 or lower.

[0198] "×"... less than 0.3 or more than 1.1.

[0199] <Corrosion rate below 0.045%>

[0200] After corrosion resistance testing based on JIS H8502, 1999, the corrosion rate was below 0.045%.

[0201] (Judgment Criteria)

[0202] "〇"…0.045% or less.

[0203] "×"...exceeds 0.045%.

[0204] <The corrosion area ratio is 3 [% / 1.05E+09μm 2 or less>

[0205] After the corrosion resistance test based on JIS H8502, 1999, the corrosion area ratio is 3 [% / 1.05E+09μm 2 or less.

[0206] (Judgment criteria)

[0207] "〇"... 3 [% / 1.05E+09μm 2 or less.

[0208] "×"... more than 3 [% / 1.05E+09μm 2 .

[0209] <The corrosion depth is 300μm or less>

[0210] After the corrosion resistance test based on JIS H8502, 1999, the corrosion depth is 300μm or less.

[0211] (Judgment criteria)

[0212] "〇"... 300μm or less.

[0213] "×"... more than 300μm.

[0214] <The size of the Mg2Si compound is 2.5μm or less>

[0215] (Judgment criteria)

[0216] "〇"... All of the Mg2Si compounds are 2.5μm or less.

[0217] "×"... There is a Mg2Si compound with a size exceeding 2.5μm.

[0218] <Comprehensive evaluation>

[0219] Based on the following judgment criteria, the five evaluation results of the Fe / Mn ratio, corrosion rate, corrosion area ratio, corrosion depth, and size of the Mg2Si compound were evaluated.

[0220] (Judgment criteria)

[0221] "〇"... All five evaluations are "〇".

[0222] "×"... One or more of the five evaluations are "×".

[0223] Table 3

[0224]

[0225] Explanation of reference numerals in the attached figures

[0226] 10…Horizontal Continuous Casting Unit

[0227] 11…Molten Receiving Section (Tundish)

[0228] 11a…Molten Inflow Section

[0229] 11b…Molten Retention Section

[0230] 11c…Outflow section

[0231] 12… casting mold

[0232] 12a…one end side

[0233] 12b…the other end side

[0234] 13…Refractory plate-shaped structures (insulating components)

[0235] 13a… Pouring passage

[0236] 21…Hollow section

[0237] 21a…inner circumferential surface

[0238] 21b…the other end side

[0239] 22…fluid supply pipe

[0240] 22a… Lubricating material supply port

[0241] 23… Cooling device

[0242] 24…Cooling water chamber

[0243] 24a…Inner bottom surface

[0244] 25…Cooling water jet passage

[0245] 25a…spray opening

[0246] 26…Cooling water supply pipe

[0247] 27…cooling stave section

[0248] B…Aluminum alloy rod

[0249] M… Alloy Molten Liquid

[0250] W...cooling water

[0251] 100… Aluminum alloy forgings

Claims

1. A billet for aluminum alloy forging, comprising the following alloy composition: Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, and other alloys in the range of 0.25% to 0. The content of Fe is 0.3% to 1.1% by mass, and the content of Cr is 0.050% to 0.30% by mass, the content of Ti is 0.01% to 0.1% by mass, the content of B is 0.0010% to 0.030% by mass, and the content of Zr is 0.0010% to 0.050% by mass. The Fe / Mn content ratio is 0.3 to 1.1 by mass, and the balance consists of Al and unavoidable impurities. In the thermal analysis curves obtained during differential thermal analysis (DSC), exothermic peaks are generated in the ranges of 200–300 °C and 400–500 °C, respectively.

2. An aluminum alloy forging having the following alloy composition: Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, and Fe in the range of 0.25% to 0% by mass. The content of Zn, Cr in the range of 0.050% to 0.30% by mass, Ti in the range of 0.01% to 0.1% by mass, B in the range of 0.0010% to 0.030% by mass, and Zr in the range of 0.0010% to 0.050% by mass, wherein the Fe / Mn content ratio is 0.3 to 1.1 by mass, and the balance consists of Al and unavoidable impurities. After corrosion resistance testing based on JIS H8502, 1999, the corrosion rate was below 0.045%, and the corrosion area was 3 [% / 1.05E+0.9μm]. 2 The corrosion depth is below 300μm.

3. The aluminum alloy forging according to claim 2, which is used in a suspension arm.

4. A method for manufacturing an aluminum alloy forging, as described in claim 2 or 3, comprising a melt formation process, a casting process, a forging process, a solution treatment process, a quenching process, and an aging treatment process. A molten aluminum alloy is obtained in the melt formation process. In the casting process, castings are obtained by casting the obtained molten metal. In the forging process, the casting is heated at a temperature above 500°C and below its melting point to perform plastic processing and obtain the forging. In the solution treatment process, the obtained forging is heated at a rate of 5.0°C / min or higher within the range of 20°C to 500°C, and held at 530°C to 560°C for 0.3 to 3 hours. In the quenching process, 5 to 60 seconds after the solution treatment, the entire surface of the forging is brought into contact with quenching water, and quenching is carried out in the water tank for more than 1 minute but less than 40 minutes. In the aging process, the forging is heated at 180℃ to 220℃ for 0.5 hours to 8 hours to perform the aging treatment. The time interval between the quenching process and the aging process is within 2 hours.

5. A method for manufacturing an aluminum alloy forging, as described in claim 2 or 3, comprising a melt formation process, a casting process, a forging process, a solution treatment process, a quenching process, and an aging treatment process. A molten aluminum alloy is obtained in the melt formation process. In the casting process, castings are obtained by casting the obtained molten metal. In the forging process, the casting is heated at a temperature above 500°C and below its melting point to perform plastic processing and obtain the forging. In the solution treatment process, the obtained forging is heated at a rate of 5.0°C / min or higher within the range of 20°C to 500°C, and held at 530°C to 560°C for 0.3 to 3 hours. In the quenching process, 5 to 60 seconds after the solution treatment, the entire surface of the forging is brought into contact with quenching water, and quenching is carried out in the water tank for more than 1 minute but less than 40 minutes. In the aging process, the forging is heated at 180℃ to 220℃ for 0.5 hours to 8 hours to perform the aging treatment. In the casting process, the solidification time at 650~600℃ is less than 20 seconds.

6. A method for manufacturing an aluminum alloy forging billet, as described in claim 1, comprising a melt formation step and a casting step. A molten aluminum alloy is obtained in the melt formation process. In the casting process, the casting is obtained by casting the obtained molten metal, and no homogenization treatment is performed after the casting process.

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