Aluminum alloy forgings

Abstract

To provide an aluminum alloy forged article having better mechanical characteristics than a conventional aluminum alloy forged article.SOLUTION: An aluminum alloy forged article according to the present invention is composed of an aluminum alloy comprising 0.2-0.5 mass% Cu, 0.6-1.2 mass% Mg, 0.4-1.25 mass% Si, 0.4-0.6 mass% Mn, 0.15-0.70 mass% Fe, 0.09-0.25 mass% Cr, 0.012-0.035 mass% Ti, with the balance consisting of Al and inevitable impurities, and contains a precipitate of a C phase and a precipitate of a β'' phase in precipitates composed of intermetallic compounds observed when an Al base phase is observed on <100>incidence by a transmission electron microscope.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy forging. [Background technology]

[0002] Due to their excellent strength and corrosion resistance, 6000 series aluminum alloys are suitable for use as structural materials for ships, vehicles, land structures, buildings, guardrails, home appliances, bus bars, electric wires, machinery, automobile parts, etc. In recent years, there has been a strong demand for weight reduction in aluminum alloy forgings for automobiles, such as vehicles and automobile parts, for reasons such as reducing vehicle weight and improving fuel efficiency. Weight reduction requires increasing the strength of the material itself, and the development of such a material has been strongly desired.

[0003] Among the commonly known strengthening mechanisms of metals, precipitation strengthening plays a major role in 6000 series aluminum alloys. After solution treatment, a supersaturated solid solution is formed, followed by low-temperature tempering (artificial aging treatment), which causes nano-sized compound particles to precipitate finely in the matrix, inhibiting dislocation motion in the matrix, thereby strengthening the matrix itself. Addition of Cu is well known as a method for further enhancing precipitation strengthening in 6000 series aluminum alloys, and it is known that Cu, when contained in the precipitates, contributes to the fine dispersion of the precipitates (Non-Patent Document 1).

[0004] Furthermore, it has been revealed that in Cu-added 6000 series aluminum alloys, a wide variety of metastable phases, including Q' and C phases, appear during the artificial aging process (Non-Patent Document 2). Various efforts have been made to improve the strength and corrosion resistance of the base material by highly controlling the atomic structure and dispersion state of these precipitates (for example, Patent Publication 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5901738 [Non-patent literature]

[0006] [Non-Patent Document 1] Haruhiko Abe, Shinya Komatsu, Katsuhiko Ikeda, Takeo Sakurai: "Study on the effect of copper addition on the 473 K aging behavior of Al-1%Mg2Si alloy using resistivity method", Light Metals, 52 (2002), 179-184. [Non-patent document 2] Takeshi Saito, Eva A. Mortsell, Sigurd Wenner, Calin D. Marioara, Sigmund J. Andersen, Jesper Friis, Kenji Matsuda, and Randi Holmestad: “Atomic Structures of Precipitates in Al-Mg-Si Alloys with Small Additions of Other Elements”, Advanced Engineering Materials, 20 (2018), 1800125. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an aluminum alloy forging having superior mechanical properties by controlling the structure of precipitates formed by artificial aging treatment to a higher degree than ever before. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides the following means.

[0009] An aluminum alloy forging according to a first aspect of the present invention is an aluminum alloy forging made of an aluminum alloy containing 0.2 to 0.5% by mass of Cu, 0.6 to 1.2% by mass of Mg, 0.4 to 1.25% by mass of Si, 0.4 to 0.6% by mass or less of Mn, 0.15 to 0.70% by mass of Fe, 0.09 to 0.25% by mass or less of Cr, 0.012 to 0.035% by mass of Ti, and the balance being Al and unavoidable impurities, and wherein the aluminum alloy forging is characterized by a crystalline structure of the aluminum alloy matrix as observed by a transmission electron microscope. <100> The precipitates consisting of intermetallic compounds observed under incidence light include C-phase and β''-phase precipitates.

[0010] In the aluminum alloy forged product according to the above embodiment, the C phase may account for 10% or more of the precipitates.

[0011] In the aluminum alloy forged product according to the above embodiment, the C phase may account for 50% or more of the precipitates.

[0012] The aluminum alloy forging according to the above aspect may include one having a plurality of Cu atomic rows on the outer periphery of the C-phase precipitates, and the average spacing between the Cu atomic rows arranged on the outer periphery is 10 nm or less.

[0013] The aluminum alloy forged product according to the above embodiment may further contain B in an amount of 0.0001% to 0.03% by mass. [Effects of the Invention]

[0014] According to the aluminum alloy forgings of the present invention, it is possible to provide aluminum alloy forgings having superior mechanical properties to conventional products. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a perspective schematic view showing the arrangement of Cu atomic rows in a part of the aluminum alloy forged product according to the present embodiment. [Figure 2]1 is a cross-sectional view showing an example of the vicinity of a mold of a horizontal continuous casting device for producing an aluminum alloy ingot. [Figure 3] FIG. 3 is an enlarged cross-sectional view showing the cooling water cavity and its vicinity in FIG. 2. [Figure 4] FIG. 2 is an explanatory diagram illustrating the heat flux of a cooling wall portion of the horizontal continuous casting device. [Figure 5] FIG. 2 is a plan view showing a typical shape of a precipitate and its atomic row arrangement in a TEM image. [Figure 6] FIG. 1 is a schematic perspective view of an aluminum alloy forged product produced in an example. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an aluminum alloy forged product according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may show characteristic portions enlarged for ease of understanding, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto. Appropriate modifications can be made within the scope of the effects of the present invention.

[0017] [Aluminum alloy forgings] 1 is a perspective schematic diagram showing the arrangement of Cu atomic rows in a part of the aluminum alloy forged product according to this embodiment. Each circle in the figure corresponds to a Cu atom, <100> A row of Cu atoms aligned in the direction is a Cu atomic row, and 10 Cu atomic rows are shown in Figure 1. In Figure 1, patterns are added to the Cu atoms arranged on the (100) plane, which is the observation surface.

[0018] The aluminum alloy forged product according to this embodiment is composed of an aluminum alloy containing 0.2 to 0.5 mass% Cu, 0.6 to 1.2 mass% Mg, 0.4 to 1.25 mass% Si, 0.4 to 0.6 mass% Mn, 0.15 to 0.70 mass% Fe, 0.09 to 0.25 mass% Cr, 0.012 to 0.035 mass% Ti, and the remainder being Al and unavoidable impurities. The aluminum alloy may contain impurity elements that may be unavoidably mixed in, as long as they do not affect the product characteristics. Examples include typical elements such as Zn and transition elements such as Zr. Furthermore, refiners such as Al-Ti-B rods are often added to control the grain size during casting, and B may be added appropriately in the range of, for example, 0.0001% to 0.03% by mass.

[0019] The aluminum alloy forged product according to this embodiment was subjected to a transmission electron microscope to determine the Al matrix. <100> The precipitates Seg consisting of intermetallic compounds observed when observed at incidence include C-phase precipitates and β''-phase precipitates.

[0020] It is preferable that the precipitates Seg contain 10% or more of C-phase precipitates, because, as will be described later, examples suggest that C-phase precipitates improve tensile strength and 0.2% proof stress. Furthermore, it is more preferable that the precipitates Seg contain 20% or more C-phase precipitates. It is even more preferable that the precipitates Seg contain 30% or more C-phase precipitates. It is even more preferable that the precipitates Seg contain 40% or more C-phase precipitates. It is even more preferable that the precipitates Seg contain 50% or more C-phase precipitates. It is even more preferable that the precipitates Seg contain 60% or more C-phase precipitates. It is even more preferable that the precipitates Seg contain 70% or more C-phase precipitates.

[0021] The aluminum alloy forged product according to this embodiment was subjected to a transmission electron microscope to determine the Al matrix. <100> It is preferable that the precipitates Seg made of intermetallic compounds observed when observed at incidence include those that contain, as their chemical composition, two or more elements selected from Mg, Si, Al, and Cu, have a plurality of Cu atomic rows on the periphery of the precipitates Seg, and the average spacing between the Cu atomic rows arranged on the periphery is 10 nm or less. For example, it is preferable that the precipitates of the C phase have a plurality of Cu atomic rows on the periphery, and the average spacing between the Cu atomic rows arranged on the periphery is 10 nm or less. In this specification, the term "transmission electron microscope" also includes a scanning transmission electron microscope (STEM).

[0022] In this specification, the scope of the "precipitate" (the boundary between the atomic rows included in and around the precipitate and those not included) can be determined, for example, by a TEM image obtained by transmission electron microscopy (TEM). The Al matrix phase can also be determined by a high-angle annular dark-field scattering (HAADF)-STEM image (hereinafter simply referred to as a "STEM image") obtained by high-angle annular dark-field scattering (HAADF)-STEM, which provides contrast dependent on the atomic number (Z), or by elemental mapping obtained by combining electron beam scanning with STEM and energy dispersive X-ray spectroscopy (EDS). In addition, in this specification, the "periphery of a precipitate" refers to the shape (dotted line P in Figure 1) formed by connecting the centers of the bright spots corresponding to each atomic row constituting the precipitate in a TEM image, STEM image, or elemental mapping. The atomic rows constituting the "periphery of a precipitate" are the atomic rows arranged on the "periphery of a precipitate." In a TEM image or STEM image, the image of the atomic rows arranged on the "periphery of a precipitate" shows a discontinuity in the lattice in which the images of the atomic rows of the Al matrix are arranged, and this allows the atomic rows arranged on the "periphery of a precipitate" to be determined. This allows the extent of the "precipitate" to be determined. In addition, in elemental mapping, the atomic rows arranged on the "periphery of a precipitate" can be determined based on the elemental species in the image of the atomic rows, and the extent of the "precipitate" can be determined. Among the atomic rows belonging to the range of the "precipitate," atomic rows other than the atomic rows arranged on the "periphery of a precipitate" are atomic rows "included in the interior of the precipitate." In this specification, the "average spacing between rows of Cu atoms arranged on the periphery" refers to the distance between adjacent rows of Cu atoms when rows of Cu atoms are evenly arranged on the circumference of a circle (equivalent circle) having an area equal to the area S0 of the shape enclosed by the "periphery of the precipitate." That is, when the circle equivalent diameter is R and the number of rows of Cu atoms arranged on the periphery of the precipitate is N, i Then, the "average spacing between rows of Cu atoms arranged on the periphery" is l Cu =2πr(perimeter of the equivalent circle) / N i (the number of Cu atomic columns arranged on the periphery of the precipitate).

[0023] In addition, the aluminum alloy forging according to this embodiment has a Cu atomic column number (n i ) relative to the number of Cu atomic columns arranged on the periphery (N i ) ratio (N i / n i ) is preferably 1 or more. This is because the rows of Cu atoms arranged on the periphery of the precipitates act as a barrier when the precipitates become coarse, leading to finer dispersion of the precipitates. In this specification, "the number of Cu atomic rows contained inside a precipitate" refers to the number of Cu atomic rows contained inside a precipitate, excluding the Cu atomic rows arranged on the periphery of the precipitate.

[0024] Furthermore, in the aluminum alloy forged product according to this embodiment, it is preferable that 70% or more of the Cu atomic rows arranged on the periphery of the precipitates coincide with the positions of the Al atomic rows in the Al matrix. This is because the Cu atomic rows arranged at positions that coincide with the positions of the Al atomic rows in the Al matrix can exist stably, which suppresses the coarsening of the precipitates and leads to the fine dispersion of the precipitates. In this specification, "corresponding to the positions of the Al atomic rows in the Al matrix" means that, in a TEM image or STEM image, if there are no precipitates, the positions correspond to the positions where the Al atomic rows in the Al matrix would be arranged.

[0025] (Cu:0.2 mass%~0.5 mass%) Cu has the effect of finely dispersing Mg-Si compounds in the aluminum alloy and improving the tensile strength of the aluminum alloy by precipitating as Al-Cu-Mg-Si compounds such as the Q phase. By keeping the Cu content within the above range, the tensile strength of the aluminum alloy can be improved.

[0026] (Mg: 0.6% by mass to 1.2% by mass) Mg has the effect of improving the tensile strength of aluminum alloys. Mg contributes to strengthening the aluminum alloy by dissolving in the aluminum matrix or by precipitating as Mg-Si compounds such as the β'' phase or Al-Cu-Mg-Si compounds such as the Q phase. By keeping the Mg content within the above range, the tensile strength of the aluminum alloy can be improved.

[0027] (Si: 0.4% by mass to 1.25% by mass) Si has the effect of improving the tensile strength of aluminum alloys. However, if excessive Si is added to an aluminum alloy, coarse primary Si grains may crystallize, which may reduce the tensile strength of the aluminum alloy. By keeping the Si content within the above range, the tensile strength of the aluminum alloy can be improved while suppressing the crystallization of primary Si.

[0028] (Mn:0.4 mass%~0.6 mass%) Mn has the effect of improving the tensile strength of the aluminum alloy by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy. By ensuring that the Mn content is within the above range, the tensile strength of the aluminum alloy can be improved.

[0029] (Fe:0.15 mass%~0.70 mass%) Fe has the effect of improving the tensile strength of the aluminum alloy by crystallizing in the aluminum alloy 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. By keeping the Fe content within the above range, the tensile strength of the aluminum alloy can be improved.

[0030] (Cr:0.09 mass%~0.25 mass%) Cr acts to improve the tensile strength of the aluminum alloy by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy. By keeping the Cr content within the above range, the tensile strength of the aluminum alloy can be improved.

[0031] (Ti:0.012 mass%~0.035 mass%) Ti has the effect of refining the crystal grains of aluminum alloy forgings and improving their wrought workability. If the Ti content is less than 0.012% by mass, the effect of refining the crystal grains may not be sufficient. On the other hand, if the Ti content exceeds 0.035% by mass, coarse crystals may form, which may reduce the wrought workability. Furthermore, if a large amount of coarse crystals containing Ti are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the Ti content is set to be in the range of 0.012% by mass to 0.035% by mass. The Ti content is preferably in the range of 0.015% by mass to 0.030% by mass.

[0032] (B:0.0001 mass%~0.03 mass%) B has the effect of refining the crystal grains of aluminum alloy forgings and improving the wrought workability. By further adding B to the aluminum alloy together with the above-mentioned Ti, the effect of refining the crystal grains is improved. When the content of B is 0.0001 If the B content is less than 0.03% by mass, the grain refinement effect may not be sufficient. On the other hand, if the B content exceeds 0.03% by mass, coarse crystals may form and be mixed into the final aluminum alloy product as inclusions. Furthermore, if a large amount of coarse crystals containing B are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the B content is set to be in the range of 0.0001% by mass or more and 0.03% by mass or less. The B content is preferably in the range of 0.005% by mass or more and 0.025% by mass or less.

[0033] (unavoidable impurities) Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from the raw materials or manufacturing process of the aluminum alloy. Examples of inevitable impurities include Zn, Ni, Zr, Sn, and Be. The content of these inevitable impurities preferably does not exceed 0.1% by mass.

[0034] Next, a method for manufacturing an aluminum alloy forged product according to this embodiment will be described. The aluminum alloy forged product of this embodiment can be manufactured by a method including, for example, a molten metal forming step, a casting step, a homogenizing heat treatment step, a forging step, a solution treatment step, a quenching treatment step, and an aging treatment step.

[0035] (Molten metal formation process) The molten metal formation process is a process in which raw materials are melted to obtain a molten aluminum alloy with an adjusted composition. The composition of the molten aluminum alloy is the same as that of the aluminum alloy forging. The molten aluminum alloy can be obtained by heating and melting an aluminum alloy. The aluminum alloy may contain impurity elements that may be inevitably mixed in, as long as they do not affect the product characteristics. Examples of impurity elements include Zn as a typical element and Zr as a transition element. Furthermore, refiners such as Al-Ti-B rods are often added to control the crystal grain size during casting. For example, B may be added appropriately in a range of 0.0001% to 0.03% by mass.

[0036] (Casting process) In the casting process, the molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain an aluminum alloy casting. The casting process is not particularly limited, and any known continuous casting method, such as horizontal continuous casting or vertical continuous casting, may be used. In addition, the molten aluminum may be degassed or filtered as appropriate to improve the reliability of the final product. FIG. 2 is a cross-sectional view showing an example of a horizontal continuous casting apparatus that can be used to produce the aluminum alloy cast product of the present embodiment, and is an enlarged cross-sectional view of a main portion near the cooling water cavity of the horizontal continuous casting apparatus shown in FIG.

[0037] The horizontal continuous casting apparatus 10 shown in Figures 2 and 3 has a molten metal receiving portion (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (insulating member) 13 arranged between one end side 12a of the mold 12 and the molten metal receiving portion 11.

[0038] The molten metal receiving portion 11 is composed of a molten metal inlet portion 11a that receives the molten aluminum alloy M obtained in the molten metal forming step, a molten metal holding portion 11b, and an outlet portion 11c to the hollow portion 21 of the mold 12. The molten metal receiving portion 11 maintains the upper liquid level of the molten aluminum alloy M at a position higher than the upper surface of the hollow portion 21 of the mold 12, and in the case of multiple casting, stably distributes the molten aluminum alloy M to each mold 12.

[0039] The molten aluminum alloy M held in the molten metal holding portion 11b in the molten metal receiving portion 11 is poured into the hollow portion 21 of the mold 12 through a pouring passage 13a provided in the refractory plate body 13. The molten aluminum alloy M supplied into the hollow portion 21 is then cooled and solidified by a cooling device 23 (described later) and drawn out from the other end 12b of the mold 12 as an aluminum alloy rod B, which is a solidified ingot.

[0040] A drawing drive device (not shown) that draws out the cast aluminum alloy rod B at a constant speed may be installed at the other end 12b of the mold 12. It is also preferable that a synchronous cutter (not shown) that cuts the continuously drawn aluminum alloy rod B to a desired length be installed.

[0041] The refractory plate 13 is a member that blocks heat transfer between the molten metal receiver 11 and the mold 12, and may be made of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, graphite, etc. Such a refractory plate 13 may also be made up of multiple layers made of different materials.

[0042] In this embodiment, the mold 12 is a hollow cylindrical member made of, for example, one or a combination of two or more materials selected from aluminum, copper, or alloys thereof. The materials for the mold 12 may be selected from the optimal combination in terms of thermal conductivity, heat resistance, and mechanical strength.

[0043] The hollow portion 21 of the mold 12 is formed to have a circular cross section in order to cast the aluminum alloy rod B into a cylindrical rod shape, and the mold 12 is held so that the mold central axis (central axis) C passing through the center of this hollow portion 21 is aligned approximately horizontally.

[0044] The inner peripheral surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0 to 3 degrees (more preferably 0 to 1 degree) with respect to the mold central axis C toward the casting direction of the aluminum alloy bar B (see FIG. 5). That is, the inner peripheral surface 21a is tapered so as to open in a cone shape toward the casting direction. The angle of this taper is the elevation angle.

[0045] If the elevation angle is less than 0 degrees, the aluminum alloy rod B may encounter resistance at the other end 12b, which is the mold outlet, when being drawn out of the mold 12, which may make casting difficult. On the other hand, if the elevation angle exceeds 3 degrees, the inner peripheral surface 21a may not make sufficient contact with the molten aluminum alloy M, which may reduce the heat transfer effect from the molten aluminum alloy M and the solidified shell formed by cooling and solidifying it to the mold 12, which may result in insufficient solidification. As a result, a remelted skin may appear on the surface of the aluminum alloy rod B, or unsolidified molten aluminum alloy M may erupt from the end of the aluminum alloy rod B, which is undesirable because it may lead to casting problems.

[0046] The cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape when the hollow portion 21 of the mold 12 is viewed from the other end side 21b) may be selected to match the shape of the aluminum alloy rod to be cast, such as 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 or plane of symmetry, in addition to the circular shape of this embodiment.

[0047] A fluid supply pipe 22 is disposed at one end 12a of the mold 12 to supply a lubricating fluid into the hollow portion 21 of the mold 12. The lubricating fluid supplied from the fluid supply pipe 22 can be one or more lubricating fluids selected from a gas lubricant and a liquid lubricant. When supplying both a gas lubricant and a liquid lubricant, 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 lubricant supply port 22a.

[0048] In this embodiment, the lubricating fluid is supplied under pressure from the lubricant supply port 22a to the inner circumferential surface 21a of the mold 12. The liquid lubricant may be heated to decompose into a gas and then supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be disposed in the lubricant supply port 22a, and the lubricating fluid may be allowed to seep out onto the inner circumferential surface 21a of the mold 12 through the porous material.

[0049] A cooling device 23, which is a cooling means for cooling and solidifying the molten alloy M, is formed inside the mold 12. The cooling device 23 of this embodiment has a cooling water cavity 24 that accommodates cooling water W for cooling the inner circumferential surface 21 a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 that connects the cooling water cavity 24 and the hollow portion 21 of the mold 12.

[0050] The cooling water cavity 24 is formed in the mold 12 outside the inner peripheral surface 21a of the hollow portion 21 and has an annular shape so as to surround the hollow portion 21, and cooling water W is supplied to the cavity 24 via a cooling water supply pipe . The inner surface 21a of the mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, which removes heat from the molten alloy M filling the hollow portion 21 of the mold 12 from the surface in contact with the inner surface 21a of the mold 12, forming a solidified shell on the surface of the molten alloy M.

[0051] The cooling water jetting passages 25 spray cooling water directly from shower openings 25a facing the hollow portion 21 toward the aluminum alloy rods B at the other end 12b of the mold 12 to cool the aluminum alloy rods B. The vertical cross-sectional shape of the cooling water jetting passages 25 may be, for example, semicircular, pear-shaped, or horseshoe-shaped, in addition to the circular shape of this embodiment.

[0052] In this embodiment, the cooling water W supplied through the cooling water supply pipe 26 is first stored in the cooling water cavity 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 cavity 24 is sprayed toward the aluminum alloy bar B from the cooling water spray passage 25. However, these may also be configured to be supplied by separate cooling water supply pipes.

[0053] The length from the position where the extension of the central axis of the shower opening 25a of the cooling water injection passage 25 hits the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate 13 is called the effective mold length L, and this effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. If this effective mold length L is less than 10 mm, a good coating cannot be formed, making casting impossible. If it exceeds 40 mm, the effect of forced cooling is reduced, solidification by the mold wall becomes dominant, and the contact resistance between the mold 12 and the molten alloy M or the aluminum alloy rod B increases, which may cause cracks on the casting surface or tearing inside the mold, making casting unstable.

[0054] It is preferable that the supply of cooling water to the cooling water cavity 24 and the spray of cooling water from the shower opening 25a of the cooling water spray passage 25 can be controlled by control signals from a control device (not shown).

[0055] The cooling water cavity 24 is formed so that the inner bottom surface 24a closer 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. Note that "parallel" here also includes the case where the inner bottom surface 24a of the cooling water cavity 24 is formed at an elevation angle of 0 to 3 degrees with respect to the inner peripheral surface 21a of the hollow portion 21 of the mold 12, that is, the case where the inner bottom surface 24a is inclined at an angle of more than 0 degrees up to 3 degrees with respect to the inner peripheral surface 21a.

[0056] As shown in FIG. 3, the cooling wall portion 27 of the mold 12, which is the portion where the inner bottom surface 24a of the cooling water cavity 24 faces the inner peripheral surface 21a of the hollow portion 21 of the mold 12, has a heat flux value per unit area of ​​10×10 5 W / m 2 That's it, 50 x 10 5 W / m 2 It is formed so as to fall within the following range.

[0057] The mold 12 may be formed so that the thickness t of the cooling wall portion 27 of the mold 12, i.e., the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner circumferential surface 21a of the hollow portion 21 of the mold 12, is within a range of, for example, 0.5 mm to 3.0 mm, and preferably 0.5 mm to 2.5 mm. The material for forming the mold 12 may be selected so that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is within a range of 100 W / m K to 400 W / m K.

[0058] In Fig. 3, molten alloy M in molten metal receptacle 11 is supplied through refractory plate 13 to one end 12a of mold 12, which is held so that its central axis C is substantially horizontal, and is forcedly cooled at the other end 12b of mold 12 to form aluminum alloy rod B. Aluminum alloy rod B is withdrawn at a constant speed by a withdrawal drive device (not shown) installed near the other end 12b of mold 12, and is thus continuously cast to form long aluminum alloy rod B. The withdrawn aluminum alloy rod B is then cut to a desired length, for example, by a synchronized cutting machine (not shown).

[0059] The composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by a method using a photoelectric photometric emission spectrophotometer as described in JIS H 1305 (eg, PDA-5500 manufactured by Shimadzu Corporation, Japan).

[0060] The difference in height between the liquid level of the molten alloy M stored in the molten metal receiver 11 and the upper inner circumferential surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting the difference in height within this range, the pressure of the molten alloy M supplied into the mold 12 and the lubricating oil and the gas produced by vaporizing the lubricating oil are suitably balanced, resulting in stable castability.

[0061] The liquid lubricant may be a vegetable oil, such as rapeseed oil, castor oil, or salad oil, which are preferred because they have little adverse effect on the environment.

[0062] The lubricating oil supply rate is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min to 1 mL / min). If the supply rate is too low, the molten alloy of the aluminum alloy rod B may not solidify and leak from the mold due to insufficient lubrication. If the supply rate is too high, the excess may get mixed into the aluminum alloy rod B and cause internal defects.

[0063] The casting speed, which is the speed at which the aluminum alloy rod B is withdrawn 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), because a casting speed within this range makes the network structure of crystals formed by casting uniform and fine, which increases the resistance of the aluminum matrix to deformation at high temperatures and improves its high-temperature mechanical strength.

[0064] The amount of cooling water sprayed from the shower openings 25a of the cooling water spray passages 25 is preferably 10 L / min to 50 L / min (more preferably 25 L / min to 40 L / min) per mold. If the amount of cooling water is less than this, the molten alloy may not solidify and leak from the mold. Also, the surface of the cast aluminum alloy bar B may remelt, forming an inhomogeneous structure that may remain as internal defects. On the other hand, if the amount of cooling water is greater than this range, the mold 12 may lose too much heat, causing it to solidify prematurely.

[0065] The average temperature of the molten alloy M flowing from the molten metal receiver 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 alloy M is too low, coarse crystals may form in the mold 12 or before that, and may be incorporated as internal defects inside the aluminum alloy rod B. On the other hand, if the temperature of the molten alloy M is too high, a large amount of hydrogen gas may be easily incorporated into the molten alloy 255, which may be incorporated as porosity in the aluminum alloy rod B and cause internal cavities.

[0066] In the cooling wall portion 27 of the mold 12, the heat flux value per unit area from the molten alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24 is 10×10 5 W / m 2 Over 50 x 10 5 W / m 2 By keeping the temperature within the following range, it is possible to prevent the aluminum alloy rod B from seizing.

[0067] The cooling wall 27 of the mold 12 receives heat from the molten alloy M and exchanges this heat by cooling it with the cooling water W contained in the cooling water cavity 24. Regarding the state of this heat exchange, we focused on the heat flux per unit area, as shown in the explanatory diagram in Figure 4. The heat flux per unit area is expressed by the following equation (1) using Fourier's law. Q = -k × (T1 - T2) / L (1) Q: Heat flux 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) T1: low temperature of the location where heat passes (in this embodiment, the inner bottom surface 24a of the cooling water cavity 24) T2: High temperature side temperature of the portion through which heat passes (in this embodiment, the inner peripheral surface 21a of the hollow portion 21 of the mold 12) L: Length (mm) of the section where heat passes (in this embodiment, the thickness t of the cooling wall portion 27 of the mold 12)

[0068] Good results were obtained even when the amount of lubricant was reduced during casting. Based on the mold material, thickness, and temperature measurement data, the heat flux value per unit area was 10 × 10 5 W / m 2 By configuring the cooling wall portion 27 of the mold 12 so that the heat flux value per unit area is 50×10 or more, it is possible to prevent the cast aluminum alloy rod B from seizing. 5 W / m 2 It is preferable to do the following:

[0069] To achieve this heat flux range for the cooling wall 27 of the mold 12, the mold 12 should be formed so that the thickness t of the cooling wall 27 of the mold 12 is, for example, in the range of 0.5 mm to 3.0 mm. Also, the thermal conductivity of at least the cooling wall 27 of the mold 12 should be in the range of 100 W / m K to 400 W / m K.

[0070] When producing the aluminum alloy rod of this embodiment, the horizontal continuous casting apparatus 10 described above is used to continuously supply the molten alloy M stored in the molten metal receiving portion 11 from one end side 12a of the mold 12 into the hollow portion 21. In addition, cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, for example, lubricating oil, is supplied from the fluid supply pipe 22.

[0071] The molten alloy M supplied into the hollow portion 21 is cooled to a temperature at which the heat flux per unit area of ​​the cooling wall portion 27 is 10×10 5 W / m 2 The aluminum alloy rod B is cooled and solidified under the above conditions to be cast. During casting of the aluminum alloy rod B, it is preferable to set the wall surface temperature of the cooling wall portion 27 of the mold 12, which is cooled by the cooling water W, to 100°C or less.

[0072] The aluminum alloy rod B thus obtained has a heat flux value per unit area in the cooling wall portion 27 of 10×10 5 W / m 2 Cooling and solidification under the above conditions suppresses the adhesion of reaction products, such as carbides, that occur due to contact between the lubricating oil gas and the molten alloy M. This eliminates the need to remove carbides and the like from the surface of the aluminum alloy rod B by cutting, and allows the aluminum alloy rod B to be produced with a high yield.

[0073] The casting process for obtaining cast products from molten aluminum alloy is not limited to the horizontal continuous casting method described above; known continuous casting methods such as vertical continuous casting can also be used. Vertical continuous casting methods are classified into the float method and the hot-top method depending on the method of supplying the molten aluminum alloy to the mold. The following briefly describes the hot-top method. The casting equipment used in the hot-top method includes a mold and a molten metal receiving vessel (header). The molten metal supplied to the molten metal receiving vessel passes through a tap and a header, where its flow rate is adjusted. It then enters a cylindrical mold installed approximately horizontally, where it is forcibly cooled to form a solidified shell on the outer surface of the molten metal. Cooling water is then sprayed directly onto the cast product as it is removed from the mold, allowing the metal to solidify throughout the casting. Molds are typically made of metal with good thermal conductivity and have a hollow structure for introducing a refrigerant. The refrigerant used can be selected from industrially available materials, but water is recommended for its ease of use. The mold used in this embodiment is appropriately selected from metals such as copper and aluminum, or graphite, in terms of heat transfer performance and durability at the contact point with the molten metal. The header is generally made of refractory material and is installed above the mold. The material and size of the header can be appropriately selected depending on the composition range of the alloy to be cast and the dimensions of the cast product, and are not particularly limited. The average cooling rate during casting can be appropriately selected from a generally recommended range, such as 10 to 300°C / sec. The casting speed can be appropriately selected from a range commonly used in horizontal continuous casting, such as 200 to 600 mm / min. The casting method described above can produce a uniform metal structure even in medium to large cast products. The diameter of the target cast product is not particularly limited, and it is preferably used for rods with a diameter of 30 to 100 mm.

[0074] (Homogenization heat treatment process) The homogenization heat treatment step is a step in which the aluminum alloy casting obtained in the casting step is subjected to homogenization heat treatment to homogenize microsegregations caused by solidification, precipitate supersaturated solid solution elements, and transform metastable phases into equilibrium phases. In this embodiment, the aluminum alloy casting obtained in the casting step is subjected to a homogenization heat treatment in which the aluminum alloy casting is held at a temperature of 370°C or higher and 560°C or lower for 4 to 10 hours. By performing the homogenization heat treatment within this temperature range, the aluminum alloy casting is homogenized and solute atoms are sufficiently dissolved, so that sufficient base material strength can be obtained by the subsequent solution treatment and artificial aging treatment.

[0075] (Forging process) The forging process is a process in which the aluminum alloy casting after the homogenizing heat treatment process is formed into a predetermined size to obtain a forging material, the obtained forging material is heated to a predetermined temperature, and then pressure is applied in a press to perform forging. In this embodiment, it is preferable to heat the forging material to a temperature of 450°C or higher and 560°C or lower, and then start forging to obtain a forged product (such as an automobile suspension arm part). If the forging start temperature is lower than 450°C, the deformation resistance may become too high, making it difficult to perform sufficient forging. On the other hand, if the forging start temperature is higher than 560°C, defects such as forging cracks and eutectic melting may easily occur.

[0076] (Solution treatment process) The solution treatment step is a step in which the forged product obtained in the forging step is heated to bring about a solution, thereby alleviating the strain introduced into the cast product and causing the solute elements to dissolve. In this embodiment, the forged product is preferably solution-treated by holding it at a treatment 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 above treatment temperature is preferably 5.0°C / min or higher. If the heating rate is less than 5°C / min, Mg-Si compounds precipitate coarsely, reducing the Mg and Si that contribute to the formation of the precipitates. Furthermore, if the treatment temperature is less than 530°C, the solution treatment does not progress, making it impossible to achieve high strength through aging precipitation. If the treatment temperature exceeds 560°C, solid solution of solute elements is further promoted, but eutectic melting and recrystallization are more likely to occur.

[0077] (Quenching process) The quenching process is a process in which the forged product in the solid solution state obtained by the solution treatment process is rapidly cooled to form a supersaturated solid solution. After the solution treatment, the forged product is rapidly cooled by being placed in a quenching water bath within 5 to 60 seconds so that the entire surface comes into contact with the quenching water, forming a supersaturated solid solution. The quenching water bath is preferably 5 to 40 minutes. Holding the forged product in water for more than 5 minutes allows the entire forged product to cool and form a uniform supersaturated solid solution. Holding the forged product in water for more than 40 minutes can lead to the growth of cluster I (Si-rich), which is known to cause negative effects of natural aging, resulting in a decrease in strength after artificial aging. Therefore, the water bath time is preferably greater than 5 minutes but not greater than 40 minutes. The water temperature used for quenching is preferably in the range of 45 to 95°C, which is less likely to form cluster I and more likely to form cluster II (GP zone) during the subsequent artificial aging treatment. Furthermore, a temperature range of 55 to 65°C is preferable, which can suppress bending of the forged product during quenching. Furthermore, controlling the time from the end of quenching to the start of artificial aging to 60 seconds or less suppresses temperature drop from the quenching temperature. This allows an aluminum alloy forging that has been quenched at, for example, 60°C to be rapidly heated from 60°C to the artificial aging temperature, stabilizing the growth of cluster II, which contributes to strengthening the base material, and the atomic structure of the precipitates. It is also desirable to control the temperature between the end of quenching and the start of artificial aging so that it is kept in the range of 55 to 65°C, from the viewpoint of similarly making it difficult for cluster I to form.

[0078] (Artificial aging treatment process) The artificial aging treatment for the forged product after the above-mentioned quenching process involves holding the product at a temperature of 170 to 190°C for 4.5 to 6.5 hours. This allows for the formation of sufficiently densely spaced Cu atomic rows around precipitates consisting of Mg, Si, and Al, which act as a barrier to the coarsening of the precipitates, thereby achieving a fine and uniform precipitate distribution. The crystalline phases of the precipitates formed here include the β''-MgSi phase (hereinafter simply referred to as the β'' phase) and the C-AlCuMgSi phase (hereinafter simply referred to as the C phase). These crystalline phases are known to form early in the artificial aging process of Cu-added 6000 series aluminum alloys. Both have been reported to have coherent interfaces with the Al matrix, and the precipitates themselves, or the strain fields introduced by lattice mismatch, function as obstacles to dislocation motion, thereby contributing to the strengthening of the base material. If the treatment temperature is below 170°C or the treatment time is less than 4.5 hours, the number density of precipitates does not reach a range sufficient for improving strength. Furthermore, if the treatment temperature exceeds 190°C or the treatment time is longer than 6.5 hours, the structural transition of the precipitates progresses, resulting in a structure in which Cu atomic rows are not contained around the precipitates (typically the Q'-AlCuMgSi phase, hereafter simply referred to as the Q phase), reducing the effect of the precipitates in improving the base material strength. Although a certain number of precipitates (β'' phase) that do not contain Cu atomic rows are present, it is desirable for their amount to be less than 10%, and even more desirable for it to be less than 5% of the observed precipitates.

[0079] <Observation method> To observe the atomic structure around precipitates, techniques capable of observation at atomic resolution, such as transmission electron microscopy (TEM), are used. Among these, high-angle annular dark-field (HAADF-STEM) observation, which can obtain (Z) contrast dependent on atomic number, is suitable. To clarify the elemental species of the atomic columns that make up the precipitates and the atomic columns that make up the periphery of the precipitates in detail, in addition to the intensity information in STEM images, elemental mapping for each atomic column using energy-dispersive X-ray spectroscopy (EDS) can be used to easily determine the elemental species and number of atomic columns in the atomic columns around the precipitates. Furthermore, to observe the interface structure around precipitates with high resolution, it is desirable to use an electron microscope that can focus the irradiated electron beam to the size of a single atom or less using a spherical aberration correction function.

[0080] Here, a specific procedure for observing the precipitates with atomic resolution will be described. The accelerating voltage of the incident electron beam can be selected from a range that allows sufficient penetration through the thin film sample and does not cause excessive damage to the sample, and a general setting of 200 kV is sufficient. In order to observe the atomic structure of the precipitates in the 6000 series aluminum alloy in detail, the incident direction of the electron beam is set to the direction of the Al matrix phase where the precipitates, including the β'' phase, are easily observed. <100> Direction and <310> It is desirable to use the orientation as the lattice arrangement of the Al matrix, so that the correspondence with the lattice arrangement of the Al matrix can be easily interpreted. <100> For example, a field of view containing many precipitates is selected from the observation field at a magnification of 500,000 times, and five precipitates with different shapes and crystal structures are extracted from the field of view. i and the number of Cu atomic rows on the periphery, N i These measurement results are used to calculate the average spacing between Cu atomic rows on the periphery of the precipitate according to the following formula (see FIGS. 1 and 5).

[0081]

number

[0082] where L i is the circumference calculated from the circle-equivalent radius of precipitate i. Furthermore, the number of Cu atomic columns contained inside the precipitate, n i By using this, the ratio of the number of Cu atomic columns on the periphery of the precipitate to the number of Cu atomic columns contained inside the precipitate can be calculated as N i / n i It can be calculated by: In addition, whether the Cu atomic row coincides with the lattice point of the (100) plane of the Al matrix can be determined by adjusting the incident direction of the electron beam to that of the Al matrix. <100> By using the orientation, it can be sufficiently read from a TEM image or STEM image. There are no particular restrictions on the method for analyzing the lattice point positions, and image analysis software may be used.

[0083] FIG. 5 is a schematic plan view showing a typical shape of a precipitate (left image) and its atomic row arrangement in a TEM image. The arrangement of the atomic row image shown schematically for precipitate 3 in the figure reproduces the actual STEM image. The needle-shaped precipitates have Cu atomic rows arranged regularly around their periphery, and it has been observed that the Cu atomic rows inside are also regularly arranged in a manner that corresponds to the regular Cu atomic rows around the periphery. In the figure, the precipitate 3 is shown by the dotted line as "lattice x (Cu)” and “lattice y The (Cu)" line indicates that the Cu atomic rows are arranged on the lattice of the Al atomic rows of the Al matrix, i.e., the Cu atomic rows are aligned with the Al atomic rows of the Al matrix. [Example]

[0084] Next, specific examples of the present invention will be described, but the present invention is not limited to these examples.

[0085] (Sample creation) Aluminum alloys having the alloy compositions shown in Table 1 were cast by a hot-top horizontal continuous casting method to produce continuous cast products in the form of long rods having a circular cross section and a diameter of 49 mm.

[0086] [Table 1]

[0087] The obtained continuous cast product was subjected to homogenization heat treatment, forging, solution treatment, quenching, and artificial aging in this order. In the hot forging, the product was preheated under the conditions shown in Table 2 (Table 2A, Table 2B), then formed into a simulated shape of an automobile suspension arm as shown in Figure 6, and then cooled in air to produce an aluminum alloy forged product 100 as a simulated forged product. The conditions for each process of homogenization heat treatment, forging, solution treatment, quenching, and artificial aging are shown in Table 2 (Table 2A, Table 2B) below. 2 For the continuous cast products having the compositions shown in Table 1, aluminum alloy forgings 100 were produced under three conditions, Condition 1 to Condition 3. 1 For the continuously cast products having the compositions shown in Table 1, aluminum alloy forgings 100 were produced under Condition 1. Conditions 1 to 3 differ only in the conditions of the quenching treatment process. The aluminum alloy forgings of "Alloy 1 + Condition 1" and "Alloy 2 + Condition 1" were subjected to structural analysis by transmission electron microscope observation and mechanical property evaluation by tensile testing. 2 +Condition 2" aluminum alloy forgings and "Alloy 2 The mechanical properties of aluminum alloy forgings under "Condition 3" were evaluated to investigate the effect of differences in the conditions of the quenching process on the mechanical properties.

[0088] [Table 2A] [Table 2B]

[0089] (evaluation) Aluminum alloy forgings of "Alloy 1 + Condition 1" ( comparison Example) and aluminum alloy forgings of "Alloy 2 + Condition 1" ( implementationFor the sample (example), HAADF-STEM observation was performed to analyze the atomic structures of five precipitates, and the average spacing of Cu atomic rows on the periphery of the precipitate, the ratio of the number of Cu atomic rows on the periphery to the number of Cu atomic rows inside, and the proportion of Cu atomic rows that match the atomic row positions of the Al matrix were determined. The results are shown in Table 3. To select the precipitates, a field of view containing many precipitates was selected from the observation field at a magnification of 500,000 times, and five precipitates were selected from these with the aim of selecting precipitates with typical shapes and crystal structures. The mechanical properties were also evaluated using the procedure described below.

[0090] <Transmission electron microscope observation> A JEM-ARM200F (manufactured by JEOL Ltd.) was used to observe the precipitates contained in each aluminum alloy forging, and aberration correction was performed using a spherical aberration corrector (manufactured by JEOL Ltd.) installed in the irradiation system. A cubic sample with a side length of 10 mm was cut from the part of the aluminum alloy forging shown in Figure 6, and then thinned to a thickness of approximately 300 nm by polishing with emery paper and ion milling using Ar gas to obtain a TEM observation sample. The accelerating voltage of the incident electron beam was 200 kV, and the observation direction was the direction of the Al matrix. <100> The incident beam was set to a 20-angle direction. HAADF-STEM observations were performed at a magnification of 20 million times, using wide-angle scattered electrons for imaging. The observation area was a region where the number density of precipitates was a representative value. Furthermore, electron energy loss spectroscopy (EELS) was used to obtain an EELS spectrum, and the sample thickness was calculated from the intensity ratio between the zero-loss peak and the plasmon peak. Only areas with a thickness of 300 nm or less were selected. The average spacing between Cu atomic rows was calculated to be 3.1 nm in the example and 10.5 nm in the comparative example. Similarly, the ratio of the number of Cu atomic rows on the periphery to the number of Cu atomic rows in the interior was calculated to be 1.0 in the example and 0.8 in the comparative example. Note that the Cu atomic rows observed on the periphery of the precipitates were all consistent with the Al matrix. Furthermore, the crystalline phases of the five precipitates (Nos. 1 to 5) each belonged to the metastable phases shown in Table 3. In the Example, three types of metastable phases, β″ phase, Q′ phase, and C phase, were observed, whereas in the Comparative Example, no C phase was found, and only two types of metastable phases, β″ phase and Q′ phase, were observed. In the Example, of the 578 precipitates in the observation field including the above-mentioned precipitates Nos. 1 to 5, the proportions of β″ phase, Q′ phase, and C phase were 8%, 18%, and 74%, respectively. Thus, the proportion of C phase among the metastable phase precipitates was 70% or more. On the other hand, in the Comparative Example, the same precipitates were observed, but no C phase was found. Considering that the number density of precipitates in this observation field was obtained from a representative field, it is estimated that the C phase was 5% or less in the Comparative Example. Thus, the proportion of C phase among the metastable phase precipitates was significantly different between the Example and the Comparative Example. As will be described later, the Examples have superior tensile strength and 0.2% yield strength to the Comparative Examples. It is believed that the difference in these mechanical properties is likely due to the large difference in the proportion of C phase. In addition, the precipitates listed as two types of metastable phases in Table 3 had the characteristics of both of those types.

[0091] [Table 3]

[0092] <Mechanical property evaluation> The mechanical properties of the examples and comparative examples were evaluated by conducting tensile tests. Specifically, test pieces with a gauge length of 25.4 mm and a parallel part diameter of 6.4 mm were taken from the aluminum alloy forgings after artificial aging treatment at the positions shown in Figure 6, and various tensile properties were measured by conducting tensile tests at room temperature (25°C) at a speed of 2 mm / min. The results are shown in Table 4. Table 4 also lists the "Alloy" 2 +Condition 2" aluminum alloy forgings and "Alloy 2 The measurement results of various tensile properties of aluminum alloy forgings under "Condition 3" are also shown.

[0093] [Table 4]

[0094] As is clear from Table 4, it was confirmed that the aluminum alloy forgings having the precipitate structure of the present invention have superior tensile strength and 0.2% yield strength compared to the comparative examples. In other words, the manufacturing method of the present invention makes it possible to obtain aluminum alloy forgings with excellent mechanical properties. These excellent mechanical properties are believed to be due to the atomic-scale crystal structure of the precipitates, namely, that the average spacing between Cu atomic rows arranged on the periphery of the precipitates is narrower in the Example than in the Comparative Example, i.e., the precipitates are more finely dispersed due to the denser arrangement on the periphery, and that the proportion of Cu atomic rows arranged at atomic row positions (positions on the lattice matrix) of the Al matrix is ​​higher in the Example than in the Comparative Example, i.e., the Cu atomic rows are arranged at more stable positions. The present invention provides an aluminum alloy forging having excellent mechanical properties by controlling the atomic-scale crystal structure of precipitates.

[0095] Measurements of various tensile properties of the aluminum alloy forgings "Alloy 1 + Condition 2" and "Alloy 1 + Condition 3" revealed that the immersion time in the quenching process and the waiting time from the end of quenching to the start of artificial aging are important parameters for improving tensile strength and 0.2% yield strength.

[0096] From the above results, it was found that in order to manufacture the aluminum alloy forgings according to the present invention, it is necessary to carry out the Cu composition, the submersion time in the quenching treatment process, and the waiting time before the artificial aging treatment under specified conditions. [Explanation of symbols]

[0097] 10...Horizontal continuous casting equipment 11...Tundish 11a...Molten metal inlet 11b...Molten metal holding section 11c...Outflow part 12...Mold 12a...One end side 12b…Other end side 13... Refractory plate (heat insulating member) 13a…Pouring passage 21...Hollow part 21a...Inner peripheral surface 21b...Other end side 22...Fluid supply pipe 22a…Lubricant supply port 23…Cooling device 24...Cooling water cavity 24a…Inner bottom surface 25…Cooling water injection passage 25a...Shower opening 26…Cooling water supply pipe 27...Cooling wall B: Aluminum alloy rod M...molten alloy W...cooling water 100...Aluminum alloy forgings

Claims

1. An aluminum alloy forging made of an aluminum alloy containing 0.2% by mass to 0.5% by mass of Cu, 0.6% by mass to 1.2% by mass of Mg, 0.4% by mass to 1.25% by mass of Si, 0.4% by mass to 0.6% by mass of Mn, 0.15% by mass to 0.70% by mass of Fe, 0.09% by mass to 0.25% by mass of Cr, 0.012% by mass to 0.035% by mass of Ti, and the balance being Al and unavoidable impurities, When observed with a transmission electron microscope at a <100> incidence angle relative to the Al matrix, precipitates made of intermetallic compounds are observed, and C-phase precipitates and β''-phase precipitates are included. An aluminum alloy forging, wherein the precipitates contain 10% or more of the C phase precipitates.

2. 2. The aluminum alloy forging according to claim 1, wherein the precipitates comprise C-phase precipitates in an amount of 50% or more.

3. 3. The aluminum alloy forging according to claim 1, wherein the C-phase precipitates have a plurality of Cu atomic rows on the outer periphery, and the average spacing between the Cu atomic rows arranged on the outer periphery is 10 nm or less.

4. The aluminum alloy forging according to any one of claims 1 to 3, further containing 0.0001% by mass to 0.03% by mass of B.

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