Aluminum alloy forgings

Abstract

To provide an aluminum alloy forging having excellent mechanical properties and corrosion resistance at room temperature.SOLUTION: There is provided an aluminum alloy forging which has a Cu content in the range of 0.3 mass% or more and 1.0 mass% or less, a Mg content in the range of 0.63 mass% or more and 1.30 mass% or less, an Si content in the range of 0.45 mass% or more and 1.45 mass% or less and the balance Al with inevitable impurities and satisfies the expressions, [Mg content]×1.587≥-4.1×[Cu content]2+7.8×[Cu content]-1.9 and [Si content]×2.730≥-4.1×[Cu content]2+7.8×[Cu content]-1.9, wherein the ratio Q1 / Q2 of the X-ray diffraction peak intensity Q1 of the CuAl2 phase to the X-ray diffraction peak intensity Q2 of the (200) plane of the Al phase obtained by the X-ray diffraction method is 2×10-1 or less.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] In recent years, aluminum alloys have been increasingly used as structural components for various products, taking advantage of their light weight. For example, high-tensile steel has traditionally been used for automobile suspension and bumper parts, but in recent years high-strength aluminum alloy materials have been used. While iron-based materials were previously used exclusively for automobile parts, such as suspension parts, they are increasingly being replaced by aluminum or aluminum alloy materials, primarily for the purpose of reducing weight.

[0003] These automotive parts require excellent corrosion resistance, high strength, and excellent workability, so Al-Mg-Si alloys, especially A6061, are widely used as the aluminum alloy material. To improve the strength of these automotive parts, they are manufactured by forging, a type of plastic processing, using aluminum alloy materials as the processing material.

[0004] Recently, due to the need to reduce costs, suspension parts have begun to be put into practical use, in which cast components are used as the raw material without extrusion, and then subjected to a solution treatment and artificial aging treatment (T6 treatment).In order to further reduce weight, development of high-strength alloys to replace the conventional A6061 is underway (see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-59477 [Patent Document 2] Japanese Patent Application Publication No. 5-247574 [Patent Document 3] Japanese Patent Application Publication No. 6-256880 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for lighter automobiles in order to reduce CO2 emissions, and the demand for aluminum is on the rise. However, as a replacement for steel, aluminum needs to be even stronger. The addition of Cu is known as one method for increasing strength. However, the addition of Cu reduces corrosion resistance, making it impossible to add large amounts.

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide an aluminum alloy forged product having excellent mechanical properties and corrosion resistance at room temperature. [Means for solving the problem]

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

[0009] (1) An aluminum alloy forging having a Cu content in the range of 0.3% by mass or more and 1.0% by mass or less, a Mg content in the range of 0.63% by mass or more and 1.30% by mass or less, a Si content in the range of 0.45% by mass or more and 1.45% by mass or less, and the balance consisting of Al and unavoidable impurities, which satisfies the following formulas (1) and (2): [Mg content] x 1.587 ≥ -4.1 x [Cu content] 2 +7.8 × [Cu content] -1.9 (1) [Si content] x 2.730 ≥ -4.1 x [Cu content] 2 +7.8 × [Cu content] -1.9 (2) The ratio Q1 / Q2 of the integrated intensity Q1 of the X-ray diffraction peak of the CuAl2 phase to the integrated intensity Q2 of the X-ray diffraction peak of the (200) plane of the Al phase obtained by X-ray diffraction method is 2 × 10 -1 An aluminum alloy forging characterized by the following:

[0010] (2) The aluminum alloy forging according to (1) above, wherein the Mg content is in the range of 0.63% by mass or more and 1.25% by mass or less, the Si content is in the range of 0.60% by mass or more and 1.45% by mass or less, and the ratio of the Si content to the Mg content, Si / Mg, is 0.5 or more in molar ratio. (3) The Mg content is in the range of 0.85% by mass or more and 1.30% by mass or less, and the Si content is in the range of 0.45% by mass or more and 0.69% by mass or less, The aluminum alloy forging according to (1) above, wherein the ratio of the Si content to the Mg content, Si / Mg, is less than 0.5 in molar ratio.

[0011] (4) The aluminum alloy forging according to any one of (1) to (3) above, wherein the Mn content is within the range of 0.03% by mass or more and 1.0% by mass or less, the Fe content is within the range of 0.2% by mass or more and 0.7% by mass or less, the Cr content is within the range of 0.03% by mass or more and 0.4% by mass or less, the Ti content is within the range of 0.012% by mass or more and 0.035% by mass or less, the B content is within the range of 0.001% by mass or more and 0.03% by mass or less, the Zn content is within the range of 0.25% by mass or less, and the Zr content is within the range of 0.05% by mass or less. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an aluminum alloy forged product having excellent mechanical properties and corrosion resistance at room temperature. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view showing an example of the vicinity of a mold of a horizontal continuous casting apparatus for producing an aluminum alloy cast product according to an embodiment of the present invention. [Figure 2] FIG. 2 is an enlarged cross-sectional view showing a main part in the vicinity of the cooling water cavity in FIG. 1. [Figure 3] FIG. 2 is an explanatory diagram illustrating the heat flux of a cooling wall portion of the horizontal continuous casting device. [Figure 4] FIG. 1 is a perspective view of an aluminum alloy forging produced in an experimental example and an example. [Figure 5]1 is a graph showing the relationship between the Cu content, the Mg2Si converted content, and the corrosion resistance of aluminum alloy forgings produced in experimental examples. DETAILED DESCRIPTION OF THE INVENTION

[0014] An aluminum alloy forged product and a method for manufacturing the same according to one embodiment of the present invention will be described below. Note that the following embodiment is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. Furthermore, the drawings used in the following description may show essential parts enlarged for convenience in order to make the features of the present invention easier to understand, and the dimensional proportions of each component may not necessarily be the same as those in reality.

[0015] An aluminum alloy forging according to one embodiment of the present invention has a Cu content in the range of 0.3% by mass to 1.0% by mass, a Mg content in the range of 0.63% by mass to 1.30% by mass, a Si content in the range of 0.45% by mass to 1.45% by mass, and the remainder being Al and unavoidable impurities. The Mg content and Cu content of the aluminum alloy forging satisfy the following formula (1), and the Si content and Cu content satisfy the following formula (2). [Mg content] x 1.587 ≥ -4.1 x [Cu content] 2 +7.8 × [Cu content] -1.9 (1) [Si content] × 2.730 ≥ -4.1 × [Cu content] 2 + 7.8 × [Cu content] - 1.9 (2)

[0016] Furthermore, in addition to the above-mentioned components, the aluminum alloy forgings may contain the following: Mn content of 0.03% by mass to 1.0% by mass; Fe content of 0.2% by mass to 0.7% by mass; Cr content of 0.03% by mass to 0.4% by mass; Ti content of 0.012% by mass to 0.035% by mass; and B content of 0.001% by mass to 0.03% by mass. The Zn content may be 0.25% by mass or less, and the Zr content may be 0.05% by mass or less. The aluminum alloy forgings of this embodiment correspond to 6000 series aluminum alloy forgings in that they contain Mg and Si.

[0017] (Cu: 0.3 mass% or more and 1.0 mass% or less) 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 mechanical properties of the aluminum alloy forgings at room temperature can be improved.

[0018] (Mg: 0.63 mass% or more and 1.30 mass% or less) Mg has the effect of improving the tensile strength of aluminum alloys. Mg contributes to strengthening aluminum alloys by dissolving in the aluminum matrix or by precipitating as Mg-Si compounds (Mg2Si) such as the β" phase or Al-Cu-Mg-Si compounds (AlCuMgSi) such as the Q phase. Mg2Si also has the effect of suppressing the formation of CuAl2 phase in aluminum alloys. Suppressing the formation of CuAl2 phase improves the corrosion resistance of aluminum alloy forgings. Keeping the Mg content within the above range can improve the corrosion resistance as well as the mechanical properties of aluminum alloy forgings at room temperature.

[0019] (Si: 0.45 mass% or more and 1.45 mass% or less) Like Mg, Si has the effect of improving the mechanical properties and corrosion resistance of aluminum alloy forgings at room temperature. However, if excessive Si is added to an aluminum alloy, coarse primary Si crystal grains may crystallize, potentially reducing the tensile strength of the aluminum alloy. By keeping the Si content within the above range, it is possible to improve the mechanical properties and corrosion resistance of aluminum alloy forgings at room temperature while suppressing the crystallization of primary Si crystals.

[0020] (Mn: 0.03 mass% or more and 1.0 mass% or less) Mn has the effect of improving the tensile strength of aluminum alloys by forming intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si as crystallized or precipitated compounds in the aluminum alloy. By ensuring that the Mn content is within the above range, the mechanical properties of aluminum alloy forgings at room temperature can be improved.

[0021] (Fe: 0.2 mass% or more and 0.7 mass% or less) Fe improves the tensile strength of aluminum alloys by forming intermetallic compounds such as Al-Fe-Si, Al-Fe-Cr, Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe as crystallized or precipitated compounds in the aluminum alloy. By keeping the Fe content within the above range, the mechanical properties of aluminum alloy forgings at room temperature can be improved.

[0022] (Cr: 0.03 mass% or more and 0.4 mass% or less) Cr acts to improve the tensile strength of aluminum alloys by forming intermetallic compounds such as Al-Cr-Si, Al-Mn-Cr-Fe-Si, and Al-Fe-Cr as crystallized or precipitated compounds in the aluminum alloy. By ensuring that the Cr content is within the above range, the mechanical properties of aluminum alloy forgings at room temperature can be improved.

[0023] (Ti: 0.012 mass% or more and 0.035 mass% or less) Ti has the effect of refining the crystal grains of an aluminum alloy and improving its 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 or precipitates may be generated, which may reduce the wrought workability. Furthermore, if a large amount of coarse crystals or precipitates containing Ti are mixed into an aluminum alloy forging, the toughness may be reduced. Therefore, the Ti content is set to 0.012% by mass or more and 0.035% by mass or less. The Ti content is preferably 0.015% by mass or more and 0.030% by mass or less.

[0024] (B: 0.001 mass% or more and 0.03 mass% or less) B has the effect of refining the crystal grains of an aluminum alloy and improving its wrought workability. Adding B to an aluminum alloy together with the aforementioned Ti improves the grain refinement effect. If the B content is less than 0.001% 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 or precipitates may be generated and may be mixed into the aluminum alloy forging as inclusions. Furthermore, if a large amount of coarse crystals or precipitates 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 0.001% by mass to 0.03% by mass. The B content is preferably in the range of 0.005% by mass to 0.025% by mass.

[0025] (Zn: 0.25% by mass or less) Zn contributes to improving the strength of aluminum alloy forgings through solid solution strengthening when the Zn content is 0.25% by mass or less. However, if the Zn content exceeds 0.25% by mass, it precipitates as MgZn2 in the aluminum matrix, which may lead to a decrease in the corrosion resistance of the aluminum alloy forgings. Therefore, the Zn content is preferably 0.25% by mass or less. Furthermore, the Zn content is preferably 0.005% by mass or more.

[0026] (Zr content: 0.05% by mass or less) When Zr is present in the form of AlZr and Al-(Ti,Zr) at 0.05% by mass or less, it contributes to improving the strength of aluminum alloy forgings by inhibiting recrystallization and promoting precipitation strengthening. However, when the Zr content exceeds 0.05% by mass, it crystallizes as coarse Zr compounds, which may lead to a decrease in the corrosion resistance of the aluminum alloy forgings. Therefore, the Zr content is preferably 0.05% by mass or less. Furthermore, the Zr content is preferably 0.005% by mass or more.

[0027] (unavoidable impurities) Inevitable impurities are impurities that are inevitably mixed into aluminum alloys from the raw materials or manufacturing process of aluminum alloy forgings. Examples of inevitable impurities include Ni, Sn, and Be. The content of these inevitable impurities preferably does not exceed 0.1% by mass.

[0028] (Mg content and Cu content, Si content and Cu content) The Mg content and Cu content are set to satisfy the above formula (1). The left side of formula (1), "[Mg content] × 1.587," corresponds to the value obtained by converting the Mg content of the aluminum alloy forging into the Mg2Si content. That is, the above formula (1) shows the relationship between the Mg2Si content converted from the Mg content of the aluminum alloy forging and the Cu content. The Si content and Cu content are set to satisfy the above formula (2). The left side of formula (2), "[Si content] × 2.730," corresponds to the value obtained by converting the Si content of the aluminum alloy forging into the Mg2Si content. That is, the above formula (2) shows the relationship between the Mg2Si content converted from the Si content of the aluminum alloy forging and the Cu content.

[0029] The above formulas (1) and (2) were experimentally determined. That is, they were determined from a graph (FIG. 5) showing the relationship between the Cu content, Mg2Si equivalent content, and corrosion resistance of aluminum alloy forgings produced in the experimental examples described below. By satisfying the above formulas (1) and (2), the formation of the CuAl2 phase in the aluminum alloy can be suppressed. The lower of the Mg2Si equivalent contents calculated by formulas (1) and (2) is preferably in the range of 1.0% by mass to 2.0% by mass.

[0030] (Ratio of Si content to Mg content (Si / Mg molar ratio)) The ratio of the Si content to the Mg content, Si / Mg, may be 0.5 or more in molar ratio (Si / Mg molar ratio), or may be less than 0.5 mol.

[0031] When the Si / Mg molar ratio is 0.5 or higher, the Mg content is preferably in the range of 0.63% by mass to 1.25% by mass, and the Si content is preferably in the range of 0.60% by mass to 1.45% by mass. When the Si / Mg molar ratio is 0.5 or higher, the content of Si that does not form MgSi or AlCuMgSi increases, resulting in the formation of Si-rich precipitates in the aluminum alloy forgings. These Si-rich precipitates contribute to improving the strength of the aluminum alloy forgings. When the Si / Mg molar ratio is 0.5 or higher, the Si / Mg molar ratio is preferably in the range of 0.60 to 1.20.

[0032] When the Si / Mg molar ratio is less than 0.5, the Mg content is preferably in the range of 0.85% by mass to 1.30% by mass, and the Si content is preferably in the range of 0.45% by mass to 0.69% by mass. When the Si / Mg molar ratio is less than 0.5, the amount of MgSi (β″ phase) and AlCuMgSi (Q phase) formed increases, resulting in aluminum alloy forgings with excellent solid solution / precipitation strengthening. When the Si / Mg molar ratio is less than 0.5, the Si / Mg molar ratio is preferably in the range of 0.48 to 0.40.

[0033] In the aluminum alloy forging of this embodiment, the ratio Q1 / Q2 of the integrated intensity Q1 of the X-ray diffraction peak of the CuAl2 phase to the integrated intensity Q2 of the X-ray diffraction peak of the (200) plane of the Al phase obtained by X-ray diffraction method is 2 × 10 -1 The integrated intensity Q2 of the X-ray diffraction peak of the (200) plane of the Al phase can be the integrated intensity of the X-ray diffraction peak detected within a diffraction angle 2θ range of 37.8° or more and 39.8° or less in an X-ray diffraction pattern obtained by X-ray diffraction using Cu-Kα radiation as the X-ray source. The X-ray diffraction peak intensity Q1 of the CuAl2 phase can be the integrated intensity of the X-ray diffraction peak detected within a diffraction angle 2θ range of 42.5° or more and 43.5° or less in an X-ray diffraction pattern obtained by X-ray diffraction using Cu-Kα radiation as the X-ray source. The aluminum alloy forging of this embodiment has a ratio Q1 / Q2 of 2×10 -1 The ratio Q1 / Q2 is 2×10 or less, and it is thought that the corrosion resistance is improved because the content of CuAl2 phase is low. -1 The following includes the case where no X-ray diffraction peak of the CuAl2 phase is detected, i.e., Q1=0.

[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 forming process) The molten aluminum alloy forming process is a process in which raw materials are melted to obtain a molten aluminum alloy with a controlled 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. Alternatively, the molten aluminum alloy can be formed by melting a mixture containing the elements or compounds containing two or more elements that are the raw materials for the aluminum alloy in the ratio required to produce the desired aluminum alloy. For example, to control the grain size of the aluminum alloy produced in the casting process, Ti or B can be mixed as a grain refiner, such as an Al-Ti-B rod.

[0036] (Casting process) In the casting process, a molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain an aluminum alloy cast product. The casting process can be performed, for example, by horizontal continuous casting. Fig. 1 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 this embodiment, and is an enlarged cross-sectional view of a main portion of the horizontal continuous casting apparatus shown in Fig. 1, showing the vicinity of a cooling water cavity.

[0037] The horizontal continuous casting apparatus 10 shown in Figures 1 and 2 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. That is, the inner peripheral surface 21a is configured in a tapered shape that opens like a cone 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) 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. 2, 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. 2, 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 M, 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 3. The heat flux per unit area is expressed by the following equation using Fourier's law. Q=-k×(T1-T2) / L 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 a 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 is, for example, in the range of 10 to 300°C / sec, preferably in the range of 100 to 200°C / sec. The casting speed can be appropriately selected from a range common in horizontal continuous casting, for example, in the range of 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 introduced. As a result, sufficient strength required for the subsequent aging treatment can be obtained. The temperature rise rate during the homogenization heat treatment of the aluminum alloy casting is, for example, 1.5°C / min or higher, preferably 4.5°C / min.

[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 (e.g., an automobile suspension arm part, etc.). If the forging starting temperature is lower than 450°C, the deformation resistance may become too high, making sufficient forging impossible. On the other hand, if the forging starting temperature exceeds 560°C, defects such as forging cracks and eutectic melting may easily occur. The heating rate when forging the forging material is, for example, 1.5°C / min or higher, preferably 4.5°C / min.

[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 treatment temperature is lower than 530°C, the solute elements may not be dissolved sufficiently, which may hinder the progress of solution treatment and make it difficult to achieve high strength through aging precipitation. On the other hand, if the treatment temperature exceeds 560°C, the solute elements may be dissolved more readily, but eutectic melting and recrystallization may occur. Furthermore, if the heating rate is lower than 5.0°C / min, coarse precipitation of Mg2Si may 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. In this embodiment, the forged product is placed in a water tank containing water (quenching water) and quenched by submerging the forged product. The water temperature in the water tank is preferably 20°C or higher and 60°C or lower. The forged product is preferably placed in the water tank so that the entire surface of the forged product comes into contact with water within 5 to 60 seconds after the solution treatment. The submersion time of the forged product varies depending on the size of the casting, but is, for example, between 5 minutes and 40 minutes.

[0078] (Aging treatment process) The aging treatment process is a process in which the forged product is heated and held at a relatively low temperature to precipitate supersaturated solid-solution elements, thereby imparting an appropriate hardness. In this embodiment, the forged product after the quenching process is heated to a temperature of 180°C to 220°C and held at that temperature for 0.5 to 7.0 hours to undergo aging treatment. If the heating temperature is less than 180°C or the holding time is less than 0.5 hours, there is a risk that Mg2Si, which improves tensile strength, will not grow sufficiently, and if the treatment temperature exceeds 220°C, there is a risk that the Mg2Si will become too coarse and will not be able to sufficiently improve tensile strength.

[0079] The aluminum alloy forgings of this embodiment have excellent mechanical properties at room temperature because the Cu, Mg, and Si contents are within the above ranges. Furthermore, the ratio Q1 / Q2 of the X-ray diffraction peak intensity Q1 of the CuAl2 phase to the X-ray diffraction peak intensity Q2 of the (200) plane of the Al phase, as determined by X-ray diffraction, is within the above range, so the aluminum alloy forgings have excellent corrosion resistance. Furthermore, when the Mn, Fe, and Cr contents are within the above ranges, the aluminum alloy forgings of this embodiment have further improved mechanical properties at room temperature. Furthermore, when the Ti and B contents are within the above ranges, the wrought workability is improved. [Example]

[0080] Next, specific examples of the present invention will be described, but the present invention is not limited to these examples.

[0081] <Experimental Example> An aluminum alloy was prepared containing 1.0 to 1.9 mass% Mg and Si, calculated as MgSi, and 0.3 to 1.0 mass% Cu. The prepared aluminum alloy was cast using the horizontal continuous casting apparatus shown in Figure 1 to produce a continuous cast product with a circular cross section and a diameter of 49 mm. The cooling rate of the molten aluminum alloy during continuous casting was 120°C / sec.

[0082] The obtained continuous cast product was subjected to homogenization heat treatment, forging, solution treatment, quenching, and artificial aging in this order to obtain an aluminum alloy forged product 100 having the shape shown in Fig. 4. The conditions for the homogenization heat treatment, forging, solution treatment, quenching, and artificial aging are shown in Table 1 below.

[0083] [Table 1]

[0084] C-ring test pieces were taken from the resulting aluminum alloy forgings and subjected to stress corrosion cracking tests (corrosion resistance evaluation). The stress corrosion cracking tests were conducted using the C-ring test pieces according to the ASTM G47 continuous immersion method. Specifically, the C-ring test pieces were subjected to a stress of 90% of the test piece's 0.2% proof stress and then immersed in a mixture of sodium chloride and sodium chromate maintained at 95°C or higher for 80 hours. The C-ring test pieces were then removed from the mixture and visually inspected for the occurrence of stress corrosion cracking. C-ring test pieces that did not exhibit stress corrosion cracking or intergranular corrosion were rated as having acceptable corrosion resistance, while C-ring test pieces that exhibited stress corrosion cracking or intergranular corrosion were rated as having unacceptable corrosion resistance.

[0085] The results of the corrosion resistance evaluation are shown in Figure 5. In the graph of Figure 5, the horizontal axis represents the Cu content, the vertical axis represents the Mg2Si equivalent content, a black circle represents that the corrosion resistance was OK, and an × represents that the corrosion resistance was OK. For each Cu content, a dashed function was calculated connecting the black circles at the positions with the lowest Mg2Si equivalent content. The obtained function was [Mg2Si equivalent content] = -4.1 × [Cu content] 2 +7.8 × [Cu content] -1.9. From this result, [Mg2Si converted content] ≥ -4.1 × [Cu content] 2 It can be seen that aluminum alloy forgings that satisfy +7.8 × [Cu content] -1.9 have excellent corrosion resistance.

[0086] <Examples 1 to 5 and Comparative Examples 1 and 2> An aluminum alloy having the alloy composition shown in Table 2 below was prepared. Using the prepared aluminum alloy, casting was performed in the same manner as in the above experimental example to produce a continuous cast product having a circular cross section with a diameter of 49 mm. Table 2 shows the Mg2Si converted content based on the Mg content calculated using the left side of equation (1), the Mg2Si converted content based on the Si content calculated using the left side of equation (2), and a value calculated using the following equation (3), which is the right side of equations (1) and (2). -4.1 x [Cu content] 2 +7.8 × [Cu content] -1.9 (3)

[0087] [Table 2]

[0088] The obtained continuous cast product was subjected to homogenization heat treatment, forging, solution treatment, quenching, and artificial aging in this order, as in the above experimental example, to obtain an aluminum alloy forged product 100 having the shape shown in Figure 4.

[0089] <Evaluation> Each of the aluminum alloy forged products obtained as described above was evaluated according to the following evaluation methods, and the results are shown in Table 3 below.

[0090] [Evaluation method for yield strength at room temperature] Tensile 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, and the obtained tensile test pieces were subjected to a tensile test at room temperature (25°C) to measure the yield strength. The obtained yield strength was evaluated based on the following criteria. (Judgment criteria) "Good": The yield strength at room temperature is 370 MPa or more. "X": The yield strength at room temperature is less than 370 MPa.

[0091] [Corrosion resistance evaluation method] C-ring test pieces were taken from the aluminum alloy forgings and subjected to stress corrosion cracking tests in the same manner as in the above experimental example. The occurrence of stress corrosion cracking in the C-ring test pieces was evaluated based on the following criteria. (Judgment criteria) "X": Stress corrosion cracking has occurred in the C-ring test piece. "△ (slightly poor)": Although the C-ring test piece is not subject to stress corrosion cracking, intergranular corrosion has occurred, which is likely to lead to stress corrosion cracking. "○ (good)": No stress corrosion cracking or intergranular corrosion occurred in the C-ring test piece.

[0092] [Method for evaluating the integrated intensity of X-ray diffraction peaks of Al phase and CuAl2 phase] X-ray diffraction measurements were performed on each aluminum alloy forging using an X-ray diffractometer (SmartLab, manufactured by Rigaku Corporation). Cu-Kα radiation was used as the X-ray source. The samples used for the X-ray diffraction measurements were 10 mm × 10 mm × 2 mm thick plates extracted from the aluminum alloy forgings. From the X-ray diffraction patterns obtained by the X-ray diffraction measurements, the integrated intensity Q2 of the X-ray diffraction peak of the (200) plane of the Al phase, which was within the diffraction angle 2θ range of 37.8° to 39.8°, and the integrated intensity Q1 of the X-ray diffraction peak of the CuAl2 phase, which was within the diffraction angle 2θ range of 42.5° to 43.5°, were determined, and the ratio Q1 / Q2 was calculated. The resulting Q1 / Q2 values were evaluated based on the following criteria. (Judgment criteria) "Good": Q1 / Q2 is 0.20 or less. "×"...Q1 / Q2 exceeds 0.20.

[0093] [comprehensive evaluation] The results of the evaluation of three items, namely, yield strength at room temperature, corrosion resistance, and metal structure, were evaluated based on the following criteria. (Judgment criteria) "Good": All three ratings are good. "×": One or more of the three ratings are ×.

[0094] [Table 3]

[0095] From the results in Table 3, forged aluminum alloys containing Cu, Mg, and Si within the ranges of the present invention and having a Cu content relative to the Mg2Si converted content within the range of the present invention, the ratio Q1 / Q2 of the integrated intensity Q1 of the X-ray diffraction peak of the CuAl2 phase to the integrated intensity Q2 of the X-ray diffraction peak of the (200) plane of the Al phase obtained by X-ray diffraction method is 2 × 10 -1 In contrast, the forged products of the aluminum alloys of Comparative Examples 1 and 2, in which the Cu content relative to the Mg2Si converted content is outside the range of the present invention, have a Q1 / Q2 ratio of 2 × 10 -1It is clear that the CuAl2 phase is generated in large amounts, resulting in a decrease in corrosion resistance. [Explanation of symbols]

[0096] 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 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 having a Cu content in the range of 0.3 mass% or more and 1.0 mass% or less, a Mg content in the range of 0.63 mass% or more and 1.30 mass% or less, a Si content in the range of 0.45 mass% or more and 1.45 mass% or less, and the balance being Al and unavoidable impurities, wherein the following formulas (1) and (2) are satisfied: [Mg content] × 1.587 ≧ −4.1 × [Cu content] ２ + 7.8 × [Cu content] − 1.9 (1) [Si content] × 2.730 ≧ −4.1 × [Cu content] ２ + 7.8 × [Cu content] − 1.9 (2) The integrated intensity Q of the X-ray diffraction peak of the (200) plane of the Al phase obtained by X-ray diffraction ２ CuAl to ２ The integrated intensity Q of the X-ray diffraction peak of the phase １ The ratio Q １ / Q ２ is 2 x 10 －１ An aluminum alloy forging characterized by the following:

2. the Mg content is in the range of 0.63 mass% or more and 1.25 mass% or less, and the Si content is in the range of 0.60 mass% or more and 1.45 mass% or less, 2. The aluminum alloy forging according to claim 1, wherein the ratio of the Si content to the Mg content, Si / Mg, is 0.5 or more in molar ratio.

3. the Mg content is in the range of 0.85% by mass or more and 1.30% by mass or less, and the Si content is in the range of 0.45% by mass or more and 0.69% by mass or less, The ratio of the Si content to the Mg content, Si / Mg, is less than 0.5 in molar ratio.

2. The aluminum alloy forging according to claim 1 .

4. 4. The aluminum alloy forging according to claim 1, wherein the Mn content is within the range of 0.03% by mass or more and 1.0% by mass or less, the Fe content is within the range of 0.2% by mass or more and 0.7% by mass or less, the Cr content is within the range of 0.03% by mass or more and 0.4% by mass or less, the Ti content is within the range of 0.012% by mass or more and 0.035% by mass or less, the B content is within the range of 0.001% by mass or more and 0.03% by mass or less, the Zn content is within the range of 0.25% by mass or less, and the Zr content is within the range of 0.05% by mass or less.

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