JP2023161784A - Aluminum alloy forging and method for manufacturing the same - Google Patents

Abstract

To provide an aluminum alloy forging having excellent mechanical properties at normal temperature.SOLUTION: An aluminum alloy forging of the present invention, in component ranges of Cu: 0.3 mass% to 1.0 mass%, Mg: 0.8 mass% to 1.8 mass%, Si: 0.9 mass% to 1.9 mass%, Mn: 0.3 mass% to 1.2 mass%, Fe: 0.2 mass% to 0.3 mass%, Zn: 0.26 mass% to 1.0 mass%, Cr: 0.05 mass% to 0.3 mass%, Ti: 0.012 mass% to 0.035 mass%, B: 0.001 mass% to 0.03 mass%, and Zr: 0.05 mass% or less, has the relationship Fe/Mn of less than 1.2, and the remainder of aluminum alloy forging made of Al and inevitable impurities. In an area where the maximum principal stress is applied, the average crystal grain size is 20 to 40 μm, a ratio of large-angle grain boundaries having a crystal orientation difference 15° or more is 27% or less, and 0.2% proof stress is 380 MPa or more.SELECTED DRAWING: None

Description

The present invention relates to an aluminum alloy forged product and a method for manufacturing the same.

In recent years, aluminum alloys have been increasingly used as structural members for various products due to their light weight. For example, high-strength steel has been used until now for automobile suspension and bumper parts. On the other hand, in recent years, high-strength aluminum alloy materials have come to be used.

In addition, iron-based materials have been used exclusively for automobile parts, especially suspension parts. On the other hand, in recent years, aluminum materials or aluminum alloy materials have been increasingly replaced with the main purpose of reducing weight.

Since these automobile parts require excellent corrosion resistance, high strength, and excellent workability, Al--Mg--Si alloys, especially A6061, are often used as aluminum alloy materials. In order to improve the strength, such automobile parts are manufactured by performing forging, which is one type of plastic working, using aluminum alloy material as a working material.

In addition, recently, due to the need to reduce costs, suspension parts obtained by forging cast members as raw materials without extrusion, and then subjecting them to solution treatment and artificial aging treatment (T6 treatment). It has begun to be put into practical use, and high-strength alloys are being developed to replace the conventional A6061 with the aim of further reducing weight (see, for example, Patent Documents 1 to 3).

Japanese Patent Application Publication No. 5-59477 Japanese Patent Application Publication No. 5-247574 Japanese Patent Application Publication No. 6-256880

In recent years, demand for aluminum has been increasing as automobiles have been required to be lighter in weight from the perspective of reducing CO ₂ emissions. However, as a substitute for steel materials, even higher strength is required. On the other hand, as one method for increasing the strength, it is known to suppress the formation of a recrystallized structure in the plastic working and solution treatment steps and to refine the crystal grain size.

However, the above-mentioned Al-Mg-Si-based high-strength alloy has the problem that it is unable to obtain sufficiently high strength due to the recrystallization of the worked structure during the forging and heat treatment processes and the generation of coarse crystal grains. Ta. Therefore, in order to prevent the formation of coarse recrystallized grains, there are some that add Zr (zirconium) to prevent recrystallization (for example, see Patent Documents 1 and 2 above).

However, although adding Zr is effective in preventing recrystallization, it has the following problems.
(1) The addition of Zr weakens the grain refinement effect of the Al-Ti-B alloy, making the crystal grains of the ingot itself coarser, leading to a decrease in the strength of the processed product (forged product) after plastic working. .
(2) Since the grain refining effect of the ingot itself is weakened, cracks in the ingot tend to occur, internal defects increase, and yield deteriorates.
(3) Zr forms compounds with Al-Ti-B alloys, and the compounds accumulate at the bottom of the furnace where the molten alloy is stored, contaminating the furnace, and these compounds are also present in the manufactured ingots. Coarse crystallization occurs in the inside, reducing strength.

Thus, although the addition of Zr is effective in preventing recrystallization, it is difficult to maintain the stability of strength.

The present invention was made in view of this technical background, and an object of the present invention is to provide an aluminum alloy forged product with excellent mechanical properties at room temperature and a method for manufacturing the same.

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

The aluminum alloy forged product according to the first aspect of the present invention includes Cu: 0.3% by mass to 1.0% by mass, Mg: 0.8% by mass to 1.8% by mass, and Si: 0.9% by mass to 1.9 mass%, Mn: 0.3 mass% to 1.2 mass%, Fe: 0.2 mass% to 0.3 mass%, Zn: 0.26 mass% to 1.0 mass%, Cr: 0.05% by mass to 0.3% by mass, Ti: 0.012% by mass to 0.035% by mass, B: 0.001% by mass to 0.03% by mass, Zr: 0.001% by mass or more, 0 An aluminum alloy forged product composed of an aluminum alloy having an alloy composition in which the Fe/Mn relationship is less than 1.2 and the balance is Al and unavoidable impurities in a component range of .05% by mass or less, wherein the aluminum In the part of the alloy forged product where the maximum principal stress is applied, the average grain size is 20 to 40 μm, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the yield strength is 0.2%. It is 380 MPa or more.

A method for manufacturing an aluminum alloy forged product according to a second aspect of the present invention is a method for manufacturing an aluminum alloy forged product according to the above aspect, comprising a molten alloy forming step of forming a molten alloy having the same composition as the aluminum alloy forged product. and a casting step of cooling and solidifying the molten aluminum alloy obtained in the molten alloy forming step to form an aluminum alloy ingot, and applying the aluminum alloy ingot at a temperature of 370° C. or higher and 560° C. or lower for 4 hours. As described above, the homogenization heat treatment step is performed to perform homogenization heat treatment for 10 hours or less, the forging step is performed to forge the aluminum alloy cast product after the homogenization heat treatment step at a heating temperature of 450° C. or more and 560° C. or less, and A solution treatment step in which the forged product obtained in the forging step is subjected to solution treatment at a treatment temperature of 530 ° C. or higher and 560 ° C. or lower for 0.3 hours or more and 3 hours or less, and 5 after the solution treatment step. A quenching process in which all surfaces of the forged product are brought into contact with quenching water for at least 60 seconds and quenched in a water bath for at least 1 minute and up to 30 minutes, and after the quenching process. and an aging treatment step of aging the forged product at a heating temperature of 170° C. or higher and 210° C. or lower for 0.5 hours or more and 7 hours or less.

According to the present invention, an aluminum alloy forged product with excellent mechanical properties at room temperature can be provided.

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. FIG. 2 is an enlarged cross-sectional view of a main part near a cooling water cavity of the horizontal continuous casting apparatus shown in FIG. 1. FIG. It is an explanatory view explaining heat flux of a cooling wall part of a horizontal continuous casting machine. FIG. 2 is a perspective view of an aluminum alloy forged product manufactured in an example.

Embodiments of the present invention will be described in detail below with reference to the drawings.
Note that the drawings used in the following explanations may show characteristic parts enlarged for convenience in order to make the characteristics easier to understand, and the dimensional ratio of each component may not be the same as the actual one. do not have. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and can be implemented with appropriate changes within a range without changing the effect. .

[Aluminum alloy forged products]
First, an aluminum alloy forged product according to an embodiment of the present invention will be described.
The aluminum alloy forged product of this embodiment includes Cu: 0.3% by mass to 1.0% by mass, Mg: 0.8% by mass to 1.8% by mass, and Si: 0.9% by mass to 1.9% by mass. %, Mn: 0.3% by mass to 1.2% by mass, Fe: 0.2% by mass to 0.3% by mass, Zn: 0.26% by mass to 1.0% by mass, Cr: 0.05% by mass % to 0.3 mass%, Ti: 0.012 mass% to 0.035 mass%, B: 0.001 mass% to 0.03 mass%, Zr: 0.001 mass% or more, 0.05 mass% An aluminum alloy forged product composed of an aluminum alloy having an alloy composition in which the Fe/Mn relationship is less than 1.2 and the balance consists of Al and unavoidable impurities in the following component ranges: In the part where the maximum principal stress is applied, the average grain size is 20 to 40 μm, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the 0.2% proof stress is 380 MPa or more. .

The aluminum alloy forged product of this embodiment corresponds to a 6000 series aluminum alloy forged product in that it contains Mg and Si.

(Cu: 0.3% by mass or more, 1.0% by mass or less)
Cu has the effect of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys by precipitating as Al-Cu-Mg-Si compounds such as Q phase. has. When the Cu content is within the above range, the mechanical properties of the aluminum alloy forged product at room temperature can be improved.

(Mg: 0.8% by mass or more, 1.8% by mass or less)
Mg has the effect of improving the tensile strength of the aluminum alloy. Mg dissolves solidly in the aluminum matrix, or precipitates as Mg-Si compounds (Mg ₂ Si) such as β'' phase, or Al-Cu-Mg-Si compounds (AlCuMgSi) such as Q phase. This contributes to strengthening the aluminum alloy. Mg ₂ Si also has the effect of suppressing the generation of the CuAl ₂ phase in the aluminum alloy. By suppressing the generation of the CuAl ₂ phase, the aluminum alloy forging The corrosion resistance of the product is improved. By having the Mg content within the above range, it is possible to improve the corrosion resistance as well as the mechanical properties at room temperature of the aluminum alloy forged product.

(Si: 0.9 mass% or more, 1.9 mass% or less)
Like Mg, Si has the effect of improving the mechanical properties and corrosion resistance of aluminum alloy forged products at room temperature. However, if Si is added excessively to the aluminum alloy, coarse primary Si grains may crystallize, which may reduce the tensile strength of the aluminum alloy. When the Si content is within the above range, the mechanical properties and corrosion resistance of the aluminum alloy forged product at room temperature can be improved while suppressing the crystallization of primary Si.

(Mn: 0.3% by mass or more, 1.2% by mass or less)
Mn increases the tensile strength of aluminum alloys by forming fine grain crystals containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si. It has the effect of improving When the Mn content is within the above range, the mechanical properties of the aluminum alloy forged product at room temperature can be improved.

(Fe: 0.2% by mass or more, 0.3% by mass or less)
Fe is present in fine particles containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe in aluminum alloys. By crystallizing as a crystallized substance, it has the effect of improving the tensile strength of the aluminum alloy. When the content of Fe is within the above range, the mechanical properties of the aluminum alloy forged product at room temperature can be improved.
Note that the Fe/Mn relationship is less than 1.2. When the Fe/Mn relationship is less than 1.2, crystallization of AlFeSi-based compounds of 1.5 μm or more can be suppressed, and mechanical properties can be improved.

(Cr: 0.05% by mass or more, 0.3% by mass or less)
Cr improves the tensile strength of aluminum alloys by forming fine grain crystals containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr. It has the effect of causing When the Cr content is within the above range, the mechanical properties of the aluminum alloy forged product at room temperature can be improved.

(Ti: 0.012 mass% or more, 0.035 mass% or less)
Ti has the effect of refining the crystal grains of the aluminum alloy and improving the stretchability. If the Ti content is less than 0.012% by mass, there is a risk that the effect of grain refinement may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.035% by mass, coarse crystallized substances may be formed and the stretchability may deteriorate. Furthermore, if a large amount of coarse crystallized substances containing Ti are mixed into an aluminum alloy forged product, the toughness may be reduced. Therefore, the content of Ti is 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.

(B: 0.001% by mass or more, 0.03% by mass or less)
B has the effect of refining the crystal grains of the aluminum alloy and improving the stretchability.
By adding B to the aluminum alloy together with the above-mentioned Ti, the grain refinement effect is improved. If the content of B is less than 0.001% by mass, there is a possibility that a sufficient crystal grain refinement effect cannot be obtained. On the other hand, if the content of B exceeds 0.03% by mass, coarse crystallized substances may be formed and may be mixed into the aluminum alloy forged product as inclusions. Furthermore, if a large amount of coarse crystallized substances containing B are mixed into the final aluminum alloy product, the toughness may be reduced. Therefore, the content of B is 0.001% by mass or more and 0.03% by mass. The content of B is preferably 0.005% by mass or more and 0.025% by mass.

(Zn: 0.26% by mass or more, 1.0% by mass or less)
If Zn is 1.0% by mass or less, it is dissolved in the Al matrix and contributes to improving the strength of the aluminum alloy forged product as solid solution strengthening. When the Zn content exceeds 1.0% by mass, MgZn ₂ is generated and precipitated from the Al matrix to the grain boundaries, causing intergranular corrosion, leading to a decrease in the corrosion resistance of the aluminum alloy forged product. In addition, solid solution of Zn has a recrystallization suppressing effect, but if it is less than 0.26 mass%, the recrystallization suppressing effect is insufficient, while when added in excess of 1.0 mass%, MgZn When ₂ is generated and the amount of solid solution decreases, recrystallization becomes more likely to occur. In addition, when Mg combines with Zn to form MgZn ₂ and Mg is taken to Zn, the amount of Mg ₂ Si decreases, so the grain refinement effect of Mg ₂ Si decreases. I end up. Therefore, the Zn content is preferably 1.0% by mass or less.

(Zr: 0.001% by mass or more, 0.05% by mass or less)
If Zr is 0.05% by mass or less, it precipitates in the form of Al ₃ Zr and Al-(Ti, Zr), which contributes to improving the strength of aluminum alloy forgings by suppressing recrystallization and strengthening precipitation. do. However, if the Zr content exceeds 0.05% by mass, it may crystallize as a coarse Zr compound, leading to a decrease in the corrosion resistance of the aluminum alloy forged product. Therefore, the content of Zr is 0.05% by mass or less. Further, in order to obtain the above-mentioned recrystallization suppressing effect and the effect of improving the strength of the forged product through precipitation strengthening, the Zr content is preferably 0.001% by mass or more.

(inevitable impurities)
Unavoidable impurities are impurities that are unavoidably mixed into the aluminum alloy from the raw materials or manufacturing process of the aluminum alloy forged product. Examples of unavoidable impurities include Ni, Sn, and Be. It is preferable that the content of these unavoidable impurities does not exceed 0.1% by mass.

The aluminum alloy forged product of this embodiment has an average crystal grain size of 20 μm or more and 40 μm or less in the cross-sectional structure of the portion of the aluminum alloy forged product where the maximum principal stress is applied, and large-angle grain boundaries with a crystal orientation difference of 15° or more. The ratio is 27% or less, and the 0.2% proof stress is 380 MPa or more.

Here, the "average grain size" refers to the diameter (circle equivalent diameter) when each grain is made into a circle with the same area in an electron microscope image or an EBSD image. , refers to the average value. It may be automatically calculated by analysis software. The "average crystal grain size" is the average of 380 or more crystal grains.

If the average grain size exceeds 40 μm, satisfactory tensile and fatigue properties cannot be obtained due to the Hall-Petch law. On the other hand, if the average crystal grain size is less than 20 μm, toughness deteriorates and impact resistance decreases. Therefore, it is necessary to control the average crystal grain size to a range of 20 μm or more and 40 μm or less.
Further, the standard deviation of the crystal grain size is preferably 30 or less. This is because impact resistance increases when variation in crystal grain size is suppressed. The standard deviation of the crystal grain size is more preferably 25 or less, and even more preferably 20 or less.

Grain boundaries with a crystal orientation difference of 15% or more (high-angle grain boundaries) serve as an indicator of the degree of progress of recrystallization. When this ratio is 27% or less, recrystallization is sufficiently suppressed, leading to excellent mechanical properties. The ratio of grain boundaries with a crystal orientation difference of 15% or more can be obtained from an EBSD image.

The aluminum alloy forged product of this embodiment has a 0.2% yield strength of 380 MPa or more, which is a high strength comparable to iron-based metal materials.

[Method for manufacturing aluminum alloy forged products]
Next, a method for manufacturing an aluminum alloy forged product according to the present embodiment will be described.
The method for manufacturing an aluminum alloy forged product of the present embodiment includes, for example, a molten metal forming process, a casting process, a homogenizing heat treatment process, a forging process, a solution treatment process, a quenching process, and an aging treatment process. The above-mentioned aluminum alloy forged product can be manufactured through the following steps.

(Molten metal formation process)
The molten metal forming step is a step in which raw materials are melted to obtain a molten aluminum alloy whose composition has been adjusted. The composition of the molten aluminum alloy is the same as the composition of the aluminum alloy forging. That is, Cu: 0.3% by mass to 1.0% by mass, Mg: 0.8% by mass to 1.8% by mass, Si: 0.9% by mass to 1.9% by mass, Mn: 0.3% by mass. % to 1.2 mass%, Fe: 0.2 mass% to 0.3 mass%, Zn: 0.26 mass% to 1.0 mass%, Cr: 0.05 mass% to 0.3 mass%, Fe/ A molten metal of 6000 series aluminum alloy is obtained by adjusting the Mn relationship to be less than 1.2 and the balance being Al and unavoidable impurities.
1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, 7000 series aluminum alloy scrap materials are used as raw materials for 10% or more, and the remainder is new aluminum ingots and the above additive elements. , these may be melted to obtain a molten aluminum alloy whose composition is adjusted.
By performing the subsequent steps using a molten aluminum alloy having the above composition, it is possible to obtain an Al--Mg--Si based aluminum alloy forged product that is resistant to recrystallization and has excellent mechanical properties at room temperature. Note that the new aluminum ingot is aluminum with a concentration of 99% or more obtained by subjecting alumina produced from minerals to electrolysis called electrolytic refining.

Molten aluminum alloy can be obtained by heating and melting an aluminum alloy. Alternatively, it may be formed by melting a mixture containing a single element or a compound containing two or more elements serving as raw materials for the aluminum alloy in a proportion that produces the desired aluminum alloy. For example, in order to control the grain size of the aluminum alloy produced in the casting process, Ti or B may be mixed as a grain refiner such as an Al--Ti--B rod.

(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. For the casting process, for example, a horizontal continuous casting method can be used.

Here, a horizontal continuous casting apparatus that can be used for manufacturing the aluminum alloy casting product of this embodiment is shown in FIGS. 1 and 2.
Note that FIG. 1 is a sectional view showing an example of the vicinity of the mold 12 of the horizontal continuous casting apparatus 10. FIG. 2 is an enlarged cross-sectional view of the main part of the horizontal continuous casting apparatus 10 near the cooling water cavity 24. As shown in FIG.

The horizontal continuous casting apparatus 10 shown in FIGS. 1 and 2 includes a molten metal receiving part (tundish) 11, a hollow cylindrical mold 12, and a space between one end side 12a of the mold 12 and the molten metal receiving part 11. It has a refractory plate-like body (insulating member) 13.

The molten metal receiving part 11 is composed of a molten metal inflow part 11a that receives the molten aluminum alloy M obtained in the above-described molten metal forming process, a molten metal holding part 11b, and an outflow part 11c to the hollow part 21 of the mold 12.

The molten metal receiving part 11 maintains the upper liquid level of the molten aluminum alloy M at a position higher than the upper surface of the hollow part 21 of the mold 12, and in the case of multiple casting, the aluminum alloy is placed in each mold 12. This is to stably distribute the molten metal M.

The molten aluminum alloy M held in the molten metal holding part 11b in the molten metal receiving part 11 is poured into the hollow part 21 of the mold 12 from the pouring passage 13a provided in the refractory plate 13. The molten aluminum alloy M supplied into the hollow portion 21 is cooled and solidified by a cooling device 23, which will be described later, and is pulled out from the other end side 12b of the mold 12 as an aluminum alloy rod B, which is a solidified ingot.

A drawer drive device (not shown) that pulls out the cast aluminum alloy rod B at a constant speed may be installed on the other end side 12b of the mold 12. Further, it is also preferable that a synchronous cutting machine (not shown) is installed to cut the continuously drawn aluminum alloy rods B into arbitrary lengths.

The refractory plate 13 is a member that blocks heat transfer between the molten metal receiver 11 and the mold 12, and is made of, for example, calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide. , graphite, or other materials. Such a refractory plate-like body 13 can also be composed of a plurality of layers made of different constituent materials.

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

The hollow part 21 of the mold 12 is formed to have a circular cross section in order to make the aluminum alloy rod B to be cast into a cylindrical rod shape, and the mold central axis (central axis) C passing through the center of the hollow part 21 is approximately horizontal. A mold 12 is held along the line.

The inner circumferential surface 21a of the hollow part 21 of the mold 12 has an angle of 0° to 3° (more preferably 0° to 1°) with respect to the mold center axis C toward the casting direction of the aluminum alloy rod B (see FIG. 1). ) is formed at an elevation angle of That is, the inner circumferential surface 21a is configured to have a tapered cone-like shape toward the casting direction. The angle formed by the taper is the elevation angle.

If the elevation angle is less than 0°, when the aluminum alloy rod B is pulled out from the mold 12, it may be difficult to cast because it will encounter resistance at the other end side 12b, which is the mold outlet. On the other hand, if the elevation angle exceeds 3°, the contact of the inner peripheral surface 21a with the molten aluminum alloy M becomes insufficient, and the heat removal effect from the molten aluminum alloy M and the solidified shell obtained by cooling and solidifying it to the mold 12 decreases. This may result in insufficient coagulation. As a result, re-melting skin may occur on the surface of the aluminum alloy rod B, or casting troubles such as unsolidified molten aluminum alloy M spouting out from the end of the aluminum alloy rod B may occur, which is not preferable.

Note that 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 have a triangular or rectangular cross-sectional shape, for example, in addition to the circular shape of this embodiment. The shape may be selected according to the shape of the aluminum alloy rod to be cast, such as a polygon, a semicircle, an ellipse, or an irregular cross-sectional shape having no axis or plane of symmetry.

A fluid supply pipe 22 for supplying lubricating fluid into the hollow portion 21 of the mold 12 is arranged at one end side 12 a of the mold 12 . The lubricating fluid supplied from the fluid supply pipe 22 can be one or more lubricating fluids selected from gas lubricants and liquid lubricants. 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 the annular lubricant supply port 22a.

In this embodiment, the pumped lubricating fluid is supplied to the inner circumferential surface 21a of the mold 12 from the lubricant supply port 22a. Note that the liquid lubricant may be heated to become a decomposed 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 exuded to the inner circumferential surface 21a of the mold 12 through the porous material.

Inside the mold 12, a cooling device 23, which is a cooling means for cooling and solidifying the molten aluminum alloy M, is formed. The cooling device 23 of this embodiment includes a cooling water cavity 24 that accommodates cooling water W for cooling the inner circumferential surface 21a of the hollow portion 21 of the mold 12, and a cooling water cavity 24 and the hollow portion 21 of the mold 12. The cooling water injection passage 25 communicates with the cooling water injection passage 25.

The cooling water cavity 24 is formed in an annular shape so as to surround the hollow part 21 outside the inner peripheral surface 21a of the hollow part 21 inside the mold 12, and is supplied with cooling water W via the cooling water supply pipe 26. Ru.

The inner peripheral surface 21a of the mold 12 is cooled by the cooling water W accommodated in the cooling water cavity 24, so that the heat of the molten aluminum alloy M filled in the hollow part 21 of the mold 12 is transferred to the inner peripheral surface of the mold 12. A solidified shell is formed on the surface of the molten aluminum alloy M by taking it away from the surface that contacts 21a.

Further, the cooling water injection passage 25 cools the aluminum alloy rod B by applying cooling water W directly toward the aluminum alloy rod B at the other end side 12b of the mold 12 from the shower opening 25a facing the hollow portion 21. The longitudinal cross-sectional shape of the cooling water injection passage 25 may be, for example, semicircular, pear-shaped, or horseshoe-shaped, in addition to the circular shape of this embodiment.

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 circumferential surface 21a of the hollow part 21 of the mold 12, and then further cooled. Although the cooling water W in the water cavity 24 is injected from the cooling water injection passage 25 toward the aluminum alloy rod B, it is also possible to configure these to be supplied by cooling water supply pipes of separate systems.

The length from the position where the extension line 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 calculated as follows: 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 film will not be formed, making it impossible to cast. If it exceeds 40 mm, the effect of forced cooling will be reduced, and solidification by the mold walls will become dominant, resulting in mold 12 This is not preferable because the contact resistance with the molten aluminum alloy M or the aluminum alloy rod B becomes large, which may cause cracks on the casting surface or breakage inside the mold, resulting in unstable casting.

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

The cooling water cavity 24 is formed such that the inner bottom surface 24 a near the hollow portion 21 of the mold 12 is parallel to the inner circumferential surface 21 a of the hollow portion 21 of the mold 12 .

Note that parallel here means that the inner circumferential surface 21a of the hollow part 21 of the mold 12 is formed at an elevation angle of 0° to 3° with respect to the inner bottom surface 24a of the cooling water cavity 24, that is, the inner This also includes the case where the bottom surface 24a is inclined at more than 0 degrees and up to 3 degrees with respect to the inner circumferential surface 21a.

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 and the inner circumferential surface 21a of the hollow portion 21 of the mold 12 are opposed, is made of aluminum alloy of the hollow portion 21. It is formed so that the heat flux value per unit area from the molten metal M toward the cooling water W in the cooling water cavity 24 is within the range of 10 × 10 ⁵ W/m ² or more and 50 × 10 ⁵ W/m ² or less. There is.

The thickness t of the cooling wall portion 27 of the mold 12, that is, the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12 is preferably, for example, 0.5 mm or more and 3.0 mm or less. It is sufficient that the mold 12 is formed so that the diameter is within the range of 0.5 mm or more and 2.5 mm or less. Further, 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 the range of 100 W/m·K or more and 400 W/m·K or less.

In FIG. 2, the molten aluminum alloy M in the molten metal receiving portion 11 is supplied from one end side 12a of the mold 12, which is held so that the center axis C of the mold is substantially horizontal, through the refractory plate 13, and The aluminum alloy rod B is forcibly cooled at the other end side 12b of 12.

The aluminum alloy rod B is drawn out at a constant speed by a drawer drive device (not shown) installed near the other end side 12b of the mold 12, so that it is continuously cast to form a long aluminum alloy rod B. . The drawn aluminum alloy rod B is cut into a desired length by, for example, a synchronous cutter (not shown).

The composition ratio of the cast aluminum alloy rod B can be determined, for example, by a method using a photoelectric photometric emission spectrometer (device example: PDA-5500 manufactured by Shimadzu Corporation of Japan) as described in "JIS H 1305". You can check it.

The difference between the liquid level of the molten aluminum alloy M stored in the molten metal receiving part 11 and the height of the upper inner peripheral surface 21a of the mold 12 is 0 mm to 250 mm (more preferably 50 mm to 170 mm). It is preferable that By setting the pressure within such a range, the pressure of the molten aluminum alloy M supplied into the mold 12 and the lubricating oil and the gas vaporized from the lubricating oil are appropriately balanced, so that castability is stabilized.

As the liquid lubricant, vegetable oil, which is a lubricating oil, can be used. Examples include rapeseed oil, castor oil, and salad oil. These are preferable because they have little negative impact on the environment.

The lubricating oil supply rate is preferably 0.05 mL/min to 5 mL/min (more preferably 0.1 mL/min or more and 1 mL/min or less). If the supply amount is too small, there is a risk that the molten aluminum alloy M of the aluminum alloy rod B will not harden and leak from the mold 12 due to insufficient lubrication.
If the supply amount is too large, there is a risk that the excess amount will mix into the aluminum alloy rod B and cause internal defects.

The casting speed, which is the speed at which the aluminum alloy rod B is pulled out from the mold 12, is preferably 200 mm/min or more and 1500 mm/min or less (more preferably 400 mm/min or more and 1000 mm/min or less). This is because, if the casting speed is within this range, the network structure of the crystallized substances formed during casting will be uniform and fine, increasing the resistance to deformation of the aluminum fabric at high temperatures and improving high-temperature mechanical strength. be.

The amount of cooling water injected from the shower opening 25a of the cooling water injection passage 25 is preferably 10 L/min or more and 50 L/min or less (more preferably 25 L/min or more and 40 L/min or less) per mold. If the amount of cooling water is less than this, there is a risk that the molten aluminum alloy M will not harden and leak from the mold 12. Furthermore, the surface of the cast aluminum alloy rod B may be remelted to form a non-uniform structure, which may remain as internal defects. On the other hand, if the amount of cooling water is greater than this range, there is a risk that the mold 12 will lose too much heat and solidify midway through.

The average temperature of the molten aluminum alloy M flowing into the mold 12 from the molten metal receiver 11 is preferably, for example, 650°C or higher and 750°C or lower (more preferably 680°C or higher and 720°C or lower). If the temperature of the molten aluminum alloy M is too low, there is a risk that coarse crystallized substances will be formed in the mold 12 and in front of the mold 12 and incorporated into the aluminum alloy rod B as internal defects. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen gas is likely to be incorporated into the molten aluminum alloy M, and may be incorporated into the aluminum alloy rod B as porosity, creating a cavity inside.

In the cooling wall portion 27 of the mold 12, the heat flux value per unit area from the molten aluminum 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 or more 50× By keeping it within the range of 10 ⁵ W/m ² or less, it is possible to prevent the aluminum alloy rod B from seizing.

The cooling wall portion 27 of the mold 12 receives heat from the molten aluminum alloy M, and performs heat exchange by cooling this heat with the cooling water W accommodated in the cooling water cavity 24. Regarding the state of heat exchange, we focused on the heat flux per unit area, as shown in the explanatory diagram shown in FIG. The heat flux per unit area is expressed by the following equation (1) according to Fourier's law.
Q=-k×(T1-T2)/L...(1)
Q: Heat flux k: Thermal conductivity (W/m・K) of the location through which heat passes (in this embodiment, the cooling wall portion 27 of the mold 12)
T1: Low temperature side temperature of the location where heat passes (in this embodiment, the inner bottom surface 24a of the cooling water cavity 24)
T2: Temperature on the high temperature side of the part through which heat passes (in this embodiment, the inner circumferential surface 21a of the hollow part 21 of the mold 12)
L: Section length (mm) of the portion through which heat passes (in this embodiment, the thickness t of the cooling wall portion 27 of the mold 12)

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

In order to make the cooling wall portion 27 of the mold 12 have such a heat flux value range, the mold 12 is set so that the thickness t of the cooling wall portion 27 of the mold 12 is, for example, in the range of 0.5 mm or more and 3.0 mm or less. Just form it. Further, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 may be set in a range of 100 W/m·K or more and 400 W/m·K or less.

When manufacturing the aluminum alloy rod B of this embodiment, using the above-described horizontal continuous casting apparatus 10, the aluminum alloy molten metal M stored in the molten metal receiving part 11 is poured from one end side 12a of the mold 12 into the hollow part. 21 continuously. Further, the cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid such as lubricating oil is supplied from the fluid supply pipe 22.

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

The aluminum alloy rod B obtained in this way is cooled and solidified under conditions where the heat flux value per unit area in the cooling wall portion 27 is 10×10 ⁵ W/m ² or more. The fixation of reaction products such as carbides due to contact with is suppressed. Thereby, there is no need to cut and remove carbides and the like on the surface of the aluminum alloy rod B, and the aluminum alloy rod B can be manufactured at a high yield.

The casting process for obtaining a cast product from the molten aluminum alloy M is not limited to the above-mentioned horizontal continuous casting method, and any known continuous casting method such as the vertical continuous casting method can be used. The vertical continuous casting method is classified into the float method and the hot top method depending on the method of supplying the molten aluminum alloy M to the mold (mold 12), and below, the case where the hot top method is used will be briefly explained.

The casting equipment used in the hot top method includes a mold, a molten metal receiver (header), and the like. The molten metal supplied to the molten metal receiving section passes through the tap outlet, the header, the flow rate is adjusted, and enters the almost horizontally installed cylindrical mold, where it is forcibly cooled and solidified on the outer surface of the molten metal. A shell is formed.

Furthermore, cooling water is directly radiated onto the cast product pulled out from the mold, and the cast product is continuously pulled out while solidification of the metal progresses to the inside of the cast product. Generally, a mold is made of a metal member with good thermal conductivity and has a hollow structure for introducing a refrigerant into the mold.

The refrigerant used may be appropriately selected from industrially available refrigerants, but water is recommended from the viewpoint of ease of use.

The mold used in this embodiment is appropriately selected from metals such as copper and aluminum, or graphite from the viewpoint of heat transfer performance and durability in the contact portion with the molten metal. The header is generally made of refractory material and is placed above the mold. The material and size of the header may 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 may be appropriately selected from a generally recommended range, such as 10 to 300° C./sec. The casting speed may be appropriately selected from a range commonly used in horizontal continuous casting, for example from a range of 200 to 600 mm/min.

The casting method described above makes it possible to obtain a uniform metal structure even for medium to large-sized cast products. The diameter of the target cast product is not particularly limited, and bar materials with a diameter of 30 to 100 mm are suitably used.

(Homogenization heat treatment process)
In the homogenization heat treatment process, the aluminum alloy castings obtained in the casting process are subjected to homogenization heat treatment to homogenize the micro-segregation caused by solidification, the precipitation of supersaturated solid solution elements, and the equilibrium phase of the metastable phase. This is the process of changing to.

In this embodiment, a homogenization heat treatment is performed on the cast product obtained in the casting process by holding it at a temperature of 370° C. or higher and 560° C. or lower for 4 to 10 hours. By performing the homogenization heat treatment in this temperature range, the ingot is sufficiently homogenized and the solute atoms are infiltrated, so that sufficient strength required by the subsequent aging treatment can be obtained.

However, if the heating temperature of the material during forging and the solution treatment temperature are high (for example, 530°C or higher), it is possible to homogenize micro-segregation in the forging process and solution treatment process. It is also possible to omit the step.

(Forging process)
In the forging process, the aluminum alloy casting after casting or homogenization heat treatment is formed into a predetermined size to obtain a forging material, the obtained forging material is heated to a predetermined temperature, and then a press machine is used. This is a process in which the material is molded using pressure.

In this embodiment, a forging process is performed on a forging material at a heating temperature of 450° C. or more and 560° C. or less to obtain a forged product (for example, a suspension arm part for an automobile). At this time, the forging starting temperature of the forging material is 450°C or higher and 560°C or lower. This is because if the starting temperature is less than 450°C, the deformation resistance becomes high and sufficient processing is not possible, whereas if it exceeds 560°C, defects such as forging cracks and eutectic melting are likely to occur.

(Solution treatment process)
The solution treatment step is a step in which the forged product obtained in the forging step is heated and turned into a solution, thereby alleviating the strain introduced in the forging step and dissolving the solute elements.

In this embodiment, the forged product is subjected to solution treatment by holding it at a treatment temperature of 530° C. or higher and 560° C. or lower for 0.3 or more and 3 hours or less. The rate of temperature increase from room temperature to the above-mentioned treatment temperature is preferably 5.0° C./min or more. If the treatment temperature is less than 530°C, there is a possibility that the solid solution of the solute element will be insufficient. On the other hand, if the temperature exceeds 560°C, solid solution of solute elements is further promoted, but eutectic melting and recrystallization may easily occur. Furthermore, if the temperature increase rate is less than 5.0° C./min, there is a risk that Mg ₂ Si will be coarsely precipitated. On the other hand, if the treatment temperature is lower than 530° C., solution treatment may not proceed and it may be difficult to achieve high strength due to aging precipitation.

(Quenching treatment process)
The quenching process is a process in which the forged product in a 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 in which water (quenching water) is stored, and the forged product is submerged in water to perform the quenching process. The water temperature in the water tank is preferably 20°C or higher and 60°C or lower. It is preferable that the forged product be placed in the water tank so that all surfaces of the forged product come into contact with water for 5 seconds or more and 60 seconds or less after the solution treatment. The submersion time of the forged product varies depending on the size of the cast product, but is, for example, more than 1 minute and less than 30 minutes.

(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 to impart appropriate hardness.

In the present embodiment, the forged product after the quenching process is heated to a temperature of 170° C. or more and 210° C. or less, and is maintained at that temperature for 0.5 hours or more and 7 hours or less to perform aging treatment. If the treatment temperature is less than 170° C. or the holding time is less than 0.5 hours, there is a risk that Mg ₂ Si-based precipitates that improve tensile strength may not be able to grow sufficiently. On the other hand, if the treatment temperature exceeds 190° C. or the holding time exceeds 7 hours, the Mg ₂ Si-based precipitates may become too coarse and the tensile strength may not be sufficiently improved.

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

(Examples 1 to 9 and Comparative Examples 1 to 2)
First, an aluminum alloy having the alloy composition shown in Table 1 below (the remainder being aluminum) was prepared. A continuous casting product with a circular cross section and a diameter of 49 mm was produced using the prepared aluminum alloy. Examples 4 to 6 and Examples 7 to 8 each have the same composition as Examples 1 to 3, but the conditions of the treatment process for the continuous casting product are different.

Next, the obtained continuous casting product is subjected to a homogenization heat treatment process, a forging process, a solution treatment process, a quenching process, and an artificial aging treatment process in this order to obtain an aluminum shape as shown in FIG. An alloy forged product 100 was obtained. The conditions of the homogenization heat treatment process, forging process, solution treatment process, quenching process, and artificial aging process are shown in Table 2 below.

"evaluation"
Each of the aluminum alloy forged products of Examples 1 to 9 and Comparative Examples 1 to 2 obtained as described above was evaluated based on the following evaluation method. The results are shown in Table 3 below.

<Tensile strength evaluation method at room temperature>
A tensile test piece with a gage distance of 25.4 mm and a parallel part diameter of 6.4 mm is taken from the evaluation part of the obtained aluminum alloy forged product 100, and a normal temperature (25 ° C.) tensile test is performed on the tensile test piece. The tensile strength was measured and evaluated based on the following criteria.
(Judgment criteria)
"〇"...0.2% yield strength at room temperature is 380 MPa or more.
"x"...0.2% proof stress at room temperature is less than 380 MPa.

<Method for measuring grain size, standard deviation of grain size, and ratio of large-angle grain boundaries with crystal orientation difference of 15° or more of aluminum alloy forgings>
For each aluminum alloy forged product of Examples 1 to 9 and Comparative Examples 1 to 2, the average grain size, standard deviation of the grain size, and large-angle grain boundary with a crystal orientation difference of 15° or more were determined using a SEM-EBSD device. The ratio was measured and evaluated based on the following criteria. Note that a plate-shaped body of 7 mm x 7 mm x 2 mm thickness was taken from the evaluation site of the aluminum alloy forged product 100 and used as a SEM-EBSD measurement sample. The measurement conditions were an accelerating voltage of 15 kV, a measurement pitch of 0.5 μm/px, an analysis area of 500×500 μm ² , and a grain boundary definition angle of 15°. These results are shown in Table 3 above.
(Judgment criteria (average grain size))
"〇"...20 μm or more and 40 μm or less.
"x": Less than 20 μm, more than 40 μm.
(Judgment criteria (standard deviation of crystal grain size))
"〇"...30 or less.
"×"...Over 30.
(Judgment criteria (ratio of large-angle grain boundaries with crystal orientation difference of 15° or more))
"〇"...27% or less.
"×"...Exceeds 27%.

<Comprehensive evaluation>
Four evaluation results were evaluated based on the following criteria: 0.2% proof stress at room temperature, average grain size, standard deviation of grain size, and ratio of large-angle grain boundaries of 15° or more.
(Judgment criteria)
“〇”…All four evaluations are “〇”.
"x"...One or more of the four evaluations is "x".

Contains Zr and Zn, the content of each element is set within a predetermined range, and the process includes a molten metal forming process, a casting process, a homogenizing process, a forging process, a solution treatment process, a quenching process, and an aging process. By manufacturing aluminum alloy forged products by carrying out each step within the predetermined processing conditions, the forged aluminum alloy can be sufficiently refined with variations suppressed, and crystal coarsening due to recrystallization can be suppressed. An aluminum alloy forged product having excellent mechanical properties at room temperature was obtained.

10... Horizontal continuous casting device 11... Molten metal receiver (tundish)
11a... Molten metal inflow part 11b... Molten metal holding part 11c... Outflow part 12... Mold 12a... One end side 12b... Other end side 13... Refractory plate-shaped body (insulation member)
13a...Mold 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 part B... Aluminum alloy rod M... Alloy molten metal W... Cooling water 100... Aluminum alloy forged product

Claims (2)

Cu: 0.3% by mass to 1.0% by mass,
Mg: 0.8% by mass to 1.8% by mass,
Si: 0.9% by mass to 1.9% by mass,
Mn: 0.3% by mass to 1.2% by mass,
Fe: 0.2% by mass to 0.3% by mass,
Zn: 0.26% by mass to 1.0% by mass,
Cr: 0.05% by mass to 0.3% by mass,
Ti: 0.012% by mass to 0.035% by mass,
B: 0.001% by mass to 0.03% by mass,
Zr: In the component range of 0.001% by mass or more and 0.05% by mass or less, the Fe/Mn relationship is less than 1.2, and the balance is composed of an aluminum alloy having an alloy composition consisting of Al and inevitable impurities. An aluminum alloy forged product,
In the portion of the aluminum alloy forged product subjected to the maximum principal stress, the average grain size is 20 to 40 μm, the ratio of large-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and 0.2%. An aluminum alloy forged product with a yield strength of 380 MPa or more. A method for manufacturing an aluminum alloy forged product according to claim 1, comprising:
a molten alloy forming step of forming a molten alloy having the same composition as the aluminum alloy forging;
a casting step of cooling and solidifying the molten aluminum alloy obtained in the molten alloy forming step to form an aluminum alloy ingot;
A homogenization heat treatment step of performing homogenization heat treatment on the aluminum alloy ingot at a temperature of 370 ° C. or higher and 560 ° C. or lower for 4 hours or more and 10 hours or less;
a forging step of forging the aluminum alloy cast product after the homogenization heat treatment step at a heating temperature of 450° C. or higher and 560° C. or lower;
A solution treatment step in which the forged product obtained in the forging step is subjected to solution treatment at a treatment temperature of 530° C. or higher and 560° C. or lower for 0.3 hours or more and 3 hours or less;
A quenching treatment step in which all surfaces of the forged product are brought into contact with quenching water for 5 seconds or more and within 60 seconds after the solution treatment step, and quenched in a water bath for 1 minute or more and 30 minutes or less; ,
An aging treatment step of subjecting the forged product after the quenching treatment step to an aging treatment at a heating temperature of 170° C. or higher and 210° C. or lower for 0.5 hours or more and 7 hours or less. Production method.

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