JP7131160B2 - Cold forged material for impeller and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cold forged material made of an aluminum alloy that is processed into rotating bodies such as various impellers and rotors, and a method for manufacturing the same.

Impellers (compressor wheels) and rotors such as turbochargers used in various internal combustion engines have a plurality of thin curved blades arranged radially on the outer peripheral side of a conical rotating shaft so as to form part of a spiral. It is common to have an arranged configuration. In addition, since the impeller of the turbocharger rotates at a high speed at a temperature of about 150° C., it is required to have high strength and rigidity at high temperatures.

In addition, impellers and rotors must be lightweight in order to reduce energy loss, and aluminum alloys are commonly used as materials for these. In particular, when the temperature rises, 2000 series aluminum alloys, which are excellent in high-temperature properties, are used, but it is difficult to sufficiently satisfy the required mechanical properties with only the composition of the aluminum alloy. there is

On the other hand, for example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2016-87624), a continuously cast bar made of an Al-Cu-Mg-based aluminum alloy having a predetermined chemical composition is used as a forging material, and the forming material is A shape having an outer diameter that is larger than the outer diameter of the compressor wheel, including the portion corresponding to the blade portion, and that the outer surface of the portion corresponding to the blade portion has an inclined surface that smoothly expands in diameter from one direction to the other direction along the rotation center axis. Moreover, a flange portion, which serves as a surplus portion for the final product of the compressor wheel, extends outside the outer diameter side end portion of the portion corresponding to the blade portion, and the flange portion is extended from the rotation center axis side to the portion corresponding to the blade portion. A forging stock for a turbocompressor wheel has been proposed in which a metal flow is formed toward the part.

The forged material for a turbo compressor wheel disclosed in Patent Document 1 has particularly high strength in the direction perpendicular to the direction along the axis of rotation of the compressor wheel. When a wheel is manufactured, it has excellent room-temperature strength, high-temperature strength, and rigidity as a whole, and at the same time, it has excellent dynamic balance during high-speed rotation. In particular, it is possible to obtain a compressor wheel having high strength and rigidity of the blade portion.

In addition, in Patent Document 2 (Japanese Patent Application Laid-Open No. 2000-119786), the Al alloy forged material contains Cu: 1.5 to 7.0%, Mg: 0.01 to 2.0%, and the balance is aluminum and unavoidable It is an aluminum alloy consisting of volatile impurities, the microstructure after solution treatment has θ' phase and / or Ω phase, and is composed of equiaxed recrystallized grains with a grain size of 500 μm or less, and has a creep rupture strength of 250 N for 1000 hours. /mm ² or higher and a high-temperature yield strength of 280 N/mm ² or higher for aluminum alloy cold forgings for high-speed dynamic parts.

In the aluminum alloy cold forged material for high-speed moving parts of Patent Document 2, high-temperature characteristics such as creep characteristics and machinability can be combined by making the recrystallized grains substantially constant in size of 500 μm or less. , and.

JP 2016-87624 A JP-A-2000-119786

In the forged material for turbo compressor wheels of Patent Document 1 and the aluminum alloy cold forged material for high-speed moving parts of Patent Document 2, the fine structure is controlled in addition to the composition, but various impellers can be adjusted from room temperature to operating temperature. It is necessary to have sufficient mechanical properties (strength, yield strength and fatigue resistance properties) in , and further increase in strength is required for higher performance. In addition, in cold forging, it is difficult for the portion in contact with the die to flow, and there are cases where a region with a coarse grain size is formed. In particular, when the impeller rotates at a high speed, a large stress is applied to the vane portions, so it is necessary to avoid a reduction in strength due to coarsening of crystal grains in the vane-corresponding portions of the cold forged material.

In view of the problems in the prior art as described above, it is an object of the present invention to have sufficient strength, yield strength, and fatigue resistance at room temperature to operating temperature, and in particular, to have a fine and homogenous structure in the portion corresponding to the blade portion. It is another object of the present invention to provide a high-strength cold forged material for impellers and an efficient manufacturing method thereof.

In order to achieve the above object, the present inventors have extensively studied the composition and structure of aluminum alloy cold forged materials and their manufacturing methods. The inventors have found that imparting deformation (increasing the degree of processing) is extremely effective, and have arrived at the present invention.

That is, the present invention
A cold forged material for an impeller made of an aluminum alloy containing Cu and Mg,
The average grain size of the base material crystal grains in the portion corresponding to the blade portion is 250 μm or less, and does not contain coarse grains with a crystal grain size of 700 μm or more;
To provide a cold forged material for an impeller characterized by:

In the impeller cold forged material of the present invention, solid solution strengthening and precipitation strengthening (precipitation of θ' phase and S' phase) caused by the addition of Cu and Mg improve the tensile properties and creep properties of the aluminum alloy at room temperature and high temperature. Improved properties and high temperature yield strength.

In addition, in the impeller cold forged material of the present invention, the average grain size of the base material crystal grains in the portion corresponding to the blade portion (the portion that will eventually become the blade portion of the impeller) is 250 μm or less, and the crystal grain size is 700 μm. Does not contain coarse grains above. As a result, the strength, yield strength, and fatigue resistance of the portion corresponding to the blade portion can be ensured, and it can be suitably used as a cold forged material for manufacturing an impeller that rotates at high speed. In addition, when the impeller rotates at high speed, a large amount of stress is applied to the impeller blades. However, since the cold forged material for impellers of the present invention has a fine and homogenous structure, such design is easy.

In general cold forging, the portion in contact with the die is less likely to flow, so the crystal grains become coarse due to the lack of strain introduced, and the strength decreases compared to other portions. For example, when cold forging (closed type forging or semi-closed type forging) is performed in a state in which an aluminum alloy formed material is in contact with the upper and lower dies, the outer edge of the cold forged material that corresponds to the blade portion A region with relatively large crystal grains is formed in the region.

On the other hand, in the impeller cold forged material of the present invention, sufficient strain is introduced in the entire region including the outer edge portion corresponding to the blade portion, and the average grain size of the base material crystal grains in the portion corresponding to the blade portion A structure that does not contain coarse grains having a diameter of 250 μm or less and a crystal grain size of 700 μm or more is formed.

In addition, in the cold forged material for impellers of the present invention,
Cu: 2.2 to 3.5% by mass,
Mg: 1.4 to 2.1% by mass,
Fe: 0.9 to 1.5% by mass,
Si: 0.10 to 0.25% by mass,
Ni: 0.9 to 1.5% by mass,
Ti: 0.01 to 0.15% by mass,
It is preferable that the balance be made of an aluminum alloy consisting of Al and inevitable impurities.

In addition, in the cold forged material for impellers of the present invention,
Cu: 5.0 to 7.0% by mass,
Mg: 0.05 to 0.5% by mass,
Fe: 0.05 to 0.35% by mass,
Si: 0.05 to 0.25% by mass,
Ti: 0.01 to 0.15% by mass,
Furthermore,
V: 0.05 to 0.20% by mass,
Mn: 0.05 to 0.70% by mass,
Cr: 0.05 to 0.35% by mass,
Zr: 0.05 to 0.25% by mass, containing one or more of
It is preferable that the balance be made of an aluminum alloy consisting of Al and inevitable impurities.

By having the cold forged material for impellers with these compositions, solid solution strengthening, precipitation strengthening, and strengthening by crystallized substances resulting from the addition of Cu, Mg, etc. improve the tensile properties and Creep characteristics and high temperature yield strength are improved.

Further, in the impeller cold-forged material of the present invention, the average grain size of the base material crystal grains in the blade portion-equivalent portion is preferably 200 μm or less, more preferably 100 μm or less. By setting the average grain size to 200 μm or less, it is possible to reliably develop grain refinement strengthening, and by setting it to 100 μm or less, the strength, yield strength, and fatigue resistance required for the impeller blades are more reliably achieved. can get to

Further, in the impeller cold forged material of the present invention, it is preferable that the tensile strength and 0.2% proof stress in the direction orthogonal to the rotation axis of the impeller are 420 MPa or more and 350 MPa or more, respectively. Sufficient reliability can be imparted to the impeller by setting the tensile strength and 0.2% proof stress in the direction orthogonal to the rotation axis of the impeller to 420 MPa or more and 350 MPa or more, respectively.

In addition, the present invention
a forging step in which one end of a cylindrical aluminum alloy material is brought into contact with a lower die, and the other end of the aluminum alloy material is pressed while being brought into contact with an upper die;
The diameter D of the aluminum alloy material is smaller than the inner diameter d of the inner peripheral surface of the upper die with which the other end abuts;
A method for manufacturing a cold forged material for an impeller characterized by

In general cold forging of aluminum alloy, the diameter of the raw material is made to substantially match the inner peripheral surface of the die. In this case, the material that is in contact with the mold from the beginning hardly flows, and sufficient strain cannot be introduced. As a result, the crystal grains in the region become coarser than the crystal grains in other regions, and the strength and proof stress are lowered. On the other hand, in the method of manufacturing the cold forged material for impellers of the present invention, the diameter of the aluminum alloy material is made smaller than the inner diameter of the mold, and the strain necessary for grain refinement is applied to the entire area of the aluminum alloy material. The most important feature is the introduction of

That is, when trying to homogenize the structure by cold forging a general aluminum alloy, for example, it is necessary to perform cold forging multiple times using different molds, but the cold forging material for impellers of the present invention In this manufacturing method, a sufficiently homogenized microstructure can be obtained by a single cold forging.

Further, in the method for manufacturing the impeller cold forged material of the present invention, the degree of processing obtained from the area (A1) of the circle having the diameter D and the area (A2) of the circle having the inside diameter d: (A2-A1 )/A1×100 is preferably 30% or more.

The degree of processing obtained from the area (A1) of a circle having a diameter D and the area (A2) of a circle having an inner diameter d: (A2-A1)/A1×100 is 30% or more, so that the entire area of the aluminum alloy material It is possible to reliably introduce the strain necessary for refining the grains.

Further, in the method of manufacturing the cold forged impeller material of the present invention, a substantially annular protrusion is formed on the outer periphery of the bottom surface of the upper die with which the aluminum alloy contacts, and the step between the protrusion and the bottom surface is formed. 1 mm or more is preferable.

When the bottom surface of the upper mold that the aluminum alloy material contacts is completely flat, it is difficult to introduce strain into the aluminum alloy material in the vicinity of the flat surface. is difficult. On the other hand, by providing a step of 1 mm or more on the bottom surface of the upper mold, the strain introduced into the aluminum alloy material can be increased, and a homogeneous microstructure can be formed also in the upper part of the cold forged material.

Further, in the method for manufacturing the cold forged material for impellers of the present invention, the aluminum alloy material is
Cu: 2.2 to 3.5% by mass,
Mg: 1.4 to 2.1% by mass,
Fe: 0.9 to 1.5% by mass,
Si: 0.10 to 0.25% by mass,
Ni: 0.9 to 1.5% by mass,
Ti: 0.01 to 0.15% by mass, with the balance being Al and unavoidable impurities.

Further, in the method for manufacturing the cold forged material for impellers of the present invention, the aluminum alloy material is
Cu: 5.0 to 7.0% by mass,
Mg: 0.05 to 0.5% by mass,
Fe: 0.05 to 0.35% by mass,
Si: 0.05 to 0.25% by mass,
Ti: 0.01 to 0.15% by mass,
Furthermore,
V: 0.05 to 0.20% by mass,
Mn: 0.05 to 0.70% by mass,
Cr: 0.05 to 0.35% by mass,
Zr: 0.05 to 0.25% by mass, containing one or more of
It is preferable that the balance be made of an aluminum alloy consisting of Al and inevitable impurities.

By using an aluminum alloy having these compositions, solid solution strengthening, precipitation strengthening, and strengthening due to crystallized substances resulting from the addition of Cu, Mg, etc., improve the tensile properties and creep properties of the impeller at room temperature and high temperature. Yield strength etc. can be improved.

Further, in the method for manufacturing the cold forged material for impellers of the present invention, after the forging step, a solution treatment step, a quenching step and an aging heat treatment step are provided, and the heating temperature in the solution treatment step is set to 500 to 540. ℃, the cooling in the quenching step is preferably water cooling at 80°C or less, and the heating temperature in the aging heat treatment step is preferably 180 to 210°C.

By setting the temperature of the aging heat treatment to 180 ° C. or higher, precipitation strengthening can be efficiently expressed, and by setting it to 210 ° C. or lower, deterioration of strength, yield strength and fatigue resistance due to coarsening of precipitates can be prevented. can be suppressed. In addition, by setting the temperature of the solution treatment to 500 ° C. or higher, the solid solution elements that contribute to precipitation strengthening, such as Cu and Mg, can be sufficiently dissolved in the aluminum. A decrease in strength and ductility of the forged material due to local melting can be suppressed. Further, in order to sufficiently dissolve solid-solution elements such as Cu and Mg that contribute to precipitation strengthening in aluminum, it is necessary to cool rapidly after heating under the conditions. If the temperature exceeds 80°C, the cooling water tends to boil, and a sufficient cooling rate cannot be stably obtained. On the other hand, the effect saturates at about room temperature, so there is no need to lower it below that. If the temperature is lowered more than necessary, quenching strain remains and the machining accuracy during cutting is lowered, so cooling at 20° C. or higher is preferable.

ADVANTAGE OF THE INVENTION According to the present invention, a cold forged material for impellers having sufficient strength, yield strength and fatigue resistance at room temperature and high temperature, and in particular, having a fine and homogenous structure in the parts corresponding to the blades, and efficient production thereof. can provide a method.

1 is a schematic perspective view of a typical impeller; FIG. FIG. 2 is a schematic cross-sectional view of a typical impeller; It is a schematic diagram of the cross section of the general cold forging member for impellers. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the cross section of the cold forged member for impellers of this invention. It is a schematic diagram (before cold forging) which shows an example of the cold forging process in the manufacturing method of the cold forged member for impellers of this invention. It is a schematic diagram (after cold forging) which shows an example of the cold forging process in the manufacturing method of the cold forged member for impellers of this invention. 1 is a photograph of a cross-sectional structure of an aluminum alloy forged material for an impeller obtained in Example 1. FIG. 4 is a photograph of a cross-sectional structure of an aluminum alloy forged material for an impeller obtained in Example 2. FIG. 4 is a photograph of a cross-sectional structure of an aluminum alloy forged material for an impeller obtained in Example 3. FIG. 1 is a photograph of a cross-sectional structure of an aluminum alloy forged material for an impeller obtained in a comparative example. 1 is a schematic diagram showing the shape and size of an aluminum alloy material for upset forging; FIG. It is an appearance photograph of the test piece before and behind upset forging. 1 is a schematic diagram of a tensile test piece used to investigate the effect of grain size on tensile properties; FIG. It is a graph which shows the relationship between a grain size and a tensile property.

Hereinafter, representative embodiments of the aluminum alloy cold forged member for impeller and the manufacturing method thereof according to the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. . In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description may be omitted. Also, since the drawings are for the purpose of conceptually explaining the present invention, the dimensions and ratios of the depicted components may differ from the actual ones.

1. Cold Forged Member for Aluminum Alloy Impeller (1) Structure A perspective view and a sectional view schematically showing a typical impeller are shown in FIGS. 1 and 2, respectively. The impeller 1 has a shaft hole 2 for inserting a shaft for connecting the impeller 1 to the rotor, and is radially inclined on the outer circumference of a substantially conical rotating shaft portion 4 so as to form a part of a spiral. It has a structure in which a plurality of blade portions 6 are integrally formed.

The shape of the impeller 1 can be obtained, for example, by processing an impeller cold-forged member made of an aluminum alloy. In this case, the crystal grain size and its distribution of the impeller 1 basically inherit the state of the impeller cold forged member.

FIG. 3 shows a schematic cross-sectional view of a general cold forged member for impellers, and FIG. 4 shows a schematic cross-sectional view of a cold forged member for impellers according to the present invention. In FIGS. 3 and 4, shaded areas indicate areas where crystal grains are coarser than other areas. A general impeller cold forged member 10 lacks strain in the vicinity of the outer periphery (especially the upper part) that contacts the die during cold forging, so the grain size in this region is remarkable compared to other regions. becomes coarse. Although it depends on the cold forging conditions, regions where the crystal grains are relatively coarse are also formed in the center and on the surface.

On the other hand, in the impeller cold forged member 12 of the present invention, there is no distinct region where the crystal grains are coarse in the vicinity of the outer periphery. A region with relatively coarse crystal grains may be formed on the surface of the central portion, but since this region is removed as the shaft hole 2, the characteristics of the impeller 1 are not affected.

Here, the vanes 6 of the impeller 1 are required to have high strength and rigidity because they are thinned for the purpose of weight reduction and are subjected to a large centrifugal force due to high-speed rotation. In particular, since a larger centrifugal force acts on the tip of the blade portion 6, it is desired to increase the strength of the outermost peripheral portion of the impeller cold forged member processed in this region. The outer periphery of the impeller cold-forged member 12 of the invention has fine grains (there is no region where the grains are coarsened), and high strength is imparted. In FIG. 4, a hatched area indicates a portion 14 corresponding to the blade portion which is finally processed into the blade portion 6. As shown in FIG. That is, the average grain size of the base material crystal grains in the blade portion corresponding portion 14 is 250 μm or less, and coarse grains with a crystal grain size of 700 μm or more are not included.

In the impeller cold-forged member 12 of the present invention, the average grain size of the base material crystal grains in the vane-corresponding portion 14 is preferably 200 μm or less, more preferably 100 μm or less. By setting the average grain size to 200 μm or less, the crystal grain refinement strengthening can be reliably realized, and by setting it to 100 μm or less, the strength, yield strength, and fatigue resistance required for the blade portion 6 of the impeller 1 can be achieved. can be obtained more reliably.

The method for determining the average grain size of the base material crystal grains is not particularly limited, and may be measured by various conventionally known methods. For example, it can be obtained by cutting the impeller cold-forged member 12, observing the resulting cross-sectional sample with an optical microscope or a scanning electron microscope, and calculating the average grain size of the base material crystal grains. In addition, it may be measured by a backscattered electron diffraction measurement device (SEM-EBSD) attached to the scanning electron microscope. The cross-sectional sample may be subjected to mechanical polishing, buffing, electrolytic polishing, etching, or the like depending on the observation method.

In addition, in the impeller cold forged material 12 of the present invention, the tensile strength and 0.2% proof stress in the direction orthogonal to the impeller rotation axis (the central axis of the shaft hole 2) are 420 MPa or more and 350 MPa or more, respectively. It is preferable to be Sufficient reliability can be imparted to the impeller by setting the tensile strength and 0.2% proof stress in the direction orthogonal to the rotation axis of the impeller to 420 MPa or more and 350 MPa or more, respectively. More preferable tensile strength and 0.2% yield strength are 440 MPa or more and 360 MPa or more, respectively, and most preferable tensile strength and 0.2% yield strength are 450 MPa or more and 370 MPa or more, respectively.

In addition, the impeller cold forged material 12 of the present invention contains Cu and Mg. The tensile and creep properties and high temperature yield strength of the aluminum alloy are improved at room temperature and high temperature.

(2) Composition (2-1) Composition 1
The impeller cold forged material 12 contains Cu: 2.2 to 3.5 mass%, Mg: 1.4 to 2.1 mass%, Fe: 0.9 to 1.5 mass%, and Si: 0.10. -0.25% by mass, Ni: 0.9 to 1.5% by mass, Ti: 0.01 to 0.15% by mass, with the balance being Al and unavoidable impurities. . Each component will be described in detail below.

Cu: 2.2 to 3.5% by mass
Cu forms Al—Cu based precipitates and has the effect of increasing mechanical properties and fatigue strength. Moreover, by adding both Cu and Mg and heat-treating, an Al ₂ CuMg compound can be formed and the strength can be increased. If the amount of Cu added is less than 2.2% by mass, the amount of precipitates is insufficient and the target strength cannot be obtained. In addition, if it is added in excess of 3.5% by mass, the Al ₂ Cu and Al ₂ CuMg crystallized substances formed during casting become coarse and remain undissolved during solution treatment, resulting in a decrease in fatigue strength and toughness. Resulting in.

Mg: 1.4-2.1% by mass
By adding Mg together with Cu, it forms an Al ₂ CuMg compound and contributes to the strength. If it is less than 1.4% by mass, sufficient strength required for the impeller cannot be obtained. Further, when the amount of addition exceeds 2.1% by mass, the Al--Cu--Mg crystallized substances remain undissolved during the solution treatment, resulting in a decrease in fatigue strength and toughness. In addition, Mg forms Mg—Si-based precipitates together with Si, and has the effect of increasing mechanical properties and fatigue strength. The effect becomes remarkable at 1.4% by mass or more, but even if it is added in excess of 2.1% by mass, almost no contribution to altitude can be expected, and a coarse intermetallic compound that becomes the starting point of fracture may be formed, and mechanical properties such as toughness may be reduced.

Fe: 0.9 to 1.5% by mass
It is an effective element for forming dispersed particles. Crystallization of the Al--Fe--(Ni)-based compound suppresses the recrystallization of Al and contributes to the improvement of the high-temperature strength. However, if added excessively, it forms a coarse intermetallic compound and lowers the toughness, so the upper limit of the amount added is set to 1.5% by mass.

Si: 0.10 to 0.25% by mass
The addition of Si increases the precipitation density of Al ₂ Cu and Al ₂ CuMg, contributing to strength. These effects become significant at 0.1% by mass or more, and if added in excess of 0.25% by mass, Al-Si-Mg-Cu-based crystallized substances may be formed, which may reduce fatigue strength and toughness. .

Ni: 0.9 to 1.5% by mass
Ni forms high-melting Al--Ni-based crystallized substances and improves heat resistance and high-temperature strength in the vicinity of 200 to 350.degree. The effect becomes remarkable at a content of 0.9% by mass or more, but if a large amount of Ni exceeding 1.5% by mass is contained, a coarse compound is formed and the toughness is lowered.

Ti: 0.01 to 0.15% by mass
Ti forms Al--Ti and Ti--B compounds when combined with B, refines the casting structure, prevents casting cracks, and promotes homogenization of the added elements. These effects are insufficient when less than 0.01% by mass, and when added in an amount exceeding 0.15% by mass, not only the effect is saturated, but also Al-Ti-based coarse crystallized substances are formed, reduce toughness; In addition, by dissolving Ti in Al, the growth of strengthening phases of Al ₂ Cu and Al ₂ CuMg precipitates is suppressed at high temperatures, and high strength can be stably obtained.

(2-2) Composition 2
The impeller cold forged material 12 contains Cu: 5.0 to 7.0% by mass, Mg: 0.05 to 0.5% by mass, Fe: 0.05 to 0.35% by mass, and Si: 0.05. ~0.25% by mass, Ti: 0.01 to 0.15% by mass, and further V: 0.05 to 0.20% by mass, Mn: 0.05 to 0.70% by mass, Cr Zr: 0.05 to 0.35% by mass, Zr: 0.05 to 0.25% by mass, and the balance being Al and inevitable impurities. Each component will be described in detail below, focusing on the differences from Composition 1 above.

Cu: 5.0 to 7.0% by mass
Mg: 0.05 to 0.5% by mass
Compared with composition 1, the amount of Cu added is increased and the amount of Mg added is decreased. By setting the amount of Cu to be added to 5.0% by mass or more, Al—Cu-based precipitates can be formed after the T6 treatment, contributing to strength. On the other hand, if it is added in excess of 7.0% by mass, a large amount of Al—Cu crystallized substances remain after the T6 treatment, resulting in a decrease in toughness. By adding 0.05% by mass or more of Mg, it is possible to promote the formation of Al-Cu(-Mg)-based precipitates after the T6 treatment and contribute to strength, but 0.5% by mass If added in excess, the growth of Al—Cu based precipitates will be accelerated in the high temperature range, so high strength in the high temperature range cannot be stably obtained.

Fe: 0.05 to 0.35% by mass
Si: 0.05 to 0.25% by mass
Ti: 0.01 to 0.15% by mass
The effect of these additive elements is the same as in composition 1.

V: 0.05 to 0.20% by mass
Mn: 0.05 to 0.70% by mass
Cr: 0.05 to 0.35% by mass
Zr: 0.05 to 0.25% by mass
In the aluminum alloy containing the above elements, dispersed particles of Al-Fe(Mn, Cr)-Si system, Al-Mg-Cr-Mn system, Al-Zr system, and Al-V system are formed during homogenization treatment. This suppresses movement of grain boundaries and suppresses recrystallization, which is a so-called pinning effect, and contributes to strength.

2. Method for producing cold forged material for aluminum alloy impeller The method for producing the cold forged member for impeller according to the present invention provides an effective and efficient method for producing the cold forged material for impeller according to the present invention. be.

In the method for manufacturing a cold forged member for an impeller according to the present invention, one end of a cylindrical aluminum alloy material is brought into contact with a lower die, and the other end of the aluminum alloy material is brought into contact with an upper die while pressing. The diameter D of the aluminum alloy material is smaller than the inner diameter d of the inner peripheral surface of the upper die with which the other end abuts.

FIG. 5 (before cold forging) and FIG. 6 (after cold forging) are schematic diagrams showing an example of the cold forging process in the manufacturing method of the cold forged impeller member of the present invention. FIG. 5 shows a state in which a cylindrical aluminum alloy material 30 is brought into contact with a lower die 32 and compressed from above by an upper die 34 . Here, in general cold forging of an aluminum alloy, the diameter D of the aluminum alloy material 30 is substantially the same as the inner diameter d of the inner peripheral surface of the upper die 34 . The lower die 32 is provided with an ejector pin 36 for ejecting the forged product, and the upper die 34 is provided with a punch knockout pin 38 for preventing sticking of the forged product.

On the other hand, in the manufacturing method of the impeller cold forged member of the present invention, the diameter of the aluminum alloy material 30 is smaller than the inner diameter d of the upper die 34 . As a result, the aluminum alloy material 30 is flattened by the compression by the upper die 34 and pressed against the inner diameter d of the upper die 34, so that sufficient strain can be introduced to the vicinity of the outer periphery of the aluminum alloy material 30 as well.

Here, the degree of processing obtained from the area (A1) of the circle having the diameter D of the aluminum alloy material 30 and the area (A2) of the circle having the inner diameter d of the upper mold 34: (A2-A1)/A1×100 = 30 % or more. By setting the workability to 30% or more, it is possible to reliably introduce the strain necessary for refining the crystal grains in the entire area of the aluminum alloy material 30 (especially in the vicinity of the outer periphery). A more preferable working degree is 35% or more, and the most preferable working degree is 50% or more.

Further, in the manufacturing method of the impeller cold forged material of the present invention, a substantially annular protrusion is formed on the outer circumference of the bottom surface of the upper mold 34 with which the aluminum alloy material 30 abuts, and the step between the protrusion and the bottom surface is formed. 1 mm or more is preferable.

When the bottom surface of the upper mold 34 with which the aluminum alloy material 30 abuts is completely flat, it is difficult to introduce strain into the aluminum alloy material 30 in the vicinity of the flat surface, and the crystal grains in the upper part of the cold forged material are uniformly fined. It is difficult to convert On the other hand, by providing a step of 1 mm or more on the bottom surface of the upper mold 34, the strain introduced into the aluminum alloy material 30 can be increased, and a homogeneous fine structure can be formed also in the upper part of the cold forged material. can. In addition, it is more preferable that the step of the bottom surface is 1.3 mm or more, and most preferably 1.5 mm or more.

Further, as shown in FIG. 6, by forging with the punch knockout pin 38 retracted, the strain introduced into the aluminum alloy material 30 can be increased, and the cold forged material has a homogeneous microstructure. can be formed.

Further, in the method for manufacturing the cold forged impeller member of the present invention, the aluminum alloy material 30 is
Cu: 2.2 to 3.5% by mass,
Mg: 1.4 to 2.1% by mass,
Fe: 0.9 to 1.5% by mass,
Si: 0.10 to 0.25% by mass,
Ni: 0.9 to 1.5% by mass,
Ti: 0.01 to 0.15% by mass, with the balance being Al and unavoidable impurities.

Further, in the method for manufacturing the cold forged impeller member of the present invention, the aluminum alloy material 30 is
Cu: 5.0 to 7.0% by mass,
Mg: 0.05 to 0.5% by mass,
Fe: 0.05 to 0.35% by mass,
Si: 0.05 to 0.25% by mass,
Ti: 0.01 to 0.15% by mass,
Furthermore,
V: 0.05 to 0.20% by mass,
Mn: 0.05 to 0.70% by mass,
Cr: 0.05 to 0.35% by mass,
Zr: 0.05 to 0.25% by mass, containing one or more of
It is preferable that the balance is made of an aluminum alloy composed of A1 and inevitable impurities.

The effects of each of these additive elements are as shown in the cold forged member for impellers of the present invention. The strengthening or the like can improve the tensile properties, creep properties, high-temperature yield strength, etc. of the cold forged material 12 for impellers at room temperature and high temperature.

Further, in the method for manufacturing the cold forged member for impeller of the present invention, after the forging step, the solution treatment step, the quenching step and the aging heat treatment step are performed, and the heating temperature in the solution treatment step is set to 500 to 540 ° C. Preferably, the cooling in the quenching step is water cooling at 80°C or less, and the heating temperature in the aging heat treatment step is 180 to 210°C.

By setting the temperature of the aging heat treatment to 180 ° C. or higher, precipitation strengthening can be efficiently expressed, and by setting it to 210 ° C. or lower, deterioration of strength, yield strength and fatigue resistance due to coarsening of precipitates can be prevented. can be suppressed. In addition, by setting the temperature of the solution treatment to 500 ° C. or higher, the solid solution elements that contribute to precipitation strengthening, such as Cu and Mg, can be sufficiently dissolved in the aluminum. A decrease in strength and ductility of the forged material due to local melting can be suppressed.

Although representative embodiments of the present invention have been described above, the present invention is not limited to these, and various design changes are possible, and all such design changes are included in the technical scope of the present invention. be

<<Example 1>>
An aluminum alloy having the composition shown in Table 1 and the balance being Al and unavoidable impurities was extruded at a billet temperature of 360° C. and an extrusion rate of 3 m/min to obtain an extruded bar with a diameter of 32 mm. Thereafter, the extruded bar was held at 415° C. for 2 hours and then cooled to room temperature at a cooling rate of 25° C./h to obtain an aluminum alloy material for forging with a material diameter of 32 mm. In addition, the components shown in Table 1 are expressed in mass%.

Using a forging die (upper die) with a minimum forging diameter of 39.5 mm, the obtained aluminum alloy material for forging was forged once to obtain an aluminum alloy forged material. In the forging, the diameter of the aluminum alloy material for forging is 32 mm and the minimum forging diameter is 39.5 mm, so the workability is 52%. A substantially annular convex portion was formed on the outer periphery of the bottom surface of the upper die with which the aluminum alloy material for forging abuts, and the step between the convex portion and the bottom surface was set to 1.5 mm.

Next, the aluminum alloy forged material was held at 525° C. for 2 hours (solution treatment), water-cooled at 25° C., and held at 197° C. for 12 hours (aging treatment) to obtain an impeller aluminum alloy forged material. FIG. 7 shows a photograph of the structure of the cross section of the obtained aluminum alloy forged material for impellers. The structure of the blade-corresponding portion (the region corresponding to the blade-corresponding portion 14 in FIG. 4), which will become the impeller blade portion after cutting, is fine and homogeneous, and does not contain coarse crystal grains of 700 μm or more. I understand.

When the average grain size of the portion corresponding to the blade portion was obtained by using the intersection line method in the X direction and the Y direction shown in FIG. 7, it was 16 μm in the X direction and 15 μm in the Y direction. Further, it can be seen that the refinement and homogenization of the structure are progressing also in the vicinity of the upper portion of the aluminum alloy forging material for an impeller, which is in contact with the bottom surface of the mold having a step.

A tensile test piece having a parallel portion width of 5 mm, a thickness of 2 mm, and a length of 20 mm was cut out from the dotted frame area shown in FIG. When the tensile properties of the tensile test piece were evaluated, it was found to be tensile strength: 448 MPa, 0.2% yield strength: 376 MPa, and elongation: 8.4%.

<<Example 2>>
An aluminum alloy forged material for an impeller was obtained in the same manner as in Example 1, except that the diameter of the extruded bar and the aluminum alloy material for forging was set to 34 mm, and the step between the bottom surface of the upper die and the convex portion was set to 1.35 mm. In the forging, since the diameter of the aluminum alloy material for forging is 34 mm and the minimum forging diameter is 39.5 mm, the workability is 35%.

FIG. 8 shows a photograph of the structure of the cross section of the obtained aluminum alloy forged material for impellers. The structure of the blade-corresponding portion (the region corresponding to the blade-corresponding portion 14 in FIG. 4), which will become the blade portion of the impeller after cutting, is fine and homogeneous, and does not contain coarse crystal grains of 700 μm or more. I understand.

When the average grain size of the portion corresponding to the blade portion was obtained by using the intersection line method in the X direction and the Y direction shown in FIG. 8, it was 16 μm in the X direction and 16 μm in the Y direction. Further, it can be seen that the refinement and homogenization of the structure are progressing also in the vicinity of the upper portion of the aluminum alloy forging material for an impeller, which is in contact with the bottom surface of the mold having a step. In addition, since the steps are smaller than in Example 1, the crystal grains are slightly large.

<<Example 3>>
An aluminum alloy having the composition shown in Table 2 and the balance being Al and unavoidable impurities was extruded at a billet temperature of 360° C. and an extrusion speed of 6 m/min to obtain an extruded bar with a diameter of 36 mm. Thereafter, the extruded bar was held at 415° C. for 2 hours and then cooled to room temperature at a cooling rate of 25° C./h to obtain an aluminum alloy material for forging with a material diameter of 36 mm. In addition, the components in Table 2 are shown in mass %.

Using a forging die (upper die) with a minimum forging diameter of 46 mm, the obtained aluminum alloy material for forging was forged once to obtain an aluminum alloy forged material. In the forging, since the diameter of the aluminum alloy material for forging is 36 mm and the minimum forging diameter is 46 mm, the workability is 63%. A substantially annular convex portion was formed on the outer periphery of the bottom surface of the upper die with which the aluminum alloy material for forging abuts, and the step between the convex portion and the bottom surface was set to 1.5 mm.

Next, the aluminum alloy forged material was held at 530° C. for 2 hours (solution treatment), cooled with water at 25° C., and held at 180° C. for 6 hours (aging treatment) to obtain an impeller aluminum alloy forged material. FIG. 9 shows a photograph of the structure of the cross section of the obtained aluminum alloy forged material for impellers. The structure of the blade-corresponding portion (region corresponding to the blade-corresponding portion 14 in FIG. 4), which will become the blade portion of the impeller after cutting, is fine (250 μm or less) and homogeneous, and coarse crystal grains of 700 μm or more are absent. I know it's not included. In addition, the structure is becoming finer and more homogenous in the vicinity of the upper portion of the aluminum alloy forging material for impellers, which is in contact with the stepped bottom surface of the die.

A tensile test piece having a parallel portion width of 5 mm, a thickness of 2 mm, and a length of 20 mm was cut out from the dotted frame area shown in FIG. When the tensile properties of the tensile test piece were evaluated, it was found to be tensile strength: 455 MPa, 0.2% yield strength: 362 MPa, and elongation: 12.1%.

≪Comparative example≫
An extruded rod with a diameter of 39 mm extruded from the alloy component billet shown in Table 1 was used as a forging material, and forging was performed in a flat state without removing a step between the bottom surface of the upper mold and the convex portion. The extrusion conditions before forging, the annealing conditions, and the T6 treatment conditions after forging were the same as in Example 1 to obtain an aluminum alloy forged material for an impeller. In the forging, the diameter of the aluminum alloy material for forging is 39 mm, and the minimum forging diameter is 39.5 mm. The diameter of the aluminum alloy material for forging is made slightly smaller than the minimum forging diameter to the extent that the material can be inserted.The workability is 3%.).

FIG. 10 shows a photograph of the structure of the cross section of the obtained aluminum alloy forged material for impellers. Coarse grains are contained in the vane-corresponding portion (the area corresponding to the vane-corresponding portion 14 in FIG. 4), which will become the vane portion of the impeller after cutting, and has an inhomogeneous structure. Further, in the vicinity of the upper portion of the impeller aluminum alloy forged material that abuts against the substantially planar die bottom surface, the refinement and homogenization of the structure have not progressed.

When the average grain size of the portion corresponding to the blade portion was obtained by using the intersection line method in the X direction and the Y direction shown in FIG. 10, it was 208 μm in the X direction and 2066 μm in the Y direction.

<<Effect of grain size on tensile properties>>
In order to confirm the effect of grain size on tensile properties, upset forging was performed on aluminum alloys having the compositions shown in Table 1 under various forging conditions. Specifically, an aluminum alloy material for forging having the shape and size shown in FIG. 11 was subjected to cold forging in which the forging direction was the LT direction and both ends were restrained. Fig. 12 shows the appearance of the test piece before and after cold forging.

Next, the aluminum alloy forged material was held at 525° C. for 2 hours (solution treatment), cooled with water, and held at 200° C. for 10 hours (aging treatment) to obtain an aluminum alloy forged material for evaluation. The average crystal grain size in the L direction was determined by observing the structure of the central portion of the aluminum alloy forging material for evaluation, and a tensile test piece shown in FIG. 13 was cut out from the region to evaluate the tensile properties. The results obtained are shown in FIG.

When the grain size becomes smaller than 250 μm, the tensile strength increases, and particularly when the grain size becomes smaller than 100 μm, a remarkable increase is observed. In addition, it can be seen that the 0.2% yield strength clearly increases when the crystal grain size becomes smaller than 100 μm.

1... impeller,
2... Shaft hole,
4 ... rotating shaft part,
6... feather part,
10 General cold forged members for impellers,
12 ... Cold forged member for impeller of the present invention,
14 . . . A portion corresponding to the blade portion
30... Aluminum alloy material,
32 Lower die,
34 Upper die,
36 Ejector out pin,
38 Punch knockout pin.

Claims (3)

A cold forged material for an impeller made of an aluminum alloy containing Cu and Mg,
The average grain size of the base material crystal grains in the portion corresponding to the blade portion is 250 μm or less, and does not contain coarse grains with a crystal grain size of 700 μm or more,
The cold forged material for the impeller is
Cu: 2.2 to 3.5% by mass,
Mg: 1.4 to 2.1% by mass,
Fe: 0.9 to 1.5% by mass,
Si: 0.10 to 0.25% by mass,
Ni: 0.9 to 1.5% by mass,
Ti: 0.01 to 0.15% by mass,
An aluminum alloy with the balance being Al and unavoidable impurities, or
Cu: 5.0 to 7.0% by mass,
Mg: 0.05 to 0.5% by mass,
Fe: 0.05 to 0.35% by mass,
Si: 0.05 to 0.25% by mass,
Ti: 0.01 to 0.15% by mass,
Furthermore,
V: 0.05 to 0.20% by mass,
Mn: 0.05 to 0.70% by mass,
Cr: 0.05 to 0.35% by mass,
Zr: 0.05 to 0.25% by mass, containing one or more of
Made of an aluminum alloy with the balance being Al and inevitable impurities,
Tensile strength and 0.2% proof stress in the direction orthogonal to the rotation axis of the impeller are 420 MPa or more and 350 MPa or more, respectively;
A cold forged material for impellers characterized by The average grain size of the base material crystal grains in the portion corresponding to the blade portion is 200 μm or less,
The cold forged material for impellers according to claim 1, characterized by: The average grain size of the base material crystal grains in the portion corresponding to the blade portion is 100 μm or less,
The cold forged material for impellers according to claim 1, characterized by:

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