JP2016087624A - Forging material for turbo compressor wheel made of aluminum alloy and manufacturing method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for a turbo compressor wheel that can be made into a turbo compressor wheel which is excellent in high temperature strength, rigidity, and dynamic balance and has optimal performances corresponding to different properties requested for respective parts.SOLUTION: A forging material for a turbo compressor wheel consists of a continuous casting rod material which is made of Al-Cu-Mg-based aluminum alloy of predetermined component composition. A shaped material form of the forging material including an impeller vane part corresponding portion is larger than the outer diameter of a compressor wheel. An outer face of the impeller vane part corresponding portion has a slope face smoothly expanding in diameter from one end to the other end in a direction along the rotation center axis. The shaped material form of the forging material includes: a flange part, which becomes an excess part when the compressor wheel is completed, and extends outside of the outer diameter side end in the impeller vane part corresponding portion; and metal flows formed from the rotation center axis to the flange part.SELECTED DRAWING: Figure 4A

Description

  The present invention relates to an aluminum alloy turbocompressor wheel forged shape material used for a turbocharger used in an internal combustion engine of a transport device such as an automobile, and a method for producing the forged shape material for the turbocompressor wheel. It is about.

  As is well known, a turbocharger used in an internal combustion engine for transportation equipment has a compressor wheel (also referred to as an impeller) that is coupled to a turbine that rotates by a pressure of exhaust gas through a connecting shaft. Is sent to the compressor housing to compress the air, and this compressed air is sent into the combustion chamber to improve the combustion efficiency of the internal combustion engine, thereby improving the output of the internal combustion engine and purifying the exhaust gas. Such a turbocharger is usually divided into a turbine side (exhaust gas) and a compressor side (intake side), and a heat insulating bearing is arranged between them. On the compressor side, a compressor wheel is arranged in the center of the compressor housing.

  The compressor wheel of such a turbocharger device has a plurality of curved thin blade portions (blade portions) for scavenging air radially and one side of a spiral on the outer peripheral side of a rotating shaft portion that is generally conical. In general, the parts are arranged so as to form parts. And the compressor wheel is arrange | positioned in the center part of the housing which has a snail-shaped spiral tube.

  About a typical example of a compressor wheel, an example of the outline of the basic shape is shown in FIGS.

1 to 3, the compressor wheel 1 is radially and spirally provided on the outer peripheral side of a substantially conical rotating shaft portion 3 having a shaft hole 2 for press-fitting a shaft connected to a turbine rotor (not shown). A plurality of blade portions 4 inclined so as to form a part are integrally formed. Here, the end portion on the small diameter side of the rotating shaft portion 3 is a boss portion 5 protruding from the end portion of the blade portion 4. Further, the outer edge portion of the rotating shaft portion 3 (except mainly in the vicinity of the boss portion 5 on one end side of the rotating shaft portion 3) corresponds to a blade root portion 7 continuous with the base end of the blade portion 4. In FIG. 1 and FIG. 3, the white arrow 9 indicates the direction of air flow when incorporated in the compressor. Here, among the edge portions of the blade portion 4, it is inclined in a twisted curved shape (relative to the rotation center axis O) between the air intake side edge portion 4B on the air intake side and the air discharge side edge portion 4C. 4A is an edge portion that forms a gap (so-called tip clearance) with the compressor housing. In this specification, the portion 4A is referred to as a tip edge. Part.
In an actual compressor wheel, it is normal that a finer shape is given to each part or fine convex parts and concave parts other than the above are formed, but here only basic parts are shown, and details are shown. The shape is omitted. In addition, in the case of a turbocharger compressor wheel in a transportation device such as an automobile, the overall dimensions thereof are, for example, a maximum outer diameter of about 30 to 150 mm with respect to the rotation axis O, and a direction along the rotation axis O. The maximum length is often about 20 to 100 mm.

  By the way, a turbocharger compressor wheel is required to have high temperature, high strength and high rigidity at a high speed exceeding 10,000 rpm at a high temperature of about 150 ° C., and at the same time, it is lightweight to reduce energy loss. It is necessary to be. In addition, in order to withstand high-speed rotation, it is also required that the dynamic balance during high-speed rotation is good, and therefore that it has a uniform density in the circumferential direction (rotation direction).

  In addition, in the compressor wheel, it is effective to increase the efficiency by increasing the temperature of the compressed air, and to transfer the heat from the turbine side to the compressed air, so that the heat dissipation (thermal conductivity) is good. desired.

  Further, considering each part of the compressor wheel, the blade part 4 is required to be thin (usually less than 1 mm thick) in order to ensure lightness. Therefore, it is required that the blade portion 4 is not easily deformed by high-speed rotation, and therefore, the high-temperature strength and rigidity of the blade portion 4 are required. In particular, the tip portion, particularly the tip edge portion of the blade portion 4 is extremely Usually, it is thin, and a particularly large centrifugal force acts on the maximum diameter part of the tip part due to high-speed rotation when used as a compressor. Therefore, high-temperature strength and rigidity are sufficient in that part. It is desirable to be high. On the other hand, the blade root portion (portion continuing from the rotating shaft portion 3 to the blade portion 4) 7 is a portion where stress is concentrated during rotation, and therefore, durability and reliability for continuous use at high speed rotation are ensured. In order to satisfy it, notch fatigue strength is required to be high. The rotating shaft portion 3 is a portion that supports a plurality of blade portions 4, and when assembling the turbocharger, the shaft is usually press-fitted into the shaft hole 2 of the rotating shaft portion 3, where the rotating shaft It is desired that the portion 3 is much thicker than the blade portion, and that the boss portion 5 on the one end side of the rotating shaft portion 3 has good strength and elongation so that cracking does not occur when the shaft is press-fitted. .

  Thus, the compressor wheel as a whole has high strength and high rigidity at high temperatures, excellent dynamic balance and light weight at high speed rotation, and at the same time, the function of each part, different shape and thickness It is desirable that each part has different characteristics depending on the situation.

  In addition, as a material for a conventional turbocharger compressor wheel, an aluminum alloy is generally used from the viewpoints of lightness, thermal conductivity, and workability, among the required characteristics as described above.

  Conventionally, this type of aluminum alloy compressor wheel has been cast directly from a molten aluminum alloy by a casting method called a lost wax method (also called a precision casting method). It has been usual to finish the compressor wheel by appropriately finishing the material such as cutting (for example, Patent Document 1).

  On the other hand, as a method of manufacturing a rotating body such as a compressor wheel of a turbocharger, an extruded material (extruded billet) of an aluminum alloy is used as a raw material, and the extruded billet is subjected to a forging process to obtain a forged base material, and further cutting There has also been proposed a method of finishing by adding (for example, Patent Document 2).

  In addition, in Patent Document 3, as in Patent Document 2, it is assumed that a rotating body such as a compressor wheel of a turbocharger is obtained from an aluminum alloy material by forging. In that case, in the forging process, A method has been proposed in which forging is performed uniformly uniformly, that is, forging is performed in three directions to obtain a forged raw material having no dead zone portion and having a metal flow portion substantially uniformly.

JP 2005-206927 A JP 2006-305629 A JP 2000-197943 A

  However, the turbocharger compressor wheel has a thick portion around the shaft hole (rotating shaft portion) and a thin portion radially extending from the thick portion (blade portion) as described above. In particular, the blade portion is extremely thin with a thickness of less than 1 mm at the tip portion, and has a special twisted curved surface. When the molten aluminum alloy is poured into the lost wax mold, the molten aluminum alloy does not sufficiently turn around the thin wall part, so internal defects such as porosity and oxides occur in the thin wall part, and fine shaped parts are formed. In many cases, it cannot be formed accurately. For this reason, the dimensional accuracy and strength of the thin blade portion and the blade root portion are lowered, and as a result, there is a problem that the dynamic balance at high speed rotation as the compressor wheel is deteriorated and the yield of non-defective products is lowered. In addition, when producing a compressor wheel by precision casting, it is necessary to select the component composition mainly from the viewpoint of molten metal flow during casting, as a raw material aluminum alloy. In many cases, various properties, particularly high-temperature strength and rigidity, cannot always be satisfied. Furthermore, as shown in Patent Document 1, when manufactured by a precision casting method, it is usually a uniform structure as a whole, and it is therefore difficult to satisfy all the different requirements for each part of the compressor wheel.

  On the other hand, as shown in Patent Document 2, in a compressor wheel obtained by forging using an extruded material as a raw material, the extruded material has a fibrous structure extending long along the extrusion direction. When viewed in a cross section perpendicular to the extrusion direction, it has a substantially uniform structure in the radial direction (structure with a substantially uniform particle diameter in the radial direction). The maximum diameter portion that is included usually has a substantially homogeneous structure in the radial direction when viewed in a cross section orthogonal to the central axis of rotation of the compressor wheel. In other words, this means that the different characteristics desired for each part of the compressor wheel cannot be fully satisfied.

  Furthermore, as shown in Patent Document 3, even when forging in three directions, a uniform structure is obtained as a whole. Therefore, it is difficult to sufficiently satisfy different characteristics desired for each part of the compressor wheel. It was. In this case, although a generally homogeneous structure can be obtained, the structure is not necessarily uniform in the circumferential direction on the basis of the rotation center position of the compressor wheel because of forging from different directions over three stages. There is a risk that the product will be inferior in dynamic balance during high-speed rotation of the compressor wheel.

  The present invention has been made against the background of the above circumstances, and is generally excellent in high-temperature strength and rigidity, and at the same time excellent in dynamic balance during high-speed rotation, and according to different required characteristics and desired characteristics for each part. Aluminum alloy compressor wheel shape material that can produce a compressor wheel with optimum performance, especially the diametric strength in the plane perpendicular to the rotation center axis of the compressor wheel, and the tip of the blade tip It is an object of the present invention to provide a compressor wheel shaped material having a high strength and to provide a method capable of actually producing the compressor wheel shaped material.

In order to solve the above-mentioned problems, the present inventors have conducted various experiments and studies on the aluminum alloy turbo compressor wheel shaped material, and as a result, the material is a continuous casting rod, that is, by rapid solidification continuous casting. By using the obtained cast bar, hot forging, especially hot sealed forging or hot semi-sealed forging, to obtain a raw material (forged raw material), and the composition of the material aluminum alloy The shape of the base material (forged base material) is adjusted to the outer periphery of the part corresponding to the blade part of the compressor wheel (the part corresponding to the blade part) with respect to the outer shape of the compressor wheel of the final product. Forged so that the flange part that will be the surplus part is formed, and the metal flow toward the surplus part from the rotation center axis side of the compressor wheel to the blade part equivalent part Be formed has been found to be optimal.
And from these knowledge, it came to the invention about the forge shape material for turbocompressor wheels made from aluminum alloy, and the invention about the manufacturing method of the forge shape material.

Therefore, the forged material for turbocompressor wheels made of aluminum alloy according to the basic aspect (first aspect) of the present invention is:
Aluminum alloy obtained by hot forging by closed die forging or semi-sealed die forging so that the forging pressure direction is along the casting direction of the raw material and the rotation center axis direction of the compressor wheel Forged material for turbo compressor wheel made of
The aluminum alloy of the material is mass%, Si: 0.05 to 0.3%, Cu: 3.0 to 5.5%, Mg: 1.1 to 2.4%, Fe: 0.8 to Including 1.3%, Mn: 0.1-0.4%, Ni: 0.7-2.8%, Zr: 0.05-0.3%, Ti: 0.005-0.06% The remainder consists of Al and inevitable impurities,
The shape of the base material is larger than the outer diameter shape of the compressor wheel including the portion corresponding to the blade portion of the compressor wheel, and the outer surface of the portion corresponding to the blade portion is from one side in the direction along the rotation center axis to the other. It has a shape having an inclined surface that is smoothly expanded toward the side,
And the flange part used as the surplus part with respect to the final product of a compressor wheel is extended to the radial direction outer side on the basis of the said rotation center axis line rather than the outer diameter side edge part in a blade | wing part equivalent part, and the said blade | wing part equivalent part Is characterized in that a metal flow from the rotation center axis side toward the flange portion is formed.

Further, the forged material for turbocompressor wheel made of aluminum alloy according to the second aspect of the present invention,
In the forged material for turbo compressor wheel made of aluminum alloy of the first aspect,
The inclined surface is a surface corresponding to a virtual curved surface including chip edge portions of a large number of blade portions of the compressor wheel.

Furthermore, the forged material for turbocompressor wheels made of aluminum alloy according to the third aspect of the present invention is:
In the forged material for turbo compressor wheel made of aluminum alloy of the second aspect,
Among the metal flows corresponding to the blade portions, at least the metal flow immediately below the inclined surface is along a virtual curved surface including the chip edge portions of the plurality of blade portions.

Furthermore, the forged material for turbocompressor wheels made of aluminum alloy according to the fourth aspect of the present invention is:
In the forged material for turbo compressor wheel made of aluminum alloy according to any one of the first to third aspects,
The height in the direction along the rotation center of the material is h, and the height at the position where the height in the direction along the rotation center is the highest in the blade equivalent portion of the forged raw material is b,
The upsetting rate U is {(h−b) / h} × 100 (%),
The upsetting ratio U is hot forged so as to be within a range of 40 to 80%.

Furthermore, the forged material for turbocompressor wheel made of aluminum alloy of the fifth aspect of the present invention,
In the forged material for turbo compressor wheel made of aluminum alloy according to any one of the first to fourth aspects,
The total volume of the forged material is V1, and the volume of the portion including the entire flange portion outside the radial tip position of the blade portion-corresponding portion is V2, and {V2 / (V1 + V2)} × 100 ( %) Is a volume ratio VR, and the volume ratio VR is in a range of 50% or more and less than 80%.

In addition, the forged material for turbocompressor wheels made of aluminum alloy according to the sixth aspect of the present invention,
In the forged material for turbo compressor wheel made of aluminum alloy according to any one of the first to fifth aspects,
The average thickness of the flange portion in the direction along the rotation center is a, and the height of the portion corresponding to the blade portion in the direction along the rotation center is b, and the aperture height The ratio SR is a / b,
The aperture height ratio SR is in the range of 10/40 to 30/40.

  Moreover, each following aspect is an aspect about the manufacturing method of the forge shape material for turbocompressor wheels made from an aluminum alloy.

That is, the method for producing a forged material for turbocompressor wheels made of aluminum alloy according to the seventh aspect of the present invention includes:
In mass%, Si: 0.05 to 0.3%, Cu: 3.0 to 5.5%, Mg: 1.1 to 2.4%, Fe: 0.8 to 1.3%, Mn: 0.1 to 0.4%, Ni: 0.7 to 2.8%, Zr: 0.05 to 0.3%, Ti: 0.005 to 0.06%, the balance being Al and inevitable Using aluminum alloy continuous cast bar made of impurities as a raw material, the material is formed by closed die forging or semi-sealed die forging so that the forging pressurization direction is along the casting direction of the raw material and along the rotation center axis direction of the compressor wheel. Hot forging, and as a forging finish, it has a forging process to obtain a forging material for turbo compressor wheel,
In the forging process, the shape of the forged material after forging is a shape larger than the outer diameter shape of the compressor wheel including the portion corresponding to the blade portion of the compressor wheel, and the outer surface of the portion corresponding to the blade portion is , In order to form a shape having an inclined surface that is smoothly expanded in diameter from one side in the direction along the rotation center axis toward the other side, and more than the outer diameter side end portion in the blade portion-corresponding portion. Forging so that the flange part that becomes the surplus part for the final product of the compressor wheel is extended radially outward with respect to the rotation center axis line,
It is characterized in that a forged material is obtained in which a metal flow from the rotation center axis side toward the flange portion is formed at the blade portion-corresponding portion.

Moreover, the manufacturing method of the forging shape material for turbocompressor wheels made of aluminum alloy according to the eighth aspect of the present invention is as follows.
In the method for producing a forged material for an aluminum alloy turbo compressor wheel according to the seventh aspect,
In the forging step, forging so that at least the metal flow immediately below the inclined surface of the metal flow corresponding to the blade portion corresponds to a virtual curved surface including chip edge portions of a large number of blade portions of the compressor wheel. Features.

Furthermore, the manufacturing method of the forging shape material for turbocompressor wheels made of aluminum alloy according to the ninth aspect of the present invention,
In the method for producing a forged material for an aluminum alloy turbo compressor wheel according to any of the seventh and eighth aspects,
In the forging step, the height of the raw material in the direction along the rotation center is h, and the height in the direction along the rotation center in the portion corresponding to the blade portion of the forged raw material is the height at the highest position. And b
The upsetting rate U is {(h−b) / h} × 100 (%),
Hot forging is performed so that the upsetting rate U is within a range of 40 to 80%.

Furthermore, the method for producing a forged material for an aluminum alloy turbo compressor wheel according to the tenth aspect of the present invention comprises:
In the method for producing a forged material for an aluminum alloy turbo compressor wheel according to any one of the seventh to ninth aspects,
In the forging step, the entire volume of the forged raw material is V1, and the volume of the portion including the entire flange portion outside the radial tip position of the blade portion-corresponding portion is V2, and (V2 / V1) Forging is performed so that the volume ratio VR is in the range of 50% or more and less than 80%, where the value of x100 (%) is the volume ratio VR.

Furthermore, the method for producing a forged material for an aluminum alloy turbo compressor wheel according to the eleventh aspect of the present invention comprises:
In the method for producing a forged material for an aluminum alloy turbo compressor wheel according to any one of the seventh to tenth aspects,
In the forging step, a is an average thickness in the direction along the rotation center in the flange portion, and b is a height at a position where the height in the direction along the rotation center in the blade portion-corresponding portion is the highest. And the aperture height ratio SR is (a / b) × 100 (%),
Forging is performed so that the drawing height ratio SR is within a range of 10/40 to 30/40.

Furthermore, the method for producing a forged material for an aluminum alloy turbo compressor wheel according to the twelfth aspect of the present invention,
In the method for producing a forged material for an aluminum alloy turbo compressor wheel according to any one of the seventh to eleventh aspects,
In the forging step, the material temperature during forging is set within a range of 350 to 450 ° C.

  The aluminum alloy turbocompressor wheel forging material according to the present invention is excellent in normal temperature strength, high temperature strength, and rigidity, and in particular, a direction (LT direction) perpendicular to a direction (L direction) along the rotation center axis of the compressor wheel. ) Is strong, and if a turbocharger compressor wheel is manufactured using the forged material, it has excellent room temperature strength, high temperature strength and rigidity as well as excellent dynamic balance during high-speed rotation. Compressor wheel Compressor wheel with optimum performance according to different required characteristics and desired characteristics of each part, especially high blade strength and rigidity (especially strength and rigidity of blade tip (tip edge)) Can be obtained. Further, according to the method for producing a forged material for turbo compressor wheel of the present invention, the forged material for compressor wheel having such excellent performance can be practically produced.

It is a perspective view which shows roughly an example of the compressor wheel for turbochargers. It is a top view of the compressor wheel shown by FIG. It is a longitudinal cross-sectional view in the III-III line in FIG. An example of a forged material for an aluminum alloy turbo compressor wheel according to the present invention, in particular, an example of a longitudinal cross-sectional shape of a forged material formed by hot-sealing forging, is used as a longitudinal cross-sectional shape of a final compressor wheel. It is a schematic diagram shown correspondingly. Another example of an aluminum alloy turbo compressor wheel forged material according to the present invention, in particular, an example of a longitudinal cross-sectional shape of a forged material formed by hot semi-hermetic forging, a longitudinal section of the final product compressor wheel It is a schematic diagram shown corresponding to a surface shape. It is a schematic diagram which shows an example of the structure | tissue of the longitudinal cross section along the casting direction in the continuous cast bar used as a raw material for forging in this invention. It is a schematic diagram which shows an example of the structure of the cross section orthogonal to the casting direction in the continuous casting bar | burr used as a raw material for forging in this invention. It is a schematic diagram which shows an example of the structure of the longitudinal cross section along the extrusion direction in the extrusion material of the extrusion material of the forging material regarding the conventional method using an extrusion material as a forging material. It is a flowchart which shows an example of the process which manufactures the turbo compressor wheel by applying the manufacturing method of the forge shape material for turbo compressor wheels of this invention. It is a schematic diagram which shows the 1st example of the cross-sectional shape of the forge shape material for turbo compressor wheels of this invention. It is a schematic diagram which shows the 2nd example of the cross-sectional shape of the forge shape material for turbo compressor wheels of this invention. It is a schematic diagram which shows the 3rd example of the cross-sectional shape of the forge shape material for turbo compressor wheels of this invention. It is a rough solution figure which shows the 4th example of the cross-sectional shape of the forge shape material for turbo compressor wheels of this invention. It is a schematic diagram which shows the cross-sectional shape of an example of the raw material for forging (continuous casting rod) used for manufacture of the forge shape material for turbo compressor wheels of this invention. It is a longitudinal cross-sectional view which shows an example of the closed forging die for carrying out the hot sealed die forging of the forge shape material of the 1st example shown in FIG. 9 in the state where an upper die is a top dead center position. It is a longitudinal cross-sectional view which shows an example of the closed forging die for carrying out the hot closed die forging of the forge shape material of the 1st example shown in FIG. 9 in the state in which an upper mold | type is a bottom dead center position. It is a longitudinal cross-sectional view which shows an example of the semi-sealing forging die for carrying out the hot semi-sealing die forging of the forge shape material of the 2nd example shown in FIG. 10 in the state in which an upper die is a top dead center position. It is a longitudinal cross-sectional view which shows an example of the semi-sealing forging die for carrying out the hot semi-sealing die forging of the forge shape material of the 2nd example shown in FIG. 10 in the state in which an upper die is a bottom dead center position. It is a schematic diagram which shows the metal flow by the hot die closed forging about the 1st example shown in FIG. It is a schematic diagram which shows the metal flow by the semi-hermetic forging between hot about the 2nd example shown in FIG. It is a schematic diagram which shows the metal flow by hot sealed die forging about the 3rd example shown in FIG. 11 in the longitudinal cross-section position in a forge finishing material. It is a schematic diagram which shows the metal flow by hot sealed die forging about the 4th example shown in FIG. 12 in the longitudinal cross-section position in a forging finished material. It is a graph which shows the relationship between the upsetting rate U and the intensity | strength of the LT direction of a forging raw material in the closed die forging in order to obtain the forging raw material for a compressor wheel. For comparison with the present invention, it is a schematic view showing a metal flow in a case where an extruded material is used as a shaped member for a compressor wheel without forging, in a longitudinal sectional position corresponding to the sectional shape of the compressor wheel of the product. For comparison with the present invention, it is a schematic view showing the metal flow of the forged material when it is upset and forged into a simple disk shape, corresponding to the sectional shape of the compressor wheel of the product, in the longitudinal sectional position.

  Hereinafter, embodiments of the aluminum alloy turbocompressor wheel forged raw material and the manufacturing method thereof according to the present invention will be described in detail. Note that the embodiments described below are merely examples, and the present invention is of course not limited to these embodiments.

  First, in the present invention, an aluminum alloy used as a material (forging material) of a forging material for a turbo compressor wheel will be described.

[Material aluminum alloy]
In the present invention, the aluminum alloy to be used is basically an Al—Cu—Mg alloy, but the Al—Cu—Mg alloy to be used in the present invention is an Al alloy that has been conventionally used for forging. The component composition is different from that of a -Cu-Mg alloy, that is, a so-called 2000 series standard alloy, for example, A2618 alloy.
Specifically, in terms of mass%, Si: 0.05 to 0.3%, Cu: 3.0 to 5.5%, Mg: 1.1 to 2.4%, Fe: 0.8 to 1. 3%, Mn: 0.1 to 0.4%, Ni: 0.7 to 2.8%, Zr: 0.05 to 0.3%, Ti: 0.005 to 0.06%, the balance Uses an alloy of Al and inevitable impurities. In this alloy, in addition to the above-mentioned essential component elements, the content of component elements or impurity elements added as necessary shall be regulated to 0.1% or less, respectively, and to 2.0% or less in total. Is desirable.

  If it is an alloy of such a component composition, it is important in the present invention by hot forging so that a surplus portion is positively formed by closed die forging or semi-sealed die forging as described later, It becomes possible to reliably obtain a forged material having a predetermined metal flow, and as a result, the strength in the direction orthogonal to the rotation center axis of the compressor wheel (so-called LT direction) is sufficiently high, and the tip of the blade portion It is possible to obtain a compressor wheel having high strength (particularly the tip edge portion). In addition, the alloy composition is adjusted as described above and at the same time the continuous cast bar is used as the forging material. As will be described later, the forging material is subjected to rapid solidification by continuous casting (here, the cast structure). ). Therefore, it is also excellent in terms of room temperature strength, high temperature strength, rigidity, fatigue strength, notch sensitivity, and the like, and also from these points, it is excellent as a material for a shape member for a compressor wheel.

  The reason why the component composition of the material aluminum alloy is defined as described above is as follows.

Si:
Si is distributed as eutectic Si in the matrix, improves the rigidity, and coexists with Mg to precipitate Mg2Si particles to improve the strength of the aluminum alloy. In order to obtain the effect, it is necessary to contain 0.05% or more of Si. On the other hand, if the amount of Si exceeds 0.3%, the elongation is lowered and the forgeability is lowered. Therefore, Si is set in the range of 0.05 to 0.3%. Since Si is an element that contributes to dispersion strengthening at about 150 ° C., it is 0 when used at a temperature higher than the operating temperature (about 150 ° C.) in a general turbocharger (for example, a temperature of about 200 ° C. or higher). 0.1 to 0.25% is desirable. On the other hand, when it is used at a general use temperature of about 150 ° C., the range is preferably 0.15 to 0.3%.

Cu:
If Cu is contained, CuAl ₂ particles are precipitated, which contributes to improving the strength of the aluminum alloy. In order to sufficiently obtain the effect of improving the strength, it is desirable to add 3.0% or more of Cu. On the other hand, if the Cu content exceeds 5.5%, the forgeability deteriorates. Was in the range of 3.0-5.5%.

Mg:
If Mg is contained, it coexists with Si and precipitates Mg ₂ Si particles, thereby contributing to the improvement of the strength of the aluminum alloy. If the Mg content is less than 1.1%, the effect of improving the strength is small, while if the Mg content exceeds 2.4%, the forgeability is lowered. Therefore, the amount of Mg is set within a range of 1.1 to 2.4%. The Mg amount is more preferably in the range of 1.7 to 2.3%.

Fe:
Fe is a component that contributes to improving high-temperature strength. If the amount is less than 0.8%, sufficient high-temperature strength improvement effect cannot be obtained. If 1.3% or more, brittleness due to excess Fe is not obtained. Occurs and cracks occur during forging. Therefore, the amount of Fe is set in the range of 0.8% to 1.3%. In order to sufficiently improve the high temperature strength, the Fe content is preferably 1.0% to 1.3%.

Ni:
If Ni is contained, the dispersion strengthening of the Al—Ni compound is effective in improving the high temperature strength, particularly in the temperature range around 200 ° C. or higher. If the Ni content is less than 0.7%, the effect of improving the strength by adding Ni cannot be obtained. On the other hand, if the Ni content exceeds 2.8%, the toughness decreases, so the Ni content is 0.7 to 2.8%. Within the range. However, the addition of Ni is effective in improving the strength at about 200 ° C. or more, but if the amount of Ni increases, the strength decreases conversely at the operating temperature of a general turbocharger (about 150 ° C.). As a raw material for a compressor wheel shaped material used at a general turbocharger operating temperature (about 150 ° C.), it is preferable to limit the Ni content to a small amount, in which case the Ni content is 1.0% or less. More preferably, it is desirable to regulate to 0.9% or less. On the other hand, when the operating temperature is about 200 ° C. or higher than the operating temperature of a general turbocharger, the Ni content should be relatively large, for example, within a range of 1.0 to 2.5%. Is desirable.

Zr:
If Zr is added, the Zr intermetallic compound undergoes a phase change during hot forging, which is hot plastic working, and forms a metastable phase in the metal flow direction that contributes to improving high temperature strength by dispersion strengthening. Thus, the effect of improving the strength in the LT direction by the forged metal flow can be obtained more remarkably. Therefore, in the present invention, Zr is positively added as an essential element. If Zr is less than 0.05%, the above effect is small. If it exceeds 0.3%, forgeability is reduced due to embrittlement due to the crystallized Zr, so that Zr is 0.05 to 0.3%. Within the range.

Mn:
Mn is an element that increases the heat resistance strength, and if it is 0.1% or less, the effect of improving the strength is small, and if it is 0.4% or more, an Fe-Mn-based crystallized product is generated, and the toughness is reduced. Since forgeability deteriorates, it was made to contain in 0.1 to 0.4% of range.

Ti:
Ti is an element that refines the cast structure and contributes to stabilization of continuous casting. Therefore, addition of 0.005% or more contributes to stabilization of continuous casting. On the other hand, excessive addition of Ti exceeding 0.06% leads to excessive refinement of the cast structure, resulting in poor creep deformation resistance due to grain boundary sliding, so the Ti amount is 0.005 to 0. Within the range of 0.06%.

  The remainder of each element of Si, Cu, Mg, Fe, Mn, Ni, Zr, and Ti in the Al—Cu—Mg alloy may be basically Al and inevitable impurities. Further, one or two of Cr and V may be contained in an amount of 0.1% or less and 2.0% or less in total with other inevitable impurities. If these elements are added, particles such as Al-Cr, Al-Cr-Fe-Si, and Al-V are precipitated, and the recrystallized grains are refined during hot forging, followed by cutting. In (finishing process), it is possible to easily process the blade portion and the like into a thin and fine shape. However, excessive addition of Cr and V may cause formation of giant crystallized materials such as Fe-Mn-Cr and Fe-Mn-V, and therefore one or two of Cr and V may be generated. Even in the case of adding, it is preferable that the content be 0.1% or less.

Cu + Ni:
In the above Al-Cu-Mg-based alloy, the Cu amount and the Ni amount are changed between the Cu amount and the Ni amount.
More preferably, the total amount (Cu + Ni) with the amount is adjusted to be in the range of 4.5 to 8.0%. When (Cu + Ni) is within this range, an alloy having a better balance between workability, forgeability and strength can be obtained.

  Furthermore, in the above alloy, B: 0.0001 to 0.05% (preferably 0.005 to 0.1%) may be added. If B is added together with Ti, the structure of the ingot can be further refined, cracking during casting can be prevented, and forgeability can be improved.

[Outline of basic structure of raw material]
The forging material for turbo compressor wheel according to the present invention is a forging material (forging) in which a continuous casting bar material having a small diameter is used as a forging material and the forging material is subjected to hot hermetic forging or semi-sealing die forging. It is made of a rising material.

The two typical cross-sectional shapes (the shape of the longitudinal section along the central axis O) of the forged finished material correspond to the longitudinal sectional shape of the final product compressor wheel (see FIGS. 1 to 3). 4A and 4B. 4A and 4B show the cross-sectional shape of the forged finished material (forged shaped material) 10 as a whole, but only the portion corresponding to the compressor wheel which is the final product is hatched, and the remainder is shown. The part of is not hatched. Conversely, the hatched parts in FIGS. 4A and 4B are parts corresponding to the compressor wheel of the final product. Further, among the hatched parts (parts corresponding to the compressor wheel), the parts with cross-hatching are parts (blade part equivalent parts) 14 corresponding to the blade part 4 of the compressor wheel. Further, in the forged finished material (forged base material) 10, a portion 13 is equivalent to the rotating shaft portion 3 in the compressor wheel of the product, and in particular, a portion 13 </ b> A on one end side thereof protrudes on one end side of the rotating shaft portion 3. The part (boss part) 5 corresponds to the part 18 and the part 18 corresponds to the blade root 7 in the compressor wheel of the product.
FIG. 4A shows an example of the forged material obtained by closed die forging as described later, and FIG. 4B shows an example of the forged material obtained by semi-sealed die forging.

  As shown in FIG. 4A, the overall shape of the forged material 10 by hot forging using a closed forging die is basically an axis object based on the rotation center axis O of the compressor wheel of the product. It has a rotating body shape and has an outer shape larger than the outer shape of the compressor wheel of the product, and also has a shape corresponding to the outer shape of the compressor wheel (a shape substantially similar to the outer shape of the compressor wheel) and its outer periphery. The flange portion 12 is formed in the direction. Here, the forged finished material 10 includes a portion 14 corresponding to the blade portion of the compressor wheel (a portion corresponding to the blade portion) 14, but the outer surface of the blade portion corresponding portion 14 is centered on the central axis O. It is made to have an inclined surface 14 </ b> A that is enlarged in a taper shape from one side (upper side in FIG. 4A) along the direction to the other side (lower side). The inclined surface 14A is a virtual curved surface including tip edge portions 4A of a large number of blade portions 4 of the compressor wheel (a virtual rotating surface including the curve at the tip of each tip edge portion and having the center axis O as the rotation center). It is along. Incidentally, the flange portion 12 is an unnecessary portion (a so-called surplus portion that is removed by cutting or cutting after forging) with respect to the compressor wheel of the product. By forging into a shape having the flange portion 12 which is a surplus part, it can greatly contribute to the formation of a predetermined metal flow which will be described in detail later.

  The overall shape of the forged material 10 by hot forging using a semi-sealed forging die is basically the flange portion 12 of the forged material shown in FIG. 4A by a closed forging die as shown in FIG. 4B. Further, the burr 16 extends from the outer periphery to the outer side. Except for the presence of the burr 16 as described above, it is the same as the forged material shown in FIG. 4A using a closed forging die.

  The details of the forged material (forged material) 10 shown in FIGS. 4A and 4B will be described later in detail in the section of the manufacturing method. In order to actually finish the forged material (forged material) into the shape of a compressor wheel, finishing such as cutting is performed. Further, heat treatment such as T6 treatment is performed as necessary.

[Structure of small-diameter continuous cast bar as a forging material]
The forging material consisting of a continuous casting bar material with a small diameter has a casting direction (and therefore a length direction as a bar material) along the rotation center axis direction of the compressor wheel as the final product. And it is desirable to have a casting structure in which the circumferential average grain boundary crossing number as viewed in a cross section perpendicular to the casting direction is minimum at the center of the cross section and maximum at the outer periphery.

FIG. 5 and FIG. 6 schematically show the cross-sectional structure of the thin continuous cast bar 20 used for the forging material.
In the continuous casting with a small diameter, not only high productivity but also a bar (cylindrical rod) having a fine cast structure and little segregation can be obtained. Moreover, the bar 20 obtained by continuous casting has an equiaxed crystal structure in which the metal structure (casting structure) is elongated radially from the center of the cylindrical axis of the bar 20 in the outer diameter direction. Grain boundaries are distributed almost evenly, and the grain boundary density in the circumferential direction is uniform. Grain boundaries are places where transition metals such as Fe, Ni, and Mn segregate, and therefore the density distribution (roughness) of the grain boundaries affects the density of the material, and therefore the weight balance in the circumferential direction. However, the continuous cast bar is a material having an excellent dynamic balance at the time of high-speed rotation required for the compressor wheel of the product because the grain boundary is uniform in the circumferential direction and the grain boundary density is uniform.
Here, the grain boundary density distribution (roughness) in the cross section of the cylindrical bar can be evaluated by the average number of crossings in the circumferential direction at each part in the radial direction.

  In the case of a shaped material obtained by a conventional extrusion method, as schematically shown in FIG. 7, the structure of the extruded shaped material 15 is elongated in a fiber shape in the extrusion direction. Therefore, the difference in structure between the extrusion direction and the direction orthogonal thereto is extremely large. Therefore, even after forging the extruded material, the influence of the structure difference due to the direction of the extruded material remains, and there is a strong possibility that the mechanical properties will vary depending on the direction. The difference in structure between the casting direction and the direction perpendicular to the casting direction is significantly smaller than that of the extruded material, so that the variation in mechanical properties depending on the direction can be suppressed to be relatively small.

  Here, if the structure is observed in more detail with respect to the continuous casting bar having a small diameter by rapid solidification, the molten metal is rapidly cooled from the outer peripheral surface side in contact with the inner surface of the mold, and rapid solidification is started from the outer peripheral surface side. Therefore, as schematically shown in FIGS. 5 and 6, the outer peripheral portion Q3 has a structure with a small particle size (that is, a dense structure), and the solidification rate slightly increases as solidification progresses toward the center. Since it becomes late | slow, in center part Q1, it becomes a structure | tissue (namely, sparse structure | tissue) with a relatively large particle size. In FIGS. 5 and 6, the size of crystal grains is exaggerated from the actual size for easy understanding.

  Here, the central portion Q1 of the cross-section of the forging material (small-diameter continuous cast bar) 20 is 1 / of the material radius r from the center position O of the cross-section in the cross-section orthogonal to the casting direction. This means a region Q1 up to a position P1 having a radius of 3 (r / 3). Further, the outer peripheral portion means, for example, a region Q3 from the center position O of the material cross section 12 to a position P2 having a radius (3r / 4) of 3/4 of the material radius r to an outer periphery position P3. The region Q2 is a region between the central region Q1 and the outer peripheral region Q3.

Moreover, the circumferential direction average grain boundary crossing number (C) in the raw material (small-diameter continuous cast bar) 20 is based on the center position O in the cross section orthogonal to the casting direction of the raw material 20. When a circle (concentric circle) is drawn, a value obtained by dividing the number N of portions of a predetermined length L on the circumference (arc) across the grain boundary by the circumferential length of the arc (N / L) is defined as the average value on the circumference. That is, on the above circle, take a plurality of fields of view with circumferential length L at equal intervals, and for each field of view, count the number of locations that the arc crosses (locations crossing grain boundaries), and total the number. The value divided by the arc length (4L in the case of 4 fields of view) is the circumferential direction average grain boundary crossing number.
That is, in this example, the circumferential average grain boundary crossing number (C) is
C = (N1 + N2 + N3 + N4) / 4L
Given in.

  In addition, the circumferential direction average grain boundary crossing number (C) of the outer peripheral part and the central part as described above is a measured value in a circle at a representative position (radius) in each of the regions Q1, Q2, and Q3. For example, in the embodiment described later, the value measured in a circle with a radius of 2 mm from the center is taken as the value at the center, and the measured value in a circle at a position 2 mm radially inward from the outer peripheral surface In practice, measurement at such representative positions is sufficient.

However, when more accuracy is required, for each region (Q1, Q2, Q3), a plurality of concentric circles (a plurality of sample circles; desirably three or more sample circles) are equally spaced in the radial direction within the region. ), Measure the average number of crossings in the circumferential direction C in each concentric circle, and determine the average number of crossings in the circumferential direction in the circumferential direction using the average value of each region (simple average value). You may go. For example, in each region Q1, Q2, Q3 (including the boundary circle position with another adjacent region), three concentric circles are drawn at equal intervals in the radial direction, and the average circumference of these three concentric circles The number of directional grain boundary crossings C1 to C3 is obtained, and the average value _Cav thereof, that is, _Cav = (C1 + C2 + C3) / 3
Thus, the density of the cast structure (the density of grain boundaries) in the cross section of the raw material (thin diameter continuous cast bar) 20 may be determined.

  When measuring the average number of crossing grain boundaries in the circumferential direction, that is, the density of grain boundaries, the grain boundaries can be observed by performing an etching process for observing the metal structure on the cross-section of a continuous cast bar with a small diameter. And measure the number of grain boundaries crossed by the arc on the concentric circle of the cross section by observing with a metal microscope, or obtain an image of the cross section after the etching process by photography etc. May be binarized as necessary, and the number of grain boundaries crossed by arcs on concentric circles in the cross section may be measured.

The ratio _(N out _/ N _in) of the circumferential average grain boundaries transverse speed _{N out,} the circumferential average grain boundaries transverse speed _{N in} the central part of the outer peripheral portion is in the range of 1.3 to 10 Is preferred. When the above ratio (N _out / N _in ) is less than 1.3, the difference in the density of the structure in the radial direction of the cross section is not sufficient, and therefore the required performance of each part in the compressor wheel as described above is not sufficient. There is a risk of failing to satisfy. On the other hand, the ratio (N _out / N _in ) exceeds 10 in practice for a thin continuous cast bar for manufacturing a compressor wheel having a diameter (about 150 mm or less) as the subject of the present invention. If the ratio (N _out / N _in ) exceeds 10, even if different required characteristics of each part can be satisfied, the difference in structure between the central part and the outer peripheral part becomes remarkably large. It may adversely affect workability, forgeability and toughness.

  Note that the specific value of the average number of transverse grain boundaries in the circumferential direction varies depending on the casting speed, cooling conditions, casting diameter, alloy composition of the alloy during continuous casting, etc. When the outer diameter is not less than 25 mm and not more than 120 mm, the Al—Cu—Mg alloy used in the present invention is generally about 1 to 30, and usually within this range, the continuous cast bar There is a difference in the number of average transverse grain boundaries in the circumferential direction between the central portion side and the outer peripheral portion side.

  Here, with respect to the thin continuous cast bar material used as the forging material in the present invention, the average number of transverse boundaries in the circumferential direction as seen in the cross section orthogonal to the casting direction as described above is the center of the cross section. The reason why it is preferable to have a cast structure that is minimum at the outer periphery and maximum at the outer peripheral portion is as follows.

  That is, in the present invention, the continuous cast bar as described above is further subjected to hot sealed semi-forged or semi-closed die forged, but in the radial direction of the cross section at the stage of the continuous cast bar (forging material). The influence of the density condition of the structure remains on the forged material. Therefore, by appropriately controlling the density of the structure in the radial direction of the cross section at the stage of the continuously cast bar (forging material), as described below, different characteristics required for each part of the compressor wheel can be obtained. Can be easily met.

For forging, a forging material consisting of a continuous casting bar with a small diameter is placed in a closed mold or semi-sealed mold so that the forging pressure direction is along the casting direction of the material and along the rotation center axis direction of the compressor wheel. Place and forge.
Here, the forged material also has a forged structure in which the number of circumferential average grain boundary crossings seen in a cross section orthogonal to the forging pressure direction is minimum at the center and maximum at the outer periphery. Is desirable. However, the average number of grain boundaries in the circumferential direction is observed in a cross section perpendicular to the forging pressurization direction at a position of one half of the total height in the direction along the axial direction of the forged material. Is appropriate. The definition and measurement method of the circumferential average grain boundary number itself are the same as those of the continuous cast bar already described.

  Thus, as a forged finished material, the circumferential average grain boundary crossing number as viewed in a cross section perpendicular to the forging pressure direction at the position of one half of the total height in the direction along the axial direction. The following effects can be obtained by having a forged structure that is minimum at the center and maximum at the outer periphery.

In forged materials, the number of circumferential average grain boundary crossings in the part corresponding to the blade root at the center is small, that is, the relatively sparse structure improves the notch fatigue strength of the blade root. It becomes effective. That is, if there are few grain boundaries that are the starting points of notch fatigue failure at the blade root where stress concentrates during high-speed rotation of the compressor wheel, this contributes to improvement of notch fatigue strength. In addition, the position on the one end side of the rotating shaft part of the compressor wheel is a boss part into which the shaft is press-fitted, but the average grain boundary crossing number of the part is small, that is, the structure is relatively sparse, It becomes possible to make it hard to produce a crack at the time of shaft press-fitting.
On the other hand, the fact that the number of transverse average grain boundary crossings in the part corresponding to the blade part in the outer peripheral part of the forged material is large, that is, that the structure is relatively dense, is that the thin blade in the compressor wheel rotating at high speed This contributes to improvement of the strength and rigidity of the part.

  In this way, the structure of the cross section at the height position in the forged finished material as the compressor wheel shape material satisfies the density condition as defined above in the radial direction, so that the compressor wheel of the product Different required performance for each part can be satisfied.

[Method of manufacturing turbo compressor wheel]
Next, from the process of obtaining the forging material (continuously cast bar) as described above, through the process of manufacturing the forged raw material for the turbo compressor wheel, the entire process from finishing to the final turbo compressor wheel is completed. A preferred embodiment of the process and preferred conditions will be described.

<Overview of overall process>
The forged material for turbo compressor wheel of the present invention is a forged material obtained by subjecting a continuous casting bar material having a small diameter to hot sealed or semi-sealed forging. FIG. 8 shows an example of an overall process for manufacturing a compressor wheel from a raw material while applying the method for manufacturing a forged shape material of the present invention.
In this example, the small-diameter continuous cast bar obtained in the continuous casting step S1 is used as a forging material, and then hot forging or semi-sealing die forging (forging step S6) is performed and the forging obtained. About the rising material, the flange portion is removed as necessary (if the burr portion is present around the flange portion by semi-sealing die forging, the flange portion is also removed including the burr portion) (flange portion removal step S7). Furthermore, if necessary, heat treatment such as T6 treatment (heat treatment step S8) is performed to form a shape material for the compressor wheel, and finishing to the shape and dimensions of the final product (compressor wheel) by machining such as cutting. Processing (finishing step S9) is performed to finish the compressor wheel product.

<Continuous casting process S1>
As a raw material manufacturing method, a continuous casting method in which a thin rod is continuously cast is applied. That is, a molten aluminum alloy adjusted to a predetermined component composition is cast into a small diameter (rod shape: cylindrical bar shape) by a continuous casting method. Here, the specific aspect of continuous casting is not particularly limited as long as it is a continuous casting method that can be cast at high speed (thus, if it is a continuous casting method with a high solidification rate), but horizontal continuous casting, vertical continuous casting. Any of these may be used, and a gas-pressing hot top continuous casting method or the like can be suitably applied.
By applying such a continuous casting method, it is possible not only to improve productivity, but also to obtain a cast bar having a fine cast structure and little segregation. Moreover, the bar material (cylindrical rod) obtained by continuous casting has a substantially equiaxed crystal structure as described above, and therefore, it has excellent dynamic balance required for the compressor wheel of the product. Moreover, in the equiaxed crystal structure of the continuous cast bar, the difference in structure between the casting direction and the direction orthogonal thereto is much smaller than that of the extruded material, so that the variation in the mechanical characteristics depending on the direction can be suppressed to be relatively small. .

Here, the continuous casting is desirably performed at a casting speed of 150 mm / min or more so that the outer diameter is 25 mm or more and 120 mm or less. By casting at a casting speed of 150 mm / min or more to 120 mm or less, the microstructure in the radial direction of the cross section is a fine structure of equiaxed crystals that does not change so much. It is possible to obtain a structure in which the number of directional average grain boundaries is minimum at the central portion and maximum at the outer peripheral portion, that is, a relatively coarse structure at the central portion and a relatively dense structure at the outer peripheral portion. More preferably, casting is performed so that the casting speed is 200 mm / min or more and the outer diameter is 25 mm to 80 mm. More preferably, it is desirable to perform casting so that the casting speed is 250 mm / min or more and the outer diameter is 25 mm to 60 mm.
Also, among the continuous casting methods, in particular, if the horizontal continuous casting method is applied, the casting speed can be set to a high speed of 900 mm / min or more on average. In that case, due to the remarkable quenching effect, overall, A finer structure can be obtained.

<Homogenization process S2>
A homogenization process is performed as needed with respect to the thin continuous casting bar material obtained as described above. If homogenization is performed, the effect of homogenizing segregation during casting can be obtained, and the transition metal element that becomes a recrystallization nucleus does not become coarse, which is preferable from the viewpoint of preventing coarse recrystallization. The conditions for the homogenization treatment are not particularly limited, but it is preferable that the Al—Cu—Mg alloy used in the present invention is heated to 470 to 520 ° C. for 8 to 24 hours.

<Roll straightening step S3 to peeling step S4>
After the homogenization treatment, roll correction for correcting the bending of the continuous cast bar is performed with a roll, if necessary, and further peeling (face milling) is performed to remove a casting defect portion and unevenness on the surface.

<Cutting step S5>
After the roll straightening process and the peeling process, the continuous cast bar is cut into a short round bar having a predetermined length. That is, it cut | disconnects in suitable length according to the subsequent process and the axial direction length of one compressor wheel of the final product.

<Forging process (hot sealed die forging or semi-sealed die forging S6>
The small-diameter continuous cast bar cut to a predetermined short length through the cutting step S5 is subjected to hot hermetic forging or semi-hermetic forging. In that case, the forging die cavity (for example, forging in the lower die) so that the center axis of the forging material (short continuous cast bar material with a small diameter) coincides with the rotation center axis of the compressor wheel product to be obtained. In one direction so that the forging pressurization direction follows the casting direction during continuous casting of the forging material. Forging is performed by pressurization to obtain a forged finished material (forged material) 10 as shown in FIG. 4A or 4B, for example. In such a forged finished material (forged raw material) 10, a portion denoted by reference numeral 13 corresponds to the rotary shaft portion 3 in the compressor wheel of the product, and in particular, a portion 13 A on one end side thereof is one end side of the rotary shaft portion 3. Further, the reference numeral 14 corresponds to the blade portion 4 of the product compressor wheel, and the reference numeral 18 corresponds to the blade root portion 7 of the product compressor wheel. .
And in the case of this invention, it forges so that the flange part 12 extended in the radial direction outer side of the site | part corresponded to the blade | wing part in a compressor wheel may be formed. When semi-hermetic forging is applied, a burr portion 16 is formed on the outer side of the flange portion 12 so as to extend further outward in the radial direction.

By performing die forging in this way, it is possible not only to refine the structure and improve overall strength and rigidity, but also to effectively use the material flow behavior (metal flow) during forging. Thus, it is possible to obtain a tissue state corresponding to desired characteristics of each part in the compressor wheel. In particular, fiber reinforcement in the circumferential direction of the blade portion can be achieved by a large metal flow to the flange portion.
In addition, about the concrete conditions of this forging process S6, a term is demonstrated in detail later anew.
<Flange removal step S7>
About the forged finished material 10, it is desirable to remove the flange part 16 which is the surplus part with respect to the compressor wheel of a product before subsequent heat treatment process S8. Thus, by removing the flange part 16 before heat processing, the thermal energy in heat processing process S8 can be reduced and the increase in energy cost can be suppressed. Of course, in the case of a forged material using a semi-sealed forging die, the burr 16 on the outer peripheral side of the flange is also removed at the same time. What is necessary is just to apply what is called roughing which processes into the rough shape of a compressor wheel including trimming or cutting, etc. as a concrete flange part removal process.

<Heat treatment step (for example, T6 treatment) S8>
After performing flange part removal process S7 as needed as mentioned above, it is preferable to give T6 process which performs artificial aging treatment, for example, after solution treatment to a forged material. Here, the T6 treatment includes so-called T61 treatment in which cooling (quenching) after heating in the solution treatment is performed by hot water quenching.

Although the specific conditions of heat processing are not specifically limited, For example, after heat-maintaining (solution treatment) for 0.5 to 4 hours at the temperature of 480 degreeC or more and below the solidus line of an alloy used, 20 degreeC-75 degreeC It is preferable to quench at a water temperature and then perform an artificial aging treatment or stabilization treatment at 170 ° C. to 230 ° C. × 2 hours to 24 hours.
Thus, the strength can be further improved by performing the T6 treatment.

<Finishing process S9>
After the heat treatment process, in order to finish the shape and dimensions of the compressor wheel of the final product, finishing processing such as cutting processing for forming the blade portion of the outer diameter portion and drilling processing (drilling processing) of the shaft hole portion is performed. In addition, when the flange part removal process S7 as described above is not performed before the heat treatment process S8, the flange part 16 is removed before finishing (in the case of a forged material using a semi-sealed forging die, the flange part 16 is removed). In order to remove the burrs 16 on the outer peripheral side of the parts at the same time, so-called roughing is performed to process the rough shape of the compressor wheel including trimming or cutting. Of course, the removal of the flange portion (and also the burr portion) may be performed simultaneously with the finishing process.
Here, for the finishing process, general machining may be applied. Note that machining such as cutting in finishing may be machining having a plurality of steps.

In this way, a product compressor wheel can finally be obtained through hot-sealing die forging or semi-sealing die forging using a continuous casting bar having a small diameter as a raw material.
Next, details of the forging process will be described with reference to FIGS.

[Details of forging step S6]
FIGS. 9 to 12 each show a forged material (forging element) obtained by hot forging or semi-sealing forging using a forging material (continuous casting bar) 20 as shown in FIG. Four examples of typical shapes / dimensions of the shape member 10 are shown.
That is, FIG. 9 shows an example of the shape of a forged finished material obtained by closed die forging as a first example of the forged finished material (forged shaped material), and FIG. 10 shows the forged finished material (forged shaped material). As a second example of), an example of the shape of the forged material obtained by semi-hermetic forging is shown. Further, FIGS. 11 and 12 show examples of the shape of the forged material obtained by closed die forging as a third example and a fourth example of the forged material (forged raw material), respectively. 9 to 13, the numerical values for the dimensions and the radius of curvature R of each part are shown in units of mm.

  In each of the forged finished materials 10 shown in FIGS. 9 to 12, as described above, the outer surface of the blade portion corresponding portion 14 is from one side (upper side in the drawing) in the direction along the central axis O. It has an inclined surface 14A that is enlarged in a taper shape toward the other side (lower side). Furthermore, it has the flange part 12 extended from the front-end | tip (outer peripheral side front-end | tip part) of the blade | wing part equivalent site | part 14 to a radial direction outer side. Of these examples, in the second example (FIG. 10) by semi-hermetic forging, the burr 16 further extends from the outer periphery of the flange 12 to the outside. By the way, in the first example (FIG. 9), the third example (FIG. 11), and the fourth example (FIG. 9) by closed die forging, such a burr portion is not formed because of forged die. . The difference between the first example (FIG. 9), the third example (FIG. 11), and the fourth example (FIG. 12) is that, as will be described later, the upsetting rate U Any one or more of the volume ratio VR and the aperture height ratio SR is made different.

On the other hand, in FIG. 14A, a mold (mold for forging mold forging) 30 for hot forging a forging material (continuous cast bar) as shown in FIG. An example is shown at the top dead center of the upper die, and FIG. 14B shows the bottom dead center of the same closed die forging die 30. That is, the die 30 shown in FIG. 14A and FIG. 14B has the forging shape of the first example shown in FIG. 9 or the third example shown in FIG. 11 or the forging shape of the fourth example shown in FIG. It is a closed mold for obtaining a material.
15A shows a die for hot forging a forging material (continuous cast bar) as shown in FIG. 13, for example, as shown in FIG. 13 (a die for semi-sealing die forging). ) 32 is shown at the top dead center of the upper die, and FIG. 15B shows the bottom dead center of the same semi-sealing die forging die 32. That is, the mold 32 shown in FIGS. 15A and 15B is a semi-hermetic mold for obtaining the forged material of the second example shown in FIG.

  Here, each die has a lower die 30B having a cavity (stepped portion) into which a forging material (a thin continuous cast bar material having a small diameter) is inserted, and descends toward the lower die 30B to form a cavity. An upper die 34A for pressing the forging material 40 therein, an ejector out pin 35 for discharging the forged material (forged material 10) from the cavity, and a punch knockout pin for preventing the forged product from sticking to the upper die 36. The press machine, the die set for mounting the mold, the upper upper plate, and the lower lower plate are not shown in these drawings because they may be the same as the conventional one.

  When subjecting a narrow continuous casting bar (cut to a predetermined short length through the cutting step 5) to hot closed die forging, a forging material (a small continuous casting bar short) Material) is inserted into the cavity of the forging die so that the direction of continuous casting at the time of manufacture coincides with the rotation center axis direction of the compressor wheel product to be obtained, and the forging pressure direction is the casting direction during continuous casting of the forging material. Forging is performed by unidirectional pressing so as to follow (the length direction of the continuously cast bar), and a forged finished material (raw material) 10 is obtained.

Here, the relationship between the forging die cavity and the forging material at the time of forging is that the forging material is positioned by the inner peripheral surface or inner peripheral edge of the cavity (usually the inner peripheral surface or inner peripheral edge of the lower die), and the forging The center axis of the material (center axis in the direction along the casting direction) should be centered so that it matches the center axis of the cavity (usually the lower mold) and therefore the rotation axis of the product compressor wheel. Forging is preferable. 14A and 14B and the semi-enclosed example shown in FIGS. 15A and 15B, the forging material 40 is simply inserted into the cavity of the lower die 34B. , The center axis of the forging material can be centered so that it almost coincides with the center axis of the cavity (usually in the lower mold), and therefore substantially coincides with the rotation axis of the product compressor wheel, Moreover, forging can be performed while maintaining the centering state.
In the case of hermetic forging, since the connection is designed so that forging starts after the upper die is fitted in the lower die cavity, the central axes of the upper die and the lower die are substantially coincident. On the other hand, in the case of semi-sealed forging, although not shown, it is preferable to provide a guide for preventing positional deviation of the upper and lower dies to prevent deviation between the central axes of the upper die and the lower die.

  And, by using such a forging die, hot-sealing die forging or semi-sealing die forging is performed so that the flange portion 12 is formed, not only can the effect of densification of the structure be obtained. A large metal flow from the rotation center axis side toward the flange portion 12 occurs in the blade portion corresponding portion 14, and a fiber reinforcing effect along the radial direction of the blade portion of the compressor wheel can be obtained. That is, the strength in the direction (LT direction) orthogonal to the direction (L direction) along the rotation center axis can be greatly improved. In particular, at a position immediately below the inclined surface 14A of the blade equivalent portion 14, a metal flow along a virtual curved surface in which the tip curves of the tip edge portions of a large number of blade portions of the product compressor wheel are arranged is generated. Strength can be improved. These metal flows will be described in detail next.

16 to 19 schematically show a metal flow by forging in the first example (FIG. 9) to the fourth example (FIG. 12).
In the first example shown in FIG. 16 (an example of closed die forging corresponding to FIG. 9), the metal flow of the material at the time of forging flows as shown by the thin line arrow inside the forged material 10 shown in FIG. It becomes. That is, in the blade portion equivalent portion 14 to be the blade portion 4 in the compressor wheel, a large metal flow that flows into the flange portion 12 from the central axis O side is roughly generated. For this reason, the strength of the blade portion, which is thin and has a large centrifugal force, can be improved by the fiber reinforcement effect of the metal flow. In particular, at a position immediately below the inclined surface 14A of the blade equivalent portion 14, the metal flow is along a virtual curved surface in which the tip curves of the tip edge portions of a large number of blade portions of the product compressor wheel are arranged. It is possible to improve the rigidity of the tip part (tip edge part) of the blade part where the force acts.

  On the other hand, the center portion inside the forged material 10 (however, the center portion on the side away from the boss portion 5; the portion including the blade mounting portion 7 in the rotating shaft portion 3 of the compressor wheel) is the material flow. Becomes a sparse part (dead metal part) DM as compared with the flange part. That is, the portion 13 corresponding to the rotating shaft portion 3 of the product and the portion 17 corresponding to the blade root portion 7 on the periphery thereof are dead metal portions DM having no metal flow at the time of forging. The structure of the bar material is substantially taken over, and a structure with a lower density than the outer peripheral portion is left. Therefore, the grain boundary that becomes the starting point of notch fatigue failure is reduced at the blade root where stress concentrates during high speed rotation of the compressor wheel, which contributes to improvement of notch fatigue strength.

  For comparison with the present invention, the metal of the extruded raw material 50 in the case of manufacturing a compressor wheel without applying forging as defined in the present invention using a conventional general extruded material as a raw material. The flow FM ′ is shown in FIG. 21 corresponding to the shape of the compressor wheel of the product. Such a metal flow FM ′ of the extruded material 50 is generally parallel to the rotation center axis O of the compressor wheel, as indicated by an arrow in FIG. That is, as in the case of the present invention, the metal flow FM directed outward in the radial direction is not formed in the portion corresponding to the blade portion. Therefore, the strength in the LT direction has to be low.

  Moreover, the metal of the forging up material (simple disk shape) 60 in the case of the conventional simple upsetting forging which obtains the forging up material of the shape which does not form the flange part 12 and does not have the inclined surface 14A like this invention. The flow FM ″ is shown in FIG. 22 corresponding to the shape of the product compressor wheel. Such a metal flow FM ″ of the upsetting forged material 60 is generally in a direction perpendicular to the rotation center axis O of the compressor wheel, as indicated by an arrow in FIG. In this case, the metal flow in the portion corresponding to the blade portion, particularly the metal flow in the vicinity of the virtual curved surface where the curves of the tip edge portions of many blade portions of the compressor wheel of the product are continuous, does not follow the virtual curved surface. Therefore, it is not possible to sufficiently enhance the tip edge portion of the blade portion of the compressor wheel.

  Furthermore, as shown in Patent Document 3, in the case of the conventional technique for forging a material in three directions, the forged material becomes a homogeneous structure as a whole, and in the portion corresponding to the blade portion as in the present invention. A metal flow directed radially outward is not formed.

  Therefore, the superiority of the technology of the present invention over the prior art is apparent from these metal flow considerations.

  Here, in order to form an appropriate metal flow toward the flange portion at the portion corresponding to the blade portion and reliably improve the strength in the LT direction, an index and a forging temperature (forging material) Regarding the temperature, it is desirable to perform forging while satisfying the following conditions.

First, the height of the forged material (continuously cast bar) 20 in the direction along the rotation center axis O is h (see FIG. 13), and the rotation center in the blade portion corresponding portion 14A of the forged raw material. The height at the position where the height in the direction along the axis O is the highest (in other words, the position corresponding to the thickest part of the blade part and the position closest to the root part of the blade part) is b (Fig. 4A, FIG. 4B, and FIG. 9 to FIG.
U = {(h−b) / h} × 100 (%)
In this case, it is desirable to perform hot forging so that the upsetting rate U is in the range of 40 to 80%.

If the upsetting ratio U is less than 40%, the plastic working in the forging is insufficient, the structure cannot be sufficiently densified, and the metal flow from the blade equivalent part to the flange part is not sufficient, so the strength is improved. May be insufficient. Then, when the present inventors investigated the relationship between the upsetting rate U and the strength (room temperature tensile strength and 0.2% yield strength), the result shown in FIG. 20 was obtained. As shown in FIG. 20, the strength increases as the upsetting rate U increases from 0% (that is, without forging), and particularly when the upsetting rate U is around 40%, the strength rapidly increases. Even if the penetration rate U increases, the strength improvement effect is substantially saturated. From such experimental results of the present invention, it is understood that the upsetting rate U is preferably 40% or more.
On the other hand, if the upsetting rate U exceeds 80%, buckling and cracking are likely to occur during forging. Therefore, the upsetting rate U is preferably in the range of 40 to 80%. In addition, even in the range of 40 to 80%, the range of 50 to 75% is particularly preferable.

  Here, the height h (see FIG. 13) in the direction along the rotation center axis O of the forging material (continuous casting bar) 20 and the radius r (see FIG. 13) of the forging material (continuous casting bar) 20 13)) (h / r) is preferably 2 or less. If the ratio (h / r) exceeds 2, the material may buckle during forging.

Second, as a value mainly related to the volume of the flange portion, the entire volume of the forged raw material is V1, and the portion including the entire flange portion outside the radial tip position of the blade portion corresponding portion (product) The volume of the surplus part) is V2, and the volume ratio VR is
VR = (V2 / V1) × 100 (%)
Forging is preferably performed so that the value of the volume ratio VR is in the range of 50% or more and less than 80%.

  When the volume ratio VR is less than 50%, the metal flow flowing from the blade equivalent portion into the flange portion at the time of forging is not sufficient, so that the strength improvement may be insufficient. On the other hand, if the volume ratio VR exceeds 80%, buckling and cracking are likely to occur during forging. The volume ratio VR is preferably in the range of 65% or more and less than 75%, more preferably in the range of 70% or more and less than 75%, even in the range of 50 to 80%.

Third, as an index regarding the ratio of the thickness of the flange portion to the portion corresponding to the blade portion (the ratio of the height in the direction along the rotation center axis), the average thickness of the flange portion in the direction along the rotation center is a. (Refer to FIGS. 4A, 4B, and 9 to 12). Similarly to the above, the above-described height at the position where the height in the direction along the rotation center in the portion corresponding to the blade portion is the highest is b (FIG. 4A, FIG. 4B, and FIGS. 9 to 12), and the aperture height ratio SR is SR = (a / b) × 100 (%)
Forging is preferably performed so that the drawing height ratio SR falls within the range of 10/40 to 30/40.

  If the drawing height ratio SR is a large value exceeding 30/40, the metal flow along the virtual curved surface formed by the tip edge portions of a large number of blade portions in the compressor wheel becomes insufficient, and in particular, the rigidity of the tip edge portion is improved. The effect may not be sufficient. On the other hand, if the drawing height ratio SR is smaller than 10/40, the thickness of the flange portion becomes small, and it becomes difficult to sufficiently secure the volume ratio VR described above. Even if the drawing height ratio SR is small, the volume ratio VR can be increased to some extent by increasing the width of the flange portion (the length of the flange portion extending from the portion corresponding to the blade portion). In this case, the metal flow to the flange portion is hindered, and it becomes difficult to form an orderly metal flow in the portion corresponding to the blade portion. Therefore, the drawing height ratio SR is preferably 10/40 or more. In addition, it is more preferable that the aperture height ratio SR is in the range of 25/40 to 15/40, even within the above range.

  In addition, although it is desirable to satisfy all the conditions of the first to third indexes (upsetting ratio U, volume ratio VR, drawing height ratio SR) related to the degree of plastic working described above, not all indexes are satisfied. It is not essential to satisfy the conditions at the same time. However, it is desirable to satisfy at least one index condition.

Fourthly, in the forging step, it is preferable that the material temperature during forging is in the range of 350 to 450 ° C. This forging temperature range 350 to 450 ° C. is a hot forging temperature range higher than the forging temperature applied to a conventional general Al—Cu—Mg alloy. The reason why the forging temperature is increased in this way is that, for example, when a forged finished material is subjected to a heat treatment such as T6 treatment to finish the product compressor wheel, an appropriate metal flow and structure obtained by forging up are obtained. This is because the compressor wheel of the product is handed over, thereby maintaining the effect of improving the strength of the blades up to the product.
That is, if the forging temperature is set relatively high in the range of 350 to 450 ° C., recovery of the sand material is likely to occur during the forging and immediately after forging. If the recovery occurs and the distortion is eliminated in this way, coarse recrystallization is less likely to occur during the heat treatment such as the subsequent T6 treatment, so that the metal flow after forging can be maintained. If there is a large amount of strain that becomes recrystallization nuclei during heat treatment such as T6 treatment, the structure in the forged up state becomes rough due to recrystallization, and as a result, the effect of the metal flow as described above can be obtained. May not be expected at the product stage.
Here, when the forging temperature is lower than 350 ° C., recovery is difficult to occur, while when it exceeds 450 ° C., local melting may occur. The forging temperature is preferably within the range of 400 to 450 ° C., even within the range of 350 to 450 ° C.
It is normal to heat the forging material in a heating furnace immediately before inserting the forging material into the forging die so that the forging temperature is uniformly reached to the inside of the material. In this case, the heating time is Although not particularly limited, it may normally be about 30 to 60 minutes.
Moreover, in order to maintain the product temperature after forging high, it is preferable to forge in the state which heated and hold | maintained the metal mold temperature to about 250 to 350 degreeC.

In the above, the metal flow according to the present invention and preferable forging conditions were described with reference to the metal flow shown in FIG. 16 by forging in the first example (FIG. 9) by closed die forging. The metal flow in the case of the second example (FIG. 10) by forging is schematically shown in FIG.
The metal flow in this case is slightly different from the metal flow of the material during forging in the case of the first example (FIG. 9) (FIG. 16), but there is a metal flow from the flange portion 12 toward the burr portion 16 further. Except for the above, the outline is the same. That is, the outer peripheral portion that should be at least the tip portion of the blade portion 4 in the compressor wheel is a portion FM having a large flow flowing into the flange portion, while the central portion inside the forged finished material 10 (however, downward from the boss portion 5) The central portion on the side far from the center; the portion including the blade attachment portion 7 in the rotation shaft portion 3 of the compressor wheel) is a portion DM in which the material flow is sparse compared to the flange portion 12.
As described above, since the portion corresponding to the blade root 7 of the product in the forged finished material 10 is the portion DM in which the metal flow during forging is sparse, the structure of the continuously cast bar that is the forging material. Is substantially inherited, leaving a sparse structure compared to the outer periphery, and there are fewer grain boundaries that become the starting point of notch fatigue fracture at the root of the blade where stress concentrates at high speed rotation of the compressor wheel, Contributes to the improvement of notch fatigue strength.
Further, at a portion corresponding to at least the tip portion of the blade portion on the outer peripheral portion, a large metal flow occurs, and the thinness in the compressor wheel rotating at high speed is combined with the direction of the metal flow and the forging effect by forging. This contributes to improving the strength and rigidity of the tip of the blade portion.

FIG. 18 shows the metal flow in the forging in the third example (FIG. 11) by the closed die forging, and FIG. 19 shows the metal flow in the forging in the fourth example (FIG. 12) by the closed die forging. Show.
The third example (FIGS. 11 and 18) and the fourth example (FIGS. 12 and 19) are both based on closed die forging as in the first example (FIGS. 9 and 17). Also, the dimensions of the forging material and the shape and dimensions of the final product compressor wheel are the same as in the first example, so that a metal flow that is not significantly different from the first example is basically formed. However, one or more conditions of the upsetting ratio U, the volume ratio VR, and the drawing height ratio SR are different from the first example, and therefore the metal flow is also different from the first example.
Here, the results of evaluating the upsetting ratio U, the volume ratio VR, the drawing height ratio SR, and the state of metal flow (smoothness and strength) in each of the first to fourth examples. Table 1 shows. In each example, as the material aluminum alloy, alloy A within the composition range of the present invention shown in Table 2 of Examples described later was used.
Here, as an evaluation of the state of the metal flow, “smoothness” is evaluated based on whether or not the metal flow in the portion immediately below the inclined surface 14A in the blade equivalent portion 14 is smooth (such as the presence or absence of a step). The “strength” was evaluated based on the strength of the metal flow from the portion corresponding to the blade portion toward the flange portion.

As shown in Table 1, the first example by closed die forging (metal flow in FIG. 16) and the second example by semi-sealed die forging (metal flow in FIG. 17) have an upsetting ratio U and volume. The ratio VR and the aperture height ratio SR are the same and are within the above-mentioned preferable condition range. In these cases, as shown in FIGS. 16 and 17, the strength of the metal flow toward the flange portion 12 in the blade portion corresponding portion 14 is sufficiently high, and the inclined surface 14 </ b> A in the blade portion corresponding portion 14. The smoothness of the metal flow in the part immediately below was sufficiently secured.
On the other hand, in the case of the third example (metal flow in FIG. 18) by closed die forging, since the drawing height ratio SR is relatively large, the strength of the metal flow toward the flange portion 12 in the blade portion corresponding portion 14. Was slightly inferior.
Further, in the case of the fourth example (metal flow in FIG. 19) by closed die forging, the upsetting rate U and the volume ratio VR are relatively small. In this case, the blade 14 corresponding portion 14 is directly below the inclined surface 14A. A level difference was caused in the metal flow of this part, and the smoothness was slightly inferior, and the strength of the metal flow toward the flange part 12 in the blade equivalent part 14 was also slightly reduced.
However, the third example and the fourth example are not completely unsuitable as a forged raw material for a compressor wheel, and can be put into practical use depending on the use condition and use mode of the compressor wheel.

  Examples of the present invention will be described below. The following examples are for clarifying the operation and effects of the present invention, and it is needless to say that the conditions described in the examples do not limit the technical scope of the present invention.

[Example 1]
Example 1 is an example in which a continuously cast bar having the dimensions shown in FIG. 13 is used as a forging material, and hot forging die forging is performed to obtain a forging material for a turbo compressor wheel. In Example 1, the forged material is the shape of the first example shown in FIG. 9, and the dimensional relationship between the closed forging die and the forging material is as shown in FIG. 14A and 14B. .
When manufacturing continuous casting bars as raw materials for forging, the additive elements are added to the aluminum ingot and dissolved, and the components are adjusted to the Al-Cu-Mg alloy A shown in Table 2, and the gas pressurized hot top Using a continuous casting method, a mold with an inner diameter of φ59 mm was continuously cast into a round bar shape with an outer diameter of 58 mm at a casting speed of 300 mm / min to obtain a continuous cast bar. The continuous cast bar was homogenized by air cooling after being held at 490 ° C. for 12 hours, and the cast skin was removed (peeling) to obtain an aluminum alloy bar having a diameter of 54 mm. This bar was cut with a saw cutter to create a columnar material (forging material) having a length of 64 mm.
Using this columnar material as a forging material, the temperature is raised to 450 ° C., and the forging temperature of the bell-shaped forged material with the shape shown in FIG. 9 is increased by the forging temperature shown in FIGS. 14A and 14B to the forging temperature. Hot forging was performed at 450 ° C. The forged material (forged material) is heated to 495 ° C., held for 2 hours and then quenched into warm water at 80 ° C. (so-called solution treatment), then heated to 200 ° C. and held for 10 hours (so-called aging) Treatment) followed by air cooling. In addition, the upsetting rate U in hot forging is about 75%.

[Example 2 and Example 3]
A forging material was obtained under the same conditions and process as in Example 1 except that the forging temperature was 400 ° C. in Example 2 and 350 ° C. in Example 3. Then, the tensile test and the metal flow were observed in the same manner as described above.

Example 4
In this Example 4, a forging material is manufactured under substantially the same conditions and process as in Example 1 except that the upsetting rate U in hot forging is changed from 75% of Example 1 to 50%. did.

Example 5
In Example 5, a forged material was manufactured under substantially the same conditions and process as Example 1 except that semi-hermetic forging was applied in hot forging. In Example 5, the forged material is the shape of the second example shown in FIG. 10, and the dimensional relationship between the semi-sealed forging die and the forging material is as shown in FIG. 15A and obtained 15B. did.

[Comparative Example 1]
A forged shape material was produced under substantially the same process and conditions as in Example 1 except that the A2618 alloy in Table 2 deviating from the component composition range of the alloy used in the present invention was used as the material aluminum alloy. The hot forging was also closed die forging as in Example 1.

[Comparative Example 2]
Comparative Example 2 is an example in which an extruded material made of an alloy having the same component composition as Alloy A used in Example 1 was used as a compressor wheel shaped material. That is, using alloy A, the cast skin of the billet (φ210 mm) obtained by the gas pressure hot top continuous casting method is removed by chamfering to φ200 mm, heated to about 420 ° C. by a billet heater, and placed in an extruder container It was loaded and extruded into a 45 mm round bar with a press ratio of 1/20 by hot extrusion to obtain a compressor wheel shaped material.

[Comparative Example 3]
Comparative Example 3 is an example in which a continuous cast bar made of an alloy having the same composition as that of Alloy A used in Example 1 is used as a compressor wheel shaped material as it is without hot forging. The manufacturing process and conditions for the continuously cast bar in this case are the same as in Example 1.

[Reference Example 1]
In Reference Example 1, a forged material was manufactured under the same process and conditions as in Example 1 except that the upsetting rate U was set at a relatively low 25% when performing hot closed die forging. .

[Reference Example 2]
In this Reference Example 2, a forged material was manufactured under the same process and conditions as in Example 1 except that the hot forging die forging was performed at a relatively low forging temperature of 300 ° C.

A direction (LT) orthogonal to the direction (L direction) along the central axis in the compressor wheel shaped material manufactured by each of the above Examples 1 to 5, Comparative Examples 1 to 3, and Reference Examples 1 and 2. Direction) and a tensile test piece was created from a position including the portion corresponding to the blade portion, and a tensile test was performed. Moreover, the cross section was subjected to an etching process suitable for observing the metal structure, and the metal flow was observed. These results are shown in Table 3.
In Table 3, regarding the tensile strength in the LT direction, when the strength is 450 MPa or more, the strength in the LT direction is determined to be sufficient and a mark is given. When the tensile strength is less than 450 MPa, the strength in the LT direction is determined to be insufficient. X mark was attached.
For the evaluation of the intensity ratio between the LT direction and the L direction (intensity ratio depending on the direction), the intensity in the LT direction is 450 MPa or more and the value of the intensity ratio between the LT direction and the L direction (LT direction intensity / L direction intensity) is A case of 0.9 or more is judged as good and a mark is given. A case where the strength in the LT direction is less than 450 MPa and the strength ratio between the LT direction and the L direction is less than 0.9 is judged as defective. Further, a mark “X” was given when the intensity ratio between the LT direction and the L direction was 0.9 or more but the strength in the LT direction was less than 450 MPa. Regarding the strength ratio between the LT direction and the L direction, with respect to the strength in the L direction, the dimension material in the L direction is too small in the shape material obtained by each of the above examples, and the test piece in the L direction is cut out. Since it was difficult, the L direction strength value measured for the material obtained by the process and conditions substantially similar to each example was used using a material having a size larger than each example.

As shown in Table 3, in each of Examples 1 to 5, it was confirmed that the strength in the LT direction showed a high value of 450 MPa or more, and the strength ratio between the LT direction and the L direction was as high as 0.9 or more. .
On the other hand, in Comparative Example 1 using an alloy (A2618 alloy) that does not satisfy the alloy component composition conditions defined in the present invention, the strength in the LT direction was not sufficient.
Furthermore, in Comparative Example 2 in which the extruded material was a shape material and Comparative Example 3 in which the as-cast material was a shape material, it was found that the strength in the LT direction was low.
Even in Reference Example 1 in which the upsetting rate U is relatively small, the LT direction strength was relatively low.
Furthermore, in Reference Example 2 where the forging temperature was relatively low, cracking occurred during forging.

 The aluminum alloy turbocompressor wheel forging shaped material of the present invention is applied to a shaped material for producing a compressor wheel (impeller) used for a turbocharger used in an internal combustion engine of an automobile or other various transport equipment. Can do.

  DESCRIPTION OF SYMBOLS 1 ... Compressor wheel, 3 ... Rotating shaft part, 4 ... Blade | wing part, 7 ... Blade | root base part, 10 ... Forging raw material (forging up material), 12 ... Flange part 14 ... Blade | equivalent part 14A ... Inclined surface, 20 ... continuous casting rod (forging material), 30 ... forging die.

Claims (12)

Aluminum alloy obtained by hot forging by closed die forging or semi-sealed die forging so that the forging pressure direction is along the casting direction of the raw material and the rotation center axis direction of the compressor wheel Forged material for turbo compressor wheel made of
The aluminum alloy of the material is mass%, Si: 0.05 to 0.3%, Cu: 3.0 to 5.5%, Mg: 1.1 to 2.4%, Fe: 0.8 to Including 1.3%, Mn: 0.1-0.4%, Ni: 0.7-2.8%, Zr: 0.05-0.3%, Ti: 0.005-0.06% The remainder consists of Al and inevitable impurities,
The shape of the base material is larger than the outer diameter shape of the compressor wheel including the portion corresponding to the blade portion of the compressor wheel, and the outer surface of the portion corresponding to the blade portion is from one side in the direction along the rotation center axis to the other It has a shape having an inclined surface that is smoothly expanded toward the side,
And the flange part used as the surplus part with respect to the final product of a compressor wheel is extended to the radial direction outer side on the basis of the said rotation center axis line rather than the outer diameter side edge part in a blade | wing part equivalent part, and the said blade | wing part equivalent part A forged base material for an aluminum alloy turbo compressor wheel, wherein a metal flow from the rotation center axis side toward the flange portion is formed.   The forged base material for an aluminum alloy turbo compressor wheel according to claim 1, wherein the inclined surface is a surface corresponding to a virtual curved surface including chip edge portions of a plurality of blade portions of the compressor wheel.   3. The aluminum alloy-made product according to claim 2, wherein at least a metal flow immediately below the inclined surface of the metal flow corresponding to the blade portion corresponds to a virtual curved surface including chip edge portions of the plurality of blade portions. Forging material for turbo compressor wheel. The height in the direction along the rotation center of the material is h, and the height at the position where the height in the direction along the rotation center is the highest in the blade equivalent portion of the forged raw material is b,
The upsetting rate U is {(h−b) / h} × 100 (%),
The aluminum alloy according to any one of claims 1 to 3, wherein the upsetting ratio U is hot forged so as to be within a range of 40 to 80%. Forging material for turbo compressor wheel.   The total volume of the forged material is V1, and the volume of the portion including the entire flange portion outside the radial tip position of the blade portion-corresponding portion is V2, and {V2 / (V1 + V2)} × 100 ( %) Is a volume ratio VR, and the volume ratio VR is in the range of 50% or more and less than 80%, and the aluminum according to any one of claims 1 to 4 Forged material for alloy turbo compressor wheels. The average thickness of the flange portion in the direction along the rotation center is a, and the height of the portion corresponding to the blade portion in the direction along the rotation center is b, and the aperture height The ratio SR is a / b,
6. The forging element for an aluminum alloy turbo compressor wheel according to any one of claims 1 to 5, wherein the drawing height ratio SR is in a range of 10/40 to 30/40. Wood. In mass%, Si: 0.05 to 0.3%, Cu: 3.0 to 5.5%, Mg: 1.1 to 2.4%, Fe: 0.8 to 1.3%, Mn: 0.1 to 0.4%, Ni: 0.7 to 2.8%, Zr: 0.05 to 0.3%, Ti: 0.005 to 0.06%, the balance being Al and inevitable Using aluminum alloy continuous cast bar made of impurities as a raw material, the material is formed by closed die forging or semi-sealed die forging so that the forging pressurization direction is along the casting direction of the raw material and along the rotation center axis direction of the compressor wheel. Hot forging, and as a forging finish, it has a forging process to obtain a forging material for turbo compressor wheel,
In the forging process, the shape of the forged material after forging is a shape larger than the outer diameter shape of the compressor wheel including the portion corresponding to the blade portion of the compressor wheel, and the outer surface of the portion corresponding to the blade portion is , In order to form a shape having an inclined surface that is smoothly expanded in diameter from one side in the direction along the rotation center axis toward the other side, and more than the outer diameter side end portion in the blade portion-corresponding portion. Forging so that the flange part that becomes the surplus part for the final product of the compressor wheel is extended radially outward with respect to the rotation center axis line,
A method for producing an aluminum alloy turbocompressor forged material for a turbo compressor wheel, characterized in that a metal flow directed from the rotation center axis side toward the flange portion is formed at a portion corresponding to the blade portion.   In the forging step, forging so that at least the metal flow immediately below the inclined surface of the metal flow corresponding to the blade portion corresponds to a virtual curved surface including chip edge portions of a large number of blade portions of the compressor wheel. The method for producing a forged material for an aluminum alloy turbo compressor wheel according to claim 7. In the forging step, the height of the raw material in the direction along the rotation center is h, and the height in the direction along the rotation center in the portion corresponding to the blade portion of the forged raw material is the height at the highest position. And b
The upsetting rate U is {(h−b) / h} × 100 (%),
9. The aluminum alloy turbo compressor wheel according to claim 7, wherein hot forging is performed so that the upsetting ratio U is in a range of 40 to 80%. A manufacturing method for forging material. In the forging process, the entire volume of the forged industrial castings and V _1, the outside than the radial end position of the wing portion corresponding site, the volume of a portion including the entirety of the flange portion and V2, (V2 / V1 ) × 100 (%) as a volume ratio VR, forging is performed so that the volume ratio VR falls within a range of 50% or more and less than 80%. A method for producing a forged material for an aluminum alloy turbo compressor wheel according to any one of the claims. In the forging step, the average thickness in the direction along the rotation center in the flange portion is defined as a, and the height at the position where the height in the direction along the rotation center in the blade portion corresponding portion is the highest is b. And the aperture height ratio SR is (a / b) × 100 (%),
11. The aluminum alloy product according to claim 7, wherein forging is performed so that the drawing height ratio SR is within a range of 10/40 to 30/40. A method for producing a forged material for a turbo compressor wheel.   The forging element for an aluminum alloy turbo compressor wheel according to any one of claims 7 to 11, wherein in the forging step, a material temperature during forging is set in a range of 350 to 450 ° C. A method for manufacturing a profile.

Images