JP2019190365A - Forged product for impeller - Google Patents

Abstract

To provide an impeller composed of a forged product of high productivity and having high temperature strength.SOLUTION: A forged product 1 for an impeller including a hub 10 having a boss portion 12 on a center of a circular disc portion 11, and a plurality of blade portions 13 radially disposed on an outer surface of the hub 10, is composed of an aluminum alloy including 0.05 mass%-0.30 mass% of Si, 0.7 mass%-1.5 mass% of Fe, 1.7 mass%-2.9 mass% of Cu, 1.0 mass%-1.9 mass% of Mg, 0.03 mass%-0.15 mass% of Ti, 0.8 mass%-1.4 mass% of Ni, and the balance Al with unavoidable impurities, and an average particle size of crystal grain on an arbitrary cross-section in parallel with a rotating shaft of the disc portion 11 is 30 μm-120 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a forged product made of an aluminum alloy impeller represented by an impeller for a turbocharger for automobiles.

  A compressor impeller such as a compressor wheel in a turbocharger as an internal combustion engine of an automobile is subjected to high-speed rotation exceeding 10,000 rpm under a high temperature condition of about 170 ° C. Therefore, high stress due to centrifugal force or the like is generated in the vicinity of the center of rotation. appear. For the above reasons, the turbocharger compressor impeller is required to have high strength and high rigidity at a high temperature of about 170 ° C. In addition, the compressor impeller is required to be lightweight in order to reduce energy loss, and also to be strong enough to withstand high-speed rotation.

  Conventional compressor impellers are made of 2618 alloy (Cu: 1.9 mass% to 2.7 mass%, Mg: 1.3 mass% to 1.8 mass%, Ni: 0.9 mass% to 1.2 mass%) Fe: 0.9 mass% to 1.3 mass%, Si: 0.1 mass% to 0.25 mass%, Ti: 0.04 mass% to 0.1 mass%, Al: balance). ing. Further, cited document 1 discloses an Al—Cu—Mg alloy containing 3.0% by mass to 5.5% by mass of Cu and improving the high-temperature strength more than ever.

  As a method of manufacturing an impeller, there is a method of cutting a material lump to finish the shape of a final product. In addition, there is a method in which an intermediate product in which blades are formed on the outer peripheral surface of a boss portion is produced by forging a lump of material, and the intermediate product is cut into a final product. The latter method is characterized in that it can be processed in a shorter time than the former method, has good productivity, has few parts removed by cutting, and has a good material yield.

JP 2017-78216 A

  However, if an impeller is made using an aluminum alloy with a large amount of various elements added to improve high-temperature strength, instability may be exposed during forging, and variations due to segregation inside the material are large. May be. The above problems are fatal in impellers that require extremely high characteristics, and suggest that there is a possibility of causing metal fatigue in the impeller blades, especially caused by repeated rapid rotation and stopping. ing.

  Further, in the technical field of internal combustion engines such as automobiles, compressor impellers have a large market scale and need to reduce costs, and are also required to be easily manufactured and inexpensive.

  In view of the above-described technical background, an object of the present invention is to provide an impeller having high temperature strength with a productive forged product.

  That is, the present invention has the configurations described in [1] to [3] below.

[1] A forged product for an impeller having a hub having a boss portion at the center of a circular disk portion and a plurality of blade portions provided radially on the outer surface of the hub,
The forged product for the impeller includes: Si: 0.05% by mass to 0.30% by mass, Fe: 0.7% by mass to 1.5% by mass, Cu: 1.7% by mass to 2.9% by mass, Mg : 1.0% by mass to 1.9% by mass, Ti: 0.03% by mass to 0.15% by mass, Ni: 0.8% by mass to 1.4% by mass, and the balance from Al and inevitable impurities Made of an aluminum alloy
A forged article for impellers, wherein an average grain size of crystal grains in an arbitrary cross section parallel to the impeller rotation axis of the disk portion is 30 μm to 120 μm.

  [2] The forged product for an impeller according to the above item 1, wherein the aluminum alloy further contains B: 0.0012 mass% to 0.006 mass%.

[3] The previous item in which an average particle diameter of the CuAl ₂ θ-phase compound in an arbitrary cross section parallel to the rotation axis of the impeller is 1.0 μm to 15 μm and an occupied area ratio is 4% to 15%. The forged product for impellers according to 1 or 2.

  According to the impeller forged product described in [1] above, high high-temperature strength is obtained by the chemical composition of the aluminum alloy material, and high high-temperature strength is obtained in the disk portion based on the crystal grain size. In addition, since the blade portion having a higher processing rate than the disk portion is made finer than the disk portion, a high temperature strength higher than that of the disk portion can be obtained. In addition, since the impeller has a disk portion, a boss portion, and a blade portion formed by forging, the productivity is better than that of a molded product by cutting and can be manufactured at low cost.

  According to the forged product for an impeller described in [2] above, the addition of B further refines the crystal grains and provides high high-temperature strength.

According to the forged product for an impeller described in [3] above, a particularly high high-temperature strength can be obtained by precipitation of a CuAl ₂ θ-phase compound.

It is a perspective view showing one embodiment of a forged product for impellers according to the present invention. It is a perspective view which shows the preparation process of the forging material for a material characteristic investigation in an Example.

  FIG. 1 shows an impeller forged product 1 used in a turbocharger as an embodiment of the present invention.

  The impeller forged product 1 includes a hub 10 having a boss portion 12 at the center of a circular disk portion 11 and a plurality of blade portions 13 provided radially on the outer surface of the hub 10. In the impeller forged product 1, the center of the boss portion 12 serves as a rotation axis.

  The impeller forged product 1 is formed by a forging process, which will be described later, and is incorporated into a turbocharger after finishing by a cutting process or the like. The impeller forged product of the present invention includes both a forged product before finishing and a forged product after finishing.

In the impeller forged product 1, the chemical composition of the material aluminum alloy and the metal structure of the disk portion 11 are defined.
(Chemical composition of aluminum alloy)
The aluminum alloy contains Si, Fe, Cu, Mg, Ti, and Ni as essential elements, and further contains B if necessary. In any alloy, the balance is Al and inevitable impurities. Hereinafter, the addition significance and concentration of each element will be described in detail.

Si forcibly dissolves as a supersaturated solid solution during the solution treatment, and fine precipitates as Mg ₂ Si during the artificial aging treatment to increase the strength. This effect is low when the amount of Si added is less than 0.05% by mass, and when it exceeds 0.30% by mass, it is produced as a coarse crystallized product at the time of casting and the mechanical properties are deteriorated. Therefore, Si shall be 0.05 mass%-0.30 mass%. A more preferable Si addition amount is 0.1% by mass to 0.25% by mass.

  Fe has the effect of improving the high-temperature strength, particularly the strength at 170 ° C., which is the practical temperature range of the impeller. The above action is due to the formation of an intermetallic compound together with Al and Ni, and crystallization preferentially at the grain boundaries to obtain dispersion strengthening. This effect is that when the added amount of Fe is less than 0.7% by mass, sufficient dispersion strengthening of the Al—Fe—Ni-based crystallized product cannot be obtained. Reduces mechanical properties. Therefore, Fe is made 0.7 mass% to 1.5 mass%. A more preferable Fe addition amount is 0.9 mass% to 1.2 mass%.

Cu has the effect of improving the high temperature strength. Cu forms a solid solution during solution treatment, forms Al and a compound (CuAl ₂ ) during artificial aging treatment, and precipitates as fine precipitates, thereby contributing to strength improvement at 170 ° C., which is a practical temperature range of the impeller. This effect is prominent when the amount of Cu added is 1.7% by mass or more, and when it exceeds 2.9% by mass, it is crystallized as a coarse crystallized product at the time of casting, and the mechanical properties are deteriorated. Therefore, Cu is 1.7% by mass to 2.9% by mass. A more preferable Cu addition amount is 1.9 mass% to 2.7 mass%.

Mg forcibly dissolves as a supersaturated solid solution during solution treatment, and finely precipitates as Mg ₂ Si during population aging treatment to increase the strength. This effect is not effective when the amount of Mg added is less than 1.0% by mass, and when it exceeds 1.9% by mass, it is produced as a coarse crystallized product at the time of casting and mechanical properties are deteriorated. Therefore, Mg is set to 1.0 mass% to 1.9 mass%. A more preferable amount of added Mg is 1.2% by mass to 1.7% by mass.

  Ti is added for the purpose of refining the crystal grains in order to promote the effect of suppressing the growth of crystal grains during casting. This effect is low when the amount of Ti added is less than 0.03% by mass, and when it exceeds 0.15% by mass, the crystallization mechanical properties are deteriorated as a coarse crystallized product during casting. Therefore, Ti is set to 0.03 mass% to 0.15 mass%. A preferable Ti addition amount is 0.05% by mass to 0.10% by mass.

  Ni has the effect of improving the high temperature strength, particularly the strength at 170 ° C., which is the practical temperature range of the impeller. The above action is due to the formation of an intermetallic compound together with Al and Fe, and preferentially crystallizing out at the grain boundary to obtain dispersion strengthening. This effect is that when the addition amount of Ni is less than 0.8% by mass, sufficient dispersion strengthening of the Al—Fe—Ni-based crystallized product cannot be obtained. Reduces mechanical properties. Therefore, Ni is made 0.8 mass% to 1.4 mass%. A preferable Ni addition amount is 0.9 mass% to 1.2 mass%.

B is added for the purpose of refining the crystal grains in order to promote the effect of suppressing the growth of crystal grains at the time of casting by adding simultaneously with Ti. This effect is low when the amount of B added is less than 0.0012% by mass, and when it exceeds 0.006% by mass, the crystallization mechanical properties are deteriorated as a coarse crystallized product during casting. Therefore, B is set to 0.0012 mass% to 0.006 mass%. A preferable B addition amount is 0.002 mass% to 0.004 mass%.
(Metal structure)
The strength of the impeller forged product 1 is affected by the metal structure as well as the chemical composition of the aluminum alloy described above. Further, the impeller forged product 1 forms a disk portion 11, a boss portion 12, and a blade portion 13 by forging a material block, for example, a cylindrical material. The metal structure is affected by the processing rate (upsetting rate) in the forging process, but the processing rate is not uniform and varies depending on the part. The upsetting rate of each part in the impeller forged product 1 is blade portion> boss portion> disk portion, and the higher the setting rate, the finer the metal structure tends to increase the strength. In the impeller forged product 1 according to the present invention, the metal structure of the disk portion 11 is defined to indirectly define the metal structure of other parts. Although this invention does not prescribe | regulate the upsetting rate of each part, the upsetting rate in the blade | wing part 13 is 45%-55%, the upsetting rate in the disk part 11 is 5%-15%, and a boss | hub part The upsetting rate at 12 is 25% to 35%.

  The impeller forged product 1 of the present invention shows that the disk part 11 has high high-temperature strength due to the metal structure of the disk part 11, and the blade part 13 having a metal structure that is indirectly refined than the disk part 11. Indicates that it has higher high-temperature strength than the disk portion 11. In the impeller forged product 1, the blade portion 13 is a portion where metal fatigue is likely to occur due to repeated rapid rotation and stop, and is a portion that requires higher high-temperature strength than the disk portion 11 and the boss portion 12. Accordingly, the fact that the blade portion 13 has a higher high-temperature strength than the disk portion 11 is suitable for the mechanical characteristics required for each part of the impeller.

  In the present invention, the disk portion having high high-temperature strength means a disk portion having a fatigue strength at 170 ° C. of 128 MPa or more, or a tensile strength at 170 ° C. of 345 MPa or more.

  In the impeller forged product 1 of the present invention, the chemical composition of the aluminum alloy is specified, and the average grain size of the crystal grains in an arbitrary cross section of the disk portion 11 parallel to the rotation axis is specified to be 30 μm to 120 μm. By defining the average grain size of the crystal grains in the disk portion 11 within the above range, high high-temperature strength can be obtained. A preferable average particle diameter in the disk portion 11 is 50 μm to 80 μm.

The metal structure of the impeller forged product 1 includes a CuAl ₂ θ-phase compound. CuAl ₂ has the effect of increasing the high-temperature strength, and the average particle diameter is 1.0 μm to 15 μm and the occupied area ratio is 4% to 15% in an arbitrary cross section parallel to the rotation axis of the disk portion 11. Is preferred. A more preferable average particle diameter is 3.0 μm to 10 μm, and a more preferable occupation area ratio is 6% to 10%.

  Although this invention does not prescribe | regulate the metal structure of the blade | wing part 13 and the boss | hub part 12, the average particle diameter of the preferable crystal grain in the blade | wing part 13 is 10 micrometers-30 micrometers, and the average particle diameter of the preferable crystal grain in the boss | hub part 12 is. Is 30 μm to 100 μm.

  The impeller forged product 1 having the above metal structure can be manufactured, for example, by the following steps.

    When a continuous casting material is used as a material for forging, the continuous casting material is homogenized at 470 ° C. to 540 ° C. for 0.5 hours to 4.0 hours, and then peeled and cut to a required length. . The cut material is bonded and heated to 20 ° C. to 450 ° C., while the mold temperature is heated to 20 ° C. to 250 ° C., and forged into the shape of the impeller forged product 1 shown in FIG. The formed forged product is quenched after solution treatment at 520 ° C. to 540 ° C. × 0.5 hours to 6 hours (for example, water cooling at 10 ° C. to 80 ° C.) and artificial at 160 to 220 ° C. for 1 hour to 48 hours. Perform aging treatment.

  A circular continuous cast material having a diameter of 50 mm was produced from the aluminum alloys adjusted to the chemical compositions of Examples 1 and 2 and Comparative Examples 1 to 12 shown in Table 1, homogenized at 30 ° C. for 7 hours, and air-cooled. . The continuous cast material was cut into a length of 80 mm after peeling to obtain a forging material 20 shown in FIG. The forging material 20 is a cylinder having a diameter of 50 mm and a length of 80 mm.

  As shown in FIG. 2, the forging material 20 is subjected to a bonding process at a material temperature of 25 ° C. and a mold temperature of 30 ° C. As shown in FIG. 2, the axial direction (L direction) of the cast material and the direction perpendicular to the axial direction (LT direction, 6 types of material characteristics including upsetting (10%, 20%, 30%, 40%, 50% upsetting) and unforged (upsetting rate 0%) A forging material 21 for investigation was formed. The thickness direction in the forging material 21 for material property investigation is defined as the ST direction.

  Further, each of the forging materials 21 for investigating the material properties was subjected to a solution treatment at 530 ° C. for 3 hours, quenched with water at 30 ° C., and then subjected to an artificial aging treatment at 200 ° C. for 20 hours to produce a forged T6 product. It was. A forged T6 product with an upsetting rate of 10% corresponds to the disk portion 11 of the impeller forged product 1, a forged T6 product with an upsetting rate of 30% corresponds to the boss portion 12, and a forged T6 product with an upsetting rate of 50% It corresponds to the blade part 13. The cross section parallel to the ST direction corresponds to the cross section parallel to the rotation axis of the impeller forged product.

The tensile strength, fatigue strength, and metal structure of each forged material 21 (forged T6 product) after heat treatment were examined by the following methods.
[Tensile strength]
In order to perform a room temperature tensile test, a room temperature tensile test piece was cut out from the forged T6 product by cutting. The shape of the test piece was a JIS No. 4 test piece, and a tensile test was performed in accordance with the provisions of JISZ2241 to measure the tensile strength.

In order to perform a high temperature tensile test, the forged T6 product was preheated at 170 ° C. for 100 hours, and a high temperature tensile test piece was cut out by cutting. The shape of the test piece was a JIS No. 4 test piece, and a tensile test was performed in accordance with the provisions of JISZ2241 to measure the tensile strength.
[Fatigue strength]
In order to perform a high temperature fatigue test, the forged T6 product was preheated at 170 ° C. for 100 hours and cut into a predetermined test piece shape by cutting. The fatigue test was measured using an Ono rotary bending tester, and each alloy was measured 8 times to obtain an SN curve. The resulting calculated fatigue strength at repeated several 10 ⁷ times from S-N curves and the fatigue strength at 170 ° C..
[Metal structure]
From the forged T6 product, a 1 cm × 1 cm × 1 cm square material in which the cross section in the L direction and the cross section in the ST direction are exposed is cut out from the forged T6 product, embedded in resin, and the cross section in the ST direction is polished with emery paper and buffed And finished to a mirror surface.

  The cross section in the ST direction of the mirror-finished sample was observed with a light microscope using an optical microscope Nikon EPIPOT 300 with an objective lens × 10. Further, the sample having a mirror finish was eroded for 3 minutes in a solution obtained by diluting borofluoric acid to 1.8%, and was corroded by applying a voltage of 20 V in the solution to obtain a sample for polarizing structure observation. The cross section in the ST direction of the sample for observing the polarized structure was observed with the objective lens × 40 using the optical microscope Nikon EPIPHOT 300.

The crystal grain size and the grain size of the CuAl ₂ θ phase compound are obtained by taking four fields from a polarization observation photograph, drawing three lines in the ST direction in each field, and dividing the length of the line by the number of crystal grains or compounds. The value obtained was defined as the particle size. The obtained particle sizes were added and divided again by the number of measurements to obtain the average particle size of crystal grains or compounds.

The occupied area ratio of the CuAl ₂ θ phase compound was calculated by calculating the area of the compound by regarding the particle diameter measured by polarization structure observation as the equivalent circle diameter in the normal light texture photograph, and calculating the occupied area ratio of the compound with respect to the visual field range. .

  Table 1 shows the metal structure and 170 ° C. fatigue strength of the forged T6 product with upsetting ratio of 10% produced from the aluminum alloys of Examples 1 and 2 and Comparative Examples 1 to 12. Table 2 shows the room temperature tensile strength of the unforged T6 products with the upsetting rate of 0%, forged T6 products with the upsetting rates of 10%, 20%, 30%, and 40%, which were produced from the aluminum alloy of Example 1, 170 ° C. The tensile strength, 170 ° C. fatigue strength, and average grain size are shown. Table 3 shows room temperature tensile strengths of unforged T6 products with an upsetting rate of 0%, forged T6 products with an upsetting rate of 10%, 20%, 30%, and 40%, made of the aluminum alloy of Example 2. 170 ° C. tensile strength, 170 ° C. fatigue strength, and average grain size of crystal grains are shown.

  As shown in Table 1, high temperature strength with a fatigue strength at 170 ° C. of 128 MPa or higher is obtained by controlling the chemical composition and metal structure of the aluminum alloy in a forged T6 product with a 10% upsetting rate corresponding to the disk portion of the impeller. It is done.

  As shown in Tables 2 and 3, the average grain size of the forged T6 product with a 50% upsetting rate corresponding to the blade portion 13 is the average grain size of the forged T6 product with a 10% upsetting rate corresponding to the disk portion 11. The high temperature strength of the forged T6 product, which is smaller than the average particle size and has an upsetting rate of 50%, is higher than that of the forged T6 product having an upsetting rate of 10%.

  The above results indicate that the impeller forged product has a high temperature strength of the disk portion 11 of 345 MPa or more and a high temperature strength of the blade portion 13 is higher than that of the disk portion 11.

  The forged product for an impeller of the present invention can be used as an impeller for a turbocharger that requires high high-temperature strength.

DESCRIPTION OF SYMBOLS 1 ... Impeller forged product 10 ... Hub 11 ... Disk part 12 ... Boss part 13 ... Blade | wing part

Claims (3)

A forged article for an impeller having a hub having a boss part at the center of a circular disk part and a plurality of blade parts provided radially on the outer surface of the hub;
The forged product for the impeller includes: Si: 0.05% by mass to 0.30% by mass, Fe: 0.7% by mass to 1.5% by mass, Cu: 1.7% by mass to 2.9% by mass, Mg : 1.0% by mass to 1.9% by mass, Ti: 0.03% by mass to 0.15% by mass, Ni: 0.8% by mass to 1.4% by mass, and the balance from Al and inevitable impurities Made of an aluminum alloy
A forged article for impellers, wherein an average grain size of crystal grains in an arbitrary cross section parallel to the impeller rotation axis of the disk portion is 30 μm to 120 μm.   The forged product for an impeller according to claim 1, wherein the aluminum alloy further contains B: 0.0012 mass% to 0.006 mass%. The average particle size of the CuAl ₂ θ-phase compound in an arbitrary cross section parallel to the impeller rotation axis of the disk portion is 1.0 μm to 15 μm, and the occupied area ratio is 4% to 15%. The forged product for impellers according to 2.

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