JP6669375B2 - Compressor impeller for turbocharger and method of manufacturing the same - Google Patents

Description

  The present invention relates to a compressor impeller for a turbocharger and a method for manufacturing the same.

  An internal combustion engine used in motors for automobiles and various industrial applications includes a turbocharger that compresses intake air by rotating a turbine wheel by exhaust gas of the internal combustion engine and rotating a compressor impeller coaxially connected to the turbine wheel. Some have a charger. In recent years, low-pressure exhaust gas circulation (LPL-EGR, Low-pressure Loop) for circulating a part of exhaust gas of an internal combustion engine upstream of an intake passage in a turbocharger for the purpose of improving the performance of the internal combustion engine and reducing the environmental load. Exhaust Gas Recirculation) system is adopted. In this LPL-EGR system, the compressor compresses intake air containing exhaust gas, so that corrosive components of the exhaust gas come into contact with the compressor impeller. At the same time, abrasion may progress rapidly. Therefore, the base material of the compressor impeller is subjected to a chemical conversion treatment, an anodic oxidation film treatment, metal plating or various coatings to modify the surface of the base material, thereby preventing corrosion and wear of the compressor impeller. For example, the configuration disclosed in Patent Document 1 discloses a configuration in which a coating layer for ensuring corrosion resistance and wear resistance is provided on the base material surface of the impeller.

JP-A-2006-169613

  However, since the compressor impeller vibrates minutely at ultra-high-speed rotation, the film of the compressor impeller is further required to have both adhesion and flexibility to the base material in order to prevent breakage due to the minute vibration. Further, there is room for improvement in order for the compressor impeller film to have a structure having sufficient adhesion and flexibility in addition to corrosion resistance and wear resistance.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a compressor impeller for a turbocharger having a film having corrosion resistance, abrasion resistance, adhesion, and flexibility.

One embodiment of the present invention is a base material including aluminum or an aluminum alloy,
A barrier layer covering the surface of the base material, and an alumite film including a porous layer laminated on the barrier layer and having a plurality of pores,
With
In the compressor impeller for a turbocharger, amorphous silica is sealed in the pores.

Another aspect of the present invention is a barrier layer that covers a surface of the base material by immersing a base material made of aluminum or an aluminum alloy in an electrolytic solution, performing an anodization film treatment on a surface of the base material, An alumite film forming step of forming an alumite film including a porous layer having a plurality of pores laminated on the barrier layer,
A silica encapsulation step of encapsulating amorphous silica in the pores,
And a method for manufacturing a compressor impeller for a turbocharger.

  According to the compressor impeller for a turbocharger according to the above aspect, corrosion resistance is imparted to the compressor impeller by the barrier layer of the alumite film formed on the surface of the base material. Furthermore, the silica impregnated in a large number of pores in the porous layer of the alumite film imparts wear resistance to the compressor impeller. The alumite film has excellent adhesion to a base material made of an aluminum alloy and has flexibility. Therefore, even if the compressor impeller rotates at high speed and vibrates minutely, breakage or cracking of the surface of the compressor impeller is prevented.

  According to the method of manufacturing a compressor impeller for a turbocharger according to the other aspect, it is possible to manufacture a compressor impeller for a turbocharger having the above-described effects. And

  ADVANTAGE OF THE INVENTION According to this invention, the compressor impeller for turbochargers which has a film which has corrosion resistance, abrasion resistance, adhesiveness, and flexibility can be provided.

FIG. 2 is a perspective view of a compressor impeller for a turbocharger in the first embodiment. FIG. 2 is a schematic diagram for explaining a film configuration of a compressor impeller for a turbocharger in the first embodiment. FIG. 2 is a schematic diagram for explaining a state of formation of alumite chromate in Example 1. FIG. 4 is a flowchart showing a method for manufacturing a compressor impeller for a turbocharger in the first embodiment. FIG. 4 is a schematic diagram for explaining a method of manufacturing a compressor impeller for a turbocharger in the first embodiment. FIG. 6 is a diagram illustrating the results of Comparative Examples 1 and 2 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Comparative Example 3 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Test Example 1 in the evaluation test of Example 1. FIG. 5 is a diagram illustrating the results of Test Example 2 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Comparative Example 3 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Test Example 1 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Test Example 1 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Comparative Example 3 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Test Example 1 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Test Example 1 in the evaluation test of Example 1. FIG. 7 is a diagram illustrating the results of Test Example 1 in the evaluation test of Example 1. FIG. 9 is a diagram showing the results of Comparative Examples 4 and 5 in the evaluation test of Example 2. FIG. 9 is a diagram illustrating the results of Test Examples 3 and 4 in the evaluation test of Example 2. FIG. 10 is a diagram illustrating a result of Comparative Example 4 in an evaluation test of Example 2. FIG. 9 is a diagram illustrating a result of Test Example 3 in an evaluation test of Example 2. FIG. 9 is a diagram illustrating a result of Test Example 3 in an evaluation test of Example 2. FIG. 10 is a diagram illustrating a result of Comparative Example 4 in an evaluation test of Example 2. FIG. 10 is a diagram illustrating a result of Comparative Example 4 in an evaluation test of Example 2. FIG. 9 is a diagram illustrating a result of Test Example 3 in an evaluation test of Example 2. FIG. 9 is a diagram illustrating a result of Test Example 3 in an evaluation test of Example 2. FIG. 9 is a diagram illustrating a result of Test Example 4 in an evaluation test of Example 2. FIG. 14 is a diagram illustrating the results of Comparative Examples 6 and 7 in the evaluation test of Example 3. FIG. 9 is a diagram showing the results of Test Examples 5 and 6 in the evaluation test of Example 3. FIG. 14 is a diagram illustrating the results of Comparative Example 6 in the evaluation test of Example 3. FIG. 13 is a diagram illustrating a result of Test Example 5 in an evaluation test of Example 3. FIG. 13 is a diagram illustrating a result of Test Example 5 in an evaluation test of Example 3. FIG. 14 is a diagram illustrating the results of Comparative Example 6 in the evaluation test of Example 3. FIG. 14 is a diagram illustrating the results of Comparative Example 6 in the evaluation test of Example 3. FIG. 13 is a diagram illustrating a result of Test Example 5 in an evaluation test of Example 3. FIG. 13 is a diagram illustrating a result of Test Example 5 in an evaluation test of Example 3. FIG. 14 is a diagram illustrating the results of Test Example 6 in the evaluation test of Example 3.

  It is preferable that the alumite film is made of alumite chromate. In this case, the adhesion and flexibility of the alumite film to the base material are further enhanced. Further, in the porous layer of the alumite film, the pores extend obliquely with respect to the thickness direction of the alumite film and are formed in a dendritic manner. It can be stably present within. According to the alumite chromate, the dimensional change due to the formation of the alumite chromate is relatively small. Therefore, the shape of the base material can be easily maintained, and the molding accuracy of the compressor impeller 1 can be improved.

The silica is amorphous silica . This makes it easier to disperse the silica in the solution, and makes it easier to encapsulate the silica in the pores of the alumite film.

  It is preferable that the thickness of the alumite film is in the range of 3 to 8 μm. If the thickness of the alumite film is smaller than 3 μm, sufficient corrosion resistance cannot be ensured. On the other hand, if the thickness of the alumite film is larger than 8 μm, it takes a long time to form the film and the corrosion resistance does not increase so much, which is disadvantageous in cost.

  It is preferable that a silica-containing layer containing silica as a main component is laminated on the porous layer. In this case, even if foreign substances contained in the exhaust gas or fine particles of the ceramic separated from the ceramic catalyst carrier in the exhaust gas purifying apparatus collide with the compressor impeller via the LPL-EGR, they are formed on the outermost surface of the compressor impeller. The silica-containing layer absorbs the impact of the collision, so that the wear resistance of the compressor impeller can be greatly improved, and the compressor impeller can be prevented from being damaged.

  In the method for manufacturing a compressor impeller for a turbocharger, in the silica enclosing step, the base material is immersed in a colloidal silica liquid, and the colloidal silica contained in the colloidal silica liquid is electrophoresed into the plurality of pores. It is preferable to enclose it in In this case, silica can be reliably enclosed in the pores of the porous layer of the alumite film. Since the alumite film forming step and the silica enclosing step can be easily performed in an integrated line, the working efficiency in the manufacturing process can be improved.

  The colloidal particle diameter D50 of the colloidal silica is preferably in the range of 5 to 55 nm. In this case, since the colloidal particles of colloidal silica are sufficiently small, the colloidal silica is easily encapsulated in the pores of the alumite film in the silica encapsulation step.

  The particle size of the colloid particles can be derived from the shape of the particles observed in the particle photograph. When the shape of the particle observed in the particle photograph is spherical, the diameter is defined as the particle size. On the other hand, when the shape of the particles is not spherical but polyhedral, unspecified, or the like, the equivalent circle diameter determined by the circular projection method is defined as the particle diameter.

Still another aspect of the present invention is a base material made of aluminum or aluminum alloy,
A barrier layer covering the surface of the base material, and an alumite film including a porous layer laminated on the barrier layer and having a plurality of pores,
With
Amorphous silica is sealed in the pores,
The alumite coating is on a compressor impeller for a turbocharger, which is made of alumite sulfate or alumite oxalate.

  In the compressor impeller for a turbocharger according to the above still another aspect, since the alumite film is made of alumite sulfate or alumite oxalate, the adhesion and flexibility of the alumite film to the base material are further enhanced. Further, since the alumite film can be formed relatively inexpensively, it is advantageous in terms of cost. Further, since the alumite sulfate has a high film forming rate, the production period can be shortened. Further, the alumite film made of sulfate alumite is relatively high in transparency and has high adsorptivity of the dyeing substance, so that it has excellent dyeability. Further, since oxalic acid alumite has a certain degree of flexibility, cracks are relatively unlikely to occur in the alumite film. Further, an alumite film made of oxalic acid alumite exhibits high corrosion resistance.

In the compressor impeller for a turbocharger according to the still another aspect, the silica is amorphous silica . This makes it easy to disperse the silica in the solution, and it becomes easy to encapsulate the silica in the pores of the alumite film made of sulfate alumite or oxalate alumite.

  In the compressor impeller for a turbocharger according to the still another aspect, it is preferable that the thickness of the alumite film made of the alumite sulfate or the oxalate alumite is in a range of 3 to 8 μm. If the thickness of the alumite film is smaller than 3 μm, sufficient corrosion resistance cannot be ensured. On the other hand, if the thickness of the alumite film is larger than 8 μm, it takes a long time to form the film and the corrosion resistance does not increase so much, which is disadvantageous in cost.

  In the compressor impeller for a turbocharger according to the still another aspect, it is preferable that a silica-containing layer containing silica as a main component is laminated on the porous layer in the alumite film made of alumite sulfate or alumite oxalate. In this case, even if foreign substances contained in the exhaust gas or fine particles of the ceramic separated from the ceramic catalyst carrier in the exhaust gas purifying apparatus collide with the compressor impeller via the LPL-EGR, they are formed on the outermost surface of the compressor impeller. The silica-containing layer absorbs the impact of the collision, so that the wear resistance of the compressor impeller can be greatly improved, and the compressor impeller can be prevented from being damaged.

(Example 1)
An embodiment of the compressor impeller for a turbocharger will be described with reference to FIGS.
The compressor impeller 1 for a turbocharger of the present embodiment shown in FIG. 1 includes a base material 10 and an alumite film 20, as shown in FIG.
The base material 10 is made of aluminum or an aluminum alloy.
The alumite film 20 includes a barrier layer 21 covering the surface 11 of the base material 10 and a porous layer 22 laminated on the barrier layer 21 and having a plurality of pores 23.
The pores 23 are filled with silica 30.

  The compressor impeller 1 for a turbocharger according to the present embodiment is configured such that, in a turbocharger (not shown), a turbine wheel is connected to the other end of a rotor shaft connected to one end to compress air supply in a compressor housing. ing. As shown in FIG. 1, the compressor impeller 1 includes a plurality of sets (six sets in this example) of large and small blades 1a and 1b, and the large and small blades 1a and 1b are alternately arranged around the axis 1c.

  The base material 10 shown in FIG. 2 is made of aluminum or an aluminum alloy, and is not particularly limited as long as an alumite film described later can be formed. For example, the base material 10 can be a high-strength aluminum alloy, and in this embodiment, an Al-Cu-based aluminum alloy A2618 (2.3Cu1.6Mg1.1Fe1Ni0.18Si0.07Ti) was employed.

  The type of the alumite film 20 shown in FIG. 2 can be, for example, alumite chromate, alumite oxalate, alumite sulfate, or alumite phosphate. In particular, it is preferable that the alumite film 20 is made of achromate alumite. As shown in FIG. 3, the alumite chromate is formed in a tree shape with the pores 23 extending obliquely to the thickness direction X of the alumite film 20. Thereby, when the silica 30 is sealed in the pores 23, the silica 30 is stably held. In FIG. 2, the sizes and shapes of the base material 10, the alumite film 20, the barrier layer 21, the porous layer 22, and the pores 23 are different from actual ones and are shown for convenience of explanation. It is.

  As shown in FIG. 2, silica 30 is sealed in the pores 23. The type of the silica 30 sealed in the pores 23 is not limited. For example, non-crystalline or amorphous silica can be used. In this embodiment, colloidal silica is employed as silica to be sealed in the pores 23 in a silica sealing step S3 described later. The particle diameter D50 of the colloidal particles in the colloidal silica can be 5 to 55 nm, preferably 20 to 40 nm.

  As shown in FIG. 2, the pores 23 in which the silica 30 is sealed are subjected to a sealing treatment, and the openings 31 are closed. The sealing treatment is not particularly limited, and may be sealing treatment by adding an inorganic or organic substance, including sealing treatment with pressurized steam, sealing treatment in boiling water, nickel acetate sealing treatment, and dichromic acid sealing treatment. Can be.

  As shown in FIG. 2, in the present embodiment, a silica-containing layer 41 is laminated on the porous layer 22. The silica-containing layer 41 contains silica as a main component. The thickness of the silica-containing layer 41 is not particularly limited, but can be 4 to 20 μm. In the present embodiment, it is assumed that the silica-containing layer 41 is mainly composed of the colloidal silica laminated on the porous layer 22 in the silica enclosing step S3 described below, and is a mixture of the hydrate formed in the sealing step S4. Is done.

Next, a method for manufacturing the compressor impeller 1 for a turbocharger of the present embodiment will be described in detail.
As shown in FIG. 4, the method for manufacturing the compressor impeller 1 for a turbocharger of the present embodiment includes an alumite film forming step S2 and a silica enclosing step S3. In this embodiment, a preparation step S1 is included before the alumite film formation step S2, and a sealing step S4 is included after the silica encapsulation step S3.

  First, in a preparation step S1 shown in FIG. 4, a base material 10 of the compressor impeller 1 is manufactured. In the preparation step S1, as shown in FIG. 5A, a high-strength aluminum alloy serving as a base material 10 of the compressor impeller 1 is prepared. Then, the material is machined to form the outer shape of the compressor impeller 1 to form the base material 10. The method of machining is not limited, but cutting, grinding, and the like using an NC turning center or a machining center can be adopted. The formed base material 10 is subjected to dimensional inspection, balanced, formed with high precision, and finished.

  Thereafter, in an alumite film forming step S2 shown in FIG. 4, as shown in FIG. 5B, an alumite film 20 is formed on the surface 11 of the base material 10 by anodizing film treatment. In the alumite film forming step S2, first, degreasing and cleaning are performed to remove oils and fats and dirt attached to the surface 11 of the base material 10. In this embodiment, the degreasing is performed by treating the acidic degreasing agent at 40 to 60 ml / L, sulfuric acid at 30 to 50 ml / L, and at a temperature of 55 ° C. for 120 seconds. Thereafter, if necessary, the surface 11 of the base material 10 is masked, fixed to a jig (not shown), and degreased and cleaned again. Then, alkali etching, smut treatment, and cleaning are performed to completely remove dirt and foreign matter on the surface 11 of the base material 10.

Then, the base material 10 fixed to the jig is immersed in an electrolytic bath (not shown) filled with an electrolytic solution, and a voltage is applied to the cathode and the base material (not shown) also immersed in the electrolytic bath. In this embodiment, chromic acid anhydride (CrO ₃₎ of 5 to 10% w / v as the electrolyte was an aqueous solution. By applying a voltage, as shown in FIG. 5B, an anodized film, that is, an alumite film 20 is formed on the surface 11 of the base material 10 using the base material 10 as an anode. The alumite film 20 includes a barrier layer 21 that covers the surface 11 of the base material 10, and a porous layer 22 that grows porous from the barrier layer 21 and is laminated on the barrier layer 21. The porous layer 22 includes a plurality of pores 23 extending in the thickness direction X of the alumite film 20. In addition, the thickness of the alumite film 20 can be set to 3 to 8 μm, preferably 5 to 8 μm, and in the present embodiment, it is in the range of 5 to 7 μm. Note that the target film thickness of the alumite film 20 is set in advance, and the magnitude of the applied voltage and the application time can be set accordingly. In this example, the target film thickness was 5 to 7 μm, the applied voltage was 40 V, and the energizing time was about 60 minutes.

  Since the alumite film 20 uses the aluminum component of the base material 10 as a raw material, it grows while eroding the surface 11 of the base material 10 before the treatment shown in FIG. Therefore, the surface 11 of the base material 10 after the processing shown in FIG. 5B is at a position retracted from the surface 11 of the base material 10 before the processing shown in FIG. However, as described above, since the thickness of the alumite film 20 is on the order of several μm, the shape change of the base material 10 is sufficiently small to be negligible. Therefore, even if the alumite film 20 is formed, the molding accuracy of the base material 10 can be maintained.

  Next, in a silica enclosing step S3 shown in FIG. 4, silica 30 is encapsulated in the pores 23 as shown in FIG. In the silica enclosing step S3, first, the base material 10 is pulled out of the electrolytic bath, and the surface of the alumite film 20 is washed. Thereafter, the base material 10 is immersed in the colloidal silica solution, and a voltage is applied to the cathode immersed in the colloidal silica solution and the base material 10. Since the colloidal silica is negatively charged in the liquid, the colloidal silica is attracted by electrophoresis to the base material 10 serving as an anode. As a result, the colloidal silica penetrates into the pores 23 of the alumite coating 20, and the silica 30 is sealed in the pores 23 as shown in FIG. In this embodiment, as the colloidal silica liquid, Hyprez liquid 20 (colloid particle diameter D50 = 20 nm) manufactured by Nippon Engis Co., Ltd. is used. In this embodiment, the applied voltage in the electrophoresis is 60 V, the applied time is 1 minute, and the temperature condition is room temperature.

  In this embodiment, in the silica enclosing step S3 shown in FIG. 4, silica 30 is encapsulated in the pores 23 shown in FIG. 5C, and a silica layer 40 made of silica 30 is formed on the alumite film 20. The silica layer 40 covers the outer surface of the porous layer 22 of the alumite coating 20 by depositing silica 30 attracted to the base material 10 by electrophoresis in the silica enclosing step S3 on the outer surface of the porous layer 22. It is laminated. The thickness of the silica layer 40 is not particularly limited, but is in the range of 4 to 15 μm in the present embodiment.

  Thereafter, in a sealing step S4 shown in FIG. 4, a sealing process is performed to close the opening 31 of the fine pore 23 as shown in FIG. In the present example, in the sealing step S4, after the base material 10 after silica encapsulation is washed, it is immersed in a nickel acetate aqueous solution at 70 to 80 ° C. for 8 minutes as a sealing treatment. Then, it is washed with hot water at 60 to 70 ° C. for 2 minutes and dried. Thereby, the opening 31 is sealed by the hydrate generated by the sealing process. Further, the hydrate generated by the sealing treatment is mixed into the silica layer 40 to form a silica-containing layer 41 containing silica as a main component on the outer surface of the porous layer 22. Then, the base material 10 is removed from the jig to complete the compressor impeller 1 of the present embodiment. In this embodiment, after the preparation step S1, the alumite film forming step S2, the silica enclosing step S3, and the sealing step S4 are performed in an integrated line.

( First evaluation test)
The following first evaluation test was performed using Test Example 1, Test Example 2, and Comparative Examples 1 to 3.
As Test Examples 1 and 2, test pieces prepared by performing the respective steps S1 to S4 in the above-described manufacturing method of Example 1 on test pieces were prepared. In addition, the target film thickness of the alumite film 20 was set to 5 to 6 μm.
As Comparative Examples 1 and 2, untreated test pieces were prepared.
As Comparative Example 3, a test piece was prepared by performing steps S1 and S2 in the above-described production method of Example 1 to form an alumite film 20 on a test piece. In addition, the target film thickness of the alumite film 20 was set to 5 to 6 μm.
Each test piece was made of an Al-Cu-based aluminum alloy A2618 (2.3Cu1.6Mg1.1Fe1Ni0.18Si0.07Ti), and was the same material as the base material 10 in Example 1. Each test piece has a substantially disk shape with an outer diameter of 56 mm and a thickness of 3 mm. In addition, each test piece includes those whose outer shapes are slightly changed for easy discrimination.

  First, the appearance of each test piece was evaluated. As shown in FIGS. 6 to 9, an enlarged view of the whole of each test piece and the central part p5 and the lower part p3 of the main surface of the test piece was observed. In Comparative Example 3 shown in FIGS. 7A to 7C, slightly yellowish color was observed compared to Comparative Examples 1 and 2 shown in FIGS. 6A to 6F. On the other hand, in Test Example 1 shown in FIGS. 8A to 8C and Test Example 2 shown in FIGS. 9A to 9E, the whiteness was observed slightly as compared with Comparative Examples 1 to 3. .

  Next, the hardness was evaluated. The hardness was evaluated by measuring Vickers hardness (HV) with a test force of 0.1 kgf. As shown in FIG. 6 (a), FIG. 6 (d), FIG. 7 (a), FIG. 8 (a) and FIG. 9 (a), the measurement points are the upper and lower right and left portions p1 to p4 of the surface of each test piece. And a central part p5 for a total of five places. Then, measurement was performed three times for each of the measurement points p1 to p5, and the average value was calculated. Note that, in Test Example 2, the measurement was performed for each of the measurement points p2 to p5 having high hardness p21, p31, p41, and p51 and the low hardness sections p22, p32, p42, and p52. The results of the hardness measurement are shown in Table 1 below.

  As shown in Table 1, in the test pieces of Comparative Examples 1 and 2 having no alumite film 20, the average value of the Vickers hardness at each measurement point was in the range of 145 to 150 HV0.1. On the other hand, in the test pieces of Comparative Example 3 and Test Example 1 having the alumite film 20, the average value of the Vickers hardness at each measurement point was in the range of 186 to 208 HV0.1, and the hardness was higher than that of Comparative Examples 1 and 2. Was shown to be large. In Test Example 2, the average value of the Vickers hardness in the hard portions p21, p31, p41, and p51 was also in the range of 184 to 200 HV0.1, and the hardness was higher than that in Comparative Examples 1 and 2. It was shown that. Since Test Example 1 has the same Vickers hardness as Comparative Example 3, it can be confirmed that the hardness of the alumite film 20 is maintained even when the silica 30 is sealed in the pores 23 of the porous layer 22. Was.

  In Test Example 2, the average value of the Vickers hardness of the soft portions p22, p32, p42, and p52 was in the range of 81 to 123 HV0.1, and the hardness was lower than that of Comparative Examples 1 and 2. Had become. This is presumably because, in Test Example 2, the silica-containing layer 41 made of a material having a relatively low hardness was laminated on the porous layer 22 of the alumite film 20, and the hardness was apparently low. You.

  Next, for Comparative Example 3, cross-sectional images at the Q position of the test piece shown in FIG. 10A were taken and shown in FIGS. 10B to 10E. Similarly, for Test Example 1, FIGS. 11 (a) to 11 (e), 12 (a) and 12 (b) show the Q position and cross-sectional images at the Q position. Then, the thickness t1 of each alumite film 20 was measured.

In Comparative Example 3, as shown in FIG. 10E, the alumite film 20 was formed so as to cover the surface 11 of the base material 10, and the thickness t1 of the alumite film 20 was 5 μm.
In Test Example 1, as shown in FIG. 12A, the alumite film 20 is formed so as to cover the surface 11 of the base material 10 at the position Q1 shown in FIG. The lengths t1 and t3 were 4 μm and 3 μm, respectively. Further, the thicknesses t2 and t4 of the silica-containing layer 41 were 9 μm and 15 μm, respectively. At the position Q2 shown in FIG. 11B, as shown in FIG. 12B, the thickness t1 of the alumite film 20 was 4 μm. Further, the thickness t2 of the silica-containing layer 41 was 4 μm. Then, the silica-containing layer 41 was in a state where the difference between the irregularities was relatively large.

  As shown in FIGS. 10 to 12, it was confirmed that the alumite film 20 having a thickness of 3 to 5 μm can be formed by the alumite film formation step S2 in this example. Further, it was confirmed that the silica-containing layer 41 having a thickness of 4 to 15 μm can be formed by the silica enclosing step S3 and the sealing step S4 in the present example.

Next, the surface roughness was evaluated. The surface roughness Ra of Comparative Example 3 and Test Examples 1 and 2 was measured, and the measurement results are shown in Table 2 below. As shown in Table 2, in Test Examples 1 and 2, it was shown that the surface roughness Ra was increased as compared with Comparative Example 3. Thereby, it can be inferred that the silica 30 and the like adhere to the alumite film 20.

  Next, the component distribution of the surface of the test piece in Comparative Example 3 and Test Examples 1 and 2 was evaluated by EPMA mapping analysis. Further, for Test Example 1, the component distribution of the cross section of the test piece by EPMA mapping analysis was also evaluated. For the EPMA mapping analysis, an electron beam microanalyzer (model number EPMA-1720) manufactured by Shimadzu Corporation was used. The measurement area on the surface of the test piece was a rectangular area of 120 μm × 90 μm, and the measurement area on the cross section of the test piece was a rectangular area of 40 μm × 30 μm.

For Comparative Example 3, acquisition of an SEM (Scanning Electron Microscope) image at the S position shown in FIG. 10A and EPMA (Electron Probe Micro Analyzer) mapping analysis of the test piece surface were performed, and the results were shown in FIG. To (12).
For Test Example 1, acquisition of an SEM image at the S position shown in FIG. 11A and EPMA (Electron Probe Micro Analyzer) mapping analysis of the test piece surface were performed, and the results were shown in FIGS. )Pointing out toungue.
Further, for Test Example 1, acquisition of a SEM image at the Q position shown in FIG. 11A and EPMA mapping analysis of a cross section of the test piece were performed, and the results are shown in FIGS. 15 (1) to (12). As described below, (1) to (12) in each of FIGS. 13 to 15 show SEM images and analysis results for each element as described below.
(1): SEM image (2): distribution of oxygen element O (3): distribution of silicon element Si (4): distribution of sulfur element S (5): distribution of aluminum element Al (6): magnesium element Mg Distribution (7): Distribution of nickel element Ni (8): Distribution of chromium element Cr (9): Distribution of iron element Fe (10): Distribution of copper element Cu (11): Distribution of calcium element Ca (12): Distribution of sodium element Na

(1) SEM image As shown in FIG. 13 (1), in the comparative example 3, the surface layer of the alumite film 20 was relatively smooth, but in the test example 1 shown in FIG. 14 (1), the surface layer had many cracks. Shape-like cracks were observed, and it was confirmed that the surface roughness was larger than that of Comparative Example 3. Further, as shown in FIG. 15A, in Test Example 1, it was confirmed that the alumite film 20 was formed on the surface of the base material 10 and the silica-containing layer 41 was formed on the outer surface side thereof. Was. In addition, it was confirmed that the crack in the surface layer did not reach the base material 10 and was formed in the silica-containing layer 41 in the surface layer.

(2) Distribution of oxygen element O Regarding the distribution of oxygen element O, as shown in FIGS. 13 (2) and 14 (2), in each of Comparative Example 3 and Test Example 1, a large amount of oxygen element O was present in the surface layer. Existed. The oxygen element O in the surface layer in Comparative Example 3 is assumed to be derived from AlO ₂ forming the alumite film 20. Then, as shown in FIG. 15 (2), in the cross section of Test Example 1, it was confirmed that a large amount of the oxygen element O was present in the alumite film 20 covering the surface 11 of the base material 10. Then, it was confirmed that the oxygen element O was also present in the silica-containing layer 41 on the outer surface side of the alumite film 20. It is considered that the oxygen element O in the silica-containing layer 41 is derived from silica (SiO ₂ ) which is a main component of the silica-containing layer 41.

(3) Distribution of Silicon Element Si Regarding the distribution of silicon element Si, as shown in FIG. 13 (3), in Comparative Example 3, only a very small amount of silicon element Si was present. On the other hand, as shown in FIG. 14C, in Test Example 1, a large amount of silicon element Si was present in the surface layer. Then, as shown in FIG. 15C, in Test Example 1, the silicon element Si was partially present in the alumite coating 20 and was present in a large amount in the silica-containing layer 41 laminated on the alumite coating 20. . Thus, in Test Example 1, it was presumed that the silica 30 was encapsulated in the porous layer 22 of the alumite coating 20 and that the silica 30 was included in the silica-containing layer 41.

(4) Distribution of sulfur element S Regarding the distribution of the sulfur element S, as shown in FIG. 13 (4), in Comparative Example 3, only a trace amount of the sulfur element S was present in the surface layer. On the other hand, as shown in FIGS. 14 (4) and 15 (4), in Test Example 1, it was confirmed that a large amount of sulfur element S was present in the surface layer. This is presumed that the sulfur element S originated from the electrolytic solution, and that the sulfur element S remained in the surface layer in Test Example 1 in which the surface was rougher than in Comparative Example 3.

(5) Distribution of aluminum element Al Regarding the distribution of aluminum element Al, as shown in FIG. 13 (5), in Comparative Example 3, it was confirmed that a large amount of aluminum element Al was present in the surface layer. This is presumed to be derived from AlO ₂ forming the alumite film 20. On the other hand, as shown in FIG. 14 (5), in Test Example 1, it was confirmed that the aluminum element Al was not substantially present in the surface layer, and as shown in FIG. It was confirmed that the aluminum element Al was present in a large amount. This means that the silica 30 is encapsulated in the alumite film 20 formed on the base material 10 in the test example 1 and is covered with the silica-containing layer 41, so that the alumite film 20 does not appear. Show.

(6) Distribution of magnesium element Mg As shown in FIGS. 13 (6), 14 (6) and 15 (6), the distribution of magnesium element Mg shows the same tendency as the distribution of aluminum element Al. I have. The magnesium element Mg is derived from the base material 10 and shows that the base material 10 is in a state where the base material 10 does not appear in Test Example 1.

(7) Distribution of Nickel Element Ni Regarding the distribution of nickel element Ni, as shown in FIG. 13 (7), in Comparative Example 3, the amount of nickel element Ni in the surface layer was very small, but FIG. 14 (7). As shown in FIG. 15 (7), in Test Example 1, the amount of nickel element Ni in the surface layer was larger than that in Comparative Example 3. This is presumably because nickel element Ni derived from the nickel acetate aqueous solution remained in the vicinity of the opening 31 when the nickel acetate sealing treatment was performed in the sealing step S4 in this embodiment. In addition, it is considered that a part of Ni eluted into the electrolyte as a cation from the base material 10 in the alumite film forming step S2 remained in the pores 23.

(8) Distribution of Calcium Element Ca Regarding the distribution of calcium element Ca, as shown in FIG. 13 (11), in comparative example 3, calcium element Ca was not substantially present in the surface layer. ), In Test Example 1, the calcium element Ca was present in the surface layer. Then, as shown in FIG. 15 (11), it was confirmed that the calcium element Ca was present in the silica-containing layer 41. This is presumed to be due to the trace amount of calcium element Ca in the colloidal silica liquid remaining in the silica-containing layer 41 during the formation of the silica-containing layer 41.

(9) Distribution of Other Elements Regarding the distribution of other elements, Comparative Example 3 and Test Example 1 showed the same tendency.

  Next, the ratio of contained elements in the film in Test Example 1 was evaluated. As shown in FIG. 16, in the cross section at the position Q shown in FIG. 11A in Test Example 1, the thickness t1 of the alumite film 20 was 5.1 μm. In the alumite coating 20, a coating deep portion A close to the base material 10, a coating central portion B on the outer surface side of the coating deep portion A and substantially at the center in the thickness direction, and an outer surface near portion C on the outer surface side than the coating central portion B. Was detected using a focused ion beam-high resolution scanning electron microscope (model number JIB-4600F) manufactured by JEOL Ltd. The detection was performed by setting the acceleration voltage to 15 kV-1 nA after performing FIB processing on the test piece. The detection results are shown in Table 3 below.

  As shown in Table 3, it can be seen that in the alumite film 20, the Si content increases as it is located on the outer surface side. In consideration of the EPMA mapping analysis shown in FIGS. 13 to 15, the silica 30 entered the alumite film 20 in Test Example 1, and the silica-containing layer 41 containing the silica 30 was formed on the outer surface of the alumite film 20. Inferred.

Next, the operation and effect of the compressor impeller 1 for a turbocharger of the present embodiment will be described in detail.
According to the compressor impeller 1 for a turbocharger of the present embodiment, corrosion resistance is imparted to the compressor impeller 1 by the barrier layer 21 of the alumite film 20 formed on the surface 11 of the base material 10. Further, since the silica 30 is sealed in the large number of pores 23 in the porous layer 22 of the alumite film 20, the compressor impeller 1 is given wear resistance. The alumite film 20 has excellent adhesion to the base material 10 made of an aluminum alloy and has flexibility. Therefore, even if the compressor impeller 1 rotates at a high speed and vibrates minutely, the surface of the compressor impeller 1 is prevented from being damaged or cracked.

  Further, in this example, the alumite film 20 is made of alumite chromate. Thereby, the adhesion and flexibility of the alumite film 20 to the base material 10 are further enhanced. Further, in the porous layer 22 of the alumite film 20, the pores 23 extend obliquely with respect to the thickness direction X of the alumite film 20 and are formed in a tree shape, so that the silica 30 sealed in the pores 23 is released. Therefore, the silica 30 can be stably present in the pores 23. According to the alumite chromate, the dimensional change due to the formation of the alumite chromate is relatively small. Therefore, the shape of the base material 10 can be easily maintained, and the molding accuracy of the compressor impeller 1 can be improved.

  In this example, the silica 30 is an amorphous silica. Thereby, the silica 30 is easily dispersed in the solution, and the silica is easily sealed in the pores 23 of the alumite coating 20.

  In this example, the thickness t1 of the alumite film 20 is in the range of 3 to 8 μm. If the thickness of the alumite film 20 is smaller than 3 μm, it is not possible to secure sufficient corrosion resistance. Further, even if the thickness of the alumite film 20 is larger than 8 μm, the corrosion resistance does not increase, which is disadvantageous in cost. In this example, by setting the thickness t1 of the alumite film 20 within the above range, sufficient corrosion resistance can be ensured and the cost can be made advantageous.

  In this example, a silica-containing layer 41 containing silica 30 as a main component is laminated on the porous layer 22. As a result, even if foreign matter contained in the exhaust gas or fine particles of the ceramic separated from the ceramic catalyst carrier in the exhaust gas purifying apparatus collide with the compressor impeller 1 via the LPL-EGR, they are formed on the outermost surface of the compressor impeller 1. The silica-containing layer 41 absorbs the impact of the collision, so that the abrasion resistance of the compressor impeller 1 can be greatly improved, and the compressor impeller 1 can be prevented from being damaged.

  According to the method for manufacturing the compressor impeller 1 for a turbocharger in the present embodiment, the compressor impeller 1 for a turbocharger having the above-described effects can be manufactured.

  In the present example, in the silica enclosing step S3, the base material 10 is immersed in the colloidal silica liquid, and the colloidal silica contained in the colloidal silica liquid is encapsulated in the plurality of pores 23 by electrophoresis. Thereby, the silica 30 can be reliably enclosed in the pores 23 of the porous layer 22 of the alumite coating 20. Further, since the alumite film forming step S2 and the silica enclosing step S3 can be easily performed in an integrated line, the working efficiency in the manufacturing process can be improved. Further, in the present embodiment, in addition to the alumite film forming step S2 and the silica enclosing step S3, the sealing step S4 is also performed on a line consistent with these steps, so that the working efficiency is further improved.

  In the present embodiment, the colloidal particle diameter D50 of the colloidal silica is in the range of 5 to 55 nm. As a result, the colloidal particles of colloidal silica become sufficiently small, so that the colloidal silica is easily encapsulated in the pores 23 of the alumite coating 20 in the silica enclosing step S3.

  In this embodiment, by performing the sealing step S4, the leakage of the silica 30 sealed in the pores 23 is prevented, and the surface of the alumite coating 20 is chemically stabilized to improve the corrosion resistance. I have. Thereby, the life of the alumite film 20 is increased.

  As described above, according to the present embodiment, it is possible to provide the compressor impeller 1 for a turbocharger having a film having corrosion resistance, abrasion resistance, adhesion and flexibility.

(Example 2)
In Example 1, in the alumite film forming step S2 in the above manufacturing method, the alumite film 20 made of chromate alumite was formed using an aqueous solution of chromic anhydride (CrO ₃ ) as an electrolytic solution. In this example, in the alumite film forming step S2, an alumite film 20 made of sulfate alumite was formed using a sulfuric acid (H ₂ SO ₄ ) aqueous solution as an electrolytic solution. The concentration of the aqueous sulfuric acid solution used can be 10 to 30% w / v. In the present example, the target film thickness of the alumite film 20 was 5 to 7 μm, the applied voltage in the anodic oxide film treatment was about 15 V, and the energizing time was about 20 minutes. The other steps were the same as in Example 1.

  In the alumite film 20 made of an alumite chromate in Example 1, the pores 23 in the porous layer 22 were formed in a tree shape by extending obliquely in the thickness direction X as shown in FIG. In the alumite film 20 made of anodized sulfuric acid of the present embodiment, a large number of pores (not shown) in the porous layer 22 extend straight in the thickness direction X. The other configuration is the same as that of the first embodiment. In this embodiment, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

(Second evaluation test)
Next, the following second evaluation test was performed using Test Example 3, Test Example 4, Comparative Example 4 and Comparative Example 5.
As Test Examples 3 and 4, those in which an alumite film 20 made of the alumite sulfate of Example 2 was formed on a test piece were prepared. In addition, the target film thickness of the alumite film 20 was set to 5 to 6 μm.
As Comparative Examples 4 and 5, those in which the test pieces were subjected to the respective steps S1 and S2 in the above-described manufacturing method of Example 2 to form an alumite film 20 made of alumite sulfate were prepared. In addition, the target film thickness of the alumite film 20 was set to 5 to 6 μm.
Each test piece was made of the same material as the base material 10 as in the first evaluation test in Example 1, and the shape of each test piece was also substantially disc-like as in the first evaluation test.
In addition, Comparative Examples 1 and 2 in the first evaluation test are referred to as untreated test pieces.

  First, the appearance of each test piece was evaluated. As shown in FIG. 17 to FIG. 21, an enlarged view of the whole of each test piece and the central part p5 and the right part p2 of the main surface of the test piece was observed. In Comparative Example 4 shown in FIGS. 17A to 17C and Comparative Example 5 shown in FIGS. 17D to 17F, Comparative Examples 1 and 2 shown in FIGS. In comparison, no significant difference in appearance was observed, but some natural color development unique to the alumite film was observed. On the other hand, in Test Example 3 shown in FIGS. 18A to 18C and Test Example 4 shown in FIGS. 18D to 18F, the whiteness is slightly higher than Comparative Examples 1, 2, 4 and 5. It was once observed.

  Next, the hardness was evaluated. The hardness was evaluated by measuring Vickers hardness (HV) with a test force of 0.1 kgf. As shown in FIG. 17 (a), FIG. 17 (d), FIG. 18 (a), and FIG. 18 (d), the measurement points are the upper and lower left and right parts p1 to p4 and the central part p5 of the surface of each test piece. There were a total of five locations. Then, measurement was performed three times for each of the measurement points p1 to p5, and the average value was calculated. In addition, in Test Example 4, at the measurement points p1 and p3, measurement was performed for each of a high hardness portion and a low hardness portion (not shown). The results of the hardness measurement are shown in Table 4 below.

  As shown in Table 4, in the test pieces of Comparative Example 4, Comparative Example 5, and Test Example 3 having the alumite film 20 made of alumite sulfate, the average value of the Vickers hardness at each measurement point was in the range of 181 to 238 HV0.1. In the first evaluation test, the hardness was higher than that of Comparative Examples 1 and 2 shown in Table 1. In Test Example 4, the average value of the Vickers hardness in the hard part of p1, the hard part of p3, and the Vickers hardness in p2 was also in the range of 180 to 200 HV0.1, and the hardness was higher than those of Comparative Examples 1 and 2. It was shown that. And since Test Example 3 has the same Vickers hardness as Comparative Examples 4 and 5, even if silica 30 is sealed in the pores 23 of the porous layer 22, the hardness of the alumite film 20 made of alumite sulfate is maintained. It was confirmed that it was done.

  In Test Example 4, the average value of the Vickers hardness at the soft part of p1, the soft part of p3, and the Vickers hardness at p4 and p5 was 101, 110, 92, and 124 HV0.1, respectively. Hardness was lower than that. This is presumably because, in Test Example 4, the silica-containing layer 41 made of a material having a relatively low hardness was laminated on the porous layer 22 of the alumite film 20, and the hardness was apparently low. You.

  Next, for Comparative Example 4, cross-sectional images of the test piece at the Q position shown in FIG. 19A were taken, and are shown in FIGS. 19B to 19E. Similarly, for Test Example 3, FIGS. 20A to 20E, FIGS. 21A and 21B show Q positions and cross-sectional images at the Q positions. Then, in FIGS. 21A and 21B, the thickness t1 of each alumite film 20 and the thickness t2 of the silica-containing layer 41 were measured.

In Comparative Example 4, as shown in FIG. 19E, the alumite film 20 was formed so as to cover the surface 11 of the base material 10, and the thickness t1 of the alumite film 20 was 6 μm.
In Test Example 3, as shown in FIG. 21A, the alumite film 20 is formed so as to cover the surface 11 of the base material 10 at the position Q1 shown in FIG. The thickness t1 was 5 μm, and the thickness t2 of the silica-containing layer 41 laminated on the alumite film 20 was 6 μm. At the position Q2 shown in FIG. 20C, as shown in FIG. 21B, the thickness t1 of the alumite film 20 is 6 μm, and the thickness t2 of the silica-containing layer 41 laminated on the alumite film 20 is 13 μm. Then, the silica-containing layer 41 was in a state where the difference between the irregularities was relatively large.

  As shown in FIGS. 17 to 21, it was confirmed that the alumite film 20 made of alumite sulfate having a thickness of 5 to 6 μm can be formed by the alumite film formation step S2 in this example. In addition, it was confirmed that the silica-containing layer 41 having a thickness of 6 to 13 μm can be formed by the silica enclosing step S3 and the sealing step S4 in this example.

Next, the surface roughness was evaluated. The surface roughness Ra of Comparative Examples 4 and 5 and Test Examples 3 and 4 was measured, and the measurement results are shown in Table 5 below. As shown in Table 5, in Test Examples 3 and 4, it was shown that the surface roughness Ra was increased as compared with Comparative Examples 4 and 5. Thereby, it can be inferred that the silica 30 and the like adhere to the alumite film 20.

  Next, the component distribution of the test piece surface and the test piece cross section in Comparative Example 4 and Test Example 3 was evaluated by EPMA mapping analysis. EPMA mapping analysis was performed in the same manner as in the first evaluation test.

Regarding Comparative Example 4, on the test piece surface at the S position shown in FIG. 19A, acquisition of an SEM image and EPMA mapping analysis were performed, and the results are shown in FIGS. 22 (1) to (11). Further, on the cross section of the test piece at the Q position shown in FIG. 19A, acquisition of an SEM image and EPMA mapping analysis were performed, and the results are shown in FIGS. 23A to 23D.
For Test Example 3, SEM images were obtained and EPMA mapping analysis was performed on the test piece surface at the S position shown in FIG. 20A, and the results are shown in FIGS. 24 (1) to (11). Further, acquisition of an SEM image and EPMA mapping analysis were performed on the cross section of the test piece at the Q position shown in FIG. 20 (a), and the results are shown in FIGS. 25 (1) to (10).
(1) to (11) in each drawing in FIGS. 22 to 25 show SEM images and analysis results for each element as described below.
(1): SEM image (2): distribution of oxygen element O (3): distribution of silicon element Si (4): distribution of sulfur element S (5): distribution of aluminum element Al (6): magnesium element Mg Distribution (7): Distribution of nickel element Ni (8): Distribution of iron element Fe (9): Distribution of copper element Cu (10): Distribution of calcium element Ca (11): SEM image (low magnification)

(1) SEM Image As shown in FIG. 22 (1), in Comparative Example 4, a plurality of holes were scattered in the surface of the alumite film 20. However, as shown in FIG. The alumite film 20 was formed, and the surface alumite film 20 had relatively few irregularities, and the film thickness was almost constant. On the other hand, in Test Example 3, as shown in FIG. 24A, a number of cracks were observed in the surface layer, and a part of the surface layer was peeled off to expose the lower layer. Then, in Test Example 3, as shown in FIG. 25A, it was presumed that the alumite film 20 was formed on the surface of the base material 10 and the silica-containing layer 41 was laminated on the alumite film 20.

(2) Distribution of oxygen element O Regarding the distribution of oxygen element O, as shown in FIGS. 22 (2) and 23 (2), in Comparative Example 4, a large amount of oxygen element O was present in the surface layer. It is presumed that the oxygen element O in the surface layer in Comparative Example 4 is derived from AlO ₂ forming the alumite film 20. Further, as shown in FIG. 24 (2) and FIG. 25 (2), also in Test Example 3, a large amount of the oxygen element O was present in the surface layer. It is presumed that the oxygen element O in Test Example 3 is derived from silica (SiO ₂ ), which is the main component of the silica-containing layer 41.

(3) Distribution of silicon element Si Regarding the distribution of silicon element Si, as shown in FIG. 22 (3) and FIG. 23 (3), in Comparative Example 3, only a very small amount of silicon element Si was present. On the other hand, as shown in FIG. 24 (3), in Test Example 3, a large amount of silicon element Si was present in the surface layer. Then, as shown in FIG. 25C, in Test Example 3, the silicon element Si was partially present in the alumite film 20 and was present in a large amount in the silica-containing layer 41 laminated on the alumite film 20. . Thus, in Test Example 3, it was presumed that silica 30 was encapsulated in the porous layer 22 of the alumite coating 20, and that silica 30 was included in the silica-containing layer 41.

(4) Distribution of sulfur element S Regarding the distribution of the sulfur element S, in Comparative Example 4, as shown in FIG. 22 (4), a large amount of the sulfur element S is present in the surface layer, and is shown in FIG. 23 (4). Thus, it was confirmed that the sulfur element S was present in the alumite film 20. This is presumed that the sulfur element S is derived from the alumite sulfate forming the alumite film 20.
On the other hand, in Test Example 3, as shown in FIG. 24 (4), the abundance of sulfur element S was small in the surface layer, but as shown in FIG. 25 (4), a large amount of sulfur element S was present inside the surface layer. Exists. It is presumed that the sulfur element S inside the surface layer is derived from alumite sulfate forming the alumite film 20. The sulfur element S in the surface layer is presumed to be the sulfur element S derived from the electrolytic solution (aqueous sulfuric acid solution) remaining in the silica-containing layer 41 formed on the alumite film 20.

(5) Distribution of aluminum element Al Regarding the distribution of aluminum element Al, in Comparative Example 4, as shown in FIGS. 22 (5) and 23 (5), a large amount of aluminum element Al was present in the surface layer. This is presumed to be derived from AlO ₂ forming the alumite film 20. On the other hand, as shown in FIG. 24 (5), in Test Example 3, the aluminum element Al was present in the crack gap, and substantially no aluminum element Al was present in most of the surface layer. Then, as shown in FIG. 25 (5), in Test Example 3, it was confirmed that the base material 10 contained a large amount of the aluminum element Al. This is presumed to be that the alumite film 20 was not exposed because the surface layer was covered with the silica-containing layer 41 in Test Example 3.

(6) Distribution of magnesium element Mg Regarding the distribution of magnesium element Mg, in Comparative Example 4, as shown in FIG. 22 (6) and FIG. 23 (6), magnesium element Mg exists in base material 10 and the surface layer Trace amounts were present. This is presumed that the magnesium element Mg is the magnesium element Mg derived from the base material 10, and the base layer 10 is covered with the alumite film 20, so that the abundance of the surface layer is reduced. As shown in FIG. 24 (6) and FIG. 25 (6), the same state was obtained in Test Example 3.

(7) Distribution of Nickel Element Ni Regarding the distribution of nickel element Ni, as shown in FIG. 22 (7) and FIG. 23 (7), in Comparative Example 4, the amount of nickel element Ni in the surface layer was very small. 24 (7) and FIG. 25 (7), in Test Example 3, the amount of nickel element Ni in the surface layer was larger than that in Comparative Example 4. This is presumably because nickel element Ni derived from the nickel acetate aqueous solution remained in the vicinity of the opening 31 when the nickel acetate sealing treatment was performed in the sealing step S4 in this embodiment. In addition, it is considered that a part of Ni eluted into the electrolyte as a cation from the base material 10 in the alumite film forming step S2 remained in the pores 23.

(8) Distribution of calcium element Ca Regarding the distribution of calcium element Ca, as shown in FIGS. 22 (10) and 23 (10), in Comparative Example 4, the calcium element Ca was not substantially present in the surface layer. However, as shown in FIGS. 24 (10) and 25 (10), in Test Example 3, the calcium element Ca was present in the surface layer. This is presumed to be due to the fact that a trace amount of calcium element Ca in the colloidal silica liquid remained in the silica-containing layer 41 when the surface silica-containing layer 41 was formed.

(9) Distribution of Other Elements Regarding the distribution of other elements, Comparative Example 4 and Test Example 3 showed the same tendency.

  Next, the ratio of contained elements in the coating in Test Example 4 was evaluated. As shown in FIG. 26, in the cross section of Test Example 4, the thickness t1 of the alumite film 20 was 5.927 to 6.052 μm. Then, in the alumite coating 20, the coating deep portion A close to the base material 10, the coating central portion B on the outer surface side of the coating deep portion A and substantially at the center in the thickness direction, and the outer surface near the outer surface side of the coating central portion B The percentage of the contained element in each part C was detected in the same manner as in the first evaluation test, and the detection results are shown in Table 6 below.

  As shown in Table 6, in the alumite film 20, it can be seen that the Si content increases as it is located on the outer surface side. Then, in consideration of the EPMA mapping analysis shown in FIGS. 22 to 25, in Test Examples 3 and 4, the silica 30 entered the alumite coating 20 and the silica-containing layer 41 containing the silica 30 was formed on the outer surface of the alumite coating 20. It is inferred that:

  In the compressor impeller 1 for a turbocharger according to the present embodiment, since the alumite film 20 is made of alumite sulfate, the adhesion and flexibility of the alumite film 20 to the base material 10 are further enhanced. Further, since the alumite film 20 can be formed relatively inexpensively, it is advantageous in terms of cost. Further, since the alumite sulfate has a high film forming rate, the production period can be shortened. Further, the alumite film made of sulfate alumite has a relatively high transparency and a high adsorptivity of a dye substance, so that the dyeability is excellent.

  Further, in this embodiment, since the pores formed by the alumite sulfate are elongated in a straight shape, the silica is easily filled into the pores of the porous layer 22 by electrophoresis in the silica filling step S3. Also in this example, the same operation and effect as those of the first embodiment are obtained, except for the operation and effect obtained when the alumite film 20 is made of the alumite chromate in the first embodiment.

(Example 3)
In Example 2, in the alumite film forming step S2 in the above-described manufacturing method, the alumite film 20 made of alumite sulfate was formed. Instead, in this example, oxalic acid was used as the electrolytic solution in the alumite film forming step S2. Using an aqueous solution of (C ₂ H ₂ O ₄ ), an alumite film 20 made of oxalic acid alumite was formed. The concentration of the oxalic acid aqueous solution used can be 3 to 8% w / v. In this example, the target film thickness of the alumite film 20 was 5 to 7 μm, the applied voltage in the anodic oxide film treatment was 60 V, and the energizing time was 30 minutes. The other steps were the same as in Example 1.

  In the alumite film 20 made of alumite oxalate of the present embodiment, the pores (not shown) of the porous layer 22 extend straight in the thickness direction X in the same manner as in the case of the alumite film 20 made of the alumite sulfate in Example 2. Many are formed. Other configurations are the same as those in the first and second embodiments. In this embodiment, the same components as those in the twelfth embodiment are denoted by the same reference numerals, and description thereof will be omitted.

(Third evaluation test)
Next, the following third evaluation test was performed using Test Example 5, Test Example 6, Comparative Example 6, and Comparative Example 7.
As Test Examples 5 and 6, those prepared by forming an alumite film 20 made of the oxalic acid alumite of Example 3 on a test piece were prepared. In addition, the target film thickness of the alumite film 20 was set to 5 to 6 μm.
As Comparative Examples 6 and 7, a test piece was prepared by performing steps S1 and S2 in the above-described manufacturing method of Example 3 to form an alumite film 20 made of alumite oxalate. In addition, the target film thickness of the alumite film 20 was set to 5 to 6 μm.
Each test piece was made of the same material as the base material 10 as in the first evaluation test in Example 1, and the shape of each test piece was also substantially disc-like as in the first evaluation test.
In addition, Comparative Examples 1 and 2 in the first evaluation test are referred to as untreated test pieces.

  First, the appearance of each test piece was evaluated. As shown in FIG. 27 to FIG. 28, an enlarged view of the whole of each test piece and the center position p5 and the right side position p2 of the main surface of the test piece was observed. In Comparative Example 6 shown in FIGS. 28A to 28C and Comparative Example 7 shown in FIGS. 28D to 28F, Comparative Example 1 and Comparative Example 2 shown in FIGS. In comparison, no significant difference in appearance was observed, but some natural color development unique to the alumite film was observed. On the other hand, in Test Example 5 shown in FIGS. 28 (a) to (c) and Test Example 6 shown in FIGS. 28 (d) to (f), the whiteness was slightly higher than Comparative Examples 1, 2, 4 and 5. It was once observed.

  Next, the hardness was evaluated. The hardness was evaluated by measuring Vickers hardness (HV) with a test force of 0.1 kgf. As shown in FIG. 27 (a), FIG. 27 (d), FIG. 28 (a), and FIG. 28 (d), the measurement points are the upper and lower left and right parts p1 to p4 and the central part p5 of the surface of each test piece. There were a total of five locations. Then, the measurement method was the same as in the first evaluation test, and the average of three measurements was calculated. The results of the hardness measurement are shown in Table 7 below.

  As shown in Table 7, in the test pieces of Comparative Examples 6 and 7 and Test Examples 5 and 6 having the alumite film 20 made of oxalic alumite, the average value of the Vickers hardness at each measurement point was 186 to 240 HV0.1. Within the range, the hardness was higher than that of Comparative Examples 1 and 2 shown in Table 1 in the first evaluation test.

  Next, for Comparative Example 6, a cross-sectional image at the Q position of the test piece shown in FIG. 29A was taken, and shown in FIGS. 29B to 29E. Similarly, for Test Example 5, FIG. 30A shows the Q1 position, and FIGS. 30B to 30E show cross-sectional images at the Q1 position. Further, for Test Example 5, FIG. 31A shows the Q2 position, and FIGS. 31B to 31E show cross-sectional images at the Q2 position. 30 (e) and FIG. 31 (e), the thickness t1 of each alumite film 20 was measured.

In Comparative Example 6, as shown in FIG. 29E, the alumite film 20 was formed so as to cover the surface 11 of the base material 10, and the thickness t1 of the alumite film 20 was 6 μm.
In Test Example 5, as shown in FIG. 30E, the alumite film 20 was formed so as to cover the surface 11 of the base material 10, and the thickness t1 of the alumite film 20 at the position Q1 was 6 μm. Further, as shown in FIG. 31 (e), the thickness t1 of the alumite film 20 at the position Q2 was 6 μm. Note that the thickness of the silica-containing layer 41 was relatively thin.

Next, the surface roughness was evaluated. The surface roughness Ra of Comparative Examples 6 and 7 and Test Examples 5 and 6 was measured, and the measurement results are shown in Table 8 below. As shown in Table 8, in Test Examples 5 and 6, the surface roughness Ra was lower than in Comparative Examples 6 and 7, and the irregularities on the surface of the alumite film 20 were covered with the silica-containing layer 41. It is presumed that it was smoothed.

  Next, the component distribution of the test piece surface and the test piece cross section in Comparative Example 6 and Test Example 5 was evaluated by EPMA mapping analysis. EPMA mapping analysis was performed in the same manner as in the first evaluation test.

For Comparative Example 6, SEM images were obtained and EPMA mapping analysis was performed on the test piece surface at the S position shown in FIG. 29A, and the results are shown in FIGS. 32 (1) to 32 (11). Further, on the cross section of the test piece at the position Q shown in FIG. 29A, acquisition of an SEM image and EPMA mapping analysis were performed, and the results are shown in FIGS. 33 (1) to (10).
For Test Example 5, SEM image acquisition and EPMA mapping analysis were performed on the test piece surface at the S position shown in FIG. 30 (a), and the results are shown in FIGS. 34 (1) to (11). Further, acquisition of an SEM image and EPMA mapping analysis were performed on the cross section of the test piece at the Q position shown in FIG. 30A, and the results are shown in FIGS. 35 (1) to (10).
In FIGS. 32 to 35, the analysis target elements and the like indicated by (1) to (11) in each drawing are the same as those in the case of the second evaluation test.

(1) SEM image As shown in FIG. 32 (1), in Comparative Example 4, a plurality of holes were scattered in the surface of the alumite film 20, but as shown in FIG. The alumite film 20 was formed, and the surface alumite film 20 had relatively few irregularities, and the film thickness was almost constant. Further, in Test Example 5, as shown in FIG. 34 (1) and FIG. 35 (1), although some surface irregularities were recognized, the film thickness was substantially constant. Then, as shown in FIG. 35A, in Test Example 5, it was presumed that the alumite film 20 was formed on the surface of the base material 10 and the silica-containing layer 41 was laminated on the alumite film 20.

(2) Distribution of oxygen element O Regarding the distribution of oxygen element O, as shown in FIGS. 32 (2) and 33 (2), in Comparative Example 6, a large amount of oxygen element O was present in the surface layer. The oxygen element O in the surface layer in Comparative Example 6 is assumed to be derived from AlO ₂ forming the alumite film 20. Further, as shown in FIG. 34 (2) and FIG. 35 (2), also in Test Example 5, a large amount of oxygen element O was present in the surface layer. It is presumed that the oxygen element O in Test Example 5 is derived from silica (SiO ₂ ) which is a main component of the silica-containing layer 41.

(3) Distribution of Silicon Element Si Regarding the distribution of silicon element Si, as shown in FIG. 32 (3) and FIG. 33 (3), in Comparative Example 5, only a very small amount of silicon element Si was present. On the other hand, as shown in FIG. 34 (3), in Test Example 5, a large amount of silicon element Si was present in the surface layer. Then, as shown in FIG. 35 (3), in Test Example 5, the silicon element Si was partially present in the alumite film 20 and was present in a large amount in the silica-containing layer 41 laminated on the alumite film 20. . Thus, in Test Example 5, it was presumed that silica 30 was encapsulated in the porous layer 22 of the alumite coating 20, and that silica 30 was included in the silica-containing layer 41.

(4) Distribution of sulfur element S Regarding the distribution of the sulfur element S, in Comparative Example 6, as shown in FIG. 32 (4), a large amount of the sulfur element S exists in the surface layer. Thus, it was confirmed that the sulfur element S was present in the alumite film 20. It is assumed that the sulfur element S in the surface layer is derived from the alumite sulfate forming the alumite film 20.
On the other hand, in Test Example 5, as shown in FIG. 34 (4), the surface layer had a small amount of sulfur element S, but as shown in FIG. 35 (4), a large amount of sulfur element S was present inside the surface layer. Existed. It is assumed that the sulfur element S inside the surface layer is derived from the alumite sulfate forming the alumite film 20. The sulfur element S in the surface layer is presumed to be the sulfur element S derived from the electrolytic solution (aqueous sulfuric acid solution) remaining in the silica-containing layer 41 formed on the alumite film 20.

(5) Distribution of aluminum element Al Regarding the distribution of aluminum element Al, in Comparative Example 6, a large amount of aluminum element Al was present in the surface layer as shown in FIGS. 32 (5) and 33 (5). This is presumed to be derived from AlO ₂ forming the alumite film 20. Further, as shown in FIG. 34 (5), the aluminum element Al exists in the surface layer also in Test Example 5, and as shown in FIG. 35 (5), also in Test Example 5, a large amount of the aluminum element Al exists in the base material 10. Was. This is because the thickness of the silica-containing layer 41 formed on the surface layer in Test Example 5 was smaller than that of the case of the alumite film made of the alumite chromate of Example 1 and the case of the alumite film made of the alumite sulfate of Example 2. It is presumed that the aluminum element Al in the alumite film 20 under the silica-containing layer 41 was detected from the surface layer because the thickness was reduced.

(6) Distribution of magnesium element Mg Regarding the distribution of magnesium element Mg, in Comparative Example 6, as shown in FIG. 32 (6) and FIG. 33 (6), magnesium element Mg exists in base material 10 and the surface layer Trace amounts were present. This is presumed that the magnesium element Mg is the magnesium element Mg derived from the base material 10, and the base layer 10 is covered with the alumite film 20, so that the abundance of the surface layer is reduced. As shown in FIG. 34 (6) and FIG. 35 (6), a similar state was found in Test Example 5.

(7) Distribution of Nickel Element Ni Regarding the distribution of nickel element Ni, as shown in FIGS. 32 (7) and 33 (7), in Comparative Example 6, the amount of nickel element Ni in the surface layer was very small. 34 (7) and FIG. 35 (7), in Test Example 5, the amount of nickel element Ni in the surface layer was larger than that in Comparative Example 6. This is presumably because nickel element Ni derived from the nickel acetate aqueous solution remained in the vicinity of the opening 31 when the nickel acetate sealing treatment was performed in the sealing step S4 in this embodiment. In addition, it is considered that a part of Ni eluted into the electrolyte as a cation from the base material 10 in the alumite film forming step S2 remained in the pores 23.

(8) Distribution of calcium element Ca Regarding the distribution of calcium element Ca, as shown in FIGS. 32 (10) and 33 (10), in comparative example 6, calcium element Ca was not substantially present in the surface layer. However, as shown in FIGS. 34 (10) and 35 (10), in Test Example 5, a trace amount of calcium element Ca was present in the surface layer. This is presumed to be due to the fact that a trace amount of calcium element Ca in the colloidal silica liquid remained in the silica-containing layer 41 when the surface silica-containing layer 41 was formed.

(9) Distribution of Other Elements Regarding the distribution of other elements, Comparative Example 6 and Test Example 5 showed the same tendency.

  Next, the ratio of the contained elements in the coating in Test Example 6 was evaluated. As shown in FIG. 36, in the cross section of Test Example 6, the thickness t1 of the alumite film 20 was 6.803 to 6.845 μm. Then, in the alumite coating 20, the coating deep portion A close to the base material 10, the coating central portion B on the outer surface side of the coating deep portion A and substantially at the center in the thickness direction, and the outer surface near the outer surface side of the coating central portion B The proportion of the contained element in each of the parts C was detected in the same manner as in the case of the first evaluation test, and the detection results are shown in Table 9 below.

  As shown in Table 9, it can be seen that in the alumite film 20, the Si content increases as it is located on the outer surface side. In view of the EPMA mapping analysis shown in FIGS. 32 to 35, in Test Examples 5 and 6, the silica 30 entered the alumite film 20, and the silica-containing layer 41 containing the silica 30 was formed on the outer surface of the alumite film 20. It is inferred that:

  In the compressor impeller 1 for a turbocharger of the present embodiment, since the alumite film 20 is made of alumite oxalate, the adhesion and flexibility of the alumite film 20 to the base material 10 are further enhanced. Further, since oxalic acid alumite has a certain degree of flexibility, cracks are relatively unlikely to occur in the alumite film 20 made of oxalic alumite. Further, the alumite film 20 made of oxalic acid alumite exhibits high corrosion resistance.

  Furthermore, in this embodiment, since the pores formed by the oxalic acid alumite are elongated in a straight line, the silica is easily encapsulated into the pores of the porous layer 22 by electrophoresis in the silica enclosing step S3. Also in this example, the same operation and effect as those of the first embodiment are obtained, except for the operation and effect obtained when the alumite film 20 is made of the alumite chromate in the first embodiment.

  The present invention is not limited to the above embodiments, and can be applied to various embodiments without departing from the gist thereof.

DESCRIPTION OF SYMBOLS 1 Compressor impeller 10 Base material 20 Alumite film 21 Barrier layer 22 Porous layer 23 Pore 30 Silica 31 Opening 40 Silica layer 41 Silica containing layer

Claims (10)

A base material made of aluminum or an aluminum alloy,
A barrier layer covering the surface of the base material, and an alumite film including a porous layer laminated on the barrier layer and having a plurality of pores,
With
A compressor impeller for a turbocharger, wherein amorphous silica is sealed in the pores.   The compressor impeller for a turbocharger according to claim 1, wherein the alumite coating is made of alumite chromate. The compressor impeller for a turbocharger according to claim 1 or 2 , wherein the thickness of the alumite film is in a range of 3 to 8 µm. The compressor impeller for a turbocharger according to any one of claims 1 to 3 , wherein a silica-containing layer containing silica as a main component is laminated on the porous layer. A base material made of aluminum or an aluminum alloy is immersed in an electrolytic solution, the surface of the base material is subjected to an anodic oxide film treatment, and a barrier layer covering the surface of the base material is provided. An alumite film forming step of forming an alumite film including a porous layer having pores of
A silica encapsulation step of encapsulating amorphous silica in the pores,
A method for producing a compressor impeller for a turbocharger, including: The turbocharger for a turbocharger according to claim 5 , wherein, in the silica enclosing step, the base material is immersed in a colloidal silica liquid, and colloidal silica contained in the colloidal silica liquid is encapsulated in the plurality of pores by electrophoresis. Manufacturing method of compressor impeller. The method for producing a compressor impeller for a turbocharger according to claim 6 , wherein the particle diameter D50 of the colloidal particles in the colloidal silica is in a range of 5 to 55 nm. A base material made of aluminum or an aluminum alloy,
A barrier layer covering the surface of the base material, and an alumite film including a porous layer laminated on the barrier layer and having a plurality of pores,
With
Amorphous silica is sealed in the pores,
The compressor impeller for a turbocharger, wherein the alumite film is made of alumite sulfate or alumite oxalate. The compressor impeller for a turbocharger according to claim 8 , wherein the thickness of the alumite film is in a range of 3 to 8 m. The compressor impeller for a turbocharger according to any one of claims 8 or 9 , wherein a silica-containing layer containing silica as a main component is laminated on the porous layer.