COATING STRUCTURE, IMPELLER, COMPRESSOR, METAL PART MANUFACTURING METHOD, IMPELLER MANUFACTURING METHOD, AND COMPRESSOR MANUFACTURING METHOD

Abstract

Said coating structure is provided with: a chemical conversion layer (11), which is formed by chemical conversion coating so as to cover the surface of an impeller body (10) obtained from a magnesium alloy that contains magnesium as the main component and which has a film thickness within a previously determined range; and a plating layer (12) formed so as to cover the chemical conversion layer (11).

Claims

1-8. (canceled)

9. A coating structure comprising: a chemical conversion layer that contains magnesium as a main component and is made of a phosphate-coated film and is formed in a manner of covering a surface of a base material which is made of a magnesium alloy containing at least one kind of element selected from a group consisting of gadolinium, terbium, thulium, and lutetium; and a plating layer that is made of a nickel-based alloy and is formed in a manner of covering the chemical conversion layer.

10. The coating structure according to claim 9, wherein the plating layer is formed of a nickel-phosphorous alloy.

11. The coating structure according to claim 9, wherein the base material contains a atom percent of zinc, contains b atom percent of at least one kind of element, in total, selected from a group consisting of gadolinium, terbium, thulium, and lutetium, has a remaining portion made of magnesium, and has the factors a and b satisfying the following expressions (1) to (3), and wherein the base material has at least one kind of precipitate selected from a precipitate group consisting of a compound of magnesium and a rare earth element, a compound of magnesium and zinc, a compound of zinc and a rare earth element, and a compound of magnesium, zinc, and a rare earth element.
0.2a5.0(1)
0.5b5.0(2)
0.5a0.5b(3)

12. An impeller comprising: the coating structure according to claim 9.

13. A compressor comprising: the impeller according to claim 12.

14. A metal part manufacturing method comprising: a step of forming a chemical conversion layer by performing chemical conversion treatment in a manner of covering a surface of a base material which is made of a magnesium alloy containing magnesium as a main component; and a step of forming a plating layer which is made of a nickel-based alloy in a manner of covering the chemical conversion layer.

15. An impeller manufacturing method comprising: the metal part manufacturing method according to claim 14.

16. A compressor manufacturing method comprising: the impeller manufacturing method according to claim 15.

17. The coating structure according to claim 10, wherein the base material contains a atom percent of zinc, contains b atom percent of at least one kind of element, in total, selected from a group consisting of gadolinium, terbium, thulium, and lutetium, has a remaining portion made of magnesium, and has the factors a and b satisfying the following expressions (1) to (3), and wherein the base material has at least one kind of precipitate selected from a precipitate group consisting of a compound of magnesium and a rare earth element, a compound of magnesium and zinc, a compound of zinc and a rare earth element, and a compound of magnesium, zinc, and a rare earth element.
0.2a5.0(1)
0.5b5.0(2)
0.5a0.5b(3)

18. An impeller comprising: the coating structure according to claim 10.

19. An impeller comprising: the coating structure according to claim 11.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0028] FIG. 1 is a view illustrating a schematic configuration of a compressor according to an embodiment of the present invention.

[0029] FIG. 2 is a view illustrating a cross-sectional view of a coating structure according to the embodiment of the present invention.

[0030] FIG. 3 is a flow of an impeller manufacturing method according to the embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0031] FIG. 1 is a view illustrating a schematic configuration of a compressor according to an embodiment of the present invention.

[0032] For example, the compressor of the embodiment is a centrifugal compressor which is provided in a turbocharger turbo-charging an internal combustion engine.

[0033] As illustrated in FIG. 1, for example, a compressor 1 employed in an engine compresses a fluid AR sent into a housing 2 when an impeller (metal part) 3 rotates inside the housing 2. Here, the shape of the impeller 3 or the configuration of the compressor 1 is not limited in any way.

[0034] The impeller 3 is disposed inside the housing 2 and compresses the fluid AR such as gas which becomes a compression subject. The impeller 3 is integrally provided with a rotary shaft 4 which is rotatably supported by a bearing 6 provided inside the housing 2. The rotary shaft 4 is rotatively driven around the central axis thereof by a turbine 5 which rotates due to exhaust gas G. Accordingly, the impeller 3 rotates together with the rotary shaft 4 and compresses the fluid AR flowing inside the housing 2.

[0035] The compressor 1 of the embodiment is embedded in a system which performs exhaust gas recirculation (EGR), and there are cases where air including exhaust gas which contains condensed moisture is taken in.

[0036] FIG. 2 is a view illustrating a cross-sectional view of a coating structure according to the embodiment of the present invention. FIG. 3 is a flow of an impeller manufacturing method according to the embodiment of the present invention.

[0037] As illustrated in FIG. 2, the impeller 3 includes an impeller body (base material) 10, a chemical conversion layer 11, and a plating layer 12. As illustrated in FIG. 3, in a method of manufacturing the impeller 3, first, a step of forming an impeller body 10 is performed (Step S01). Thereafter, a step of forming a chemical conversion layer 11 is performed (Step S02), and then a step of forming a plating layer 12 is performed (Step S03).

[0038] The impeller body 10 is made of a magnesium alloy. The magnesium alloy forming the impeller body 10 contains zinc (Zn) and at least one kind of element selected from a group consisting of gadolinium (Gd), terbium (Tb), thulium (Tm), and lutetium (Lu), and the remaining portion is made of magnesium (Mg).

[0039] Here, it is preferable that a content a (atom percent) of zinc (Zn) is set to 0.2a3.0. Moreover, it is preferable that a content b (atom percent) of at least one kind of element selected from the group consisting of gadolinium (Gd), terbium (Tb), thulium (Tm), and lutetium (Lu) is set to 0.5b5.0. Here, moreover, it is preferable that a relationship of 0.5a0.5b is satisfied.

[0040] in a case where gadolinium (Gd) is added, it is more preferable that the upper limit content is less than 3 atom percent. Moreover, it is particularly preferable that the ratio of the content of gadolinium (Gd) and the content zinc (Zn) is 2:1 or a ratio close thereto.

[0041] Due to such a content ratio, it is possible to particularly improve high strength high fracture toughness.

[0042] When the impeller body 10 is formed, a magnesium alloy made of the above-described composition is caused to melt and is cast into a mold, thereby forming a magnesium alloy cast.

[0043] In this magnesium alloy cast, at least one kind of precipitate selected from a precipitate group consisting of a compound of magnesium (Mg) and a rare earth element, a compound of magnesium (Mg) and zinc (Zn), a compound of zinc (Zn) and a rare earth element, and a compound of magnesium (Mg), zinc (Zn), and a rare earth element is precipitated.

[0044] Subsequently, the magnesium alloy cast is subjected to solution heat treatment. In the solution heat treatment, at least one kind of precipitate described above remains.

[0045] Thereafter, the magnesium alloy cast is subjected to machining, thereby acquiring the impeller body 10 having a predetermined shape.

[0046] For example, as the machining, it is possible to employ processing accompanying plastic deformation, such as extruding, an equal-channel-angular-extrusion (ECAE) processing method, rolling, drawing, forging, repetitive processing thereof, and friction stir welding (FSW).

[0047] The plastic processing can be performed alone or in combination of rolling, extruding, ECAE, drawing processing, and forging.

[0048] The chemical conversion layer 11 is formed in a manner of covering a surface of the impeller body 10. For example, the chemical conversion layer 11 is made of a phosphate-coated film. The phosphate-coated film is made of phosphate such as iron phosphate, manganese phosphate, and zinc phosphate. Such a phosphate-coated film is formed after the impeller body 10 is washed, and the impeller body 10 which becomes the base material is immersed in an aqueous solution containing phosphate for a predetermined time.

[0049] In a case where there is minute unevenness or the like on the surface of the base material 10, the chemical conversion layer 11 made of a phosphate-coated film may be formed to be thick such that the chemical conversion layer can completely cover the unevenness. When the film thickness of the chemical conversion layer 11 made of such a phosphate-coated film is excessively thick, the weight thereof increases, thereby adversely affecting the response while the impeller 3 rotates.

[0050] Therefore, it is preferable that the chemical conversion layer 11 made of a phosphate-coated film has a film thickness ranging from 0.5 m to 5 m, and more preferably ranging from 2 m to 5 m.

[0051] Such a chemical conversion layer 11 may be formed by repeating the treatment of forming a phosphate-coated film multiple times and laminating multiple layers of phosphate-coated films.

[0052] The plating layer 12 is formed in a manner of covering the chemical conversion layer 11. The plating layer 12 is a plating film made of a nickel-based alloy which is formed by performing electroless plating treatment. As a specific example of the nickel-based alloy forming the plating layer 12, it is preferable to employ a nickel-phosphorous alloy.

[0053] The plating layer 12 made of the nickel-phosphorous alloy is formed to have a film thickness ranging from 10 m to 30 m, and more preferably ranging from 15 m to 30 m.

[0054] The plating layer 12 made of such a nickel-based alloy is formed by causing the impeller body 10 which is the base material having the chemical conversion layer 11 formed on the surface thereof to be immersed in a plating solution for a predetermined time and to be subjected to electroless plating.

[0055] The embodiment described above includes the chemical conversion layer 11 that is formed by performing chemical conversion treatment in a manner of covering a surface of the impeller body 10 which is made of a magnesium alloy, and the plating layer 12 that has a film thickness within a range set in advance and is formed in a manner of covering the chemical conversion layer 11. According to the configuration, the plating layer 12 more favorably comes into tight contact with the chemical conversion layer 11. When there is provided such a plating layer 12, it is possible to have high corrosion resistance.

[0056] In the compressor 1 including the impeller 3 having such a coating structure, and the impeller 3, the impeller 3 is formed of a magnesium alloy, so that it is possible to have high adhesion and corrosion resistance, and to enhance an operation response of the impeller 3 and the compressor 1.

[0057] Moreover, the chemical conversion layer 11 is a phosphate-coated film, and the plating layer 12 is formed of a nickel-phosphorous alloy.

[0058] Accordingly, adhesion between the magnesium alloy and the plating layer 12 can be particularly and effectively enhanced.

[0059] Moreover, the impeller body 10 contains zinc (Zn) and at least one kind of element selected from the group consisting of gadolinium (Gd), terbium (Tb), thulium (Tm), and lutetium (Lu), and the remaining portion is made of magnesium (Mg). Moreover, the impeller body 10 has at least one kind of precipitate selected from the precipitate group consisting of a compound of magnesium (Mg) and a rare earth element, a compound of magnesium (Mg) and zinc (Zn), a compound of zinc (Zn) and a rare earth element, and a compound of magnesium (Mg), zinc (Zn), and a rare earth element.

[0060] In the impeller body 10 made of such an alloy, even though the impeller body 10 is intended to be directly coated with the plating layer 12, the corrosion resistance deteriorates. In this case, when the chemical conversion layer 11 is interposed by means of the chemical conversion treatment, adhesion between the impeller body 10 and the plating layer 12 can be effectively enhanced.

EXAMPLE

[0061] Next, in regard to the coating structure described above, the presence or absence of an occurrence of corrosion resistance and erosion was checked, and the result thereof will be shown.

[0062] [Base Material]

[0063] First, a magnesium alloy which contained 2 atom percent of Gd and 1 atom percent of Zn and of which the remaining portion thereof was made of Mg and unavoidable impurities was put into a vacuum melting furnace, and melting was performed.

[0064] Next, a heated and melted material was put into a mold and was cast, thereby producing a rectangular-shaped base material of 150 mm60 mm made of a magnesium alloy.

[0065] [Surface Treatment]

[0066] After the produced base material was washed, the following surface treatment was executed.

Example 1

[0067] After producing a phosphate-coated film on a surface of the base material, plating was executed by means of a nickel-phosphorous alloy.

[0068] For the phosphate-coated film, the base material was immersed in a phosphate treatment solution for a predetermined time, thereby obtaining a phosphate-coated film having a film thickness of 3 m.

[0069] For the plating performed by means of the nickel-phosphorous alloy, plating treatment was executed by employing a plating bath. Accordingly, a plating layer having a film thickness of 15 m was obtained.

Comparative Example 1

[0070] A base material was used as a test piece without executing surface treatment for the base material.

Comparative Example 2

[0071] Only a phosphate-coated film was formed in a base material under the conditions similar to those of Example.

Comparative Example 3

[0072] Resin coating was executed for a base material.

[0073] A Si-based resin was employed for resin coating, and a resin coat layer was formed on a surface of the base material by performing painting.

Comparative Example 4

[0074] After a phosphate-coated film was formed on a base material under the conditions similar to those of Example, resin coating was executed under the conditions similar to those of Comparative Example 3.

Comparative Example 5

[0075] Only plating treatment was executed for a base material by means of a nickel-phosphorous alloy under the conditions similar to those of Example.

Comparative Example 6

[0076] After resin coating was executed for a base material under the conditions similar to those of Comparative Example 3, plating treatment was executed by means of a nickel-phosphorous alloy under the conditions similar to those of Example.

[0077] [Adhesion of Film]

[0078] In regard to the test pieces of Example 1 and Comparative Examples 1 to 6, first, adhesion with respect to the base material which was a film formed by performing surface treatment was visually checked.

[0079] Table 1 shows the result thereof.

TABLE-US-00001 TABLE 1 Film Corrosion Coating adhesion resistance erosion Example 1 Phosphate-coated film + NiP alloy plating Comparative None X X Example 1 Comparative Phosphate-coated film X X Example 2 Comparative Resin coating X X Example 3 Comparative Phosphate-coated film + X Example 4 resin coating Comparative Plating by means of X X Example 5 NiP alloy Comparative Resin coating + plating X Example 6 by means of NiP alloy

[0080] As a result, in Example 1 and Comparative Examples 2 to 5, a film was formed in each of the base materials by performing the surface treatment.

[0081] In contrast, in Comparative Example 6 in which the resin coating was executed for the base material and then the plating treatment was executed by means of the nickel-phosphorous alloy, peeling of the generated plating layer was checked when the plating treatment was performed with respect to the base material which was subjected to the resin coating.

[0082] [Corrosion Resistance]

[0083] Next, in Example 1 and Comparative Examples 1 to 5 in which the films were favorably formed, a salt spray test was performed based on a salt spray cycle test conforming to H 8502 in Japanese Industrial Standard, thereby verifying the corrosion resistance.

[0084] In each of Example 1 and Comparative Examples 1 to 5, evaluation after the salt spray test was carried out by visually observing the circumstances of corrosion failure which occurred on the surface of the test piece, and measuring and checking a corrosion weight loss.

[0085] As a result, as shown in Table 1, in Example 1, an occurrence of corrosion was not particularly recognized.

[0086] In contrast, in Comparative Example 1 in which a bare base material was employed, corrosion was recognized in its entirety. Moreover, in Comparative Example 2 in which only a phosphate-coated film was provided, an amount of corrosion more than that in Comparative Example 1 was checked. Also in Comparative Example 3 in which only resin coating was employed, an amount of corrosion more than that in Comparative Example 1 was checked.

[0087] In Comparative Example 4 in which a phosphate-coated film and resin coating were provided, corrosion due to the salt spray test was not recognized.

[0088] In Comparative Example 5 in which only plating was executed by means of a NiP alloy, peeling of the plating film due to the salt spray test was checked.

[0089] [Erosion Resistance]

[0090] Next, in Example 1 and Comparative Examples 1 to 4 in which peeling of the film due to the salt spray test was not recognized, an erosion resistance test was performed by putting water droplets into an inlet of the compressor, and while the quantity of water droplets was controlled, the presence or absence of an occurrence of erosion was verified.

[0091] In each of Example 1 and Comparative Examples 1 to 4, the evaluation of the presence or absence of an occurrence of erosion was carried out by visually checking the surface of the test piece.

[0092] As a result, as shown in Table 1, no occurrence of erosion was recognized in Example 1.

[0093] In contrast, in each of Comparative Examples 1 to 4, an occurrence of erosion was recognized.

[0094] In this manner, in only Example 1 in which a phosphate-coated film and a plating layer by means of a NiP alloy were provided, it was checked that the adhesion, the corrosion resistance, and the erosion resistance of the film were high.

Other Embodiments

[0095] The present invention is not limited to the embodiment described above and the design can be changed within a scope not departing from the gist of the present invention.

[0096] For example, in the embodiment described above, the impeller 3 for the compressor 1 has been exemplified as a metal part having the coating structure. However, without being limited to the impeller, the configuration can be employed in various other metal members including a magnesium alloy as a base material.

[0097] Moreover, in the embodiment described above, the compressor of the turbocharger has been exemplified. However, the configuration can also be applied to an impeller of a compressor other than the turbocharger.

[0098] Moreover, in the embodiment described above, a case of laminating only one plating layer formed of a nickel-phosphorous alloy on the phosphate-coated film has been exemplified. However, multiple plating layers formed by means of the nickel-phosphorous alloy may be provided without being limited to one layer. For example, after a first plating layer made of a nickel-phosphorous alloy is laminated on the phosphate-coated film, a second plating layer made of a nickel-phosphorous alloy may be laminated in the same manner.

[0099] In a case where the first plating layer and the second plating layer are provided, compared to the case where one plating layer is formed of a nickel-phosphorous alloy, the film thickness of the first plating layer can be reduced. Therefore, adhesion of the first plating layer with respect to the phosphate-coated film can be improved.

[0100] Moreover, the composition of the nickel-phosphorous alloy forming the first plating layer and the second plating layer is not limited to the nickel-phosphorous alloy of the same composition. For example, a nickel-phosphorous alloy having adhesion with respect to a phosphate-coated film higher than that of the second plating layer may be employed for the first plating layer.

INDUSTRIAL APPLICABILITY

[0101] When there is provided a chemical conversion layer which is formed by performing chemical conversion treatment in a manner of covering a surface of a base material made of a magnesium alloy and has a film thickness within a range set in advance, adhesion and corrosion resistance of a plating layer can be enhanced.

REFERENCE SIGNS LIST

[0102] 1 COMPRESSOR [0103] 2 HOUSING [0104] 3 IMPELLER [0105] 4 ROTARY SHAFT [0106] 5 TURBINE [0107] 10 IMPELLER BODY [0108] 11 CHEMICAL CONVERSION LAYER [0109] 12 PLATING LAYER