JP6489720B2 - Coating structure, impeller, compressor, metal part manufacturing method, impeller manufacturing method, and compressor manufacturing method - Google Patents

Description

  The present invention relates to a coating structure, an impeller, a compressor, a metal part manufacturing method, an impeller manufacturing method, and a compressor manufacturing method.

In a member constituting various machines such as an engine and a turbine, the material of the member is switched from an aluminum alloy to a magnesium alloy in order to reduce the weight.
When a member is formed from a magnesium alloy, the amount of corrosion is greater than when a member is formed from an aluminum alloy. Therefore, in order to improve the corrosion resistance of the base material made of a magnesium alloy, the surface of the base material is covered by chemical conversion treatment or the like. Furthermore, the surface of the base material is also coated with a resin.

However, for example, when a part that performs exhaust gas recirculation (EGR) in an engine is formed of a magnesium alloy, chemical conversion treatment or resin coating may be affected by moisture condensed in the exhaust gas recirculation process. As a result, erosion and corrosion occur in the parts.
Therefore, it is desired to further improve the corrosion resistance of the parts formed of the magnesium alloy.

For example, Patent Document 1 discloses a configuration in which a nickel base plating is applied to a base material made of a magnesium alloy. By plating the surface, higher corrosion resistance can be obtained compared to chemical conversion treatment or resin coating.
Here, in the configuration disclosed in Patent Document 1, pretreatment such as chemical etching is performed before the nickel base plating treatment is performed on the base material. Such pretreatment is performed in order to improve the adhesion between the base material and the plating film.

JP 2003-73843 A

By the way, in the magnesium alloy used as a base material, the composition of the magnesium alloy is changed by adding an additive or the like in order to further improve the strength. However, depending on the component of the additive added to the magnesium alloy in order to increase the strength, sufficient adhesion between the base material and the plating film may not be obtained even if a pretreatment such as chemical etching is performed.
The present invention provides a coating structure, an impeller, and a compressor capable of improving the adhesion between a base material made of a magnesium alloy and a plating layer made of a nickel-based alloy to obtain high corrosion resistance and erosion resistance and improve reliability. An object of the present invention is to provide a metal part manufacturing method, an impeller manufacturing method, and a compressor manufacturing method.

According to the first aspect of the present invention, the coating structure is composed of a magnesium alloy containing magnesium as a main component and containing at least one element selected from the group consisting of gadolinium, terbium, thulium, and lutetium. A conversion layer comprising a phosphate coating formed to cover the surface of the base material is provided. The coating structure further includes a plating layer made of a nickel-based alloy formed so as to cover the chemical conversion layer.
According to such a configuration, since the plating layer made of the nickel-based alloy adheres well due to the chemical conversion layer made of the phosphate coating, the reliability can be improved. By providing such a plating layer, high corrosion resistance and erosion resistance can be obtained.

According to the second aspect of the present invention, in the coating structure, the plating layer in the coating structure of the first aspect may be formed of a nickel-phosphorus alloy.
By providing the chemical conversion layer in this manner, the adhesion between the magnesium alloy and the plating layer can be particularly effectively increased.

According to the third aspect of the present invention, the coating structure is selected from the group consisting of gadolinium, terbium, thulium and lutetium, wherein the base material in the coating structure of the first or second aspect contains zinc at a% by atom. A total of at least one element selected from the group consisting of b atom%. In this coating structure, the balance is made of magnesium. a and b satisfy the following formulas (1) to (3). Further, the coating structure has at least one kind of precipitate selected from the group consisting of magnesium and rare earth compound, magnesium and zinc compound, zinc and rare earth compound and magnesium, zinc and rare earth compound. You may do it.
(1) 0.2 ≦ a ≦ 5.0
(2) 0.5 ≦ b ≦ 5.0
(3) 0.5a-0.5 ≦ b
In a base material made of such an alloy, even if an attempt is made to directly coat the base material with a plating layer, the adhesion is poor. In this case, since the adhesion between the base material and the plating layer can be effectively increased by interposing a chemical conversion layer formed by chemical conversion treatment, the reliability can be improved. Furthermore, corrosion resistance can be improved by the chemical conversion treatment layer. In addition, corrosion resistance and erosion resistance can be improved by the plating layer.

According to the fourth aspect of the present invention, the impeller has the coating structure according to any one of the first to third aspects.
Thereby, the corrosion resistance and erosion resistance of the magnesium alloy can be enhanced. Therefore, it is possible to effectively increase the operation response of the compressor using the impeller by forming the impeller with a magnesium alloy and making it lightweight.

According to the fifth aspect of the present invention, the compressor includes the impeller of the fourth aspect.
Thereby, when an impeller is formed with a magnesium alloy, the corrosion resistance and erosion resistance of an impeller can be improved. Therefore, it is possible to effectively increase the operation response of the compressor using the impeller by making the impeller lightweight.

According to the sixth aspect of the present invention, the metal part manufacturing method contains magnesium as a main component, and contains at least one element selected from the group consisting of gadolinium, terbium, thulium, and lutetium. It includes a step of forming a chemical conversion layer made of a phosphate coating by performing chemical conversion treatment so as to cover the surface of the base material made of an alloy. The method for manufacturing a metal part further includes a step of forming a plating layer made of a nickel-based alloy so as to cover the chemical conversion layer.
Thereby, since the plating layer which consists of a nickel base alloy adheres to a base material favorably, reliability can be improved. Furthermore, by providing a plating layer, high corrosion resistance and erosion resistance can be obtained.

According to the seventh aspect of the present invention, the impeller manufacturing method includes the metal part manufacturing method according to the sixth aspect.
Thereby, the corrosion resistance and erosion resistance of the magnesium alloy can be enhanced. Therefore, the operational response of the compressor using the impeller can be effectively enhanced by forming the impeller with a magnesium alloy and making it lightweight.

According to the eighth aspect of the present invention, the compressor manufacturing method includes the impeller manufacturing method according to the seventh aspect.
Thereby, since an impeller can be reduced in weight, the operation response of the compressor using an impeller can be improved effectively.

  According to the above-described coating structure, impeller, and compressor, the adhesion between the base material made of a magnesium alloy and the plating layer made of a nickel-based alloy is improved to obtain high corrosion resistance and erosion resistance and improve reliability. Is possible.

It is a figure which shows schematic structure of the compressor in embodiment of this invention. It is sectional drawing which shows the coating structure in embodiment of this invention. It is a flow of the manufacturing method of the impeller in embodiment of this invention.

FIG. 1 is a diagram showing a schematic configuration of a compressor in an embodiment of the present invention.
The compressor in this embodiment is, for example, a centrifugal compressor provided in a supercharger that supercharges an internal combustion engine.
As shown in FIG. 1, for example, a compressor 1 used in an engine compresses a fluid AR fed into the housing 2 by rotating an impeller (metal part) 3 within the housing 2. Here, the shape of the impeller 3 and the configuration of the compressor 1 are not limited at all.

The impeller 3 is disposed in the housing 2 and compresses a fluid AR such as a gas to be compressed. The impeller 3 is provided integrally with a rotating shaft 4 that is rotatably supported by a bearing 6 provided in the housing 2. The rotary shaft 4 is driven to rotate around its central axis by a turbine 5 that is rotated by exhaust gas G. Thereby, the impeller 3 rotates together with the rotating shaft 4 and compresses the fluid AR flowing in the housing 2.
The compressor 1 in this embodiment is incorporated in a system that performs exhaust gas recirculation (EGR), and air containing exhaust gas containing condensed moisture may be taken in.

FIG. 2 is a cross-sectional view showing a coating structure in the embodiment of the present invention. FIG. 3 is a flow of the method for manufacturing the impeller in the embodiment of the present invention.
As shown in FIG. 2, the impeller 3 includes an impeller body (base material) 10, a chemical conversion layer 11, and a plating layer 12. As shown in FIG. 3, in the method for manufacturing the impeller 3, first, the step of forming the impeller body 10 (step S01) is performed, and then the step of forming the chemical conversion layer 11 (step S02) is performed. 12 is performed (step S03).

The impeller body 10 is made of a magnesium alloy. The magnesium alloy forming the impeller body 10 includes zinc (Zn), at least one element selected from the group consisting of gadolinium (Gd), terbium (Tb), thulium (Tm), and lutetium (Lu), The balance is made of magnesium (Mg).
Here, the content a (atomic%) of zinc (Zn) is preferably 0.2 ≦ a ≦ 3.0. Furthermore, the content b (atomic%) of at least one element selected from the group consisting of gadolinium (Gd), terbium (Tb), thulium (Tm), and lutetium (Lu) is 0.5 ≦ b ≦ 5. 0.0 is preferred. Here, it is further preferable that the relationship of 0.5a−0.5 ≦ b is satisfied.

When gadolinium (Gd) is added, the more preferable upper limit content is less than 3 atomic%. Furthermore, the ratio of the gadolinium (Gd) content to the zinc (Zn) content is particularly preferably 2: 1 or a ratio close thereto.
High strength and high toughness can be particularly improved by using such a content ratio.

In order to form the impeller body 10, a magnesium alloy having the above composition is melted and cast into a mold to form a magnesium alloy casting.
This magnesium alloy casting includes magnesium (Mg) and rare earth element compound, magnesium (Mg) and zinc (Zn) compound, zinc (Zn) and rare earth element compound, and magnesium (Mg) and zinc (Zn). At least one type of precipitate selected from the group of precipitates made of rare earth element compounds is deposited.

  Next, the magnesium alloy casting is subjected to a solution treatment. In the solution treatment, at least one kind of precipitate is left.

Thereafter, the magnesium alloy casting is machined to obtain an impeller body 10 having a predetermined shape.
As this machining, for example, extrusion, ECAE (equal-channel-angular-extrusion) processing method, rolling, drawing and forging, repetitive processing thereof, processing with plastic deformation such as FSW (friction stir welding) may be used. it can.
This plastic working can be performed alone or in combination among rolling, extrusion, ECAE, drawing and forging.

  The chemical conversion layer 11 is formed so as to cover the surface of the impeller body 10. The conversion layer 11 is made of, for example, a phosphate coating. The phosphate coating is made of a phosphate such as iron phosphate, manganese phosphate, or zinc phosphate. Such a phosphate coating is formed by immersing the impeller body 10 serving as a base material in an aqueous solution containing a phosphate for a predetermined time after washing the impeller body 10.

The chemical conversion layer 11 made of a phosphate coating may be formed thick enough to completely cover at least the surface of the base material 10 when there are fine irregularities. When the film thickness of the chemical conversion layer 11 made of such a phosphate coating is too large, the chemical conversion layer 11 increases in weight and adversely affects the response when the impeller 3 rotates.
Therefore, the chemical conversion layer 11 made of a phosphate coating is preferably formed with a film thickness of 0.5 μm or more and 5 μm or less, more preferably 2 μm or more and 5 μm or less.
Such a chemical conversion layer 11 may be formed by repeating the treatment for forming the phosphate coating a plurality of times and laminating the phosphate coating in a plurality of layers.

  The plating layer 12 is formed so as to cover the chemical conversion layer 11. The plating layer 12 is a plating film made of a nickel-based alloy formed by electroless plating. As a specific example, it is preferable to use a nickel-phosphorus alloy as the nickel-based alloy for forming the plating layer 12.

The plating layer 12 made of a nickel-phosphorous alloy is formed with a film thickness of 10 μm to 30 μm, more preferably 15 μm to 30 μm.
The plating layer 12 made of such a nickel-based alloy is formed by immersing an impeller body 10 which is a base material having the chemical conversion layer 11 formed on the surface thereof in a plating solution for a predetermined time and performing electroless plating.

According to the embodiment described above, the chemical conversion layer 11 formed by chemical conversion treatment so as to cover the surface of the impeller body 10 made of a magnesium alloy and having a film thickness within a predetermined range, and the chemical conversion layer 11 are covered. And a formed plating layer 12. According to such a configuration, the plating layer 12 adheres well due to the chemical conversion layer 11. By providing such a plating layer 12, it can have high corrosion resistance.
In the impeller 3 having such a coating structure and the compressor 1 provided with the impeller 3, the impeller 3 and the compressor 1 have high adhesion and corrosion resistance by forming the impeller 3 from a magnesium alloy. The operating response can be improved.

Furthermore, the chemical conversion layer 11 is a phosphate coating, and the plating layer 12 is formed of a nickel-phosphorus alloy.
Thereby, the adhesiveness of a magnesium alloy and the plating layer 12 can be improved especially effectively.

Furthermore, the impeller body 10 contains zinc (Zn) and at least one element selected from the group consisting of gadolinium (Gd), terbium (Tb), thulium (Tm), and lutetium (Lu), The balance consists of magnesium (Mg). Further, the impeller body 10 includes a magnesium (Mg) and rare earth element compound, a magnesium (Mg) and zinc (Zn) compound, a zinc (Zn) and rare earth element compound, and a magnesium (Mg), zinc (Zn) and rare earth element. It has at least one type of precipitate selected from the group of precipitates made of elemental compounds.
In the impeller body 10 made of such an alloy, even if the impeller body 10 is directly covered with the plating layer 12, the corrosion resistance is inferior. In this case, the adhesion between the impeller body 10 and the plating layer 12 can be effectively enhanced by interposing the chemical conversion layer 11 formed by chemical conversion treatment.

  Next, regarding the coating structure as described above, it was confirmed whether or not corrosion resistance and erosion occurred, and the results are shown below.

[Base material]
First, a magnesium alloy containing 2 atomic% Gd and 1 atomic% Zn and the balance being Mg and inevitable impurities was charged into a vacuum melting furnace for melting.
Next, the heat-dissolved material was placed in a mold and cast to prepare a 150 mm × 60 mm rectangular base material made of a magnesium alloy.

[surface treatment]
The prepared base material was washed and then subjected to the following surface treatment.
Example 1
A phosphate coating was formed on the surface of the base material, and then plated with a nickel-phosphorus alloy.
The phosphate coating was obtained by immersing the base material in a phosphate treatment solution for a predetermined time to obtain a phosphate coating with a thickness of 3 μm.
Plating with a nickel-phosphorus alloy was performed using a plating bath. Thereby, a plating layer having a film thickness of 15 μm was obtained.
(Comparative Example 1)
The base material was not subjected to surface treatment, and the base material was used as a test piece.
(Comparative Example 2)
Only the phosphate coating was formed on the base material under the same conditions as in the example.
(Comparative Example 3)
A resin coating was applied to the base material.
For the resin coating, a Si-based resin was used, and a resin coat layer was formed on the surface of the base material by painting.
(Comparative Example 4)
A phosphate film was formed on the base material under the same conditions as in the example, and then a resin coating was applied under the same conditions as in Comparative Example 3.
(Comparative Example 5)
The base material was only plated with a nickel-phosphorus alloy under the same conditions as in the example.
(Comparative Example 6)
The base material was coated with a resin under the same conditions as in Comparative Example 3, and then plated with a nickel-phosphorus alloy under the same conditions as in the example.

[Membrane adhesion]
About the test piece of Example 1 prepared as mentioned above and Comparative Examples 1-6, first, the adhesiveness with respect to the base material of the film | membrane formed by surface treatment was confirmed visually.
The results are shown in Table 1.

As a result, about Example 1 and Comparative Examples 2-5, the film | membrane by each surface treatment was formed in the base material.
On the other hand, in Comparative Example 6 in which the base material was resin-coated and then plated with a nickel-phosphorus alloy, the plating generated when the base material coated with the resin was plated Peeling of the layer was confirmed.

[Corrosion resistance]
Next, the salt spray test based on the salt spray cycle test based on JIS standard "H8502" was performed on Example 1 and Comparative Examples 1 to 5 in which the film was satisfactorily formed, and the corrosion resistance was verified.
About each of Example 1 and Comparative Examples 1-5, the evaluation after a salt spray test was performed by confirming the condition of the corrosion defect which generate | occur | produced on the test piece surface by measuring visually and corrosion weight loss.

As a result, as shown in Table 1, no corrosion was particularly observed in Example 1.
On the other hand, in Comparative Example 1, which is the base material itself, corrosion was recognized throughout. Furthermore, it was confirmed that in Comparative Example 2 in which only the phosphate coating was provided, the amount of corrosion was greater than in Comparative Example 1. It was confirmed that the amount of corrosion was larger in Comparative Example 3 using only the resin coating than in Comparative Example 1.
In Comparative Example 4 in which the phosphate coating and the resin coating were provided, no corrosion by the salt spray test was observed.
In Comparative Example 5 in which only plating with the Ni-P alloy was performed, peeling of the plating film was confirmed by the salt spray test.

[Erosion resistance]
Next, with respect to Example 1 and Comparative Examples 1 to 4 in which peeling of the film was not observed in the salt spray test, an erosion test such as putting water droplets into the inlet of the compressor was performed, and the amount of water droplets was controlled while controlling the amount of water droplets. Existence of occurrence was verified.
About each of Example 1 and Comparative Examples 1-4, evaluation of the presence or absence of erosion generation | occurrence | production was performed by confirming the test piece surface visually.

As a result, as shown in Table 1, in Example 1, no erosion was observed.
In contrast, in Comparative Examples 1 to 4, generation of erosion was observed.

  Thus, only Example 1 which provided the phosphate film and the plating layer by a Ni-P alloy was confirmed that the adhesiveness of a film | membrane, corrosion resistance, and erosion resistance are high.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and design changes can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the impeller 3 for the compressor 1 is shown as an example of the metal part having the coating structure. However, the present invention is not limited to the impeller, and can be used for various other metal members including a magnesium alloy as a base material.
Further, in the above-described embodiment, the compressor of the supercharger is shown as an example, but the present invention can also be applied to an impeller of a compressor other than the supercharger.

Furthermore, in embodiment mentioned above, the case where only one layer of the plating layer formed of the nickel-phosphorus alloy was laminated | stacked on the phosphate film was illustrated. However, the nickel-phosphorus alloy plating layer is not limited to one layer, and a plurality of layers may be provided. For example, after a first plating layer made of a nickel-phosphorus alloy is laminated on the phosphate coating, a second plating layer also made of a nickel-phosphorus alloy may be laminated.
Thus, when the 1st plating layer and the 2nd plating layer are provided, the film thickness of a 1st plating layer can be made thin compared with the case where the plating layer of a nickel- phosphorus alloy is formed in one layer. Therefore, the adhesion of the first plating layer to the phosphate coating can be improved.
Furthermore, the composition of the nickel-phosphorus alloy that forms the first plating layer and the second plating layer is not limited to the nickel-phosphorus alloy having the same composition. For example, a nickel-phosphorus alloy having higher adhesion to the phosphate coating than the second plating layer may be used for the first plating layer.

  By providing a chemical conversion layer formed by chemical conversion treatment so as to cover the surface of the base material made of magnesium alloy and having a film thickness within a predetermined range, the adhesion and corrosion resistance of the plating layer can be enhanced.

DESCRIPTION OF SYMBOLS 1 Compressor 2 Housing 3 Impeller 4 Rotating shaft 5 Turbine 10 Impeller body 11 Chemical conversion layer 12 Plating layer

Claims (8)

From a phosphate coating formed so as to cover the surface of a base material made of a magnesium alloy containing magnesium as a main component and containing at least one element selected from the group consisting of gadolinium, terbium, thulium and lutetium The formation stratification
A plating layer made of a nickel-based alloy formed so as to cover the chemical conversion layer;
Coating structure comprising.   The coating structure according to claim 1, wherein the plating layer is formed of a nickel-phosphorus alloy. The base material is
It contains a atom% of zinc, contains at least one element selected from the group consisting of gadolinium, terbium, thulium and lutetium in total, and contains b atom%, with the balance being magnesium, and a and b are represented by the following formula (1 ) To (3),
The compound of magnesium and rare earth elements, the compound of magnesium and zinc, the compound of zinc and rare earth elements, and at least one kind of precipitate selected from the precipitate group consisting of compounds of magnesium, zinc and rare earth elements, or 3. The coating structure according to 2.
(1) 0.2 ≦ a ≦ 5.0
(2) 0.5 ≦ b ≦ 5.0
(3) 0.5a-0.5 ≦ b   An impeller having the coating structure according to any one of claims 1 to 3.   A compressor provided with the impeller according to claim 4. Phosphorus conversion is performed by covering the surface of a base material made of a magnesium alloy containing magnesium as a main component and containing at least one element selected from the group consisting of gadolinium, terbium, thulium and lutetium. Forming a conversion layer comprising an acid salt film ;
Forming a plating layer made of a nickel-based alloy so as to cover the chemical conversion layer;
A method for manufacturing metal parts including   An impeller manufacturing method including the metal part manufacturing method according to claim 6.   A method for manufacturing a compressor including the method for manufacturing an impeller according to claim 7.

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