JPH1172042A - Piston of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a film layer which prevents the adhesion and has a uniform thickness and prevent the deposition of Ni3 P in the film layer even under high heat load conditions so as to suppress excessive rise of hardness by setting P content of Ni-P alloy in the film layer to a specific amount. SOLUTION: A piston main body 1 cast by using melted aluminum alloy is immersed in a plating bath after ordinary zincate treatment. After plating treatment, baking treatment is done. In this treatment process, a uniform plated film layer 4 made of Ni-P alloy is formed on the whole outer peripheral face including inner peripheral faces of each ring groove 2, 3 of the piston main body 1. P content in the film layer 4 is set to 0.2 to 5 weight %. Consequently, the deposition of Ni3 P is prevented, and a rise of hardness is suppressed, thereby ensuring the rigidity of a piston.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for use in an internal combustion engine for an automobile, for example, and particularly to a method of depositing an aluminum alloy from an inner peripheral surface of a ring groove of a piston body formed of an aluminum alloy material to an outer peripheral surface of a piston ring. The present invention relates to a piston of an internal combustion engine for preventing the adhesion.

[0002]

2. Description of the Related Art As is well known, in an internal combustion engine for an automobile, a heat load is extremely high in accordance with a demand for high performance and high output, and an aluminum alloy operating under such severe conditions is required. In a piston made of a material, aluminum alloy is easily adhered to the outer peripheral surface of the piston ring from the inner peripheral surface of the ring groove.

[0003] Various proposals have been made to prevent the occurrence of the above-mentioned adhesion. One of the proposals is to form an electrodeposition layer of chromium on the outer peripheral surface of a piston ring. May not be able to withstand use under severe conditions such as a large heat load and a high oil temperature.
Further, in the case of using the electroplating method, a uniform electric field is not formed on the inner peripheral surface of the ring groove, and there is a possibility that a plating layer having a uniform thickness cannot be formed.

For this reason, a ring groove is formed on the outer periphery of a crown portion of an aluminum alloy piston body, and a ring groove is formed on the outer peripheral surface of the piston body, as disclosed in, for example, Japanese Patent Application Laid-Open No. 57-2443. An electroless plating process is performed to form a film layer, that is, a bath temperature of 85 ° C. and a pH of
It has also been proposed to hold for 1 hour during melting at 5.5 = 5.5, thereby forming a uniform coating layer of Ni-P alloy on the outer peripheral surface of the piston body including the inner peripheral surface of the ring groove.

[0005]

However, in the conventional example described in the above publication, the PH value of the electroless plating bath is 5.
It is considered that the P amount (phosphorus content) contained in the Ni—P alloy is 6 to 12% by weight at this PH value. With a P content of 6 to 12% by weight, under severe conditions such as a large heat load as described above, Ni ₃ P precipitates, and the coating layer is hardened, and the toughness is reduced. That is, the crown portion of the piston body is generally exposed to high heat by the combustion gas, and the crown surface is about 250 ° C. to 300 ° C.
In the vicinity of the inner peripheral surface of the top ring groove, high heat of 220 ° C. to 280 ° C. is generated. For this reason, the high heat causes Ni ₃ P to be precipitated in the coating layer and the hardening to proceed, thereby reducing the toughness of the coating layer.

[0006] This is because the inventor of the present application incorporated the piston described in the publication into a 4-cycle, 4-cylinder, 2,000 cc internal combustion engine and operated at 6000 rpm for 100 hours. Hv500 at the time
To Hv1050, and many cracks were found on the inner peripheral surface of the top ring groove. It is considered that such a phenomenon is apparently due to precipitation of Ni ₃ P due to high heat.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the problems caused by the conventional electroless plating, and the invention according to claim 1 is directed to a piston body formed of an aluminum alloy material. A ring groove is formed on the outer periphery of the upper end of the piston, and a Ni-P alloy film layer is formed on the outer peripheral surface of the piston body by electroless plating. Is characterized in that the P content is set to 0.2 to 5% by weight.

According to a second aspect of the present invention, there is provided a Ni-P-Mo alloy formed by electroless plating on the outer peripheral surface of the piston body, while forming a ring groove on the outer periphery of an upper end portion of the piston body formed of an aluminum alloy material. A piston of an internal combustion engine having a coating layer formed of Ni-
It is characterized in that the P content of the P-Mo alloy is set to 0.2 to 5% by weight.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is based on the results of a detailed experimental study of the relationship between the composition of a plating film layer and the increase in hardness due to heating based on the above-mentioned conventional example.
It has been found that the lower the P content in the coating layer of the -P-Mo alloy, the smaller the increase in hardness due to heating, that is, the lower the toughness even when heated.

FIG. 2 shows Ni-P or N in the heat treatment.
The results of experiments on the relationship between the change in hardness of the i-P-Mo alloy film and the amount of phosphorus (P) are shown. As is clear from the results of the experiment, the initial hardness before heating was Ni up to 12% by weight of Ni. −
The P alloy film shows the highest hardness on the low phosphorus side and is about HV600. Thereafter, the initial hardness decreases with an increase in the phosphorus amount, and 5
Exceeding the weight percentage shows a constant value of about HV550. Ni-P
-Mo alloy film shows the minimum hardness on the low phosphorus side and is about HV400. Thereafter, the initial hardness increases with an increase in the amount of phosphorus, and when it exceeds 5% by weight, a constant value of about HV55 is obtained.
Indicates 0. However, after heating at 280 ° × 100 hours, when the amount of phosphorus is about 5% by weight or more, the Ni—P alloy film has a value of about HV1050, and the Ni—P—Mo alloy film has a sufficiently high value of about HV900. On the other hand, if it is set to 0.2% by weight to 5% by weight, about HV850 to 1050 and Ni-P-M
In the case of an o-alloy film, the hardness sharply decreases to about HV600 to 900. Note that the Ni-P-Mo alloy film has a smaller increase in hardness than the Ni-P alloy film.

Therefore, if the phosphorus content is set in the range of 0.2 to 5% by weight, an excessive increase in hardness is suppressed even when a heat load of 220 ° C. or more is high, and toughness can be secured.

[0012] Of course, compared to the Ni-P alloy film, Ni
The -P-Mo alloy film is more excellent in securing toughness.

Incidentally, it is impossible in the case of nickel salt hypophosphorous type electroless plating to make the phosphorus content less than 0.2% by weight.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment 1 of a piston of an internal combustion engine according to the present invention will be described below with reference to FIG.

In this embodiment, Kanigen S-795 was used as an electroless plating bath.

That is, first, an aluminum alloy (AC8A
After the normal zincate treatment, the piston body 1 that was melt-cast with the material was immersed in the plating solution of S-795 for 1 hour. The bath temperature was set at 90 ± 1 ° C. and the pH was 6 ± 0.1.
Set to. Depending on the conditions of this bath temperature and PH, phosphorus
(P) The content is set to 1.5 ± 0.5% by weight.

After the plating, a paging treatment was performed at 150 ° C. for 1 hour.

The piston body 1
A uniform plating film layer 4 made of a Ni—P alloy having a thickness of about 18 μ was formed on the entire outer peripheral surface including the inner peripheral surface of each of the ring grooves 2 and 3.

As described above, the piston rings 5 and 6 are respectively inserted into the ring grooves 2 and 3 where the plating film layer 4 is formed.
The piston body 1 fitted with
It was incorporated in a 00 cc internal combustion engine and operated at 6000 rpm for 100 hours. As a result, the hardness after the plating treatment was Hv500, but became Hv700 after the operation. Although the hardness increased slightly, the excessive increase was sufficiently suppressed, and the plating film layer applied to the inner peripheral surface of the top ring groove 2 was obtained. No cracking was observed in No. 4.

This is because the phosphorus in the coating layer 4
(P) By setting the content to 1.5% by weight, Ni ₃
This is because the precipitation of P was prevented and the increase in hardness was suppressed, so that the toughness was ensured.

Also, on the crown surface 1a of the piston body 1,
Since the plating layer 4 is formed, the coating layer 4 on the crown surface 1a is also prevented from cracking due to heat load.

In another embodiment, a Ni-Mo-P ternary plating bath shown in Table 1 was used as the electroless plating bath.

[0023]

[Table 1]

The amount of Mo and the amount of P in Ni can be changed by appropriately changing the amounts of sodium molybdate and hypophosphorous acid in the plating bath. The obtained Ni-PM
With respect to the o-alloy plating film, it was found that the Mo content and the P content in Ni contained the determined ratios shown in FIG.
It was also found that the deposition rate was also uniquely determined by the amount of P. The following shows a processing method in which the precipitation rate decreases as the P content decreases.

After the normal zincate treatment, first, the Ni-P plating shown in Example 1 or shown in Table 1 is treated to a thickness of 3 μm. After that, immediately Ni-Mo
The -P plating is processed under the processing conditions shown in Table 1, and the processing time is determined with reference to the deposition rate shown in FIG. 3 so that the thickness becomes about 15 microns.

For example, when sodium hypophosphite is 0.1 M / l and sodium molybdate is 0.003 M / l, nickel plating containing 0.7% by weight of phosphorus and 28% by weight of molybdenum can be obtained. After treating the piston, it was installed in an internal combustion engine in the same manner as in Example 1 and an experimental operation was performed. As a result, the hardness after the plating treatment was HV450, and after the actual operation, the hardness was HV600, which was a slight increase in hardness. Further, no crack was observed in the plating layer 4 provided on the inner surface side of the top ring groove 2.

[0027]

As is apparent from the above description, according to the piston of the internal combustion engine according to the present invention, the outer peripheral surface of the piston body of the aluminum alloy material is formed by Ni electroless plating.
The formation of a coating layer of a -P alloy or a Ni-P-Mo alloy and the setting of the P content of the Ni-P alloy or the Ni-P-Mo alloy to 0.2 to 5% by weight prevent adhesion. In addition to obtaining a coating layer having a uniform thickness, for example, even under the condition of a high heat load of 220 ° C. or more, precipitation of Ni ₃ P in the coating layer can be prevented and an excessive increase in hardness can be suppressed. . As a result, the toughness of the coating layer is improved and the occurrence of cracks is prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a piston to which the present invention is applied.

FIG. 2 is a graph showing a relationship between a change in hardness of a coating layer and a phosphorus concentration in a heat treatment.

FIG. 3. Effect of phosphorus content on deposition rate and Ni
The characteristic view which shows the molybdenum content of the -Mo-P alloy film layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piston main body 2, 3 ... Ring groove 4 ... Ni-P alloy plating film layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F16J 1/01 F16J 1/01 9/00 9/00 A

Claims (2)

[Claims] 1. A ring groove is formed on the outer periphery of an upper end portion of a piston main body formed of an aluminum alloy material, and Ni-P is formed on an outer peripheral surface of the piston main body by electroless plating.
An internal combustion engine piston having an alloy coating layer formed thereon, wherein the P content of the Ni-P alloy in the coating layer is set to 0.2 to 5% by weight. 2. A ring groove is formed on an outer periphery of an upper end portion of a piston main body formed of an aluminum alloy material, and Ni-P is formed on an outer peripheral surface of the piston main body by electroless plating.
In a piston of an internal combustion engine having a -Mo alloy coating layer formed thereon, the Ni content of the Ni-P-Mo alloy in the coating layer is set to 0.2.
A piston for an internal combustion engine, wherein the piston is set to about 5% by weight.