JPH0586972A - Piston for engine and manufacture thereof - Google Patents

Abstract

PURPOSE:To make wear resistance of a piston ring groove compatible with initial drape property, in a piston made of an aluminum alloy. CONSTITUTION:A nickel.phosphorus plated layer 9 is formed on the surface of a top ring groove, formed in the piston base material 2 made of an aluminum alloy, in a state that pro-eutectic silicone particles 10...10 contained in the piston base material 2 are protruded in a dispersed state from the surface of the base material 10.

Description

Detailed Description of the Invention

[0001]

This invention relates to an engine piston,
Particularly, it relates to a piston made of aluminum alloy.

[0002]

2. Description of the Related Art In engines for vehicles, pistons made of aluminum alloy are sometimes used.

When this type of aluminum alloy piston is used under high power, the temperature around the top land exposed to high temperature combustion gas becomes high, and the aluminum separated from the piston material is attached to the piston ring. Due to this suspiciously attached aluminum, abnormal wear is caused in the piston ring groove, and wear loss of the upper and lower surfaces of the ring groove hinders sealing performance.

To solve this problem, for example, as disclosed in Japanese Patent Application Laid-Open No. 1-190951, a hard alumite treatment layer is formed on the surface of the top ring groove close to the combustion chamber, and the alumite treatment layer is formed. There is a treatment layer in which primary crystal silicon particles are dispersed and crystallized. According to this, it is expected that the wear resistance and the aluminum adhesion resistance of the piston ring groove are improved.

[0005]

However, in the prior art described in the above publication, the following new problems will occur.

That is, since the alumite treatment layer formed in the piston ring groove has a large hardness but a large surface roughness, cracks are likely to occur on the contrary, so that the oil consumption increases in the early stage of use and blowby gas Therefore, the engine output will be reduced.

The present invention addresses the above-mentioned problems in aluminum alloy pistons, and its object is to achieve both wear resistance and initial conformability.

[0008]

That is, an engine piston according to the invention of claim 1 of the present application (hereinafter referred to as the first invention) has a piston ring groove provided on a piston base material made of an aluminum alloy. A precipitation hardening type plating layer having a small initial hardness is formed in a state where the silicon particles contained in the piston base material are projected and dispersed from the surface of the base material.

The piston of the engine according to the invention of claim 2 of the present application (hereinafter referred to as the second invention) has the above-mentioned piston base material in the surface of the piston ring groove provided in the piston base material made of aluminum alloy. The nickel-phosphorus plating layer having a small initial hardness is formed in a state in which the silicon particles contained in the above are dispersed and projected from the surface of the base material.

On the other hand, the invention of claim 3 of the present application (hereinafter, referred to as the third
A method for manufacturing an engine piston according to the invention)
The surface of the piston ring groove in the piston base material made of aluminum alloy is removed to disperse silicon particles in a protruding manner, and then a thermosetting precipitation hardening type plating layer with a small initial hardness is formed on the ring groove surface. And

[0011]

According to the piston of the first aspect of the invention, the precipitation hardening type plating layer formed on the surface of the piston ring groove in the piston base material made of an aluminum alloy has a small initial hardness and therefore has a good initial familiarity. Will be obtained. Further, since the silicon particles are dispersedly arranged in the plated layer in a state of protruding from the piston base material,
A proper wear resistance will also be ensured.

According to the piston of the second aspect of the present invention, since the piston ring groove is covered with the nickel / phosphorus plating layer having excellent plating properties, good quality can be obtained.

Further, according to the piston manufacturing method of the third aspect of the present invention, since the precipitation hardening type plating layer formed on the surface of the piston ring groove in the piston base material has a small initial hardness, it has good initial conformability. Will be obtained.
Further, since silicon particles are dispersedly arranged in the plated layer in a state of protruding from the piston base material, appropriate wear resistance can be ensured.

In particular, according to the third aspect of the present invention, the surface of the piston base material is removed so that the silicon particles project, so that the silicon particles do not fall off, which allows precipitation hardening plating. Silicon particles are appropriately dispersed in the layer, and an appropriate initial hardness is secured.

[0015]

EXAMPLES Examples of the present invention will be described below.

1 and 2, the piston base material 2 constituting the main body portion of the piston 1 according to this embodiment is formed of an aluminum alloy containing silicon in the range of 11 to 13% by weight. At the upper part of the outer peripheral surface of the piston base material 2, a top ring groove 5 and a second ring groove 6 in which the compression rings 3 and 4 are respectively locked.
And a third ring groove 8 into which an oil ring 7 for scraping off excess oil is locked.

In this embodiment, the top and bottom surfaces 2a, 2a of the top ring groove 5 in the piston base material 2 are used.
In b, the precipitation hardening type nickel-phosphorus plating layers 9 and 9 are formed. As shown in FIG. 3, primary crystal silicon particles 10 ... 10 are dispersedly arranged in the nickel / phosphorus plated layer 9 in a state in which the upper part thereof protrudes from the piston base material 2.

Since the precipitation hardening nickel-phosphorus plating layers 9 and 9 are formed on the upper and lower surfaces 2a and 2b of the top ring groove 5 of the piston base material 2 as described above, the initial hardness is small, and as a result, the initial hardness is reduced. Also in this case, good initial familiarity can be obtained. Moreover, since the primary crystal silicon particles 10 ... 10 are dispersedly arranged in the nickel-phosphorus-plated layer 9 in a state in which the upper part thereof projects from the piston base material 2, proper wear resistance is obtained even in the initial stage of use. Will be secured.

When the engine is in an operating state and the combustion temperature rises, the heat reacts with the phosphorus and nickel forming the plating layer 9 to cause precipitation hardening particles (Ni).
₃ P) will be co-deposited, which will increase the hardness of the nickel-phosphorus plated layer 9.

Next, a method of manufacturing the piston according to this embodiment will be described.

First, a piston base material 2 made of an aluminum alloy (JIS AC8A9) obtained by gravity casting is heat treated by a T6 treatment method defined by JIS, and then the surface of a top ring groove 5 formed by machining is processed. As shown in FIG. 4, an electrolytic bath is used to electrolytically remove a predetermined thickness t ₁ . As a result, as shown in FIG. 5, the primary crystal silicon particles 10 ... 10 contained in the piston base material 2 are in a state where the upper portions thereof are exposed.

Here, the electrolytic removal of the piston base material 2 is specifically performed as follows.

That is, an electrolytic solution in which a perchloric acid aqueous solution having a specific gravity of 1.4 and glacial acetic acid are mixed at a ratio of 1: 3 is put in an electrolytic bath, and the piston base material 2 is immersed in this electrolytic solution to form an anode. At the same time, a cathode made of an aluminum plate is arranged so as to surround the outer periphery thereof, and electrolysis is performed for 2 minutes at 50 V, 3 A / dm ² , and a liquid sound of 40 ° C. Then, the piston base material 2 is removed by a thickness of 8 μm. At that time, the applied voltage is set lower than the voltage at which gas starts to be generated from the piston base material 2 as the anode. As a result, the gas does not adhere to the piston base material 2 and the electrolysis is performed uniformly. Further, since the electrolytic rate of the primary crystal silicon particles 10 is slower than the melting rate of the piston base material 2, the piston base material 2 is selectively removed.

Next, the electrolytically removed piston base material 2 is dipped in a predetermined zinc displacing agent and left for 1 minute at a temperature of 20 ° C. to replace the aluminum on the exposed surface with zinc.

After that, the piston base material 2 is melted by electroless plating.
Liquid (NiCl ₂・ 6H₂O 5 x 10^-2 mol / l, Na
H₂PO₃ 3.63 x 10^-2 mol / l, PH 5.
8), and electroless plating is performed in a warm bath at 80 ° C.
As a result, nickel phosphorus with a phosphorus content of 7% by weight
A clear layer 9 was obtained. Coating of this nickel-phosphorus plating layer 9
The hardness shows a value of 630 in Vickers hardness (Hv), and
Greater than hardness (Hv150) of Ston base metal
It became smaller than the con particles (Hv1000). This
The hardness of nickel-phosphorus plating is higher than that of primary silicon
By making it smaller, the initial hardness becomes smaller and the conformability becomes better.
Will improve.

Here, as shown in FIG. 6, the content of phosphorus in the plating layer 9 is in the range of 5 to 10% by weight, and an appropriate surface hardness can be obtained. When the content of is small, the initial hardness cannot be obtained,
On the other hand, if the phosphorus content is too high, the brittleness becomes large and cracks easily occur, which is not preferable.

Further, the film thickness t of the nickel-phosphorus plated layer 9
₂ is preferably in the range of 5 to 10 μm. If it is less than 5 μm, the primary crystal silicon particles are exposed to lower the surface roughness, and conversely, if it exceeds 10 μm, the outer peripheral portion of the ring groove is enlarged due to the edge effect, and the required clearance may not be secured. Because there is.

Next, an explanation will be given of the experimental results of the heating test of the thus obtained piston on the assumption of an actual machine. As shown in FIG. 7, the Hv630 which initially showed hardness was fully opened. It was confirmed that the hardness of the nickel-phosphorus plated layer was hardened to Hv 790 at around 230 ° C. In addition, this experiment was performed by leaving it to stand under a plurality of treatment temperatures for 1 hour.

Next, the results of experiments conducted to confirm the initial conformability will be described.

First, as shown in FIG. 8, a disc 1 having an aluminum alloy of the same quality as the piston base material and a diameter φ of 80 mm is used.
1 was molded, and a nickel / phosphorus plated layer 12 was formed on the surface thereof. Then, by rotating the disk 11 with the sliding member 13 formed in a horseshoe shape abutting on the nickel-phosphorus plated layer 12, the surface roughness Ra of the portion abutting the sliding member 13 is increased. Was measured. As shown in FIGS. 9 and 10, the sliding member 13 has a width W of 3 mm, a contact portion radius r of 2 mm, a total height H of 8.5 mm, and a total length L of 5 mm.

Then, while maintaining the surface pressure between the sliding member 13 and the disk 11 at 12 kg / mm ² , the disk 11 was rotated at a peripheral speed of 10 m / s. Then, assuming actual use, lubricating oil at 100 ° C. was supplied to the contact portion between the disk 11 and the sliding member 13.

FIG. 11 shows the experimental result. That is,
Although the surface roughness Ra was 0.45 μm at the beginning, it was confirmed that the surface roughness Ra dropped sharply after the start of the experiment and the surface roughness Ra became almost constant after 60 minutes. At that time, it was also confirmed that the smaller the hardness, the lower the surface roughness Ra.

Next, the result of the actual machine test using the piston obtained as described above will be described.

That is, H is used as the test material for the piston material.
With a nickel-phosphorus plating layer of v610 formed,
A Hv1010 nickel-phosphorus plated layer and an untreated one were prepared.
The material specified in S440C was combined with a ring member produced by nitriding treatment, mounted on an engine with a displacement of 1600 cc, and continuously operated for 153 hours. Was measured respectively.

The experimental results are shown in FIG. That is,
As shown in FIG. 4A, the untreated type has a large wear amount of the piston member of about 60 μm, while the nickel-plated type has a large wear amount as shown in FIGS. It was also confirmed that the amount of wear was reduced.

As shown in FIG. 6C, it was also found that if the hardness of the nickel-phosphorus plating is too large, the amount of wear of the ring material increases. From this, it was confirmed that the initial hardness of nickel-phosphorus plating should not be too high.

Incidentally, nickel boron (Ni-B),
The deposition effect type plating layer may be formed using nickel-cobalt-phosphorus (Ni-Co-P).

[0038]

As described above, according to the present invention, the precipitation hardening type plating layer formed on the surface of the piston ring groove in the piston base material made of the aluminum alloy has a small initial hardness, and thus has a good initial familiarity. Will be obtained. Further, since silicon particles are dispersedly arranged in the plated layer in a state of protruding from the piston base material, appropriate wear resistance can be ensured.

According to the piston of the second aspect of the present invention, since the piston ring groove is covered with the nickel / phosphorus plating layer having excellent plating property, good quality can be obtained.

Further, according to the method for manufacturing a piston of the third aspect of the present invention, since the precipitation hardening type plating layer formed on the surface of the piston ring groove in the piston base material has a small initial hardness, good initial conformability is obtained. Will be obtained.
Further, since silicon particles are dispersedly arranged in the plated layer in a state of protruding from the piston base material, appropriate wear resistance can be ensured.

In particular, according to the third aspect of the invention, since the silicon particles are removed so that the silicon particles project from the surface of the piston base material, the silicon particles do not fall off, whereby the precipitation hardening plating is performed. Silicon particles are appropriately dispersed in the layer, and an appropriate initial hardness is secured.

[Brief description of drawings]

FIG. 1 is an overall view of a piston according to an embodiment.

FIG. 2 is an enlarged sectional view of a main part of a piston.

FIG. 3 is an enlarged schematic view of the periphery of a nickel / phosphorus plated layer.

FIG. 4 is an enlarged schematic diagram showing a state before electrolytic removal of a piston base material.

FIG. 5 is an enlarged schematic view showing a state after electrolytic removal of the piston base material.

FIG. 6 is a graph showing the relationship between the phosphorus content in nickel-phosphorus plating and the film hardness.

FIG. 7 is a graph showing the relationship between the heat treatment temperature and the film hardness in nickel-phosphorus plating.

FIG. 8 is a schematic configuration diagram of an apparatus used for measuring a change in surface roughness of nickel / phosphorus plating over time.

FIG. 9 is a side view of a sliding member.

FIG. 10 is a front view of a sliding member.

FIG. 11 is a graph showing changes over time in the surface roughness of nickel-phosphorus plating.

FIG. 12 is a graph showing a relationship between wear amounts of a ring member and a piston member in an actual machine test.

[Explanation of symbols]

 1 Piston 2 Piston Base Material 5 Top Ring Groove 9 Nickel / Phosphorus Plating Layer 10 Primary Crystalline Silicon Particles

Claims (3)

[Claims] 1. Precipitation with a small initial hardness in a state in which silicon particles contained in the piston base material project and disperse from the surface of the piston base material provided on the piston base material made of an aluminum alloy. An engine piston having a hardened plating layer formed thereon. 2. Nickel having a small initial hardness in a state in which silicon particles contained in the piston base material are dispersed and protruded from the surface of the base material of the piston ring groove provided in the piston base material made of an aluminum alloy. -An engine piston characterized by having a phosphor-plated layer. 3. A surface of a piston ring groove in an aluminum alloy piston base material is removed to disperse silicon particles in a protruding manner, and then a thermosetting precipitation hardening type plating layer having a small initial hardness is formed on the surface of the ring groove. A method of manufacturing an engine piston, the method comprising: forming.