JPH02264142A - Piston for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a trouble, e.g. crack, by a method wherein composite reinforcement is effected so that the volume rate of a porous metallic substance formed such that chrome of at least a specified % or more is contained is in a range of a specified %, and chrome is formed in a thickness of specified mm or more on the surface part of the porous metallic substance. CONSTITUTION:In an aluminum alloy piston 1 for an internal combustion engine in which composite reinforcement is made on a link groove 2 by using a porous metal, composite reinforcement in 8-70% volume ratio is applied on a porous metallic substance formed such that chrome of at least 10% or more is contained. The chrome is formed in a thickness of 0.001mm or more on the surface part of the porous metallic substance. This constitution prevents formation of a brittle intermetallic compound due to reaction between aluminum and a reinforcing substance, resulting in prevention of the production of a crack at an intermetallic compound and improvement of wear resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piston for an internal combustion engine, and more particularly to an aluminum alloy piston with an improved method of reinforcing a ring groove of a piston ring.

(Prior art) In general, the ring grooves of aluminum alloy pistons for internal combustion engines are not only exposed to high temperatures, but also wear progresses due to mechanical sliding with the piston rings. Oil consumption increases and engine life is affected.

In order to reduce such wear, especially in diesel engines where groove wear is significant, a method of casting special cast iron is commonly used.

Furthermore, Japanese Patent Application Laid-Open No. 53-31014 discloses a method in which a porous metal is used to reinforce the groove portion, and high pressure is applied during casting to infiltrate the porous portion with aluminum alloy, which is the matrix of the piston.

Furthermore, JP-A-59-21.393, JP-A-59-21
No. 8341 and JP-A No. 59-212159 use a porous reinforcing material such as iron, nickel, copper, etc. to improve wear resistance by forming a compound of this material and an aluminum alloy. is disclosed.

(Problems to be Solved by the Invention) While continuing tests to reinforce piston ring grooves using the above porous materials, the inventors discovered that aluminum and porous materials differed depending on the type of porous material. The formation tendency of intermetallic compounds changes, and ■If intermetallic compounds are formed, cracks may occur from the brittle intermetallic compounds when the piston is subjected to a thermal cycle of heating and cooling for a long period of time. I found a problem like this.

The above-mentioned cracks do not pose a particular problem when the volume fraction V of the reinforcing material is low, but when V becomes large, the interface between the reinforcing part and the aluminum base material peels off macroscopically, and the reinforcement is removed from the piston. It turned out that there was such a problem that entire counties were dropping out.

Furthermore, a problem with reinforcing the ring groove of a piston with a porous metal body is that if the vf of the reinforcing material is low, even if the amount of intermetallic compounds is increased, Niresist, which is normally used for aluminum pistons, Since the wear resistance is inferior to that of the wear-resistant ring of In some cases, there is the aforementioned problem that the entire reinforcement group is likely to fall off.

An object of the present invention is to solve the above problems.

(Means and effects for solving the problems) This invention has been made in view of the above problems.

The purpose of the present invention is to provide a piston for an internal combustion engine in which the ring groove of the piston is reinforced with a porous material without using an intermetallic compound, and which is constructed to have a high heat load.

That is, in an internal combustion engine aluminum alloy piston in which the ring groove is compositely reinforced with porous metal, a layer containing at least 10% chromium is formed on the surface of the porous reinforcement to a thickness equal to or greater than o,oot. This prevents the formation of brittle intermetallic compounds caused by the reaction between aluminum and the reinforcing body, thereby preventing cracks caused by the intermetallic compounds and improving wear resistance.

There is no difference in the tendency for the formation of intermetallic compounds even if chromium is contained only in the surface layer or uniformly throughout the material.
From the point of view of wear resistance.

The higher the chromium content, the better; a layer with a chromium content of 15% or more has a chromium content of 0.
It is desirable that the thickness be 003+am or more.

Further, the amount of chromium may be 100% in the surface layer, and from the viewpoint of wear resistance, the larger the amount of chromium, the better.

On the other hand, the volume fraction of the reinforcing body is 8 to 70%, preferably 10 to 6
0% is good. This is because when it is less than 10%, the effect of improving wear resistance is small, and when it is more than 60%, it becomes difficult to completely infiltrate the porous parts with aluminum, making it difficult to composite, and the reinforcement This is because unless the preheating temperature is set high, it will be difficult for aluminum to penetrate, and the higher the preheating temperature is, the more likely a compound with aluminum will be formed on the surface of the reinforcing body, which is not preferable.

The reinforcing body is made of iron, nickel, monel alloy, etc., and chromizing treatment is used to diffuse and infiltrate the surface layer of the reinforcing body, or a powder of austenitic stainless steel with a high chromium content is used and sintered. Manufactured by.

Further, the chromium layer may be formed by plating.

(Example) The present invention will be explained in detail below.

(Example 1) FIG. 1 shows a piston of the present invention, where 1 is a piston, 2 is a top ring groove, and 3 is a composite part.

In order to reinforce the top ring 1l12 of the piston 1, a ring-shaped nickel foam metal (Selmesoto manufactured by Sumitomo Electric Industries, Ltd.) was pressed and molded so that the volume fraction V after compounding with the aluminum alloy was 30%.

On the other hand, another ring groove reinforcing ring was manufactured in which the same nickel foam metal was subjected to chromizing treatment to form a chromium permeation layer of about 0.003 mm on the nickel surface.

Next, set these in a mold for molten metal forging and heat to 740°C.
800 kg/cu after pouring molten aluminum
A piston with a reinforced top ring groove was manufactured by applying a pressure of 100 m to infiltrate 2 foamed metal rings with molten aluminum.

Then, this piston was subjected to heat treatment including solution treatment at 495° C. for 5 hours and aging treatment at 200° C. for 5 hours, and a test piece was cut out to observe the microstructure.

Figure 2 is a microscopic photograph of the Sokel foam metal-reinforced aluminum alloy composite in the nickel foam composite, and it can be seen that a reaction layer of aluminum and nickel is formed as shown by the arrow. The results of quantitative analysis of aluminum and nickel using an X-ray microanalyzer using a scanning electron microscope are shown in FIGS. 3 and 4.

From these results, it can be seen that the center of the nickel foam is a single layer of nickel, but as it approaches the surface, the amount of aluminum increases, and a compound of nickel and aluminum is formed.

Figures 5 to 7 show samples obtained by scanning electron microscopy of materials in which a nickel foam is chromized and a chromium layer with a thickness of 0.003 to 0.005 mm is formed on two surfaces, combined with aluminum. The results of X4% microanalyzer analysis of nickel, chromium, and aluminum are shown. It can be seen that a chromium layer is formed on the surface by the chromizing treatment, which prevents aluminum from penetrating inside.

When this piston is operated for 500 hours under the conditions of cyclic heat load such as full load maximum speed and no load idling operation, it differs depending on the engine, but if the Vf of the nickel foam exceeds 20%, the composite part and aluminum There is a tendency for cracks to occur easily at the interface of the base material. In order to reproduce the crack between the composite part and the aluminum matrix without using an engine test, it is easier to heat the piston to 500°C and then rapidly immerse it in water at room temperature.

Therefore, we created both pistons with chromized nickel foam and those without chromized nickel foam.

When color-checked by repeating the process of heating to 500°C and then water-cooling four times, no cranks were observed in the chromized nickel foam, whereas no cranks were observed in the non-chromized nickel foam. It was confirmed that the aluminum alloy interface was completely peeled off.

Furthermore, the results of the Great War type abrasion test of these pistons are shown in FIG. 8, which also shows that the abrasion resistance of the chromized nickel foam is improved.

(Example 2) Porous metal can also be manufactured by pressing and sintering at low pressure.

Now, a V, 50% porous sintered body made by mixing 5%, 10%, and 20% chromium in mild steel powder is composited with aluminum by molten metal forging, and after solution treatment at 495'C for 5 hours,
A heat treatment was performed at 200° C. for 5 hours, and the thickness of the aluminum-iron compound layer was measured. The measurement results are shown in FIG.

In the case of a composite material made of a porous sintered body with v r of 50%, if it does not contain chromium, the boundary between the sintered body composite part and the aluminum part will peel off after three water cooling treatments from 500°C, but with 10% chromium No peeling was observed when it contained chromium, thus demonstrating the effect of containing chromium.

(Example 3) The abrasion test results of a V, 50% composite of SUS316L (chromium 16-18%) are shown in the above-mentioned FIG. 8. In this case, the V of the metal to be strengthened is high.

Less wear than nickel foam.

Further, no peeling at the interface between the composite part and the aluminum base material was observed even after three heat treatments of water cooling from 500°C.

Note that the present invention is not limited to the above embodiments, and there is no problem in plating the surface of the porous metal body with chromium, and if the amount of chromium is 10% or more, it can be plated not only on the three surfaces but also inside the porous metal body. Of course, it may be evenly included.

(Effects of the Invention) The present invention is constructed as described in detail above, and it is possible to reinforce the piston ring groove with excellent wear resistance and machinability, and without fear of peeling between the reinforcing member and the aluminum interface.

Therefore, according to the present invention, even when used in an engine with a high heat load, defects such as cracks can be reliably prevented from occurring, the durability of the piston can be improved, and a good service life can be obtained.

[Brief explanation of drawings]

Fig. 1 is a partially sectional front view of an aluminum alloy piston to which the present invention is applied, Fig. 2 is a micrograph of a nickel foam metal reinforced aluminum alloy composite, Figs.
The figures also show X-ray analysis photographs of the composite materials.
Figures 7 to 7 show X-ray analysis photographs of nickel foams subjected to chromizing treatment, Figure 8 is a graph of the piston wear test results, and Figure 9 shows the relationship between the amount of chromium and the aluminum and iron compound layers. It is a graph showing the relationship with thickness. ■...Piston, 2...Top link groove. 3...Complex part. Patent Applicant: Izumi Kogyo Co., Ltd. Agent (Patent Attorney) Toshi Matsuzawa Engraving of drawings (no change in content) Engraving of diagram drawings (no change in content) Engraving of diagram drawings (no change in content) Diagram procedure Amendment (1) Patent claim on page 1, line 4 to line 14 of the specification filed in October 1999 by Mr. Bunki Yoshida, Commissioner of the License Agency 1. Indication of the case Patent Application No. 222239 of 1988 2. Name: Internal combustion engine piston 3, person making the amendment Address name related to the case

Claims (3)

[Claims] (1) In an aluminum alloy piston for internal combustion engines whose ring grooves are compositely reinforced with porous metal, the surface portion contains at least 10% chromium.
A piston for an internal combustion engine, characterized in that a porous metal body formed with a thickness of 1 mm or more is compositely reinforced by 8 to 70% in volume ratio. (2) The piston for an internal combustion engine according to claim (1), wherein the porous metal body is a nickel-based metal. (3) Claim (1) wherein the porous metal body is an iron-based metal.
) pistons for internal combustion engines.