JP2006328482A - Forged piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forged piston of an aluminum alloy, which has superior heat resistance, superior abrasion resistance, and reduced weight. <P>SOLUTION: The forged piston is made from an aluminum alloy which comprises, by wt.%, 8-18% Si, 0.5-3% Cu, 1-5% Ni, while controlling a content of Ni so as to be higher than that of Cu, and the balance Al with unavoidable impurities, and which includes intermetallic compounds that are formed from Al and Ni and have a maximum length of 3 to 100 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a forged piston made of an aluminum alloy.

  Pistons used in internal combustion engines are parts for converting energy from combustion into motive power, and are required to be lighter and have better heat resistance and wear resistance. Forging pistons made of aluminum alloy have attracted attention as satisfying such requirements. In order to achieve these objects, various aluminum alloys for pistons have been proposed (see Patent Documents 1 to 3).

  For example, Patent Document 1 provides wear resistance by Si, contains precipitation strengthening elements of Cu and Mg, further contributes to high strength improvement of Fe and Ni, and suppresses recovery and recrystallization at high temperatures. There has been proposed an aluminum alloy in which Mn, Ti, Zr, and V have an effect. However, since the effect of improving the strength in this case is about 250 ° C. at the maximum, in the case of a piston made of such an aluminum alloy, it is not possible to obtain a sufficient strength in the piston ceiling at a high temperature.

  On the other hand, Patent Document 2 proposes an aluminum alloy in which the maximum length of a crystallized product by casting is controlled to 200 μm, and the strength is further improved at a high temperature by strengthening the crystallized product dispersion. However, in this case, since a large amount of a transition element that causes the intermetallic compound to crystallize is added, the specific gravity is increased, which hinders improvement in engine performance due to weight reduction. In addition, coarse crystallized products cause internal defects and cracks during forging, and it is difficult to improve the quality of the material by forging.

  On the other hand, Patent Document 3 proposes to improve the high-temperature strength of 250 ° C. or higher by setting the Ni content to 2 to 6 wt% among the elements of the Al—Si based aluminum alloy used for the piston. ing. However, in this case, since Cu and Ni are contained in a large amount, the specific gravity increases and the weight increases, so that the merit of increasing the strength is lost. In addition, the coarse crystallized product causes defects during forging and causes a significant decrease in strength.

Furthermore, examples of the aluminum alloy for the forged piston include JIS standard A4032 and A2618. However, since A4032 is a material obtained by precipitation strengthening, the strength of the piston decreases when exposed to high temperatures. On the other hand, since A2618 has a small Si content, the coefficient of thermal expansion is high, and the slidability of the piston is deteriorated.
Japanese Patent Laid-Open No. 7-216487 JP 2000-54053 A JP-A-8-260089

  This invention is proposed in view of such a conventional situation, and it aims at providing the forge piston made from an aluminum alloy which is excellent in heat resistance and abrasion resistance, and is lightweight.

As a means for solving the above-mentioned problems, the invention according to claim 1 contains, by weight, Si: 8 to 18%, Cu: 0.5 to 3%, Ni: 1 to 5%, with the balance being Al and It is a forged piston made of an aluminum alloy that consists of inevitable impurities, contains more Ni than Cu, and has a maximum length of 3 to 100 μm of an intermetallic compound formed of Al and Ni.
The invention according to claim 2 contains, by weight, Si: 8 to 18%, Cu: 0.5 to 3%, Ni: 1 to 5%, Fe: 2.0% or less, with the balance being Al. And the sum of Ni and Fe is more than Cu and less than 5% by weight, and the maximum length of the intermetallic compound formed by Al, Ni and Fe is 3 to 100 μm. A forged piston made of an aluminum alloy.
The invention according to claim 3 is the forged piston according to claim 1 or 2, wherein the aluminum alloy further contains Mg: 2.0% or less by weight%.
According to a fourth aspect of the present invention, the aluminum alloy further contains at least one of Zr: 0.25% or less and Ti: 0.25% or less by weight%, and Zr and Ti are contained. The forged piston according to any one of claims 1 to 3, wherein the total amount when contained is 0.3% or less by weight.
According to a fifth aspect of the present invention, in the aluminum alloy, the total amount of Mn: Fe and Mn is 2.0% or less and the total of Cr: Fe and Cr × 5 is 2.0% or less by weight%. The forged piston according to any one of claims 1 to 4, comprising at least one kind.
The invention according to claim 6 is characterized in that the average grain size of eutectic Si and primary Si in the metal structure of the aluminum alloy is 10 to 100 μm. This is a forged piston.

  As described above, according to the present invention, it is possible to obtain a lightweight aluminum alloy forged piston that is excellent in heat resistance and wear resistance by an aluminum alloy with improved high-temperature strength while ensuring toughness and productivity. .

Hereinafter, a forged piston to which the present invention is applied will be described in detail with reference to the drawings.
As shown in FIG. 1, the forged piston includes, for example, a piston head 1 that receives an explosion load in a cylinder of an internal combustion engine, a skirt 2 for smoothly reciprocating the piston in the cylinder, and a piston that slides on the inner wall of the cylinder. It has a structure provided with a plurality of ring grooves 3 for incorporating piston rings to be contacted and a pin hole 4 for inserting a piston pin for coupling the piston to the connecting rod.

  The forged piston to which the present invention is applied contains, by weight%, Si: 8 to 18%, Cu: 0.5 to 3%, Ni: 1 to 5%, the balance is made of Al and inevitable impurities, Ni is It is characterized by being made of an aluminum alloy containing more than Cu and having an intermetallic compound formed of Al and Ni having a maximum length of 3 to 100 μm.

  The forged piston to which the present invention is applied contains, by weight, Si: 8 to 18%, Cu: 0.5 to 3%, Ni: 1 to 5%, Fe: 2.0% or less, and the balance Is made of Al and inevitable impurities, the sum of Ni and Fe is more than Cu and 5% by weight or less, and the maximum length of the intermetallic compound formed by Al, Ni, and Fe is 3 to 3. It consists of an aluminum alloy which is 100 micrometers.

In the forged piston to which the present invention is applied, the linear expansion coefficient of the piston reciprocating in a high-temperature cylinder can be suppressed by Si, and the dimensional change can be minimized. Moreover, sliding durability at high speed can be improved.
In the forged piston to which the present invention is applied, the material strength from room temperature to 200 ° C. can be improved by Cu.
Moreover, in the forged piston to which the present invention is applied, the aluminum alloy crystallizes the ternary compound of Al—Cu—Ni and improves the material strength up to 250 ° C.
Further, in the forged piston to which the present invention is applied, the Al—Ni compound in the aluminum alloy improves the high temperature strength at 250 ° C. or higher, suppresses the formation of coarse crystallized products, prevents internal defects and forging. Prevent cracking at times.
Further, in the forged piston to which the present invention is applied, the Al—Ni compound in the aluminum alloy improves the high temperature strength at 250 ° C. or higher, suppresses the formation of coarse crystallized products, prevents internal defects and forging. Prevents the occurrence of cracks, etc.

  Therefore, in the forged piston to which the present invention is applied, a forged piston made of an aluminum alloy having excellent heat resistance and wear resistance and a light weight can be obtained by an aluminum alloy having improved high temperature strength while ensuring toughness and productivity. .

  In the forged piston to which the present invention is applied, the aluminum alloy can further contain Mg. In this case, the Mg content is 2.0% by weight or less. Thereby, the intensity | strength of cloth | dough can be improved by solid solution reinforcement | strengthening.

  In the forged piston to which the present invention is applied, the aluminum alloy can contain at least one of Zr and Ti. In this case, the Zr content is 0.25% by weight or less, and the Ti content is 0.25% by weight or less. Further, when Zr and Ti are contained, the total of these Zr and Ti is made 0.3 wt% or less. Thereby, refinement | miniaturization of a crystal grain and improvement of durability can be aimed at, suppressing the production | generation of a coarse crystallization thing.

  In the forged piston to which the present invention is applied, the aluminum alloy can contain at least one of Mn and Cr. In this case, the content of Mn is 2.0% by weight or less for the total of Fe and Mn, and the content of Cr is 2.0% by weight or less for the total of Fe and Cr × 5. Thereby, in the range which does not produce a coarse compound, a structure can be refined | miniaturized and forgeability can be improved.

  In the forged piston to which the present invention is applied, the particle sizes of the eutectic Si and the primary crystal Si in the metal structure of the aluminum alloy are 10 to 100 μm. Thereby, while ensuring sufficient toughness and productivity, the sliding property of a piston can be improved.

Hereinafter, the reasons for defining each element added to the aluminum alloy of the forged piston to which the present invention is applied, the amount of addition thereof, and the metal structure of the aluminum alloy will be described.
(Si: 8-18%)
Si is an element necessary for suppressing the linear expansion coefficient of a piston used at a high temperature, minimizing its dimensional change, and withstanding sliding at a high speed. However, when a large amount is added, coarse primary crystal Si is crystallized, and the toughness and workability of the material are lowered. Therefore, in the present invention, in order to obtain a sufficient effect, the lower limit is 8%, and in order to ensure sufficient toughness and workability as a piston, the upper limit is 18%.

(Cu: 0.5-3%)
Cu is an element that improves the material strength from room temperature to about 200 ° C. by solid solution strengthening. However, when added in a large amount, the crystallization of the Al—Ni compound is prevented, the improvement of the material strength at 250 ° C. or higher is prevented, and a lightweight piston cannot be obtained due to an increase in the specific gravity of the material.
Therefore, to obtain the minimum necessary strength at 200 ° C., the lower limit is set to 0.5%, and the upper limit is set to 3% in order to suppress the increase in specific gravity without preventing the crystallization of the Al—Ni compound. %.

(Ni: 1-5%)
Ni is an element that causes Al—Cu—Ni ternary compounds to crystallize and improve high-temperature strength by coexisting with Cu. However, the effect is up to 250 ° C., and in order to improve the strength at 250 ° C. or higher, it is necessary to crystallize the Al—Ni compound. Moreover, in order to crystallize an Al-Ni type compound, it is necessary to add more than Cu. However, if added in a large amount, the crystallized material becomes coarse, the toughness of the material is lowered, and cracks and defects during forging are generated. Therefore, Ni crystallizes the Al-Ni compound necessary for high-temperature strength, so the lower limit is 1%, and the upper limit is 5% to suppress crystallization of coarse compounds. Furthermore, Ni is added more than Cu.

(Fe: 2.0% or less)
Fe, like Ni, is an element that crystallizes a compound with Al and improves the high-temperature strength, and can be optionally added. However, in order to suppress the coarsening of the crystallized product, it should contain 2% at the maximum. Further, when Fe and Ni are added simultaneously, an Al—Ni—Fe-based compound is crystallized, so the total of these Ni and Fe is made 5% or less. Furthermore, the total of Ni and Fe is made larger than Cu.

(Mg: 2.0% or less)
Mg is an element that improves the strength of the dough by solid solution strengthening and can be arbitrarily added. However, when added in a large amount, Mg ₂ Si crystallizes to lower the toughness of the material, so that the maximum is 2.0. % Is included.

(Zr: 0.25% or less)
(Ti: 0.25% or less)
Zr and Ti are elements that contribute to refinement of crystal grains and improvement of heat resistance. However, if a large amount is added, either one or both will crystallize a coarse compound with Al. Accordingly, Zr and Ti contain a maximum of 0.25% in order to suppress the formation of coarse crystallized products. Further, the total of Zr and Ti is set to 0.3% or less.

(Mn: Fe and Mn total is 2.0% or less)
(Cr: Fe and Cr × 5 total is 2.0% or less)
Mn and Cr are elements that improve the high-temperature strength and refine the structure, but if added simultaneously with Fe, Al and Fe and coarse compounds are produced, and forgeability is reduced. Therefore, these Mn and Cr define the upper limit in total with Fe. That is, the total of Fe and Mn is 2.0% or less, and the total of Fe and Cr × 5 is 2.0% or less.

Next, the metal structure of the aluminum alloy will be described.
(Intermetallic compound)
An intermetallic compound of Al and a transition element such as Ni or Fe improves the material strength to a high temperature by suppressing the deformation of the material. However, since the effect of the intermetallic compound is reduced when it is too fine, the lower limit of the maximum length is set to 3 μm. On the other hand, if the intermetallic compound is excessively large, it causes cracks and defects during forging, so the upper limit of the maximum length is set to 100 μm so that it can withstand forging.

(Eutectic Si, Primary Si)
Eutectic Si and primary crystal Si are effective for improving the slidability, but if the particle size becomes excessively large, it causes cracks and defects during forging. Therefore, the grain size of these eutectic Si and primary crystal Si is 3 μm at the lower limit in order to obtain a sufficient effect, and 100 μm at the upper limit so that it can withstand forging.

Hereinafter, the effects of the present invention will be clarified by examples. In addition, this invention is not limited to a following example, In the range which does not change the summary, it can change suitably and can implement.
First, an aluminum alloy containing each additive element shown in Table 1 was forged into a piston shape, and forged pistons of Samples 1 to 12 were produced. And about the forge piston of each of these samples 1-12, mechanical characteristics and forgeability were evaluated. Among these, samples 1 to 5 are examples that satisfy the conditions of the present invention, and samples 6 to 10 are comparative examples that do not satisfy the conditions of the present invention. Sample 11 is JIS standard A4032, and sample 12 is JIS standard AC8A.

  Of the evaluation results shown in Table 1, for mechanical properties, test pieces were cut out from the forged pistons of Samples 1 to 12, held at 300 ° C. for 100 hours, and then pulled in an atmosphere at 300 ° C. A test was conducted and the tensile strength and elongation of each test piece were measured. Moreover, about the forgeability, each sample 1-12 was heated to 350 degreeC or more, and the presence or absence of the crack when forging to a piston shape was investigated. In Table 1, ◯ indicates a case where no crack occurred, and × indicates a case where a crack occurred.

  From the evaluation results shown in Table 1, it can be seen that Samples 1 to 6 (Examples) all show higher tensile strength than A4032, and higher elongation than AC8A. Samples 1 to 6 have no problem with forgeability, and the specific gravity does not increase so much as to affect the actual piston. In addition, Examples 2 and 3 show higher tensile strength and elongation than AC8A. On the other hand, although Examples 1, 4, and 5 have inferior tensile strength to AC8A, the fatigue strength important for actual pistons is higher than that of AC8A due to the fine structure and improvement of internal quality by forging.

  In contrast, Samples 6, 8, 9, and 10 (Comparative Examples) showed high values for mechanical strength, but cracks occurred during forging. Further, when the metal structures of these samples 6, 8, 9, and 10 were examined, in Comparative Example 6, an Al—Ni based coarse compound crystallized, and in Comparative Example 8, an Al—Ni—Fe based coarse compound was crystallized. Crystallization, it was found that in Comparative Example 9, an Al—Ni—Fe—Mn coarse compound was crystallized, and in Comparative Example 10, an Al—Ni—Fe—Cr coarse compound was crystallized. These coarse compounds are all over 100 μm.

  In addition, the above-mentioned Patent Document 2 shows an effect of refining a crystallized substance by Mn, and shows that the maximum length is shortened by changing the form of the crystallized substance from a needle shape to a lump shape. . However, this does not reduce the volume of each crystallized product itself, and its maximum length is also at the 100 μm level. Therefore, the refinement effect to the extent that the forgeability is improved as in the present invention is not recognized.

  Sample 7 (Comparative Example) has high strength, no coarse crystallized material, and good forgeability. However, the specific gravity is about 5% larger than the conventional A4032 or AC8A. This is contrary to the original purpose of making a lightweight piston. On the other hand, samples 1 to 6 (examples) all have a specific gravity of 2.75 or less, and by keeping the high temperature strength and excellent forgeability from being suppressed, the increase in specific gravity is further reduced. Is possible.

  Next, a fatigue strength test was performed on the forged pistons of Sample 4 (present invention), Sample 11 (A4032), and Sample 12 (AC8A). In this fatigue strength test, the fatigue curve was measured with a tension swing close to the stress generated in an actual piston in an atmosphere of 300 ° C. The measurement results are shown in FIG.

  From the measurement results shown in FIG. 2, Sample 4 showed a fatigue strength higher by 10% or more than AC8A, despite the above-mentioned tensile strength being lower than AC8A. In addition, the strength is 40% or more higher than that of A4042, and it can be seen that the strength is greatly improved.

  Next, a microstructure photograph of the forged piston of sample 4 (present invention) is shown in FIG. 3, and a microstructure photograph of sample 9 (comparative example) is shown in FIG. From the microstructure photographs shown in FIGS. 3 and 4, the forged piston of the comparative example has a maximum length of the intermetallic workpiece in the metal structure of 100 μm or more, whereas the forged piston of the present invention has a metal structure of It can be seen that the intermetallic workpiece in the inside is finely and uniformly dispersed and is controlled to a level that does not impair forgeability.

FIG. 1 is a perspective view showing an example of a forged piston. FIG. 2 is a graph showing measurement results obtained by measuring the fatigue strength of the forged piston of the present invention and the conventional forged piston. FIG. 3 is a photograph showing a metal structure in the forged piston of the present invention. FIG. 4 is a photograph showing a metal structure in a forged piston of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piston head 2 ... Skirt 3 ... Ring groove 4 ... Pin hole

Claims (6)

% By weight
Si: 8-18%,
Cu: 0.5-3%,
Ni: 1 to 5%
And the balance consists of Al and inevitable impurities,
Ni is contained more than Cu,
A forged piston made of an aluminum alloy having a maximum length of 3 to 100 μm of an intermetallic compound formed of Al and Ni. % By weight
Si: 8-18%,
Cu: 0.5-3%,
Ni: 1-5%
Fe: 2.0% or less, the balance consists of Al and inevitable impurities,
The total of Ni and Fe is greater than Cu and less than 5% by weight,
A forged piston made of an aluminum alloy in which the maximum length of an intermetallic compound formed of Al, Ni, and Fe is 3 to 100 μm. The aluminum alloy is further in wt%,
The forged piston according to claim 1 or 2, characterized by containing Mg: 2.0% or less. The aluminum alloy is further in wt%,
Zr: 0.25% or less,
Ti: contains at least one or more of 0.25% or less,
The forged piston according to any one of claims 1 to 3, wherein the total amount containing Zr and Ti is 0.3% or less by weight. The aluminum alloy is further in wt%,
Mn: Total of Fe and Mn is 2.0% or less,
The forged piston according to any one of claims 1 to 4, wherein the sum of Cr: Fe and Cr × 5 contains at least one of 2.0% or less.   The forged piston according to any one of claims 1 to 5, wherein the aluminum alloy has a particle size of eutectic Si and primary Si in the metal structure of 10 to 100 µm.

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