JP2014152375A - Piston material for internal combustion engine and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength and light weight piston material for an internal combustion engine, which has high thermal conductivity and whose strength reduction due to temperature influence is prevented, and to provide a method of manufacturing the piston material.SOLUTION: The piston material for an internal combustion engine is an Al-Si-based alloy material having an electric conductivity (%IACS) of 18 or more. It is preferable that an Al-Cu-Mg-based compound having a size of 1 μm or less is deposited uniformly and that the total area ratio of an Al-Fe-Mn-Ni-Cr-based crystallized product and an Al-Cu-Ni-based crystallized product at a cutting cross section is 10% or less. Also it is preferable that Cu is contained in the range of 1.2 mass% to 5 mass% and Cr is contained in an amount of 0.05 mass% or more. The piston material is manufactured by casting an Al-Si-based alloy containing Cu n the range of 1.2 mass% to 5 mass% and containing Cr in an amount of 0.05 mass% or more, and subjecting the cast Al-Si-based alloy to aging treatment.

Description

  The present invention relates to a piston material for an internal combustion engine having a high thermal conductivity and a method for manufacturing the same, and more particularly, a high-strength and lightweight piston material for an internal combustion engine having a high thermal conductivity and preventing a decrease in strength due to the influence of temperature. And a manufacturing method thereof.

  As environmental problems are greatly taken up, internal combustion engines such as automobile engines are required to have higher efficiency and lower exhaust gas, and higher engine output is also required. Under such circumstances, a piston used in an internal combustion engine such as an automobile engine is used in a severe environment of high temperature and high pressure in a cylinder in order to realize high efficiency with further improved combustion efficiency. Therefore, there is a demand for a high-strength piston material for an internal combustion engine that can be used even in such a high-temperature and high-pressure environment.

  In response to these requirements, various pistons have been proposed that have increased strength by adjusting material components and the like. For example, an aluminum alloy for an internal combustion engine piston described in Patent Document 1 includes a P content, a Ca content, and a P / Ca content contained in an Al—Si—Cu—Mg based alloy having components and compositions whose contents are specified. By adjusting the weight ratio, eutectic Si is grown greatly and primary crystal Si is refined. Thereby, high temperature strength, wear resistance, and the like are improved, and an aluminum alloy suitable as a piston material for an internal combustion engine is obtained.

  Similarly, the aluminum content for die casting described in Patent Document 2 includes a P content contained in an Al—Si—Cu—Mg—Fe—Mn (—Ni) alloy having a component and a composition whose content is specified, By adjusting the Ca content and P / Ca weight ratio, the eutectic Si and the primary Si are refined, and the Fe-Mn-Ni based crystallized product is also refined by regulating the cooling rate during solidification. Yes. As a result, the high temperature strength, wear resistance, vibration resistance and the like are improved, and an aluminum alloy suitable as an internal combustion engine part for die casting is obtained.

  In addition, the aluminum alloy for castings described in Patent Document 3 adjusts the content of the alloy components to narrow the temperature range of the solid-liquid coexistence region during solidification, so that the crystallized product is crystallized almost simultaneously. Thus, the crystallized product is uniformly and finely distributed without increasing the cooling rate (solidification rate), and the α-Al phase that is the matrix is finely divided into a metal structure. By doing so, an Al—Si aluminum alloy for casting excellent in high-temperature strength is obtained without being affected by the casting method.

JP-A-8-104937 JP-A-8-134777 JP 2004-256873 A

  The technology described in each of the above patent documents increases the strength of the aluminum alloy constituting the piston for the internal combustion engine by adjusting the material components. However, with the recent demand for higher engine efficiency, the temperature of the piston tends to increase. Due to the characteristics of the aluminum material, the aluminum alloy constituting the piston for an internal combustion engine has its strength lowered as a result of its temperature rise, and it has been difficult to improve the strength of the aluminum alloy.

  The present invention has been made to solve the above-mentioned problems, and its object is to provide a high-strength, lightweight piston material for an internal combustion engine that has high thermal conductivity and prevents a decrease in strength due to the effect of temperature, and its It is to provide a manufacturing method.

  (1) A piston material for an internal combustion engine according to the present invention for solving the above problems is an Al—Si based alloy material used for a piston for an internal combustion engine, and has a conductivity (% IACS) of 18 or more. It is characterized by.

  According to this invention, since the electrical conductivity (% IACS) of the Al—Si based alloy is 18 or more, the Al—Si based alloy having such electrical conductivity exhibits high thermal conductivity. As a result, a decrease in strength due to the influence of temperature can be suppressed, and a high-strength and lightweight piston for an internal combustion engine can be provided.

  In addition, the piston material for internal combustion engines which concerns on this invention is comprised so that Cu, Mg, Ni, Cr, Fe, and Mn may be contained. These elements are contained in an Al—Si alloy as a high-strength and lightweight piston material for an internal combustion engine.

  In the piston material for an internal combustion engine according to the present invention, it is preferable that an Al—Cu—Mg compound having a size of 1 μm or less is uniformly deposited.

  According to this invention, since the Al—Cu—Mg-based compound having a size of 1 μm or less is uniformly deposited, a high conductivity of 18% (IACS) or more and a high thermal conductivity are exhibited. As a result, an increase in the temperature of the piston can be suppressed, and a decrease in strength can be suppressed.

  In the piston material for an internal combustion engine according to the present invention, the total area ratio of the Al—Fe—Mn—Ni—Cr-based crystallized product and the Al—Cu—Ni-based crystallized product in the cut section is preferably 10% or less. .

  According to this invention, since the total area ratio of these both crystallized substances is 10% or less, it means that the production | generation of an Al-Cu-Ni type crystallized substance is suppressed. As a result, more Cu that is not trapped by the crystallized matter becomes a solid solution in a supersaturated state in the matrix of the Al—Si based alloy, and fine precipitates of Al (Al—Cu—) are obtained by subsequent aging treatment. Since the Mg-based compound) is uniformly deposited, it exhibits high conductivity and high thermal conductivity.

  In the piston material for an internal combustion engine according to the present invention, it is preferable that Cu is contained within a range of 1.2% by mass or more and 5% by mass or less, and Cr is contained by 0.05% by mass or more.

  According to the present invention, Cu is contained in the range of 1.2% by mass or more and 5% by mass or less and Cr is contained in an amount of 0.05% by mass or more. A system crystallized product is produced. And since Ni is trapped by the crystallized product due to the generation of the crystallized product, the generation of the Al-Cu-Ni-based crystallized product is suppressed. As a result, more Cu is supersaturated in the matrix of the Al—Si alloy, and fine precipitates (Al—Cu—Mg compounds) of Cu are uniformly deposited by subsequent aging treatment. , High conductivity and high thermal conductivity can be exhibited.

  (2) A method for manufacturing a piston material for an internal combustion engine according to the present invention for solving the above-mentioned problems contains Cu in a range of 1.2 mass% or more and 5 mass% or less, and Cr is 0.05 mass%. It has the process of casting the Al-Si type alloy which is the piston material for internal combustion engines contained above, and the process of aging-treating the cast Al-Si type alloy.

  According to the present invention, an Al—Si alloy, which is a piston material for an internal combustion engine, containing Cu in a range of 1.2 mass% to 5 mass% and Cr containing 0.05 mass% or more is cast. Therefore, an Al-Fe-Mn-Ni-Cr-based crystallized product is generated. And since the Ni contained in the Al-Si based alloy is captured by the crystallized product due to the generation of the crystallized product, the generation of the Al-Cu-Ni based crystallized product is suppressed, and as a result, more Cu dissolves in a supersaturated state in the matrix of the Al—Si alloy. By subjecting such a cast alloy to subsequent aging treatment, the supersaturated Cu is uniformly deposited as a fine Al—Cu—Mg compound having a size of 1 μm or less. The piston material for an internal combustion engine thus obtained exhibits a high conductivity of 18% (IACS) or higher and a high thermal conductivity, so that an increase in piston temperature can be suppressed and a decrease in strength can be suppressed.

  According to the piston material for an internal combustion engine according to the present invention, an Al—Si alloy having an Al—Si alloy conductivity (% IACS) of 18 or more has high thermal conductivity. In comparison, the temperature rise of the piston due to heat generated from the internal combustion engine can be suppressed. As a result, a high-strength and lightweight piston material for an internal combustion engine that can suppress a decrease in strength due to a temperature rise of the piston can be obtained.

It is the SEM image (A) and TEM image (B) which show the metal structure of the measurement sample of Example 2. It is the SEM image (A) and TEM image (B) which show the metal structure of the measurement sample of the comparative example 1.

  The piston material for an internal combustion engine and the manufacturing method thereof according to the present invention will be described in detail. In addition, the following embodiment is an example and the other form to which the technical scope of this invention belongs is also included by this invention.

[Piston material for internal combustion engines]
The piston material for internal combustion engines according to the present invention is an Al—Si based alloy material used for high-strength and lightweight pistons for internal combustion engines, and is characterized in that its electrical conductivity (% IACS) is 18 or more. An Al—Si-based alloy having a conductivity (% IACS) of 18 or higher exhibits high thermal conductivity, and therefore, it is possible to provide a high-strength and lightweight piston for an internal combustion engine that can suppress a decrease in strength due to the influence of temperature.

Here, IACS is an abbreviation for International Annealed Copper Standard, and is expressed as a comparative value of what percentage of electrical conductivity when standard annealed Cu wire is 100%. Is. The volume resistivity of the standard annealed Cu wire is defined as 1.7241 × 10 ⁻² μΩm (conductivity 100% IACS).

  The present inventor has found that, as a piston material for an internal combustion engine, a high strength and light weight Al-Si alloy casting having excellent thermal conductivity, the lower the electrical resistance, the better the thermal conductivity. Specifically, it has been found that the thermal conductivity is 120 (w / m · k) or more when the conductivity (% IACS) is 18 or more. Furthermore, in observing the metal structure using a transmission electron microscope, when an Al—Cu—Mg compound is precipitated in the Al matrix of the Al—Si alloy, the thermal conductivity is excellent (the conductivity is excellent). It was found that the thermal conductivity is poor (conductivity is low) when no Al—Cu—Mg compound is precipitated.

  Further, when attention is paid to the crystallized product of the Al—Si based alloy, in a high strength and light weight Al—Si based alloy casting containing Si, Cu, Mg, Ni, Cr, Fe and Mn, Al—Fe—Mn— Thermal conductivity is good when the amount of Ni-Cr-based crystallized material and the amount of Al-Cu-Ni-based crystallized material are small, that is, when the area ratio of these crystallized materials is small at any section. I found out that More specifically, when the total area ratio of the Al—Fe—Mn—Ni—Cr crystallized product and the Al—Cu—Ni based crystallized product is 10% or less, the thermal conductivity is 120 (w / m · k). ) I found out that. Such a result can be realized by controlling the contents of Cu and Cr contained in a high-strength and lightweight Al-Si alloy. Specifically, Cu is within a range of 1.2 mass% to 5 mass%. It was found that the thermal conductivity becomes 120 (w / m · k) or more when Cr is contained and 0.05% by mass or more.

  The piston material for an internal combustion engine according to the present invention is based on such knowledge and will be described in detail below.

(Al-Si alloy)
The Al—Si based alloy is a high-strength and lightweight Al—Si based alloy used as a piston material for internal combustion engines. Such an Al—Si alloy is not particularly limited, and various materials can be used. For example, an Al—Si alloy containing about 5 mass% of silicon in aluminum may be used. May be an Al—Si based alloy containing about 25% by mass, or may be an Al—Si based alloy containing about 11 to 13% by mass of silicon as shown in the examples described later. .

  Silicon, which is the main element of the Al—Si based alloy, can improve the flowability of the molten metal during casting and also acts to improve the wear resistance. The content of silicon is arbitrarily set as described above in consideration of the entire characteristics including hot water flowability and wear resistance.

  When an Al—Si alloy is used as a high-strength and lightweight piston material for an internal combustion engine, the Al—Si alloy is usually configured to contain Cu, Mg, Ni, Cr, Fe, and Mn. ing. By including these elements, a piston material for an internal combustion engine having high strength and light weight is obtained.

  Cu acts to improve the strength by forming Al-Cu-Mg-based precipitates. Mg acts to form an Al—Cu—Mg-based precipitate and improve the strength or improve the strength by solid solution strengthening. Ni acts to improve the heat resistance by forming an Al-Cu-Ni-based crystallized product. Cr acts to form an Al-Fe-Mn-Ni-Cr-based crystallized product. Fe acts to refine crystal grains. Mn also acts to refine crystal grains.

  Among these metal elements, in the present invention, Cu and Cr contained in the Al—Si based alloy exhibit a particularly important action. Details will be described in the explanation section of "Al-Cu-Mg compound precipitation mechanism". However, the piston material for an internal combustion engine according to the present invention has conventionally included Cu containing, as a main function, strength improvement in an Al matrix. This is characterized in that the precipitate is uniformly deposited as a precipitate (Al—Cu—Mg compound) to increase the electrical conductivity and thermal conductivity. Furthermore, conventionally, Cr, which mainly produces Al-Fe-Mn-Ni-Cr-based crystallized substances, is dissolved as Cu in a supersaturated state, and after being subjected to aging treatment, as precipitates (Al-Cu-Mg-based compounds) It is characterized by acting as a component for uniform precipitation. Cu and Cr exhibiting such actions improve the electrical conductivity and thermal conductivity of the piston material for internal combustion engines.

  The Al—Si-based alloy contains the above-described Cu, Mg, Ni, Cr, Fe, Mn and the like within a range in which at least the mechanism of the present invention can be realized. Furthermore, elements other than these may be included as necessary. For example, P: 0.003-0.1 mass%, Ti: 0.005-0.3 mass%, Zr: 0.02-0.3 mass%, V: 0.02-0.3 mass%, B: 0.001-0.1 mass% of at least 1 sort (s) or more may be contained. Moreover, these elements may be contained as inevitable impurities. In addition, as an unavoidable impurity, all of S, O, etc. may be contained by about 0.05 mass% or less content.

(Al-Cu-Mg compound)
An Al—Cu—Mg compound is precipitated in the Al—Si alloy. As a precipitation form, it is uniformly deposited in the matrix of the Al—Si based alloy, and the size (size) of the Al—Cu—Mg based compound is preferably 1 μm or less. Since the fine Al—Cu—Mg based compound of 1 μm or less is uniformly deposited in the matrix, the conductivity of the Al—Si based alloy can be as high as 18% (IACS) or more. This Al—Cu—Mg-based compound is a highly conductive Cu alloy, and as shown in FIG. 1B, fine particles of the Cu alloy are uniformly dispersed in the Al matrix. It shows conductivity. Since the improvement in conductivity exhibits high thermal conductivity, it is possible to provide a high-strength and lightweight piston material for an internal combustion engine according to the present invention that can suppress a decrease in strength due to the influence of temperature.

  When the Al—Cu—Mg compound is precipitated nonuniformly, the electrical conductivity cannot be remarkably improved to 18% (IACS) or more as shown in the conventional example of FIG. Thermal conductivity cannot be increased. As a result, the strength due to the influence of temperature tends to decrease. “Uniform” means that when a field of view of about 1 μm × 1 μm is arbitrarily selected with an electron microscope, precipitates can be visually observed and specified, and “nonuniform” In this case, when a field of view of about 1 μm × 1 μm is arbitrarily selected with an electron microscope, there are a field where a precipitate is observed and a field where a precipitate is not observed.

  When the size of the Al—Cu—Mg compound exceeds 1 μm, the Al—Cu—Mg compound tends to segregate in the Al matrix. As a result, it is difficult to say that the fine particles of the Al—Cu—Mg compound are uniformly dispersed in the Al matrix, and the conductivity may not be improved.

  The “size” is the size of the Al—Cu—Mg compound measured in an arbitrary cross section of the piston material for an internal combustion engine, and the Al—Cu—Mg compound is spherical. Is the diameter, and when it is oval, rectangular or needle-shaped, it is the size of its major axis. Moreover, the minimum of a magnitude | size (size) is not specifically limited, For example, about 0.01 micrometer may be sufficient.

(Area ratio of crystallized product)
Al-Si-based alloys show Al-Fe-Mn-Ni-Cr-based crystallized products and Al-Cu-Ni-based crystallized products, but their total area ratio is 10% or less. It is preferable. The Al—Si based alloy having such an area ratio means that the generation of Al—Fe—Mn—Ni—Cr based crystallized product and Al—Cu—Ni based crystallized product is suppressed. Therefore, since the amount of Cu trapped by the crystallized product is reduced, more Cu is dissolved in the supersaturated state in the matrix of the Al-Si alloy, and is subsequently dissolved in the supersaturated state by the aging treatment. Cu in the matrix is uniformly deposited as fine precipitates (Al—Cu—Mg compound). As a result, high conductivity based on the uniform dispersion precipitation of the precipitate (Al—Cu—Mg compound) and high thermal conductivity are exhibited.

  Al-Fe-Mn-Ni-Cr-based crystallized substances are formed so that the liquid phase during solidification is in a thermodynamically stable state (so that the energy is in the lowest state), Al, Fe, Mn. , Ni and Cr combine to form (crystallize). The production amount of the Al—Fe—Mn—Ni—Cr-based crystallized product can be controlled by increasing or decreasing the Cr content. By such control, the area ratio of the Al-Fe-Mn-Ni-Cr-based crystallized product can be set within a range of 4% or more and 7% or less.

  On the other hand, the Al-Cu-Ni-based crystallized substance combines Al, Cu and Ni so that the liquid phase during solidification becomes thermodynamically stable (so that the energy is at its lowest). To produce (crystallize). The production amount of the Al—Cu—Ni-based crystallized product can be controlled by increasing or decreasing the Cr content, as described above. In other words, Cr acts to increase or decrease the above-described Al—Fe—Mn—Ni—Cr-based crystallized matter. Therefore, when Cr is increased, the amount of Al—Fe—Mn—Ni—Cr-based crystallized product generated is increased. In addition, more Ni is trapped, and generation of Al—Cu—Ni-based crystallized products is suppressed. By such control, the area ratio of the Al—Cu—Ni-based crystallized product can be set in the range of 2% or more and 4% or less.

  The “area ratio” means that an Al—Si-based alloy is cut and an arbitrary cross section is observed, and when the area surrounded by a specific dimension is 100%, Al—Fe—Mn— appearing in the area It is a total value (%) of the area of the Ni-Cr-based crystallized product and the area of the Al-Cu-Ni-based crystallized product. The area can be measured and evaluated by SEM observation and EDX analysis. In particular, in the EDX analysis, the contrast based on the difference in composition between the Al-Fe-Mn-Ni-Cr-based crystallized product and the Al-Cu-Ni-based crystallized product is remarkably different. The area of the crystallized product can be specified.

(Precipitation of Al-Cu-Mg compound)
The precipitation of the Al—Cu—Mg compound described above can be controlled by Cu and Cr contained in the Al—Si alloy. In the present invention, among the metal elements contained in the Al—Si based alloy, Cu and Cr affect the precipitation of the Al—Cu—Mg compound. The Cu content is preferably in the range of 1.2 mass% or more and 5 mass% or less, and the Cr content is preferably 0.05 mass% or more. By controlling Cu and Cr so as to be within these ranges, an Al—Si alloy having a conductivity (% IACS) of 18 or more can be obtained.

  When the content of Cu is within the above range, the Al—Si based alloy acts to improve the strength by forming Al—Cu—Mg based precipitates. There is a feature in the precipitation form of the system compound, and the Al—Cu—Mg system compound is uniformly deposited in the Al matrix (see FIG. 1B of Example 2). On the other hand, even when the Cu content is the same, when the Al—Cu—Mg compound is not uniformly deposited in the Al matrix (see FIG. 2B of Comparative Example 1), in terms of strength improvement. Although it is the same as the case where it uniformly precipitated, the effect of the present invention (notable improvement in conductivity and thermal conductivity) is not achieved. Such a difference in crystal state (crystal structure) is due to the action of Cr described above.

  In addition, if Cu content is less than 1.2 mass%, it will not fully contribute to the strength improvement of an Al-Si type alloy, and if Cu content exceeds 5 mass%, specific gravity will become large and will become heavy, and casting In view of deterioration of the properties, it is preferably within the range of 1.2% by mass or more and 5% by mass or less.

  In the present invention, the Cr content is set to 0.05% by mass or more within the range of the Cu content described above. By doing so, an Al-Fe-Mn-Ni-Cr-based crystallized product is generated by the action of Cr described above. And since Ni is trapped by the crystallized product due to the generation of the crystallized product, the generation of the Al-Cu-Ni-based crystallized product is suppressed. Therefore, most of Cu that should have been contained in the Al-Cu-Ni-based crystallized substance is dissolved in a supersaturated state in the matrix of the Al-Si-based alloy. As a result, fine precipitates (Al—Cu—Mg-based compounds) of Cu are uniformly deposited by the subsequent aging treatment, exhibiting high conductivity and high thermal conductivity.

  Even when the Cu content does not change, the thermal conductivity can be changed by changing the crystal state (crystal structure). In other words, the thermal conductivity does not change just by dissolving Cu in the Al matrix, but even if the Cu content is the same, Cu dissolved in the Al matrix can be easily precipitated by aging treatment. Improves the thermal conductivity. This is because the thermal conductivity was improved by the precipitated Cu compound being dispersed as fine particles. Cr contained in an amount of 0.05% by mass or more acts so that Cu dissolved in an Al matrix can be easily precipitated as a fine-particle Al—Cu—Mg compound by aging treatment. As a result, the thermal conductivity can be enhanced by the uniform dispersion of the Al—Cu—Mg compound.

  The degree of solid solution of Cu can be controlled by the content of Cr. By making the Cr content 0.05% by mass or more, an Al-Fe-Mn-Ni-Cr-based crystallized product is formed, and the generated Al-Fe-Mn-Ni-Cr-based crystallized product is Ni. Will be caught. Therefore, the formation of Al-Cu-Ni-based crystallized substances is suppressed, Cu that should have been captured by the Al-Cu-Ni-based crystallized substances overflows, and Cu is supersaturated in the Al matrix. Can be made.

  When the content of Cr is less than 0.05% by mass, the Al—Fe—Mn—Ni—Cr-based crystallized product cannot be sufficiently generated, and the generated Al—Fe—Mn—Ni—Cr-based crystallized product has Ni. Is not caught. Therefore, generation of Al—Cu—Ni-based crystallized substances cannot be suppressed, Cu is trapped in the Al—Cu—Ni-based crystallized substances, and Cu is supersaturated in the Al matrix. I can't. As a result, the Al—Cu—Mg compound cannot be sufficiently precipitated by the subsequent aging treatment.

  The Cu content is in the range of 1.2 mass% or more and 5 mass% or less, but when the Cu content is small within the range (for example, about 1.2 mass% to 2.5 mass%), It is preferable that the Cr content within the above range tends to be small. For example, when the Cr content is about 0.05% by mass to 0.15% by mass, the generation of Al-Fe-Mn-Ni-Cr-based crystallized products is not so much, and is captured by the crystallized products. There is not much Ni that ends up. For this reason, the effect of suppressing the formation of Al-Cu-Ni-based crystals is also small. Therefore, the amount of Cu that should have been trapped by the Al—Cu—Ni-based crystallized material is reduced, but since the Cu content itself is small as described above, a certain amount of Cu overflows. As a result, the overflowing Cu dissolves into the Al matrix in a supersaturated state, and the Al—Cu—Mg compound can be uniformly precipitated in the Al matrix after the aging treatment.

  On the other hand, when the Cu content is large within the above range (for example, about 2.5% by mass to 5% by mass), the effect can be maintained even if the Cr content within the above range increases. For example, when the Cr content is 0.15% by mass to 0.25% by mass or more, Al-Fe-Mn-Ni-Cr-based crystallized products are often produced and trapped in the crystallized products. There is also a lot of Ni that gets lost. For this reason, the effect of suppressing the formation of Al-Cu-Ni-based crystals is increased. Therefore, the amount of Cu that should have been captured by the Al—Cu—Ni-based crystallized substance increases, but since the Cu content itself is large as described above, a certain amount of Cu overflows. As a result, the overflowing Cu dissolves into the Al matrix in a supersaturated state, and the Al—Cu—Mg compound can be uniformly precipitated in the Al matrix after the aging treatment.

  In addition, although the upper limit of Cr content is not specifically limited, Since Cr itself worsens thermal conductivity, the upper limit can be 1 mass% or less normally, Preferably it can be 0.5 mass% or less.

  By the mechanism described above, the piston material for an internal combustion engine according to the present invention is a high-strength and lightweight piston material for an internal combustion engine that has high thermal conductivity and prevents a decrease in strength due to the influence of temperature. Therefore, Cu, Mg, Ni, which are elements involved in the formation of Al-Fe-Mn-Ni-Cr-based crystals and Al-Cu-Ni-based crystals, and elements involved in precipitation of Al-Cu-Mg compounds. If it is an Al-Si alloy containing Cr, Fe and Mn, the effect of the piston material for an internal combustion engine according to the present invention can be obtained by the same mechanism as described above. Therefore, for example, any Al—Si alloy having a Si content in the range of 5 mass% to 25 mass% can be said to be included in the piston material for an internal combustion engine according to the present invention.

  As described above, according to the piston material for an internal combustion engine according to the present invention, an Al—Si alloy having a conductivity (% IACS) of 18 or more has a high thermal conductivity. In comparison, the temperature rise of the piston due to heat generated from the internal combustion engine can be suppressed. As a result, a decrease in strength due to a temperature rise of the piston can be suppressed.

  The present invention is characterized in that by specifying the Cu content and the Cr content, the electrical conductivity and thermal conductivity can be adjusted without greatly changing the material strength of the Al—Si based alloy. And the adjustment of the conductivity and thermal conductivity is performed by adjusting the contents of Cu and Cr, and by specifying the structure of the Al-Si alloy, the piston used in the environment of the internal combustion engine where high heat is applied. The strength is substantially increased.

[Method of manufacturing piston material for internal combustion engine]
The method for producing a piston material for an internal combustion engine according to the present invention is a piston material for an internal combustion engine containing Cu in a range of 1.2 mass% to 5 mass% and containing Cr in an amount of 0.05 mass% or more. It is characterized by having a step of casting an Al—Si based alloy and a step of aging treatment of the cast Al—Si based alloy.

  The casting step is a step of casting an Al—Si alloy which is a piston material for an internal combustion engine containing Cu in a range of 1.2 mass% to 5 mass% and Cr containing 0.05 mass% or more. is there. Various forging means known in the art can be applied to the forging. For example, an Al—Si based alloy in a molten state within a range of 700 ° C. to 800 ° C. is cast into a predetermined mold.

  The aging treatment step is a step of aging treatment of the cast Al—Si alloy. The aging treatment can be performed, for example, by performing heat treatment at 170 ° C. to 250 ° C. for 240 minutes to 600 minutes in an atmospheric environment. By this aging treatment, the Al—Cu—Mg compound described above can be uniformly deposited.

  As mentioned above, according to the manufacturing method of the piston material for internal combustion engines which concerns on this invention, it contains Cu in the range of 1.2 mass% or more and 5 mass% or less, and for internal combustion engines containing Cr 0.05 mass% or more. Since an Al—Si based alloy that is a piston material is cast, an Al—Fe—Mn—Ni—Cr based crystallization product is generated. And since the Ni contained in the Al-Si based alloy is captured by the crystallized product due to the generation of the crystallized product, the generation of the Al-Cu-Ni based crystallized product is suppressed, and as a result, more Cu dissolves in a supersaturated state in the matrix of the Al—Si alloy. By subsequent aging treatment of such a cast alloy, Cu dissolved in supersaturation is uniformly deposited as a fine Al—Cu—Mg compound having a size of 1 μm or less. The piston material for an internal combustion engine obtained in this way exhibits a high conductivity of 18% (IACS) or higher and a high thermal conductivity, so that an increase in piston temperature can be suppressed and a decrease in strength can be suppressed.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

[Experiment 1]
First, an Al—Si based alloy having the components shown in Table 1 was prepared, and the Al—Si based alloy was melted at 750 ° C. ± 10 ° C. and heated to 250 ° C. 22 mm long × 190 mm wide × 45 mm high boat An Al-Si alloy casting sample was produced by casting into a shaped mold by ordinary gravity casting. In addition, the cooling rate was performed within the range of 0.5-5 degree-C / sec. The produced casting samples were subjected to an aging treatment at 220 ° C. for 4 hours to produce measurement samples of Examples 1 to 5 and Comparative Examples 1 and 2 as test materials.

[Measurement]
About the measurement sample, tensile strength, electrical conductivity (% IACS), and thermal conductivity were measured. The metal structure was observed by cutting, embedding and polishing the measurement sample, and then preparing a measurement sample with an osmium coating and observing precipitates and crystallized substances.

  Tensile strength was measured by preparing a measurement sample having a total length of 80 mm, a parallel part length of 25 mm, and a parallel part diameter of 6 mm, and measuring and evaluating with a tensile tester (manufactured by Shimadzu Corporation).

The electrical conductivity was measured by a direct current four-terminal method in vacuum (1 × 10 ⁻⁵ torr) using an electrical resistance measuring device (manufactured by ULVAC-RIKO, Inc., model name: TER2000RH / L type). Of the results of the five measurement points, the results of three points excluding the maximum value and the minimum value were averaged.

  The thermal conductivity was measured and evaluated with a thermal conductivity meter (manufactured by NETZSCH, model name: DSC404C).

  The size of the Al—Cu—Mg compound was obtained by preparing a measurement sample by the electrolytic thin film method (twin jet method) using TEM (field emission transmission electron microscope, manufactured by Hitachi, Ltd., model name: HF-2000). It was measured from the obtained TEM image. Examples of this TEM image are shown in FIG. 1 (B) and FIG. 2 (B).

  The area ratio of the crystallized product was obtained by taking a SEM image with an SEM (manufactured by JEOL Ltd., field emission scanning electron microscope, model name: JSM-7001F, acceleration voltage: 10 kV, photographing method: reflected electron image), SEM images were taken with an EDX analyzer (Kevex, model name: Sigma (attached to HF-2000), acceleration voltage: 200 kV, observation direction: <100> direction). The obtained SEM image was subjected to image analysis to measure the area ratio of the crystallized product. For image analysis, an area ratio of white crystallized substances and gray crystallized substances in the low-magnification SEM photograph was calculated using an image analysis apparatus (Nanosystem Corporation, model name: NanoHunter NS2K-Pro). For the calculation, first, the area ratio of the white crystallized product and the white crystallized product were measured, then the area ratio of the white crystallized product was measured, and then the area ratio of the gray crystallized product was determined as the white crystallized product and The area ratio of white crystals was subtracted from the area ratio of gray crystals, and the total area ratio of Al-Fe-Mn-Ni-Cr crystals and Al-Cu-Ni crystals was determined.

[result]
The results obtained from the measurement samples of Examples 1 to 5 shown in Table 1 and the measurement samples of Comparative Examples 1 and 2 are shown in Table 2. 1 shows an SEM image (A) and a TEM image (B) showing the metal structure of the measurement sample of Example 2, and FIG. 2 shows an SEM image showing the metal structure of the measurement sample of Comparative Example 1. (A) and a TEM image (B) are shown.

  From the TEM observation result shown in FIG. 1B, fine precipitates were uniformly distributed in the measurement sample of Example 2 containing 0.1% by mass of Cr. As a result of analysis by EDX analysis, this fine precipitate was an Al—Cu—Mg compound. The measurement sample had a conductivity of 19% IACS. From the image analysis of the SEM photograph shown in FIG. 1A, the total area ratio of the crystallized substances is 8.5%, and the area ratio of the white Al—Cu—Ni-based crystallized substances is 3.5%. The area ratio of the gray Al—Fe—Mn—Ni—Cr crystallized product was 5%.

  From the TEM observation result shown in FIG. 2B, fine precipitates were not uniformly distributed in the measurement sample of Comparative Example 1 containing 0.01% by mass of Cr. In addition, as a result of analyzing by EDX analysis, the heterogeneous fine deposit was an Al-Cu-Mg type compound. The measurement sample had a conductivity of 16% IACS. Further, from the image analysis of the SEM photograph shown in FIG. 2A, the total area ratio of the crystallized substances is 14%, and the area ratio of the white Al—Cu—Ni-based crystallized substances is 5.3%. The area ratio of the gray Al-Fe-Mn-Ni-Cr crystallized product was 8.7%.

  As described above, from the results shown in Table 2 and FIGS. 1 and 2, in Examples 1 to 5, the conductivity was high and the thermal conductivity was also high. Further, the electrical conductivity is 10% when the total area ratio of Al-Cu-Mn-Ni-Cr-based crystallized substance and Al-Fe-Mn-Ni-Cr-based crystallized substance is 1% or less. By being below, high electrical conductivity of 18% IACS or higher and high thermal conductivity of relative value 113 or higher were exhibited.

  From this experimental result, by including a predetermined amount of Cr, the Al-Fe-Mn-Ni-Cr-based crystallized product is stabilized, and as a result, Ni is an Al-Fe-Mn-Ni-Cr-based crystallized product. Therefore, Al-Cu-Ni-based crystallized substances are reduced. As a result, more Cu is supersaturated in the Al matrix, and as a result, the Cu compound (Al—Cu—Mg-based compound) precipitates as a fine precipitate during the aging treatment, and the thermal conductivity and conductivity are improved. It can be said that it became high.

Such a phenomenon can be similarly applied to an Al—Si alloy-based piston material for an internal combustion engine. As exemplified in this example, at least Si: 11-13 mass%, Cu: 1.2-5 mass%, Mg: 0.5-1.3 mass%, Ni: 0.8-3 mass% , Cr: 0.05% by mass or more, Fe: 1.0% by mass or less, Mn: 1.0% by mass or less, the same is true for the Al—Si based alloy in which the balance is Al, and the same result was confirmed. . Further, if the material for the piston for an internal combustion engine can control the precipitation of the Al—Cu—Mg compound by Cu and Cr contained in the Al—Si based alloy, the technical idea of the present invention is applied by the same mechanism. In the above example, evaluation is made with a specific Al-Si alloy, but the elements involved in the formation of Al-Fe-Mn-Ni-Cr-based crystallization products and Al-Cu-Ni-based crystallization products and If it is an Al-Si alloy containing Cu, Mg, Ni, Cr, Fe and Mn, which are elements involved in the precipitation of the Al-Cu-Mg compound, the piston for the internal combustion engine according to the present invention will be used by the same mechanism as described above. The effect of the material can be exhibited. Therefore, for example, any Al—Si alloy having a Si content in the range of 5 mass% to 25 mass% can be said to be included in the piston material for an internal combustion engine according to the present invention.

Claims (6)

  A piston material for an internal combustion engine, which is an Al-Si alloy material used for a piston for an internal combustion engine and has a conductivity (% IACS) of 18 or more.   The piston material for an internal combustion engine according to claim 1, comprising Cu, Mg, Ni, Cr, Fe and Mn.   The piston material for an internal combustion engine according to claim 1 or 2, wherein an Al-Cu-Mg compound having a size of 1 µm or less is uniformly deposited.   The total area ratio of the Al-Fe-Mn-Ni-Cr-based crystallized product and the Al-Cu-Ni-based crystallized product in the cut section is 10% or less, according to any one of claims 1 to 3. Piston material for internal combustion engines.   The piston material for an internal combustion engine according to any one of claims 1 to 4, wherein Cu is contained in a range of 1.2 mass% or more and 5 mass% or less, and Cr is contained in an amount of 0.05 mass% or more. A step of casting an Al—Si based alloy which is a piston material for an internal combustion engine containing Cu in a range of 1.2 mass% or more and 5 mass% or less and Cr containing 0.05 mass% or more;
And a step of aging the cast Al-Si alloy. A method for producing a piston material for an internal combustion engine.