JP6875795B2 - Internal combustion engine piston and its manufacturing method - Google Patents

Description

The present invention relates to a piston for an internal combustion engine having excellent wear resistance and heat resistance and a method for manufacturing the same.

Pistons for internal combustion engines are manufactured by a casting method or a forging method. In the casting method, a molten aluminum alloy is poured into a mold to form a piston shape, and after heat treatment such as aging treatment, machining is performed to manufacture a piston for an internal combustion engine. On the other hand, in the forging method, first, the melted aluminum alloy is continuously cast into a billet for extrusion, and after being heat-treated such as homogenization, it is extruded into a small-diameter round bar, or it is made into a round bar by the continuous casting method. After undergoing heat treatment such as homogenization, it is cut into a small diameter round bar. After that, a small-diameter round bar is cut into a forging material, and the forging material is hot-forged into a piston shape, which is then machined through heat treatment such as aging treatment to manufacture a piston for an internal combustion engine.

Regarding the piston for an internal combustion engine by the forging method, Patent Document 1 proposes a technique for providing an aluminum alloy piston that exhibits excellent fatigue strength even in a high temperature range of 200 to 250 ° C. In this technique, after forging, Si: 11 to 13%, Fe: 0.2 to 1.2%, Cu: 3.5 to 4.5%, Mn: 0.2 to 0.5%, Mg: 0. Contains 3 to 1.0%, Ti: 0.01 to 0.2%, B: 0.0002 to 0.02%, P: 0.005 to 0.02%, and Ca to 0.005% or less. It has a forged structure in which Si and intermetallic compounds crystallized during casting are uniformly dispersed in the matrix with an average particle size of 5 to 35 μm after forging, and the gas content is regulated to 0.25 cc / 100 g-Al or less. This is for an aluminum alloy piston formed by forging, in which the ^{average number of inclusions is regulated to 0.01 pieces / cm 2} or less in the K10 value at the ingot stage.

Patent Document 2 provides a forged piston for an internal combustion engine, which has excellent high-temperature strength characteristics of a head surface and a piston pin portion, excellent forging formability of a skirt portion, and stable machinability and wear resistance of an oil ring groove portion. The target technology has been proposed. This technique is a forged piston for an internal combustion engine made of an aluminum alloy containing 6 to 25% by mass of silicon, and has an average grain size of eutectic silicon (A) in the oil ring groove and an average grain size of eutectic silicon at the tip of the skirt. The ratio (A / B) to the diameter (B) is 1.5 or more, and the average particle size of eutectic silicon (A) in the oil ring groove is 4 μm or more, or the primary crystal in the oil ring groove. The ratio (C / D) of the silicon average particle size (C) to the primary silicon silicon average particle size (D) at the tip of the skirt is 1.3 or more, and the primary silicon average particle size of the oil ring groove is 1. (C) is for a forged piston for an internal combustion engine having a diameter of 15 μm or more.

Japanese Unexamined Patent Publication No. 2000-265232 Japanese Unexamined Patent Publication No. 2003-035198

In an internal combustion engine engine of an automobile or the like, further weight reduction of the piston for the internal combustion engine and improvement of wear resistance and heat resistance are required.

An object of the present invention is to provide a piston for an internal combustion engine having excellent wear resistance and heat resistance and a method for manufacturing the piston.

(1) The piston for an internal combustion engine according to the present invention has Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, and Ni. It is made of an aluminum alloy containing at least 0.3 to 0.8% by mass and Mg: 1.5 to 2.0% by mass, and particulate precipitates are present at the grain boundary and inside the grains in the cross section. The particulate precipitate present at the grain boundary is characterized by having Fe, Cu, and Ni.

According to the present invention, particulate precipitates are present at the grain boundaries and inside the grains in the cross section, and the particulate precipitates present at the grain boundaries have Fe, Cu, and Ni. It is considered that the particulate precipitate acts to improve the wear resistance and the heat resistance. It is also considered that the particulate precipitates existing inside the grains also contribute to the improvement of wear resistance and heat resistance.

In the piston for an internal combustion engine according to the present invention, the particle size of the particulate precipitate at the grain boundary is in the range of 3 μm or more and 30 μm or less, and the area ratio of 12% or more and 22% or less per unit area in each part of the cross section. It exists within the range of. According to the present invention, since the particulate precipitates having the above particle size are present at the grain boundary in each part of the cross section at the above ratio, it is considered that they contribute to the improvement of wear resistance and heat resistance.

In the piston for an internal combustion engine according to the present invention, the particle size (D1) of the particulate precipitate at the grain boundary is larger than the particle size (D2) of the particulate precipitate inside the grain, and the ratio (D1 / D2) thereof. ) Is 5 or more. According to the present invention, it is considered that the large particulate precipitate present at the grain boundary contributes to the wear resistance and the heat resistance.

In the piston for an internal combustion engine according to the present invention, the ratio (P1) of the particulate precipitates at the grain boundary portion among the particulate precipitates existing in the cross section is the ratio of the particulate precipitates inside the grains (P2). The ratio (P1 / P2) is in the range of 6 or more and 11 or less. According to the present invention, since the particulate precipitates present at the grain boundary are present in each part of the cross section in the above range, it is considered that the particulate precipitates contribute to wear resistance and heat resistance.

(2) The method for manufacturing a piston for an internal combustion engine according to the present invention is as follows: Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass. A step of preparing an aluminum alloy continuous casting material containing at least%, Ni: 0.3 to 0.8% by mass, and Mg: 1.5 to 2.0% by mass, and a hot forging of the aluminum alloy continuous casting material. It has at least a step of heat-treating after hot forging and a step of machining after heat-treating, and particulate precipitates are present in the grain boundary portion and the inside of the grain of the cross section of the manufactured internal combustion engine piston. The particulate precipitate present at the grain boundary portion is characterized by having Fe, Cu, and Ni.

According to the present invention, the piston for an internal combustion engine manufactured by sequentially performing the hot forging, heat treatment, and machining steps of the prepared aluminum alloy continuous casting material having the above composition is formed in the grain boundary portion and the inside of the grain in the cross section. Since the particulate precipitate exists and the particulate precipitate existing at the grain boundary portion has Fe, Cu, and Ni, the particulate precipitate may improve the abrasion resistance and the heat resistance strength. It is considered to be working. It is also considered that the particulate precipitates existing inside the grains also contribute to the improvement of wear resistance and heat resistance.

According to the present invention, it is possible to provide a piston for an internal combustion engine having improved wear resistance and heat resistance and a method for manufacturing the piston.

It is a schematic form diagram which shows an example of the piston for an internal combustion engine which concerns on this invention. It is sectional drawing of the top of the piston for an internal combustion engine of Example 1. FIG. It is a structure photograph of each part of the cross section of the piston top shown in FIG. It is element mapping of the cross section of the piston for an internal combustion engine of Example 1. It is an analysis result of the particle size and the area ratio of the particulate precipitate appearing in the cross section of the piston for an internal combustion engine of Example 1. It is a cross-sectional photograph of the top of the piston for an internal combustion engine of Comparative Examples 1 and 2. It is a structure photograph of each part of the cross section of the piston top of Comparative Example 1. It is a structure photograph of each part of the cross section of the piston top of Comparative Example 2. It is an element mapping of the cross section of the piston for an internal combustion engine of Comparative Example 1. It is an elemental mapping of the cross section of the piston for an internal combustion engine of Comparative Example 2. It is an analysis result of the particle size and the area ratio of the particulate precipitate appearing in the cross section of the piston for an internal combustion engine of Comparative Examples 1 and 2. It is a graph which shows the evaluation result of the wear resistance of the piston for an internal combustion engine obtained in Example 1, Comparative Example 1 and Comparative Example 2. It is a graph which shows the evaluation result of the tensile strength of the piston for an internal combustion engine obtained in Example 1, Comparative Example 1 and Comparative Example 2. It is a graph which shows the evaluation result of the 0.2% proof stress of the piston for an internal combustion engine obtained in Example 1, Comparative Example 1 and Comparative Example 2. It is a graph which shows the evaluation result of the fatigue strength of the piston for an internal combustion engine obtained in Example 1, Comparative Example 1 and Comparative Example 2.

A piston for an internal combustion engine and a method for manufacturing the piston according to the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments as long as it is within the scope of the gist thereof.

[Piston for internal combustion engine]
As shown in FIG. 1, the piston 1 for an internal combustion engine according to the present invention is composed of an upper top portion 11 and a lower skirt portion 12. A plurality of piston ring grooves are provided on the outer circumference of the top portion 11. Examples of the piston ring groove include a first compression ring groove 11a, a second compression ring groove 11b, an oil ring groove 11c, and the like from the side of the top portion 11 toward the side of the skirt portion 12. A piston ring corresponding to each is mounted on each of the grooves. Reference numeral 11d is the surface of the top portion 11, and reference numeral 2 is a pin hole. The structure and dimensions of the top 11 are not limited to the example of FIG. 1, and may be other structural forms and dimensions, and the shape and size of the entire piston are not limited to the example of FIG. It may be in shape or size.

The piston 1 for an internal combustion engine has Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni: 0.3 to 0.3 to It is composed of an aluminum alloy containing at least 0.8% by mass and Mg: 1.5 to 2.0% by mass. Then, particulate precipitates are present at the grain boundaries and inside the grains in the cross section, and the particulate precipitates existing at the grain boundaries have Fe, Cu, and Ni. With such a configuration, it is possible to provide a piston for an internal combustion engine having improved wear resistance and heat resistance.

Hereinafter, the components of the piston for an internal combustion engine will be described in detail. The piston for an internal combustion engine is simply called a "piston".

(Ingredient composition)
The composition of the piston is Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni: 0.3 to 0. It contains at least 8% by mass and Mg: 1.5 to 2.0% by mass, and the rest is composed of an aluminum alloy. The components other than the above are trace components (including unavoidable impurities) usually contained in the aluminum alloy material for pistons. Examples of the trace component include Ti, Mn, Cr, Zn and the like.

Si is contained in the range of 0.4% by mass or more and 0.7% by mass or less, and acts to improve the mechanical strength (heat resistance and wear resistance). If the Si content is less than 0.4% by mass, the heat resistance and wear resistance may not be sufficiently improved, and if the Si content exceeds 0.7% by mass, the heat resistance and wear resistance are high. It may not improve sufficiently.

Fe is contained in the range of 1.4% by mass or more and 2.0% by mass or less, and forms a particulate precipitate together with Cu and Ni, and the particulate precipitate forms abrasion resistance and heat resistance of the piston. Contributes to the improvement of strength. If the Fe content is less than 1.4% by mass, the heat resistance and abrasion resistance may not be sufficiently improved, and if the Fe content exceeds 2.0% by mass, the heat resistance is not sufficiently improved. Sometimes.

Cu is contained in the range of 3.5% by mass or more and 5.5% by mass or less, and constitutes a particulate precipitate together with Fe and Ni, and the particulate precipitate forms abrasion resistance and heat resistance of the piston. Contributes to the improvement of strength. If the Cu content is less than 3.5% by mass, the heat resistance and abrasion resistance may not be sufficiently improved, and if the Cu content exceeds 5.5% by mass, the heat resistance is not sufficiently improved. There is.

Ni is contained in the range of 0.3% by mass or more and 0.8% by mass or less. Ni contained in this range acts to increase high-temperature strength due to its heat resistance, and forms particulate precipitates together with Fe and Cu, and the particulate precipitates improve the abrasion resistance and heat resistance of the piston. Contribute to. If the Ni content is less than 0.3% by mass, the heat resistance and wear resistance may not be sufficiently improved, and if the Ni content exceeds 0.8% by mass, the heat resistance is not sufficiently improved. There is.

Mg is contained in the range of 1.5% by mass or more and 2.0% by mass or less, and acts to increase the mechanical strength (heat resistance and wear resistance). If the Mg content is less than 1.5% by mass, the heat resistance and wear resistance may not be sufficiently improved, and if the Mg content exceeds 2.0% by mass, the heat resistance and wear resistance are sufficient. May not improve.

As other components, for example, Ti is contained in the range of 0.05% by mass or more and 0.10% by mass or less. Ti contained in this range acts to make the cast crystal grains finer. Further, Mn, Cr, Zn and the like may be contained as unavoidable impurities in an amount of about 0.05% by mass or less. Further, P, S and the like may also be contained as unavoidable impurities.

(Cross-sectional shape)
2 and 3 are cross-sectional photographs of the piston according to the present invention (Example 1 described later) after etching. FIG. 2 is a cross section of the top of the piston before machining the pin hole 2, and FIG. 3 is an enlarged photograph thereof. FIG. 3 (A) is the upper tissue, FIG. 3 (B) is the central tissue, and FIG. 3 (C) is the lower tissue. These photographs are a cross-sectional photograph of the piston shown in FIGS. 6 (A) and 7 (comparative example 1 described later) and a cross-sectional photograph of the piston shown in FIGS. 6 (B) and 8 (comparative example 2 described later). Shows a distinctly different tissue morphology.

As shown in FIGS. 2 and 3, the cross-sectional structure of the piston according to the present invention has grain boundaries, and the grain boundaries and the inside of the grains appear. Particulate precipitates are present at both the grain boundary and the inside of the grain. The particulate precipitate has a large particle size at the grain boundary, but has a smaller particle size inside the grain than that at the grain boundary.

A large number of large particulate precipitates present at the grain boundaries have Fe, Cu, and Ni according to the element mapping shown in FIG. It is not clear at this time whether Fe, Cu and Ni are intermetallic compounds, composites or mixtures, but from the results of Examples and Comparative Examples described later, Fe, Cu and Ni were provided. It is considered that the particulate precipitate acts to improve the wear resistance and the heat resistance.

The particulate precipitate at the grain boundary exists in the range of the particle size of 3 μm or more and 30 μm or less. The abundance ratio is within the range of 12% or more and 22% or less in terms of the area ratio per unit area in each part of the cross section. In the present invention, since the particulate precipitate having the above particle size is present at the grain boundary in the above ratio, it is considered that it contributes to the improvement of wear resistance and heat resistance.

The particle size of the particulate precipitate inside the grain is smaller than the particle size of the particulate precipitate at the grain boundary and exists in a size of 3 μm or less. The fine particulate precipitates inside the grains have Mg and Ni, unlike the particulate precipitates at the grain boundaries having Fe, Cu, and Ni, and are abrasion resistant together with the particulate precipitates at the grain boundaries. It is considered that it contributes to the improvement of properties and heat resistance. Since some of the particulate precipitates inside the grains are quite small, the lower limit of the particle size is not particularly limited, but is about 0.1 μm.

The particle size (D1) of the particulate precipitate at the grain boundary was considerably larger than the particle size (D2) of the particulate precipitate inside the grain, and the ratio (D1 / D2) was 5 or more. The significance of D1 / D2 being 5 or more is not clear at present, but it is considered that the difference in size contributes to the improvement of wear resistance and heat resistance. The upper limit of D1 / D2 was about 50, although it is not clear because some of the particulate precipitates inside the grains are quite small.

Of the particulate precipitates present in the cross section, the proportion of particulate precipitates at the grain boundaries (P1: 12% or more and 22% or less) is larger than the proportion of particulate precipitates inside the grains (P2), and the ratio thereof. (P1 / P2) was in the range of 6 or more and 11 or less. The significance of P1 / P2 being within the above range is not clear at present, but it is considered that the difference in the ratio contributes to the improvement of wear resistance and heat resistance. From the P1 / P2 ratio (6 or more and 11 or less), when the ratio of granular precipitates at the grain boundaries (P1) is 12%, which is the lower limit, the ratio of granular precipitates inside the grains (P2) is When the ratio is in the range of 2% to about 1.1% and the ratio of granular precipitates at the grain boundaries (P1) is 22%, which is the upper limit, the ratio of particulate precipitates inside the grains (P2) is about. It is in the range of 3.7% to 2%.

As described above, the piston for an internal combustion engine according to the present invention is excellent in wear resistance and heat resistance. The cause of the excellent wear resistance and heat resistance is not clear at this time, but the particulate precipitates having Fe, Cu, and Ni present at the grain boundaries contribute significantly, and the particulate precipitates inside the grains also contribute. It is considered to be contributing.

[Manufacturing method of piston for internal combustion engine]
The method for manufacturing a piston for an internal combustion engine according to the present invention is Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni. A step of preparing an aluminum alloy continuous casting material containing at least 0.3 to 0.8% by mass and Mg: 1.5 to 2.0% by mass (preparation step) and hot the aluminum alloy continuous casting material. It has at least a step of forging (hot forging step), a step of heat treatment after hot forging (heat treatment step), and a step of machining after heat treatment (processing step). Particulate precipitates are present at the grain boundaries and inside of the grains in the cross section of the manufactured piston for internal combustion engine, and the particulate precipitates existing at the grain boundaries have Fe, Cu, and Ni. ..

(Preparation process)
The preparation step is a step of preparing an aluminum alloy continuous cast material (hereinafter, referred to as a continuous cast material) containing at least the above component composition. The continuous cast material can be prepared by a conventionally known general method except that an aluminum alloy having the above-mentioned composition is used. For example, a melted aluminum alloy having the above component composition can be continuously cast into a billet for extrusion, homogenized, extruded into a small-diameter round bar having a predetermined size, and then cut to a predetermined size for preparation. it can. Alternatively, the melted aluminum alloy having the above component composition may be continuously cast into a round bar, homogenized, cut into a small-diameter round bar having a predetermined size, and then cut to prepare. Prior to continuous casting, degassing treatment and floating separation treatment of inclusions may be performed, if necessary. Further, after continuous casting, homogenization treatment may be performed.

(Hot forging process)
The hot forging step is a step of hot forging the prepared continuous cast material. Hot forging can also be performed by a conventionally known general method except that a continuous cast material having the above-mentioned composition is used. For example, a rear extrusion method in which a forging material cut to a predetermined size is pressed against a die and the forging material is allowed to flow in the die may be used, or a forging material is pressed against a fixed die and the forging material is pressed into a die. It may be a forward extrusion method in which the mold is allowed to flow. Before hot forging, the continuous casting material or the die may be preheated if necessary.

(Heat treatment process)
The heat treatment step is a step of heat-treating after hot forging. As for the heat treatment step, a general heat treatment known in the past can be performed except that the continuous cast material having the above-mentioned component composition is used. For example, a method of heating the forged product, then performing a solution treatment of cooling with water, and then performing an aging treatment can be mentioned.

(Processing process)
The processing process is a process of machining after heat treatment. Machining can also be performed by a conventionally known general method. For example, the forged piston is subjected to drilling for a piston pin, piston surface drilling, oil ring groove processing, and other processing to finish the piston shape.

According to the method for manufacturing a piston for an internal combustion engine having such a step, the prepared continuous aluminum alloy casting material having the above composition is manufactured through each step of hot forging, heat treatment, and machining in sequence, and thus is peculiar to the component composition. The morphology appears. That is, since particulate precipitates are present at the grain boundaries and inside the grains in the cross section, and the particulate precipitates existing at the grain boundaries have Fe, Cu, and Ni, the particulate precipitates are present. It is considered that it acts to improve wear resistance and heat resistance. It is also considered that the particulate precipitates existing inside the grains also contribute to the improvement of wear resistance and heat resistance.

The present invention will be specifically described with reference to Examples and Comparative Examples.

[Example 1]
Si: 0.50% by mass, Fe: 1.70% by mass, Cu: 4.1% by mass, Ni: 0.60% by mass, Mg: 1.80% by mass, Ti: 0.07% by mass, and trace amounts are inevitable. Impurities, balance: A continuous cast material of an aluminum alloy composed of aluminum was prepared. The composition of this aluminum alloy is the result of measurement by a spark discharge emission spectrophotometer (model name: SPECTRO LAB, manufactured by SPECTRO) (the same applies to Examples 2 and 3 below). In this continuous casting material, an aluminum alloy melted at about 700 ° C. to 800 ° C. is continuously cast to obtain a billet for extrusion having a diameter of 100 mm, and the billet for extrusion is cut to obtain a continuous casting material having a length of 30 mm and a diameter of 95 mm. did. The continuous cast material was homogenized at about 500 ° C. for 8 hours before cutting the extrusion billet.

The prepared continuous casting material and the die were preheated to about 400 ° C. and then hot forged. The hot forging was performed by the forward extrusion method. After hot forging, it was held at about 530 ° C. for 2 hours and then put into water at about 100 ° C. for solution treatment. Then, the aging treatment was carried out at about 200 ° C. for 20 hours. Then, the pin hole, the piston ring groove, and the like were machined and finished by machining to produce the piston for the internal combustion engine of Example 1.

[Comparative Example 1]
A continuous cast material of A2618 alloy was prepared. The A2618 alloy is based on JIS (Japanese industrial standard) and AA (US standard), Si: 0.10 to 0.25% by mass, Fe: 0.9 to 1.3% by mass, Cu: 1.9 to 2 .7% by mass, Ni: 0.9 to 1.2% by mass, Mg: 1.3 to 1.8% by mass, Ti: 0.04 to 0.10% by mass, Zn: 0.10% by mass or less, And trace unavoidable impurities, balance: Aluminum alloy standardized as aluminum. Other than that, the piston for the internal combustion engine of Comparative Example 1 was produced in the same manner as in Example 1.

[Comparative Example 2]
A continuous cast material of A4032 alloy was prepared. The A4032 alloy is based on JIS (Japanese Industrial Standards), AA (US Standards), NF (French Standards), and CSA (Canada Standards), Si: 11.0-13.5% by mass, Fe: 1.0% by mass. Hereinafter, Cu: 0.5 to 1.3% by mass, Ni: 0.5 to 1.3% by mass, Mg: 0.8 to 1.3% by mass, Cr: 1.0% by mass or less, Zn: 0 .25% by mass or less, trace amount of unavoidable impurities, balance: Aluminum alloy standardized as aluminum. Other than that, the piston for the internal combustion engine of Comparative Example 2 was produced in the same manner as in Example 1.

[Example 2]
In Example 1, Si: 0.40% by mass, Fe: 2.0% by mass, Cu: 3.5% by mass, Ni: 0.30% by mass, Mg: 2.00% by mass, Ti: 0.07 Mass% and trace amount of unavoidable impurities, balance: A continuous cast material of an aluminum alloy composed of aluminum was prepared. Other than that, the piston for the internal combustion engine of Example 2 was produced in the same manner as in Example 1.

[Example 3]
In Example 1, Si: 0.70% by mass, Fe: 1.40% by mass, Cu: 5.5% by mass, Ni: 0.80% by mass, Mg: 1.50% by mass, Ti: 0.09. Mass% and trace amount of unavoidable impurities, balance: A continuous cast material of an aluminum alloy composed of aluminum was prepared. Below that, the piston for the internal combustion engine of Example 3 was produced in the same manner as in Example 1.

[Cross-sectional structure and particulate precipitate]
(Piston of Example 1)
In the piston of Example 1 shown in FIGS. 2 and 3, the grain boundary portion and the inside of the grain appear due to the presence of the grain boundary, and the grain boundary portion and the inside of the grain have particulate precipitates in both of them. Was. The particulate precipitate has a large particle size at the grain boundary, but the particle size inside the grain is smaller than that at the grain boundary. The particulate precipitate at the grain boundary had Fe, Cu, and Ni according to the element mapping shown in FIG. On the other hand, although not shown, the particulate precipitate inside the grains had Mg and Ni as a result of element mapping.

Regarding the size and abundance ratio of the particulate precipitates, as shown in FIG. 5, an image analysis software (product name: WinRooF Ner. 7.4, manufactured by Mitani Shoji Co., Ltd. The same applies hereinafter.) When the image was processed and measured in detail, the range was slightly different in each part of the cross section, but the particle size of the particulate precipitate at the grain boundary was 3 μm. It was confirmed that the average particle size was 8.1 μm in the range of 30 μm or less, and the area ratio per unit area in each part was in the range of 12% or more and 22% or less. Further, it was confirmed that the particle size of the particulate precipitate inside the grains was about 0.6 μm, and the area ratio per unit area in each part was about 2%. From this, the ratio (D1 / D2) of the particle size of the particulate precipitate at the grain boundary (D1: 3 μm to 30 μm) and the particle size of the particulate precipitate inside the grain (D2: about 0.6 μm) is , 5 to 50. The ratio (P1 / P2) of the ratio of particulate precipitates at the grain boundaries (P1: 12% to 22%) to the ratio of particulate precipitates inside the grains (P2: about 2%) is 6 to P2. It was in the range of 11.

(Piston of Comparative Example 1)
The pistons of Comparative Example 1 shown in FIGS. 6 (A) and 7 also have grain boundaries and grain interiors due to the presence of grain boundaries, and the grain boundaries and grain interiors are both particulate precipitates. Was present. However, the particle size of the particulate precipitate at the grain boundary was smaller than that of Example 1. According to the element mapping shown in FIG. 9, the particulate precipitate at the grain boundary had Fe, Cu, and Ni as in Example 1. On the other hand, although the particulate precipitate inside the grains is not shown, the elemental mapping results show that the precipitates have Mg and Si, unlike in Example 1.

As shown in FIG. 11 (A), the size and abundance ratio of the particulate precipitates were measured in detail by image processing an inverted metal micrograph with image analysis software, and the range was slightly different in each part of the cross section. However, the particle size of the particulate precipitate at the grain boundary was in the range of 3 μm or more and 25 μm or less, and the average particle size was 6.3 μm, but the area ratio per unit area was about 10%. , It was confirmed that it was smaller than the case of Example 1. Further, it was confirmed that the particle size of the particulate precipitate inside the grains was about 0.4 μm, and the area ratio per unit area was about 7%. From this, the ratio (D1 / D2) of the particle size of the particulate precipitate at the grain boundary (D1: 3 μm to 25 μm) and the particle size of the particulate precipitate inside the grain (D2: about 0.4 μm) is , Unlike the case of Example 1, it was in the range of 7.5 to 62.5. Further, the ratio (P1 / P2) of the area ratio of the particulate precipitates at the grain boundaries (P1: about 10%) to the ratio of the particulate precipitates inside the grains (P2: about 7%) is also shown in Example 1. Unlike the case of, it was about 1.4.

(Piston of Comparative Example 2)
The pistons of Comparative Example 2 shown in FIGS. 6 (B) and 8 also had grain boundaries and grain interiors due to the presence of grain boundaries, and particulate precipitates were present at the grain boundaries. There were not many particulate precipitates inside the grains. The particle size of the particulate precipitate at the grain boundary was larger than that in Example 1. According to the element mapping shown in FIG. 10, the particulate precipitate at the grain boundary had Si, unlike Example 1 and Comparative Example 1.

As shown in FIG. 11 (B), the size and abundance ratio of the particulate precipitates were measured in detail by image processing an inverted metal micrograph with image analysis software, and the range was slightly different in each part of the cross section. However, the particle size of the granular precipitate at the grain boundary was in the range of 3 μm or more and 45 μm or less, and the average particle size was 8.4 μm, but the area ratio per unit area was about 35%. It was confirmed that the size was considerably larger than that of Example 1 and Comparative Example 1. Since there was almost no particulate precipitate inside the grain, the ratio of the average particle size (D1) of the particulate precipitate at the grain boundary to the average particle size (D2) of the particulate precipitate inside the grain (D1). / D2) was not calculated. In addition, the ratio (P1 / P2) of the ratio of particulate precipitates at the grain boundaries (P1: about 35%) to the proportion of particulate precipitates inside the grains (P2) was not calculated. The A4032 alloy is a general Si-based aluminum alloy, and is intended to suppress thermal expansion and improve wear resistance by containing Si.

[Abrasion resistance and heat resistance]
The wear resistance and heat resistance of the pistons of Example 1 and Comparative Examples 1 and 2 were measured. The wear resistance was evaluated by collecting a test piece from the piston body, measuring it by a reciprocating sliding test using a pin-on disk, and comparing the measured values of the amount of wear of the sliding part relative to each other. In the relative comparison, the result of the piston of Example 1 was set to 100, and the result of each piston of Comparative Examples 1 and 2 was shown as a relative value in Table 1 and FIG. On the other hand, regarding the heat resistance, a test piece was taken from the piston body and subjected to a high temperature tensile test and a high temperature rotational bending fatigue test, and the tensile strength (Tables 1 and 13) and 0.2% proof stress (Tables 1 and 14) were performed. ), The measured values of breaking stress (fatigue strength: Table 1 and FIG. 15) of 1 × 10 ^{7 cycles were compared relative to each other.} In the relative comparison, the result of the piston of Example 1 was set to 100, and the result of each piston of Comparative Examples 1 and 2 was shown as a relative value. The smaller the value of wear resistance, the better, and the larger the value of tensile strength, 0.2% proof stress, and fatigue strength, the better the heat resistance.

From the results of Table 1 and FIGS. 12 to 15, it was confirmed that the piston of Example 1 had improved wear resistance and heat resistance as compared with the pistons of Comparative Examples 1 and 2. The reason why the piston of the present invention is excellent in abrasion resistance and heat resistance is that particulate precipitates are present at the grain boundaries and inside the grains in the cross section, and the particulate precipitates existing at the grain boundaries are Fe. This is because it has Cu and Ni, and it is considered that the particulate precipitates act to improve the wear resistance and the heat resistance. It was also considered that the particulate precipitates present inside the grains also contributed to the improvement of wear resistance and heat resistance.

[Cross section of piston for internal combustion engine produced in Example 2 and Example 3]
The pistons for internal combustion engines made of the aluminum alloys of Examples 2 and 3 were also able to observe the same cross-sectional morphology as the pistons for internal combustion engines made of the aluminum alloys of Example 1. That is, particulate precipitates were present at the grain boundaries and inside the grains in the cross section, and the particulate precipitates present at the grain boundaries contained Fe, Cu, and Ni. It was confirmed that the other characteristic elements were the same as those of the piston for the internal combustion engine of Example 1.

1 Piston 2 Pin hole 11 Top 11a 1st compression ring groove 11b 2nd compression ring groove 11c Oil ring groove 11d Top surface of piston body 12 Skirt

Claims (3)

Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni: 0.3 to 0.8% by mass (however, 0) .) , Mg: 1.5 to 2.0% by mass, Ti: 0.05 to 0.10% by mass, Mn, Cr, Zr are not essential and inevitable impure part Consists of an aluminum alloy that may be included as
Particle-like precipitates are present at the grain boundaries and inside the grains in the cross section, and the particle-like precipitates present at the grain boundaries have Fe, Cu, and Ni, and are in the form of particles at the grain boundaries. The precipitate has a particle size in the range of 3 μm or more and 30 μm or less, exists in the range of an area ratio of 12% or more and 22% or less per unit area in each part of the cross section, and is a particulate precipitate existing in the cross section. Of these, the ratio (P1 / P2) of the ratio (P1) of the particulate precipitates at the grain boundaries to the ratio (P2) of the particulate precipitates inside the grains is in the range of 6 or more and 11 or less. , A piston for an internal combustion engine. Particle size (D1) of the particulate precipitate of the grain boundary portion is larger than the particle size (D2) of the particle inside of the particulate precipitate is the ratio of the outer (D1 / D2) is 5 or more, wherein Item 2. The piston for an internal combustion engine according to Item 1. Si: 0.4 to 0.7% by mass, Fe: 1.4 to 2.0% by mass, Cu: 3.5 to 5.5% by mass, Ni: 0.3 to 0.8% by mass (however, 0) .) , Mg: 1.5 to 2.0% by mass, Ti: 0.05 to 0.10% by mass at least, Mn, Cr, Zr are not essential and inevitable impure part There are at least a step of preparing an aluminum alloy continuous casting material which may be included as, a step of hot forging the aluminum alloy continuous casting material, a step of heat treatment after hot forging, and a step of machining after the heat treatment. And
The grain boundary and the grain interior of the cross-section of a piston for an internal combustion engine produced there particulate precipitate particulate precipitates present in the grain boundary portion has Fe and Cu and Ni The granular precipitates at the grain boundary have a particle size in the range of 3 μm or more and 30 μm or less, and are present in each part of the cross section within an area ratio of 12% or more and 22% or less per unit area. Of the particulate precipitates present in the cross section, the ratio (P1 / P2) of the ratio of the granular precipitates at the grain boundaries (P1) to the proportion of the particulate precipitates inside the grains (P2) is 6. A method for manufacturing a piston for an internal combustion engine , which is within the range of 11 or less.

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