JP2000265232A - Aluminum alloy piston excellent in high temperature fatigue strength and wear resistance, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum alloy piston exhibiting excellent fatigue strength even in a temperature region as high as 200 to 250 deg.C. SOLUTION: After forging, this aluminum alloy piston has a composition containing 11-13% Si, 0.2-1.2% Fe, 3.5-4.5% Cu, 0.2-0.5% Mn, 0.3-1.0% Mg, 0.01-0.2% Ti, 0.0002-0.02% B, 0.005-0.02%s P, and Ca in an amount controlled to <=0.005%. The aluminum alloy piston has a forged structure in which Si and an intermetallic compound both crystallized out at the time of casting are uniformly dispersed, in 5-35 μm average grain size, in a matrix after forging and gas content is controlled to <=0.25 cc/100 g-Al. Further, the average number of inclusions is controlled to <=0.01 piece/cm2 by K10 value in a stage of an ingot, and forming is performed by forging.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston made of an aluminum alloy which is used in various internal combustion engines and has excellent high-temperature fatigue strength and wear resistance, and a method for producing the piston.

[0002]

2. Description of the Related Art As an engine mounted on a vehicle represented by a motorcycle, an engine made of an aluminum alloy is used because it is required to be lightweight. Cylinder cases, pistons, and the like, which are engine parts, are manufactured by casting, forging, or the like of an aluminum alloy having excellent high-temperature strength and heat resistance. Recently, there has been a strong demand for reducing the weight of vehicles and improving fuel efficiency from the viewpoint of protecting the global environment. Therefore, a material that is lighter and more resistant to high-temperature combustion is also desired for an aluminum alloy piston used for an engine component. In order to satisfy the required characteristics, forged pistons are expected to be promising in terms of thinning and quality stability. However, the forged pistons currently on the market are 200-
In the high temperature range of 250 ° C., the fatigue strength is significantly reduced.
In a powder forged piston using aluminum alloy powder,
Sufficient high-temperature strength is maintained even in a high-temperature range of 200 to 250 ° C. However, powder forgings cannot be processed into complex-shaped pistons because of their higher material costs compared to ingots and poor forgeability.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been devised to solve such a problem. The present invention reduces the content of gas and inclusions which have a detrimental effect on the high-temperature fatigue strength, and provides a systematic method. In addition, by dispersing a large amount of the high melting point crystallized material uniformly in the matrix, it has excellent high-temperature fatigue strength compared to conventional materials even in the high temperature range of 200 to 250 ° C, and is excellent in forgeability. The aim is to get a piston. In order to achieve the object, the aluminum alloy piston of the present invention has, after forging, Si: 11 to 13% by weight, Fe: 0.2 to 1.2% by weight, Cu: 3.5 to 4.0.
5% by weight, Mn: 0.2-0.5% by weight, Mg: 0.3
To 1.0% by weight, Ti: 0.01 to 0.2% by weight, B:
0.0002-0.02% by weight, P: 0.005-0.
Contains 0.2% by weight, Ca is controlled to 0.005% by weight or less, and the balance substantially has a composition of Al, and Si and intermetallic compounds crystallized at the time of casting have an average particle size of 5 to 35 μm after forging.
m uniformly dispersed in the matrix, the gas content was 0.25
has been forged tissue restricted below cc / 100 g-Al, inclusions average number in the ingot stage 0.01 or at K ₁₀ value /
cm ² or less, and is characterized by being formed by forging.

[0004] This aluminum alloy piston is made by refining the aluminum alloy melt whose components have been adjusted,
Ar gas of 0.05 to 0.20 g / 100 g-Al is added to a molten aluminum alloy having a molten metal temperature of 750 to 800 ° C.
The aluminum alloy melt is degassed by blowing over 5 to 1.5 hours, and the aluminum alloy melt is heated to 750 to 800 ° C.
Hold for at least 45 minutes in the temperature range of
After deslagging, the molten aluminum alloy is continuously cast into an ingot, subjected to a homogenization treatment of 490 to 510 ° C. × 3 to 5 hours, and cooled at a cooling rate of 200 ° C./hour or more. It is manufactured by cutting into slices for forging, heating to 400 to 500 ° C., and forging into a predetermined shape. After performing solution treatment at 490 to 510 ° C. × 3 to 5 hours, quenching with water, and performing aging treatment at 160 to 180 ° C. × 6 to 10 hours on the forged product, Mg ₂ Si, Al ₂ Cu
The required strength is imparted by the precipitation of the like. After forging, aging treatment at 190 to 200 ° C. for 5 to 7 hours can be performed.

[0005]

In order to increase the high-temperature strength of an aluminum alloy piston, it is necessary to improve the high-temperature strength and to reduce the content of gas and inclusions that are the core of fatigue fracture. In the present invention, the intermetallic compounds such as Fe, Cu, and Si, which are crystallized at the time of casting, and primary crystal Si are controlled to an appropriate size by forging and uniformly dispersed in the matrix, thereby suppressing the softening of the aluminum solid solution of the matrix. Improves high temperature strength. The wear resistance is improved by controlling the primary crystal Si to an appropriate size and crystallizing the fine eutectic Si as large as possible. Less than,
Each condition specified in the present invention will be described.

[Component / composition after forging] Si: 11 to 13% by weight An alloy component effective for abrasion resistance and heat resistance, and also has a function of lowering the thermal expansion coefficient in a high temperature range. Also. Precipitates as Mg ₂ Si by aging treatment and improves the mechanical strength of the alloy material. However, the Si content is 13% by weight.
If the cooling rate exceeds 100 ° C./sec or more during the continuous casting, coarse primary crystal Si having a particle size exceeding 50 μm tends to be generated. Coarse primary crystal Si remains in a large shape even after being crushed by forging and becomes a nucleus of fatigue fracture, which causes a decrease in mechanical strength and fatigue strength at room temperature and high temperature. However, if the Si content is less than 11% by weight, strength and wear resistance are insufficient. Fe: 0.2 to 1.2% by weight Al-Fe-based or Al-Fe-Si-based intermetallic compound having a high melting point has a high tensile strength and a low tensile strength when the alloy material is exposed to a high temperature region exceeding 200 ° C. Exhibits the effect of increasing fatigue strength,
The effect becomes significant when the Fe content is 0.2% by weight or more. However, when a large amount of Fe exceeding 1.2% by weight is contained, crystallization of a coarse intermetallic compound serving as a nucleus of fatigue fracture is promoted, which has a detrimental effect on elongation, forging formability, and toughness.

Cu: 3.5-4.5% by weight An alloy component for solid solution strengthening of the matrix. When the content is 3.5% by weight or more, the effect of adding Cu becomes remarkable. The solid solution Cu precipitates as Al ₂ Cu by the aging treatment, and also has an effect of improving the strength of the alloy material. However, the effect of improving the tensile strength by Cu is saturated at 4.5% by weight. _3. Al ₂ Cu crystallized during casting has a high hardness and is dispersed in a matrix to increase the high-temperature strength.
When an excessive amount of Cu exceeding 5% by weight is included, coarse Al ₂ Cu, which is a nucleus of fatigue fracture, tends to crystallize, and forgeability and corrosion resistance are also reduced. Mn: 0.2 to 0.5% by weight Crystallizes as an Al-Mn-based compound and exhibits an effect of improving heat resistance and wear resistance. The Al-Mn-based compound acts on the acicular Al-Fe-based compound at the time of crystallization to form Al-Fe-M.
It changes the form into an n-type bulk compound and suppresses a decrease in toughness. Such an operation and effect can be achieved by using Mn of 0.2% by weight or more.
It becomes remarkable in the content. However, if an excessive amount of Mn exceeding 0.5% by weight is contained, a coarse compound of the Al-Si-Fe-Mn system is crystallized, which causes cracks during plastic working such as extrusion and forging, and causes strength. And a decrease in growth. Coarse Al-Si-Fe-Mn compounds become nuclei for fatigue fracture and are therefore harmful to normal temperature and high temperature fatigue strength.

Mg: 0.3 to 1.0% by weight Precipitates as Mg ₂ Si by aging treatment to increase the mechanical strength of the alloy material. The strength improving effect is observed at a Mg content of 0.3% by weight or more, and increases as the Mg content increases. However, when an excessive amount of Mg exceeding 1.0% by weight is contained, the elongation is significantly reduced and the plastic workability is also reduced. Ti: 0.01 to 0.2% by weight An alloy component added as an Al-Ti-B alloy for refining cast crystal grains. The effect of refining the cast structure becomes significant at a Ti content of 0.01% by weight or more. By refining the cast crystal grains, the intermetallic compound having a high melting point becomes a network and crystallizes at the grain boundaries. The network-like intermetallic compound is finely crushed and dispersed by the subsequent forging, and improves heat resistance and high-temperature fatigue strength. But,
When an excessive amount of Ti exceeding 0.2% by weight is added, Al
A coarse needle-like compound of Ti ₃ is easily crystallized and becomes a nucleus of fatigue fracture, and the strength and elongation are also reduced.

B: 0.0002 to 0.02% by weight A component added to the molten aluminum alloy together with Ti as a refining agent. However, since a large amount of B is likely to combine with Ti, V, etc. to form a coarse intermetallic compound serving as a nucleus of fatigue fracture, in the present invention, the B content is set to 0.0002 to 0.0002 in consideration of the fineness effect. It was set in the range of 0.02% by weight. P: 0.005 to 0.02% by weight A component conventionally used as a refiner of primary crystal Si added to a hypereutectic alloy having a Si content of 13% by weight or more. There is a tendency that the grain size of crystalline Si increases. The refinement of primary crystal Si becomes remarkable at a P content of 0.005% by weight or more. Various investigations and studies on the effect of P on the size of primary and eutectic Si revealed that S
In the hypoeutectic composition having an i content of 11 to 13% by weight, the addition of P makes the primary crystal Si finer and coarsens the eutectic Si, so that the particle size difference between the primary Si and the eutectic Si becomes smaller, and the distribution state also It was found that it was homogenized. Uniform dispersion of primary crystal Si and eutectic Si is effective for mechanical strength, fatigue strength and wear resistance in a high temperature range. However, if the P content exceeds 0.02% by weight, oxides of P are mixed in the molten metal and inclusions harmful to fatigue strength tend to increase. Ca: 0.005% by weight or less Ca is a component exhibiting an action of refining eutectic Si. In the present invention, since the eutectic Si is increased to contribute to wear resistance, the upper limit of the Ca content is set to 0.005% by weight so as not to affect the miniaturization of the eutectic Si. In addition, Ca
Since the content is reduced, the action of P for making primary crystal Si fine is effectively exhibited.

[Degassing] When the forged aluminum alloy piston contains a large amount of gas, the porosity caused by the gas is crushed by forging, but the porosity caused by the gas is high in a high temperature range of 200 to 250 ° C. When used, the contained gas tends to gather at one location and become the core of fatigue cracks.
Considering the required characteristics of an aluminum alloy piston used in a high temperature range, the gas content is 0.25 cc / 100 g.
It was found from the experimental results shown in FIG. 1 by the present inventors that -Al and below are effective. In order to reduce the gas content, in the present invention, the molten aluminum alloy is sufficiently degassed by blowing Ar gas which does not cause viscosity in the molten aluminum alloy in the molten metal stage. In this regard, N ₂ gas is not preferable because it increases the viscosity of the molten metal. When blowing Ar gas, 750
It is important to maintain the molten aluminum alloy in the temperature range of -800 ° C. When the temperature of the molten metal is lower than 750 ° C., the molten metal becomes viscous, and the blown Ar gas becomes difficult to escape. Conversely, at a melt temperature exceeding 800 ° C., the life of the furnace is shortened. As the degassing by blowing Ar gas, a method of using a casting facility equipped with a degassing unit, for example, a method of continuously degassing a molten metal or the like flowing through a gutter to a mold at the time of casting can also be adopted. Ar gas is blown into A
In order to disperse the r gas as fine bubbles in the molten metal, an injection method using a rotary nozzle is preferable. Fine bubbles of Ar gas adsorb gas components such as H contained in the molten metal and float and separate from the molten metal. In order to effectively degas the molten metal, it is necessary to blow Ar gas of 0.05 to 0.20 g / 100 g-Al over 0.5 to 1.5 hours. If the Ar gas amount and the blowing time are less than the predetermined values, the degassing effect due to the Ar gas blowing is insufficient. Conversely, if the Ar gas amount and the blowing time exceed the predetermined values, the degassing effect is saturated.

[Holding treatment of molten metal] When holding the degassed molten metal in a temperature range of 750 to 800 ° C. for 45 minutes or more, Al ₂ O ₃ , other oxides, brick debris, tool protective agent, etc. Inclusions float and separate from the molten metal. Inclusions tend to separate from the molten metal as the temperature of the molten metal increases. At a melt temperature of less than 750 ° C., the viscosity of the melt is large and inclusions are unlikely to float. If the holding time does not reach 45 minutes, the floating of the inclusions does not sufficiently proceed. However, at a melt temperature exceeding 800 ° C., the thermal load on the furnace wall refractory is large, and the life of the furnace is shortened. The molten metal that has been degassed and removed in the holding furnace is injected into the mold through a gutter. When the molten metal flowing through the gutter is continuously degassed, passed through the filter device, and inclusions floating in the molten metal are trapped by weirs, filter cartridges, etc., the molten metal with higher cleanliness is injected into the mold. And
An ingot with few inclusions can be obtained.

[Casting] The cleaned molten metal is poured into a mold and continuously cast into an ingot of a predetermined shape. As a casting method, a method in which the cooling rate of the molten metal is increased in order to reduce the dendrite arm spacing (preferably 50 μm or less), specifically, DC casting is employed. DC casting may be either vertical casting or horizontal casting. Since the aluminum alloy used in the present invention contains Ti and B as a refining agent, it becomes an ingot having fine cast crystal grains. However, in the alloy composition specified in the present invention, the cast structure is likely to be columnar, so that it is preferable to increase the number of equiaxed crystals as much as possible by the refinement treatment. Because the dendrite arm spacing is small and the cast crystal grains are fine,
Al-Fe, Al-Cu, Al-Mn with high melting point
Compounds such as Al-Si-Fe (Mn) -based compounds
It is finely dispersed in a network and crystallizes at the boundaries of the cast crystal grains and the boundaries of the dendrite arms. Since the crystallized intermetallic compound is further finely crushed and dispersed in the matrix at the time of extrusion or forging in the subsequent step, the heat resistance of the forged product is improved.

[0013] Since the ingot is obtained from an aluminum alloy melt in which inclusions have been reduced by degassing and holding treatment, the amount of inclusions brought in is extremely small.
Usually, the inclusions mixed in the forged product have a length of 0.1 to 3 mm, and when the fracture surface of the ingot is inspected with a 10-fold loupe, it is observed to be blackish. Therefore, the present inventor has a fracture surface of the ingot was observed in 10-fold loupe was determined K ₁₀ values in terms of the number of counted inclusions per unit area. And
When checking the relationship between the K ₁₀ value and the fatigue strength, the K ₁₀ value is 0.01 pieces / cm ² or less, the fatigue strength is found to be significantly improved. In contrast, when K ₁₀ value exceeds 0.01 pieces / cm ^2, inclusions tends to be the nucleus of fatigue cracks, no high-temperature fatigue strength required for the piston is obtained. A small diameter round bar is made from the ingot through an extrusion process, and a slice cut out from the round bar is forged. In this case, considering the final shape of the piston, the diameter is 100 mm.
An ingot of ~ 400 mm is used. Alternatively, after removing black scale on the surface of the ingot by facing, it is also possible to cut out a slice from the ingot without going through an extrusion step and to forge. In this case, an ingot having a diameter of 50 to 100 mm is used.

[Homogenization Treatment] The obtained ingot is made of Si, M
In order to sufficiently dissolve g and Cu in the matrix to increase aging hardening, homogenization treatment is performed at 490 to 510 ° C for 3 to 5 hours. If the heating temperature is less than 490 ° C. or the heating time does not reach 3 hours, solid solution does not sufficiently proceed, and Si, M
Effective amounts such as g and Cu tend to be insufficient during the aging treatment.
However, if the heating temperature is higher than 510 ° C., there is a risk of partial melting (burning), and if the heating time is longer than 5 hours, the effect corresponding to the time is not increased and it is not economical. The homogenized ingot is cooled at a cooling rate of 200 ° C./hour or more. As a result, a sufficient amount of Si, Mg, and Cu is maintained in a solid solution state, and a precipitation amount effective for imparting strength during aging treatment is secured. When the cooling rate is lower than 200 ° C./hour, Mg ₂ Si, Al ₂ Cu and the like are liable to precipitate in the cooling process, and the effective amount of Si, Mg, Cu and the like tends to be insufficient during the aging treatment.

[Forging] Diameter 100 after homogenization
An ingot of ~ 400 mm is cut into an extruded billet, extruded into a round bar for forging, and then cut into predetermined slices. Ingots with a diameter of 50 to 100 mm are cut into forging slices after removing black scale on the surface of the ingot by face milling without going through an extrusion step. A slice cut from the ingot can be used for forging without removing black scale. In this case, if a metal mold having a metal reservoir between an inner surface of a female mold parallel to a forging direction and an outer surface of a male punch (Japanese Patent Laid-Open No. Hei 10-118735) is used, black scale on a forged product is obtained. Contamination is prevented. The forging slice is heated to 400 to 500 ° C. and hot forged prior to forging. When the forging slice is heated to the temperature range of 400 to 500 ° C., the smooth flow of the metal in the forging die is promoted, and the pressure during forging can be smaller than that of cold forging.

The heated forging slice is set in a forging die and forged into a predetermined shape. The material is kneaded by forging to impart toughness to the product. In addition, network-like crystallized substances such as primary crystal Si and intermetallic compounds generated during casting are finely crushed by forging and dispersed in a matrix, so that heat resistance is improved. Above all, when primary crystal Si and intermetallic compounds are crushed by forging to an average particle size of 5 to 35 μm and uniformly dispersed in a matrix, primary crystal Si which becomes a nucleus of fatigue fracture is obtained.
Since the crystallized substances such as the above are eliminated, the ordinary temperature and high temperature fatigue strength are improved. If crystallized substances having an average grain size of more than 35 μm are distributed in the structure after forging, they tend to become fatigue crack nuclei.
Forging large primary crystal Si into a size having an average particle size of 5 to 35 μm by forging is also effective for improving wear resistance.
As the forging method, any of rear extrusion in which a mandrel is pressed against a fixed slice and metal flows along the mandrel, and front extrusion in which the slice is pressed against a fixed mandrel and metal flows along the mandrel can be used.

[Heat treatment] The forged product is provided at 490-510 ° C ×
After performing a solution treatment for 3 to 5 hours, water quenching is carried out.
Aging treatment is performed at 0 to 180 ° C for 6 to 10 hours. In the solution treatment, Mg, Si, Cu, and the like are sufficiently dissolved in the matrix. The solid solution state of Mg, Si, Cu, etc. is maintained at room temperature by water quenching, and Mg ₂ Si, A
Precipitates as l ₂ Cu or the like to give a predetermined strength. Also, the forged product is not solution-treated to prevent dimensional change.
Aging treatment at 0 to 200 ° C. for 5 to 7 hours can be performed to impart strength. The forged product that has been aged is machined at the required points and finished into a product piston.

[0018]

EXAMPLE An aluminum alloy melt whose composition was adjusted to a predetermined composition was maintained at 770 ° C., and degassing was performed by injecting 0.1 g / 100 g-Al Ar gas for 40 minutes from a rotary nozzle immersed in the melt. Next, the molten metal was kept at 760 ° C. for 60 minutes to float and separate inclusions, and then the diameter was 86 mm and the length was 5 m.
Was subjected to vertical DC casting. The ingot was subjected to a homogenization treatment at 500 ° C. for 4 hours, and was forcedly cooled by a fan at a cooling rate of 250 ° C./hour. The surface of the ingot after cooling was 2 mm thick, and a forging slice having a length of 21 mm was cut out. The slice 1 for forging was set in a forging device of a backward extrusion system schematically shown in FIG. Prior to forging, the forging slice 1 was heated to 460 ° C, and the lower mold 2 and the mold 3 equipped with a punch were heated to 200 to 250 ° C. The mandrel 4 is pushed into the forging slice 1 on the lower mold 2 from above, and 35
A pressure of 0 ton was applied to forging slice 1. The tip of the mandrel 4 cut into the forging slice 1 and the metal flowed upward along the mandrel 4 as shown by the arrow F.
After lowering the mandrel 4 to a predetermined position, the mandrel 4 was pulled out and at the same time the punch incorporated in the lower mold 2 was raised, and a forged product having a piston shape with a diameter of 84 mm and a height of 47 mm was taken out of the mold 3. The upsetting ratio at this time was 76% in the head portion.

The forged product was subjected to a solution treatment at 500 ° C. × 4 hours, water-quenched, and aged at 170 ° C. × 8 hours.
The structure after the aging treatment was observed, the gas content was measured, and the mechanical properties were investigated. The gas content was measured by a Lansley method by cutting out a sample from the forged product after the aging treatment. Regarding inclusions, since Zuraka' cutaway forging with a hammer, dividing the slices cut from the cast bar with a hammer, fracture and were observed at 10-fold loupe counts the number of inclusions, determine the K ₁₀ value Was. The observation area was 20 cm ^{2 for} both fracture surfaces. Table 1 shows the composition of the obtained piston. In the table, Comparative Alloys A and B are examples in which primary crystal Si was not refined with P, and Comparative Alloy A in which eutectic Si was refined with Sb. Table 2 shows the gas content as a result of observing the microstructure after the aging treatment. In Table 3,
The measurement results of tensile strength and fatigue strength are shown.

As is clear from Table 3, the products C to F of the present invention
Has a higher tensile strength and a higher fatigue strength at high temperatures than the comparative products A and B. Comparative product A has a composition corresponding to the current forged piston. However, since primary crystal Si is not refined by P, the average particle diameter of primary crystal Si is large as shown in Table 2, and eutectic Si is composed of Sb. It was small due to miniaturization. As a result, it is presumed that the large primary crystal Si acts as a nucleus of fatigue cracks and appears as a result of Table 3 inferior in high-temperature fatigue strength. Moreover, the comparative product A is Cu and F
Since the content of e is small, the high-temperature strength is inferior to the product of the present invention. The comparative product B has a low content of Cu, Mn, and Ti, so that the amount of the high-melting-point crystallized product is small and the high-temperature strength is low. In addition, the deviation from the eutectic point was small due to the extremely small amount of Cu, and thus the primary crystal Si was small and the fatigue strength was poor. On the other hand, the products C to G of the present invention exhibited excellent tensile strength and fatigue strength at both room temperature and high temperature. When this mechanical property is compared with the crystallized substance measurement results in Table 2, controlling the forged primary crystal Si, eutectic Si and intermetallic compound to an appropriate size requires mechanical strength, fatigue strength and heat resistance. It turns out that it is effective for improvement.

[0021]

[0022]

[0023]

Next, after degassing the molten aluminum alloy having the composition D shown in Table 1, the piston was manufactured at a relatively low temperature of 720 ° C. for a short time of 15 minutes, and a piston was manufactured under the same conditions as the other conditions. The resulting piston Although gas content is less and 0.20 cc / 100 g-Al, inclusions number was often 0.25 pieces / cm ² at K ₁₀ value. Also,
The high temperature fatigue strength showed a low value of 56 MPa (10 ⁷ cycles) at 250 ° C. The low high-temperature fatigue strength is presumed to be the result of a large amount of inclusions acting as nuclei for fatigue cracks.

Furthermore, a piston was manufactured by removing the inclusions under the same conditions as those of the product of the present invention by merely degassing the aluminum alloy melt having the composition E shown in Table 1 at 760 ° C. for 15 minutes.
The gas content of the obtained piston is 0.35 cc / 100.
g-Al, and the number of inclusions is K ₁₀ = 0.003 / c
m ² and showed a small value. The high temperature fatigue strength showed a low value of 59 MPa (10 ⁷ cycles) at 250 ° C. The low high-temperature fatigue strength is presumed to be due to the large amount of gas contained in the piston. When the wear resistance of each piston was investigated, as shown in Table 4, the products C to G of the present invention were obtained.
Showed better abrasion resistance than the comparative products A and B, while the Si content was the same level as the conventional comparative products A and B. This is because the eutectic Si of the comparative products A and B has an average particle size of 3.8.
μm and 4.2 μm, but in the products C to G of the present invention, the grain size of eutectic Si is increased by the P treatment, and a relatively large amount of F
Since it contains e and Cu, it is presumed that eutectic Si and Fe, Cu-based crystallization contribute to the improvement of wear resistance.

[0026]

[0027]

As described above, in the aluminum alloy piston of the present invention, the primary crystal Si, the eutectic Si, and the intermetallic compound crystallized at the time of casting in the system whose components and compositions are specified are appropriately sized. To a forged structure that is uniformly dispersed by controlling the gas content and the number of inclusions. Thereby, it exhibits excellent mechanical strength and fatigue strength at normal temperature and high temperature, and is used as a piston for an engine that tends to utilize a light weight and increase a thermal load.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of gas content on tensile strength.

FIG. 2 is an explanatory view of forging a slice set in a forging die into a piston.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C22C 32/00 C22C 32/00 R C22F 1/043 C22F 1/043 F02F 3/00 F02F 3/00 G 302 302Z F16J 1/01 F16J 1/01 // C22C 1/02 503 C22C 1/02 503J C22F 1/00 603 C22F 1/00 603 630 630D 650 650D 651 651B 681 681 682 682 683 691 692 691 691 691 691 69 Inventor Tatsu Yamada 1-34-1 Kambara, Kambara-cho, Abara-gun, Shizuoka Prefecture F-term in Nippon Light Metal Co., Ltd. Group Technology Center (reference) 3J044 AA01 AA02 BA04 BC02 DA09 EA01 EA04 4E014 NA08

Claims (4)

[Claims] 1. After forging, Si: 11 to 13% by weight, F
e: 0.2-1.2% by weight, Cu: 3.5-4.5% by weight, Mn: 0.2-0.5% by weight, Mg: 0.3-1.
0% by weight, Ti: 0.01 to 0.2% by weight, B: 0.0
002-0.02% by weight, P: 0.005-0.02% by weight, Ca is restricted to 0.005% by weight or less, and the balance substantially has a composition of Al, and crystallized during casting. Si
And the intermetallic compound is uniformly dispersed in the matrix with an average particle size of 5 to 35 μm after forging, and the gas content is 0.25 cc /
Has regulated forged tissue below 100 g-Al, inclusions average number in the ingot stage is regulated to 0.01 pieces / cm ² or less at K ₁₀ value, high-temperature fatigue strength molded by forging and Aluminum alloy piston with excellent wear resistance. 2. After forging, the aluminum alloy melt whose composition is adjusted to have the composition described in claim 1 is refined, and then an Ar gas of 0.05 to 0.20 g / 100 g-Al is melted at a melt temperature of 750 to 750 g. The molten aluminum alloy is degassed by blowing into the molten aluminum alloy at 800 ° C. for 0.5 to 1.5 hours, and the molten aluminum alloy is heated to 750 to 8 hours.
The inclusions were floated and separated by holding at a temperature range of 00 ° C for 45 minutes or more, and after slag removal, the molten aluminum alloy was continuously cast into an ingot and subjected to homogenization treatment at 490 to 510 ° C for 3 to 5 hours. , Cooling at a cooling rate of 200 ° C./hour or more, cutting the cooled ingot into slices for forging, heating to 400 to 500 ° C., and forging into a predetermined shape; A method for manufacturing aluminum alloy pistons with excellent wear resistance. 3. After subjecting the forged product to a solution treatment at 490 to 510 ° C. for 3 to 5 hours, it is quenched with water and then subjected to 160 to 180.
3. The method for producing an aluminum alloy piston excellent in high temperature fatigue strength and wear resistance according to claim 2, wherein aging treatment is performed at 6 [deg.] C. for 6 to 10 hours. 4. The method for producing an aluminum alloy piston excellent in high-temperature fatigue strength and wear resistance according to claim 2, wherein the forged product is subjected to aging treatment at 190 to 200 ° C. for 5 to 7 hours.