JP6670603B2 - Manufacturing method of forged piston - Google Patents

Description

  The present invention relates to a method for manufacturing an aluminum alloy forged piston such as an engine piston.

  In the specification and the claims, the term "continuous casting" is used to mean "semi-continuous casting" unless otherwise specified.

  In an internal combustion engine mounted on a vehicle such as a four-wheeled or two-wheeled vehicle (hereinafter simply referred to as an "automobile"), for example, a piston made of an aluminum alloy is used in order to improve combustion efficiency and output by reducing the weight of the internal combustion engine. Have been.

  For example, Japanese Patent Application Laid-Open No. 2009-19167 (Patent Document 1) discloses a method of manufacturing an aluminum alloy molded product including a forging process using a continuous cast rod made of an aluminum alloy having a predetermined composition as a material. Thus, an engine piston is mentioned as an example of an aluminum alloy molded product. Such a piston is required to have high high-temperature strength.

JP-A-2009-19167 (Claim 1, paragraph 0027)

  In recent years, pistons have been required to have higher high-temperature strength in order to further improve combustion efficiency, output, and the like of internal combustion engines.

  Therefore, an object of the present invention is to provide a method for manufacturing a forged piston having high high-temperature strength.

The present inventor has conducted intensive studies on a forged piston made of an aluminum alloy containing Ni as an essential element in order to achieve the above object. As a result, the forged piston is in a solid solution state in which Ni contained in the forged piston is not precipitated as Al ₃ Ni _2. This contributes to the improvement of the high-temperature strength of the forged piston, and has completed the present invention.

  The present invention provides the following means.

[1] Si: 9 to 14% by mass,
Fe: 0.15 to 0.8% by mass;
Cu: 2 to 6% by mass;
Mg: 0.3 to 1.0% by mass, and Ni: 1 to 5.5% by mass.
Including, a step of preparing a forging material composed of an aluminum alloy continuous cast material having a composition consisting of unavoidable impurities and aluminum,
When the first exothermic peak temperature of 400 ° C. or more of the material measured by the differential scanning calorimeter is Tn ° C.,
Pre-heating the material at a pre-heating temperature of 300 ° C. to {Tn + 30 ° C .;
Obtaining a raw material for a piston by hot forging the material at a forging temperature of 300 ° C. to {Tn + 30} ° C. after the preheating step;
A step of water quenching while maintaining the shaped material at a temperature of 420 ° C. to {Tn + 30 ° C .;
Aging the shaped material at an aging temperature of 180 ° C. to 230 ° C. after the water quenching step.

[2] a step of homogenizing the material at a homogenization temperature of {Tn + 30} ° C. or lower before the step of preheating;
2. The method for manufacturing a forged piston according to the above item 1, wherein the preheating step is performed after the homogenizing step.

[3] The composition further comprises:
Ti: 0.05 to 0.2% by mass
3. The method for manufacturing a forged piston according to the above item 1 or 2, comprising:

[4] The composition further comprises:
B: 0.01 to 0.1% by mass
4. The method for producing a forged piston according to any one of the above items 1 to 3, which comprises:

[5] In the preheating step, the material is preheated at a preheating temperature of 450 ° C. to {Tn + 30} ° C.,
In the step of obtaining the shaped material, using a forging die having a temperature of 400 ° C. to {Tn + 30 ° C., the temperature of the material is reduced to less than 30 ° C. due to heat removal from the material to the forging die. 5. The method for manufacturing a forged piston according to any one of the above items 1 to 4, wherein the shaped material having a temperature of 420 ° C. to {Tn + 30} ° C. is obtained by hot forging.

  [6] The method for manufacturing a forged piston according to any one of the preceding items 1 to 5, wherein in the step of water quenching, the raw material is water quenched within 10 seconds after hot forging the material.

In the preceding paragraph [1], the step of preheating a material having a predetermined composition, the step of hot forging, the step of water quenching, and the step of aging are sequentially performed in a predetermined temperature range, respectively, so that Al ₃ Ni ₂ is suppressed, whereby a forged piston having high high-temperature strength can be obtained.

  In the above [2], the high-temperature strength of the forged piston can be reliably increased.

  In the above [3], the crystal grains are refined by the composition of the material containing a predetermined amount of Ti. This improves the high temperature strength of the forged piston.

  In the above item [4], the crystal grain is refined by the composition of the material containing a predetermined amount of B. This improves the high temperature strength of the forged piston.

  In the above item [5], the high-temperature strength of the forged piston can be reliably increased, and the manufacturing time and the manufacturing cost of the forged piston can be reduced.

  In the above item [6], the high-temperature strength of the forged piston can be more reliably increased, and the production time and production cost of the forged piston can be further reduced.

FIG. 1 is a graph showing the relationship between the maximum heat history relative temperature (horizontal axis) and the amount of 1 / Al ₃ Ni ₂ (vertical axis) with respect to the exothermic peak temperature Tn of an aluminum alloy continuous cast material. FIG. 2 is a graph showing the relationship between the maximum thermal history relative temperature (horizontal axis) of Tn and the high-temperature strength at 300 ° C. (vertical axis). FIG. 3 is a diagram showing a forging production system which is an example of a forged product production line for realizing the forged piston manufacturing method according to the embodiment of the present invention. FIG. 4 is a sectional view showing the vicinity of a mold of the hot-top vertical continuous casting apparatus.

  An embodiment of the present invention will be described below.

The method for manufacturing a forged piston according to the present embodiment includes:
Si: 9 to 14% by mass,
Fe: 0.15 to 0.8% by mass;
Cu: 2 to 6% by mass;
Mg: 0.3 to 1.0% by mass, and Ni: 1 to 5.5% by mass.
A step of preparing a forging material made of an aluminum alloy continuous cast material having a composition consisting of unavoidable impurities and aluminum, including
When the first exothermic peak temperature of 400 ° C. or more of a material measured by a differential scanning calorimeter (DSC) is Tn ° C.,
Preheating the material at a preheating temperature of 300 ° C. to {Tn + 30 ° C .;
Obtaining a raw material for a piston by hot forging at a forging temperature of 300 ° C. to {Tn + 30} ° C. after the preheating step;
Water quenching while maintaining the cast material at a temperature of 420 ° C. to {Tn + 30 ° C .;
Aging the shaped material at an aging temperature of 180 ° C to 230 ° C after the step of water quenching.

Further, the method for manufacturing a forged piston includes a step of homogenizing the material at a homogenization processing temperature of {Tn + 30} ° C. or lower before the step of preheating,
It is desirable to perform a preheating step after the homogenizing step.

Furthermore, the composition of the continuous cast material is
Ti: 0.05 to 0.2% by mass
It is desirable to include.

Furthermore, the composition of the continuous cast material is
B: 0.01 to 0.1% by mass
It is desirable to include.

  Further, in the preheating step, the material is preheated at a preheating temperature of 450 ° C. to {Tn + 30 ° C., and in the step of obtaining a shaped material, a forging die having a temperature of 400 ° C. to {Tn + 30 ° C. is used. It is desirable to obtain a shaped material having a temperature of 420 ° C. to {Tn + 30 ° C. ”by forging the material while suppressing the temperature decrease of the material due to heat removal to the forging die to less than 30 ° C.

  Further, in the step of water quenching, it is desirable that the raw material be water quenched within 10 seconds after the material is hot forged.

  Further, Tn is desirably 430 ° C or higher and lower than 450 ° C.

  Next, the reasons for limiting the content of the component elements in the composition of the continuous aluminum alloy casting material constituting the material will be described below.

<Si: 9 to 14% by mass>
When the content of Si is less than 9% by mass, strength, wear resistance, and heat resistance are insufficient. When the content of Si exceeds 14% by mass, coarse primary crystal Si is generated, and the primary crystal Si becomes a starting point of fatigue strength, which causes a decrease in mechanical strength and fatigue strength. A particularly desirable Si content is 10% by mass or more and 12% by mass or less.

<Fe: 0.15 to 0.8% by mass>
Fe has an effect of improving mechanical properties in a high temperature range by an intermetallic compound having a high melting point. If the Fe content is less than 0.15% by mass, the amount of the network structure that stops dislocation at a high temperature is reduced at the temperature of the post heat treatment step, and the high-temperature characteristics in a high-temperature region are insufficient. If the Fe content exceeds 0.8% by mass, the intermetallic compound becomes coarse, which causes a reduction in formability, mechanical strength and fatigue strength. A particularly desirable Fe content is 0.2% by mass or more and 0.5% by mass or less.

<Cu: 2 to 6% by mass>
When the content of Cu is 2 to 6% by mass, Al ₂ Cu is precipitated in the post-heat treatment step, which has an effect of improving the strength. If the Cu content is less than 2% by mass, even if Cu forms a solid solution with the matrix in the solution heat treatment temperature range, the solid solution amount is small and the strength is insufficient. When the content of Cu exceeds 6% by mass, the occurrence of coarse crystallized substances causes a decrease in fatigue strength and corrosion resistance. Particularly desirable Cu content is 3% by mass or more and 5% by mass or less.

<Mg: Mg: 0.3 to 1.0% by mass>
When the content of Mg is 0.3 to 1.0% by mass, Mg is combined with Si in a post heat treatment step to form a Mg ₂ Si compound, and the precipitation improves the strength of the base material. When the content of Mg is less than 0.3% by mass, even if Mg forms a solid solution in the mother phase in the solution temperature range of the post heat treatment step, the amount of precipitation is small and the above-mentioned effects are small. When the content of Mg exceeds 1.0% by mass, elongation is reduced and workability is reduced. A particularly desirable content of Mg is 0.4% by mass or more and 0.8% by mass or less.

<Ni: 1 to 5.5% by mass>
When the content of Ni is 1 to 5.5% by mass, an intermetallic compound having a high melting point has an effect of improving mechanical properties in a high temperature range. If the Ni content is less than 1% by mass, the amount of the network structure that stops dislocations at high temperatures decreases at the temperature of the post heat treatment step, and the high-temperature characteristics in the high-temperature region become insufficient. If the content of Ni exceeds 5.5% by mass, the intermetallic compound becomes coarse, which causes a reduction in formability, mechanical strength, and fatigue strength. A particularly desirable Ni content is 2% by mass to 4.5% by mass.

<Ti: 0.05 to 0.2% by mass>
When the content of Ti is 0.05 to 0.2% by mass, mechanical properties are surely improved due to refinement of crystal grains. In particular, when Ti is 0.2% by mass or less, it is possible to reliably suppress the reduction in formability, mechanical strength, and fatigue strength due to coarsening of the intermetallic compound. A particularly desirable Ti content is 0.05% by mass or more and 0.1% by mass or less.

<B: 0.01 to 0.1% by mass>
When the content of B is 0.01 to 0.1% by mass, mechanical properties are surely improved due to refinement of crystal grains. In particular, when B is 0.1% by mass or less, it is possible to reliably suppress a decrease in formability, mechanical strength, and fatigue strength due to coarsening of the intermetallic compound. A particularly desirable B content is 0.01% by mass or more and 0.05% by mass or less.

  Next, the reason for defining the temperature range in each step of the method for manufacturing forged aluminum will be described below.

Using an aluminum alloy continuous cast material having the above-described composition as a sample, the sample is heated to various temperatures and then cooled to approximately room temperature, and the maximum heat history relative temperature of the sample to the exothermic peak temperature Tn of the continuous cast material, The relationship between the amount of Al ₃ Ni ₂ contained in the sample and the high-temperature strength of the sample at 300 ° C. was examined, and the results are shown in FIGS.

In FIG. 1, the horizontal axis represents the maximum thermal history relative temperature of the sample with respect to Tn of the continuous casting material, and the vertical axis represents the amount (relative amount) of 1 / Al ₃ Ni ₂ contained in the sample.

  In FIG. 2, the horizontal axis represents the relative maximum temperature of the sample with respect to Tn of the continuous cast material, and the vertical axis represents the high-temperature strength of the sample at 300 ° C.

  Here, Tn is the first exothermic peak temperature (unit: ° C.) of 400 ° C. or more of the continuous casting material measured by the differential scanning calorimeter as described above, and specifically, measured by the differential scanning calorimeter. It is the exothermic peak temperature first seen at the time of temperature rise in the temperature range of 400 ° C. or higher in the DSC curve of the continuous cast material.

This peak is presumed to be caused by the heat energy being consumed in the phase transformation when Ni contained in the continuous casting material changes from a solid solution state to a state of being precipitated as Al ₃ Ni _2. .

The amount of Al ₃ N ₂ was defined as an integral area of a diffraction peak corresponding to Al ₃ Ni ₂ by X-ray diffraction analysis of the sample.

  The high temperature strength at 300 ° C. is the tensile strength of the sample at a temperature of 300 ° C.

  As can be seen from FIG. 2, the high-temperature strength at 300 ° C. decreases sharply when the maximum thermal history relative temperature to Tn exceeds {Tn + 30} ° C.

As can be seen from FIG. 1, the amount of Al ₃ Ni ₂ rapidly increases when the maximum thermal history relative temperature to Tn exceeds {Tn + 30} ° C. (that is, 1 / Al ₃ Ni ₂ amount). The value has suddenly decreased).

Further, the precipitation phenomenon of Al ₃ Ni ₂ is an irreversible phenomenon because it is a precipitation change from a metastable phase to a stable phase, and once a sample has received its thermal history even once, the temperature is changed at a temperature lower than that. Also did not return to the previous Ni solid solution state.

From the above results, in the case of manufacturing a forged piston from a material made of an aluminum alloy continuous cast material having the above-described predetermined composition, the material does not receive a heat history at a temperature exceeding {Tn + 30} ° C. throughout the manufacturing process. By manufacturing the piston as described above, it can be seen that the precipitation of Al ₃ Ni ₂ can be suppressed, thereby obtaining a forged piston having high high-temperature strength.

  Next, an outline of a method for manufacturing the forged piston of the present embodiment will be described below.

  An example of the steps of the method for manufacturing a forged piston according to the present embodiment is as follows. The forged piston obtained in this process example is, for example, an engine piston used for an internal combustion engine.

  1) Continuous casting → 2) Homogenization treatment at ｛Tn + 30 ° C. or lower → 3) Roll straightening → 4) Peeling → 5) Cutting → 6) Preheating at 300 ° C. to {Tn + 30} ° C. → 7) 300 ° C. to ｛Tn + 30 Hot forging at｝ ° C → 8) Solution treatment → 9) Water quenching → 10) Aging treatment at 180 ° C to 230 ° C → 11) Machining.

  Here, in the step of 8) solution treatment and the step of 9) water quenching, in order to obtain a high high-temperature strength of 300 ° C. or less required especially for the pin boss portion and the skirt portion of the piston, the solution treatment temperature should be as low as possible. It is desirable that the cast material be water-quenched at a high temperature. Therefore, the cast material after hot forging is preferably directly water-quenched without lowering the temperature as much as possible. Further, this eliminates the need to raise the temperature of the raw material before water quenching, which is desirable in that the manufacturing time and the manufacturing cost can be reduced.

  In order to ensure such advantages, 6) the material is preheated at a preheating temperature of 450 ° C. to {Tn + 30 ° C.} in the preheating step, and 7) 400 in the hot forging step. The temperature of the raw material is reduced by using a forging die having a temperature of ℃ ~ {Tn + 30 ℃】 to reduce the temperature of the raw material due to heat removal to the forging die to less than 30 ℃ and hot forging. The temperature is set to 420 ° C. to {Tn + 30} ° C., and at this temperature, it is desirable that the raw material be water-quenched within 10 seconds after hot forging the raw material.

  Next, a specific example of the method for manufacturing a forged piston of the present embodiment will be described below with reference to FIG.

  FIG. 3 is a diagram illustrating a forging production system that is an example of a forged product production line that implements the forged piston manufacturing method of the present embodiment. In the figure, a forging product production system is a continuous casting device that manufactures a round bar-shaped continuous cast material from a molten aluminum alloy having a predetermined composition in a vertical direction by continuous casting and cuts the bar into a predetermined length. Vertical continuous casting device) 81, a homogenizing device 82 for homogenizing the continuous cast material obtained by the continuous casting device 81, and a homogenizing process performed by the homogenizing device 82 to bend the continuous cast material. In this case, a straightening device 83 for correcting the bending of the continuous casting material, a peeling device (eg, a lathe machine) 84 for removing the outer peripheral portion of the continuous casting material corrected by the straightening device 83, A cutting device 85 that cuts the continuous cast material from which a part has been removed to a length necessary for manufacturing a forged product by forging, and obtains a disc-shaped or column-shaped forging material; An upsetting device (not shown) for preheating and upsetting the material thus prepared for upsetting, and the material upset by this upsetting device is immersed in a lubricant liquid or upset. Lubricant coating devices 86a and 86b for coating the swaged material with a lubricant by spraying a lubricant (eg, a graphite-based lubricant) on the raw material, and the lubricant coating devices 86a and 86b. A pre-heating device 87 for pre-heating the material coated with the lubricant, a hot forging device 88 for hot-forging the material pre-heated by the pre-heating device 87 to obtain a forged product, Post-heat treatment devices 89, 90, and 91 for post-heat-treating the forged product obtained by the forging device 88 are provided.

  The post-heat treatment devices 89, 90, and 91 include, for example, a solution heating device 89 for performing solution treatment on the forged product, a water quenching device 90 for water-quenching the forged product heated by the solution heating device 89, and a water quenching device. And an aging treatment device 91 for aging the forged product water-quenched by the quenching device 90. When the solution treatment is omitted, it is preferable to provide the water quenching device 90 and the aging treatment device 91 after the hot forging device 88 without providing the solution heating device 89.

  The straightening device 83, the peeling device 84, and the upsetting device can be omitted. The transfer between the devices can be performed by an automatic transfer device. The lubricant coating process in the lubricant coating devices 86a and 86b can be replaced with a bond process (phosphate coating process) 86c.

  Here, the homogenization processing device 82 has a function of maintaining the temperature of the material at {Tn + 30} ° C or less (preferably 400 ° C to {Tn + 30 ° C) for 2 to 12 hours.

  The preheating device 87 has a function of setting the temperature of the raw material to 300 ° C. to {Tn + 30 ° C. (preferably 450 ° C. to {Tn + 30 ° C.).

  The hot forging device 88 has a function of setting the temperature of the material at the time of forging (that is, the forging temperature) to 300 ° C. to {Tn + 30} ° C. (preferably 400 ° C. to {Tn + 30 ° C.). Further, the hot forging device 88 keeps the temperature of the forging die at 400 ° C. to {Tn + 30 ° C. (preferably 450 ° C. to {Tn + 30 ° C.), and reduces the temperature drop of the material due to the heat removal to the forging die by 30 ° C. Less than (preferably less than 20 ° C.).

  The solution heating device 89 and the water quenching device 90 in the post-heat treatment devices 89, 90, 91 set the temperature of the forged product for solution treatment of the forged product to 420 ° C. to {Tn + 30} ° C. (preferably 450 ° C. to {Tn + 30}). C) for 1 to 6 hours, and then has a function of water-quenching the forged product.

  The aging treatment device 91 in the post heat treatment devices 89, 90, 91 has a function of maintaining the temperature of the forged product at 180 ° C. to 230 ° C. for 1 to 12 hours.

The method of manufacturing a forged piston using the above-described forging production system includes:
The forging material made of the aluminum alloy continuous cast material having the above-described predetermined composition is homogenized by the homogenization processing device 82 at a homogenization temperature of {Tn + 30} C or less (preferably 400C to {Tn + 30} C). Process and
After the step of homogenizing, preheating the material by a preheating device 87 at a preheating temperature of 300 ° C to {Tn + 30 ° C (preferably 450 ° C to {Tn + 30 ° C);
After the preheating step, the raw material is hot forged into a piston shape at a forging temperature of 300 ° C. to {Tn + 30 ° C. (preferably 400 ° C. to {Tn + 30 ° C.) by a hot forging device 88. A step of obtaining a shaped material;
A step of holding the cast material at a temperature of 420 ° C. to {Tn + 30 ° C. (preferably 450 ° C. to {Tn + 30 ° C.) by a solution heating device 89 and a water quenching device 90 to perform water quenching;
After the water quenching step, aging the cast material at an aging temperature of 180 ° C to 230 ° C (preferably 190 ° C to 220 ° C) by the aging treatment device 91.

  In the homogenization step, the material is preferably kept at a homogenization temperature of {Tn + 30} C or lower (preferably 400C to {Tn + 30C) for 2 to 12 hours.

  In the step of water quenching, it is desirable that the cast material is kept at a temperature of 420 ° C. to {Tn + 30 ° C. (preferably 450 ° C. to ΔTn + 30 ° C.) for 1 to 6 hours and then water quenched.

  In the step of aging treatment, the water-quenched shaped material is desirably kept at 180 ° C to 230 ° C (preferably 190 ° C to 220 ° C) for 1 to 12 hours.

  The step of water quenching and the step of aging can be performed within one week after the step of hot forging.

  Here, as described above, in the preheating step, the material is preheated at a preheating temperature of 450 ° C. to {Tn + 30 ° C., and in the hot forging step, a forging metal at a temperature of 400 ° C. to {Tn + 30 ° C. ” The temperature of the raw material is set to 420 ° C. to {Tn + 30 ° C. by subjecting the material to hot forging with a temperature drop of less than 30 ° C. due to heat removal from the forging die using a mold, and water quenching. In this step, it is desirable that the cast material at this temperature be water-quenched within 10 seconds after hot forging of the material. By doing so, the solution treatment can be omitted.

  The reason why the temperature of the forging die is desirably within the above-mentioned predetermined range in the step of hot forging is that a sufficient plastic flow can be obtained at the time of hot forging. Specifically, by using a forging die having a heater, the temperature of the forging die can be set in the above-described predetermined range.

  Here, the step of performing the homogenization treatment may be omitted, but by performing the step of performing the homogenization treatment, the high-temperature strength of the forged piston can be reliably increased.

  The shaped material obtained through the aging process is finished to a final product shape (that is, a final piston shape) by machining using a lathe, a machining center, or the like.

  Here, in the present embodiment, a step of preheating and upsetting the raw material for upsetting may be provided between the step of performing the homogenization processing and the step of preheating.

  Further, a step of coating the material with a lubricant may be provided between the step of upsetting and the step of preheating.

  Further, in the step of hot forging, the shaped material obtained by hot forging in the forging die is discharged from the forging die by the knockout mechanism.

In the preheating step, the preheating temperature is set in the above-mentioned predetermined range, thereby improving the deformation of the material while maintaining a solid solution state in which Ni contained in the material is not precipitated as Al ₃ Ni _2. However, it becomes easy to form a complicated shape during hot forging.

In the alloy composition of the cast material obtained by the manufacturing method of the present embodiment, the precipitation of Ni is difficult to proceed, and the cast material has a preferable Ni solid solution state formed during continuous casting (that is, Ni precipitates as Al ₃ Ni _2). (A solid solution state that has not been formed) partially remains even after hot forging and after heat treatment. Therefore, a forged piston having excellent high-temperature mechanical strength can be obtained by subjecting the shaped material to final finishing.

  As a method for producing a continuous cast material, any of the known hot-top continuous casting method, vertical continuous casting method, horizontal continuous casting method, and DC casting method can be used.

The continuous cast material is desirably a thin rod-shaped continuous cast material having a solid solution state in which Ni contained in the continuous cast material is not precipitated as Al ₃ Ni ₂ . By continuously casting a molten aluminum alloy having a predetermined composition at a casting speed of 150 to 300 mm / min and a diameter of a continuous casting material of 50 to 90 mm, Ni is rapidly solidified. Since a solid solution state is ensured, a continuous cast material having a preferable Ni solid solution state (that is, a solid solution state in which Ni is not precipitated as Al ₃ Ni ₂ ) can be reliably obtained.

In particular, when the diameter of the continuous casting material is D (m) and the casting speed is V (m / min), the molten metal supply amount C (m ³ / min) per minute defined by D ² V = C is It is desirable to cast the molten metal in the range of 1 to ³ m ³ / min. This makes it possible to more reliably obtain a continuous cast material having a preferable Ni solid solution state.

  Next, a method of manufacturing a continuous cast material of the present embodiment in the case of manufacturing a continuous cast material by a hot-top vertical continuous casting method will be described below with reference to FIG.

  In the figure, reference numeral 11 denotes a molten metal receiving tank to which a molten metal M of an aluminum alloy is supplied, and an outlet 12 through which the molten metal M flows out is provided at a lower side. Reference numeral 21 denotes a mold, which has a cylindrical inner peripheral surface 22 for casting the molten metal M, which is attached to the lower side of the molten metal receiving tank 11 in an airtight state and communicates coaxially with the outlet 12.

  Reference numeral 31 denotes a cooling medium flow path, which is constituted by an annular flow path portion 31a provided so as to circulate in the mold 21 and an introduction portion 31b for communicating the annular flow path portion 31a to the outside of the mold 21. Is supplied as a cooling medium for cooling the water. Reference numeral 32 denotes an ejection hole, which is communicated with the annular flow path portion 31a so that water W as a cooling medium can be sprayed on the outer periphery of the ingot I to cool the ingot I, and a plurality of Alternatively, it is provided so as to be circulated.

  Reference numeral 33 denotes a gas flow path, and an annular flow path portion 33a provided around the mold 21 so as to supply gas, for example, air A, to a joint portion of the cylindrical inner peripheral surface 22 with the molten metal receiving tank 11, And an introduction portion 33b for communicating the annular flow path portion 33a to the outside. Reference numeral 34 denotes a lubricant flow path, and an annular flow path portion 34a provided around the mold 21 so as to supply a liquid lubricant (eg, lubricating oil) O to the cylindrical inner peripheral surface 22; And an introduction portion 34b for communicating the flow path portion 34a to the outside.

  Next, a casting method will be described. The molten metal M adjusted to a desired composition is supplied to the molten metal receiving tank 11. Then, the molten metal M having a casting temperature of 750 ° C. ± 50 ° C. is primarily cooled by the water W supplied to the cooling medium channel 31 while being extruded from the outflow port 12 into the mold 21, Is cooled by a cooling rate of 10 ° C./sec or more, more preferably at a cooling rate of 20 ° C./sec or more, and solidified, thereby forming an ingot I. .

  The ingot I is continuously drawn downward by lowering a bottom plate (not shown) supporting the ingot I at a constant speed, that is, at a casting speed of 240 ± 50 mm / min. Then, when the length of the ingot I reaches a certain length, the casting is interrupted to obtain a round bar-shaped continuous cast material, and the continuous cast material is drawn upward. In this way, the molten metal M is cast to successively produce a round bar-shaped continuous cast material.

  The air A supplied to the gas flow path 33 at the time of casting is supplied to the cylindrical inner peripheral surface 22 of the mold 21 and has a function of cutting off the contact between the mold 21 and the molten metal M. Then, the excess air A flows downward between the mold 21 and the ingot I. Further, the lubricant O supplied to the lubricant flow path 34 is supplied to the cylindrical inner peripheral surface 22 of the mold 21 to prevent seizure of the molten metal M on the cylindrical inner peripheral surface 22, evaporate, and vaporize the mold 21. Has the function of cutting off the contact between the metal and the molten metal M. By the air A and the lubricant O, an ingot I (that is, a continuous cast material) having a sound casting surface is obtained.

  If the casting temperature is lower than 700 ° C., the temperature of the molten metal M before casting is low, the temperature gradient during solidification becomes gentle, and the crystal grains coarsened in the molten metal M held at a high temperature are cast as it is. In addition, a floating crystal in which coarse crystal grains exist in a part of the ingot I is generated. On the other hand, when the casting temperature exceeds 800 ° C., the temperature gradient at the time of solidification becomes steep, and the effect of the refining material is reduced. Therefore, the crystal grain size of feathered crystals becomes larger than that of ordinary granular crystals. , Strength and ductility decrease. Therefore, the casting temperature is preferably 750 ° C. ± 50 ° C., more preferably 750 ° C. ± 20 ° C., and even more preferably 750 ° C.

  In FIG. 4, the cooling water for forced cooling of the mold 21 and the cooling water for forced cooling of the ingot I are supplied through the cooling medium flow path 31, but the cooling water may be separately supplied. it can.

  The material of the mold 21 is preferably one or a combination of two or more selected from aluminum, copper, and alloys thereof. A combination of materials can be selected from the viewpoint of thermal conductivity, heat resistance, and mechanical strength.

  The composition ratio of the alloy components of the molten metal M can be confirmed, for example, by a method using a photoelectric photometric emission spectrometer (apparatus example: PDA-5500 manufactured by Shimadzu Corporation) as described in JIS H 1305.

  As the lubricant, a vegetable oil which is a lubricating oil can be used. For example, rapeseed oil, castor oil, and salad oil can be mentioned. It is preferable because the adverse effect on the environment is small.

  The supply amount of the lubricant is preferably 0.05 to 5 mL / min (more preferably 0.1 to 1 mL / min).

  The amount of water jetted as a cooling medium is preferably 5 to 30 L / min (more preferably 25 to 30 L / min) per mold.

  The average temperature of the molten metal M flowing into the mold 21 from the molten metal receiving tank 11 is the liquidus temperature of the aluminum alloy + 40 ° C. to + 230 ° C. (more preferably the liquidus temperature + 60 ° C. to + 200 ° C., further preferably the liquidus temperature + 60 ° C. to + 150 ° C.). ° C).

  By continuously casting the molten metal M under these casting conditions, a continuous cast material having a preferable Ni solid solution state can be obtained more reliably. This is preferable because the effects of each subsequent heat treatment for controlling the Ni solid solution state to be maintained are effectively exhibited.

  The obtained continuous cast material is homogenized at the above-mentioned predetermined homogenizing temperature and cut into a predetermined length to obtain a disc-shaped or column-shaped forging material. Thereafter, the material is preheated at the above-mentioned predetermined preheating temperature. Note that the homogenization process can be omitted as described above.

When the material subjected to the pre-heat treatment (homogenization treatment, pre-heating) is subjected to hot forging, the preferable Ni solid solution state formed at the time of continuous casting partially remains after the hot forging and after the post heat treatment. A shaped material is obtained. This preferred Ni solid solution state acts as resistance to deformation of the aluminum fabric at high temperatures, and as a result, excellent mechanical strength is obtained even at high temperatures of 300 ° C or more (more than 300 ° C) and 400 ° C or less. can get. That is, a preferable Ni solid solution state at a high temperature at which the aluminum material softens becomes a resistance to deformation, so that a cast material excellent in high-temperature mechanical strength can be obtained. On the other hand, if the pre-heat treatment temperature (homogenization treatment temperature, pre-heating temperature) is higher than the upper limit of the above-mentioned predetermined range, the preferable Ni solid solution state is lost, and Ni precipitates as Al ₃ Ni ₂ . As a result, the resistance to deformation of the aluminum fabric at high temperature in the Ni solid solution state is reduced, and the high-temperature mechanical strength cannot be increased.

  That is, the cast material of the present embodiment has the above-described alloy composition, and is deformed in a high temperature range of more than 300 ° C. and 400 ° C. or less where the aluminum material is softened and very easily deformed. The high temperature mechanical strength is enhanced by leaving a Ni solid solution state that resists the high temperature.

  The aluminum alloy disclosed in Japanese Patent Application Laid-Open No. 2002-294383 belongs to the 6000 series alloy, and the purpose of suppressing the homogenization treatment temperature or omitting the homogenization treatment is to provide high-temperature characteristics. It is not to obtain, but to improve the mechanical properties at room temperature by suppressing recrystallization. Further, the aluminum alloy of the publication is different from the aluminum alloy of the present embodiment in the alloy system, and the solid solution state of the transition metal that contributes to the high-temperature strength is hardly observed. The invention disclosed in this publication is to lower the temperature of the homogenization treatment and suppress it, thereby precipitating Al-Mn and Al-Cr-based compounds that suppress recrystallization. Therefore, the invention of this publication is different from the present embodiment.

  Furthermore, the invention disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2009-191367 (Patent Document 1) listed as a prior art document is intended to maintain a network structure of crystallized substances and intermetallic compounds that can be observed with an optical microscope. First, a pre-heat treatment step is performed at a low temperature. Therefore, the invention of the publication is different from the present invention.

  In the present embodiment, the pre-heat treatment step (homogenization treatment, pre-heating treatment) may be provided between after the casting and before the hot forging step. For example, a pre-heat treatment step is performed within one day after casting, and a hot forging step is performed within one week after performing the pre-heat treatment step. In the meantime, a straightening step and a peeling step are performed as necessary.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be variously modified without departing from the gist of the present invention.

  Next, specific examples and comparative examples of the present invention are shown below. However, the present invention is not limited to the following examples.

  Continuous cast materials of aluminum alloys A to G having the compositions shown in Table 1 were prepared. The manufacturing method is as follows.

  A melt of an aluminum alloy having the composition shown in Table 1 was vertically and continuously cast by a gas pressurized hot-top continuous casting apparatus at a casting temperature of 800 ° C. or more and a casting speed of 200 mm / min. A round bar-shaped continuous cast material was obtained. The composition analysis of the aluminum alloy was performed by emission analysis.

When the X-ray diffraction analysis of the continuous cast material was performed, no diffraction peak corresponding to Al ₃ Ni ₂ was found in any case.

  Further, the continuous cast material was measured by a differential scanning calorimeter, and the exothermic peak temperature Tn (° C.) first observed at the time of temperature rise in a high temperature region of 400 ° C. or higher in the DSC curve was examined. The results are shown in the “Tn (° C.)” column in Table 1. Here, the exothermic peak was not observed in the continuous cast material of the alloy G. It is presumed that the reason for this is that the Ni content is small and the continuous cast material of the alloy G does not have a favorable Ni solid solution state.

  Next, the continuous cast material was homogenized. The homogenization temperature applied at that time is shown in the column of "homogenization temperature" in Table 2. The holding time at the homogenization temperature was 4 to 12 hours. Here, in Example 9, the continuous cast material was not homogenized.

  Thereafter, the continuous cast material was roll-corrected by a roll straightening machine to remove the bending of the continuous cast material.

  Next, the outer peripheral portion of the continuous cast material was cut and removed by a lathe machine, thereby reducing the diameter of the continuous cast material to 80 mm.

  Thereafter, the continuous cast material was cut into a predetermined length by a cutting machine, thereby obtaining a material for forging.

  Next, the material was preheated in a gas atmosphere furnace. The preheating temperature applied at this time is shown in the column of "Preheating temperature" in Table 2. The holding time of the preheating temperature was 20 minutes. In Comparative Examples 2 and 3, the raw material was not preheated, and further, hot forging, water quenching (solution treatment), and aging treatment described below were not performed.

  Then, the raw material was hot forged into a piston shape by a closed hot forging device to obtain a piston raw material. The forging temperature of the material applied at that time is shown in the “forging temperature” column in Table 2. The mold temperature at that time was 420 ° C. Prior to forging the material, a graphite-based lubricant was applied to the mold in advance. In Comparative Example 4, the material preheated to 490 ° C. was air-cooled and hot forged at 450 ° C. before forging.

  Immediately after hot forging, the temperature of the cast material was lower by 10 ° C. than the forging temperature due to the effect of heat removal to the mold.

  Then, the shaped material is immersed in water (water temperature 40 ° C.) in a water tank installed adjacent to the side of the closed hot forging device within 10 seconds from the time when the material is hot forged and water-quenched. did. In Example 6, the cast material was heated again to raise the temperature to 490 ° C., and then the cast material was water-quenched.

  Next, the cast material was drained by air blow, and thereafter, the cast material was subjected to aging treatment in an aging furnace. The aging treatment temperature applied at that time is shown in the “aging temperature” column in Table 2. After the aging treatment, the shaped material was taken out of the aging furnace and air-cooled to approximately room temperature.

  Thereafter, the cast material was subjected to a tensile test at a temperature of 300 ° C., thereby evaluating the high-temperature strength of the cast material at 300 ° C. The results are shown in the column of “Tensile strength at 300 ° C.” in Table 2.

  The meanings of the symbols in the same column are as follows.

  “○”: The tensile strength at 300 ° C. was 75 MPa or more, and the tensile strength ratio at 300 ° C. to the continuous cast material before the homogenization treatment was 0.9 or more.

  “×”: The tensile strength at 300 ° C. was less than 75 MPa, and / or the tensile strength ratio at 300 ° C. to the continuous cast material before the homogenization treatment was less than 0.9.

  As can be seen from the column “Tensile strength at 300 ° C.” in Table 2, the cast materials in Examples 1 to 9 all had high high-temperature strength (tensile strength). On the other hand, in each of Comparative Examples 1 to 6, the high-temperature strength (tensile strength) of the cast material was low.

  INDUSTRIAL APPLICATION This invention is applicable to the manufacturing method of the forged piston used for an internal combustion engine etc.

M: Molten metal I: Ingot (continuous cast material)

Claims (6)

Si: 9 to 14% by mass,
Fe: 0.15 to 0.8% by mass;
Cu: 2 to 6% by mass;
Mg: 0.3 to 1.0% by mass, and Ni: 1 to 5.5% by mass.
Including, a step of preparing a forging material composed of an aluminum alloy continuous cast material having a composition consisting of unavoidable impurities and aluminum,
When the first exothermic peak temperature of 400 ° C. or more of the material measured by the differential scanning calorimeter is Tn ° C.,
Pre-heating the material at a pre-heating temperature of 300 ° C. to {Tn + 30 ° C .;
Obtaining a raw material for a piston by hot forging the material at a forging temperature of 300 ° C. to {Tn + 30} ° C. after the preheating step;
A step of water quenching while maintaining the shaped material at a temperature of 420 ° C. to {Tn + 30 ° C .;
Aging the shaped material at an aging temperature of 180 ° C. to 230 ° C. after the water quenching step. Before the preheating step, a step of homogenizing the material at a homogenization processing temperature of {Tn + 30} ° C or lower,
The method for manufacturing a forged piston according to claim 1, wherein the preheating step is performed after the homogenizing step. The composition further comprises:
Ti: 0.05 to 0.2% by mass
The method for manufacturing a forged piston according to claim 1 or 2, comprising: The composition further comprises:
B: 0.01 to 0.1% by mass
The method for producing a forged piston according to claim 1, comprising: In the preheating step, the material is preheated at a preheating temperature of 450 ° C. to {Tn + 30} ° C.,
In the step of obtaining the shaped material, using a forging die having a temperature of 400 ° C. to {Tn + 30 ° C., the temperature of the material is reduced to less than 30 ° C. due to heat removal from the material to the forging die. The method for manufacturing a forged piston according to any one of claims 1 to 4, wherein the shaped material having a temperature of 420C to {Tn + 30} C is obtained by hot forging.   The method for manufacturing a forged piston according to any one of claims 1 to 5, wherein, in the water quenching step, the shaped material is water quenched within 10 seconds after hot forging the material.