JP2025070094A - Manufacturing method of Mg alloy material, manufacturing method of Mg alloy member, Mg alloy material and Mg alloy member - Google Patents

Abstract

The present invention provides a method for producing an Mg alloy material having excellent heat resistance and mechanical strength.
[Solution] A method for producing an Mg alloy material includes a preparation step of preparing an alloy material for processing containing first particles of _Mg2Si , a refining step of refining the alloy material for processing to obtain alloy flakes, and an Mg alloy material production step of molding the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of _Mg2Si .
[Selected Figure] Figure 1A

Description

The present invention relates to a method for producing an Mg alloy material, a method for producing an Mg alloy part, an Mg alloy material, and an Mg alloy part.

As a lightweight material, Mg alloys are being considered for various applications. One such application is transportation equipment, and in particular, their application to engine components is expected to improve the fuel efficiency of transportation equipment. Various manufacturing methods have been proposed for Mg alloys in order to obtain the desired properties.

Patent Document 1 describes an Mg-Si alloy chip having fine primary crystals of Mg2Si, which is obtained by rapidly solidifying a molten alloy containing 1 to 18% by weight of silicon, ₁₂ % by weight or less of at least one of aluminum, zinc and silver, and the remainder being magnesium.

Patent document 2 describes a manufacturing method for magnesium alloys in which additive components for improving material quality are added during the manufacturing stage, the method including a silicon addition process in which silicon is added as an additive component to a specified magnesium alloy, and a particle dispersion process in which the Mg ₂ Si compound produced by the silicon addition process is converted into Mg ₂ Si particles with a particle size of 40 μm or less, the specified magnesium alloy being a flame-retardant magnesium alloy AM602, the amount of silicon added in the silicon addition process being adjusted in the range of 5.0 to 15.0 mass%, converted into the silicon content relative to the mass of the magnesium alloy produced, the silicon addition process being carried out using a casting method, and the particle dispersion process being carried out using an extrusion method as a plastic processing treatment in a temperature range of 200 to 400°C.

JP 2011-074469 A Japanese Patent Publication No. 8-120390

For example, when Mg alloys are used in engine parts, they are expected to improve fuel efficiency. However, it is difficult for Mg alloys containing Mg, which has low heat resistance, to have heat resistance sufficient to withstand the high temperatures inside the engine.
Addition of rare earth elements is considered to be effective in improving the heat resistance of Mg alloys, but rare earth elements are often expensive, and even if rare earth elements are added and used to produce engine pistons by casting, the pistons often do not achieve sufficient mechanical strength to withstand the high temperatures inside the engine.
The present inventors have investigated a method for using as few rare earth metals as possible and have found that the addition of Si is effective.
It is expected that the addition of Si will form _Mg2Si particles and improve the heat resistance of the Mg alloy, but in order to obtain sufficient heat resistance, it is necessary to highly refine the _Mg2Si particles and disperse them highly uniformly.
Furthermore, in the case of Mg alloys containing Si, the viscosity of the molten metal increases due to the presence of Si in the casting process, so the upper limit of the amount of Si added is often about 1 mass %, and as a result, the mechanical strength of the resulting Mg alloy is often insufficient.

The problem that the present invention aims to solve is to provide a method for manufacturing Mg alloy materials and Mg alloy parts that have excellent heat resistance and mechanical strength.

The present invention includes the following aspects.
<1> A method for producing an Mg alloy material, comprising: a preparation step of preparing an alloy material for processing containing first particles of Mg ₂ Si; a refining step of refining the alloy material for processing to obtain alloy flakes; and an Mg alloy material production step of molding the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of Mg ₂ Si.
<2> The method for producing an Mg alloy material according to <1>, wherein the Mg alloy material production process includes a step of forming a preform by molding the alloy flakes by a hot press method, and a step of producing an Mg alloy material by extruding the preform at 300°C or higher.
<3> The method for producing an Mg alloy material according to <1> or <2>, wherein the pressure in the hot pressing method is 50 MPa to 300 MPa.
<4> The method for producing an Mg alloy material according to any one of <1> to <3>, wherein the temperature in the hot pressing method is 300°C to 700°C.
<5> The method for producing an Mg alloy material according to any one of <1> to <4>, wherein the average particle size of the second particles of Mg ₂ Si is 1.0 μm to 50.0 μm.
<6> The method for producing an Mg alloy material according to any one of <1> to <5>, wherein the Mg alloy material contains a matrix, and the crystal grain size of the matrix is 2.0 μm to 80.0 μm.
<7> The method for producing an Mg alloy material according to any one of <1> to <6>, wherein the Mg alloy material has a thermal conductivity of 100 W/m·K or less at 300° C.
<8> A method for manufacturing an Mg alloy part, comprising: a preparation step of preparing an alloy material for processing containing first particles of Mg ₂ Si; a refinement step of refinement of the alloy material for processing to obtain alloy flakes; an Mg alloy material production step of molding the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of Mg ₂ Si; and a forging step of forging the Mg alloy material to obtain an Mg alloy part.
<9> A Mg alloy material which is a compact of alloy flakes which are finely divided pieces of an alloy material for processing containing first particles of Mg ₂ Si, and which contains second particles of Mg ₂ Si.
<10> A Mg alloy part which is a forging of the Mg alloy material according to <9>.

The present invention provides a method for producing Mg alloy materials and Mg alloy parts that have excellent heat resistance and mechanical strength.

1 is a schematic diagram showing a working alloy material before undergoing a refinement process in this embodiment. FIG. 2 is a schematic diagram showing the alloy material for processing and the alloy flakes after the refinement process in this embodiment. FIG. FIG. 2 is an optical microscope diagram of the Mg alloy material of Comparative Example 1. FIG. 2 is an optical microscope diagram of the Mg alloy material of Example 1.

Hereinafter, an embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail.
It should be noted that the following embodiment is merely an example for explaining the present invention, and the present invention is not limited to the following embodiment. The present invention can be practiced with appropriate modifications within the scope of the gist thereof.
In the present embodiment, the numerical range indicated using "to" means a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the numerical ranges described in this embodiment, the upper limit or lower limit of a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described in a stepwise manner. In addition, in the numerical ranges described in this disclosure, the upper limit or lower limit of a certain numerical range may be replaced with a value shown in the examples.
In this embodiment, a combination of two or more preferred aspects is a more preferred aspect.
In this embodiment, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances, unless otherwise specified.

<Method for manufacturing Mg alloy material>
The manufacturing method of the Mg alloy material of this embodiment (also simply referred to as the manufacturing method of this embodiment in this specification) includes a preparation process of preparing an alloy material for processing containing first particles of Mg ₂ Si, a refining process of refining the alloy material for processing to obtain alloy flakes, and an Mg alloy material manufacturing process of molding the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of Mg ₂ Si.

In the manufacturing method of the present embodiment, an alloy material for processing containing first particles of _Mg2Si is refined to obtain alloy flakes, and then the alloy flakes are solidified and molded by hot pressing to produce an Mg alloy material in which fine second particles of _Mg2Si are uniformly dispersed. As a result, the obtained Mg alloy material has excellent heat resistance and mechanical strength.
The Mg alloy material in this embodiment can be suitably used as a precursor for producing a member by a forging method.

Furthermore, the manufacturing method of this embodiment allows the amount of Si to be set to a relatively large amount. In Mg alloy materials obtained by casting, the addition of a large amount of Si tends to cause aggregation and reduce dispersibility, and the mechanical strength of the obtained Mg alloy material tends to decrease, especially in high temperature regions. Since the manufacturing method of this embodiment includes a refinement step, Mg ₂ Si particles can be uniformly dispersed in the obtained Mg alloy material even if a relatively large amount of Si is added. Therefore, the mechanical strength is excellent.
Furthermore, when an Mg alloy material is manufactured from rapidly cooled powder produced by gas atomization, for example, the strength at high temperatures decreases because not only the _Mg2Si particles but also the crystal grain size of the matrix Mg alloy becomes fine grains of 1 μm or less. However, the Mg alloy material manufactured by the manufacturing method of this embodiment does not have such a drawback and has excellent mechanical strength.
In this embodiment, the matrix means the base structure that is the main component of the Mg alloy material, and the matrix can affect the properties of the Mg alloy material.

The manufacturing method of this embodiment is also superior in terms of cost, since it does not require expensive equipment. Furthermore, although the alloy flakes in the manufacturing method of this embodiment contain Mg alloy, which is an active material, there is no risk of explosion, as there is with rapidly cooled powders produced by gas atomization, for example, so it is also superior in safety.

In addition, since the manufacturing method of this embodiment uses alloy flakes, it can be used in areas where the alloy material to be processed (e.g., billet) has shrinkage cavities. Furthermore, when cutting is performed to process Mg alloy material into components such as pistons, the alloy flakes generated during this process can be reused as raw material for Mg alloy material, resulting in excellent yields. In addition, used components such as pistons can be re-cut into alloy flakes, which can be molded into components again, resulting in excellent recyclability.

<Preparation process>
The preparing step is a step of preparing an alloy material for processing that includes first particles of Mg ₂ Si.
The wrought alloy material may be commercially available or may be manufactured.

(Method of manufacturing alloy material for processing)
The preparation step may be a step of producing a wrought alloy material containing first particles of Mg ₂ Si by melting a mixture containing an Mg alloy and Si in an inert gas atmosphere and casting the resulting melt.

(Mixture)
The mixture contains an Mg alloy and Si. The mixture may also contain other components as necessary.

[Mg alloy]
The Mg alloy refers to an alloy containing Mg as the main component.
An alloy containing Mg as a main component means an alloy in which the Mg content is 50 mass % or more with respect to the total mass of the alloy.

[Mg]
The Mg alloy contains Mg as a main component.
The Mg content is preferably 60 mass % to 99 mass % based on the total mass of the Mg alloy.
By making the Mg content 60 mass % or more relative to the total mass of the Mg alloy, the mass of the Mg alloy material can be reduced.
From the above viewpoints, the Mg content is more preferably 70 mass % or more, and further preferably 80 mass % or more, based on the total mass of the Mg alloy.
When the Mg content is 99 mass % or less based on the total mass of the Mg alloy, the Mg alloy material has excellent heat resistance and mechanical strength.
From the above viewpoints, the Mg content is more preferably 97 mass % or less, and further preferably 95 mass % or less, based on the total mass of the Mg alloy.

[Other elements]
The Mg alloy in this embodiment further contains elements other than Mg.
As another element, the Mg alloy preferably further contains at least one element selected from the group consisting of Al, Zn, Ca, Mn, Ag, Cu, B and Ni.
More preferably, the Mg alloy further contains at least one element selected from the group consisting of Al, Zn, and Ca.

From the viewpoint of reducing the mass of the Mg alloy material, the content of the elements other than Mg is preferably 1 mass% to 20 mass%, more preferably 3 mass% to 17 mass%, and even more preferably 7 mass% to 15 mass%, in total relative to the total mass of the Mg alloy.
When the content of elements other than Mg is equal to or greater than the lower limit, the Mg alloy material has excellent heat resistance and mechanical strength. When the content of elements other than Mg is equal to or less than the upper limit, the mass of the Mg alloy material can be reduced.

When the Mg alloy further contains Al, the content of Al is preferably 3 mass% to 20 mass%, more preferably 5 mass% to 15 mass%, and further preferably 7 mass% to 12 mass%, based on the total mass of the Mg alloy.
When the content of Al is equal to or more than the lower limit, the strength can be improved, whereas when the content of Al is equal to or less than the upper limit, the heat resistance is excellent.

When the Mg alloy contains Zn, the Zn content is preferably 0.1% to 5% by mass, more preferably 0.3% to 3% by mass, and even more preferably 0.5% to 2% by mass, based on the total mass of the Mg alloy.

When the Mg alloy contains calcium, the calcium content is preferably 0.1 mass % to 10 mass %, and more preferably 1 mass % to 7 mass %, based on the total mass of the Mg alloy.
When the calcium content is within the above range, the resulting Mg alloy has excellent flame retardancy.

As the Mg alloy, a ready-made product may be used.
Examples of ready-made products include Mg-Al-Zn based alloys (AZ type) such as AZ92, AZ91, AZ80, AZ63, AZ61, and AZ31; Mg-Al based alloys (AM type) such as AM100, AM60, AM50, and AM20; Mg-Al-Si based alloys (AS type) such as AS41 and AS21; Mg-Al-RE based alloys (AE type) such as AE42; Mg-Zn-Zr based alloys (ZK type) such as ZK51 and ZK61; and ZC63. Mg-Cu-Zn-based alloys (ZC system) such as ZE41, ZE61, etc.; Mg-Zn-RE-Zr-based alloys (ZE system) such as QE22, etc.; Mg-Y-RE-based alloys (WE system) such as WE43, WE54, etc.; Mg-Al-Zn-Ca-based alloys (AZX system) such as AZX612, AZX912, etc.; Mg-Al-Ca-based alloys (AMX system) such as AMX602, AMX602, etc.
Among the above, AZX912 (Mg-9% Al-1% Zn-2% Ca) is preferable as a ready-made Mg alloy.

The content of the Mg alloy is preferably 60 mass % to 97 mass %, more preferably 70 mass % to 95 mass %, and further preferably 80 mass % to 93 mass %, based on the total mass of the mixture.
By setting the content of Mg alloy to be equal to or more than the lower limit, the mass of the Mg alloy material can be reduced, and by setting the content of elements other than Mg to be equal to or less than the upper limit, the Mg alloy material has excellent heat resistance and mechanical strength.

As a method for producing an Mg alloy, for example, there is a method in which an alloy ingot is produced from raw materials such as Mg, Zn, Al, and Ca, and the ingot is processed into a desired shape.
Specifically, pure metals of various alloy elements are placed in a graphite crucible for melting so as to obtain a desired mass ratio. The graphite crucible for melting is placed inside a high-frequency coil in a high-frequency melting furnace chamber, and a mold is placed in front of the high-frequency coil. The high-frequency melting furnace chamber is then filled with helium gas either at atmospheric pressure or after evacuation, and the graphite crucible is heated to 750°C or higher. After confirming that the metals are completely melted, the molten alloy in the graphite crucible is poured into a copper mold, and after cooling, the Mg alloy is obtained from the mold.

[Si]
The mixture includes Si.
The Si content is preferably 1 mass % to 15 mass %, more preferably 3 mass % to 12 mass %, and further preferably 5 mass % to 9 mass %, based on the total mass of the mixture.
When the Si content is equal to or more than the lower limit, the heat resistance is excellent, and when the Si content is equal to or less than the upper limit, the dispersibility of Si is excellent, and the mechanical strength of the Mg alloy material is excellent.

[Sb]
The mixture may further include Sb.
The Sb content is preferably 0.1% by mass to 5% by mass, and more preferably 1% by mass to 4% by mass, based on the total mass of the mixture.

A specific example of a process for producing the above-mentioned alloy material for processing includes, for example, mixing 7.5% by mass of Si and 2% by mass of Sb into an Mg alloy, melting and casting the mixture in an inert gas atmosphere to produce a billet (alloy material for processing) having a diameter of 50 mm containing first particles of Mg ₂ Si.

<Micronization process>
The grain refinement step is a step of refinement of the alloy material to be processed to obtain alloy flakes.
The method for making the particles fine is not particularly limited, and the particles may be cut using a grinder or may be made fine by lathe processing.

There is no particular restriction on the size of the alloy flakes, but the size of the alloy flakes is preferably such that the average particle size of the secondary particles of Mg ₂ Si in the resulting Mg alloy material falls within the range described below.
For example, when the alloy material to be processed is refined using lathe machining, it is preferable to obtain alloy pieces by cutting the end face on the lathe, preferably in increments of 10 μm to 100 μm, more preferably in increments of 20 μm to 80 μm, and even more preferably in increments of 30 μm to 60 μm.

The miniaturization process in this embodiment will be described with reference to FIGS. 1A and 1B.
FIG. 1A is a schematic diagram showing the processed alloy material before the refinement process in this embodiment, and FIG. 1B is a schematic diagram showing the processed alloy material and alloy flakes after the refinement process in this embodiment.
As shown in Figure 1A, the alloy material to be processed before the refinement process includes relatively large first particles of _Mg2Si . By applying a desired refinement method to this alloy material to be processed, an alloy flake as shown in Figure 1B can be obtained. In the obtained alloy flake, the _Mg2Si particles are also refined, and smaller sized _Mg2Si particles can be obtained.

<Mg alloy material manufacturing process>
The Mg alloy material production step is a step of forming alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of Mg ₂ Si.
The hot pressing method is a method of sintering while applying pressure in an atmosphere such as vacuum, air, or an inert gas.

The pressure in the hot pressing method is not particularly limited, but is preferably 50 MPa to 300 MPa, more preferably 70 MPa to 200 MPa, and further preferably 100 MPa to 150 MPa.
When the pressure in the hot pressing method is equal to or higher than the lower limit, excellent forgeability is achieved, and when the pressure in the hot pressing method is equal to or lower than the upper limit, the life of the pressing jig is excellent.

The temperature in the hot pressing method is preferably 300°C to 700°C, more preferably 320°C to 500°C, and further preferably 350°C to 400°C.
Although the above temperature range is relatively high, the Mg alloy material of this embodiment has excellent heat resistance and can therefore be hot pressed satisfactorily even within the above temperature range.

The time for the hot pressing method is preferably 1 to 60 minutes, more preferably 5 to 45 minutes, and even more preferably 10 to 30 minutes.

The Mg alloy material manufacturing process preferably includes a process of forming a preform by molding the alloy pieces by a hot press method (also called a preform forming process), and a process of extruding the preform at 300°C or higher to manufacture the Mg alloy material (also called an extrusion process).

(Preform forming process)
The preform forming step is a step of forming a preform by molding an alloy piece by a hot press method, and by the preform forming step, a preform of an Mg alloy material can be obtained before the extrusion processing step is performed.
In the preform forming step, the preferred ranges of pressure, temperature and time in the hot pressing method are the same as the preferred ranges of pressure, temperature and time in the hot pressing method in the above-mentioned <Mg alloy material manufacturing step>.

(Extrusion process)
The extrusion process is a process in which the preform is extruded at 300° C. or higher to produce an Mg alloy material.

From the viewpoint of ease of extrusion, the temperature in the extrusion process is preferably 330° C. or higher, and more preferably 350° C. or higher.
The temperature in the extrusion process is preferably 500° C. or less, and more preferably 450° C. or less, from the viewpoint of reducing damage to the properties due to coarsening of the structure of the preform.

As an example of the Mg alloy material manufacturing process, the above alloy pieces may be hot pressed in air at 150 MPa, 400°C, and 30 minutes to produce a preform with a diameter of 44 mm and a height of 40 mm, which may then be extruded at 400°C to produce the Mg alloy material.

<Mg alloy material>
The Mg alloy material of this embodiment includes second particles of Mg ₂ Si.
In the Mg alloy material, the secondary particles of Mg ₂ Si are uniformly dispersed, so that the Mg alloy material has excellent heat resistance and mechanical strength.

The Mg alloy material of this embodiment is a compact of alloy flakes that are finely divided pieces of an alloy material for processing that contains first particles of Mg ₂ Si, and may contain second particles of Mg ₂ Si.

Since the manufacturing method of this embodiment includes a refinement process for refinement of the alloy material for processing, it is preferable that the average grain size of the second particles of Mg ₂ Si in the obtained Mg alloy material is smaller than the average grain size of the first particles of Mg ₂ Si in the alloy material for processing.

The average particle size of the secondary particles of Mg ₂ Si is preferably 1.0 μm to 50.0 μm.
When the average particle size of the second particles of Mg ₂ Si is 50.0 μm or less, the dispersibility of the second particles of Mg ₂ Si is excellent, and therefore the mechanical strength of the Mg alloy material is excellent.
From the above viewpoints, the average particle size of the Mg ₂ Si second particles is more preferably 40.0 μm or less, even more preferably 30.0 μm or less, particularly preferably 20.0 μm or less, and even more preferably 10.0 μm or less.
When the average particle size of the secondary particles of Mg ₂ Si is 1.0 μm or more, the mechanical strength of the Mg alloy material is excellent.
From the above viewpoints, the average particle size of the second particles of Mg ₂ Si is more preferably 2.0 μm or more, and further preferably 3.0 μm or more.

The average particle size of the Mg ₂ Si first particles may be 30.0 μm to 100.0 μm, or 50.0 μm to 80.0 μm.

The Mg alloy material may include a matrix.
In this case, the crystal grain size of the matrix is preferably 2.0 μm to 80.0 μm.
By setting the crystal grain size of the matrix to 80.0 μm or less, the dispersibility of the secondary particles of Mg ₂ Si is excellent, and therefore the mechanical strength of the Mg alloy material is excellent.
From the above viewpoints, the crystal grain size of the matrix is more preferably 60.0 μm or less, further preferably 40.0 μm or less, particularly preferably 20.0 μm or less, and even more preferably 10.0 μm or less.
When the crystal grain size of the matrix is 2.0 μm or more, the Mg alloy material has excellent mechanical strength at high temperatures.
From the above viewpoints, the crystal grain size of the matrix is more preferably 3.0 μm or more, further preferably 4.0 μm or more, and particularly preferably 5.0 μm or more.

The average grain size of the Mg ₂ Si particles and the crystal grain size of the matrix are measured by an intercept method in accordance with ASTM E112-60T.
Specifically, five straight lines with a total length L are drawn on the cross section of the sample observed under an optical microscope, the number n of crystal grains that cross these lines is found, and the average grain size d is calculated by the following formula: The average value of the five ds thus obtained is the average grain size of the _Mg2Si grains and the grain size of the matrix.
d = L / n

The Mg alloy material preferably has a thermal conductivity of 100 W/m·K or less at 300° C. Since the thermal conductivity at 300° C. is 100 W/m·K or less, the Mg alloy material can be suitably used for pistons of engines that use fuels such as bio-methanol and hydrogen.
The thermal conductivity of the Mg alloy material at 300° C. is preferably 90 W/m·K or less, more preferably 80 W/m·K or less, and even more preferably 70 W/m·K or less.
In addition, although there is no particular restriction on the lower limit of the thermal conductivity at 300°C, the thermal conductivity of the Mg alloy material at 300°C is preferably 10 W/m·K or more, more preferably 20 W/m·K or more, and even more preferably 40 W/m·K or more.

The thermal conductivity at each given temperature is calculated from the following formula.
Thermal conductivity at each temperature = λT CpT dT (formula)
λT: Thermal diffusivity at each temperature measured by the laser flash method CpT: Specific heat capacity dT: Room temperature density (d0) measured by the Archimedes method, and density at each temperature obtained from the volume change at each temperature measured by a thermal dilatometer

<Method for manufacturing Mg alloy member>
The manufacturing method of the Mg alloy part in this embodiment includes a preparation process of preparing an alloy material for processing containing first particles of _Mg2Si , a refining process of refining the alloy material for processing to obtain alloy flakes, an Mg alloy material manufacturing process of molding the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of _Mg2Si , and a forging process of forging the Mg alloy material to obtain an Mg alloy part.

The manufacturing method of the Mg alloy part of this embodiment is a method of manufacturing an Mg alloy part using the Mg alloy material of this embodiment by performing a forging process following the manufacturing method of the Mg alloy material of this embodiment. Therefore, the details of the specific aspects and preferred aspects of each step in the manufacturing method of the Mg alloy part are the same as the details of the specific aspects and preferred aspects of each step described in the above section "Manufacturing method of the Mg alloy material".

<Mg alloy member>
The Mg alloy part of this embodiment is a forging of the Mg alloy material of this embodiment.
The Mg alloy material in this embodiment can be suitably used for forging, and the resulting Mg alloy part has excellent heat resistance and mechanical strength because it contains the Mg alloy material including the uniformly dispersed second particles of _Mg2Si .

The present embodiment will be described in more detail below with reference to specific examples and comparative examples, but the present invention is not limited in any way to the following examples and comparative examples.

[Example 1]
(Preparation process)
A mixture of 7.5 mass% Si and 2 mass% Sb was obtained by mixing AZX912 (Mg-9%Al-1%Zn-2%Ca), which is a flame-retardant Mg alloy, and then the mixture was melted and cast in an inert gas atmosphere to produce a billet (cast material) of φ50 mm.

(Micronization process)
Thereafter, the end face of the billet was cut by 40 μm at a time using a lathe to produce alloy pieces.

(Mg alloy material manufacturing process)
The alloy pieces were hot pressed in air at 150 MPa, 400° C. for 10 minutes to produce preforms with a diameter of 44 mm and a height of 40 mm, which were then extruded at 400° C. to produce Mg alloy materials.

[Comparative Example 1]
A cast material obtained by the method described in (Preparation step) of Example 1 was used as the Mg alloy material.
FIG. 2A shows an optical microscopic structure diagram of the Mg alloy material of Comparative Example 1, and FIG. 2B shows an optical microscopic structure diagram of the Mg alloy material of Example 1.

(evaluation)
[Particle size measurement]
In the Mg alloy materials of the examples and comparative examples, the grain sizes of the matrix and Mg ₂ Si grains were measured by an intercept method in accordance with ASTM E112-60T. The results are shown in Table 1.

As shown in Table 1, the Mg alloy material of Example 1 obtained by the manufacturing method of an Mg alloy material including a preparation process of preparing an alloy material for processing containing first particles of Mg ₂ Si, a refinement process of refinement of the alloy material for processing to obtain alloy flakes, and an Mg alloy material manufacturing process of molding the alloy flakes by a hot press method to manufacture an Mg alloy material containing second particles of Mg ₂ Si had smaller crystal grain sizes of both the Mg ₂ Si particles (second particles of Mg ₂ Si) and the matrix in the Mg alloy material compared to the Mg alloy material of Comparative Example 1, which is a cast material.

[Thermal conductivity]
The thermal conductivity at each given temperature was calculated from the following formula.
Thermal conductivity at each temperature = λT CpT dT (formula)
λT: thermal diffusivity at each temperature measured by the laser flash method CpT: specific heat capacity dT: room temperature density (d0) measured by the Archimedes method, and density at each temperature obtained from the volume change at each temperature measured by a thermal dilatometer. The results are shown in Table 2.

As shown in Table 2, the Mg alloy material of Example 1 had a sufficiently low thermal conductivity at 300°C. For this reason, the Mg alloy material of this embodiment can be suitably used for pistons of engines that use fuels such as biomethanol and hydrogen.

[Heat resistance and strength]
After obtaining stress-strain curves at each temperature by the compression test, the stress at which the plastic deformation amount reached 0.2% (also called 0.2% yield strength) was measured. The results are shown in Table 3.
The higher the 0.2% yield strength, the better the strength.

As shown in Table 3, the Mg alloy materials of the examples had superior 0.2% yield strength values at 25°C to 300°C compared to the Mg alloy material of Comparative Example 1, which was a cast material. Therefore, the Mg alloy materials of the examples had superior mechanical strength in the low to high temperature ranges.
In addition, the Mg alloy material of the embodiment had a superior 0.2% yield strength value at 300°C compared to the Mg alloy material of Comparative Example 1, and therefore had excellent mechanical strength in the high temperature range and also excellent heat resistance.

Claims (10)

A preparation step of preparing a wrought alloy material comprising first particles of _Mg2Si ;
a refining step of refining the alloy material to obtain alloy flakes;
a Mg alloy material production step of forming the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of _Mg2Si ;
A method for producing an Mg alloy material comprising the steps of: The Mg alloy material manufacturing process includes:
forming the alloy flakes into a preform by hot pressing;
extruding the preform at 300° C. or higher to produce an Mg alloy material;
The method of claim 1 comprising the steps of: The method for producing Mg alloy material according to claim 1 or 2, wherein the pressure in the hot pressing method is 50 MPa to 300 MPa. The method for producing Mg alloy material according to claim 1 or 2, wherein the temperature in the hot pressing method is 300°C to 700°C. 3. The method for producing an Mg alloy material according to claim 1, wherein the average particle size of the second particles of Mg ₂ Si is 1.0 μm to 50.0 μm. the Mg alloy material comprises a matrix;
The method for producing an Mg alloy material according to claim 1 or 2, wherein the crystal grain size of the matrix is 2.0 μm to 80.0 μm. The method for producing an Mg alloy material according to claim 1 or 2, wherein the Mg alloy material has a thermal conductivity of 100 W/m·K or less at 300°C. A preparation step of preparing a wrought alloy material comprising first particles of _Mg2Si ;
a refining step of refining the alloy material to obtain alloy flakes;
a Mg alloy material production step of forming the alloy flakes by a hot pressing method to produce an Mg alloy material containing second particles of _Mg2Si ;
a forging step of forging the Mg alloy material to obtain an Mg alloy part;
A method for producing an Mg alloy part comprising the steps of: The alloy flakes are formed into a compact, which is a finely divided alloy material for processing, and includes first particles of _Mg2Si ;
A Mg alloy material comprising second particles of _Mg2Si . A Mg alloy part which is a forged product of the Mg alloy material according to claim 9.