MEDIUM ENTROPY ALLOYS AND METHODS OF PREPARING THE SAME

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2024-0046146 filed with the Korean Intellectual Property Office on Apr. 4, 2024, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a medium entropy alloy and a manufacturing method thereof, and more specifically, to a medium entropy alloy and a manufacturing method thereof capable of improving the tensile characteristics of an alloy by refining the multiphase of the medium entropy alloy.

(b) Description of the Related Art

A typical metal alloy is composed of a major element and a small amount of alloying elements. As the alloying elements are added, the possibility of forming an intermetallic compound increase. The intermetallic compound can weaken the mechanical properties, such as causing brittleness of the material.

High-entropy alloys (HEAs) and medium-entropy alloys (MEAs) are multi-element alloys that have a plurality of elements as their main elements, unlike conventional alloys that are composed of a main element and other elements. Since high-entropy alloys and medium-entropy alloys have a plurality of elements as their main elements, they can dramatically increase the number of alloys that can be designed compared to existing alloys, and since they contain equivalent plurality of alloy elements, they have high solute efficiency. In addition, the high-entropy alloys and medium-entropy alloys also exhibit excellent mechanical properties utilizing multiple and synergistic strengthening mechanisms including deformation twinning-induced plasticity (TWIP), transformation-induced plasticity (TRIP), grain boundary strengthening, dislocation density strengthening, and precipitation hardening.

Conventional alloys are divided into high-entropy alloys, medium-entropy alloys (MEAs), and low-entropy alloys (LEAs) according to the compositional entropy (ΔSconf) of the alloy system obtained by the following relationship equation 1. If [Configurational Entropy≥1.5 R], it is classified as a high-entropy alloy, if [1.5 >Configurational Entropy≥1.0 R], it is classified as a medium-entropy alloy, and if [1.0 R>Configurational Entropy], it is classified as a low-entropy alloy.

Δ ⁢ S conf = - R ⁢ ∑ i = 1 n X i ⁢ ln ⁢ X i [ Relationship ⁢ equation ⁢ 1 ]

(R: gas constant, Xi: mole fraction of i element, n: number of constituent elements)

In the case of conventional high-entropy alloys and medium-entropy alloys, expensive constituent elements such as Co, Cr, Fe, Mn, and Ni-based FCC high-entropy alloys and W, Nb, Mo, Ta, and V-based BCC high-entropy alloys are widely used, so their price competitiveness is low, and it has been difficult to commercially use them because heavy elements are mainly used.

However, recently, interest in lightweight structural materials has increased in various fields such as the aerospace industry, mobility industry, and wearable device industry, and research on medium entropy alloys that add lightweight alloy elements or serve as the basis for major elements is attracting attention. Al and Ti are widely used as lightweight structural materials for medium entropy alloys. In the case of Ti, it has excellent strength-to-weight ratio and is widely used in aerospace and other demanding industries, but it has a problem in that its thermal conductivity is lower than that of metals such as aluminum because its thermal conductivity is relatively low at 21.9 W/(m·K).

In contrast, Al has an excellent strength-to-weight ratio, is highly price competitive, and has a significantly lower density than Ti, so it is attracting attention in industries such as aerospace and vehicle design where a 1 g weight reduction can result in significant energy savings.

However, in the case of Al, when other alloy elements are added, it easily forms an intermetallic compound, and the intermetallic compound is brittle and can cause sudden fracture during a tensile test. Therefore, research and development on an Al-based medium entropy alloy with sufficient tensile characteristics is necessary.

SUMMARY OF THE INVENTION

The technical object that the present invention seeks to solve is to provide a medium entropy alloy of lightweight structural material capable of improving tensile characteristics.

Another technical object that the present invention seeks to solve is to provide a medium entropy alloy manufacturing method having the aforementioned advantages.

An embodiment is a medium entropy alloy including an Al-rich FCC phase, a Zn-rich HCP phase, and an intermetallic compound, wherein the Al-rich FCC phase, the Zn-rich HCP phase, and the intermetallic compound include Al, Zn, and Cu, and the intermetallic compound satisfies the following Equation 1.

1 ⁢ 9 ⁢ 3 ≤ ( A × B ) / C ≤ 2 ⁢ 4 ⁢ 0 [ Equation ⁢ 1 ]

(In Equation 1, A represents the atom % of Al in the intermetallic compound, B represents the atom % of Cu in the intermetallic compound, and C represents the atom % of Zn in the intermetallic compound.)

The medium entropy alloy can satisfy the following Equation 2.

0.14 ≤ ( a ⁢ first ⁢ peak × a ⁢ fourth ⁢ peak ) / a ⁢ fifth ⁢ peak ≤ 0.33 [ Equation ⁢ 2 ]

(In Equation 2, the first peak is the peak intensity when 2θ is 36±5°, the fourth peak is the peak intensity when 2θ is 65±5°, and the fifth peak is the peak intensity when 2θ is 78+5°, in the X-ray diffraction analysis (XRD) spectrum.)

With atom % as reference, the ratio of Zn to Al can be 0.8 to 1.2.

With atom % as reference, the ratio of Cu to Al can be 0.2 to 1.0.

The medium entropy alloy may contain Al: 33.3 to 45.0%, Zn: 33.3 to 45.0%, Cu: 10 to 33.3% and other impurities in atom %.

The medium entropy alloy may contain a triple phase, and the triple phase may include a first phase having Al as a primary component; a second phase having Zn as a primary component; and a third phase with an Al-based intermetallic compound and a Cu-rich.

The first phase may include an Al-rich FCC phase.

The second phase may contain a Zn-rich HCP phase.

The composition of the first phase can include Al: 45 to 60%, Zn: 35 to 50%, Cu: 5 to 10% and impurity of the balance in atom %, with the entire mole number of the first phase as a reference.

The composition of the second phase can include Al: 5 to 20%, Zn: 65 to 80%, Cu: 10 to 25% and impurity of the balance in atom %, with the entire mole number of the second phase as a reference.

The composition of the third phase can include Al: 40 to 55%, Zn: 5 to 20%, Cu: 35 to 50%, and inevitable impurities, with the entire mole number of the third phase as a reference.

The Al based intermetallic compound may include AlCu and Al2Cu.

The yield strength of the medium entropy alloy at room temperature 298K can be 350 to 380 MPa.

The tensile strength of the medium entropy alloy at room temperature 298K can be 405 to 470 MPa.

The elongation of the medium entropy alloy at room temperature 298K can be 1.2 to 5.0%.

The Al and Zn can satisfy the following Equation 3.

[ Al ] = [ Zn ] [ Equation ⁢ 3 ]

(Here, [X] means atom % of X)

Another embodiment of the present invention may include the steps of: manufacturing an ingot by casting a mixed powder including Al, Zn, and Cu; quenching the ingot; subjecting the quenched ingot to severe plastic deformation; and performing a post heat treatment for 2 to 50 minutes.

The severe plastic deformation process may include a High-Pressure Torsion (HPT) process or an Equal Channel Angular Pressing (ECAP) process.

The load applied during the High-Pressure Torsion (HPT) process can be 38 to 50 tons; and the overall rotation speed can be 5 to 40 times.

The heat treatment temperature of the post heat treatment step can be 250 to 350° C.

A medium entropy alloy according to an embodiment can form a triple phase and have a solid solution effect. In addition, the room temperature mechanical characteristics can be improved due to the phase interface strengthening effect.

A medium entropy alloy according to another embodiment of the present invention has finer and more evenly distributed intermetallic compounds than the ingot through severe plastic deformation and a post heat treatment process. Additionally, mechanical characteristics can be improved by bypassing crack propagation and obtaining excellent ductility.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

FIG. 1 shows the scanning electron microscope and energy dispersive spectroscopy results of the as-cast state of a medium entropy alloy according to a comparative example of the present invention.

FIG. 2 shows the scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) results of the as-deformed state of a medium entropy alloy according to an embodiment.

FIG. 3 shows the X-ray diffraction analysis results of the microstructure after casting and the microstructure after severe plastic deformation of a medium entropy alloy according to an embodiment.

FIG. 4 shows the X-ray diffraction analysis results of the microstructure of a medium entropy alloy according to an embodiment and a comparative example.

FIG. 5 shows the scanning electron microscope result of the microstructure of a medium entropy alloy according to an embodiment 1.

FIG. 6 shows the scanning electron microscope result of the microstructure of a medium entropy alloy according to an embodiment 2.

FIG. 7 shows the scanning electron microscope result of the microstructure of a medium entropy alloy according to Comparative Example 1 of the present invention.

FIG. 8 shows the tensile test results at room temperature 298K of a medium entropy alloy according to an embodiment and a comparative example.

FIG. 9 shows the scanning electron microscope (SEM) result of the microstructure of a fractured specimen after a tensile test at room temperature 298K of a medium entropy alloy according to Comparative Example 1 of the present invention.

FIG. 10 shows the scanning electron microscope (SEM) result of the microstructure of a fractured specimen after a tensile test at room temperature 298K of a medium entropy alloy according to Comparative Example 2 of the present invention.

FIG. 11 shows the scanning electron microscope (SEM) result of the microstructure of a fractured specimen after a tensile test at room temperature 298 K of a medium entropy alloy according to an embodiment 1.

FIG. 12 shows the scanning electron microscope (SEM) result of the microstructure of a fractured specimen after a tensile test at room temperature 298 K of a medium entropy alloy according to an embodiment 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The terms such as first, second, and third are used to describe various portions, components, regions, layers, and/or sections, but various parts, components, regions, layers, and/or sections are not limited to these terms. These terms are only used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

Terminologies as used herein are to mention only a specific exemplary embodiment, and are not to limit the present invention. Singular forms used herein include plural forms as long as phrases do not clearly indicate an opposite meaning. The term “including/comprising/containing” as used herein concretely indicates specific characteristics, regions, integer numbers, steps, operations, elements, and/or components, and is not to exclude presence or addition of other specific characteristics, regions, integer numbers, steps, operations, elements, and/or components.

When any portion is referred to as being “above” or “on” another portion, any portion may be directly above or on another portion or be above or on another portion with the other portion interposed therebetween. In contrast, when any portion is referred to as being “directly on” another portion, the other portion is not interposed between any portion and another portion.

Unless defined otherwise, all terms including technical terms and scientific terms as used herein have the same meaning as the meaning generally understood by a person of an ordinary skill in the art to which the present invention pertains. Terms defined in a generally used dictionary are additionally interpreted as having the meaning matched to the related art document and the currently disclosed contents and are not interpreted as ideal or formal meaning unless defined.

Also, unless otherwise stated, % means wt %, and 1 ppm is 0.0001 wt %.

In this specification, the term “combination thereof(s)” described in a Markush format expression means one or more mixtures or combinations selected from the group consisting of components described in the Markush format expression, and means including one or more selected from the group consisting of the components.

Below, an embodiment is described in detail so that a person of ordinary skill in the technical field to which the present invention belongs can easily carry out the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

1. Medium Entropy Alloy

A medium entropy alloy according to an embodiment is a medium entropy alloy including an Al-rich FCC phase, a Zn-rich HCP phase, and an intermetallic compound, wherein the Al-rich FCC phase, the Zn-rich HCP phase, and the intermetallic compound include Al, Zn, and Cu, and the intermetallic compound satisfies the following Equation 1.

1 ⁢ 9 ⁢ 3 ≤ ( A × B ) / C ≤ 2 ⁢ 4 ⁢ 0 [ Equation ⁢ 1 ]

(In Equation 1, A represents the atom % of Al in the intermetallic compound, B represents the atom % of Cu in the intermetallic compound, and C represents the atom % of Zn in the intermetallic compound.)

Equation 1 is the value obtained by dividing the product of the atom % of Al and Cu by the atom % of Zn in an intermetallic compound dispersed in a medium entropy alloy, which represents the degree of dispersion of Al, Cu, and Zn in the intermetallic compound. Equation 1 can satisfy 193 to 240, specifically, 215 to 222. By satisfying Equation 1, the intermetallic compounds within the alloy are appropriately dispersed, so that an excellent medium entropy alloy with both strength and ductility can be realized.

If the Equation 1 exceeds the lower limit of the aforementioned range, there is a problem that the ductility becomes excessively high. When the equation 1 exceeds the upper limit of the aforementioned range, there is a problem that the ductility is excessively reduced, making it difficult to implement an excellent medium entropy alloy with ductility and strength simultaneously. In a medium entropy alloy according to an embodiment, the medium entropy alloy can satisfy the following Equation 2.

0.14 ≤ ( a ⁢ first ⁢ peak × a ⁢ fourth ⁢ peak ) / a ⁢ fifth ⁢ peak ≤ 0.33 [ Equation ⁢ 2 ]

(In Equation 2, the first peak is the peak intensity when 2θ is 36±5°, the fourth peak is the peak intensity when 2θ is 65±5°, and the fifth peak is the peak intensity when 2θ is 78±5°, in the X-ray diffraction analysis (XRD) spectrum.)

Equation 2 is the value obtained by dividing the product of the first peak value and the fourth peak value of the medium entropy alloy by the fifth peak value, and is a formula for determining the degree of formation of intermetallic compounds. Equation 2 can be 0.14 to 0.33, specifically, 0.21 to 0.27. By satisfying Equation 2, the intermetallic compounds within the alloy are appropriately dispersed, so that an excellent medium entropy alloy with both strength and ductility can be realized.

If Equation 2 exceeds the upper limit of the aforementioned range, there is a problem that the ductility becomes excessively high. When the Equation 2 exceeds the lower limit of the aforementioned range, there is a problem that the ductility is excessively reduced, making it difficult to implement an excellent medium entropy alloy with ductility and strength simultaneously.

A medium entropy alloy according to an embodiment can have a ratio of Zn to Al of 0.8 to 1.2, with atom % as a reference. When the ratio of Zn to Al satisfies the range, there may be an advantage of maximizing the solid solution strengthening based on Zn that can be dissolved in Al without forming an intermetallic compound. On the other hand, if the ratio of Zn to Al is out of the range, it can have a detrimental effect on the alloy's properties such as light weight and strength.

A medium entropy alloy according to an embodiment can have a ratio of Cu to Al of 0.2 to 1.0, with atom % as a reference. If the ratio of Cu to Al satisfies the range, the mechanical characteristics at room temperature can be improved, and if it goes out of the range, it may be difficult to obtain a sufficient strengthening effect.

In an embodiment of a medium entropy alloy, the medium entropy alloy may include, in atom %, Al: 33.3 to 45.0%, Zn: 33.3 to 45.0%, Cu: 10 to 33.3% and other impurities, and specifically may include Al: 35 to 43%, Zn: 35 to 43%, Cu: 15 to 28%. When the atom % of Al satisfies the range, ductility can be secured by forming an Al-rich FCC phase. On the other hand, if Al is less than 33.3 atom %, the density of the alloy may increase, and if Al is over 45.0 atom %, the fraction of soft FCC phase may increase, which may cause a problem of reduced strength.

When the atom % of Zn satisfies the range, Zn can be dissolved in Al up to 67 atom %, which has the advantage of maximizing the strengthening effect of the alloy. On the other hand, if the atom % of Zn is out of the range, a problem may occur in which the density of the alloy increases and the strength decreases.

When the atom % of Cu satisfies the range, there may be an advantage of maximizing precipitation hardening by forming an intermetallic compound. On the other hand, if the atom % of Cu is less than 10 atom %, there may be a problem that the strength of the alloy decreases due to a decrease in the fraction of precipitates. In addition, when the atom % of Cu exceeds 33.3 atom %, the size of the precipitate becomes coarse, which may cause a problem of deterioration of ductility.

The other impurities may be components other than the alloy elements that are inevitably mixed in the raw material or manufacturing process.

In an embodiment of a medium entropy alloy, the medium entropy alloy may include a triple phase, and the triple phase may include a first phase having Al as a primary component; a second phase having Zn as a primary component; and a third phase having an Al-based intermetallic compound and Cu-rich.

In a medium entropy alloy according to an embodiment, the first phase may include an Al-rich FCC phase.

In a medium entropy alloy according to an embodiment, the second phase may include a Zn-rich HCP phase. The Al-rich FCC phase and the Zn-rich HCP phase can be separated by the miscibility gap, and the interface strengthening effect of the medium entropy alloy can be maximized by the phase interface formed by the phase separation.

In a medium entropy alloy according to an embodiment, with the entire mole of the first phase as a reference, the composition of the first phase may include Al: 45 to 60%, Zn: 35 to 50%, Cu: 5 to 10% and inevitable impurities in atom %, and specifically may include Al: 50 to 55%, Zn: 40 to 45%, Cu: 5 to 8%. If the first phase satisfies the range, ductility can be secured by forming an Al-rich FCC phase. On the other hand, if the first phase is out of the range, the density of the alloy may increase or the fraction of the FCC phase may increase, which may cause a problem in that the strength may decrease.

In a medium entropy alloy according to an embodiment, with the entire mole of the second phase as a reference, the composition of the second phase may include, in atom %, Al: 5 to 20%, Zn: 65 to 80%, Cu: 10 to 25% and inevitable impurities, specifically Al: 10 to 15%, Zn: 70 to 75%, Cu: 15 to 20%. If the second phase satisfies the range, the strengthening effect of the alloy can be maximized, and if the second phase goes out of the range, a problem may occur in which the density of the alloy increases and the strength decreases.

In a medium entropy alloy according to an embodiment, the composition of the third phase may include, in atom %, Al: 40 to 55%, Zn: 5 to 20%, Cu: 35 to 50%, and inevitable impurities, with the entire mole number of the third phase as a reference, and specifically, Al: 45 to 50%, Zn: 10 to 15%, Cu: 35 to 45%. When the atom % of the third phase satisfies the range, an AlCu solid solution having a BCC structure is formed, which may have the advantage of contributing to precipitation hardening while maintaining ductility. On the other hand, if the atom % of the third phase is out of the range, a problem may occur in which a regular intermetallic compound such as AlCu₄ is formed, causing brittleness, or the size of the precipitate becomes coarse, resulting in deterioration of ductility. In a medium entropy alloy according to an embodiment, the Al based intermetallic compound may include AlCu and Al₂Cu.

In a medium entropy alloy according to an embodiment, the yield strength of the medium entropy alloy at room temperature 298K can be 350 to 380 MPa, specifically 355 to 375 MPa, more specifically 360 to 373 MPa. If the yield strength satisfies the range, the alloy may have a solid solution strengthening effect due to the precipitation hardening effect.

In a medium entropy alloy according to an embodiment, the tensile strength of the medium entropy alloy at room temperature 298K can be 405 to 470 Mpa, specifically 405 to 465 Mpa, more specifically 405 to 462 Mpa. If the tensile strength satisfies the range, the mechanical characteristics can be improved at room temperature due to the precipitation hardening effect.

In a medium entropy alloy according to an embodiment, the elongation at room temperature 298K of the medium entropy alloy can be 1.2 to 5.0%, specifically 1.4 to 4.8%. If the elongation satisfies the range, it may have advantages in commercial use, such as easy processing and increased stability and durability by delaying sudden fracture.

In a medium entropy alloy according to an embodiment, the Al and Zn can satisfy the following equation 3.

[ Al ] = [ Zn ] [ Equation ⁢ 3 ]

(Here, [X] means atom % of X)

• • the X can stand for Al or Zn.

In the medium entropy alloy, if the Al and Zn satisfy Equation 3, there may be an advantage in maximizing the solid solution strengthening by increasing the Zn content in the Al-rich FCC and the Al content in the Zn-rich HCP. On the other hand, if the Al and Zn deviate from the equation 3, there may be a problem that the strength is lowered due to lowered solidification enhancement.

2. Method of Preparing Medium Entropy Alloy

A method of manufacturing a medium entropy alloy according to an embodiment includes a step of manufacturing an ingot by casting a mixed powder including Al, Zn, and Cu; a step of quenching the ingot; a step of subjecting the quenched ingot to severe plastic deformation; and a step of performing a post heat treatment for 2 to 50 minutes. The heat treatment time of the post heat treatment step can be from 2 to 50 minutes. Specifically, the heat treatment time can be 3 to 10 minutes, more specifically 5 to 10 minutes. A solid solution strengthening effect may be achieved in the alloy if the heat treatment time is within the appropriate range. On the other hand, if the heat treatment time is outside the lower limit of the aforementioned range, the annealing effect of the microstructure may not be sufficient, and if the heat treatment time exceeds 50 minutes, there may be a problem that the intermetallic compound becomes coarse, thereby degrading the mechanical properties of the alloy.

The step of manufacturing an ingot by casting the mixed powder is to first charge the mixed powder into a crucible, heat it to dissolve it, and pour it into a mold to cast the ingot. At this time, the heating temperature can be 400 to 1,100° C. or 500 to 1,000° C. If the heating temperature is less than 400° C., there may be a problem in obtaining an ingot with a uniform composition because the elements do not melt sufficiently. In addition, if the heating temperature exceeds 1,100° C., there may be a problem of Al evaporation, which reduces the Al content.

The next step of quenching the ingot can be quenching at room temperature, and the cooling method and cooling speed are not particularly limited, and anything that can quench the ingot can be done.

In a medium entropy alloy manufacturing method according to an embodiment, the severe plastic deformation process may include a High Pressure Torsion (HPT) process or an Equal Channel Angular Pressing (ECAP) process.

In a medium entropy alloy manufacturing method according to an embodiment, the load applied during the High Pressure Torsion (HPT) process can be 38 to 50 tons; and the entire rotation speed can be 5 to 40 times. If the load satisfies the range, there may be an advantage in improving the strength by effectively refining the crystal grains and intermetallic compounds of the alloy. On the other hand, if the load is lower than the range, sufficient plastic deformation may not be applied to the microstructure of the alloy, or if it is higher than the range, there may be a problem that the High-Pressure Torsion (HPT) process equipment is strained, reducing the equipment life-span and increasing the processing cost.

If the entire rotation speed satisfies the range, there may be an advantage in that the crystal grains and intermetallic compounds of the alloy can be effectively refined. On the other hand, if the entire rotation speed is out of the range, there may be a problem that the intermetallic compound of the alloy is not sufficiently distributed or the processing time increases, resulting in reduced producibility.

In a medium entropy alloy manufacturing method according to an embodiment, the heat treatment temperature of the post heat treatment step can be 250 to 350° C. or 270 to 330° C. When the heat treatment temperature satisfies the range, excellent yield strength and mechanical characteristics at room temperature can be achieved due to crystal grain refinement. On the other hand, if the heat treatment temperature is less than 250° C., the annealing effect of the microstructure may not be sufficient. Also, if the heat treatment temperature is 350° C., the heat treatment cost may increase and the problem of partial dissolution may occur.

Below, an implementation example of the present invention is explained in more detail through an example. However, the following Example is only a preferable embodiment, and the present invention is not limited by the following

EXAMPLE

Example 1: Manufacturing of Medium Entropy Alloy

First, Al, Zn and Cu metals with a purity of 99.9% or higher were prepared and weighed at a mixing ratio of Al: 40 at %, Zn: 40 at % and Cu: 20 at %. Afterwards, the prepared raw material metal was placed in a zirconia crucible, heated to 1,100° C. to dissolve, and a 55 g alloy ingot having a rectangular hexahedral shape with a thickness of 7.5 mm, a width of 33 mm, and a length of 40 mm was cast using a mold.

Afterwards, the microstructure of the ingot, which was quenched immediately after casting, was refined through the High-Pressure Torsion (HPT) process. The High-Pressure Torsion (HPT) process was performed for a total of 5 rotations under a load of 48 tons. Afterwards, annealing was performed at 350° C. for 3 minutes to recover the microstructure, and then quenched back to room temperature to obtain an AlZnCu medium entropy alloy.

Example 2: Manufacturing of Medium Entropy Alloy

The same method as Example 1 was used, except that annealing was performed at a temperature of 350° C. for 10 minutes.

Comparative Example 1

First, Al, Zn and Cu metals with a purity of 99.9% or higher were prepared and weighed at a mixing ratio of Al: 40 at %, Zn: 40 at % and Cu: 20 at %. Afterwards, the prepared raw material metal was placed in a zirconia crucible, heated to 1,100° C. to dissolve, and a 55 g alloy ingot having a rectangular hexahedral shape with a thickness of 7.5 mm, a width of 33 mm, and a length of 40 mm was cast using a mold. The specimen immediately after casting was named as-cast for specimen differentiation, and the specimen immediately after severe plastic deformation was named as-deformed.

Comparative Example 2

The same method as Example 1 was used, except that annealing was performed at a temperature of 350° C. for 60 minutes.

Table 1 below shows the classification according to process conditions of Example and Comparative Example.

	TABLE 1
	Annealing condition

Applying

Mixing ratio of raw material (atom %)

annealing

Temperature

Time

Division	Al	Zn	Cu	step	(° C.)	(min)

Example 1	40.00	40.00	20.00	◯	350	3
Example 2	40.00	40.00	20.00	◯	350	10
Comparative	40.00	40.00	20.00	X	—	—
Example 1
Comparative	40.00	40.00	20.00	◯	350	60
Example 2

Experimental Example 1: Scanning Electron Microscope (SEM) and Energy Dispersion Spectroscopy (EDS) Evaluation

The medium entropy alloys manufactured according to Example and Comparative Example were pretreated by polishing with sandpaper of 600 to 1,200 grit, and then experiments were conducted using a scanning electron microscope of JEOL JSM-7100F. The results are shown in FIG. 1, FIG. 2, FIGS. 5 to 7, and FIGS. 9 to 12.

Referring to FIG. 1, in the scanning electron microscope image, it was confirmed that the light gray Al, Cu-rich intermetallic compound, black color Al-rich phase, and white color Zn-rich phase were distinguished according to the composition of each region, and the energy dispersion spectroscopy results for this are shown in Table 2 below.

	TABLE 2
	atom %

Equation 1

Medium entropy alloy	Al	Zn	Cu	(Al × Cu/Zn)
Total composition	43.2 ± 0.2	36.0 ± 0.9	20.8 ± 0.7	—

Example 1	Al-rich FCC	51.6 ± 0.6	39.3 ± 1.1	9.0 ± 0.6	—
	Zn-rich HCP	28.6 ± 1.7	62.4 ± 3.4	9.1 ± 1.7	—
	intermetallic	50.8 ± 0.6	9.2 ± 0.8	40.1 ± 1.3	221.4
	compound
Example 2	Al-rich FCC	55.0 ± 2.0	37.8 ± 3.9	7.2 ± 2.8
	Zn-rich HCP	29.7 ± 2.6	64.1 ± 3.0	6.2 ± 0.9
	intermetallic	54.3 ± 0.8	9.2 ± 0.2	36.5 ± 0.9	215.4
	compound
Comparative	Al-rich FCC	60.0 ± 5.1	33.8 ± 5.4	6.2 ± 1.8
Example 1	Zn-rich HCP	31.5 ± 2.7	63.8 ± 3.6	4.8 ± 0.9
	intermetallic	48.1 ± 0.2	10.4 ± 0.3	41.6 ± 0.1	192.4
	compound
Comparative	Al-rich FCC	55.4 ± 2.2	40.6 ± 1.2	3.9 ± 1.0
Example 2	Zn-rich HCP	25.7 ± 2.8	71.8 ± 2.3	2.5 ± 0.5
	intermetallic	52.2 ± 0.6	8.5 ± 0.2	39.4 ± 0.4	242.0
	compound

Referring to Table 2 above, although there was a slight error due to impurities that were inevitably mixed in during the raw material or manufacturing process, it was confirmed that the entire composition of the alloy showed almost the same value as the theoretical mixing ratio of Table 1. Referring to FIG. 2, it was confirmed that each phase was refined in the as-deformed state after severe plastic deformation of the medium entropy alloy, and it was confirmed that particularly coarse Al, Cu-rich intermetallic compounds were refined and evenly distributed.

Referring to FIGS. 5 to 7, it was confirmed that as the annealing time increased, the Al-rich FCC phase, Zn-rich HCP phase, and Al and Cu-rich intermetallic compound became coarser. In particular, in the specimen of Example 1 heat treated for 3 minutes and in Example 2 heat treated for 10 minutes, it was confirmed that intermetallic compounds with a size of less than 1micrometer were distributed between the Al-rich FCC phase and the Zn-rich HCP phase through severe plastic deformation. However, in the specimen of Comparative Example 1 heat treated for 60 minutes, it was confirmed that the intermetallic compounds were bonded to each other and coarse intermetallic compounds larger than 1 micrometer were mainly present.

FIGS. 9 to 12 are scanning electron microscope results of microstructural analysis of fractured specimens after tensile testing of an embodiment and a comparative example.

Referring to FIGS. 9 to 12, Comparative Example 1 confirmed that crack propagation occurred in a coarse intermetallic compound because refinement of the intermetallic compound did not occur through severe plastic deformation. Meanwhile, in the Example 1 and Example 2 specimens, the intermetallic compound was finely and evenly distributed, and it was observed that, although cracks were initiated in the intermetallic compound, they did not propagate continuously but deviated and propagated along a deflected path. However, when the heat treatment time increased and the size of the intermetallic compound increased, it was confirmed that the crack propagated along the intermetallic compound and the ductility deteriorated.

Experimental Example 2: X-ray Diffraction Analysis (XRD) Evaluation

The medium entropy alloys manufactured according to Example and Comparative Example were measured at 0.02 degree intervals using Cu Kα X-rays with a wavelength of 0.154 nm using Bruker's D8-Advance X-ray diffraction analysis equipment, and the results are shown in FIGS. 3 and 4.

FIG. 3 shows the X-ray diffraction analysis results of the as-cast and as-deformed specimens. Referring to FIG. 3, it was confirmed that Al-rich FCC phase and Zn-rich HCP phase, AlCu and Al₂Cu intermetallic compounds exist. At this time, the sum of Zn and Cu to Al content of the intermetallic compound shown in Table 2 was close to 1:1, indicating that the AlCu intermetallic compound was the main intermetallic compound. In addition, the X-ray diffraction analysis peak of the as-deformed specimen broadened immediately after severe plastic deformation, confirming that significant deformation remained.

FIG. 4 shows the X-ray diffraction analysis results of specimens that were annealed for 3, 10, and 60 minutes to relieve residual stress in a specimen with severe plastic deformation. Each specimen was formed of Al-rich FCC phase, Zn-rich HCP phase, AlCu, and Al₂Cu intermetallic compound, and the peaks became thinner compared to the as-deformed specimen, confirming that recovery had occurred after annealing.

	TABLE 3
		Equation 2
	XRD peak intensity	(first peak ×

	First	Second	Third	Fourth	Fifth	fourth peak/
	peak	peak	peak	peak	peak	fifth peak)

degree	36 ± 5	43 ± 5	54 ± 5	65 ± 5	78 ± 5	—
Example 1	0.223	1.000	0.149	0.026	0.027	0.215
Example 2	0.232	1.000	0.106	0.061	0.054	0.262
Comparative	0.086	1.000	0.080	0.077	0.019	0.349
Example 1
Comparative	0.130	0.979	0.079	0.060	0.057	0.137
Example 2

Table 3 shows the normalized intensity results of X-ray diffraction analysis (XRD) spectrum 2θ using Cu-Kα for a medium entropy alloy according to an embodiment and a comparative example.

Experimental Example 3: Tensile Evaluation

The tensile evaluation was performed at room temperature and the strain rate was maintained at 10⁻³s⁻¹, after which the tensile characteristics were measured. The tensile change rate before and after the test was calculated and used as an index, and the results are shown in Table 4.

FIG. 8 and Table 4 below show the tensile test results at room temperature 298 K for a medium entropy alloy according to an embodiment and a comparative example.

	TABLE 4
	Comparative	Comparative
	Example 1	Example 2	Example 1	Example 2

yield strength (MPa)	293	348	370	372
tensile strength	355	400	405	461
(MPa)
elongation (%)	1.1	1.1	1.5	4.8

Referring to FIG. 8 and Table 4, it was confirmed that the medium entropy alloy manufactured according to an embodiment had the characteristics of yield strength of 370 to 372 MPa, tensile strength of 405 to 461 MPa, and elongation of 1.4 to 4.8%. Particularly, Example 2 exhibited excellent ductility compared to other specimens, and through work hardening during deformation, it had excellent room temperature tensile characteristics with a tensile strength of 461 MPa, and a ductility of 4.8%, which was more than four times higher than before severe plastic deformation. This trend may be due to the refinement of the brittle intermetallic compound by severe plastic deformation and the recovery of the deformed microstructure by post heat treatment. On the other hand, Comparative Example 2 showed that the yield strength and tensile strength increased through severe plastic deformation and heat treatment, but the ductility was low at 1.1% when the annealing time was too long. Meanwhile, in the specimens of Example 1 and Example 2 with short annealing times, a ductility of more than 1.5% was confirmed.

Although the present invention has been described above with regard to a preferably example, the present invention is not limited thereto, and it is possible to implement the present invention by modifying it in various ways within the scope of the patent claims and the detailed description and accompanying drawings of the invention, and this also naturally falls within the scope of the present invention.

Therefore, it can be said that the actual scope of the present invention is defined by the attached patent claims and their equivalents.