US20170240998A1

US20170240998A1 - Engineered aluminum alloy and method of fabricating the same

Info

Publication number: US20170240998A1
Application number: US15/438,913
Authority: US
Inventors: Dong Hyun Bae; Je Heon Jeon; Se Eun Shin
Original assignee: University Industry Foundation UIF of Yonsei University
Current assignee: University Industry Foundation UIF of Yonsei University
Priority date: 2016-02-23
Filing date: 2017-02-22
Publication date: 2017-08-24
Also published as: JP2019143249A; JP2017150076A

Abstract

Provided are an aluminum alloy having an adjusted microstructure in an aluminum matrix or an aluminum alloy matrix for high elongation percentage or high strength and a method of fabricating the same. The aluminum alloy includes an aluminum-based matrix; and a nonmetal element solidified in the aluminum-based matrix, wherein stacking fault energy of the aluminum alloy is decreased compared to that of pure aluminum.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority of Korean Patent Application No. 10-2016-0021495, filed on Feb. 23, 2016 and priority of Korean Patent Application No. 10-2016-0183446, filed on Dec. 30, 2016, in the KIPO (Korean Intellectual Property Office), the disclosure of which is incorporated herein entirely by reference.

BACKGROUND OF THE INVENTION

Field of the Invention
The present disclosure relates to a metal material, and more particularly, to aluminum that is adjusted to have high elongation or high strength and a method for fabricating the same.
Description of the Related Art
Generally, aluminum or its alloy is a material having a wide range of industrial applications because it may be fabricated in various shapes due to lightweight and durable characteristics of aluminum. Aluminum itself is easily deformed due to its low strength, but an aluminum alloy has high strength and high reliability due to elements added thereto to the extent that it may be applied to the automobile or aircraft industry. Recently, due to their excellent mechanical strengths and lightweights, aluminum alloys have been applied to various fields, such as automobiles and aircraft, as well as various other fields, such as architecture, chemistry, robots, and electronic products.
Recently, high-strength aluminum and method of fabricating the same are being actively researched for development of components used in the fields of automobiles, bicycles, electric or electronics, or robots. Generally, as the number of kinds of elements added to an aluminum matrix increases, improvements of strength and corrosion resistance may be expected, but elongation percentage for improving the workability of aluminum-based material is not improved or is rather reduced.
Furthermore, in order to improve the strength of pure aluminum having a low strength, it is generally preferable to form an aluminum alloy with an element, such as silicon (Si), magnesium (Mg), copper (Cu), manganese (Mn) and strengthen solid solution of the corresponding element in an aluminum-based matrix or strengthen precipitation of compound or second phase precipitation, thereby improving strength of the aluminum alloy. The aluminum alloy may be classified into a non-heat-treated alloy and a heat-treated alloy depending on whether it is hardened via a heat treatment. The above-stated non-heat-treated alloy is improved in strength by strengthening by a second phase or a compound based on an element, such as silicon, magnesium, or manganese, as described above. Examples of the non-heat-treated alloys include Al—Si alloys, Al—Mg alloys, and Al—Mn alloys.
The strength of the heat-treated alloy may be determined depending on the kind of alloying elements. For example, in an aluminum alloy to which copper (Cu) or zinc (Zn) is added, solid solubility of the added element increases as the temperature rises, and may be hardened by formation of precipitates via an aging treatment. The heat-treated alloys include Al—Cu alloys, Al—Zn alloys, and Al—Mg—Si alloys. However, in the case of the above-stated heat-treated alloy, since it is necessary to take main composition or brittleness into account, alloying elements to be added are limited. An aluminum alloys, which is strengthened by formation of a precipitate (a metal compound) by adding a heterogeneous metal to aluminum may be expected to exhibit improved strength as compared to conventional heat-treated alloys.

SUMMARY OF THE INVENTION

Provided is a highly-stretchable aluminum alloy exhibiting excellent mechanical properties such as strength and improved elongation percentage that provides improved workability, the aluminum alloy that may be obtained at a high yield.
Provided is a method of fabricating the highly-stretchable aluminum alloy.
Provided is an aluminum alloy capable of improving the strength of the aluminum alloy by forming a new reaction compound in the aluminum alloy through heat treatment to provide an efficient strengthening mechanism of the aluminum alloy.
Provided is a method of easily fabricating an aluminum alloy having the above advantages.
Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments.
According to an aspect of an embodiment, an aluminum alloy includes an aluminum-based matrix; and a nonmetal element solidified in the aluminum-based matrix, wherein stacking fault energy of the aluminum alloy is decreased compared to that of pure aluminum. The nonmetal element may include at least one of oxygen and nitrogen.
The nonmetal element may be solidified to less than or equal to 1 wt % of aluminum of the aluminum-based matrix. In this case, the stacking fault energy of the aluminum alloy may be less than 100 mJ/m².
In the aluminum alloy, at least a portion of the aluminum-based matrix may include a twin boundary or a partial dislocation. The nonmetal element may be solidified in the aluminum alloy by adding nanoparticles of a metal compound between the nonmetal element and a heterogeneous metal element to molten aluminum and decomposing the nanoparticles into the nonmetal element and the heterogeneous metal element.
According to an embodiment, the aluminum alloy may be hardened via a cooling operation. Furthermore, the aluminum alloy may be aged without being cooled.
According to an aspect of another embodiment, a method of fabricating an aluminum alloy, the method includes providing the melt of aluminum or an aluminum alloy providing an aluminum-based matrix; adding nanoparticles of a metal compound between a nonmetal element and a heterogeneous metal element to the melt; uniformly dispersing the nonmetal element and the heterogeneous metal element in the melt through decomposition of the nanoparticles into the nonmetal element and the heterogeneous metal element; and cooling the melt so as to solidify the nonmetal element in at least a portion of the aluminum-based matrix.
The stacking fault energy of the aluminum alloy may be less than 100 mJ/m². The nonmetal element may include at least one of oxygen and nitrogen. Furthermore, the nonmetal element may be solidified to less than or equal to 1 wt % of aluminum of the aluminum-based matrix. The heterogeneous metal element may include copper, iron, zinc, titanium, magnesium, or a mixture of two or more thereof.
The average size of the nanoparticles may be from about 20 nm to about 100 nm. According to some embodiments, the aluminum alloy in which the nonmetal element is solidified may be hardened via a cooling operation. According to another embodiment, the aluminum alloy in which the nonmetal element is solidified may be artificially aged without being cooled.
According to an aspect of another embodiment, an aluminum alloy includes an aluminum-based matrix; and a precipitation compound dispersed in the aluminum-based matrix, wherein the precipitation compound includes a compound containing aluminum, one or more transition metals, and one or more nonmetal elements or a compound containing the above-stated elements.
According to an embodiment, the average size of the precipitation compound may be from about 10 nm to about 1 μm. The transition metal may include at least one of chromium (Cr), iron (Fe), and manganese (Mn).
Furthermore, the nonmetal element may be supersaturated in the aluminum alloy and includes at least one of oxygen, nitrogen, and carbon. The precipitation compound may be formed via a heat treatment.
The aluminum-based matrix may include an aluminum alloy, and alloying elements of the aluminum alloy may include at least one of silicon (Si), zinc (Zn), magnesium (Mg), and copper (Cu). In addition, in an embodiment, the aluminum alloy may be work hardened by plasticity.
According to an aspect of another embodiment, a method of fabricating an aluminum alloy, the method includes providing the melt of an aluminum alloy including aluminum and a first transition metal; adding a nonmetal element-containing precursor including at least one of a first reaction compound between the first transition metal and a nonmetal element, a second reaction compound between a second transition metal different from the first transition metal and the nonmetal element, and a third reaction compound between a non-transition metal and the nonmetal element to the melt; supersaturating the nonmetal element in the melt through decomposition of the nonmetal element-containing precursor in the melt; forming a casted material by hardening the melt; and forming a precipitation compound between aluminum, a transition metal, and a nonmetal element dispersed in an aluminum-based matrix by heat-treating the hardened casted material.
Furthermore, the first transition metal may include at least one of chromium (Cr), iron (Fe), and manganese (Mn). The nonmetal element may include at least one of oxygen, nitrogen, and carbon.
According to an embodiment, the non-transition metal of the third reaction compound may include at least one of aluminum (Al), silicon (Si), magnesium (Mg), and tungsten (W). The nonmetal element-containing precursor may be added to the melt in the form of power having the average diameter within a range from about 5 nm to about 50 nm.
The nonmetal element-containing precursor may be added in the range from 0.01 wt % to 5.0 wt % of the total weight of the melt. Furthermore, the method may further include plastic working and hardening the hardened casted material before the hardened casted material is heat treated. The heat treatment may be performed at a temperature within a range from 120° C. to 600° C.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments with reference to the attached drawings, in which:

FIGS. 1A and 1B are transmission electron microscope (TEM) analysis images showing the microstructure of an aluminum alloy according to an embodiment of the present invention;

FIG. 2 is a graph showing a result of X-ray diffraction analysis for measuring stacking fault energy (SFE) of an aluminum alloy having a twin boundary or partial dislocation according to an embodiment of the present invention;

FIGS. 3A through 3C are stress-deformation graphs showing results of measurement of elongation percentages of aluminum alloys having different compositions according to an embodiment of the present invention;

FIG. 4 is a flowchart of a method of fabricating an aluminum alloy according to an embodiment of the present invention;

FIGS. 5A and 5B are transmission electron microscope images showing precipitation compounds in an aluminum-based matrix by heat treatment according to an embodiment of the present invention, and FIG. 5C is a graph showing ingredients of the precipitation compounds analyzed via an energy dispersive X-ray spectroscopy (EDS);

FIG. 6 is a scanning electron microscope image showing a cross-sectional microstructure of an aluminum alloy casted material supersaturated with a nonmetal element before heat treatment, according to a comparative embodiment;

FIG. 7 is a graph showing results of measuring tensile strength of an aluminum alloy according to an embodiment of the present invention and tensile strength of an aluminum alloy according to a comparative embodiment;

FIGS. 8A and 8B are graphs showing increases tensile strength and strength of aluminum alloys according to various compositions of a precipitation compound according to an embodiment of the present invention, respectively;

FIG. 9 is a graph showing results of measuring tensile strength of an aluminum alloy including a precipitation compound according to another embodiment and an aluminum alloy according to a comparative embodiment; and

FIG. 10 is a graph showing results of measuring tensile strength of an aluminum alloy (solid line curve) including a precipitation compound according to another embodiment and an aluminum alloy according to a comparative embodiment.

In the following description, the same or similar elements are labeled with the same or similar reference numbers.

DETAILED DESCRIPTION

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes”, “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. In addition, a term such as a “unit”, a “module”, a “block” or like, when used in the specification, represents a unit that processes at least one function or operation, and the unit or the like may be implemented by hardware or software or a combination of hardware and software.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Preferred embodiments will now be described more fully hereinafter with reference to the accompanying drawings. However, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
An aluminum alloy according to an embodiment of the present invention has a structure in which a nonmetal element is solidified in an aluminum-based matrix. The aluminum-based matrix refers to a matrix formed of pure aluminum or an aluminum alloy. In the aluminum alloy, a result of X-ray diffraction analysis in which no peak related to a compound due to a reaction between aluminum and the nonmetal element is shown other than a peak related to the crystalline phase of aluminum supports that, in the aluminum alloy, the nonmetal element is a solid solution solidified in the aluminum-based matrix. The fact has been confirmed through X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS) over a wide area of a fabricated aluminum-based matrix and, as shown in the XRD result of FIG. 2 (refer to the curve As-cast), only a pure aluminum crystal structure was detected.
The nonmetal element may include at least one of oxygen and nitrogen. The nonmetal element may be solidified to an amount of 1 wt % or less of the amount of aluminum. When the amount of the nonmetal element exceeds 1 wt % of aluminum, oxidation of the aluminum alloy occurs at a high priority, and thus it becomes difficult to harden the aluminum alloy. As a result, the elongation percentage of the aluminum alloy decreases.
The aluminum alloy may include a heterogeneous metal element other than aluminum. The heterogeneous metal element may include at least one of copper, iron, zinc, titanium, and magnesium. The heterogeneous metal element may be solidified to a range of 4 wt % or less, and the heterogeneous metal element may be solidified in an aluminum-based matrix in a substitutional or interstitial manner, but the present invention is not limited thereto. According to an embodiment, considering the atomic size and crystal structure of aluminum, the heterogeneous metal element, and a nonmetal heterogeneous element, the heterogeneous metal element may be mainly solidified in a substitutional manner and the heterogeneous nonmetal element may be mainly solidified in an interstitial manner.
An aluminum alloy as a solid solution according to an embodiment of the present invention may be fabricated using a casting process. According to an embodiment, the fabrication of the aluminum alloy may be initiated by providing melt. For example, the melt may be provided by heating pure aluminum by using an electric melting furnace.
In order to provide a nonmetal element that is solidified in the aluminum-based matrix, oxide particles or nitride particles of the heterogeneous metal element may be added to the melt. The oxide particles or nitride particles may have an average size (or diameter) from about 20 nm to about 100 nm. When the average size of the particles exceeds 100 nm, the oxide particles or nitride particles of the heterogeneous metal element may not be decomposed or may not be dispersed evenly in the aluminum matrix, and thus it becomes easier to form the second phase and it becomes difficult to form a solid solution of a nonmetal element. When the average size of the particles is less than 20 nm, it becomes difficult for the particles to be uniformly dispersed in the aluminum matrix due to the attractive force between the particles, and thus the second phase may be formed or solidification may become difficult.
The heterogeneous metal element may be copper, iron, zinc, titanium, magnesium or a mixture of two or more thereof, and the oxide particles or nitride particles may be, for example, copper oxide powder, iron oxide powder, zinc oxide powder, titanium oxide powder, magnesium oxide powder, copper nitrate powder, iron nitride powder, zinc nitride powder, titanium nitride powder, magnesium nitride powder, or a mixture of two or more thereof. The powder selected from among the above-stated powders may be added to the melt within a range of 1 wt % or less of aluminum, which is the solidifying rate of the nonmetal element. A stirring process for uniform mixing of the powder added into the melt may be performed.
The melt may be maintained at a temperature at which the added oxide particles or nitride particles may be decomposed. For example, while maintaining the melt at a temperature in the range of 500° C. to 1,000° C., the melt may be stirred with the added particles, such that the added particles may be homogeneously decomposed. In this process, the particles are decomposed into the heterogeneous metal element and the nonmetal element and are uniformly dispersed in the melt, and thus the heterogeneous metal element and the nonmetal element may be solidified in the aluminum-based matrix. According to an embodiment, at this stage, the heterogeneous metal element and the nonmetal element may be completely solidified. Alternatively, according to another embodiment, the nonmetal element may be completely solidified in a subsequent additional heat treatment process.
The heterogeneous metal element and the heterogeneous nonmetal element are uniformly dispersed in the melt and then cooled to form an aluminum casted material. According to another embodiment, an operation for artificially aging a casted material at a high temperature may be further performed to form the aluminum casted material. The artificial aging treatment may increase the strength of an aluminum alloy.
According to another embodiment, the aluminum casted material may be subjected to a plastic deformation process to form a processed aluminum material. The plastic deformation process may be a cold process and, through the plastic deformation process, work hardening of the aluminum casted material may occur. The plastic deformation process may be performed by rolling or pressing the aluminum casted material. However, the processes are merely examples, and the present invention is not limited thereto. Any process capable of providing appropriate compression or shearing stress that causes deformation may be performed. A twin boundary or partial dislocation described below may be induced through the plastic deformation process.
According to another embodiment, a heat treatment may be performed on the aluminum casted material or on the processed aluminum material. The heat treatment may be carried out at temperatures within different ranges according to purposes. In unlimited examples, a heat treatment for solidification may be performed at a temperature from about 400° C. to about 500° C., a heat treatment for artificial aging may be performed at a temperature from about 120° C. to about 180° C. for a period of time from about 6 hours to about 24 hours. A heat-treated aluminum material may maintain all of the microstructure, the strength, and the elongation as described above even after the heat treatment(s).
The inventors of the present invention conducted structural analysis and evaluation of elongation for the aluminum casted material, the processed aluminum material, or heat-treated aluminum material fabricated as described above. As a result, the presence of twin boundaries and partial dislocations were confirmed in all of the aluminum casted material, the processed aluminum material, and heat-treated aluminum material, and remarkable characteristics including significant decrease of the stacking fault energy of an aluminum alloy due to the solidification of oxygen or nitrogen and the improved elongation percentage due to the same were obtained.
FIGS. 1A and 1B are transmission electron microscope (TEM) analysis images showing the microstructure of an aluminum alloy according to an embodiment of the present invention.
Referring to FIGS. 1A and 1B, the aluminum alloy is an aluminum casted material in which zinc is solidified as a metal heterogeneous element and oxygen is solidified as a nonmetal element. As described above, zinc and oxygen were solidified in the aluminum-based matrix to an amount of about 0.5 wt % each, which is less than or equal to 1 wt % of the aluminum. Zinc oxide powder was added to the molten aluminum to solidify the oxygen, and the zinc powder was decomposed and kneaded in the molten aluminum.
It is confirmed that the aluminum alloy has a twin boundary (indicated by a yellow arrow in FIG. 1A) whose lattices on both sides are symmetrical or a partial dislocation (indicated by a yellow arrow in FIG. 1B). The twin boundary is a structure in which atoms on a first side and atoms on a second side are symmetrically arranged around an interface between crystal grains of the both sides as if the atoms are reflected in a mirror. The twin boundary may be formed through the above-stated mechanical plastic deformation or the aging treatment after plastic deformation.
Simultaneously as the elongation percentage of the aluminum alloy is improved as the stacking fault energy is reduced due to the solidification of oxygen, the twin boundary effectively interrupts slip action due to a dislocation based on the reduction of the stacking fault energy, thereby providing a mechanism for improving material strength. Therefore, an aluminum alloy according to the embodiment of the present invention exhibits improved workability and improved mechanical strength simultaneously due to improved elongation percentage.
FIG. 2 is a graph showing a result of X-ray diffraction analysis for measuring stacking fault energy (SFE) of an aluminum alloy having a twin boundary or partial dislocation according to an embodiment of the present invention. As a method of calculating stacking fault energy, a method of calculating the stacking fault energy from an X-ray diffraction analysis result was selected to measure stacking fault energy of the aluminum alloy according to the embodiment of the present invention.
Referring to FIG. 2, micro-deformation of about 5% of an as-cast casted aluminum alloy was induced and stacking fault energy (SFE) was calculated from movements and/or size changes of peaks. The respective constants required in the Equations 1 through 4 below may be calculated based on the disclosures and experiment results of the thesis “The effect of nitrogen on the stacking fault energy in Fe-15Mn-2Cr-0.6C-xN twin boundary-induced plasticity steels” (Lee, et al., Vol. 92, pages 23-24 of Scripta Materialia, 2014), the thesis “Thermodynamic and physical properties of FeAl and Fe₃Al: anatomistic study by EAM simulation” (Ouyang et al., the 2012 edition of Physica B. Vol. 407, pp. 4530-4536)), and the thesis “The Relationship between Stacking-fault energy and x-ray measurements of stacking-fault probability and microstrain ((R. P. Reed and R. E. Schramm, the 1974 edition of J. Appl. Phys. Volume 45, page 4705).
$\begin{matrix} Δ (2 θ_{200} - 2 θ_{111}) = - \frac{90 \sqrt{3}}{π^{2}} (\frac{\tan θ_{200}}{2} + \frac{\tan θ_{111}}{4}) P_{sf} & [Equation 1] \end{matrix}$
Here, θ₂₀₀is the Bragg angle of an aluminum crystal surface 200, θ₁₁₁is the Bragg angle of an aluminum crystal surface 111, and P_sfis the stacking fault probability. The θ₂₀₀may be determined according to Equation 2, and the θ₁₁₁may be determined according to Equation 3.
2θ₂₀₀=2₂₀₀ ^cw−2θ₂₀₀ ^ANN [Equation 2]
Here, θ₂₀₀ ^cwis the Bragg angle of the crystal surface 200 of a sample in which the 5% deformation is induced, and 2θ₂₀₀ ^ANNis the Bragg angle of the crystal surface 200 of an annealed sample. 2θ₂₀₀is a shift value of a relative X-ray peak appearing on the crystal surface 200.
2θ₁₁₁=2₁₁₁ ^cw−2θ₁₁₁ ^ANN [Equation 3]
Here, θ₁₁₁ ^cwthe Bragg angle of the crystal surface 111 of the sample in which the 5% strain is induced, and 2θ₁₁₁ ^ANNis the Bragg angle of the crystal surface 111 of the annealed sample. 2θ₁₁₁is a shift value of a relative x-ray peak appearing on the crystal surface 111.
$\begin{matrix} SFE = \frac{K_{111} w_{0} G_{(111)} a_{0} A^{- 0.37}}{π \sqrt{3}} \frac{< ɛ_{5 0}^{2} > 111}{α} & [Equation 4] \\ α = \frac{C_{44} + C_{11} - C_{12}}{3 P_{sf}} & [Equation 5] \end{matrix}$
In Equation 4, the value of K_111ω0is 5.4 (refer to the thesis “Thermodynamic and physical properties of FeAl and Fe₃Al: anatomistic study by EAM simulation”), G₍₁₁₁₎is the shearing stress and is about 24.3667 GPa for aluminum, a₀is the lattice constant and is about 0.40495 nm, and A is the vector constant and is 2.8571 for aluminum. ε² ₅₀is the microstrain and the value thereof is determined according to intensity regarding a corresponding surface in an X-ray diffraction analysis. C₄₄, C₁₁, and C₁₂in Equation 5 are the elastic constants of materials, where the subscripted numbers indicate respectively given stress directions.
The stacking fault energy of pure aluminum is about 162 mJ/m². However, in the case of the aluminum alloy according to the embodiment of the present invention, the stacking fault energy is reduced by about ⅓. The stacking fault energy may be appropriately adjusted within a range of less than 100 mJ/m²depending on types or added amounts of the heterogeneous metal element and the heterogeneous nonmetal element. Specifically, in the aluminum alloy according to an embodiment of the present invention, at least one fault from between twin boundary and partial dislocation appears. The stacking fault energy may be appropriately adjusted within a range of 100 mJ/m²even in the case of a processed material and a heat-treated material of an aluminum alloy according to an embodiment to the present invention in which oxygen or nitrogen is limitedly solidified as well as the above-stated casted material.
Table 1 shows measured stacking fault energies of aluminum alloys, which are a casted material, a processed material, and a heat-treated material, according to an embodiment of the present invention, compared to the stacking fault energy of pure aluminum. In the A16061 alloy and the A356 alloy as well as pure aluminum, according to embodiments of the present invention, stacking fault energies are remarkably reduced. The A16061 alloy and the A356 alloy are merely examples, and the present invention is not limited thereto. For example, elongation of other aluminum alloys from AL1xxx series to AL7xxx series, such as AL1050, AL1060, AL1070, AL2011, AL2024, AL3003, AL4032, AL5052, AL5052, AL6063, or AL7075, may be improved through solidification of oxygen or nitrogen.

TABLE 1

		Stacking fault energy
Material	Composition	(mJ/m²)

Pure Aluminum	100% AL	162
Aluminum Casting	100% AL-O	48.65
Material
Processed	AL6061-O	60.55
Aluminum Material
Heat-Treated	AL6061-O	82.4
Aluminum Material

The reduction of the stacking fault energy facilitates formations of the twin boundary and the partial dislocation, and thus elongation percentage may be improved while securing strength.
FIGS. 3A through 3C are stress-deformation graphs showing results of measurement of elongation percentages of aluminum alloys having different compositions according to an embodiment of the present invention.
Referring to FIG. 3A, the elongation percentage of an oxygen-solidified aluminum alloy (see the curve As-cast A356-O), which is a casted material according to an embodiment of the present invention, increased by up to 100% as compared to a casted material (see the curve As-cast A356) according to a comparative embodiment. The increase of the elongation percentage is due to reduction of stacking fault energy according to an embodiment of the present invention.
Referring to FIG. 3B, the elongation percentage of an oxygen-solidified aluminum alloy (see the curve Treated A356-O), which is a heat-treated material according to an embodiment of the present invention, increased by up to 100% as compared to a heat-treated aluminum alloy (see the curve Treated A356) according to a comparative embodiment. Furthermore, the tensile strength (M) of the oxygen-solidified aluminum alloy according to an embodiment of the present invention was improved by 30% or more as compared to the heat-treated aluminum alloy according to a comparative embodiment, together with the improvement of the elongation percentage. The improvement in the tensile strength is due to reduction of stacking fault energy and a twin boundary and/or a partial dislocation associated with the same.
Referring to FIG. 3C, an A356 alloy (see the Curved Treated A356-O), which is another processed material according to an embodiment of the present invention, was also oxygen-solidified, and thus tensile strength thereof was improved by 30% and the elongation percentage thereof was also increased by 100% or more.
The reduced stacking fault energy may improve the elongation of an aluminum alloy, thereby improving the workability of the aluminum alloy. The aluminum alloy is not limited to a casted material, and the elongation percentage may be improved in both of the processed material and the heat-treated material as described above.
According to another embodiment of the present invention, the aluminum alloy may have a structure in which a precipitated compound is dispersed in an aluminum alloy base. The precipitation compound refers to aluminum, a transition metal, a nonmetal element, and a compound that may be formed by including the same. The aluminum-based matrix refers to a matrix formed of pure aluminum or a conventional aluminum alloy. The aluminum alloy may be fabricated via a casting process described below.
FIG. 4 is a flowchart of a method of fabricating an aluminum alloy according to an embodiment of the present invention.
Referring to FIG. 4, according to an embodiment of the present invention, melt of an aluminum alloy may be provided (operation S10). The melt may be provided by heating the aluminum alloy using an electric melting furnace. The heating temperature of the melt may be within a range from 650° C. to 850° C. The heating temperature of the melt is merely an example, and an appropriate temperature may be determined according to compositions of the aluminum alloy in the melt and/or an impurity in the aluminum alloy. Therefore, the present invention is not limited thereto.
The aluminum alloy may include any alloying element that may be solidified in aluminum. According to an embodiment, the alloying element may include a transition metal. For example, the transition metal may be scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni), copper (Cu), silver (Ag), zinc (Zn), or at least two or more thereof. According to an embodiment, the transition metal may include at least one of chromium (Cr), iron (Fe), and manganese (Mn), which are Groups VI to VIII element in period 4. According to another embodiment, in addition to the transition metal, the alloying element may further include a non-transition metal element, such as silicon (Si), magnesium (Mg), tungsten (W), calcium (Ca), strontium (Sr), and beryllium (Be). Furthermore, the aluminum alloy may be a known alloy including the transition metal. For example, as a known alloy, an A356 alloy including Fe from 0.2 to 0.3 wt % or an A6061 alloy including Fe from 0.5 to 0.7 wt % is available.
In the present specification, a transition metal of a kind actually included in an aluminum alloy as a starting material provided as a melt from among the above-stated transition metals is referred to as a first transition metal, whereas a transition metal not included in the aluminum alloy and is of a kind different from the first transition metal is referred to as a second transition metal. For example, when chromium (Cr), iron (Fe), and manganese (Mn), which are transition metals, are included as the alloying element in the molten aluminum as the starting material, chromium (Cr), iron (Fe) and manganese (Mn) that are included in the molten aluminum in advance may be referred to as first transition metals in the present specification. According to an embodiment, powder of a compound of at least one of the first transition metals and a nonmetal element is added into the molten aluminum preliminarily including the first transition metals to form a casted material therefrom and heat treatment is performed thereto, thereby forming a ternary precipitation compound including at least one of the first transition metals in an aluminum-based matrix. According to another embodiment, since the first transition metal is preliminarily included in the molten aluminum, powder of a compound of a non-transition metal and a nonmetal element is added to the molten aluminum to form a casted material and heat treatment is performed thereto, thereby forming a ternary precipitation compound including aluminum, a first transition metal, and a nonmetal element in an aluminum-based matrix.
According to another embodiment, when the molten aluminum includes only chromium (Cr) and iron (Fe) and does not include manganese (Mn), the first transition metal may include chromium (Cr) and iron (Fe) and manganese (Mn) not included in the molten aluminum may be referred to as a second transition metal. As described below, powder of a compound of the second transition metal and a nonmetal element is added to the molten aluminum to form a casted material and heat treatment is performed thereto, thereby forming a ternary precipitation compound including at least one of the first transition metal and the second transition metal in an aluminum-based matrix.
According to another embodiment, there is no transition metal in the molten aluminum. In this case, powder of a compound of the second transition metal and a nonmetal element is added to the aluminum melt to form a casted material and a heat treatment is performed thereto, thereby forming a ternary precipitation compound including the second transition metal in an aluminum-based matrix.
A nonmetal element-containing precursor including at least one of oxygen (O), nitrogen (N), and carbon (C) may be added to and mixed in the molten aluminum (operation S20). Next, the added nonmetal element-containing precursor is decomposed in the molten aluminum, and thus the nonmetal element may be supersaturated in the molten aluminum (S30). The nonmetal element-containing precursor is a compound of a first reaction compound, which is a compound between the first transition metal and the nonmetal element, or a second reaction compound, which is a compound between the second transition metal (a transition metal different from the first transition metal) and the nonmetal element. According to another embodiment, the nonmetal element-containing precursor may also be a third reaction compound, which is a compound between a non-transition metal and the nonmetal element.
According to an embodiment, when zinc (Zn), which is a first transition metal, is present as an aluminum alloying element in the molten aluminum, the first reaction compound may be, for example, a second transition metal, e.g., an oxide including chromium (CrO₂), and a nonmetal element-containing precursor including the first reaction compound may be added to the molten aluminum. In another example, the nonmetal element-containing precursor may include a third reaction compound including a non-transition metal element (e.g., silicon), e.g., silicon oxide (SiO₂). When the first transition metal already exists in the molten aluminum, the third reaction compound may be used as the nonmetal element-containing precursor, thereby forming a ternary precipitation compound including aluminum, a first transition metal, and a nonmetal element in a casted aluminum-based matrix.
In the case where a transition metal such as zinc, titanium, copper, and iron is not included in the molten aluminum as the alloying element, the nonmetal element-containing precursor is a second reaction compound that is a compound of a second transition metal and a nonmetal element, where a nonmetal element-containing precursor including zinc oxide (ZnO), titanium oxide (TiO₂), copper oxide (CuO₂), iron oxide (Fe₂O₃), copper nitride (CuN), iron nitride (FeN), zinc nitride (ZnN), titanium nitride TiN), magnesium nitride (MgN), or a mixture thereof may be added to the molten aluminum. These are merely examples, and the present invention is not limited thereto.
According to another embodiment, the nonmetal element-containing precursor may be a third reaction compound between a non-transition metal element and a nonmetal element. For example, the third reaction compound may include a reaction compound between a non-transition metals, such as aluminum (Al), magnesium (Mg), silicon (Si), or tungsten (W), and the non-metal element, that is, aluminum oxide (Al₂O₃), aluminum nitride (AlN), magnesium oxide (MgO₂), silicon oxide (SiO₂), silicon carbide (SiC), silicon nitride (Si₃N₄), tungsten oxide (WO), tungsten nitride (WN), or a mixture thereof. However, they are merely examples, and the present invention is not limited thereto. Furthermore, the first through third reaction compounds, which are the nonmetal element-containing precursors, may be added to the molten aluminum alone or in combination of two or more thereof.
According to an embodiment, the nonmetal element-containing precursor may be provided in the form of powders, such that the specific surface area of the nonmetal element-containing precursor is large and the nonmetal element-containing precursor may be easily decomposed at a high temperature. For example, the nonmetal element-containing precursor may have an average diameter within a range from about 5 nm to about 50 nm. When the diameter is 50 nm or more, the decomposition of the nonmetal element-containing precursor is difficult, and thus formation of a precipitation compound described later may be difficult. The above-stated first reaction compound and second reaction compound may be added to the molten aluminum alone or in combination with each other.
According to an embodiment, the nonmetal element-containing precursor may be mixed in the range from 0.01 wt % to 5.0 wt % of the total weight of the molten aluminum. When the mixing amount of the nonmetal element-containing precursor is less than 0.01 wt %, it is difficult for the nonmetal element to be supersaturated in the molten aluminum alloy. On the contrary, when the mixing amount exceeds 5.0 wt %, it is difficult to form a precipitation compound having a uniform composition including three ingredients, that is, aluminum, a transition metal, and a nonmetal element. When an excessive amount of nonmetal element-containing precursor is present in the molten aluminum, formation of a second phase, such as a reaction compound between the transition metal and the nonmetal element or a reaction compound between aluminum and the non-metal element, may be accelerated. The nonmetal element may be mixed over the solubility limit, such that the nonmetal element may be supersaturated with respect to aluminum of an aluminum-based matrix at the room temperature within the composition range of the nonmetal element-containing precursor.
The molten aluminum in which the nonmetal element is uniformly mixed and supersaturated is solidified, and thus a casted material is formed (operation S40). The molten aluminum may be solidified by cooling the same.
Next, the solidified casted material is heat-treated to precipitate a ternary reaction compound between aluminum-a transition metal-a nonmetal element, thereby forming the precipitated compound uniformly dispersed in an aluminum-based matrix (operation S50). The transition metal of the ternary reaction compound may include at least one kind of transition metal. For example, the ternary reaction compound may be an aluminum-zinc-oxygen ternary reaction compound or the ternary reaction compound may include iron, chromium, scandium, manganese or two or more metals in place of or in addition to zinc. These compounds are merely examples, and the present invention is not limited thereto. The nonmetal element of the ternary reaction compound may also include at least one nonmetal element. For example, the ternary reaction compound may be aluminum-zinc-oxygen ternary reaction compound or may include nitrogen, carbon, which are nonmetal elements other than oxygen, or all of them in addition to or in place of oxygen.
As described below with reference to FIG. 4, the precipitation compound is a nano-sized crystal grain and may have an average size from about 10 nm to about 1 μm. When the size of the precipitated compound is less than 10 nm, it cannot strongly interact with dislocations formed in an aluminum alloy and cannot contribute to the improvement of strength. When the size exceeds 1 μm, the precipitation compound becomes rather brittle, and thus it cannot contribute to the improvement of strength.
The precipitation compound, which is a ternary reaction compound, is stably formed in the aluminum-based matrix through heat treatment, rather than being formed in a cooling process for solidification as described later. As a result, according to an embodiment of the present invention, the precipitation compound may be uniformly formed in an aluminum-based matrix without segregation or coagulation as compared to a non-heated alloy.
The heat treatment may be performed at a temperature within a range from about 120° C. to about 600° C. When the temperature is lower than 120° C., precipitation of the reaction compound may not occur. When the temperature exceeds 600° C., an aluminum-based matrix is melted and, even when the precipitation compound is formed, the precipitation compound and the aluminum-based matrix are agglomerated with each other, and thus an aluminum alloy structure having the precipitation compound uniformly dispersed therein cannot be obtained.
According to an embodiment, the heat treatment may include a single heating operation or at least two heating operations. For example, a solidified product may be heat-treated at 540° C. for 12 hours and at 160° C. for 8 hours. The above-stated temperature ranges and times are merely examples and may be appropriately selected to prevent agglomeration and segregation of the precipitation compound.
According to an embodiment, the casted material may be further subjected to plastic working and hardening before the heat treatment (operation S45). The above plastic working may be performed through plastic deformation, such as rolling, extrusion, drawing, or forging. The plastic working may be a hot process or a cold process, but the present invention is not limited thereto. For example, the plastic working may be artificially aged without cold working after a solution treatment. The above-stated precipitation compound may be additionally formed in the aluminum-based matrix through the above-stated plastic working or the precipitation compound may have a strong interaction with a dislocation formed due to a deformation, and thus the strength of an aluminum alloy may be further improved.
The below examples relate to specific experimental examples. However, the examples are not intended to limit the invention, but are representative examples for illustrative purposes and, due to common electrical, chemical and physical characteristics of transition metals, embodiments other than those shown therein are also included in the present invention.

Experimental Example

An aluminum alloy (e.g., A356 alloy) including an aluminum alloy, iron as a first transition metal, and silicon as a non-transition metal was melted by using an electric heating furnace to form a melt. Next, zinc oxide particles or powder having an average particle size of about 30 nm, which is within a range from 5 nm to 50 nm, were added to the melt as a nonmetal element-containing precursor and decomposed. The zinc oxide particles were injected and stirred by about 1 wt % or 1.5 wt %, which is in the range from 0.01 wt % to 5.0 wt % of the total wt % of the melt. A nonmetal element was supersaturated in the melt of the aluminum alloy and solidified as it is to form a casted material of the aluminum alloy in which oxygen as a nonmetal element is supersaturated. Next, the casted material was subjected to a standard T6 heat treatment.
FIGS. 5A and 5B are transmission electron microscope images showing precipitation compounds in an aluminum-based matrix by heat treatment according to an embodiment of the present invention, and FIG. 5C is a graph showing ingredients of the precipitation compounds analyzed via an energy dispersive X-ray spectroscopy (EDS). FIG. 6 is a scanning electron microscope image showing a cross-sectional microstructure of an aluminum alloy casted material supersaturated with a nonmetal element before heat treatment, according to a comparative embodiment.
The aluminum alloy shown in FIGS. 5a and 5b is an aluminum alloy in which a precipitation compound was formed after an aluminum alloy casted material to which a ZnO precursor is added by about 1.5 wt % was subjected to T6 heat treatment for 12 hours at 540° C. and for 8 hours at 160° C. In order to observe the deformation behavior of the aluminum alloy including the precipitation compound, the aluminum alloy was subjected to tensile deformation of about 15%, and then observed with a transmission electron microscope. It may be observed that the precipitation compound (NP) according to an embodiment of the present invention strongly interacts with the dislocation (DL).
Referring to FIG. 5C, it may be observed that the precipitation compound includes three kinds of elements, aluminum-iron-oxygen. Here, silicon is an ingredient derived from an aluminum alloy existing in the melt and is independent from the composition of the precipitation compound. The precipitation compound is a new reaction compound between aluminum-transition metal-nonmetal element which are not precipitated from a conventional aluminum alloy, forms a very favorable interface with an aluminum-based matrix, and strongly interacts with a dislocation in the aluminum-based matrix, thereby improving strength of the aluminum alloy.
Referring to FIG. 6, the bright needle-shaped structure is a silicon phase in an aluminum alloy, and the dark region is an aluminum-based matrix. Since the aluminum casted material was not subjected to a heat treatment, no observable-sized precipitation compound according to an embodiment of the present invention is observed in the aluminum-based matrix.
FIG. 7 is a graph showing results of measuring tensile strength of an aluminum alloy according to an embodiment of the present invention and tensile strength of an aluminum alloy according to a comparative embodiment.
Referring to FIG. 7, an aluminum alloy according to an embodiment of the present invention is fabricated by adding a precursor powder of ZnO to the melt of an A356 alloy to form a casted material and performing a heat treatment to the casted material. The aluminum alloy according to the comparative embodiment was fabricated by forming a casted material without adding precursor powder to molten aluminum and performing heat treatment thereto under the same conditions. It may be seen that the tensile strength of the aluminum alloy according to the embodiment of the present invention (the solid line curve) is improved by about 35% or more as compared to the aluminum alloy according to the comparative embodiment (dotted line curve).
FIGS. 8A and 8B are graphs showing increases tensile strength and strength of aluminum alloys according to various compositions of a precipitation compound according to an embodiment of the present invention, respectively.
For example, referring to FIGS. 8A and 8B, various aluminum alloys including precipitation compounds containing transition metals, that is, manganese (curve b), titanium (curve c), and iron (b) in aluminum-based matrix including 7 wt % of silicon and 0.3 wt % of magnesium exhibited improved strengths as compared to an aluminum alloy including no transition metal (curve a). Particularly, the aluminum alloys including precipitation compound containing chromium and iron exhibited improved strength, and the aluminum alloy including precipitation compound containing manganese also exhibited improved tensile strength.
FIG. 9 is a graph showing results of measuring tensile strength of an aluminum alloy including a precipitation compound according to another embodiment and an aluminum alloy according to a comparative embodiment.
Referring to FIG. 9, the aluminum alloy according to an embodiment of the present invention is an aluminum alloy including a precipitation compound formed by adding 1.0 wt % of ZnO precursor powder to the melt of an aluminum alloy of Al—Si (7 wt %)-Mg (0.3 wt %)-Fe (0.3 wt %). On the contrary, the aluminum alloy according to the comparative embodiment is an aluminum alloy obtained by forming a casted material without adding ZnO, which is a nonmetal element-containing precursor, to the melt of an aluminum alloy and heat-treating the casted material. It was observed that the aluminum alloy according to an embodiment of the present invention (solid line curve) shows an improvement in yield strength of about 22% as compared to the aluminum alloy according to the comparative embodiment (dotted curve).
FIG. 10 is a graph showing results of measuring tensile strength of an aluminum alloy (solid line curve) including a precipitation compound according to another embodiment and an aluminum alloy according to a comparative embodiment.
Referring to FIG. 10, the aluminum alloy according to an embodiment of the present invention indicated by the solid line is an aluminum alloy fabricated by forming a casted material by adding about 2.0 wt % of ZnO precursor powder to the melt of an aluminum alloy of Al—Si (2 wt %)-Mg (1.0 wt %)-Mn (0.3 wt %), re-crystallizing the casted material via 90% plastic rolling, and performing a heat treatment thereto. The aluminum alloy according to the comparative embodiment is an aluminum alloy fabricated by forming a casted material without adding the precursor powder to the melt of an aluminum alloy, performing the plastic operation to the casted material, and heat-treating the same. The aluminum alloy according to an embodiment of the present invention exhibited yield strength improvement by about 13% as compared to the aluminum alloy according to the comparative embodiment.
As described above, an aluminum alloy including the precipitation compound between aluminum-transition metal-nonmetal elements according to an embodiment of the present invention may be fabricated using a casting operation and a heat treatment operation. The above-described experimental examples are merely examples, and the present invention is not limited thereto. For example, even in the case of nitrogen and carbon, which are nonmetal elements capable of forming ternary reaction compounds as stable as a ternary reaction compound formed by using oxygen, which is a nonmetal element, may form a precipitation compound uniformly din an aluminum-based matrix, thereby improving strength of an aluminum alloy.
According to the above embodiments, material properties of an aluminum alloy are enhanced and improved by controlling stacking fault energy or employing a precipitation compound including a transition metal, which is obtained via a process employing nanoparticle precursor powder.
According to the embodiment of the present invention, there may be provided an aluminum alloy with high strength and improved workability based on elongation percentage improved as stacking fault energy is reduced due to solidification of a nonmetal element in an aluminum-based matrix and strength improved by a microstructure including a twin boundary or a partial dislocation.
According to another embodiment of the present invention, particles of a metal oxide or a metal nitride are added in the form of powders to the melt of aluminum or an aluminum alloy providing an aluminum matrix to reduce stacking fault energy and/or form a partial dislocation, thereby providing a highly-stretchable aluminum alloy having the above-described advantages in high production yield.
According to another embodiment of the present invention, a compound including aluminum-transition metal-nonmetal element or a compound including the above-stated elements is precipitated in an aluminum-based matrix via a heat treatment. As the precipitate is formed uniformly in the aluminum-based matrix and the precipitation compound strongly interacts with a dislocation, an aluminum alloy with significantly improved strength may be provided.
According to another embodiment of the present invention, a method of reliably fabricating an aluminum alloy having the above advantages may be provided.
While the present disclosure has been described with reference to the embodiments illustrated in the figures, the embodiments are merely examples, and it will be understood by those skilled in the art that various changes in form and other embodiments equivalent thereto can be performed. Therefore, the technical scope of the disclosure is defined by the technical idea of the appended claims.
The drawings and the forgoing description gave examples of the present invention. The scope of the present invention, however, is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of the invention is at least as broad as given by the following claims.

Claims

What is claimed is:

1. An aluminum alloy comprising:

an aluminum-based matrix; and

a nonmetal element solidified in the aluminum-based matrix,

wherein stacking fault energy of the aluminum alloy is decreased compared to that of pure aluminum.

2. The aluminum alloy of claim 1, wherein the nonmetal element comprises at least one of oxygen and nitrogen.

3. The aluminum alloy of claim 1, wherein the nonmetal element is solidified to less than or equal to 1 wt % of aluminum of the aluminum-based matrix.

4. The aluminum alloy of claim 1, wherein the stacking fault energy of the aluminum alloy is less than 100 mJ/m².

5. The aluminum alloy of claim 1, wherein at least a portion of the aluminum-based matrix comprises a twin boundary or a partial dislocation.

6. The aluminum alloy of claim 1, wherein the nonmetal element is solidified in the aluminum alloy by adding nanoparticles of a metal compound between the nonmetal element and a heterogeneous metal element to molten aluminum and decomposing the nanoparticles into the nonmetal element and the heterogeneous metal element.

7. A method of fabricating an aluminum alloy comprising:

providing the melt of aluminum or an aluminum alloy providing an aluminum-based matrix;

adding nanoparticles of a metal compound between a nonmetal element and a heterogeneous metal element to the melt;

uniformly dispersing the nonmetal element and the heterogeneous metal element in the melt through decomposition of the nanoparticles into the nonmetal element and the heterogeneous metal element; and

cooling the melt so as to solidify the nonmetal element in at least a portion of the aluminum-based matrix.

8. The method of claim 7, wherein the stacking fault energy of the aluminum alloy is less than 100 mJ/m².

9. The method of claim 7, wherein the heterogeneous metal element comprises copper, iron, zinc, titanium, magnesium, or a mixture of two or more thereof.

10. The method of claim 7, wherein the nonmetal element comprises at least one of oxygen and nitrogen.

11. The method of claim 7, wherein the nonmetal element is solidified to less than or equal to 1 wt % of aluminum of the aluminum-based matrix.

12. The method of claim 7, wherein the average size of the nanoparticles is from about 20 nm to about 100 nm.

13. An aluminum alloy comprising:

an aluminum-based matrix; and

a precipitation compound dispersed in the aluminum-based matrix,

wherein the precipitation compound comprises a compound containing aluminum, one or more transition metals, and one or more nonmetal elements or a compound containing the above-stated elements.

14. The aluminum alloy of claim 13, wherein the average size of the precipitation compound is from about 10 nm to about 1 μm.

15. The aluminum alloy of claim 13, wherein the transition metal comprises at least one of chromium (Cr), iron (Fe), and manganese (Mn).

16. The aluminum alloy of claim 13, wherein the nonmetal element is supersaturated in the aluminum and comprises at least one of oxygen, nitrogen, and carbon.

17. The aluminum alloy of claim 13, wherein the precipitation compound is formed via a heat treatment.

18. The aluminum alloy of claim 13, wherein the aluminum-based matrix comprising:

an aluminum alloy; and

alloying elements of the aluminum alloy comprises at least one of silicon (Si), zinc (Zn), magnesium (Mg), and copper (Cu).

19. A method of fabricating an aluminum alloy comprising:

providing the melt of an aluminum alloy comprising aluminum and a first transition metal;

adding a nonmetal element-containing precursor comprising at least one of a first reaction compound between the first transition metal and a nonmetal element, a second reaction compound between a second transition metal different from the first transition metal and the nonmetal element, and a third reaction compound between a non-transition metal and the nonmetal element to the melt;

supersaturating the nonmetal element in the melt through decomposition of the nonmetal element-containing precursor in the melt;

forming a casted material by hardening the melt; and

forming a precipitation compound between aluminum, a transition metal, and a nonmetal element dispersed in an aluminum-based matrix by heat-treating the hardened casted material.

20. The method of claim 19, wherein the first transition metal comprises at least one of chromium (Cr), iron (Fe), and manganese (Mn).

21. The method of claim 19, wherein the nonmetal element comprises at least one of oxygen, nitrogen, and carbon.

22. The method of claim 19, wherein the non-transition metal of the third reaction compound comprises at least one of aluminum (Al), silicon (Si), magnesium (Mg), and tungsten (W).

23. The method of claim 19, wherein the nonmetal element-containing precursor is added to the melt in the form of power having the average diameter within a range from about 5 nm to about 50 nm.

24. The method of claim 23, wherein the nonmetal element-containing precursor is added in the range from 0.01 wt % to 5.0 wt % of the total weight of the melt.

25. The method of claim 19, further comprising plastic working and hardening the hardened casted material before the hardened casted material is heat treated.

26. The method of claim 19, wherein the heat treatment is performed at a temperature within a range from 120° C. to 600° C.