High-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, and a method for manufacturing the same.

Abstract

To provide an aluminum casting alloy with high strength, high elongation, and high thermal conductivity, and to provide a method for manufacturing the same. [Solution] The present invention provides a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy comprising 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.32% to 0.85% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities, and containing an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy and a method for producing the same, and more particularly, to an aluminum casting alloy having high strength, high elongation, and high thermal conductivity, and a method for producing the same.

Background Art

[0002] Due to environmental regulations and the demand for improved fuel efficiency, the electric-powered vehicle market is expanding rapidly. In the case of electric-powered vehicles, due to the increase in batteries, electrical components, and safety components, lightweight technologies for ensuring driving range are essential. In particular, it is important to ensure the high heat dissipation characteristics of aluminum, which directly affect the performance and lifespan of the finished products of major electrical modules. High-performance aluminum casting material technologies that take into account the characteristics of "high strength vs. high elongation", "high strength vs. high thermal conductivity", and "high fluidity vs. high thermal conductivity", which generally have an opposing relationship in aluminum alloys, are in an absolutely insufficient situation.

[0003] On the other hand, it has been reported that recycling aluminum can save about 95% of the energy required to make metal from virgin raw materials. Despite such strong economic and environmental advantages, in the recycling process, aluminum alloys accumulate Fe at a level of 0.4 to 0.8% by weight as the main impurity, which acts as a cause for restricting the use of scrap in many automotive parts industries by reducing the ductility of the material.

[0004] It has been reported that the presence of a small amount of Fe in an Al-Si alloy generates a β-Al5FeSi phase, a hard and brittle Fe-based intermetallic compound with low cohesive force with the aluminum matrix. For example, when 0.4% or more of Fe is added to an Al-7Si alloy, a coarse, needle-shaped β-Al5FeSi phase, reaching several hundred micrometers in size, is formed during solidification before the Al-Si eutectic reaction. In practice, attempts are being made to neutralize the β-Al5FeSi intermetallic compound by modifying it with chemical additives (e.g., Mn, Co, Cr, Mo). However, such research is mainly limited to reports on the phenomenological aspects, and there is absolutely no research on the control mechanism of the generated phase or its relationship to physical / mechanical properties.

[0005] A relevant prior art document is Korean Published Patent No. 10-2016-0048777. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] The technical problem that this invention aims to solve is to provide an aluminum casting alloy with high strength, high elongation, and high thermal conductivity, and to provide a method for manufacturing the same. As described above, the formation of coarse needle-like β-Al5FeSi phases can negatively affect the strength, ductility, and conductivity of the material. However, by changing the approach and controlling the formation phase of such Fe-based intermetallic compounds, this invention aims to provide an aluminum casting alloy that can simultaneously increase 'strength and elongation', and to provide a method for manufacturing the same. [Means for solving the problem]

[0007] An embodiment of the present invention for solving the above problems provides a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy comprising 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.32% to 0.85% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and containing an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0008] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the α-AlFeSi intermetallic compound having a cubic crystal structure has the same crystal structure as the α-AlMnSi phase, but does not contain Mn and can undergo a phase change from the β-Al5FeSi intermetallic compound.

[0009] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the aluminum casting alloy is characterized in that it does not contain manganese (Mn), cobalt (Co), chromium (Cr), or molybdenum (Mo) as an additive for neutralizing the β-Al5FeSi intermetallic compound. Neutralizing the β-Al5FeSi intermetallic compound includes controlling the shape of the β-Al5FeSi intermetallic compound or reducing brittleness through phase transformation.

[0010] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the α-AlFeSi intermetallic compound can have a composition of Al: 74.9-86.7 at.%, Fe: 6.9-14.3 at.%, and Si: 6.2-11.3 at.%.

[0011] The aforementioned high-strength, high-elongation, and high-thermal-conductivity aluminum casting alloy can have a yield strength in the range of 100 MPa to 140 MPa, a maximum tensile strength in the range of 180 MPa to 220 MPa, an elongation in the range of 2.5% to 8.5%, and a thermal conductivity in the range of 160 W / mK to 190 W / mK.

[0012] A method for producing a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy according to one embodiment of the present invention for solving the above problems comprises: a first step of providing a molten aluminum casting alloy containing 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.32% to 0.85% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and a second step of applying external energy to the molten aluminum casting alloy at a temperature higher than the liquidus temperature, and then cooling it, so that it contains an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0013] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include maintaining the molten aluminum casting alloy at a temperature 200°C to 300°C higher than the liquidus temperature, and then cooling it at a cooling rate of 1 K / sec or more.

[0014] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include maintaining the molten aluminum casting alloy at a temperature 100°C to 150°C higher than the liquidus temperature, and then cooling it at a cooling rate of 10K / sec or more.

[0015] In the method for producing the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the molten aluminum casting alloy can be characterized by maintaining a temperature higher than the liquidus temperature for 1 to 2 hours.

[0016] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the molten aluminum casting alloy can be characterized by applying ultrasonic waves to it at a temperature higher than the liquidus temperature and maintaining it for 1 to 2 minutes.

[0017] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include a phase change from a β-Al5FeSi intermetallic compound having a monoclinic crystal structure to an α-AlFeSi intermetallic compound having a cubic crystal structure.

[0018] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step allows the formation of the β-Al5FeSi intermetallic compound to occur before the Al-Si eutectic reaction, and the α-Al phase, which is the aluminum matrix, to be formed before the β-Al5FeSi intermetallic compound.

[0019] To solve the above problems, another embodiment of the present invention provides a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy comprising 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.2% to 0.3% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and containing an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0020] A method for producing a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy according to another embodiment of the present invention for solving the above problems comprises: a first step of providing a molten aluminum casting alloy containing 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.2% to 0.3% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and a second step of applying external energy to the molten aluminum casting alloy at a temperature higher than the liquidus temperature, and then cooling it, so that it contains an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix. [Effects of the Invention]

[0021] According to the embodiments of the present invention, it is possible to realize an aluminum casting alloy with high strength, high elongation, and high thermal conductivity, and a method for manufacturing the same. According to this, while increasing the allowable iron (Fe) content level of the aluminum casting material, it is possible to realize an aluminum casting alloy material that improves strength and at the same time has no decrease in elongation rate, and a method for manufacturing the alloy. Specifically, by applying external energy that can disintegrate the structure (e.g., bonding, clustering) of the molten aluminum liquid metal for casting to the liquid metal, controlling the generated phases such as intermetallic compounds, and inducing changes in the crystal phases, types, sizes, distributions, etc. of the intermetallic compounds generated during solidification, it is possible to realize a high-strength, high-elongation, and high-thermal-conductivity aluminum casting alloy that can simultaneously improve contradictory properties such as strength, conductivity, and ductility, and a method for manufacturing the same.

[0022] Of course, the scope of the present invention is not limited by such effects.

Brief Description of the Drawings

[0023] [Figure 1] It is a diagram showing the liquidus projection of the Al-Si-Fe ternary system. [Figure 2] It is a schematic diagram showing the step mold used to form an aluminum alloy casting according to an experimental example of the present invention. [Figure 3] It is a photograph of the microstructure of an aluminum casting alloy taken according to the cooling rate in an experimental example of the present invention. [Figure 4] It is a photograph of the microstructure of an aluminum casting alloy taken according to the cooling rate in an experimental example of the present invention. [Figure 5A] It is a graph showing the morphology of the microstructure according to the application temperature and method of external energy and the cooling rate in an experimental example of the present invention. [Figure 5B] It is a graph showing the morphology of the microstructure according to the holding time at a molten metal temperature of 800 °C of an aluminum casting alloy in an experimental example of the present invention. [Figure 5C] In the experimental example of the present invention, it is a diagram showing a backscattered electron image of an aluminum casting alloy heated to a molten metal temperature of 600 to 800 °C and solidified at a cooling rate of 0.8 K / s. [Figure 6] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 7] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 8] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 9] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 10] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 11] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 12] It is a diagram showing a backscattered electron image and a three-dimensional microstructure of an alloy solidified at a cooling rate of 2.2 K / s after each liquid phase process. [Figure 13] In the manufacturing method of the aluminum casting alloy of the present invention, it is a photograph analyzing the crystal structure of the β-Al5FeSi intermetallic compound. [Figure 14] In the manufacturing method of the aluminum casting alloy of the present invention, it is a photograph analyzing the crystal structure of the α-AlFeSi intermetallic compound. [Figure 15] It is a diagram showing the physical properties of the aluminum casting alloy according to Experimental Example A of the present invention described above. [Figure 16]This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 17] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 18] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 19] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 20] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 21] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 22] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 23] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 24] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 25] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 26] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 27] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 28] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 29] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 30] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 31] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 32] This figure shows the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above. [Figure 33] These are photographs of the microstructure of aluminum immediately after casting (as cast) in experimental examples 11 to 13 of the present invention, taken at different cooling rates. [Figure 34] These are photographs of the microstructure of aluminum immediately after casting (as cast) in experimental examples 11 to 13 of the present invention, taken at different cooling rates. [Figure 35] These are photographs of the microstructure of aluminum immediately after casting, taken in Experimental Examples 14 to 16 of the present invention, depending on the cooling rate. [Figure 36] These are photographs of the microstructure of aluminum immediately after casting, taken in Experimental Examples 14 to 16 of the present invention, depending on the cooling rate. [Figure 37] This graph compares the tensile properties of aluminum immediately after casting, depending on the cooling rate, in experimental examples 14 to 16 of the present invention. [Figure 38] This graph compares the thermal conductivity characteristics of aluminum immediately after casting, depending on the cooling rate, in experimental examples 14 to 16 of the present invention. [Figure 39] This graph compares the thermal conductivity characteristics of aluminum immediately after casting, depending on the cooling rate, in experimental examples 14 to 16 of the present invention. [Figure 40] This graph compares the thermal conductivity characteristics of aluminum immediately after casting, depending on the cooling rate, in experimental examples 14 to 16 of the present invention. [Figure 41] Figure 41 is a photograph of the microstructure of an aluminum casting alloy at different cooling rates in another modified embodiment of the present invention (Table 7). [Figure 42] Figure 42 shows the tensile properties of aluminum casting alloys immediately after casting according to other modified embodiments of the present invention (Table 7). [Figure 43] Figure 43 shows the electrical conductivity characteristics of aluminum casting alloys after T6 heat treatment according to other modified embodiments of the present invention (Table 7). [Best Mode for Carrying Out the Invention]

[0024] A high-strength, high-tension, and high-thermal-conductivity aluminum casting alloy according to one embodiment of the present invention, as well as a method for manufacturing the same, will be described in detail. The terms used later are appropriately selected considering the function of the present invention, and the definitions of such terms should be based on the content throughout this specification.

[0025] In this invention, external energy capable of disrupting the structure (e.g., bonding, clustering) of liquid aluminum for casting is applied to the liquid metal to control the resulting phases, such as intermetallic compounds. By inducing changes in the type, size, and distribution of the crystallized phase and intermetallic compounds formed during solidification, the invention provides a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, as well as a method for producing the same, which can simultaneously improve conflicting properties such as strength, conductivity, and ductility.

[0026] An embodiment of the present invention provides a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy comprising 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.32% to 0.85% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and containing an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0027] The aforementioned aluminum casting alloy may further contain strontium (Sr): 0.02% by weight or less, titanium (Ti): 0.15% by weight or less, or zirconium (Zr): 0.15% by weight or less.

[0028] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the α-AlFeSi intermetallic compound having a cubic crystal structure has the same crystal structure as the α-AlMnSi phase, but does not contain Mn and can undergo phase change from the β-Al5FeSi intermetallic compound. Since the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy does not contain manganese, it does not contain the α-AlMnSi phase in its final structure. However, this means that the α-AlFeSi intermetallic compound having a cubic crystal structure has the same crystal structure as the α-AlMnSi phase.

[0029] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the aluminum casting alloy is characterized in that it does not contain manganese (Mn), cobalt (Co), chromium (Cr), or molybdenum (Mo) as an additive for neutralizing the β-Al5FeSi intermetallic compound.

[0030] Table 1 shows the results of an analysis of the composition of the α-AlFeSi intermetallic compound embodied in a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy according to one embodiment of the present invention.

[0031] [Table 1]

[0032] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the α-AlFeSi intermetallic compound can have a composition of Al: 74.9-86.7 at.%, Fe: 6.9-14.3 at.%, and Si: 6.2-11.3 at.%. Figure 1 shows the liquidus projection of the Al-Si-Fe ternary system.

[0033] Referring to Figure 1, the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy according to one embodiment of the present invention is an alloy in which Fe is added to an Al-Si alloy, and can be limited to a composition range of Al, Si, and Fe in which the β-Al5FeSi phase can be formed during the solidification pathway process according to the liquidus projection phase diagram of the Al-Si-Fe ternary system.

[0034] In an aluminum casting alloy with high strength, high elongation, and high thermal conductivity according to one embodiment of the present invention, the composition range of iron (Fe) may be 0.32% by weight or more and 0.85% by weight or less. When the iron (Fe) content is lower than 0.32% by weight, the Al-Si eutectic reaction may occur before the formation of the β-Al5FeSi phase during the solidification process of the Al-7Si-xFe alloy. On the other hand, when the iron (Fe) content exceeds 0.85% by weight, the β-Al5FeSi phase may be formed before the α-Al phase, which is the matrix, during solidification. Therefore, in an aluminum casting alloy with high strength, high elongation, and high thermal conductivity according to one embodiment of the present invention, it is preferable to control the composition range of iron (Fe) to 0.32% by weight or more and 0.85% by weight or less.

[0035] In an embodiment of the present invention, an aluminum casting alloy possessing high strength, high elongation, and high thermal conductivity may have a silicon (Si) composition range of 6.5% by weight or more and 11.5% by weight or less. If the silicon (Si) content is lower than 6.5% by weight, the fluidity of the molten metal decreases, making it difficult to ensure castability. On the other hand, if the silicon (Si) content exceeds 11.5% by weight, the thermal conductivity of the aluminum casting alloy may decrease.

[0036] In an embodiment of the present invention, an aluminum casting alloy possessing high strength, high elongation, and high thermal conductivity may have a magnesium (Mg) composition range of 0.2% by weight or more and 0.4% by weight or less. If the magnesium (Mg) content is lower than 0.2% by weight, the age-hardening ability of the aluminum casting alloy may decrease, potentially reducing its strength. Conversely, if the magnesium (Mg) content exceeds 0.4% by weight, the ductility of the aluminum casting alloy may decrease.

[0037] On the other hand, a method for producing a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy according to one embodiment of the present invention comprises: a first step of providing a molten aluminum casting alloy containing 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.32% to 0.85% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and a second step of applying external energy to the molten aluminum casting alloy at a temperature higher than the liquidus temperature, and then cooling it, so that it contains an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0038] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include maintaining the molten aluminum casting alloy at a temperature 200°C to 300°C higher than the liquidus temperature, and then cooling it at a cooling rate of 1 K / sec or more. For example, the cooling rate may be in the range of 1 K / sec to 100 K / sec.

[0039] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include maintaining the molten aluminum casting alloy at a temperature 100°C to 150°C higher than the liquidus temperature, and then cooling it at a cooling rate of 10K / sec or more. For example, the cooling rate may be in the range of 10K / sec to 100K / sec.

[0040] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, in the second step, although the temperature of the molten aluminum casting alloy is higher than the liquidus temperature, it is necessary to control the cooling rate so that the smaller the difference between the temperature of the molten metal and the liquidus temperature, the greater the cooling rate.

[0041] In the method for producing the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the molten aluminum casting alloy can be characterized by maintaining a temperature higher than the liquidus temperature for 1 to 2 hours.

[0042] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the molten aluminum casting alloy can be characterized by applying ultrasonic waves to it at a temperature higher than the liquidus temperature and maintaining it for 1 to 2 minutes.

[0043] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include a phase change from a β-Al5FeSi intermetallic compound having a monoclinic crystal structure to an α-AlFeSi intermetallic compound having a cubic crystal structure.

[0044] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step allows the formation of the β-Al5FeSi intermetallic compound to occur before the Al-Si eutectic reaction, and the α-Al phase, which is the aluminum matrix, to be formed before the β-Al5FeSi intermetallic compound.

[0045] Experimental example

[0046] The following are preferred experimental examples to aid in understanding the present invention. However, these experimental examples are merely for the purpose of aiding in understanding the present invention, and the present invention is not limited to these experimental examples.

[0047] Design of composition and process for aluminum alloy castings

[0048] Table 2 shows the composition and process conditions of the aluminum casting alloy produced by Experimental Example A of the present invention. Experimental Example A was evaluated against the composition (unit: weight %) of a hypoeutectic Al-Si alloy.

[0049] [Table 2]

[0050] In this experimental example, in order to control the formation phase of Fe-based intermetallic compounds, the following two liquid-phase processes (Thermal Rate (TR) and Ultrasonic Treatment (UST)) were performed in addition to the conventional casting method during the step of dissolving the liquid metal. Thermal Rate refers to a treatment method in which the molten metal is maintained at a superheated state for a certain period of time. In Table 2, the "TR" column refers to a process in which the molten metal is maintained at a set temperature for 1 hour, then cooled to approximately 700°C, and then poured into a mold for casting. The "UST" column refers to a process in which the molten metal at a set temperature is ultrasonically treated for 1 minute, then cooled to approximately 700°C, and then poured into a mold for casting.

[0051] In Table 2, Experimental Example 1, item 'Alloy 1', corresponds to alloy A356.2, Experimental Example 2, item 'Alloy 2', corresponds to an alloy with an iron (Fe) content approximately 0.3-0.4% more by weight compared to alloy A356.2, Experimental Example 3, item 'Alloy 3', is the case where the molten metal of alloy 2 is maintained at a set temperature of 800°C for 1 hour, then the molten metal is cooled to approximately 700°C, and then poured into a mold for casting, and Experimental Example 4, item 'Alloy 4' is In the case of alloy 2, the molten alloy is ultrasonically treated at 800°C for 1 minute, then cooled to approximately 700°C, and then poured into a mold for casting. In the case of experimental example 5, item 'Alloy 5', the molten alloy is maintained at a set temperature of 900°C for 1 hour, then cooled to approximately 700°C, and then poured into a mold for casting. In the case of experimental example 6, item 'Alloy 6', the process is applied to the case where the conditions for alloy 5 are followed by remelting. On the other hand, Experimental Example 7, item 'Alloy 7', corresponds to an alloy with an iron (Fe) content that is approximately 0.5 to 0.6% more by weight compared to alloy A356.2. Experimental Example 8, item 'Alloy 8', is the case where the molten alloy of alloy 7 is ultrasonically treated at 700°C for 1 minute, and then poured into a mold at a temperature of approximately 700°C for casting. Item 'Alloy 9' corresponds to the case where the molten alloy of alloy 7 is maintained at a set temperature of 1100°C for 1 hour, then cooled to approximately 700°C, and then poured into a mold for casting.

[0052] Figure 2 is a schematic diagram showing a step mold used to form an aluminum alloy casting material according to an experimental example of the present invention.

[0053] In the experimental examples of the present invention, an alloy weighing approximately 8 kg was melted at the normal melting temperature of 700°C using an induction melting furnace and an electric resistance melting furnace, and the molten metal was poured into a step mold (cooling rate 2.2 K / s to 40 K / s) as shown in Figure 2 for casting. Alloys 1 to 6 were melted and degassed in an electric resistance melting furnace, and the injection temperature was fixed at 700°C in all cases. On the other hand, alloys 7 to 9 were melted in an induction melting furnace, but no degassing treatment was applied, and the injection temperature was fixed at 700°C in all cases.

[0054] Figures 3 and 4 are photographs of the microstructure of an aluminum casting alloy taken at different cooling rates in an experimental example of the present invention, and Figure 5A is a graph showing the morphology of the microstructure at different cooling rates and with respect to the temperature and method of applying external energy in an experimental example of the present invention.

[0055] On the other hand, Figures 6 to 12 are photographs of the two-dimensional or three-dimensional microstructures in experimental examples of the present invention. Specifically, Figure 6 is a scanning electron microscope image of the two-dimensional microstructure of alloy 9 in experimental examples of the present invention; Figure 7 is an image photograph of the three-dimensional microstructure of alloy 9 in experimental examples of the present invention; Figure 8 is a scanning electron microscope image of the two-dimensional microstructure of alloy 3 in experimental examples of the present invention; Figure 9 is a scanning electron microscope image of the two-dimensional microstructure of alloy 4 in experimental examples of the present invention; Figure 10 is an image photograph of the three-dimensional microstructure of alloy 4 in experimental examples of the present invention; Figure 11 is a scanning electron microscope image of the two-dimensional microstructure of alloy 2 in experimental examples of the present invention; and Figure 12 is an image photograph of the three-dimensional microstructure of alloy 2 in experimental examples of the present invention.

[0056] Referring to Figures 3 to 12, when an external energy is applied to a molten aluminum casting alloy at a temperature higher than the liquidus temperature (approximately 600°C) and then cooled, if the molten aluminum casting alloy is maintained at a temperature 200°C to 300°C higher than the liquidus temperature (approximately 800°C to 900°C) and then cooled at a cooling rate of 1 K / sec or more, it can be confirmed that a phase change occurs from a plate-like β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound having the shape of Chinese characters. The β-Al5FeSi intermetallic compound can have a plate-like shape in three dimensions and a needle-like shape in a two-dimensional cross-section.

[0057] In the experimental example of alloy 5 (Alloy5), when the process of casting was applied in which molten alloy (A5) having the composition shown in Table 2 was maintained at a set temperature of 900°C for 1 hour, then the injection temperature was lowered to 700°C, and the molten metal was injected into a mold at a cooling rate of 1 K / sec or more (2.2 K / sec, 6.9 K / sec, 16 K / sec, 40 K / sec), it could be confirmed that all of the plate-shaped β-Al5FeSi intermetallic compounds underwent a phase change into α-AlFeSi intermetallic compounds having the shape of Chinese characters.

[0058] In the experimental example of Alloy 3, when the molten alloy (A3) having the composition shown in Table 2 is maintained at a set temperature of 800°C for 1 hour, then the injection temperature is lowered to 700°C, and the molten metal is injected into a mold at a cooling rate of 1 K / sec or more (2.2 K / sec, 6.9 K / sec, 16 K / sec, 40 K / sec) to cast, it can be confirmed that all of the plate-shaped β-Al5FeSi intermetallic compounds undergo a phase change into α-AlFeSi intermetallic compounds that have the shape of Chinese characters.

[0059] In the experimental example of Alloy 4, when the molten alloy (A4) having the composition shown in Table 2 is ultrasonically treated at 800°C for 1 minute, then the injection temperature is lowered to 700°C, and the molten metal is injected into a mold at a cooling rate of 1 K / sec or more (2.2 K / sec, 6.9 K / sec, 16 K / sec, 40 K / sec) for casting, it can be confirmed that at least a portion of the plate-like β-Al5FeSi intermetallic compounds undergo a phase change into α-AlFeSi intermetallic compounds having the shape of Chinese characters. Furthermore, when the process of injecting the metal into a mold at a cooling rate of 10 K / sec or more (16 K / sec, 40 K / sec) for casting is applied, it can be confirmed that all of the plate-like β-Al5FeSi intermetallic compounds undergo a phase change into α-AlFeSi intermetallic compounds having the shape of Chinese characters.

[0060] On the other hand, in the experimental example of alloy 9 (Alloy9), when the process of casting was applied in which molten alloy (A9) having the composition shown in Table 2 was maintained at a set temperature of 1100°C for 1 hour, then the injection temperature was lowered to 700°C, and the molten metal was injected into a mold at a cooling rate of 1 K / sec or more (2.2 K / sec, 6.9 K / sec, 16 K / sec, 40 K / sec), it could be confirmed that all of the plate-shaped β-Al5FeSi intermetallic compounds underwent a phase change into α-AlFeSi intermetallic compounds having the shape of Chinese characters.

[0061] Furthermore, referring to Figures 3 to 12, when an external energy is applied to the molten aluminum casting alloy at a temperature higher than the liquidus temperature (approximately 600°C) and then cooled, it can be confirmed that when the molten aluminum casting alloy is maintained at a temperature 100°C to 150°C higher than the liquidus temperature (approximately 700°C to 750°C) and then cooled at a cooling rate of 10K / sec or more, a phase change occurs from a plate-shaped β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound having the shape of Chinese characters.

[0062] In the experimental example of Alloy 8, when the process of casting is applied to molten alloy (A8) having the composition shown in Table 2, ultrasonically treated at 700°C for 1 minute, then the injection temperature is lowered to 700°C, and the molten metal is injected into a mold at a cooling rate of 10K / sec or more (16K / sec, 40K / sec), it can be confirmed that at least a portion of the plate-like β-Al5FeSi intermetallic compounds undergoes a phase change into α-AlFeSi intermetallic compounds having the shape of Chinese characters. However, in the experimental example of Alloy 8, when the process of casting is applied to molten alloy (A8) having the composition shown in Table 2, ultrasonically treated at 700°C for 1 minute, then the injection temperature is lowered to 700°C, and the molten metal is injected into a mold at a cooling rate of less than 10K / sec (2.2K / sec, 6.9K / sec), it can be confirmed that the plate-like β-Al5FeSi intermetallic compounds do not undergo a phase change into α-AlFeSi intermetallic compounds having the shape of Chinese characters.

[0063] Referring to Figure 4, ultrasonic treatment at each cooling rate causes refinement without changing the shape of the β-Al5FeSi phase, while thermal-rate is observed to change the shape of the needle-shaped β-Al5FeSi to that of Chinese characters. As the cooling rate increases from 6.9 to a maximum of 40 K / s, the refinement effect of the generated phase by ultrasonic treatment (alloy 8) and thermal-rate (alloy 9) is significantly observed compared to the normally treated material (alloy 7).

[0064] Fe-based intermetallic compounds in the shape of Chinese characters are judged to be quasi-equilibrium phases that cannot be predicted by thermodynamic calculations, and are observed in all thermal-rate alloys regardless of the cooling rate. On the other hand, in conventionally treated materials and ultrasonically treated materials, the quasi-equilibrium phase is partially observed only when the cooling rate is fast (e.g., 40 K / s).

[0065] As described above, in order to derive the process conditions under which such a quasi-equilibrium phase is generated, thermal-rate tests were performed on A356.2+0.4~0.6Fe alloy at molten metal temperatures of 700~1100°C and cooling rates of 0.3~40K / s. The thermal-rate tests were performed by superheating the molten metal to each target temperature, maintaining the temperature for 1 hour, then lowering the injection temperature to 700°C and casting it into a steel step mold as shown in Figure 2. In addition, ultrasonic treatment was also performed, but the experiment was conducted by ultrasonically treating molten metal at 700°C and 800°C for 1 minute, then lowering the injection temperature to 700°C and casting it into the same steel step mold.

[0066] Figure 5A shows a process map in which a quasi-equilibrium phase may appear.

[0067] As can be seen in Figure 5A, in the case of A356 alloy with approximately 0.4 wt.% Fe added, it was confirmed that a quasi-equilibrium phase with the shape of Chinese characters could be formed during solidification after being heated to a temperature of 800°C or higher and maintained for about 1 hour. Importantly, even though a liquid phase process was performed to generate this quasi-equilibrium phase, when the cooling rate during casting was very slow (e.g., 0.3 K / s), it was observed that all of it was needle-shaped β-Al5FeSi equilibrium phase. This suggests that when the cooling rate is sufficiently slow, the Chinese character phase transforms entirely into needle-shaped β-Al5FeSi equilibrium phase by a peritectic reaction. An even more interesting fact is that when liquid metal is subjected to ultrasonic treatment for 1 minute without being maintained at a temperature of 800°C, a quasi-equilibrium phase with the shape of Chinese characters can be observed in part of the solidification structure. As can be seen in Figure 5A, when liquid metal is ultrasonically treated at 800°C for 1 minute and then cast at a fast cooling rate of 16 K / s or higher, it is observed that all of the Fe-based intermetallic compounds are formed as quasi-equilibrium phase during solidification. On the other hand, when the cooling rate is 2.2 to 6.9 K / s, it is confirmed that Fe-based intermetallic compounds with the shape of Chinese characters and needle-like structures are present together. In particular, the β-Al5FeSi equilibrium phase observed in needle-like structures in ultrasonically treated materials is found to be remarkably finer than the needle-like structures observed in normally treated materials or alloys maintained at 700°C for 1 hour.

[0068] Figure 5B is a graph showing the microstructure morphology of an aluminum casting alloy at a molten metal temperature of 800°C over time in an experimental example of the present invention. The cooling rate during casting was approximately 10 K / s.

[0069] Referring to Figure 5B, it can be confirmed that when molten aluminum casting alloy is maintained at a temperature higher than the liquidus temperature, 800°C, for 1 to 2 hours, a phase change occurs from a plate-like β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound with the shape of Chinese characters.

[0070] Figure 5C shows a backscattered electron image of an aluminum casting alloy that was heated to a molten metal temperature of 600-800°C and solidified at a cooling rate of 0.8 K / s in an experimental example of the present invention.

[0071] Referring to Figure 5C, it can be seen that when the cooling rate is slow (for example, a cooling rate of less than 1 K / s), almost no phase change due to the application of external energy (for example, superheating) is observed.

[0072] Figures 6 to 12 show backscattered electron images and three-dimensional microstructures for alloys solidified at a cooling rate of 2.2 K / s after each liquid phase step. As can be seen, when the liquid metal is maintained at 700°C for 1 hour, coarse needle-shaped β-Al5FeSi phases with a size of several hundred μm are formed during solidification, while when maintained at 800°C for 1 hour, Fe-based intermetallic compounds exist in the form of a quasi-equilibrium phase. In addition, it is observed that in the liquid metal sonicated at 800°C for 1 minute, both the quasi-equilibrium phase and fine needle-shaped β-Al5FeSi equilibrium phase coexist during solidification.

[0073] Figure 13 is a photograph showing the crystal structure of the β-Al5FeSi intermetallic compound analyzed in the aluminum casting alloy manufacturing method of the present invention, and Figure 14 is a photograph showing the crystal structure of the α-AlFeSi intermetallic compound analyzed in the aluminum casting alloy manufacturing method of the present invention.

[0074] Table 3 shows the results of analyzing the crystal structure of Fe-based intermetallic compounds in the method for producing aluminum casting alloys according to the present invention.

[0075] [Table 3]

[0076] In this experimental example, it can be confirmed that a quasi-equilibrium phase can be generated during solidification of liquid metal A356.2 containing a large amount of Fe by applying external energy such as superheating (heat) or UST (ultrasound). At this time, it is observed that the shape of the thermodynamically equilibrium phase, β-Al5FeSi phase, clearly changes, and this is judged to be due to the crystallographic changes of the phase.

[0077] To analyze the crystal structure of the generated phases, thin foil samples of the regions containing each phase were prepared by FIB (Focused Ion Beam) milling and then analyzed by TEM (Transmission Electron Microscopy).

[0078] Figures 13 and 14 show TEM images and diffraction pattern analysis results for the equilibrium phase, the needle-shaped β-Al5FeSi phase, and the quasi-equilibrium phase (hereinafter referred to as the α-AlFeSi phase), respectively. As can be seen, the needle-shaped β-Al5FeSi phase was analyzed to have a monoclinic structure with low symmetry, and the lattice constant and angle of the unit cell were analyzed as shown in Table 3. On the other hand, in the case of the α-AlFeSi phase, which has the shape of a Chinese character, diffraction pattern analysis results showed that it has the same crystal structure as the α-AlMnSi phase, but does not contain Mn and has a cubic crystal structure with a 4-fold structure. In other words, the change from an asymmetric shape like a needle to a radial, symmetric shape like a Chinese character is judged to be due to the crystal structure of the generated phase.

[0079] A more important point in this mechanism of phase change is that the application of external energy to the liquid metal is judged to affect the short-range ordering (SRO) bonding structure, which absolutely influences the formation of intermetallic compounds. However, considering the limitations in accurately analyzing the liquid phase structure, there are clearly limitations to inferring theoretical possibilities based on phenomenological changes. Nevertheless, it is understood that the application of such external energy can affect the bonding structure inside the liquid metal (the bonding structure that makes up Fe-based intermetallic compounds, e.g., Al-Fe or Fe-Si bonds) or the quasi-crystalline cluster structure, thereby causing changes in the crystal structure and shape of the resulting phase crystallized during solidification.

[0080] As can be seen from Figure 5A above, the liquid phase process can induce a change in the crystal structure of the generated phase through structural changes within the liquid phase. However, it can be seen that the sustainability of such a quasi-equilibrium phase depends greatly on the cooling rate during casting that takes place after the liquid phase process.

[0081] In other words, the α-AlFeSi phase, which is a quasi-equilibrium phase, can be generated during solidification by the liquid phase process. However, as solidification progresses, some or all of it may transform into the β-Al5FeSi phase through a peritectic reaction involving Si diffusion. Specifically, if the α-AlFeSi phase (containing ~10 at.% Si), which has relatively low Si solubility, is generated first, Si will be concentrated in the residual liquid phase as it grows. Subsequently, through a peritectic reaction between the liquid phase and the α-AlFeSi phase, transformation occurs into the β-Al5FeSi phase (containing 15~20 wt.% Si), which has relatively high Si solubility. At this time, the thinner and smaller the branch thickness of the α-AlFeSi phase, and the more time given for diffusion (e.g., a slow cooling rate), the more likely the entire quasi-equilibrium phase is to transform into the β-Al5FeSi phase.

[0082] Based on the concept of the peritectic reaction "Liquid + α-AlFeSi → α-Al + β-Al5FeSi" and theoretical predictions of the reaction and transformation rates, it can be seen that the peritectic reaction rate depends on both the rate of formation of the β-Al5FeSi phase by the reaction between the liquid phase and the α-AlFeSi phase, and the α→β transformation rate. In particular, the rate of formation of the β-Al5FeSi phase by the reaction between the liquid phase and the α-AlFeSi phase, which has a significantly slower reaction rate, is judged to be the rate-limiting factor. According to the prediction results, at a cooling rate of 2.2 K / s, it is predicted that the α-AlFeSi phase, which theoretically has a maximum thickness of approximately 2.5 μm, can all be transformed into the β-Al5FeSi phase by the peritectic reaction during solidification. On the other hand, when the cooling rate increases to 6.9 K / s or higher, it is predicted that only the α-AlFeSi phase with a thickness of 1 μm or less can be transformed into the β-Al5FeSi phase. In other words, the higher the cooling rate, the less possible a complete peritectic reaction occurs from the already formed quasi-equilibrium phase, α-AlFeSi, to the β-Al5FeSi phase. This is consistent with the fact that, as confirmed by observing the actual solidification structure, the faster the cooling rate after the thermal rate to the molten metal, the more likely it is to exist as a quasi-equilibrium phase. Considering this kinetics, the quasi-equilibrium-equilibrium mechanism can be elucidated, and process variables for the realization of the quasi-equilibrium phase can be derived.

[0083] Referring to Figures 3 to 5A, it was found that the application of external energy to the liquid metal could induce the formation of a quasi-equilibrium phase of the Fe-based intermetallic compound. At a molten metal temperature of 700°C, almost no microstructural changes were observed due to the thermal rate treatment. However, as the cooling rate increased, a significant refinement of the needle-like β-Al5FeSi phase was observed, and at a cooling rate of 40 K / s, it was confirmed that some of the quasi-equilibrium phase remained unchanged without completely transforming into the equilibrium phase.

[0084] On the other hand, when the thermal rate is maintained at a molten metal temperature of 800°C or higher for 1 hour, all Fe-based intermetallic compounds are observed as α-AlFeSi quasi-equilibrium phases with the shape of Chinese characters across the entire cooling rate range of 2.2 to 40 K / s. Interestingly, in the case of UST treatment, which is performed as part of the external energy application method, it is confirmed that even treatment at 800°C for only 1 minute has a refinement effect on the generated phase. However, although little change in shape was observed due to ultrasonic treatment, this cannot be simply interpreted as ultrasonic waves being ineffective in inducing structural changes in liquid metals and quasi-equilibrium phases.

[0085] When UST (ultrasound) is applied to liquid metal, it is accompanied by two main phenomena: cavitation and acoustic streaming. Here, cavitation is a concept that includes a series of processes such as bubble formation, growth, and collapse. In particular, since bubble collapse is known to generate hot spots with localized high temperatures and pressures of 5000°C and 500 atm, ultrasound is considered to be a means of applying sufficient energy to cause changes in the internal structure of liquid metal.

[0086] Therefore, even if sufficient external energy is applied to a molten metal at a high temperature of 800°C for just one minute, it is possible to influence the bonding structure or cluster structure of the liquid metal. In parallel with this, it is judged that the quasi-equilibrium phase is formed in a small and uniform manner due to the homogenization effect of the molten metal by acoustic streaming. Subsequently, such a fine quasi-equilibrium phase can rapidly transform into the β-Al5FeSi equilibrium phase during the solidification process kinetically, and as a result, it can be observed as a fine needle-shaped β-Al5FeSi phase in the microstructure.

[0087] Figures 15 to 32 show the physical properties of the aluminum casting alloy produced by experimental example A of the present invention described above.

[0088] Specifically, Figure 15 is a graph showing the maximum tensile strength of aluminum casting alloys (cooling rate 2.2 K / s) subjected to T5 heat treatment (artificial aging at 155°C, 8 hours) according to Experimental Examples 1 to 6 of the present invention; Figure 16 is a graph showing the yield strength of aluminum casting alloys (cooling rate 2.2 K / s) subjected to T5 heat treatment (artificial aging at 155°C, 8 hours) according to Experimental Examples 1 to 6 of the present invention; Figure 17 is a graph showing the elongation ratio of aluminum casting alloys (cooling rate 2.2 K / s) subjected to T5 heat treatment (artificial aging at 155°C, 8 hours) according to Experimental Examples 1 to 6 of the present invention; and Figure 18 is a graph showing the thermal conductivity of aluminum casting alloys (cooling rate 2.2 K / s) subjected to T5 heat treatment (artificial aging at 155°C, 8 hours) according to Experimental Examples 1 to 6 of the present invention. Figures 15 to 18 were obtained by applying the condition of a cooling rate of 2.2 K / sec.

[0089] Figure 19 is a graph showing the maximum tensile strength of aluminum casting alloys (cooling rate 6.9 K / s) after T5 heat treatment (artificial aging at 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figure 20 is a graph showing the yield strength of aluminum casting alloys (cooling rate 6.9 K / s) after T5 heat treatment (artificial aging at 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figure 21 is a graph showing the elongation ratio of aluminum casting alloys (cooling rate 6.9 K / s) after T5 heat treatment (artificial aging at 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figure 22 is a graph showing the thermal conductivity of aluminum casting alloys (cooling rate 6.9 K / s) after T5 heat treatment (artificial aging at 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figures 19 to 22 were obtained by applying the condition of a cooling rate of 6.9 K / sec.

[0090] Figure 23 is a graph showing the maximum tensile strength of aluminum casting alloys (cooling rate 16 K / s) after T5 heat treatment (artificial aging 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figure 24 is a graph showing the yield strength of aluminum casting alloys (cooling rate 16 K / s) after T5 heat treatment (artificial aging 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figure 25 is a graph showing the elongation ratio of aluminum casting alloys (cooling rate 16 K / s) after T5 heat treatment (artificial aging 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figure 26 is a graph showing the thermal conductivity of aluminum casting alloys (cooling rate 16 K / s) after T5 heat treatment (artificial aging 155°C, 8 hours) according to experimental examples 1 to 6 of the present invention. Figures 23 to 26 were obtained by applying the condition of a cooling rate of 16 K / sec.

[0091] Figure 27 is a graph showing the thermal conductivity and electrical conductivity of aluminum casting alloys according to experimental examples 2 to 6 of the present invention, and Figure 28 is a graph showing the thermal conductivity in the R1 region of Figure 27.

[0092] Referring to Figures 15 to 28, it can be confirmed that alloys 3 to 6 exhibit significantly improved maximum tensile strength and elongation characteristics compared to alloy 2, and that yield strength and thermal conductivity characteristics are at or above the same level.

[0093] Tables 4 and 5 show the physical properties (T5 and as-cast) of aluminum cast alloys measured using experimental examples of the present invention.

[0094] [Table 4]

[0095] [Table 5]

[0096] Tables 4 and 5 show that, according to alloys 3 to 6, the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloys according to the embodiments of the present invention can achieve a yield strength in the range of 100 MPa to 140 MPa, a maximum tensile strength in the range of 180 MPa to 220 MPa, an elongation in the range of 2.5% to 8.5%, and a thermal conductivity in the range of 160 W / mK to 190 W / mK.

[0097] This experiment evaluated how controlling the generated phase in a liquid-phase process ultimately affects the mechanical and physical properties. A356.2+0.4Fe alloy was molten using the previously described liquid-phase process method and cast at a cooling rate of 2.2-16 K / s. Tensile samples were then taken from the cast samples, and their tensile properties were evaluated. All samples underwent a T5 treatment, which involved aging treatment without solution treatment, at 155°C for 8 hours. It was found that controlling the generated phase through the liquid-phase process (e.g., realization and refinement of the quasi-equilibrium phase of Fe-based intermetallic compounds) increased the elongation from 2% to 6%, up to a maximum of 300%, compared to the TR@700°C condition where there was no change in the generated phase. Furthermore, it was evaluated that yield strength and tensile strength increased slightly with increasing elongation. In the case of UST-treated materials, the yield strength met the target characteristic of 130 MPa at some cooling rates, but at other liquid-phase processes and cooling rates, the yield strength was estimated to be in the 100-120 MPa range. It was confirmed that controlling the generated phase based on such liquid-phase processes affects not only the tensile properties but also the thermal conductivity properties.

[0098] Figures 27 and 28 show the change in thermal conductivity due to the previously presented liquid phase process and cooling rate. This is a graph showing the results. In this experimental example, the thermal conductivity at room temperature was measured for T5 heat-treated material, similar to the tensile test.

[0099] As can be confirmed, the alloys used in the test showed that the thermal conductivity of the T5 treated material exceeded 160 W / mK regardless of the casting process (liquid phase process, cooling rate). On the other hand, it was confirmed that the thermal conductivity characteristics increased as the cooling rate increased, regardless of the conditions of the liquid phase process. When the cooling rate was increased to 40 K / s, both alloy 4 and alloy 5 were evaluated to reach a thermal conductivity value of 190 W / mK, indicating an improvement in thermal conductivity compared to alloy 2.

[0100] It is understood that as the cooling rate increases, the solid solubility increases due to the trapping behavior of solute elements within the matrix, and therefore, the amount of aged precipitates is expected to increase proportionally even after T5 heat treatment. Considering this point, the fact that the thermal conductivity increases rather than decreases at the fastest cooling rate of 40 K / s compared to other cooling rate conditions suggests that this is due to other microstructural factors rather than the solute-precipitation effect within the matrix. This result supports the hypothesis that not only the matrix precipitate phase, but also the shape, size, and distribution of the solidified crystallized phase can influence the thermal conductivity.

[0101] On the other hand, in the case of Fe-based intermetallic compounds observed at a cooling rate of 40 K / s, it was confirmed that the induction of the quasi-equilibrium phase was promoted by the thermal rate at temperatures above 800 °C, and at the same time, significant refinement occurred. Furthermore, it was observed that the distribution of the generated phases became even more uniform. Assuming that there are no changes in the other solidification and crystallization phases, namely eutectic Si and π-Al8FeMg3Si6 phases, the backscattered electron images suggest that these changes in the shape, size, and distribution of Fe-based intermetallic compounds directly affect the thermal conductivity.

[0102] Figure 29 is a graph showing the magnitude of Fe-based intermetallic compounds as the cooling rate of aluminum casting alloys according to experimental examples 2 to 5 of the present invention, and Figure 30 is a graph showing the volume fraction of Fe-based intermetallic compounds as the cooling rate of aluminum casting alloys according to experimental examples 2 to 5 of the present invention.

[0103] Referring to Figures 29 and 30, it can be confirmed that the size and fraction of the β-Al5FeSi phase generally decrease during the liquid phase process. When the cooling rate is 2.2 K / s, it can be confirmed that the size (46.5 μm → 10.3 μm) and fraction (1.1% → 0.7%) decrease by the maximum amount during the liquid phase process.

[0104] The size and fraction of Fe-based intermetallic compounds observed in cast samples across the entire range of liquid-phase processes and cooling rates attempted in this experiment were quantitatively analyzed. Figures 29 and 30 show the results, indicating that regardless of the liquid-phase process variables, both the size and fraction of Fe-based intermetallic compounds decrease as the cooling rate increases. On the other hand, at each cooling rate, the size of Fe-based intermetallic compounds generally decreases from alloy 2 to alloy 4, and then to alloy 3 or alloy 5. This difference in the size of Fe-based intermetallic compounds across casting processes is greatest at a cooling rate of 2.2 K / s, and when increased to 6.9 K / s or higher, alloys 3, 4, and 5 all show similar degrees of refinement. Similar to the size, the fraction of Fe-based intermetallic compounds also decreases significantly from alloy 2 to alloys 4 and 5, while slightly increasing under alloy 3 conditions.

[0105] Figure 31 is a graph showing the stress-deformation ratio correlation of aluminum casting alloys according to experimental examples 7-9 of the present invention under the condition of a cooling rate of 6.9 K / sec, and Figure 32 is a graph showing the stress-deformation ratio correlation of aluminum casting alloys according to experimental examples 7-9 of the present invention under the condition of a cooling rate of 16 K / sec.

[0106] Referring to Figures 31 and 32, it can be confirmed that ultrasonic treatment increases the elongation rate through the refinement of the generated phase (alloy 8). When the cooling rate is 16 K / s, it can be confirmed that the elongation rate increases by approximately 200%, and at the same time, the strength is also improved.

[0107] On the other hand, in the case of alloy 9, which is heat-treated at 1100°C, it can be confirmed that the effect of improving properties is almost negligible due to the problem of magnesium volatilization and the increase in hydrogen capture degree. In other words, when superheating is performed at a temperature 300°C or more above the liquidus temperature, highly reactive alloying elements such as magnesium volatilize, and it can be confirmed that the intrinsic properties of the alloy deteriorate.

[0108] Table 6 shows the composition and process conditions of the aluminum casting alloy produced by Experimental Example B of the present invention. Experimental Example B evaluates the composition (unit: weight %) of a eutectic Al-Si alloy system.

[0109] [Table 6]

[0110] In this experimental example, in order to control the formation phase of Fe-based intermetallic compounds, the following two liquid-phase processes (Thermal Rate (TR) and Ultrasonic Treatment (UST)) were performed in addition to the normal casting method during the step of dissolving the liquid metal. In Table 6, the "TR" column refers to the process of maintaining the molten metal at the set temperature for 1 hour, then cooling it to approximately 700°C, and then pouring it into a mold for casting. The "UST" column refers to the process of ultrasonically treating the molten metal at the set temperature for 1 minute, then cooling it to approximately 700°C, and then pouring it into a mold for casting. The "Mn-free" column refers to an alloy in which Mn is not added to control the formation phase of Fe-based intermetallic compounds in the A365 alloy.

[0111] In Table 6, Experimental Example 10, item 'Alloy 10', corresponds to alloy A365, Experimental Example 11, item 'Alloy 11', corresponds to an alloy with an iron (Fe) content approximately 0.4% more by weight compared to alloy A365, and Experimental Example 12, item 'Alloy 12', is the result of applying the process of maintaining the molten alloy of alloy 11 at a set temperature of 800°C for 1 hour, then cooling the molten metal to approximately 700°C, and then pouring it into a mold for casting, and Experimental Example 13 is Item 'Alloy 13' is the case where the molten alloy of alloy 11 is maintained at a set temperature of 900°C for 1 hour, then the molten metal is cooled to approximately 700°C, and then poured into a mold for casting. Item 'Alloy 14', which is Experimental Example 14, corresponds to an alloy in A365 alloy where Mn is not added to control the formation phase of the Fe intermetallic compound. Item 'Alloy 15', which is Experimental Example 15, is the case where the molten alloy of alloy 14 is maintained at a set temperature of 800°C for 1 hour, In the case where the process of cooling the molten metal to approximately 700°C and then pouring it into a mold for casting is applied, experimental example 16, item 'Alloy 16', is the case where the process of maintaining the molten alloy of alloy 14 at a set temperature of 900°C for 1 hour, then cooling the molten metal to approximately 700°C, and then pouring it into a mold for casting is applied, experimental example 17, item 'Alloy 17', corresponds to an alloy of A365 alloy in which Mn is not added to control the formation phase of the Fe intermetallic compound, and Sr and Ti are added, experimental example 18, item 'Alloy 18', is the case where the process of maintaining the molten alloy of alloy 17 at a set temperature of 800°C for 1 hour, then cooling the molten metal to approximately 700°C, and then pouring it into a mold for casting is applied, experimental example 19, item 'Alloy 19', is the case where the process of ultrasonically treating the molten alloy of alloy 17 at a set temperature of 800°C for 1 minute, then cooling it to approximately 700°C, and then pouring it into a mold for casting is applied.

[0112] Figures 33 and 34 are photographs of the microstructure of aluminum immediately after casting (as cast) in experimental examples 11 to 13 of the present invention, depending on the cooling rate. Referring to Figure 33, the improvement phenomenon due to the addition of Sr in the eutectic Si can be confirmed, and it can be confirmed that it disappears in the liquid phase process. Referring to Figure 34, the Fe intermetallic compound can be confirmed, and it can be confirmed that when manganese is present, an α-AlMnSi phase with the shape of coarse Chinese characters is formed.

[0113] Figures 35 and 36 are photographs of the microstructure of aluminum immediately after casting, taken at different cooling rates in experimental examples 14 to 16 of the present invention. Referring to Figure 35, it can be confirmed that there is no change in the microstructure in eutectic Si. Referring to Figure 36, Fe intermetallic compounds can be identified, and it can be confirmed that in alloys that do not contain manganese, the needle-like structure of β-Al5FeSi, which has an existing monoclinic crystal structure, changes to the shape of Chinese characters in α-AlFeSi, which has a cubic crystal structure.

[0114] Figure 37 is a graph comparing the tensile properties of aluminum immediately after casting, depending on the cooling rate, in experimental examples 14 to 16 of the present invention.

[0115] Referring to Figure 37, it can be seen that as the cooling rate increases, the maximum tensile strength increases slightly, and the yield strength decreases slightly.

[0116] Figures 38 to 40 are graphs comparing the thermal conductivity characteristics of aluminum immediately after casting, depending on the cooling rate, in experimental examples 14 to 16 of the present invention. Referring to Figures 38 to 40, it can be confirmed that at cooling rates of 4-6 K / s or higher, the general inverse relationship between yield strength and conductivity is not followed.

[0117] The following describes a modified embodiment of the present invention: a high-strength, high-tension, and high-thermal-conductivity aluminum casting alloy.

[0118] In Al-Si alloys, the β-Al5FeSi phase, which is formed before the Al-Si eutectic reaction (Fe addition amount of 0.32 wt.%), as well as the β-Al5FeSi phase formed before the Al-Si eutectic reaction (Fe addition amount of less than 0.32 wt.%), can significantly reduce the ductility of the alloy. Therefore, we investigated whether the technical concept of the present invention can be further applied to alloys with an Fe addition amount of 0.2-0.3 wt% (a level at which the β-Al5FeSi phase can be formed in the period before the Al-Si eutectic reaction), and confirmed that the technology can be implemented as follows.

[0119] A modified embodiment of the present invention provides a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy comprising 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.2% to 0.3% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and containing an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0120] The aforementioned aluminum casting alloy may further contain strontium (Sr): 0.02% by weight or less, titanium (Ti): 0.15% by weight or less, or zirconium (Zr): 0.15% by weight or less.

[0121] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the α-AlFeSi intermetallic compound having a cubic crystal structure has the same crystal structure as the α-AlMnSi phase, but does not contain Mn and can undergo a phase change from the β-Al5FeSi intermetallic compound.

[0122] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the aluminum casting alloy is characterized in that it does not contain manganese (Mn), cobalt (Co), chromium (Cr), or molybdenum (Mo) as an additive for neutralizing the β-Al5FeSi intermetallic compound.

[0123] In the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the α-AlFeSi intermetallic compound can have a composition of Al: 74.9-86.7 at.%, Fe: 6.9-14.3 at.%, and Si: 6.2-11.3 at.%.

[0124] The aforementioned high-strength, high-elongation, and high-thermal-conductivity aluminum casting alloy can have a yield strength in the range of 100 MPa to 140 MPa, a maximum tensile strength in the range of 180 MPa to 220 MPa, an elongation in the range of 2.5% to 8.5%, and a thermal conductivity in the range of 160 W / mK to 190 W / mK.

[0125] A method for producing a high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy according to another modified embodiment of the present invention comprises: a first step of providing a molten aluminum casting alloy containing 6.5% to 11.5% by weight of silicon (Si); 0.2% to 0.4% by weight of magnesium (Mg); 0.2% to 0.3% by weight of iron (Fe); and the remainder being aluminum (Al) and unavoidable impurities; and a second step of applying external energy to the molten aluminum casting alloy at a temperature higher than the liquidus temperature, and then cooling it, so that it contains an α-AlFeSi intermetallic compound having a cubic crystal structure within the aluminum matrix.

[0126] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include maintaining the molten aluminum casting alloy at a temperature 200°C to 300°C higher than the liquidus temperature, and then cooling it at a cooling rate of 1 K / sec or more.

[0127] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include maintaining the molten aluminum casting alloy at a temperature 100°C to 150°C higher than the liquidus temperature, and then cooling it at a cooling rate of 10K / sec or more.

[0128] In the method for producing the aforementioned high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the molten aluminum casting alloy can be characterized by maintaining a temperature higher than the liquidus temperature for 1 to 2 hours.

[0129] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the molten aluminum casting alloy can be characterized by applying ultrasonic waves to it at a temperature higher than the liquidus temperature and maintaining it for 1 to 2 minutes.

[0130] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step may include a phase change from a β-Al5FeSi intermetallic compound having a monoclinic crystal structure to an α-AlFeSi intermetallic compound having a cubic crystal structure.

[0131] In the method for producing the high-strength, high-strength, and high-thermal-conductivity aluminum casting alloy, the second step allows the formation of the β-Al5FeSi intermetallic compound to occur before the Al-Si eutectic reaction, and the α-Al phase, which is the aluminum matrix, to be formed before the β-Al5FeSi intermetallic compound.

[0132] Table 7 shows experimental examples of the composition and process conditions of aluminum casting alloys according to other modified embodiments of the present invention. The composition is evaluated in terms of the composition (unit: weight %) of the Al-Si alloy system.

[0133] [Table 7]

[0134] In this experimental example, in order to control the formation phase of Fe-based intermetallic compounds, the following two liquid-phase processes (Thermal Rate (TR) and Ultrasonic Treatment (UST)) were performed in addition to the conventional casting method during the step of dissolving the liquid metal. Thermal Rate refers to a treatment method in which the molten metal is maintained at a superheated state for a certain period of time. In Table 7, the "TR" column refers to a process in which the molten metal is maintained at a set temperature for 1 hour, then cooled to approximately 700°C, and then poured into a mold for casting. The "UST" column refers to a process in which the molten metal at a set temperature is ultrasonically treated for 1 minute, then cooled to approximately 700°C, and then poured into a mold for casting.

[0135] In Table 7, Experimental Example 20, 'Alloy 20', corresponds to the basic alloy; Experimental Example 21, 'Alloy 21', applies the process of ultrasonically treating the molten alloy of Alloy 20 at 800°C for 1 minute, then cooling it to approximately 700°C, and then pouring it into a mold for casting; and Experimental Example 22, 'Alloy 22', applies the process of maintaining the molten alloy of Alloy 20 at a set temperature of 800°C for 1 hour, then cooling the molten metal to approximately 700°C, and then pouring it into a mold for casting. The casting process for forming the aluminum casting alloy according to other modified embodiments of the present invention is the casting process described with reference to Figure 2. Figure 41 is a photograph of the microstructure of the aluminum casting alloy according to the cooling rate in other modified embodiments of the present invention (Table 7). Figure 41 shows the cases where Step 1 has a cooling rate of 2.2 K / sec, Step 2 has a cooling rate of 6.9 K / sec, Step 3 has a cooling rate of 16 K / sec, and Step 4 has a cooling rate of 40 K / sec.

[0136] Referring to Figure 41, it can be confirmed that in alloy 20, plate-like β-Al5FeSi intermetallic compounds are observed, but α-AlFeSi intermetallic compounds with the shape of Chinese characters are not observed.

[0137] In alloy 21, which is prepared by applying a process to which the molten alloy of alloy 20 is ultrasonically treated at 800°C for 1 minute, then cooled to approximately 700°C, and subsequently injected into a mold for casting, it can be confirmed that when the cooling rate is 10K / sec or higher, a phase change occurs from a plate-like β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound having the shape of Chinese characters.

[0138] In alloy 22, which is produced by applying a process in which the molten alloy of alloy 20 is maintained at a set temperature of 800°C for 1 hour, then cooled to approximately 700°C, and subsequently poured into a mold for casting, it can be confirmed that when the cooling rate is 1 K / sec or higher, a phase change occurs from a plate-like β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound having the shape of Chinese characters.

[0139] Figure 42 and Table 8 show the tensile properties of aluminum casting alloys immediately after casting according to other modified embodiments of the present invention (Table 7). In Table 8, UTS represents tensile strength, YS represents yield strength, and EL represents elongation.

[0140] [Table 8]

[0141] Referring to Figures 41 and 42 and Table 8, it can be confirmed that a phase change occurs from a plate-like β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound with the shape of Chinese characters, which reduces the fraction of the brittle β-Al5FeSi intermetallic compound and increases the elongation rate.

[0142] Table 9 shows the tensile properties of aluminum casting alloys after T6 heat treatment according to other modified embodiments of the present invention (Table 7). T6 heat treatment refers to a heat treatment in which solution treatment and aging treatment are performed sequentially.

[0143] [Table 9]

[0144] Referring to Table 9, it can be confirmed that when a phase change occurs from a plate-like β-Al5FeSi intermetallic compound to an α-AlFeSi intermetallic compound with the shape of Chinese characters, the fraction of the brittle β-Al5FeSi intermetallic compound decreases and the elongation increases. Furthermore, it can be confirmed that the strength and elongation increase when T6 heat treatment is performed compared to immediately after casting.

[0145] Figure 43 shows the electrical conductivity characteristics of aluminum casting alloys after T6 heat treatment according to other modified embodiments of the present invention (Table 7). A cooling rate of 1-2 K / s was applied to the samples.

[0146] Referring to Figure 43, it can be confirmed that in alloy 22, which is produced by applying the process of maintaining the molten alloy of alloy 20 at a set temperature of 800°C for 1 hour, then cooling the molten metal to approximately 700°C, and then injecting it into a mold for casting, the electrical conductivity characteristics are significantly improved.

[0147] The above description has focused on embodiments of the present invention, but various modifications and variations can be made at the level of those skilled in the art. Such modifications and variations can be said to fall within the scope of the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of the rights of the present invention must be determined by the appended claims.

Claims

1. Silicon (Si) in an amount of 9.85% by weight or more to 11.24% by weight or less. Magnesium (Mg) in amounts of 0.25% by weight or more and 0.41% by weight or less. Iron (Fe) in an amount of 0.39% by weight or more and 0.53% by weight or less, and It consists of aluminum (Al) and the remainder of unavoidable impurities. It contains an α-AlFeSi intermetallic compound having a cubic crystal structure within an aluminum matrix. The α-AlFeSi intermetallic compound having the cubic crystal structure has the same crystal structure as the α-AlMnSi phase and has a monoclinic crystal structure. ５ An aluminum casting alloy characterized by a phase change from an FeSi intermetallic compound.

2. The aluminum casting alloy according to claim 1, further comprising at least one of strontium (Sr): 0.01% by weight or less, and titanium (Ti): 0.15% by weight or less.

3. The aluminum casting alloy according to claim 2, characterized in that the α-AlFeSi intermetallic compound has a composition of Al: 74.9 to 86.7 at.%, Fe: 6.9 to 14.3 at.%, and Si: 6.2 to 11.3 at.%.

4. A first step is to provide molten aluminum casting alloy composed of 9.85% to 11.24% by weight of silicon (Si), 0.25% to 0.41% by weight of magnesium (Mg), 0.39% to 0.53% by weight of iron (Fe), and the remainder consisting of aluminum (Al) and unavoidable impurities. The process includes a second step of applying external energy to the molten aluminum casting alloy at a temperature higher than the liquidus temperature, and then cooling it, so that the aluminum matrix contains an α-AlFeSi intermetallic compound having a cubic crystal structure. The second step includes a phase change from a β-Al5FeSi intermetallic compound having a monoclinic crystal structure to an α-AlFeSi intermetallic compound having a cubic crystal structure. The method for producing an aluminum casting alloy is characterized in that the second step includes maintaining the molten aluminum casting alloy at a temperature higher than the liquidus temperature for 1 to 2 hours, or maintaining the molten aluminum casting alloy at a temperature higher than the liquidus temperature by applying ultrasonic waves for 1 to 2 minutes.

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