DEFORMED ALUMINUM ALLOY CASTING AND METHOD OF MANUFACTURING THE SAME

Abstract

 Provided are a deformed Al alloy casting with improved formability by local heat treatment, and a method of manufacturing the same, and the method includes a casting step for forming an Al alloy casting by casting molten metal formed by melting alloying elements of Al alloy, a solid solution treatment step for solid solution-treating the Al alloy casting, an aging step for aging the solid solution-treated Al alloy casting, a local heat treatment step for locally heat-treating a deformation target area of the aged Al alloy casting, and a deformation step for deforming the locally heat-treated deformation target area of the Al alloy casting.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION

[0001] This application claims the benefit of Korean Patent Application No. 10-2023-0131989, filed on October 4, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention relates to aluminum alloy and, more particularly, to a deformed Al alloy casting with improved formability by local heat treatment, and a method of manufacturing the same.

2. Description of the Related Art

[0003] Recently, the demand for lightweight and high-strength materials has increased based on the global trend to increase the efficiency of fuel by reducing the weight of transportation equipment parts, and the use of aluminum (Al) alloy is rapidly increasing due to its excellent castability, processability, mechanical properties, durability, recyclability, etc.

[0004] Suspension parts of vehicles have traditionally been manufactured mainly using Al forgings, but currently, there is an increasing trend to use Al castings to reduce manufacturing costs and carbon emissions. However, compared to Al forgings, Al castings are limited in use because of difficulties in plastic deformation such as swaging due to high brittleness and low elongation. Therefore, in order to increase the formability of Al alloy castings, microstructure control, e.g., a reduction in particle diameter of eutectic silicon (Si), is required.

SUMMARY OF THE INVENTION

[0005] The present invention provides a deformed aluminum (Al) alloy casting with improved formability by local heat treatment, and a method of manufacturing the same.

[0006] However, the above description is an example, and the scope of the present invention is not limited thereto.

[0007] According to an aspect of the present invention, there is provided a method of manufacturing a deformed aluminum (Al) alloy casting, the method including a casting step for forming an Al alloy casting by casting molten metal formed by melting alloying elements of Al alloy, a solid solution treatment step for solid solution-treating the Al alloy casting, an aging step for aging the solid solution-treated Al alloy casting, a local heat treatment step for locally heat-treating a deformation target area of the aged Al alloy casting, and a deformation step for deforming the locally heat-treated deformation target area of the Al alloy casting.

[0008] The solid solution treatment step may be performed at a temperature ranging from 420°C to 540°C for 30 minutes to 8 hours.

[0009] The aging step may be performed at a temperature ranging from 100°C to 200°C for 5 hours to 30 hours.

[0010] The local heat treatment step may be performed at a temperature ranging from 300°C to 450°C for 30 seconds to 60 minutes.

[0011] In the local heat treatment step, a non-deformation area other than the deformation target area may be maintained at a temperature ranging from 20°C to 200°C.

[0012] The deformation step may be performed by swaging the deformation target area.

[0013] The swaging may be performed by rotating a swaging tool at a speed ranging from 800 RPM to 1200 RPM, maintaining pressure for a time ranging from 0.1 second to 1 second, and lowering the swaging tool at a speed ranging from 0.4 mm/s to 0.8 mm/s.

[0014] The deformed Al alloy casting may include at least one of AC1B alloy, AC2A alloy, AC2B alloy, AC3A alloy, AC4A alloy, AC4C alloy, AC4CH alloy, AC4B alloy, AC4D alloy, AC7A alloy, AC8A alloy, AC8B alloy, AC8C alloy, AC9A alloy, and AC9B alloy.

[0015] The deformed Al alloy casting may include 6 wt% to 10 wt% of silicon (Si), 0.2 wt% to 0.5 wt% of magnesium (Mg), and a balance of Al and unavoidable impurities.

[0016] The deformed Al alloy casting may further include at least one of more than 0 wt% and not more than 0.2 wt% of copper (Cu), more than 0 wt% and not more than 0.3 wt% of zinc (Zn), more than 0 wt% and not more than 0.5 wt% of iron (Fe), more than 0 wt% and not more than 0.6 wt% of manganese (Mn), more than 0 wt% and not more than 0.2 wt% of titanium (Ti), and more than 0 wt% and not more than 0.05 wt% of chromium (Cr).

[0017] According to another aspect of the present invention, there is provided a deformed aluminum (Al) alloy casting manufactured using the above-described method.

[0018] The deformed Al alloy casting may have a softened area where local heat treatment is performed and a hardened area where local heat treatment is not performed.

[0019] The deformed Al alloy casting may have an average secondary dendrite arm spacing (SDAS) of 35 µm or less.

[0020] The deformed Al alloy casting may include eutectic silicon (Si) having an average particle diameter ranging from 8 µm to 12 µm.

[0021] The deformed Al alloy casting may have a hardness ranging from 50 HB to 70 HB.

[0022] The deformed Al alloy casting may satisfy a yield strength (YS) of 220 MPa or more, an ultimate tensile strength (UTS) of 300 MPa or more, and an elongation (EL) of 6% or more.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and other features and advantages of the present invention will become more apparent by describing in detail embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a flowchart of a method of manufacturing a deformed aluminum (Al) alloy casting, according to an embodiment of the present invention;

FIG. 2 is a schematic diagram for describing a local heat treatment process applied to a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention;

FIG. 3 is a schematic diagram for describing a swaging process applied to a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention;

FIG. 4 is a schematic diagram for describing a method of generating a deformed Al alloy casting based on a swaging process applied to a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention;

FIG. 5 is a top exterior image of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention;

FIG. 6 includes optical microscope images of deformed areas of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention;

FIG. 7 includes optical microscope images showing microstructures of deformed areas of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention; and

FIG. 8 includes top exterior images of deformed Al alloy castings manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, the present invention will be described in detail by explaining embodiments of the invention with reference to the attached drawings. The invention may, however, be embodied in many different forms and should not be construed as being 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 concept of the invention to one of ordinary skill in the art. Like reference numerals refer to like elements throughout. Further, various elements and regions in the drawings are schematically illustrated. Therefore, the scope of the present invention is not limited by the relative sizes or distances shown in the attached drawings.

[0025] A deformed aluminum (Al) alloy casting according to an embodiment of the present invention will now be described.

Deformed Al Alloy Casting

[0026] A deformed Al alloy casting according to an embodiment of the present invention may include various Al alloys for casting. For example, the deformed Al alloy casting may include at least one of AC1B alloy (Al-Cu-Mg-based alloy), AC2A alloy (Al-Cu-Si-based alloy), AC2B alloy (Al-Cu-Si-based alloy), AC3A alloy (Al-Si-based alloy), AC4A alloy (Al-Si-Mg-based alloy), AC4C alloy (Al-Si-Mg-based alloy), AC4CH alloy (Al-Si-Mg-based alloy), AC4B alloy (Al-Si-Cu-based alloy), AC4D alloy (Al-Si-Cu-Mg-based alloy), AC7A alloy (Al-Mg-based alloy), AC8A alloy (Al-Si-Ni-Cu-Mg-based alloy), AC8B alloy (Al-Si-Ni-Cu-Mg-based alloy), AC8C alloy (Al-Si-Ni-Cu-Mg-based alloy), AC9A alloy (Al-Si-Cu-Mg-Ni-based alloy), and AC9B alloy (Al-Si-Cu-Mg-Ni-based alloy).

[0027] A case in which the deformed Al alloy casting includes the AC4C alloy which is an Al-Si-Mg-based alloy will now be described as an example.

[0028] The deformed Al alloy casting may include 6 wt% to 10 wt% of silicon (Si), 0.2 wt% to 0.5 wt% of magnesium (Mg), and the balance of Al and unavoidable impurities.

[0029] The deformed Al alloy casting may further include at least one of more than 0 wt% and not more than 0.2 wt% of copper (Cu), more than 0 wt% and not more than 0.3 wt% of zinc (Zn), more than 0 wt% and not more than 0.5 wt% of iron (Fe), more than 0 wt% and not more than 0.6 wt% of manganese (Mn), more than 0 wt% and not more than 0.2 wt% of titanium (Ti), and more than 0 wt% and not more than 0.05 wt% of chromium (Cr).

[0030] The functions and contents of the components included in the deformed Al alloy casting according to the present invention will now be described.

Si: 6 wt% to 10 wt%

[0031] Si is an element for increasing fluidity, castability, and tensile strength of the deformed Al alloy casting. When the content of Si is less than 6 wt%, castability may decrease and strength may not be easily ensured. When the content of Si is greater than 10 wt%, the content of eutectic Si which propagates cracks may increase to deteriorate mechanical properties. Therefore, Si may be added at 6 wt% to 10 wt% of a total weight of the deformed Al alloy casting.

Mg: 0.2 wt% to 0.5 wt%

[0032] Mg is a solid solution strengthening element which is dissolved in a matrix to increase strength and formability. When the content of Mg is less than 0.2 wt%, the strength may not be easily ensured and the formability may not be easily increased. When the content of Mg is greater than 0.5 wt%, elongation may be remarkably reduced to cause cracks. Therefore, Mg may be added at 0.2 wt% to 0.5 wt% of the total weight of the deformed Al alloy casting.

Cu: not more than 0.2 wt%

[0033] Cu is an element for increasing strength and corrosion resistance of the deformed Al alloy casting. When the content of Cu is greater than 0.2 wt%, cracks may be created due to segregation during casting. Therefore, Cu may be added not more than 0.2 wt% and, more specifically, more than 0 wt% and not more than 0.2 wt% of the total weight of the deformed Al alloy casting.

Zn: not more than 0.3 wt%

[0034] Zn is an element for increasing castability and strength of the deformed Al alloy casting. When the content of Zn is greater than 0.3 wt%, fluidity of molten metal may be reduced to reduce castability, and segregation may occur at the center of the manufactured alloy to deteriorate mechanical properties. Therefore, Zn may be added not more than 0.3 wt% and, more specifically, more than 0 wt% and not more than 0.3 wt% of the total weight of the deformed Al alloy casting.

Fe: not more than 0.5 wt%

[0035] Fe is an element crystallized as an intermetallic compound to minimize a reduction in thermal conductivity and increase strength of the deformed Al alloy casting. When the content of Fe is greater than 0.5 wt%, segregation may occur at the center of the manufactured alloy to deteriorate mechanical properties. Therefore, Fe may be added not more than 0.5 wt% and, more specifically, more than 0 wt% and not more than 0.5 wt% of the total weight of the deformed Al alloy casting.

Mn: not more than 0.6 wt%

[0036] Mn may form an intermetallic compound of AlMnSi phase to increase an elastic modulus. When the content of Mn is greater than 0.6 wt%, the intermetallic compound may become coarse to reduce castability, deteriorate mechanical properties and, particularly, increase brittleness due to a reduction in elongation. In addition, primary Si may become coarse. Therefore, Mn may be added not more than 0.6 wt% and, more specifically, more than 0 wt% and not more than 0.6 wt% of the total weight of the deformed Al alloy casting.

Ti: not more than 0.2 wt%

[0037] Ti is an element precipitated as an intermetallic compound such as Al₃ Ti in an Al matrix to improve mechanical properties and corrosion resistance, refine crystal grains of the Al alloy, and prevent cracks of the casting. When the content of Ti is greater than 0.2 wt%, a coarse intermetallic compound may be formed to reduce ductility. Therefore, Ti may be added not more than 0.2 wt% and, more specifically, more than 0 wt% and not more than 0.2 wt% of the total weight of the deformed Al alloy casting.

Cr: not more than 0.05 wt%

[0038] Cr may refine crystal grains by suppressing recrystallization. When the content of Cr is greater than 0.05 wt%, a coarse intermetallic compound may be formed to reduce ductility. Therefore, Cr may be added not more than 0.05 wt% and, more specifically, more than 0 wt% and not more than 0.05 wt% of the total weight of the deformed Al alloy casting.

[0039] The remaining component of the deformed Al alloy casting is Al. However, in a general manufacturing process, unintended impurities may be unavoidably included from a raw material and an ambient environment and thus may not be completely avoided. These impurities are known to one of ordinary skill in the art and thus will not be particularly mentioned herein.

[0040] The deformed Al alloy casting may be manufactured using a manufacturing method described below.

[0041] The deformed Al alloy casting may have a softened area where local heat treatment is performed and a hardened area where local heat treatment is not performed.

[0042] The deformed Al alloy casting may have, for example, an average secondary dendrite arm spacing (SDAS) of 35 µm or less. The deformed Al alloy casting may have, for example, an average SDAS ranging from 20 µm to 35 µm.

[0043] The deformed Al alloy casting may include, for example, eutectic Si having an average particle diameter ranging from 8 µm to 12 µm.

[0044] The deformed Al alloy casting may have, for example, a hardness ranging from 50 HB to 70 HB. Herein, "HB" denotes the Brinell hardness.

[0045] The deformed Al alloy casting may satisfy, for example, a yield strength (YS) of 220 MPa or more, an ultimate tensile strength (UTS) of 300 MPa or more, and an elongation (EL) of 6% or more and, more specifically, a YS of 220 MPa to 300 MPa, a UTS of 300 MPa to 400 MPa, and an EL of 6% to 12%.

Method of Manufacturing Deformed Al Alloy Casting

[0046] A method of manufacturing a deformed Al alloy casting will now be described in detail.

[0047] FIG. 1 is a flowchart of a method S100 of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0048] Referring to FIG. 1, the method 5100 of manufacturing a deformed Al alloy casting includes a casting step S110, a solid solution treatment step S120, an aging step S130, a local heat treatment step S140, and a deformation step S150.

[0049] The casting step S110 is a step for casting molten metal formed by melting alloying elements constituting a deformed Al alloy casting.

[0050] In the casting step S110, the molten metal may be formed by melting alloying elements of Al alloy including, for example, 6 wt% to 10 wt% of Si, 0.2 wt% to 0.5 wt% of Mg, and the balance of Al and unavoidable impurities. The molten metal may further include at least one of more than 0 wt% and not more than 0.2 wt% of Cu, more than 0 wt% and not more than 0.3 wt% of Zn, more than 0 wt% and not more than 0.5 wt% of Fe, more than 0 wt% and not more than 0.6 wt% of Mn, more than 0 wt% and not more than 0.2 wt% of Ti, and more than 0 wt% and not more than 0.05 wt% of Cr, as the alloying elements.

[0051] The alloying elements may be melted in a graphite crucible by using a high-frequency induction furnace or an electrical resistance furnace at a temperature at which the alloying elements are completely melted. The alloying elements may be added individually, or all or some of the alloying elements may be added in the form of master alloy. For example, a pure element of Si may be added to molten Al, or an Al-Si master alloy with a high content of Si may be added to molten Al. This method may also be applied to the other additive elements such as Mg and Cu.

[0052] An Al alloy casting may be formed through casting by pouring the molten metal into a cavity of a mold and solidifying the molten metal. The Al alloy casting may be formed through gravity casting, low-pressure casting, or counter-pressure casting. However, the above-mentioned casting methods are examples, and the scope of the present invention is not limited thereto.

[0053] After the casting step S110 is performed, the Al alloy casting may be cooled to room temperature, e.g., a temperature ranging from 0°C to 40°C. The cooling may be performed using various methods such as water-cooling quenching, air cooling, or furnace cooling.

[0054] In the solid solution treatment step S120, the Al alloy casting is solid solution-treated. The solid solution treatment step S120 may be performed, for example, at a temperature ranging from 420°C to 540°C for 30 minutes to 8 hours and, more specifically, at 470°C for 1 hour by heating the Al alloy casting. Due to the solid solution treatment, the composition uniformity of the Al matrix of the Al alloy casting may be increased.

[0055] After the solid solution treatment step S120 is performed, the Al alloy casting may be cooled to room temperature, e.g., a temperature ranging from 0°C to 40°C. The cooling may be performed using various methods such as water-cooling quenching, air cooling, or furnace cooling.

[0056] In the aging step S130, the solid solution-treated Al alloy casting is aged. The aging step S130 may be performed, for example, at a temperature ranging from 100°C to 200°C for 5 hours to 30 hours and, more specifically, at 160°C for 12 hours by heating the Al alloy casting. Due to the aging, solute elements may be extracted from the supersaturated solid solution to form an aging precipitation phase.

[0057] After the aging step S130 is performed, the Al alloy casting may be cooled to room temperature, e.g., a temperature ranging from 0°C to 40°C. The cooling may be performed using various methods such as water-cooling quenching, air cooling, or furnace cooling.

[0058] The solid solution treatment step S120 and the aging step S130 may be sequentially performed. Alternatively, only the solid solution treatment step S120 may be performed or only the aging step S130 may be performed.

[0059] In the local heat treatment step S140, local heat treatment is performed to locally heat-treat a deformation target area of the aged Al alloy casting. The local heat treatment step S140 may be performed, for example, at a temperature ranging from 300°C to 450°C for 30 seconds to 60 minutes and, more specifically, at 400°C for 30 minutes. Due to the local heat treatment step S140, the Al matrix may be softened and spheroidization of eutectic Si may be optimized. The local heat treatment step S140 may be referred to as annealing heat treatment. The heat treatment temperature and time of the local heat treatment step S140 may be controlled to ensure a sufficient ductility for swaging. Therefore, even when the local heat treatment step S140 is performed at 300°C for 1 minute to 5 minutes, a desired ductility may be ensured.

[0060] In the local heat treatment step S140, a non-deformation area other than the deformation target area may be maintained at a temperature at which the local heat treatment effect does not occur, e.g., a temperature ranging from 20°C to 200°C.

[0061] After the local heat treatment is performed, the Al alloy casting may be cooled to room temperature, e.g., a temperature ranging from 0°C to 40°C. The cooling may be performed using various methods such as water-cooling quenching, air cooling, or furnace cooling.

[0062] In the deformation step S150, the deformation target area of the Al alloy casting is deformed. The deformation step S150 may be performed using swaging. The swaging may be performed by rotating a swaging tool at a speed ranging from 800 RPM to 1200 RPM, maintaining pressure for a time ranging from 0.1 second to 1 second, and lowering the swaging tool at a speed ranging from 0.4 mm/s to 0.8 mm/s. However, the above-mentioned conditions are examples, and the scope of the present invention is not limited thereto.

[0063] A deformed Al alloy casting may be manufactured using the above-described method of manufacturing a deformed Al alloy casting.

[0064] FIG. 2 is a schematic diagram for describing a local heat treatment process applied to a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0065] Referring to FIG. 2, an Al alloy casting 100 is inserted into a local heat treatment apparatus 10. The local heat treatment apparatus 10 may include a heater 12 disposed at an upper side, and a cooler 14 disposed at a lower side. A deformation target area 110 of the Al alloy casting 100 may be locally heated by the heater 12 so as to be heat-treated. On the other hand, a non-deformation area 120 of the Al alloy casting 100 may be cooled by the cooler 14 so as to be maintained at room temperature or at a temperature lower than the temperature of the deformation target area 110. Alternatively, the cooler 14 may be omitted and the non-deformation area 120 may be exposed to the outside and cooled. The heater 12 and the cooler 14 may be configured in various forms.

[0066] FIG. 3 is a schematic diagram for describing a swaging process applied to a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0067] FIG. 4 is a schematic diagram for describing a method of generating a deformed Al alloy casting based on a swaging process applied to a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0068] Referring to FIGS. 3 and 4, the Al alloy casting 100 is mounted on a jig 32 provided at a lower side, a cap 34 is placed on the Al alloy casting 100, and a swaging tool 36 provided at an upper side is placed on the cap 34. Then, the deformation target area 110 of the Al alloy casting 100 is swaged by rotating and pressing the swaging tool 36. For example, a protruding portion of the deformation target area 110 may be pressed and bent inward so as to engage with the cap 34.

Test Examples

[0069] Test examples about a deformed Al alloy casting according to an embodiment of the present invention will now be described in detail. The following test examples are examples for describing an embodiment of the present invention, and the present invention is not limited thereto.

[0070] AC4C alloy was prepared as a raw material for a deformed Al alloy casting. The deformed Al alloy casting includes 8 wt% of Si, 0.4 wt% of Mg, and the balance of Al and unavoidable impurities.

[0071] An Al alloy casting was formed by casting the Al alloy.

[0072] Then, the Al alloy casting was heated and solid solution-treated at about 470°C for about 1 hour, and water-cooled. After that, the Al alloy casting was heated again and aged at about 120°C for about 12 hours. That is, the Al alloy casting was T6-heat-treated.

[0073] Then, a deformation target area of the Al alloy casting was locally heat-treated at about 400°C for about 30 minutes. Subsequently, the Al alloy casting was air-cooled to room temperature.

[0074] Then, a deformed Al alloy casting was generated by swaging the Al alloy casting. The swaging was performed by rotating a swaging tool at about 1000 RPM, maintaining pressure for about 0.5 seconds, and lowering the swaging tool at about 0.6 mm/s.

[0075] Table 1 comparatively shows process conditions of the deformed Al alloy casting manufactured using the method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention, and those of comparative examples.

[Table 1]

Process	No.(pcs)	Solid solution Treatment	Aging	Local Heat Treatment	Swaging Temperature
Comparative Example 1	3	O	X	X	20°C
Comparative Example 2	3	O	X	X	20°C
Comparative Example 3	3	O	X	X	200°C
Embodiment	3	O	O	O	20°C

[0076] Referring to Table 1, Comparative Example 1 is a sample manufactured by performing solid solution treatment and not performing aging and local heat treatment. Comparative Examples 1 and 2 are samples manufactured by performing solid solution treatment under the same conditions as in Embodiment, not performing aging and local heat treatment, and performing swaging at room temperature (20°C). Comparative Example 3 is a sample manufactured by performing solid solution treatment under the same conditions as in Embodiment, not performing aging and local heat treatment, and performing swaging at 200°C. Embodiment is a sample manufactured by performing all of solid solution treatment, aging, and local heat treatment and performing swaging at room temperature (20°C).

[0077] FIG. 5 is a top exterior image of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0078] Referring to FIG. 5, Comparative Examples 1 and 2 show surface exfoliation. Comparative Example 3 shows Al stuck to the swaging tool, and thus subsequent tests were not performed. On the other hand, Embodiment does not show surface exfoliation.

[0079] FIG. 6 includes optical microscope images of deformed areas of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0080] Referring to FIG. 6, optical microscope images of areas "A", "B", and "C" as the deformed areas of the deformed Al alloy casting are shown. Comparative Example 1 shows surface exfoliation in area "B". Comparative Example 2 shows surface exfoliation in area "C". On the other hand, Embodiment does not show such surface exfoliation.

[0081] FIG. 7 includes optical microscope images showing microstructures of deformed areas of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0082] Referring to FIG. 7, optical microscope images of areas "D" and "E" as the deformed areas of the deformed Al alloy casting are shown. Cracks are found at the interface of eutectic Si in area "E" of Comparative Example 1. When solid solution treatment is excessively performed to destroy the eutectic Si network, eutectic Si becomes coarse to cause cracks. Defects are not found in the microstructure of Comparative Example 2. Defects are not found in the microstructure of Embodiment.

[0083] Table 2 comparatively shows properties of a deformed Al alloy casting manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention, and those of comparative examples.

[Table 2]

Classification	Inner Portion Cracks (pcs)	Central Portion Cracks (pcs)	Central Portion Exfoliation (pcs)	SDAS (µm)	Average Particle Diameter of Eutectic Si (µm)	Hardness (HB)
Comparative Example 1	0	2	1	36	17	50
Comparative Example 2	0	3	1	33	13	64
Embodiment	0	0	0	33	10	58

[0084] Referring to Table 2, any of the comparative examples and the embodiment does not show inner portion cracks in area "A" of FIG. 6. However, the comparative examples show central portion cracks and central portion exfoliation in area "B" of FIG. 6.

[0085] The comparative examples and the embodiment show very similar average SDASs of 33 µm to 36 µm.

[0086] The embodiment shows a smaller average particle diameter of eutectic Si than those of the comparative examples. Therefore, the average particle diameter of eutectic Si, which needs to be small to suppress the creation and propagation of cracks, may range from 5 µm to 12 µm.

[0087] The comparative examples and the embodiment show similar hardnesses.

[0088] FIG. 8 includes top exterior images of deformed Al alloy castings manufactured using a method of manufacturing a deformed Al alloy casting, according to an embodiment of the present invention.

[0089] Referring to FIG. 8, the deformed Al alloy castings were manufactured using the same method except that local heat treatment was performed at 300°C for 1 minute and for 5 minutes. Because both samples do not show cracks and surface exfoliation, it may be analyzed that a sufficient ductility is ensured with the above-mentioned temperature and times of local heat treatment.

[0090] According to the present invention, using a method of manufacturing a deformed Al alloy casting, by solid solution-treating and aging an Al alloy casting and then locally heat-treating a deformation target area of the Al alloy casting, swaging formability may be increased. Therefore, because brittleness of an Al matrix is reduced due to the local heat treatment, ductility of the Al alloy casting may be increased. The deformed Al alloy casting may be applied to vehicle parts, e.g., compression arms and rear lower arms.

[0091] The above-described effects of the present invention are examples, and the scope of the present invention is not limited thereto.

[0092] While the present invention has been particularly shown and described with reference to embodiments thereof, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the scope of the present invention as defined by the following claims.

Claims

1. A method of manufacturing a deformed aluminum (Al) alloy casting, the method comprising:

a casting step for forming an Al alloy casting by casting molten metal formed by melting alloying elements of Al alloy;

a solid solution treatment step for solid solution-treating the Al alloy casting;

an aging step for aging the solid solution-treated Al alloy casting;

a local heat treatment step for locally heat-treating a deformation target area of the aged Al alloy casting; and

a deformation step for deforming the locally heat-treated deformation target area of the Al alloy casting.

2. The method of claim 1, wherein the solid solution treatment step is performed at a temperature ranging from 420°C to 540°C for 30 minutes to 8 hours.

3. The method of claim 1, wherein the aging step is performed at a temperature ranging from 100°C to 200°C for 5 hours to 30 hours.

4. The method of claim 1, wherein the local heat treatment step is performed at a temperature ranging from 300°C to 450°C for 30 seconds to 60 minutes.

5. The method of claim 1, wherein, in the local heat treatment step, a non-deformation area other than the deformation target area is maintained at a temperature ranging from 20°C to 200°C.

6. The method of claim 1, wherein the deformation step is performed by swaging the deformation target area.

7. The method of claim 6, wherein the swaging is performed by rotating a swaging tool at a speed ranging from 800 RPM to 1200 RPM, maintaining pressure for a time ranging from 0.1 second to 1 second, and lowering the swaging tool at a speed ranging from 0.4 mm/s to 0.8 mm/s.

8. The method of claim 1, wherein the deformed Al alloy casting comprises at least one of AC1B alloy, AC2A alloy, AC2B alloy, AC3A alloy, AC4A alloy, AC4C alloy, AC4CH alloy, AC4B alloy, AC4D alloy, AC7A alloy, AC8A alloy, AC8B alloy, AC8C alloy, AC9A alloy, and AC9B alloy.

9. The method of claim 1, wherein the deformed Al alloy casting comprises 6 wt% to 10 wt% of silicon (Si), 0.2 wt% to 0.5 wt% of magnesium (Mg), and a balance of Al and unavoidable impurities.

10. The method of claim 9, wherein the deformed Al alloy casting further comprises at least one of more than 0 wt% and not more than 0.2 wt% of copper (Cu), more than 0 wt% and not more than 0.3 wt% of zinc (Zn), more than 0 wt% and not more than 0.5 wt% of iron (Fe), more than 0 wt% and not more than 0.6 wt% of manganese (Mn), more than 0 wt% and not more than 0.2 wt% of titanium (Ti), and more than 0 wt% and not more than 0.05 wt% of chromium (Cr).

11. A deformed aluminum (Al) alloy casting manufactured using the method of any one of claim 1 through claim 10.

12. The deformed Al alloy casting of claim 11, wherein the deformed Al alloy casting has an average secondary dendrite arm spacing (SDAS) of 35 µm or less.

13. The deformed Al alloy casting of claim 11, wherein the deformed Al alloy casting comprises eutectic silicon (Si) having an average particle diameter ranging from 8 µm to 12 µm.

14. The deformed Al alloy casting of claim 11, wherein the deformed Al alloy casting has a hardness ranging from 50 HB to 70 HB.

15. The deformed Al alloy casting of claim 11, wherein the deformed Al alloy casting satisfies a yield strength (YS) of 220 MPa or more, an ultimate tensile strength (UTS) of 300 MPa or more, and an elongation (EL) of 6% or more.

Drawing