WO2007139306A1

WO2007139306A1 - Hot chamber die casting apparatus for semi-solid metal alloy and the manufacturing method using the same

Info

Publication number: WO2007139306A1
Application number: PCT/KR2007/002503
Authority: WO
Inventors: Young Chul Lee; Du Ho Lee; Do Yeon Lee; Kwang Il Youn; Hyoung Jin Park; Tae Youn Park
Original assignee: Futurecast Co., Ltd.
Priority date: 2006-05-26
Filing date: 2007-05-23
Publication date: 2007-12-06
Also published as: KR100682372B1

Abstract

The present disclosure provides a new hot chamber die casting technology which is developed to substantially solve the problems of the conventional art, and particularly to a hot chamber die casting apparatus for magnesium alloy and a manufacturing method using the same. More particularly, the present disclosure provides a hot chamber die casting apparatus for magnesium alloy, wherein electromagnetic or ultrasonic wave is applied to magnesium alloy along a passageway connecting a furnace and a mold so as to control the microstructure of the semisolid metal to be finer, and a method for manufacturing a metal product by injecting the semisolid metal with controlled microstructure.

Description

HOT CHAMBER DIE CASTING APPARATUS FOR SEMISOLID METAL ALLOY AND THE MANUFACTURING METHOD USING THE SAME

Technical Field

[1] The present disclosure relates to a new hot chamber die casting technology which is developed to substantially solve the problems of the conventional art, and particularly to a hot chamber die casting apparatus for magnesium alloy and a manufacturing method using the same. More particularly, the present disclosure relates to a hot chamber die casting apparatus for magnesium alloy, wherein electromagnetic or ultrasonic wave is applied to magnesium alloy on a passageway of the magnesium alloy between a furnace and a mold so as to control the microstructure of the semisolid metal to be finer, and a method for manufacturing a metal product by injecting the semisolid magnesium alloy with controlled semisolid microstructure. Background Art

[2] Die casting apparatuses can be divided into cold chamber die casting apparatuses and hot chamber die casting apparatuses by methods for transporting molten metal produced in a furnace into a mold. FIG. 1 illustrates a typical cold chamber die casting apparatus, and FIG. 2 illustrates a typical hot chamber die casting apparatus.

[3] In a typical cold chamber die casting method, molten metal produced in a melting furnace 21 is transported into a pressure cylinder 29 by a plunger 25 while being exposed to the atmosphere, and then is injected into a mold 15 and 19, to be solidified to a product. Accordingly, the typical cold chamber die casting method has the disadvantage that it is difficult to manufacture good casting products because a wide portion of molten metal is exposed to the atmosphere during the transportation, and gas is entrapped into the molten metal during the pressing in the pressure cylinder 29 to remain in the finished castings.

[4] A hot chamber die casting method has been developed to solve the above described disadvantages. Referring to FIG. 2, in a hot chamber die casting method, molten metal 46 produced in a furnace 44 is pressed into a nozzle 41 and then into a mold by a pressure unit 42 without being exposed to the atmosphere. That is, the molten metal is pressed in a pressure cylinder 48 inside the furnace to flow into goose neck 45 and nozzle, and then into a mold cavity 17. Accordingly, because molten metal is not exposed to the atmosphere, the hot chamber die casting method has the advantage of reduced porosity in a finished casting in comparison with the cold chamber die casting method. The hot chamber die casting method is especially available for such metals such as magnesium which are susceptible to be oxidized rapidly under atmosphere, because an oxidation of molten metal can be avoided as described above.

[5] The hot chamber die casting apparatus typically has such a construction as shown in

FIG. 2 or FIG. 4 (horizontal type). The apparatus shown in FIG. 4 is distinguished from that shown in FIG. 2 by a stirrer provided around a furnace.

[6] A semisolid forming, a method for die-casting a semisolid metal instead of a liquid metal may also be used to improve mechanical properties of a casting. In the semisolid forming, molten metal is cooled down to a temperature range between its liquidus and solidus temperatures, and then the semisolid metal slurry is casted or forged into a billet or a final product. In general, referring to FIG. 4, semisolid metal is injected into a mold when the apparatus is provided with an electromagnetic stirrer 87, whereas liquid metal is injected into a mold when the apparatus is not provided with the electromagnetic stirrer.

[7] The semisolid forming has many advantages in comparison with other forming methods where molten metal is used, such as casting and squeeze casting. For example, because metal slurry used in the semisolid forming shows fluidity at a temperature lower than that of the molten metal, it is possible to lower the temperature of a mold contacting the slurry in comparison with the case where the mold contacts molten metal, and thus to increase lifetime of the mold. Also, since turbulence is reduced while the slurry flows through a cylinder, it is possible to reduce gas entrapment, and thus to reduce porosities in a final product. In addition, a finer, uniformly distributed, and spheroidized microstructure can be realized, and thus mechanical properties and corrosion resistance of a product can be improved. Examples of the stirring during the formation of semisolid slurry are disclosed in Japanese Patent Laid-Open Publication No. Hei. 11-33692 and Japanese Patent Laid- Open Publication No. Hei. 10-128516.

[8] It is preferable to stir the slurry in the semisolid forming process. The stirring of the slurry between the liquidus and solidus temperatures may break up already formed dendrites and prevent initially solidified layer from growing to a dendrite, thereby spheroidizing the dendrites to form a slurry of spheroidized solid particles in liquid. A mechanical stirring or an electromagnetic stirring is commonly used for the stirring.

[9] The following apparatuses and methods have been developed to apply an external stirrer, such as an electromagnetic stirrer and a mechanical stirrer, to a hot chamber die casting.

[10] US Patent Application Pub No. US 2001/0037868 (Nov. 8, 2001) discloses an electromagnetic coil 87 surrounding a furnace 44 to apply electromagnetic field to semisolid metal bath. This publication also discloses a screw type mechanical stirrer in addition to the electromagnetic coil. Such a method, however, has a disadvantage that it is difficult to reduce the perimeter of the furnace as a pressure unit 42 is included therein, semisolid metal 46 in a pressure chamber is substantially no longer affected by the electromagnetic field, and the furnace is too big to apply available electromagnetic field to semisolid metal. Increasing the electromagnetic field also has a finite limitation in view of apparatus manufacture and power consumption. The mechanical stirring has a problem that the insertion of the screw could break the vacuum sate of the furnace, and thus external impurities may be included in the molten metal. In addition, there is a finite limitation in breaking primary crystal and preventing the growth of a dendrite by the mechanical stirring.

[11] Furthermore, the above described method has a problem that although a condition for finer microstructure is accomplished by the electromagnetic stirring or the mechanical stirring, the condition is no longer maintained as the semisolid metal flows into a nozzle via a goose neck 45. Disclosure of Invention Technical Problem

[12] Accordingly, the present disclosure is directed to a hot chamber die casting apparatus that can produce a die casting product having finer microstructure and therefore increased strength, and a manufacturing method using the same to substantially obviate one or more above described problems. The finer die casting microstructure enables castings to be increased in strength and thus to be decreased in thickness. Therefore, application of the hot chamber die casting in accordance with exemplary embodiments to a framework of an expensive electronic device, such as a notebook computer and a mobile phone, which is manufactured by die casting magnesium alloy makes it possible to decrease the thickness of the framework while maintaining its strength, and thus to reduce the material cost and product weight of the electronic device. Technical Solution

[13] Exemplary embodiments provide a hot chamber die casting apparatus for magnesium alloy, wherein electromagnetic or ultrasonic wave is applied to magnesium alloy on a passageway of the magnesium alloy between a furnace and a mold so as to control microstructures of the semisolid metal to be finer, and a method for manufacturing magnesium alloy product by injecting the semisolid magnesium alloy with controlled microstructure to the mold.

Advantageous Effects

[14] In accordance with an exemplary embodiment, it is possible to manufacture casting product having a finer microstructure and thus an increased strength, and having a densified microstructure and thus a uniform thickness. Accordingly, it is also possible to decrease a defect rate and to increase productivity. Brief Description of the Drawings

[15] Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:

[16] FIG. 1 is a schematic view illustrating a typical cold chamber die casting apparatus;

[17] FIG. 2 is a schematic view illustrating a typical hot chamber die casting apparatus;

[18] FIG. 3 is a schematic view illustrating the cold chamber die casting apparatus of

FIG. 1 provided with a stirrer;

[19] FIG. 4 is a schematic view illustrating the hot chamber die casting apparatus of

FIG. 2 provided with a stirrer;

[20] FIG. 5 is a schematic view illustrating a hot chamber die casting apparatus provided with a stirrer in accordance with an exemplary embodiment;

[21] FIG. 6 is a partial enlarged view of a stirrer and a portion of the hot chamber die casting apparatus with the stirrer coupled thereto in accordance with an exemplary embodiment;

[22] FIG. 7 is a micrograph of a product manufactured by a typical hot chamber die casting (when liquid metal is injected into a mold);

[23] FIG. 8 is a micrograph of a product manufactured by a typical hot chamber die casting when electromagnetic field is applied around a furnace (when a semisolid metal is injected from a furnace into a mold); and

[24] FIGS. 9 through 11 are micrographs of products manufactured by a hot chamber die casting in accordance with an exemplary embodiment (when liquid metal is transformed into semisolid metal on a passageway between the furnace and the mold, and then injected into a mold). Best Mode for Carrying Out the Invention

[25] A hot chamber die casting apparatus for magnesium alloy in accordance with an exemplary embodiment will be described as follows. The hot chamber die casting apparatus for pressing a plunger at a pressure higher than atmospheric pressure so that magnesium alloy is forced into a mold by the plunger to be formed into a shape of the mold without being exposed to the atmosphere, the hot chamber die casting apparatus including a furnace which is made airtight and provided with a heating device, a pressure unit for pressing magnesium alloy, the mold for giving shape to a final casting product, and a pressure chamber having the shape of a goose neck for horizontally injecting magnesium alloy in the furnace into the mold, each injection of magnesium alloy into the mold through the nozzle being performed when the pressure chamber is filled with the molten magnesium alloy, is characterized in that an electromagnetic stirrer is disposed around a nozzle, for stirring magnesium alloy which is being transformed to semisolid state, the nozzle being disposed between the mold and an end of the goose neck of the pressure chamber in the furnace to horizontally connect the goose neck to the mold.

[26] An inner diameter of the nozzle may be smaller than 30 mm. The nozzle may have a size such that the pressure of the plunger pressing the magnesium alloy is 2 Mpa or higher.

[27] The furnace 230 may be a melting furnace for melting a sold material with a heating device provided thereto. The furnace 230 may also be a reservoir for containing molten material received from other melting furnace. Molten metal 240 melted or received by the furnace may flow into the pressure chamber 220, disposed inside the furnace, through an intake port 210.

[28] The plunger 250 of the pressure unit may press molten metal in the pressure chamber 220 so that the molten metal flows into the nozzle 105, and then into the mold 130 and 140. A pneumatic or a hydraulic cylinder may be used for the pressure unit.

[29] The mold 130 and 140 may be a typical mold widely used in hot chamber die casting. Typically, the mold 130 and 140 may include a fixed mold part 140 and a movable mold part 130.

[30] The stirrer 101 may be an electromagnetic field generator or an ultrasonic wave generator. The electromagnetic field generator and the ultrasonic wave generator have been widely used in continuous casting and strip casting. They also have been widely used in die casting as described above.

[31] The exemplary embodiment is characterized by the position of the stirrer. In accordance with the exemplary embodiment, the stirrer is disposed on a passageway through which metal 240 is provided from the furnace 230 into the mold 130 and 140. The passageway refers to a path through which metal flows just after leaving the furnace and until arriving at the mold. Accordingly, the passageway may include the nozzle 105. An outlet end of the pressure chamber may terminate at a sidewall of the furnace. Also, the outlet end of the pressure chamber may be recessed from the sidewall or may protrude from the sidewall of the furnace. The nozzle connects the outer end of the pressure chamber to the mold. The outlet end of the pressure chamber may even extend out of the sidewall until directly being connected to the mold. In this case, the stirrer is disposed at the portion of the pressure chamber that extends out of the furnace. As described above, the stirrer may be disposed at a passageway through which molten metal flows out of the furnace to the mold. When the outlet end of the pressure chamber terminates at a sidewall of the furnace, the stirrer covers only the nozzle. On the other hand, when the outlet end of the pressure chamber is recessed from the sidewall, the stirrer may not cover the whole nozzle 105; when the outlet end of the pressure chamber protrudes from the sidewall, the stirrer 101 may cover a portion of the pressure chamber as well as the nozzle. Further, when the pressure chamber is directly connected to the mold, the stirrer may cover a portion of the pressure chamber that extends out of the furnace.

[32] The present disclosure is also characterized by the size of the nozzle. The size of the nozzle may be smaller than 30 mm, desirably smaller than 20 mm. If the size of the nozzle is greater than 30 mm, high pressure may not be exerted on the nozzle, and unnecessary free space may be formed inside the nozzle to increase the possibility of turbulence in the slurry, and thus increase the possibility of gas entrapment within the casting product. In addition, as the size of the nozzle increases, free space for slurry movement may increase, thereby increasing turbulence, porosities, and casting defects. Accordingly, to avoid them, the stirrer may be provided around the nozzle, and further the size of the nozzle may be controlled as well. In the case that the size of the nozzle should exceed a critical value, the effect of the size increase may be compensated by increasing pressure applied by the plunger. Mode for the Invention

[33] Hereinafter, specific exemplary embodiments will be described in detail with reference to the accompanying drawings. FIG. 5 is a schematic view illustrating a hot chamber die casting apparatus, wherein a stirrer in accordance with an embodiment is disposed on a passageway (at a nozzle) through which semisolid metal flows out of a furnace into a mold 130 and 150, instead of being disposed around the furnace. In this case, molten metal 240 that has flowed into a pressure chamber 220 through an intake port 210 is transformed to a liquid-solid coexisting state at an outlet end of the pressure chamber 220, and then is forced to the mold 130 and 150 while or after being affected by electromagnetic field. FIG. 6 is a partial enlarged view of a core portion of FIG. 5.

[34] A method for manufacturing a die casting product using the above described hot chamber die casting apparatus will be described as follows. The method for manufacturing magnesium alloy casting product using a hot chamber die casting apparatus for pressing a plunger at a pressure higher than atmospheric pressure so that magnesium alloy is forced into a mold by the plunger to be formed into a shape of the mold without being exposed to the atmosphere. Herein, the magnesium alloy flows out of a furnace that is made airtight and provided with a heating device to a pressure chamber having a shape of goose neck and is pressed by a pressure unit to be injected horizontally into the mold to be formed into the shape of the mold. Each injection of magnesium alloy into the mold through the nozzle is performed when the pressure chamber is fully filled with the molten magnesium alloy. The method is characterized in that an electromagnetic stirrer is disposed around a nozzle disposed between the mold and an outlet end of the goose neck of the pressure chamber in the furnace for horizontally connecting the outlet end of the goose neck and the mold, to stir magnesium alloy which is being transformed to semisolid state.

[35] As for an electromagnetic field generator, electromagnetic field may be approximately 50 Gauss or higher, and desirably in the range of approximately 200 to approximately 10,000 Gauss. The experiments have shown that the stirring effect is not sufficient when the electromagnetic field is lower than approximately 50 Gauss. Because the stirring effect increases with the electromagnetic field, it is effective to apply the electromagnetic field with intensity as high as possible, theoretically. However, in practice, the appropriate maximum electromagnetic field may be determined in due consideration of a space for the stirrer, an electric power, and the like.

[36] An electric current of the electromagnetic field generator may be approximately 0.5

A or greater, desirably, in the range of approximately 1 to approximately 100 A. The experiments have shown that the stirring effect is not sufficient when the electric current is approximately 0.5 A or smaller. Although a greater electric current is better in theory, the size of the apparatus, economic matters and the like should be considered to determine the appropriate maximum electric current.

[37] As for an ultrasonic wave generator, frequency may be approximately 5 kHz or higher, desirably in the range of approximately 13 kHz to approximately 10 MHz. The experiments have shown that the stirring effect is not sufficient when the frequency is lower than approximately 5 kHz. An ultrasonic wave may have a frequency as high as possible.

[38] A method for manufacturing a magnesium alloy casting product using a die casting apparatus in accordance with an exemplary embodiment begins with opening upper cover of a furnace 230 and providing molten metal or solid metal to be melted into the furnace. A heating device of the furnace may also be used for retaining heat. When the molten metal is maintained above a predetermined temperature, a piston or a plunger in a pressure chamber 220 operates to supply molten metal to a mold 130 and 140. Then, molten metal 240 in the furnace flows into the pressure chamber through an intake port 210 of the pressure chamber 220 in the furnace 230. When molten metal in the pressure chamber 220 is pressed by the plunger 250, the molten metal flows toward a goose neck 270 or an outlet end of the pressure chamber.

[39] A nozzle is disposed at the outlet end 270 of the pressure chamber to connect the pressure chamber to a mold 130 and 140. As the molten metal cools down while flowing through the goose neck 270 or the outlet end 270 of the pressure chamber, the molten metal enters the nozzle 105 while liquid-solid coexisting state is beginning to occur or at the same time when liquid-solid coexisting state just begins to occur. An electromagnetic field generator or an ultrasonic wave generator stirs the semisolid metal while it flows through the nozzle. The stirring may be performed while the semisolid metal flows through the nozzle to the mold 130 and 140, or while the semisolid metal waits for next injection in the nozzle after the previous injection.

[40] Magnesium alloy is in a substantially liquid phase while it flows in the pressure chamber in the furnace 230. However, the liquid phase magnesium alloy gradually cools down to a liquid-solid coexisting phase, i.e., a semisolid phase as it flows out of the furnace 230 to the nozzle 105 through an outlet end 270 of the pressure chamber or a goose neck 270. It is important to control the temperature of the nozzle such that the liquid-solid coexisting state is maintained in the nozzle. At this time, an external electromagnetic vibration or an ultrasonic vibration is applied thereto to prevent nucleation of a primary dendrite or to break already nucleated primary dendrite, so that finer and more uniform nuclei may be formed. This results in a finer, and thus a stronger mi- crostructure of a final casting product.

[41] A typical hot chamber die casting apparatus suffers from great heat loss and particularly a rapid cooling of molten metal at a nozzle protruding from a furnace. Accordingly, a heating device and an insulating device have been applied to the nozzle to prevent the heat loss and cooling of molten metal at a nozzle, which are disclosed in Japanese Patent Laid-Open Publication No. Sho. 55-436554 and US Patent No. 5,960,854.

[42] In a furnace, because magnesium alloy is in substantially liquid phase, it is hardly affected by an external electromagnetic field or an external ultrasonic wave. On the other hand, in a passageway, because the magnesium alloy is in a semisolid phase, it is easy to be affected by the external electromagnetic field or an external ultrasonic wave. Accordingly, an exemplary embodiment provides a stirrer disposed on a passageway between the furnace and a mold to prevent a rapid cooling and to supply the mold with a semisolid metal having an appropriate fraction of solid phase and fine microstructure. A heating device or an insulating device may also be applied to the hot chamber die casting apparatus in accordance with an exemplary embodiment to prevent a rapid cooling of the nozzle.

[43] It was found that stirring within the above described ranges of current and electromagnetic field does not affect process time for the hot chamber die casting. That is, a sufficient stirring was performed while a mold 150 receives molten metal, solidifies the molten metal, discharges the solidified metal, and then prepare to receive another molten metal.

[44] A variety of magnesium alloys can be used in the hot chamber die casting in accordance with an exemplary embodiment. The variety of magnesium alloys includes AZ91A, AZ91B, ZA91D, AM60A, AM60B, and AS41A, by ASTM standard. Compositions of the magnesium alloys for the above described die casting are listed in TABLE 1.

[45] Table 1

[46] Complete melting temperatures of the typical magnesium alloys ranges from approximately 590 ⁰C to approximately 630 ⁰C. The furnace may be controlled to have a temperature higher than the complete melting temperature of the above magnesium alloy by a temperature range of approximately 30 ⁰C to approximately 100 ⁰C. The temperature of the furnace is controlled to be in the range of approximately 62O⁰C to approximately 750 ⁰C. The temperature of the molten magnesium alloy is decreased to liquid-solid coexisting region as the molten magnesium flows out of a pressure chamber in the furnace 230 to a nozzle 105 or an outlet end of the pressure chamber. When the temperature of the nozzle is controlled to be too low, the content ratio of solid phase to liquid phase is so high that the semisolid metal cannot be easily supplied to the mold, which may increase the probability of casting defects in die casting products. On the other hand, when the temperature of the nozzle 105 is controlled to be too high, the content ratio of solid phase to liquid phase is so low that the semisolid metal cannot be affected sufficiently by an electromagnetic field or an ultrasonic wave. Note that the temperature of the nozzle is to be controlled to be substantially lower than an ideal temperature of the semisolid magnesium alloy. This is because the real temperature of the semisolid magnesium alloy 109 flowing in the nozzle is lower than the ideal temperature. The ideal temperature of the semisolid magnesium alloy 109 flowing in the nozzle ranges from approximately 480 ⁰C to approximately 620 ⁰C.

[47] FIG. 7 is a micrograph of a product manufactured by a typical hot chamber die casting apparatus. The grain size ranges from approximately 30D to approximately 250D, approximately 100 D on the average.

[48] FIG. 8 is a micrograph of a product manufactured by a typical hot chamber die casting when electromagnetic field is applied to a periphery of a furnace. The grain size ranges from approximately 1OD to approximately 80D, approximately 4OD on the average.

[49] FIGS. 9 and 10 are micrographs of products manufactured when an electromagnetic field is applied by a stirrer 101 disposed on a passageway through which molten metal 240 flows between a furnace and a mold 130 and 140. The grain size ranges from approximately 2 D to approximately 18 D, approximately 10 D on the average.

[50] FIG. 11 is a micrograph of a product manufactured when an ultrasonic wave is applied by a stirrer 101 disposed on a passageway through which molten metal 240 flows out of a furnace to a mold 130 and 140.

[51] Comparison of FIGS. 8 through 11 illustrates that the microstructure, which is obtained by applying electromagnetic field across a passageway through which semisolid metal flows out of a furnace to a mold and controlling inner diameter of the nozzle (FIGS. 9 through 11), is finer and densified in comparison with that obtained by applying electromagnetic field to the periphery of the furnace (FIG. 8).

[52] Hereinafter, a die casting method of magnesium alloy in accordance with exemplary embodiments will be described. A method of an exemplary embodiment was performed under conditions that a magnesium alloy of AZ91D was used, a temperature of furnace was 650 ⁰C, a pressure of a plunger was 10 MPa, a temperature of nozzle was 600⁰C, an electromagnetic field was 650 Gauss, an electric current was 6 A, and an injection rate was 2.5 m/sec. The resultant microstructure is shown in FIG. 9. Grain size of the microstructure is about 9 D.

[53] A method of another exemplary embodiment was performed under conditions that a magnesium alloy of AM60B was used, a temperature of furnace was 68O⁰C, a pressure of a plunger was 7 MPa, a temperature of nozzle was 580 ⁰C, an electromagnetic field was 800 Gauss, an electric current was 9 A, and an injection rate was 1.5 m/sec. The resultant microstructure is shown in FIG. 10. Grain size of the microstructure is about 10 D.

[54] A method of still another exemplary embodiment is performed under conditions that a magnesium alloy of AZ91B was used, a temperature of furnace was 66O⁰C, a pressure of a plunger was 10 MPa, a temperature of nozzle was 610 ⁰C, a frequency and a power of an ultrasonic wave was 30 kHz, and 1.2 kW, respectively, and an injection rate was 2.5 m/sec. The resultant microstructure is shown in FIG. 11. Grain size of the microstructure is about 15 D.

[55] In addition to the above-described exemplary embodiments, a variety of experiments have been done with the variation of the temperature ranges of the furnace and the nozzle, the electromagnetic field, and the electric current in order to determine the ideal condition. [56] In general, a hot chamber die casting method in accordance with an exemplary embodiment is available for a metal of a low melting temperature, such as zinc, tin, lead, aluminium, and magnesium. It is adapted to prevent high temperature oxidation, and thus to manufacture die casting product with good quality because molten metal is not exposed to the atmosphere during the hot chamber die casting. It is particularly available for magnesium alloy. It can also be applied to other alloys having a low- meting-point metals such as aluminium, zinc, tin, and lead, if necessary.

[57] Although the hot chamber die casting apparatus and the manufacturing method using the same have been described with reference to the specific exemplary embodiments, they are not limited thereto. Therefore, it will be understood that various modifications, changes and supplements can be made by those skilled in the art. Accordingly, following claims should be construed that they include all the modifications, changes and supplements without departing from the spirit and scope of the present invention. Industrial Applicability

[58] In accordance with the exemplary embodiment, an electromagnetic field or an ultrasonic wave is applied on a passageway between a furnace and a mold, to control the microstructure of semisolid magnesium alloy to be finer and then to inject the semisolid magnesium alloy with controlled microstructure into a mold. Accordingly, it is possible to manufacture casting product having a finer microstructure and thus an increased strength, and having a densified microstructure and thus a uniform thickness.

[59]

Claims

[1] A hot chamber die casting apparatus for pressing a plunger at a pressure higher than atmospheric pressure so that magnesium alloy is forced into a mold by the plunger to be formed into a shape of the mold without being exposed to the atmosphere, the hot chamber die casting apparatus including a furnace that is made airtight and provided with a heating device, a pressure unit for pressing magnesium alloy, the mold for giving a shape to a final casting product, and a pressure chamber having a shape of goose neck for horizontally injecting magnesium alloy in the furnace into the mold, the hot chamber die casting apparatus being characterized in that the hot chamber die casting apparatus comprises a stirrer disposed around a nozzle, and configured to stir magnesium alloy which is being transformed to semisolid state, the nozzle being disposed between the mold and an end of the goose neck of the pressure chamber in the furnace to horizontally connect the goose neck to the mold.

[2] The hot chamber die casting apparatus of claim 1, characterized in that an inner diameter of the nozzle is equal to or smaller than approximately30 mm.

[3] The hot chamber die casting apparatus of claim 1, characterized in that the nozzle has a predetermined size such that the pressure of the plunger pressing the magnesium alloy is equal to or higher than approximately 2 MPa.

[4] The hot chamber die casting apparatus of claim 1, characterized in that the stirrer comprises an electromagnetic field generator.

[5] The hot chamber die casting apparatus of claim 1, characterized in that the stirrer comprises an ultrasonic wave generator.

[6] A method for manufacturing magnesium alloy casting product using a hot chamber die casting apparatus for pressing a plunger at a pressure higher than atmospheric pressure so that magnesium alloy is forced into a mold by the plunger to be formed into a shape of the mold without being exposed to the atmosphere, wherein the magnesium alloy flows out of a furnace that is made airtight and provided with a heating device to a pressure chamber having a shape of goose neck and is pressed by a pressure unit to be injected horizontally into the mold to be formed into the shape of the mold, the method being characterized in that the method comprises stirring magnesium alloy which is being transformed to semisolid state using a stirrer disposed around a nozzle provided between the mold and an outlet end of the goose neck of the pressure chamber in the furnace, the nozzle horizontally connecting the outlet end of the goose neck and the mold. [7] The method of claim 6, characterized in that the stirring of the magnesium alloy is performed using an electromagnetic field generator with an electromagnetic field equal to or higher than approximately 50 Gauss. [8] The method of claim 7, characterized in that the stirring of the magnesium alloy is performed using the electromagnetic field generator with an electric current equal to or greater than approximately 0.5 A. [9] The method of claim 6, characterized in that the stirring of the magnesium alloy is performed using an ultrasonic wave generator with a frequency equal to or higher than approximately 5 kHz. [10] A die casting product manufactured by the method of any one of claims 6 to 9.