WO2017135486A1 - Apparatus and method for manufacturing magnesium alloy billet for extrusion - Google Patents

Abstract

The present invention relates to manufacturing a magnesium alloy billet for extrusion, and particularly, to an apparatus and a method for manufacturing a magnesium alloy billet of which the firing processability is improved by improving a casting method for the magnesium alloy billet so that an alloy element of which the specific gravity is at least 4 is uniformly distributed. To this end, the present invention relates to the apparatus for manufacturing the magnesium alloy billet, which injects a magnesium alloy melt into a billet casting mold and solidifies the melt to cast a billet through cooling by means of spraying a coolant on the surface of the billet casting mold into which the alloy melt has been injected, wherein a cover provided with a through-hole for installing an impeller and a gas pipe for injecting shielding gas is formed on the upper portion of the mold, and wherein the alloy melt is mixed by the impeller inserted through the through-hole on the cover during cooling of the surface of the mold, and desirably, a mushy zone during melting of the alloy is mixed to manufacture the magnesium alloy billet. According to the present invention, alloy melting is performed by mechanical mixing during cooling of the mold, wherein the mechanical mixing is effectively performed in the mushy zone to enable uniform distribution of alloy elements such as zinc or cadmium having large specific gravity, and as a result, segregation during a low-temperature process is reduced and manufacturing of a billet having fine crystalline grains can be enabled. As a result, the billet has superior firing processability compared to a magnesium alloy billet manufactured according to an existing method, thereby providing the advantages of easy extrusion and excellent uniformity of quality.

Description

Manufacturing apparatus and method for manufacturing magnesium alloy billet for extrusion

The present invention relates to the production of magnesium alloy billet for extrusion, in particular, to improve the processability of the magnesium alloy billet by improving the casting method of the magnesium alloy billet so as to uniformly distribute the alloying elements having a specific gravity of 4 or more, and the manufacturing apparatus and production of It is about a method.

As is well known, magnesium alloy is the lightest metal among the metal materials currently being used, and the use of magnesium alloys is rapidly expanding into the materials of various parts in place of aluminum in use of metal materials to achieve further weight reduction. As a matter of fact, demand for electronic products is rapidly increasing by replacing plastics, which have many problems in recycling.

Magnesium alloys have the lightest density of 1.74 g / cc of commercially available structural alloys, equivalent to two-thirds of aluminum. In addition, the magnesium alloy has excellent machinability, high vibration damping properties, excellent absorbency against vibration and shock, excellent electromagnetic wave blocking function, and the like. In addition, the reason for the rapid expansion of magnesium alloys into computers, mobile phones, automobile parts, etc. is due to its excellent light weight and reproducibility, shielding against electromagnetic waves, and molding into thin shapes.

This suggests that magnesium alloy is a good material as a structural material for portable electronic products, which has recently gained popularity among consumers.

Generally, materials such as portable electronic built-in structural members, automotive parts, or aircraft parts require lightweight, high strength, high toughness, and high formability.

However, magnesium has a dense hexagonal lattice structure with a small slip system, which is essential for plastic deformation, and is mainly formed by casting due to poor extrudability and formability.

However, sand casting has many limitations in shape, and molding by die casting causes many problems in subsequent surface treatment processes because the cast structure is porous in its characteristics. Meanwhile, materials such as AZ31 and AM20 alloyed with aluminum were developed to enable plastic processing using ductility of aluminum single-solution solid solution in which aluminum was used.

However, these alloys include MgxZny process phases having a low melting point of less than 350 ° C. in a single-phase solid solution despite excellent workability and ductility. Therefore, an anisotropy is strong in a plate or a member that is plastically deformed in one direction, and when it locally rises to 350 ° C. or higher due to friction during machining, fine cracks occur due to low melting point processes. .

In addition, there is a lithium additive alloy which is converted to a body-centered cubic lattice structure capable of plastic working to improve plastic workability. Lithium has a high solubility in magnesium and is effective. However, the difference in solid solution according to temperature is small and the difference in lattice constant is small so that a large amount of 10 to 20% by weight is added. Therefore, lithium alloyed materials are expensive and are not commonly used due to their unique battery reaction characteristics.

 The presence of low melting process phases in magnesium alloy billets has the same problem in magnesium alloy extrusion, and when extruded at temperatures above 350 ° C, the frictional heat with the die shows surface defects such as fingerprints on the surface, resulting in clean and flawless products. It was hard to get. Since the surface cracks of such fine wrinkles reduce fatigue strength, they have to be extruded at a temperature of 350 ° C. or less to prevent such defects. Therefore, the productivity is low and the defect rate is high in complex shapes, which causes a high price of magnesium extruded materials.

Recently, in order to overcome these problems, magnesium alloys having improved plastic processability have emerged, or technologies for easily plasticizing have been developed.

The patent 10-0509648 developed by the present inventors introduces a magnesium alloy excellent in plastic workability. However, although the process for rolling a sheet is mentioned in this patent, the extrusion method could not be introduced in detail, and commercialization of the magnesium extruded material did not proceed. Moreover, no method for dispersing fine high melting point precipitates in large diameter billets or suppressing central segregation has been proposed.

Conventional extrusion billets are manufactured by injecting molten metal into a cast iron mold in which an annular cavity is formed and cooling it. In this method, the molten metal is preheated to 200 ° C. or higher to remove moisture and injected to prevent the molten metal from exploding as the temperature difference and the moisture adsorbed on the mold evaporate while the molten metal contacts the mold.

Due to the slow cooling rate, the solidification time of magnesium alloy is increased in the mold, and the specific gravity is 4 or more, and elements such as zinc and yttrium, which have a large difference in specific gravity from magnesium, are segregated in the center or the bottom of the mold. The problem is that the macroscopic composition of the billet becomes uneven and causes the extrusion performance to drop. In the case of severe segregation, hot tearing occurs in the center of billet, which causes deformation, cracking, and fine wrinkles during the extrusion process, as well as reducing the fracture and fatigue strength during stretching or straightening of the extruded material. And reliability. In order to solve this problem, Pokorni et al. Conducted a study to predict the occurrence of hot crack during casting of magnesium alloy.

As a method for avoiding the low plasticity of magnesium, a method of casting in a form close to the final product by a twin roll casting method or a strip casting method has been devised. Not suitable

Qui et al. Studied the improvement of plastic workability by extruding and rolling the AZ31 alloy which is most used for plastic working in magnesium alloy to obtain recrystallized microstructure. In this study, there was no visible problem, but the presence of microcracks in the grain at intervals of several microns was observed. Rao et al. Also reported that the AZ31 alloy is easily extruded in the 300-350 ° C range and the texture becomes brittle when extruded at higher temperatures to improve productivity.

In addition, a method of improving plastic workability by heat treating billets and extruding them at high ductility by controlling the temperature of the extrusion container and the die was introduced, but the extrusion speed should be lowered due to the low melting point process present in the magnesium alloy. Due to the limitations, there is no practical improvement plan.

In addition, efforts have been made to improve the machinability of magnesium by processing hard materials such as ECAP and ECAE at high firing ratios through angle-changing channels in the die, but the die structure is complicated and requires high pressing force. It is limited and not suitable for commercialization to apply to actual product production.

In order to solve this problem, the present inventors added yttrium and zinc to form a high melting point precipitated phase in Korean Patent Registration No. 10-1392480 to increase the extrusion temperature and improve the extrusion die to reduce the flow stress and improve the extrudability. A method was provided. However, even in the case of the alloy having excellent plastic workability, there is a problem in that the alloying element occurs due to the difference in the solidification rate between the upper and lower parts during the manufacturing of the billet, and zinc and yttrium, which have a high specific gravity, segregate in the lower part in the process. 1 shows an example of fracture during extrusion due to a difference in plastic processability due to variations in upper and lower alloying elements of a billet cast with an average diameter of 180 mm by this method. FIG. 1 shows a billet manufactured by a crucible casting method without stirring the molten metal. This is an example of manufactured billets. The left side is the billet extracted after casting and the center is broken during extrusion. The right side is the lower part of the cut billet, and there is a case that hot crack occurs in the center part as a picture due to the segregation of the center. In the middle broken billet of Figure 1, the arrow is the extrusion direction and the arrow below is the upper part during billet casting.

In addition, in the case of the direct chilled continuous casting billet as shown in FIG. 2, central segregation occurs as the difference between the internal and external cooling rates becomes too large, and internal cracks may occur in the central segregation due to stress due to shrinkage during solidification. 2 is an example of hot cracks generated in the center of the billet due to segregation and shrinkage stress in the direct cooling continuous casting.

In direct cooling continuous casting in which the molten metal is quenched at the outer periphery and solidified, segregation is relatively low due to the rapid cooling. For example, a 150mm diameter AZ31 billet has a relatively low segregation amount of about 0.7% of aluminum and about 0.4% of zinc in comparison with the surface and the center, which are 1.74 magnesium and 2.7 aluminum. This is also because the difference in specific gravity between the alloys is smaller than that of other alloy elements, and the content of zinc with a specific gravity of 7.13 is small. However, as shown in Table 1, when the amount of alloys having a specific gravity of 4 or more, such as yttrium-zinc, increases, the total segregation amount is 1.1%, which leads to severe segregation of alloy elements compared to the AZ alloy. If this degree of segregation is larger than the difference in extrusion performance, even if broken or extruded during extrusion as shown in Figure 1, the occurrence rate of bending deformation or surface defects is large. In addition, as the diameter of the billet increases, the cooling rate also needs to increase. If the segregation is severe, cracking occurs in the center of the billet during extrusion. Therefore, in alloys containing elements with specific gravity greater than aluminum, the degree of central segregation will determine the extrusion performance of the billet.

	Element	content(%)	Location in Billet
Top	zinc	1.56	Arrow down in FIG. 1
	yttrium	0.76	Arrow down in FIG. 1
bottom	zinc	9.8	Arrow upward in FIG. 1
	yttrium	1.45	Arrow upward in FIG. 1

Extruded magnesium alloys, such as AZ alloys and AM alloys, which are alloyed with aluminum or zinc, have wider mash zones as the alloy amount increases. The surface of the billet may be rough or cracked. Therefore, there is a problem that the casting speed and productivity are lowered due to the difficulty of forming a shell layer by cooling the mold wall quickly while increasing the temperature of the molten metal with a high power electromagnetic casting device.

In the prior art, the magnesium molten metal in the crucible was stirred with a metal rod before injection into the mold as a means to remove this segregation. However, the stirring method using manpower while the upper part of the furnace is open is difficult to continuously stir due to the risk of heat and ignition, and there is no method to stir in the solidification process after injecting magnesium alloy molten metal into the mold.

There is an electromagnetic stirring method using an induction coil for stirring during casting. However, magnesium does not have unpaired hole electrons, so even when it is stirred, its magnetization strength is weak. Therefore, compared with other metals, magnesium has less force of induction and viscosity of molten metal. For example, casting a magnesium alloy billet at 20 L / min requires a high power electromagnetic casting (EMC) of 20 kHz and 1400 A and an electronic stirrer (EMS) of 15 kHz and 150 A, which is required for continuous casting of aluminum billets. Of 4-5 times.

In recent years, aluminum billet casting has been manufactured by electrostirring continuous casting as in the method of FIG. 3 rather than by direct cooling continuous casting. Efforts to curb dendritic development continued.

Fleming et al. US Pat. No. 3,902,544 provided a method for preparing solid or liquid-solid metals containing non-residual primitive tissues, which includes agitation of the liquid metal prior to casting, which limits the control of tissues during solidification. There was.

Nielsen et al. US Pat. In 4,315,538, a method of rotating a mold die was proposed to reduce the temperature deviation of the melt in continuous casting of copper alloy rods. This method is effective in reducing friction and reducing grain size by rotating the mold die in contact with the molten metal in continuous casting of small-diameter bars. However, this method is not suitable for controlling central segregation in large-diameter billets.

Yu et al. US Pat. In 4,709,747, a method of inserting a strainer type device into a mold into which an aluminum alloy molten metal is injected is provided. This injects the molten metal, as well as the outer peripheral portion in contact with the mold surface, the inner surface in contact with the strainer causes nucleation, thereby solidifying uniformly in the mold. Conventionally, segregation is concentrated only in the central part to be finally solidified, and since nucleation proceeds inside, there is an effect of uniformly solidifying. However, this method is difficult to expect the effect of nucleation continuously because the cooling capacity is lowered because the strainer is heated when continuous casting or molten metal is continuously injected.

Unlike in the case of aluminum and copper alloys, the mechanical agitation of the molten magnesium alloy has to be prevented from ignition by blocking the atmosphere, and many studies have been conducted due to the difficulty in making alloy elements have a low melting point. Therefore, in the prior art, a method of directly injecting a mold through a tube in a magnesium molten metal preservation furnace is often applied, and it is difficult to apply other methods except for electromagnetic stirring. In the background of late technology development, there is a large reason for the lack of commercialization due to the small market of magnesium extruded materials. Nevertheless, there have been cases where magnesium-based studies have been developed in the gingomolding method or the development of high strength and lightweight MMC (metal matrix composite).

Camado et al. Reported the results obtained by stirring the AZ91D alloy in a semi-melt state for application to the gingham molding method of injection molding in a semi-melt state. However, this method was difficult to apply to continuous casting or billet production by stirring the semi-solid molten metal in the mold for a long time while maintaining it at a constant temperature for 30 minutes.

As such, mechanical agitation may be a good alternative to electron agitation for the macroscopic segregation and improvement of microstructure of magnesium alloy billets. However, in-depth studies have been conducted to suggest a concrete manufacturing method due to the stagnation of magnesium market. There was no.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) Korean Laid-Open Patent Publication No. 2002-0078936. Oct 19, 2002

(Patent Document 2) Korean Unexamined Patent Publication No. 2007-0091239. 2007. 09. 07

(Patent Document 3) Korean Laid-Open Patent Publication No. 2008-0085662. 2008. 09. 24

(Patent Document 4) US Patent Publication No. 7,028,749. Apr 18, 2006

(Patent Document 5) Korean Patent Publication No. 10-1392480. 2014. 04. 29

(Patent Document 6) US Patent Publication No. 3,902,544. 1975. 09. 02

(Patent Document 7) US Pat. No. 4,315,538. February 16, 1982

(Patent Document 8) US Pat. No. 4,373,950. 1983. 02. 15

(Patent Document 9) US Pat. No. 4,709,747. October 1, 1987

(Patent Document 10) US Pat. No. 4,960,163. 1990. 10. 02

[Non-Patent Documents]

(Paper 1) Qiu Wei et al., Effect of heat treatment on Microstructures and mechanical properties of extruded-rolled AZ31 Mg alloys, Trans. Nonferrous Met. Soc. China 20 (2010), 481-s487

(Paper 2) Kamineni Pitcheswara Rao et al., Hot Deformation Mechanisms in AZ31 Magnesium Alloy Extruded at Different Temperatures: Impact of Texture, Metals 2012, 2, 292-312

(Paper 3) M. Pokorny et al., Prediction of Hot Tear Formation in a Magnesium Alloy Permanent Mold Casting, International Journal of Metalcasting, Fall 2008, 41-53

(Paper 4) Shigeharu Kamado et al., 輕 金屬, Vol. 42, no. 12, 1992, 734-740

(Paper 5) V. Laurent et al., Journal of Materials Science 27, 1992, 4447-4459

(Paper 6) Chang-Dong Lim et al., Journal of the Korean Foundry Engineering Society, Vol. 23, No. 3, 2003.6, pp.130-136

(Paper 7) Liqing Chen et al., J. Mater. Sci. Technol., Vol. 23 No. 2, 2007, 207-212

(Paper 8) Y. X. Jin et al., Materials Science-Poland, Vol. 27, No. 1, 2009, 171-185

The present invention has been made to eliminate the above problems, the magnesium alloy billet of the magnesium alloy billet to improve the extrusion by reducing the segregation of the magnesium alloy billet for extrusion and to reduce the defect rate to refine the grain and reduce the segregation It is an object of the present invention to provide a manufacturing apparatus and a manufacturing method.

To this end, the present invention is a billet casting mold for injecting a molten magnesium alloy to cast a billet, and a manufacturing apparatus of a magnesium alloy billet comprising a cooling means for solidifying the molten metal by cooling the surface of the mold, An upper part of the extruded magnesium alloy billet formed of an impeller for impregnating the molten alloy is formed in the upper part is provided with an impeller installation through-hole and a gas pipe for injecting shielding gas. It is characterized by a manufacturing apparatus.

In another aspect, the present invention is to prepare a magnesium alloy molten metal containing zinc and yttrium in the melting furnace, while injecting the magnesium alloy molten metal through the molten metal inlet of the cover installed on the billet casting mold of the continuous casting device shielded through a gas pipe Injecting a gas, the refrigerant is sprayed at an angle of 15 to 70 degrees to the surface of the mold and the surface of the billet extracted so that the surface temperature of the billet extracted in the billet casting mold injected with the molten metal is cooled to 350 ℃ or less 250 Cooling at a rate of ˜900 ° C./min, inserting and stirring the impeller into the melt zone where the molten metal solidifies through the impeller insertion through hole formed in the upper cover of the mold during the cooling of the mold, and stirring the stirred melt The solidified billet is made into a billet, and the solidified billet is extracted in succession and continuously cast into a dummy block. It is characterized by a method for producing a magnesium alloy billet.

The billet casting mold is characterized in that the casting of the continuous casting method or the crucible mold of the cylindrical casting method,

The cover is composed of a fixed cover and a removable cover, the fixed cover has a fixed jaw to be fixed to the inner diameter of the mold and a central space is formed, the removable cover is inscribed in the inner diameter of the central space of the fixed cover It has a removable jaw to be fixed and characterized in that the through-hole is formed in the center,

The continuous casting method billet casting mold has a refrigerant injection nozzle around the mold to cool by injecting a refrigerant,

Billet casting mold of the continuous casting method is further provided with an electromagnetic stirring device around the mold to perform the electromagnetic stirring together,

The cover installed in the continuous casting method billet casting mold is further formed with a molten metal inlet so that the tundish nozzle is inserted into the upper portion,

The impeller is driven by a motor,

Cooling of the crucible mold is cooled in a separately provided cooling tank,

The cooling tank is provided with a refrigerant injection nozzle, a circulation pump, a mold support,

The cover of the mold is installed detachably,

The impeller installed in the mold is characterized in that the billet moves up and down in the mesh zone in accordance with the speed of solidification.

According to the present invention, it is possible to uniformly disperse alloy elements such as zinc or cadmium with high specific gravity by performing alloy stirring by mechanical stirring while cooling the mold, by effectively performing mechanical stirring in the marsh zone region. It is possible to reduce the segregation in the low temperature process and to manufacture the fine grains, so that the plasticity is excellent compared to the magnesium alloy billets manufactured by the conventional method, so that the extrusion is easy and the quality uniformity is excellent.

1 is a photograph showing an example of a billet manufactured by a conventional gravity casting method.

2 is a photograph of the center crack of a billet manufactured by a conventional direct chilled continuous casting.

3 is a conceptual diagram of a magnesium continuous casting apparatus using a conventional electron stirring.

Figure 4 is a conceptual diagram using the EMC and mechanical stirring in a continuous casting in the first stirring method of the present invention.

5 is a conceptual view applying only mechanical stirring in the continuous casting in the second stirring method of the present invention.

6 is a conceptual diagram applied to gravity casting molds by the second stirring method of the present invention.

7 is an example of sectional drawing of the crucible melting furnace which concerns on this invention.

8 is an example of the present invention mold cover.

9 is an example of the cross-sectional structure of the magnesium billet after stirring.

10 is a conceptual diagram of operating the stirrer in the melting furnace equipped with an elevator.

11 is a conceptual diagram of an impeller installed in the removable cover of the present invention.

12 is a micrograph of the cast microstructure of the billet manufactured by the prior art.

Figure 13 is a micrograph of the cast microstructure of the billet prepared according to the present invention.

14 is an external photograph of the extruded material of the billet manufactured according to the present invention.

15 is a cross-sectional microscopic histogram of the extruded material produced by the present invention.

16 is a tensile curve of an extruded material produced by the present invention.

17 is a photograph of appearance of a continuous casting billet manufactured according to the present invention.

18 is a cross-sectional photograph of a continuous casting billet manufactured according to the present invention.

19 is a microscopic histogram of the continuous casting billet prepared according to the present invention.

Hereinafter, the present invention will be described in detail.

In casting a magnesium alloy billet, the present invention is characterized by reducing the segregation by miniaturizing the crystal grains produced during the solidification of the molten metal by stirring the molten metal in the mold by mechanical means during casting. Apparatus and method for manufacturing a magnesium alloy billet provided in the present invention include both a continuous casting method and a cylindrical mold casting method.

In the case of the continuous casting method, as shown in FIGS. 4 and 5, the cover 3 is placed on the upper part of the mold 1, the dummy block 6 is installed at the lower part of the mold to prepare casting, and then the cover 3 is closed. While injecting the shielding gas 4 into the shielding gas pipe, the molten alloy prepared in a separate melting furnace is injected into the mold 1 through the molten metal inlet 5 formed in the cover of the continuous casting machine. The solidified billet is solidified into the billet 2 while being cooled by the refrigerant 7 sprayed onto the mold surface, and the solidified billet is continuously cast while being extracted from the mold by the dummy block 6 installed under the mold. At this time, the mold (1) into which the magnesium alloy molten metal is injected is first blocked by a sealing device such as a cover (3), in order to block the atmosphere, and the second is a shielding gas (4), for example SF6, Magnesium alloy molten metal is injected in a state in which Ar or CO2 is mixed with or separated from the atmosphere in an atmosphere used alone, and stirring of the molten metal is covered in a section of the mesh zone (8) in the center of the molten metal produced during cooling. Place the impeller 22 inserted through the through hole of 3) and drive the motor to stir the molten metal.

In the case of casting by the cylindrical mold method, after placing the billet casting crucible mold (1-11) in the melting furnace shown in Fig. 7, the magnesium molten alloy and the alloying elements are added to the crucible mold (1-1) to manufacture the molten alloy. 6, the crucible mold containing the molten alloy is covered with the cover 3 on the top of the crucible mold 1-1, and then taken out from the melting furnace to move to the cooling tank 31 to the pedestal 32. After being deposited, a coolant is injected into the crucible mold 1-1 to cool the molten alloy to prepare a billet.

 At this time, the molten alloy is cut off from the atmosphere by the shielding gas injected through the shielding gas pipe formed in the cover 3, the molten metal blocked from the atmosphere is formed while the mash zone section is formed, the cover (3) The impeller 22 inserted through the through hole formed in Fig. 2) is positioned and mechanically agitated by the driving of the motor. As the stirred molten metal is solidified, the billet is manufactured, and thus the mash zone section also rises, thereby stirring while raising the impeller 22 according to the solidification speed.

The cooling tank 31 is composed of a circulating pump, a refrigerant spray nozzle, and a mold support 32 to draw up the refrigerant in the lower portion of the cooling tank to the pump and to spray the crucible mold 1-1 through the refrigerant spray nozzle. The coolant circulates to cool the mold 1-1.

In the present invention, the stirring of the molten metal during the process of cooling the mold to solidify the molten metal, in particular, in the molten zone (mush zone) in which the solid phase and the liquid phase coexist in the stirring by mechanical means such as an impeller, The reason is that stirring the mash zone where precipitates are generated during cooling not only allows the precipitates to be uniformly mixed, but also finely disperses the precipitates generated during cooling, thereby forming lattice defects in the solid solution to form lamination defects, This is because it is possible to produce a billet excellent in plastic workability by increasing the slip system by easily generating twins and partial potentials, and in the molten metal of the present invention, which is weak in magnetization, such as magnesium, the effect of such stirring, that is, the fine dispersion of precipitates is maximized. To stir the magnetic stirring room outside the mold In because they can not be expected.

In addition, only mechanical means can accurately stir the mash zone (8) section because it is possible to maximize the fine dispersion of precipitates generated during cooling.

If the crystal nuclei produced by such agitation are evenly dispersed, the internal coagulation rate is increased from the surface of the billet, so that the grains become finer and segregation is reduced, thereby reducing the time required for the coagulation of the billet. .

Particularly, yttrium alloys form high temperature precipitates, which reduces the mash zone, resulting in a faster solidification rate and a faster extraction of billets at higher temperatures, which leads to increased casting speed and increased productivity for uniform diffusion of alloying elements in subsequent processes. There is an advantage to reduce the heat treatment and holding time.

In addition, the present invention is characterized in that mechanical agitation is performed by an impeller because it is easily inserted through the crucible cover into the molten metal and moved in accordance with the solidification speed of the billet. The impeller is operated by a motor as a stirring device in which a small impeller 22 is attached to a lever 21 made of stainless steel as shown in FIG. 11, and the impeller is inserted into the molten metal through the crucible cover 3 and billeted. The reason for the movement according to the speed of solidification is that the alloy component can be promoted to be uniformly dispersed and dissolved, and the stirring can be omitted during the dissolution.

Impeller 22 used in the present invention is also included in the scope of the present invention using other metals, ceramic materials, composite materials, or depositing, plating, penetrating or spray coating other materials on the impeller. The diameter of the impeller is 1/5 to 2/3 of the diameter of the billet. If it is larger than this, it is limited because it requires a large motor due to the load. In addition, less than 1/5 of the billet diameter is limited because the stirring effect is inadequate to prevent segregation.

In the present invention, when the surfaces of the molds (1) and (1-1) are cooled to cast the billet (2), the refrigerant (until the surface temperature of the billet extracted through the mold is cooled to 350 ° C or less) Water, a water-soluble polymer, thermal oil, nitrogen, argon, air, a fluid such as steam, or a mixture thereof) to circulate by installing a cooling jacket, or the refrigerant (7) on the surface of the mold and billet 15 ~ It is characterized by spraying to contact at 70 ° angle to adjust the cooling rate of 250 ~ 900 ℃ / min. The reason for determining the coolant spray angle is that some of the coolant is sprayed at less than 15 ° will not contact the mold and billet surface If the temperature exceeds 70 °, the coolant particles hitting the mold and billet surfaces may prohibit the smooth flow of the coolant and the mold and billet surfaces may not be cooled quickly and uniformly. In addition, the reason for adjusting the cooling rate is that if the cooling rate is lower than 250 ° C / min, segregation remains at the center of the billet during solidification, which may cause uneven plastic processability of the extruded product at a high temperature and may cause defects. If the speed is faster than 900 ℃ / min, the thickness of the shell on the billet surface is excessively increased, the amount of cutting is increased and the surface may be cracked due to the shrinkage stress.

In the present invention, when preparing a billet having a commercial size of 100 mm or more in diameter, a cooling rate of 250 to 900 ° C / min, and preferably 300 to 600 ° C / min, was confirmed to form a dense structure without central segregation or surface cracking.

In addition, the present invention is to cover the mold (1), (1-1) cover 3, as shown in Figure 8, at least one through-hole 11 for inserting the impeller or injecting molten metal is formed It is characterized in that the shielding gas pipe is installed,

The reason why the cover 3 is installed is because the impeller is stably installed through the cover, and the molten metal is effectively blocked from the atmosphere, thereby maximizing work efficiency.

At this time, the impeller insertion through-hole 11 formed in the cover, in the case of the mold (1) of the continuous casting device, the molten inlet (5) is connected to the tundish in the center and the impeller insertion through-hole (11) to one side Alternatively, in the case of crucible mold 1-1, the impeller insertion through-hole 11 may be installed in the center, and other inlets may be installed around it if necessary. Of course, changing their positions does not diminish the effect.

The cover 3 is composed of a fixed cover 12 and a removable cover 13, as shown in FIG.

The removable cover 13 has a removable jaw 16 on the lower surface thereof to be fixed to the inscribed circle of the fixed cover 12, and has a through hole 11 having a diameter sufficient for the impeller wing to pass therethrough. In addition, the removable cover is divided into two to be divided around the through hole 11 so as to be separated and installed to be detachable, and the through hole 11 has an inner diameter such that the shaft of the impeller passes. Detachable cover 13 has a detachable jaw 16 is formed on the lower surface is fixed to the fixed cover 12, if necessary to form a dowel and a pin, or a concave-convex coupling to each other to be assembled by separation Or to prevent separation. If the diameter of the mold is not significantly different from the diameter of the impeller, the cover may consist of only a removable pair.

The fixed cover 12 has a fixing jaw 15 at the bottom thereof to fix the inscribed circle of the mold, and the center portion is formed with a space to fix the removable cover 13.

In addition, the cover 3 may be further provided with a gas inlet and a molten metal inlet for shielding gas injection if necessary. The position of these inlets is centered or biased, or the position of the inlet is not different.

In the present invention, even if only mechanical stirring with a simple device as shown in Figure 5 and 6 can improve the casting productivity by improving the solidification rate while reducing segregation and obtain a uniform structure, as shown in Figure 4, 1000A around the mold The following low-power EMC can be installed at the same time with mechanical agitation, in which case the effects of agitation can be maximized.

Hereinafter, the present invention will be described through examples.

EXAMPLE

In an elevator furnace, magnesium is now dissolved in a stainless steel crucible with an average diameter of 180 mm, shielded with Ar by a mixture of SF6 in a volume ratio of 2-3%, and the magnesium molten metal is kept at 650 to 750 ° C. After the low-melting alloy element is added, when all of the low-melting alloy material is melted, the molten metal temperature is increased and maintained at 750 to 850 ° C. A high-melting alloy element such as a magnesium-yttrium mother alloy containing 25% of yttrium is added by weight. Maintain sufficient dissolution. After opening the cover of the furnace and protecting the molten metal with shielding gas, the fixed cover 12 of FIG. 8 is mounted, and a 70 mm diameter stirring impeller is inserted into the molten metal through the central space, and then the removable cover 13 is mounted to provide a through hole ( 11), the impeller shaft was supported, the impeller was stirred at 100 to 300 rpm for 5 seconds while moving up from the bottom, and the crucible was taken out to the elevator and placed in a cooling tank as shown in FIG.

The surface of the crucible is then cooled until the surface temperature of the crucible is cooled to 350 ° C. or lower at a cooling rate of 250 to 900 ° C./min, preferably 300 to 600 ° C./min while spraying cooling water at an angle of 15 to 70 ° relative to the surface of the crucible. When the molten metal reaches 500 ~ 650 ℃ which is the mash zone temperature zone during cooling, the stirring impeller inserted through the through hole of the removable cover is placed in the mash zone section, and then slowly moves from below to 100 ~ 300rpm. The molten metal was stirred for about 5 seconds. After the crucible was cooled to room temperature, the billets were extracted and heated at a temperature of 380 ° C. for 3 hours in a heat treatment furnace.

The composition of the billet manufactured by such a process is shown in Table 2, the center casting structure picture of the billet is shown in Figure 13, the center casting structure picture of the billet manufactured by the prior art is shown in Figure 12, As shown in Table 2, the first and second billets showed the sum of the upper and lower component differences of 0.37%, and the second billet was 0.35%, indicating that the billets were manufactured with a uniform composition. As shown in FIG. It can be seen that the core casting structure is more uniformly distributed with fine precipitates than shown in the billet central tissue photograph prepared by the prior art of FIG.

	Element	Billet No. 1	Billet No. 2
Top	zinc(%)	4.7	4.3
	yttrium(%)	0.95	1.39
bottom	zinc(%)	4.6	4.1
	yttrium(%)	1.22	1.24

In addition, Figure 14 shows an external photograph of the extruded material extruded billet of the present embodiment at 200 ℃ (above) and 250 ℃, Figure 15 is a structure photograph of the cross section of the extruded material in the left side of the cross section of the center portion, the right side The edge tissue photograph is shown, and FIG. 16 shows the tensile test results of the specimen 5t processed in the extruded state of 5mm thickness and the 2mm thick plate specimen 2t obtained by cutting both sides of the material by 1.5mm.

14 and 15 it can be seen that the extruded materials extruded into the billet prepared in this embodiment is a uniform structure to obtain a low deformation and beautiful appearance, according to Figure 16 obtained by cutting the extruded material of the present invention Tensile test results indicate that the plasticity is excellent.

17 to 19 show the appearance and cross-sectional texture picture of the billet manufactured by continuous casting, the billet according to the present invention is less segregation than the billet manufactured by the prior art and can obtain a uniform cross-sectional structure.

Therefore, the billet manufactured according to the present invention is capable of uniform distribution of elements having a high specific gravity by mechanical agitation, and thus uniform dispersion of fine high temperature precipitates results in excellent work hardening and plastic workability, thereby showing excellent performance when used for extrusion. do.

[Description of the code]

1: mold 2: billet 3: cover

4: shielding gas 5: molten metal inlet 6: dummy block

7 Refrigerant 8 Machin Zone 11 Through Hole

12: fixed cover 13: removable cover 15: fixed jaw

16: removable jaw 22: impeller 31: cooling tank

32: pedestal

Claims (10)

1. In the apparatus for producing a magnesium alloy billet comprising a billet casting mold for injecting a magnesium alloy molten metal to cast a billet, and a cooling means for cooling the surface of the mold to solidify the molten metal,

   The upper part of the mold is formed with an impeller installation through-hole is provided with a cover having a gas pipe to inject a shielding gas, it is inserted through the through hole of the cover characterized in that it consists of an impeller for stirring the molten alloy Apparatus for manufacturing magnesium alloy billet for extrusion
2. The method of claim 1,

   The billet casting mold is used in a continuous casting method or a cylindrical casting method, the cover is composed of a fixed cover and a removable cover, the fixed cover has a fixed jaw to be fixed to the inner diameter of the mold in the center The space portion is formed, the removable cover has a removable jaw to be fixed to the inner diameter of the central space portion of the fixed cover has a through-hole formed in the center,

   The impeller is the manufacturing apparatus of the magnesium alloy billet for extrusion, characterized in that the diameter is 1/5 ~ 2/3 of the billet diameter
3. The method of claim 2,

   The billet casting mold used in the continuous casting method is further provided with an electromagnetic stirring device in the vicinity thereof to perform electromagnetic stirring together, and the cover is further formed with a molten metal inlet for inserting a tundish nozzle. Apparatus for manufacturing magnesium alloy billet for extrusion
4. The method of claim 2,

   The impeller is a device for producing an extrusion magnesium alloy billet, characterized in that driven by a motor
5. The method of claim 2,

   Billet casting mold used in the cylindrical casting method is a manufacturing apparatus of the magnesium alloy billet for extrusion, characterized in that the crucible mold
6. The method of claim 5,

   Cooling of the crucible-type mold is an apparatus for producing magnesium alloy billet for extrusion, characterized in that carried out in a separate cooling tank
7. The method of claim 6,

   The cooling tank is a manufacturing apparatus of the magnesium alloy billet for extrusion, characterized in that the refrigerant injection nozzle, circulation pump, the mold support is provided.
8. The method of claim 5,

   Apparatus for manufacturing an extruded magnesium alloy billet, characterized in that the impeller inserted through the through-hole formed in the cover of the crucible mold is driven by a motor
9. The method of claim 8,

   The impeller is a device for producing an extruded magnesium alloy billet, characterized in that the billet is operated while moving up and down in the mesh zone in accordance with the solidification speed
10. Preparing a molten magnesium alloy containing zinc and yttrium in a melting furnace,

    Injecting the shielding gas through the gas pipe while injecting the magnesium alloy molten metal through the molten metal inlet of the cover installed on the billet casting mold of the continuous casting device,

    The refrigerant is sprayed at an angle of 15 to 70 degrees on the surface of the mold and the surface of the billet to be extracted so that the surface temperature of the billet extracted into the billet casting mold into which the molten metal is injected is cooled to 350 ° C. or less. Cooling at speed,

    A step of inserting and stirring the impeller into the melt zone where the molten metal solidifies through the impeller insertion through hole formed in the upper cover of the mold during the cooling of the mold;

    The stirred molten metal is solidified and manufactured as a billet, and the solidified billet is continuously extracted while being extracted in a dummy block.

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