Method for horizontal continuous casting of magnesium slab or magnesium alloy slab and apparatus therefor

Info

Publication number: 20050224146
Type: Application
Filed: Apr 8, 2005
Publication Date: Oct 13, 2005
Applicant: SANYU SEIKI CO., LTD. (Tano-gun)
Inventors: Koichi Tada (Tano-gun), Kiichi Miyazaki (Tano-gun)
Application Number: 11/101,426

Abstract

A molten Mg or Mg alloy is supplied into a mold, which is sheltered from the surroundings, from a pool in a tundish, which is shielded from the surroundings. An Mg slab or Mg alloy slab in the mold is drawn out to the outside from an outlet of the mold. A cooling medium is jetted onto the slab on an outer side of and in a vicinity of the outlet to cool the slab. A sealing gas is sprayed over an entire width of a free surface of the molten Mg or Mg alloy on an inner side of and in the vicinity of the outlet, to seal a portion above the entire width of the free surface of the molten Mg or Mg alloy, whereby preventing oxygen from flowing into the mold from the portion and preventing the cooling medium from running back to the mold side.

Description

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for horizontally drawing-out type (horizontal) continuous casting for horizontally drawing out and continuously casting a magnesium slab (hereinafter, referred to as Mg slab) or a magnesium alloy slab (hereinafter, referred to as Mg alloy slab), and relates to an apparatus for horizontally drawing-out type (horizontal) continuous casting which is used for the method.

2. Description of the Related Art

Recently, recyclable magnesium alloys (Mg alloys), which are light in weight and have high strength, have been used for cases and frames of household appliances such as personal computers and portable telephones in many cases. Further, in recent years, the alloys have been applied to automobile parts in many cases for the reduction in weight of an automobile in the West.

A conventional method for producing a laminate plate is generally a method in which a slab manufactured through casting (slab manufactured by a continuous casting method) is subjected to rolling. In order to produce a laminate plate D from a slab B having crystal grain boundaries A without the occurrence of coming-off and edge cracks C of a surface as shown in FIG. 14, a large number of (in general, over 25) processing steps are required, including grinding of a surface layer of a slab and cutting of side edges thereof, and further, hot rolling, cold rolling, and heat treatment. Accordingly, this conventional method has a problem in that the cost of a rolling plate member is high. In addition, in the case of a slab with poor workability which is made of magnesium (Mg) or Mg alloy, it is extremely difficult with the above method to plastically work the slab into a laminate plate without the occurrence of coming-off or edge cracks of a surface thereof.

Examples of existing Mg alloys include cast products made by die casting and Thixomolding and products made by extrusion. On one hand, the case of the cast products involves low productivity because of a batch type process; on the other hand, the case of extrusion also involves low productivity despite a semi-batch type process. This is one of the causes of high cost. In any manufacturing method, the following problems exist. That is, in the case of a slab or billet produced by conventional continuous casting, the crystal grain boundaries A are generated which extend from a surfaces of a cast product or an extrusion billet to an interior portion thereof as shown in FIG. 13, and the boundaries remain as traces in the product. Further, a hydrogen gas and impurities J in a molten metal gather in the product, and shrinkage holes I and gas porosities are generated due to solidification shrinkage. This leads to many inferior products, a low yield, and low reliability of the product quality. Moreover, there is a limitation to the size of a die for Die casting and Thixomolding even if the size is to be increased. That is, there is a limitation to the maximum dimension of the product that can be produced. Thus, a product with a large dimension is hard to be produced.

As a method of manufacturing a strip of a nonferrous metal such as an Al (aluminum) alloy or Sn (tin) alloy, a horizontal continuous casting method has been developed in the prior art. In the method, as shown in FIG. 15, a casting molten metal E is supplied into a mold L having a gutter shape, which has been heated to a temperature not lower than a solidification temperature of the casting metal; a metallic molding (metallic strip) G, which is formed in the mold L, is drawn out by a dummy member; and at this point, the drawn-out metallic molding G is sprayed with a cooling water H from an upper portion of the mold L, thereby cooling the metallic molding G. In this case, an upper opening portion of the mold L is provided with an air curtain member K, and an air curtain is made from a gas jetted from the air curtain member, whereby the cooling water H, droplets thereof, and the like are prevented from entering the molten metal E in the mold L. This method is commonly called an OSC method. Symbol 1 in FIG. 15 denotes a gap between a bottom surface of the mold L and the metallic molding G which is generated by slanting the bottom surface of the mold L downward toward the outlet side (refer to JP 6-88106 B).

In some conventional strip manufacturing apparatuses, as shown in FIG. 16, a sheltered member M shields a part of an upper surface which is closer to an inlet of the heating mold L; a gas supply pipe N is perpendicularly inserted into the sheltered member M; an inert gas is jetted from the pipe to form an air curtain; the air curtain shields a gap between an upper surface of a molten metal O in the heating mold L and a back surface of the sheltered member M, thus preventing water vapor, which is generated by spraying the cooling water H onto the drawn-out metallic strip G, from entering the molten metal side to thereby avoid oxidation of cupper, silicon, stainless steel, and the like (refer to JP 4-125046 ).

The method of manufacturing a strip of a nonferrous metal as disclosed in JP 6-88106 B (the OSC method) is superior to conventional manufacturing methods in that formation of a solidified shell on an inner wall surface of the mold is prevented because the inside of the mold is heated to a temperature not lower than a solidification temperature of a casting metal, and thus, a strip can be obtained which consists of a complete unidirectional solidification structure in which crystals are grown only in a casting direction. Further, the air curtain is formed to prevent the cooling water H, droplets thereof, and the like from entering the molten metal E side in the mold L, and this provides an oxidation prevention effect. However, the air curtain member K is located apart from an outlet f of a tundish F. Thus, air enters the mold L from an upper surface opening portion P of the mold L between the air curtain member K and the outlet f, which inevitably results in oxidation of the molten metal in the mold L. Therefore, in the OSC method, in the case of Mg or Mg alloy which is easy to be oxidized, a surface of an Mg slab or Mg alloy slab burns at the same time the slab is drawn out from the mold L, and the surface becomes black due to the generation of a large gray and black oxide. Accordingly, it has been difficult to produce a slab of which surface does not become black. Further, when oxygen flows into the mold L, a molten Mg burns through reaction with oxygen in the air; when the combustion contacts with the cooling water, the water is decomposed to generate hydrogen and oxygen, possibly leading to an explosion. Furthermore, in manufacturing of an AZ31B slab with the OSC method, a surface thereof is uneven as shown in FIG. 12. Thus, it has been impossible to produce a smooth plate-like slab.

In the strip manufacturing apparatus of Japanese Utility Model Application Laid-open No. Hei 4-125046, the inert gas is jetted from the gas supply pipe N to form the air curtain; the air curtain shields the gap between the upper surface of the molten metal O in the heating mold L and the back surface of the sheltered member M, thus preventing water vapor, which is generated by spraying the cooling water, from entering the molten metal side to thereby avoid oxidation of cupper, silicon, stainless steel, and the like. However, the gas supply pipe N is located perpendicular to the molten metal O in the heating mold L, and thus, the gas jetted from the gas supply pipe N is not easily dispersed to the outlet side of the heating mold L. Therefore, it has been difficult to sufficiently prevent oxygen from entering the mold L from the outlet side of the heating mold L even if a large quantity of expensive inert gas is flown into the mold L. According to the experiment conducted by the inventors of the present invention, it has been found that the manufacturing apparatus cannot be used for casting of Mg or Mg alloy which is easy to be oxidized and which is attended by the danger of explosions through contact with water. Further, the gas supply pipe N is a mere pipe. Thus, a jetting area of the gas jetted from the outlet is narrow, and therefore, the pipe cannot be used for manufacturing of an Mg slab or Mg alloy slab which has a wide width (for example, a width of 100 mm or more).

In either of the cases of JP 6-88106 B and Japanese Utility Model Application Laid-open No. Hei 4-125046, since the cooling water is sprayed onto the metallic strip G on the mold L to cool the metallic strip G, not only the metallic strip G but also the mold L is cooled. Thus, it is necessary to heat the mold in advance to a higher temperature than needed while taking into account this cooling amount. The mold needs to be heated to a temperature higher than a melting point of a pure metal or a solidification temperature of a metal alloy by approximately 300° C. to 350° C. Such a high temperature leads to the large transformation of the mold due to thermal expansion and the shorter life of the mold or mold heater R. Thus, these components need to be exchanged frequently (for example, 1 batch: every 29 kg) . As a result, mass production has been difficult to achieve in actuality. Further, in the case where the mold L is formed of a metal, when the Mg slab or Mg alloy slab is cast, a center portion in a width direction of a slab S is curved upward as shown in FIG. 17A. As a result, it is impossible to produce the Mg slab or Mg alloy slab S with a uniform thickness in the width direction. In the case of a marked transformation, as shown in FIG. 17B, the molten Mg or Mg alloy, which is to be supplied to the mold L, is separated to both the side surface sides of the mold L from the upper curved portion of the Mg slab or Mg alloy slab S, as a result of which it is impossible to produce the Mg slab or Mg alloy slab with a wide width. Besides, the Mg slab or Mg alloy slab S that has been separated on both the sides of the mold L has an uneven thickness, which makes rolling in subsequent working difficult. In either of the cases of the OSC method (JP 6-88106 B) and the OSC method with a sheltered board (Japanese Utility Model Application Laid-open No. Hei 4-125046), when casting of the metal such as Mg is performed, the temperature of the mold needs to be set pretty higher than the melting point of the casting metal (Mg) or the solidification temperature of the casting alloy (Mg alloy) (approximately m.p.+300 to 350 K) in consideration of a fact that the latter half of the heat molding process involves cooling with the cooling water. Thus, under the condition of such a high temperature, the insulation resistance values (MΩ) of a heater panel, which supports and holds an electric heater of a heating element for heating a mold, and a refractory and a heat insulating material, which surround the periphery of the heater to avoid heat radiation of the heater to the outside of the mold, are vastly reduced (normally, reduced from a value not less than about 2 MΩ to a value not more than about 0.1 MΩ). Therefore, the leak of a heater temperature control current occurs. This results in a problem in that continuous casting is impossible to achieve.

Against the background described above, there has been an increased market demand for expanded products formed through press working molding of Mg laminate plates or Mg alloy laminate plates with high productivity and highly reliable product quality. However, a safe and stable casting method of an Mg slab or Mg alloy slab, which is a raw material for a laminate plate, has not been sufficiently established. Thus, at the present, domestic mass production of slabs has not been realized. There is only one commercial supply maker of slabs in the U.S. Accordingly, it has been strongly desired that the domestic supply of slabs be realized as soon as possible also in view of the necessity of lowering high costs.

SUMMARY OF THE INVENTION

The inventors of the present invention have made effortful studies of a method of easily manufacturing an Mg slab or Mg alloy slab and a manufacturing apparatus used for the method in a horizontal continuous casting method including an OSC method. From the studies, they succeeded in stable manufacturing of an Mg slab or Mg alloy slab which has no crystal grain boundary (A in FIG. 14), the crystal grain boundary being formed on a surface or an end portion toward an interior portion of the slab and being a main cause of occurrence of coming-off and edge cracks of the surface in hot or cold rolling working, which does not have inner holes, gas porosities, inclusions, and the like, and which is not oxidized to become black, without the danger of explosions.

According to a method for horizontal continuous casting of an Mg slab or Mg alloy slab of this patent application, a molten Mg or Mg alloy is supplied from a pool in a tundish, which is shielded from surroundings, into a mold, which communicates with the pool and is shielded from the surroundings. Then, the Mg slab or Mg alloy slab formed in the mold is drawn out to the outside from an outlet of the mold. After the mold is drawn out, a cooling medium is jetted onto the Mg slab or Mg alloy slab on the outer side of the mold outlet and in the vicinity of the outlet to cool the Mg slab or Mg alloy slab. A sealing gas such as an inert gas, nitrogen gas, or incombustible gas is jetted toward the outlet side of the mold over the entire width of a free surface of the molten Mg or Mg alloy on the inner side of the mold outlet and in the vicinity of the outlet. The gas seals a portion above the entire width of the free surface of the molten Mg or Mg alloy in the mold to prevent oxygen from flowing into the mold. As a result, in the case where the cooling medium is liquid, the liquid, droplets, spray, and the like are prevented from running back to the mold side. A surface temperature of the mold is set at a temperature exceeding or not exceeding a melting point of Mg or a solidification temperature of an Mg alloy. In the case of the temperature not exceeding the melting point or solidification temperature, a bottom surface and an inner wall surface of the mold are covered with a thin solidified shell formed of the molten Mg or Mg alloy supplied from the pool in the tundish. The unsolidified molten residue is solidified on the solidified shell to form the Mg slab or Mg alloy slab. Further, between the mold outlet and the cooling medium jetting part, a second sealing gas such as air, an inert gas, nitrogen gas, or incombustible gas is jetted onto the cooling medium jetting side over the entire width of the Mg slab or Mg alloy slab, which has been drawn out from the outlet of the mold. The second sealing gas seals the portion above the entire width of the Mg slab or Mg alloy slab. In the case where the cooling medium is liquid, the seal also prevents the liquid, droplets, spray, and the like from running back to the mold side (in a two-staged manner). Further, when the Mg slab or Mg alloy slab formed in the mold is to be drawn out from the outlet of the mold, a tip end of the molten Mg or molten Mg alloy is made to contact with a dummy member at the time of the start of drawing-out. The Mg slab or Mg alloy slab is drawn out by drawing out the dummy member. After being drawn out, the Mg slab or Mg alloy slab is drawn out by a drawing device without the use of the dummy member. Moreover, the sealing gas is jetted along the free surface of the molten Mg or Mg alloy; and the second sealing gas is jetted to the cooling medium jetting side along an upper surface of the Mg slab or Mg alloy slab.

An apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to this patent application is provided with: a sheltered board which covers an area extending from a portion above a pool in a tundish to a portion above a mold outlet to shield the area from the outside; a cooling medium jetting tool which is provided on the outer side of the mold outlet or at an outlet end of the mold and which jets a cooling medium onto the Mg slab or Mg alloy slab, which has been drawn out from the outlet, on the outer side of the mold outlet and in the vicinity of the outlet to cool the slab; and a gas jetting tool which is provided on the inner side of the mold outlet and which jets a sealing gas such as an inert gas, nitrogen gas, or incombustible gas on the side of a free surface of a molten Mg or Mg alloy to seal a portion above the entire width of the free surface of the molten Mg or molten Mg alloy in the mold. The sealing gas jetted from the gas jetting tool seals the above-mentioned portion to prevent oxygen from flowing into the mold from the portion. In the case where the cooling medium is liquid, the sealing gas prevents the liquid, droplets, spray, and the like from running back to the mold side. Between the outlet of the mold and the cooling medium jetting tool, a second gas jetting tool is provided which jets a second sealing gas such as air, inert gas, nitrogen gas, or incombustible gas on the Mg slab or Mg alloy slab drawn out from the outlet mold to thereby seal a portion above the entire width of the Mg slab or Mg alloy slab. In the case where the cooling medium is liquid, the seal also prevents the liquid, droplets, spray, and the like from running back to the mold side. The second gas jetting tool is provided at an angle at which the second sealing gas is jetted along the Mg slab or Mg alloy slab. A drawing device, which draws out the Mg slab or Mg alloy slab from the outlet, is provided on the outer side of the mold outlet. The mold is provided with a heating element so as to be heated, or is not provided with the heating element so as not to be heated. In the case where the heating element is provided, the operation of the heating element is made switchable between on and off.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are a schematic view showing a cross section of an apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to the present invention and a sectional view of a dummy portion, respectively;

FIG. 2 is a schematic view showing a cross section of an outlet portion of a mold having a built-in heater in the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab;

FIGS. 3A and 3B are a schematic view, as seen from above, of the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab, and a sectional view of a sight window and a hinge portion attached thereto, respectively;

FIG. 4 is a schematic view showing a cross section of an outlet portion of a mold in the case where the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab is additionally provided with a jetting tool for air or gas;

FIG. 5 is a schematic view of an outlet end of the mold of the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab;

FIG. 6 shows an appearance of an AZ31B magnesium slab manufactured through horizontal continuous casting of an Mg slab or Mg alloy slab;

FIG. 7 shows a macrostructure of a section taken in a longitudinal direction of the AZ31B magnesium slab;

FIG. 8 shows a macrostructure of a section taken in a width direction of the AZ31B magnesium slab;

FIG. 9 shows a microstructure of the section taken in the longitudinal direction of the AZ31B magnesium slab;

FIG. 10 shows a microstructure of the section taken in the width direction of the AZ31B magnesium slab;

FIG. 11 shows a microstructure of a raw material of the AZ31B magnesium ingot (ingot);

FIG. 12 shows an appearance of the AZ31B magnesium slab produced by a prior art (OSC method);

FIG. 13 is an explanatory plan view for the formation of crystals (grain boundaries) in general continuous casting of a slab (slab produced through continuous casting) and a billet (billet produced through continuous casting);

FIG. 14 is a schematic view showing crystal grain boundaries and influence at the time of rolling;

FIG. 15 is a schematic view showing a cross section of a casting apparatus of the prior art (OSC method: JP 6-88106 B);

FIG. 16 is a schematic view showing a cross section of another casting apparatus of the prior art (Japanese Utility Model Application Laid-open No. Hei 4-125046); and

FIGS. 17A and 17B are a longitudinal sectional view in the case where a mold and an Mg slab or Mg alloy slab are curved upward and a longitudinal sectional view in the case where the mold and the Mg slab or Mg alloy slab are extremely curved upward, respectively, in the case of casting the Mg slab or Mg alloy slab with the casting apparatus of FIG. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(Embodiment 1 of an Apparatus for Horizontal Continuous Casting of an Mg Slab or Mg Alloy Slab according to the Present Invention)

Prior to explanation of a method for horizontal continuous casting of an Mg slab or Mg alloy slab according to the present invention, detailed description will be made of Embodiment 1 of an apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab which is used for the method with reference to the accompanying drawings. In the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab which is shown in FIGS. 1A to 3B, a sheltered board 5 is provided to cover an area ranging from a portion above a pool 2 in a tundish 1 to a portion above an outlet 4 of a mold 3, thereby shielding the area from the outside; a cooling medium jetting tool 7, which jets a cooling medium 18 onto an Mg slab or Mg alloy slab 6 drawn out from the outlet 4 to thereby cool the slab 6, is provided on the outer side with respect to the outlet 4 of the mold 3; and a gas jetting tool 8 is arranged on the inner side with respect to the outlet 4 of the mold 3, as shown in FIG. 3A and FIG. 5.

Heaters 12 are built in a bottom wall 10 and a peripheral wall 11 of the tundish 1, but no heater 12 is built in the mold 3. The outlet side of the tundish 1 and the mold 3 each have a gutter shape (upwardly facing concave shape) having an upper opening. The sheltered board 5 covers the upper opening portions, thereby covering the upper surfaces from the outside. Thus, a molten Mg or Mg alloy 13 in the tundish 1 and the Mg slab or Mg alloy slab 6 in the mold 3 do not contact with the air. A calcium silicate board, kaowool board, or the like can be used for the sheltered board 5. The mold 3 is provided horizontal to the bottom wall 10 of the tundish 1, or provided such that the outlet side is inclined downward by 1 to 3 degrees with respect to the inlet side, whereby the molten Mg or Mg alloy 13 in the tundish 1 flows to the outlet side of the mold 3 more smoothly.

Stainless steel (SUS 304 or 430 etc.) is suitably used for the mold 3, and it is preferable that a mold be used in which an inner surface thereof has been subjected to molten aluminum plating. The mold 3 may have a built-in heating device such as the heater as in FIG. 2 or other heating elements. When the mold is heated by the heating device, solidification of the molten Mg alloy, which is supplied from the pool in the tundish into the mold, progresses more slowly. Thus, at the time of the start of drawing-out, a tip end of the molten Mg or Mg alloy can be coupled with a dummy member relatively slowly with a margin of time. Also, the thickness of a solidified shell, which is generated along an inner wall surface of the mold, can be reduced. Further, when a surface temperature of the mold is raised to a temperature exceeding a melting point of casting Mg or a solidification temperature of an Mg alloy, crystal grain boundaries, which are formed on a surface or an end portion side toward an inner portion, are not generated. Thus, the Mg slab or Mg alloy slab can be produced, of which lower surface and side wall are smooth and which has no casting defect, without the generation of the solidified shell. Therefore, heating is desirably performed with a condition that the mold temperature within a temperature range close to or exceeding the melting point of casting Mg or the solidification temperature of an Mg alloy (a range approximately from m.p.+70 K to m.p.+170 K). In casting of a metal such as Mg, for example, induction heating or heating with a gas burner may be adopted as a casting heating method instead of heating with an electric heater. However, the electric heater, which is more compact and has high stability in temperature, is desirably used.

As shown in FIGS. 3A and 3B, a sight window 14 is formed at a tip end of the sheltered board 5 covered on the mold 3. The sight window 14 is formed by cutting out the tip end from the sheltered board 5. The sight window 14 is covered by a movable lid 15, and the movable lid 15 is openably and closably attached to the sheltered board 5 by means of a hinge 16. When the movable lid 15 is opened, the Mg slab or Mg alloy slab 6 in the outlet 4 of the mold 3 can be seen. When the movable lid 15 is closed, the sight window 14 is shut.

A slit-shaped nozzle, round pipe nozzle, or the like can be used for a jetting outlet 7a (FIGS. 1A to 4) of the cooling medium jetting tool 7. The jetting outlet 7a is arranged downward such that the cooling medium 18 is jetted onto the Mg slab or Mg alloy slab 6 drawn out from the outlet 4 of the mold 3. The width of the jetting outlet 7a is substantially the same as or slightly narrower than the width of the Mg slab or Mg alloy slab 6 as shown in FIG. 3A such that the medium is jetted all over the Mg slab or Mg alloy slab 6. The cooling medium jetting tool 7 is supplied with the cooling medium 18 such as water or cooling gas from a cooling medium supply device (not shown).

In the gas jetting tool 8, a supply opening 8a is located above a free surface 13a of the molten metal 13 in the mold 3; a sealing gas 19 such as an inert gas, nitrogen gas, or incombustible gas is supplied from the supply opening 8a toward the free surface 13a side to form a gas curtain 21 for sealing a gap 20 between the free surface 13a and a part of the sheltered board 5 which surrounds the upper surface of the mold 3; and as a result, the gap 20 is sealed. The gas jetting tool 8 is supplied with a high-pressure gas from a gas supply device (not shown).

A liquid receiving portion 22 having an upper opening is provided on the lower downstream side with respect to the outlet 4 of the mold 3. The liquid receiving portion 22 receives the cooling medium 18, which has been jetted onto the Mg slab or Mg alloy slab 6, and exhausts it to the outside.

(Embodiment 2 of an Apparatus for Horizontal Continuous Casting of an Mg Slab or Mg Alloy Slab according to the Present Invention)

Shown in FIG. 4 is Embodiment 2 of the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to the present invention. The apparatus shown in FIG. 4 is provided with a second gas jetting tool 9 between the outlet 4 of the mold 3 and the cooling medium jetting tool 7. A second sealing gas 24 such as air, inert gas, nitrogen gas, or incombustible gas is jetted from a jetting outlet 9a toward the Mg slab or Mg alloy slab 6 drawn out from the outlet 4 of the mold 3 to thereby form an air curtain or gas curtain 26 above the Mg slab or Mg alloy slab. The gas curtain 26 seals the portion above the Mg slab or Mg alloy slab. In the case where the cooling medium jetted from the cooling medium jetting tool 7 is liquid, the seal also can prevent the liquid, droplets, spray, and the like from running back to the mold side.

(Embodiment 1 of a Method for Horizontal Continuous Casting of an Mg Slab or Mg Alloy Slab according to the Present Invention)

In the method for horizontal continuous casting of an Mg slab or Mg alloy slab according to the present invention, the entire upper surface from the portion above the pool 2 in the tundish 1 to the portion above the outlet 4 of the mold 3 is covered by the sheltered board 5; the molten Mg or Mg alloy (at 650° C. or more) in the tundish 1 in FIGS. 1A and 3A is supplied to the mold 3 which is heated by the heater or the like or is not heated; and the Mg slab or Mg alloy slab under solidification in the mold 3 is drawn out to the outside from the outlet 4 of the mold 3. At the time of the start of drawing-out, as shown in FIG. 1B, the tip end of the molten Mg or Mg alloy under solidification, which is drawn out from the outlet 4 of the mold 3, is coupled with the dummy member 23. The dummy member 23 is drawn out, whereby the Mg slab or Mg alloy slab 6 under solidification is drawn out. Thereafter, the cooling medium 18 is jetted onto the Mg slab or Mg alloy slab 6 from the jetting outlet 7a of the slit-shaped nozzle, round pipe nozzle, or the like to cool the Mg slab or Mg alloy slab 6. The cooled Mg slab or Mg alloy slab 6 is continuously drawn out by means of a drawing device 25. Two or more pairs of pinch rolls, which sandwich the Mg slab or Mg alloy slab 6 from both the upper and lower sides to draw out the slab, are appropriately used as the drawing device 25. Water, liquid nitrogen, or the like is appropriately used as the cooling medium 18.

In this case, the sealing gas 19 such as the inert gas, nitrogen gas, or incombustible gas is jetted into the gap 20 between the free surface 13a of the molten Mg or Mg alloy 13 and the sheltered board 5 surrounding the upper surface of the mold 3 by means of the gas jetting tool 8 provided on the inner side with respect to the outlet 4 of the mold 3, thereby forming the gas curtain 21 in the gap 20. The gas curtain 21 seals the outlet 4 side and the inner side of the mold 3. In the case of the cooling medium being liquid, the seal prevents oxygen and liquid, droplets, spray, and the like from entering the mold 3 through the gap 20. Therefore, it is desirable that the sealing gas 19 be jetted so as to lick (move along) the free surface 13a. An argon gas or nitrogen gas can be used as the inert gas. A sulfur hexafluoride gas, gas obtained by adding a nitrogen gas to the gas, or the like can be used as the incombustible gas.

As shown in FIG. 4, the air or gas jetting tool 9 is provided between the outlet 4 of the mold 3 and the cooling medium jetting tool 7. The air, inert gas, nitrogen gas, or incombustible gas is jetted from the jetting outlet 9a toward the Mg slab or Mg alloy slab 6, thereby forming the air curtain or gas curtain. In the case where the cooling medium is liquid, it is desirable to prevent the liquid, droplets, spray, and the like from running back to the mold side. That is, such prevention is preferably achieved by the two curtains, the above curtain and the gas curtain 21 formed by the sealing gas 19 jetted from the gas jetting tool 8. An ordinary compressor may be used as a jetting device. Thus, the usage amount of expensive inert gas, nitrogen gas, or incombustible gas can be vastly saved.

As described above, the molten metal 13, which is supplied to the mold 3 kept at a temperature not more than the solidification temperature of the casting Mg alloy, first forms a thin solidified shell 13b with a thickness of about 1 to 2 mm along the inner wall surface of the mold 3. Next, the unsolidified molten residue on a portion above the solidified shell is drawn out to the outside from the outlet 4 of the mold 3 without a fear of breakout while being mounted on the thin solidified shell 13b. The drawn-out Mg slab or Mg alloy slab under solidification is cooled by the cooling medium to be completely solidified. In this case, a drawing speed of the Mg slab or Mg alloy slab 6 can be easily raised to approximately 16.66 mm/sec. The plate width of the Mg slab or Mg alloy slab 6 is adjusted by changing the width dimension of the mold. The plate thickness can be easily adjusted by changing the level of the free surface 13a of the molten metal 13 supplied to the tundish 1 and the mold 3 or changing the depth of the mold 3. The width of the tundish 1 on the outlet side is made wider than the width of the inlet of the mold 3. Also, the width of the outlet of the mold 3 is made slightly wider than the width of the inlet of the mold 3 (with a taper of 1 to 2 degrees). As a result, the width of the Mg slab or Mg alloy slab 6 easily becomes stable, and the Mg slab or Mg alloy slab can be more easily drawn out to the outside of the mold.

(Embodiment 2 of a Method for Horizontal Continuous Casting of an Mg Slab or Mg Alloy Slab of the Present Invention)

With the use of the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, about 29 kg of an AZ31B magnesium alloy for an expanded material was subjected to casting with a casting speed ranging from 1.66 mm/sec. to 16.66 mm/sec. Examinations and studies were made of the influence of casting conditions on the surface condition and solidification structure of the obtained AZ31B slab having a size of a width of 100 mm×a thickness of 5 to 20 mm×a span of 10 m or more. Further, the relation between mechanical property such as a tensile strength, proof stress of 0.2%, or elongation and a microstructure was explained. Moreover, a comparison examination was performed between the AZ31B slab and a commercial laminate plate product produced by another company from the viewpoint of rolling and pressing workability. As a result, the AZ31B slab, which was manufactured with the manufacturing method and manufacturing apparatus of the present invention, widely differed from a conventional slab, and had a smooth outer circumferential surface as shown in FIG. 6. FIG. 7 shows a macrostructure of a section in a longitudinal direction (casting direction) of the same slab, and FIG. 8 shows a macrostructure of a section in a width direction (perpendicular direction to the casting direction) . In addition, FIG. 9 shows a microstructure of the section in the longitudinal direction (casting direction) of the same slab, and FIG. 10 shows a microstructure of the section in the width direction (perpendicular direction to the casting direction) . The figures have revealed that: the AZ31B slab, which is manufactured with the manufacturing method and manufacturing apparatus of the present invention, has a solidification structure of which section has a mirror surface and in which eutectic crystals of dissolved elements, Al and Zn, are uniformly and minutely distributed in a form of fine particles in Mg primary crystals serving as basis metal; the slab has no casting defects, in its inner side, such as holes, gas porosities, segregation of the dissolved elements or impurity elements, and inclusions; and the slab is a high-quality slab having excellent mechanical property and excellent characteristics such as rolling and pressing workability.

Table 1 is a chemical composition table of an expanded material, AZ31B which is used in the embodiment. Further, FIG. 11 shows an example of a microstructure of an AZ31B ingot raw material (ingot).

TABLE 1 Chemical composition (wt %) Al Zn Mn Si Fe Cu Ni Be Mg AZ31B 3.17 0.92 0.28 0.02 0.002 0.002 0.0004 0.0005 Bal.

The method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention has the following effects because the cooling medium is jetted to the Mg slab or Mg alloy slab, which has been drawn out from the mold, on the outside and in the vicinity of the outlet of the mold.

1. Since the temperature of the mold hardly lowers due to the cooling medium, the temperature of the mold does not need to be raised to a temperature higher than needed. Thus, the lives of the mold and heater are not shortened extremely, and these components do not need to be exchanged frequently. Further, an excessive current does not need to be flown through the mold heating heater. Thus, the insulation resistance values of a heater panel, refractory, and heat insulating material are not lowered extremely, which does not invite the danger of an electric leakage. Therefore, the Mg slab or Mg alloy slab can be produced continuously, thereby being stably supplied. Further, in the case of being cooled at the outlet end of the mold, the Mg slab or Mg alloy slab, which has been drawn out from the outlet of the mold, is cooled immediately after being drawn out from the outlet of the mold. Accordingly, it does not occur that the slab surface is oxidized to be black until the slab is cooled after being drawn out from the outlet.

2. The mold temperature does not need to be raised to a temperature higher than needed. Thus, the Mg slab or Mg alloy slab in the mold does not transform as shown in FIG. 17A. Therefore, there does not arise the problem in the case of the transformation as shown in FIG. 17A.

3. The slab can be continuously produced for a necessary length. Therefore, there is no limitation on a manufacturing possible length.

4. When the molten metal is rapidly cooled and solidified at a relatively high cooling speed (10 to 10²K/sec.), the Mg slab or Mg alloy slab can be produced which has a microstructure, in which the dissolved elements (Al, Zn) and an intermetallic compound (Mg—Mn) are minutely and uniformly distributed, and which has high corrosion resistance.

According to the method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, the pool in the tundish and the portion above the mold are sheltered from the surroundings; the sealing gas such as the inert gas, nitrogen gas, or incombustible gas is jetted over the entire width of the free surface of the molten Mg or Mg alloy in the mold to thereby seal the portion above the entire width of the free surface; and oxygen and liquid, droplets, spray and the like in the case of the cooling medium being the liquid, are prevented from flowing into the mold from the portion. Accordingly, there are provided the following effects.

1. The air is securely prevented from flowing into the mold. The molten Mg or Mg alloy is sent to the mold from the pool in the tundish, and thus, is shielded against the air until being drawn out from the outlet. Therefore, combustion of the molten Mg or Mg alloy and the Mg slab or Mg alloy slab can be avoided reliably. As a result, the Mg slab or Mg alloy slab, of which surface is not black, can be obtained.

2. The cooling water, spray, and the like can be securely prevented from flowing into the mold. Thus, there is no danger of explosions, which is safe.

According to the method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, the mold is provided with the heating device such as the heater, and the heating device raises the surface temperature of the mold to the temperature exceeding the melting point of the casting Mg or the solidification temperature of the Mg alloy. This provides the following effects.

1. The molten Mg or Mg alloy supplied to the mold does not form the solidified shell along the inner wall surface of the mold, and a solidified interface is formed on the mold. Thus, the crystal grain boundaries are not generated, which are formed from a surface or end portion to an inner portion. Therefore, there can be produced safely and stably the Mg slab or Mg alloy slab with high reliability and high quality which has a smooth surface, which is not accompanied with the generation of inner holes, gas porosities, inclusions, and the like due to solidification shrinkage, and which has no casting defect. Accordingly, the yield is improved, and the reduction of costs can be realized.

2. The mass production of Mg slabs or Mg alloy slabs, which have excellent mechanical properties and characteristics that enable easy working through rolling, pressing, and the like, can be achieved at low cost.

According to the method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, the surface temperature of the mold is kept so as not to exceed the melting point of the casting Mg or the solidification temperature of the Mg alloy; the molten Mg or Mg alloy is supplied to the mold; the thin solidified shell (13b in FIG. 1B) with a thickness of about 1 to 2 mm is formed of the molten metal along the inner wall surface (bottom surface and both the side surfaces) of the mold; and the unsolidified molten residue on a part above the solidified shell is drawn out to the outside from the outlet of the mold while being mounted on the thin solidified shell. Thus, the following effects are also provided.

1. The Mg slab or Mg alloy slab can be drawn out without a fear of breakout.

2. The Mg slab or Mg alloy slab, which has been drawn out as in 1 described above, can have a ground surface like a mirror surface by grinding a surface layer (portion of the solidified shell) thereof. The grinding amount is much smaller than that of a general slab.

According to the method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, the second sealing gas such as the air, inert gas, nitrogen gas, or incombustible gas is jetted over the entire width of the Mg slab or Mg alloy slab, which has been drawn out from the outlet of the mold, between the outlet of the mold and the cooling medium jetting part; the second sealing gas seals the portion above the Mg slab or Mg alloy slab; and in the case of the cooling medium being liquid, the seal also prevents the liquid, droplets, spray, and the like from running back to the mold side (with the two steps). Accordingly, the following effects are provided.

1. The above-described various effects of the manufacturing method of this application are further improved.

2. The sealing gas jetted in the mold is jetted along the free surface of the molten Mg or Mg alloy, and the second sealing gas is jetted along the upper surface of the Mg slab or Mg alloy slab. This provides a high sealing effect.

According to the method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, at the time of the start of drawing-out the Mg slab or Mg alloy slab, the molten Mg or molten Mg alloy is made to contact with the dummy member, and the Mg slab or Mg alloy slab is drawn out by drawing out the dummy member. Therefore, drawing-out at the time of the start is performed easily.

According to the method for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, the mold is provided with the heating element, and the operation of the heating element is made switchable between on and off. Thus, the mold can be used both at a temperature not more than the melting point of the casting Mg or the solidification temperature of the Mg alloy and at a temperature exceeding the point or temperature. Therefore, the mold can be properly used in correspondence with applications, which is useful.

The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention is provided with: the sheltered board which covers the area ranging from the portion above the pool in the tundish to the portion above the mold outlet to shield the area against the outside; the cooling medium jetting tool which is provided on the outer side of the mold outlet and which jets the cooling medium onto the Mg slab or Mg alloy slab, which has been drawn out from the outlet, on the outer side of the mold outlet and in the vicinity of the outlet to thereby cool the slab; and the gas jetting tool which is provided on the inner side of the mold outlet and in the vicinity of the outlet, which jets the inert gas, nitrogen gas, or incombustible gas to seal the portion above the entire width of the free surface, and which prevents oxygen from flowing into the mold from the outside and also prevents the droplets, spray, and the like of the cooling medium from flowing into the mold. Therefore, the following effects are provided.

1. The molten Mg or Mg alloy and the Mg slab or Mg alloy slab can be shielded from the surroundings with simple manufacturing facilities until they are drawn out from the outlet of the mold after having been sent to the mold from the pool in the tundish. Thus, the molten metal and slab do not become black through combustion, and can be continuously manufactured without explosions. As a result, the Mg slabs or Mg alloy slabs can be supplied stably.

2. Since the molten metal is rapidly cooled and solidified at a relatively high cooling speed (10 to 10²K/sec.), the Mg slab or Mg alloy slab can be produced which has a microstructure, in which the dissolved elements (Al, Zn) and an intermetallic compound (Mg—Mn) are minutely and uniformly distributed, and which has high corrosion resistance.

In the apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention, in the case where the mold is provided with the heating element, the operation of the heating element is made switchable between on and off. Therefore, the following effects are provided.

1. The mold can be used both at the temperature not more than the melting point of the casting Mg or the solidification temperature of the Mg alloy and at the temperature exceeding the point or temperature. Therefore, the mold can be properly used in correspondence with applications, which is useful.

2. In the case of 1 described above, when the surface temperature of the mold is raised so as to exceed the melting point of Mg or the solidification temperature of the Mg alloy, the molten Mg or Mg alloy supplied to the mold does not form the solidified shell on the surface of the mold, and the solidified interface is formed on the mold. Thus, the crystal grain boundaries are not generated, which are formed from a surface or end portion to an inner portion. Therefore, there can be safely and stably realized the mass production of Mg slabs or Mg alloy slabs with high reliability and high quality each of which has a smooth surface, which are not accompanied with the generation of inner holes, gas porosities, inclusions, and the like due to solidification shrinkage, and which have no casting defect. Accordingly, the yield is improved, and the reduction of costs can be also realized. Besides, the Mg slabs or Mg alloy slabs have excellent mechanical properties and characteristics that enable easy working through rolling, pressing, and the like. Further, the molten Mg or Mg alloy supplied from the pool in the tundish into the mold is not solidified. Thus, the tip end of the molten Mg or Mg alloy can be easily and relatively slowly coupled with the dummy member with a margin for time at the time of the start of drawing-out. Therefore, drawing-out with the dummy member can be performed easily and reliably.

3. In the case of 1 described above, the surface temperature of the mold is kept so as not to exceed the melting point of the casting Mg or the solidification temperature of the Mg alloy, and the molten Mg or Mg alloy is supplied to the mold. Resultingly, the thin solidified shell (13b in FIG. 1B) with a thickness of about 1 to 2 mm is formed of the molten metal along the inner wall surface (bottom surface and both the side surfaces) of the mold, and the unsolidified molten residue on a part above the solidified shell can be drawn out to the outside from the outlet of the mold while being mounted on the thin solidified shell. Therefore, the Mg slab or Mg alloy slab can be drawn out without a fear of breakout. Moreover, the Mg slab or Mg alloy slab, which has been drawn out as described above, can have a ground surface like a mirror surface by grinding the surface layer (portion of the solidified shell). Therefore, the grinding amount is much smaller than that of a general slab in which the entire surface of an Mg slab or Mg alloy slab is ground.

The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention is provided, between the outlet of the mold and the cooling medium jetting tool, with the second gas jetting tool which jets the second sealing gas such as the air, inert gas, nitrogen gas, or incombustible gas on the Mg slab or Mg alloy slab drawn out from the mold outlet to thereby seal the portion above the entire width of the Mg slab or Mg alloy slab. In the case where the cooling medium is liquid, the seal also prevents the liquid, droplets, spray, and the like from running back to the mold side. Thus, the effects 1 and 2 are further improved. Further, the second gas jetting tool is provided at the angle at which the second sealing gas is jetted along the Mg slab or Mg alloy slab. Accordingly, the sealing effect is further increased.

The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab of the present invention is provided, on the outer side of the outlet of the mold, with the drawing device that draws out the Mg slab or Mg alloy slab from the outlet. As a result, continuous casting can be realized.

Claims

1. A method for horizontal continuous casting of an Mg slab or Mg alloy slab, comprising: supplying a molten Mg or Mg alloy from a pool in a tundish, which is shielded from surroundings, into a mold that communicates with the pool and is shielded from the surroundings; drawing out the Mg slab or Mg alloy slab formed in the mold to an outside from an outlet of the mold; jetting, after the mold is drawn out, a cooling medium onto the Mg slab or Mg alloy slab on an outer side of the mold outlet and in a vicinity of the outlet to cool the Mg slab or Mg alloy slab; and jetting a sealing gas over an entire width of a free surface of the molten Mg or Mg alloy on an inner side of the mold outlet and in the vicinity of the outlet, the gas sealing a portion above the entire width of the free surface of the molten Mg or Mg alloy in the mold to prevent oxygen from flowing into the mold.

2. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 1, wherein, a surface temperature of the mold is set at a temperature exceeding one of a melting point of Mg and a solidification temperature of an Mg alloy.

3. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 1, wherein, a surface temperature of the mold is set at a temperature not exceeding one of a melting point of Mg and a solidification temperature of an Mg alloy such that the molten Mg or Mg alloy supplied from the pool in the tundish into the mold forms a thin solidified shell along an inner wall surface of the mold, and unsolidified molten residue is solidified on the solidified shell to form the Mg slab or Mg alloy slab.

4. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 1, wherein, between the mold outlet and a cooling medium jetting part, a second sealing gas is jetted over the entire width of the Mg slab or Mg alloy slab, which has been drawn out from the outlet of the mold, the second sealing gas sealing the portion above the entire width of the Mg slab or Mg alloy slab.

5. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 1, wherein when the Mg slab or Mg alloy slab formed in the mold is to be drawn out from the outlet of the mold, a tip end of the molten Mg or molten Mg alloy is made to contact with a dummy member at a start of drawing-out, the Mg slab or Mg alloy slab is drawn out by drawing out the dummy member, and after being drawn out, the Mg slab or Mg alloy slab is drawn out by a drawing device.

6. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 2, wherein when the Mg slab or Mg alloy slab formed in the mold is to be drawn out from the outlet of the mold, a tip end of the molten Mg or molten Mg alloy is made to contact with a dummy member at a start of drawing-out, the Mg slab or Mg alloy slab is drawn out by drawing out the dummy member, and after being drawn out, the Mg slab or Mg alloy slab is drawn out by a drawing device.

7. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 3, wherein when the Mg slab or Mg alloy slab formed in the mold is to be drawn out from the outlet of the mold, a tip end of the molten Mg or molten Mg alloy is made to contact with a dummy member at a start of drawing-out, the Mg slab or Mg alloy slab is drawn out by drawing out the dummy member, and after being drawn out, the Mg slab or Mg alloy slab is drawn out by a drawing device.

8. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 4, wherein when the Mg slab or Mg alloy slab formed in the mold is to be drawn out from the outlet of the mold, a tip end of the molten Mg or molten Mg alloy is made to contact with a dummy member at a start of drawing-out, the Mg slab or Mg alloy slab is drawn out by drawing out the dummy member, and after being drawn out, the Mg slab or Mg alloy slab is drawn out by a drawing device.

9. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 1, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

10. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 2, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

11. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 3, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

12. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 4, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

13. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 5, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

14. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 6, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

15. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 7, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

16. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 8, wherein the sealing gas is jetted toward an outlet side of the mold along the free surface of the molten Mg or molten Mg alloy.

17. The method for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 4, wherein the second sealing gas is jetted toward a cooling medium jetting side along an upper surface of the Mg slab or Mg alloy slab.

18. An apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab, comprising: a sheltered board that covers an area extending from a portion above a pool in a tundish to a portion above a mold outlet to shield the area from an outside; a cooling medium jetting tool that is provided one of on an outer side of the mold outlet and at an outlet end of the mold and jets a cooling medium onto the Mg slab or Mg alloy slab, which has been drawn out from the outlet, on the outer side of the mold outlet and in a vicinity of the outlet to cool the slab; and a gas jetting tool having a wide width that is provided on an inner side of the mold outlet and jets a sealing gas over an entire width of the free surface of the molten Mg or Mg alloy to seal a portion above the entire width of the free surface of the molten Mg or molten Mg alloy in the mold,

wherein the sealing gas jetted from the gas jetting tool seals the portion above the entire width of the free surface of the molten Mg or molten Mg alloy to prevent oxygen from flowing into the mold therefrom.

19. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 18, further comprising a second gas jetting tool provided between the outlet of the mold and the cooling medium jetting tool, the second gas jetting tool jetting a second sealing gas over the entire width of the Mg slab or Mg alloy slab that has been drawn from the outlet of the mold to seal the portion above the entire width of the Mg slab or Mg alloy slab.

20. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 19, wherein the second gas jetting tool is provided at an angle at which the second sealing gas is jetted to a cooling medium jetting side along the Mg slab or Mg alloy slab.

21. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 18, further comprising, on the outer side of the outlet of the mold, a drawing device that draws out the Mg slab or Mg alloy slab.

22. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 18, wherein the mold comprises a heating element.

23. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 19, wherein the mold comprises a heating element.

24. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 20, wherein the mold comprises a heating element.

25. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 21, wherein the mold comprises a heating element.

26. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 18, wherein the mold comprises no heating element.

27. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 19, wherein the mold comprises no heating element.

28. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 20, wherein the mold comprises no heating element.

29. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 21, wherein the mold comprises no heating element.

30. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 18, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

31. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 19, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

32. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 20, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

33. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 21, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

34. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 22, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

35. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 23, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

36. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 24, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

37. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 25, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

38. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 26, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

39. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 27, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

40. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 28, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

41. The apparatus for horizontal continuous casting of an Mg slab or Mg alloy slab according to claim 29, wherein, in a case where the mold comprises the heating element, the heating element is made switchable between on and off.

42. The method according to claim 1

wherein the cooling medium is a liquid, and the jetting of the sealing gas seals the portion above the entire width of the free surface of the molten Mg or Mg alloy in the mold to prevent any liquid or vapor substance that is generated due to the jetting liquid from returning to the mold.

43. The method according to claim 42, wherein the liquid or vapor substance includes at least one of liquid, droplets, spray and vapor.

44. The method according to claim 4, wherein the cooling medium is a liquid, and the jetting of the sealing gas seals the portion above the entire width of the free surface of the molten Mg or Mg alloy in the mold to prevent any liquid or vapor substance that is generated due to the jetting liquid from returning to the mold.

45. The method according to claim 44, wherein the liquid or vapor substance includes at least one of liquid, droplets, spray and vapor.

46. The apparatus according to claim 18, wherein the cooling medium is a liquid, and the jetting of the sealing gas seals the portion above the entire width of the free surface of the molten Mg or Mg alloy in the mold to prevent any liquid or vapor substance that is generated due to the jetting liquid from returning to the mold.

47. The apparatus according to claim 46, wherein the liquid or vapor substance includes at least one of liquid, droplets, spray and vapor.

48. The apparatus according to claim 19, wherein the cooling medium is a liquid, and the jetting of the sealing gas seals the portion above the entire width of the free surface of the molten Mg or Mg alloy in the mold to prevent any liquid or vapor substance that is generated due to the jetting liquid from returning to the mold.

49. The apparatus according to claim 48, wherein the liquid or vapor substance includes at least one of liquid, droplets, spray and vapor.