JP2003113430A - Melting and casting method for magnesium and magnesium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting method which can prevent a molten magnesium or alloy from oxidation and burning and can cast the molten metal into a mold in a good work environment. SOLUTION: This method includes melting magnesium or the alloy, with heat generating when induction heating a crucible 1 made from iron or an iron-based alloy. The method preferably includes further arranging the crucible and an induction heating device 11 in the same gastight chamber 13, to melt magnesium or the alloy in the chamber made to be an inert gas atmosphere. The method preferably includes adding the flux containing potassium chloride, magnesium chloride, and calcium chloride in the crucible, to melt magnesium or the alloy. The method includes arranging the crucible, the induction heating device and a mold 12 in the same gastight chamber, to melt and cast magnesium or the alloy in the chamber made to be an inert gas atmosphere.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for melting magnesium and a magnesium alloy, and a method for casting a magnesium alloy.

[0002]

2. Description of the Related Art Magnesium alloy has a density of about 2/3 that of aluminum alloy and is the lightest of practical metal materials.
It has good machinability, has a high strength / density ratio, and the refinement process has improved the purity of the metal to obtain a material with good corrosion resistance, which has attracted attention as a material for automobiles and aircraft.

Magnesium is more susceptible to oxidative combustion than metals such as aluminum, and when magnesium and magnesium alloys are dissolved in the atmosphere, magnesium is more susceptible to oxidative combustion in the atmosphere. If a flux is added to the surface of the molten metal to seal the atmosphere, the added flux is likely to be mixed in the cast metal when the molten magnesium alloy molten metal is cast. The final product of magnesium alloy, which is made of metal containing flux, has problems such as deterioration of corrosion resistance. Thus, when magnesium and a magnesium alloy are melted and a magnesium alloy is cast, it is often necessary to have skill in those operations.

When melting magnesium and magnesium alloy, a method of melting magnesium and magnesium alloy by covering the crucible with a lid and heating the crucible by burning fuel gas, that is, a closed crucible furnace method is generally used. Has been adopted by.

FIG. 2 is a view showing an example of a closed crucible furnace which has been conventionally used. The crucible 1 arranged in the furnace 5 made of the refractory heat insulating material 4 is heated by burning the fuel gas using the burner 6 to melt the magnesium or the magnesium alloy, and at that time, the surface of the molten metal 9 and the atmosphere are brought into contact with each other. To prevent this, a flux 8 is added to the surface of the molten metal, and a lid 3 is placed on the crucible. As a material for the crucible, steel having a low solubility in a molten magnesium, such as carbon steel, low alloy steel, stainless steel containing no Ni, Co, etc., is used. In the figure, reference numeral 7 indicates a flame of combustion gas, and reference numeral 10 indicates an exhaust stack.

[0006] Although the lid is used, since the atmosphere around the crucible is an air atmosphere, it is necessary to prevent the oxidative combustion of the magnesium alloy melt. Normally, the surface of the melt is covered with a protective gas, or flux is formed on the surface of the melt. Is added.

As a protective gas, sulfur hexafluoride (SF
₆ ) is generally used, but it is expensive and
Since it is a greenhouse gas, it may be difficult to use due to environmental problems.

[0008] Further, as a flux, potassium chloride,
Fluxes containing magnesium chloride, calcium chloride, calcium fluoride, etc. are usually used, but when added in large amounts, there are problems such as securing a disposal site and environmental protection, so reduce the amount used as much as possible. Is required.

Furthermore, in the method of melting the magnesium or magnesium alloy by heating the crucible by burning the fuel gas, it takes time to dissolve the material, during which the molten metal is oxidized or added to the surface of the molten metal. The chance that the generated flux gets caught in the molten metal increases. Therefore, improvement in shortening the dissolution time is desired.

As a method for casting a molten magnesium alloy, a die casting method, that is, a method of applying pressure to a molten metal and pouring it into a precision mold to produce a casting has been widely used recently. It is also done. When casting in a sand mold, it is performed in an air atmosphere, so sulfur hexafluoride is generally used as a protective gas to prevent oxidative combustion of the molten metal surface in the sand mold immediately after casting. ing. As mentioned above, sulfur hexafluoride is expensive and may be difficult to use in the future due to environmental problems.

[0011]

DISCLOSURE OF THE INVENTION According to the present invention, it is possible to efficiently dissolve magnesium or a magnesium alloy, and it is not necessary to use an expensive protective gas for preventing oxidative combustion of the molten metal. In addition, even when using a flux, it provides a method for melting magnesium and magnesium alloys that can minimize the amount used, and further, when casting a molten metal of magnesium or magnesium alloy in a mold, the molten metal surface immediately after casting It is an object of the present invention to provide a casting method of magnesium and magnesium alloy, which can be cast without using an expensive protective gas for preventing the oxidative combustion of slag.

[0012]

The gist of the present invention resides in a melting method shown in the following (1) to (3) and a casting method shown in the following (4). (1) When magnesium or a magnesium alloy is melted using an iron crucible or an iron-based alloy crucible, the heat generated by induction heating the crucible causes the magnesium or the magnesium alloy to dissolve magnesium or a magnesium alloy. Dissolution method. (2) The crucible and the induction heating device are arranged in the same closed chamber, the chamber is filled with an inert gas atmosphere, and the induction heating device is used to induction-heat the crucible to obtain magnesium in the crucible. Alternatively, the method for melting magnesium and the magnesium alloy according to (1) above, which dissolves the magnesium alloy. (3) The method for dissolving magnesium and magnesium alloy according to the above (1) or (2), wherein a flux containing potassium chloride, magnesium chloride and calcium chloride is added and dissolved in the crucible. (4) In the crucible, the crucible, the induction heating device, and the mold are arranged in the same closed chamber, and the chamber is filled with an inert gas atmosphere to induction-heat the crucible using the induction heating device. 1. A method for casting magnesium and a magnesium alloy, which comprises melting magnesium or a magnesium alloy, and casting the molten magnesium or a molten magnesium alloy in a mold.

When melting magnesium or a magnesium alloy using an iron crucible or an iron-based alloy crucible, the melting material in the crucible is melted by induction heating the crucible to heat the conventional fuel gas. It was found that the melting material can be melted more effectively and in a shorter time than the method of heating the crucible by burning the above. The induction heating method of the crucible is a method suitable for melting a melting material in a closed chamber described later.

When magnesium or a magnesium alloy is melted in an atmosphere using a crucible, the surface of the molten magnesium alloy comes into contact with the atmosphere, whereby the magnesium is oxidized and burned. In order to eliminate this oxidative combustion of magnesium, it is sufficient to eliminate the contact between the molten metal and the atmosphere. As a replacement for the expensive protective gas, sulfur hexafluoride (SF ₆ ), which is conventionally used, the relatively inexpensive A
A method using an inert gas such as r gas can be considered.

However, since the density of the inert gas such as Ar gas is smaller than the density of the sulfur hexafluoride gas which has been used conventionally, even when used in the air atmosphere, it is diffused around the crucible by thermal convection. It is easy to form a stable film of an inert gas such as Ar gas on the surface of the molten metal.

Even when an inert gas such as Ar gas having a low density is used, as a method for obtaining a sufficient molten metal surface coating effect, a melting-related apparatus is arranged in the same closed chamber and the atmosphere in the closed chamber is set to Ar gas. It is effective to use an inert gas atmosphere such as.

Further, since the crucible and the crucible heating device are arranged in the same closed chamber, the use of the combustion system of the fuel gas which requires the atmosphere or oxygen as the heating device results in an excessive exhaust device. , Not realistic.
Therefore, it is effective that the crucible is made of iron or an iron-based alloy and the heating device is an induction heating device.

When the iron crucible or iron-based alloy crucible is induction-heated to dissolve magnesium or magnesium alloy in the air or in the above-mentioned closed chamber, potassium chloride, magnesium chloride or calcium chloride is added. Even if the flux containing it is added and dissolved in the crucible, it will dissolve in the air, but the dissolution time will be short, or it will be blocked by the air and will dissolve. can do.

Furthermore, when casting a molten and melted magnesium alloy melt into a mold, if the mold is placed in the same closed chamber as when melting, the surface of the melt immediately after casting will be Since it can be covered with an inert gas such as Ar gas, oxidative combustion on the surface of the molten magnesium alloy can be prevented.

[0020]

1 is a cross-sectional view showing an example of an apparatus used when the melting method and the casting method of the present invention are carried out simultaneously. An example in which the crucible 1, the induction heating device 11, and the mold 12 are arranged in the closed chamber body 13 is shown. Reference numeral 2 in the figure denotes a protective crucible arranged so as to enclose the crucible 1, and reference numeral 14 denotes a lid of the closed chamber, reference numeral 1
Reference numeral 5 indicates a base, reference numeral 16 indicates a mold surface plate, and reference numeral 17 indicates a bed on which the apparatus is arranged. In addition, in order to perform melting and casting in a closed chamber, a closed chamber peep window, flux addition device, crucible tilting device, molten metal temperature measuring device, exhaust device, Ar gas introduction pipe, safety valve, lighting equipment, etc. It can be arranged, but is not shown. In addition, it is desirable that the mold and the mold surface plate are integrated. Can effectively prevent leakage of hot water.

After charging a small piece or scrap of magnesium or magnesium alloy ingot which is a melting material for magnesium alloy into the crucible, the chamber is closed and the inner atmosphere is filled with an inert gas such as Ar gas. Replace. The crucible is heated using an induction heating device to heat and melt the material inside the crucible. Flux may be appropriately added to the surface of the molten metal by a flux addition device arranged above the crucible. A molten magnesium alloy melt is cast into a mold by tilting the crucible. After the temperature of the ingot has dropped to around room temperature, the lid of the closed chamber is removed, the mold is taken out, and the ingot and the ingot can be separated to obtain a magnesium alloy ingot.

As the iron crucible or the iron-based alloy crucible, for example, steel such as carbon steel, low alloy steel, and stainless steel containing no Ni and Co can be used. Ni and Co in the steel dissolve in the molten metal of magnesium or magnesium alloy, so that the quality of the product made from them deteriorates. The size of the crucible may be determined depending on the weight of the melt and the size of the ingot to be cast. Since the thickness of the crucible is repeatedly induction-heated, it is desirable to set the thickness to about 1/30 to 1/20 of the diameter. From the viewpoint of preventing heat dissipation, the ratio of the diameter of the crucible to the height of the crucible (diameter / height) is preferably about 1/2.

As a gas for the atmosphere in the closed chamber,
Use an inert gas. As the inert gas, Ar gas,
He gas or the like can be used. Further, as the induction heating device, a usual high frequency induction heating device can be used. Further, the mold is preferably made of the same material as the crucible. Further, the size of the mold may be determined by the weight of casting.

In the melting method of the present invention, when the crucible made of iron or the crucible made of iron-based alloy is used for melting, the magnesium or magnesium alloy is melted by the heat generated by induction heating the crucible. It is possible to melt the crucible more effectively and in a shorter time than the conventional method of heating the crucible by burning the fuel gas.

Further, in the melting method of the present invention, when melting magnesium or a magnesium alloy by the above method, a crucible and an induction heating device are arranged in the same closed chamber, and an inert gas atmosphere is provided in the chamber.
It is desirable to dissolve. The atmosphere in the closed chamber
Since the atmosphere is an inert gas such as Ar gas, oxidative combustion of the molten magnesium alloy can be prevented more effectively.

In addition, in the melting method of the present invention, it is more preferable to add a flux containing potassium chloride, magnesium chloride and calcium chloride into the steel crucible and dissolve it during the melting.

Even when melting in the air, the melting time is shorter than before, so that the amount of flux used can be reduced, the atmosphere and the molten metal can be shielded, and oxidation of the molten metal can be prevented.
Evaporation of magnesium can be suppressed by using a flux when melting in a closed chamber. Further, since only evaporation is prevented, the amount of flux used can be reduced as compared with the conventional case.

In the casting method of the present invention, the crucible, the induction heating device and the mold are arranged in the same closed chamber, and the chamber is filled with an inert gas atmosphere to induction-heat the crucible using the induction heating device. The magnesium or magnesium alloy in the crucible is melted, and the molten magnesium or magnesium alloy melt is cast in a mold.

Since the molten metal of the molten magnesium alloy is cast as it is in a mold placed in the same closed chamber without being oxidatively burned, oxidative combustion of the molten metal immediately after casting can be prevented and non-metal It is possible to obtain a magnesium alloy ingot having a small amount of inclusions and good internal quality.

[0030]

EXAMPLE A test for melting a magnesium alloy containing 3% by mass of Al and 1% by mass of Zn was carried out using an apparatus having the structure shown in FIG.

The amount of dissolution was 1.2 kg, the holding temperature during dissolution was 750 ° C., and the holding time after dissolution was 30 minutes. The atmosphere in the closed chamber was an Ar gas atmosphere at 1 atm.
In some tests, the closed chamber lid was opened and melted under air. The crucible was made of steel, and the type of steel was changed and tested. The crucible size is 90
mm, outer diameter 105 mm, and height 205 mm. The heating method was a method using a high frequency induction heating device of 10 kHz or 5 kW, or a method of burning CH ₄ fuel gas. In some tests, the flux having the composition shown in Table 1 was added to the crucible and dissolved.

[0032]

[Table 1]

In each test, the degree of generation of oxides produced by oxidative combustion of magnesium was investigated. The investigation method was a method in which the oxides formed on the surface of the molten metal during melting were scraped using a stainless steel net, and the weight and oxygen analysis value were used to determine. The weight of the oxide was divided by the weight of the initial charge and converted to% to obtain the oxide production rate (%). Test No. of the comparative example. The value of the production rate of the oxide of No. 3 was set to an index of 1.0, and the production state of the oxide of magnesium in the test of the example of the present invention was displayed as an index.

In each test, the degree of evaporation of magnesium from the molten magnesium alloy was investigated. The investigation method was a method in which after the dissolution test, magnesium attached to the inner wall of the closed chamber was collected with a brush and the weight thereof was measured. The weight of the evaporated and attached magnesium was divided by the weight of the initial charge and converted into% to obtain the steam generation rate (%). Test No. of the comparative example. The value of the steam generation rate of No. 3 was set as an index of 1.0, and the occurrence state of evaporation of magnesium during the test of the example of the present invention was displayed as an index.

Further, the operating cost was estimated by obtaining the vapor generation rate of magnesium and the production rate of magnesium oxide in each test, and the loss time for cleaning the inside of the closed chamber estimated from these values. .
Test No. of the comparative example. The operating cost of 3 was set as an index of 1.0, and the operating cost at the time of the test of the present invention example was displayed as an index.
Table 2 shows each test condition and test result.

[0036]

[Table 2]

Test No. of the present invention example In No. 1, ferritic stainless steel with a Cr content of about 17 mass% (SUS430 specified in JIS G 4304)
And The crucible was heated using a high frequency induction heating device. After the temperature of the melting material reached just above the melting point of the magnesium alloy, the melting material completely melted. At that time, 36 g of flux was added to the surface of the molten metal in the crucible by using a flux addition device arranged above the crucible.

Test No. In No. 1, no magnesium oxide was formed on the surface of the molten metal during melting. Further, magnesium vapor was not adhered to the inner wall of the closed chamber after the dissolution was completed. Further, the operating cost index is the test number of the comparative example described later. 3 based on 1.
When it was set to 0, the operating cost was 0.1, which was low.

Test No. of the present invention example In 2, the crucible is made of carbon steel, which is a steel plate for a boiler (for example, JIS
SB410) defined in G 3103. The crucible was heated using a high frequency induction heating device. After the temperature of the melting material reached just above the melting point of the magnesium alloy, the melting material completely melted. At that time, no flux was added.

Test No. In No. 2, no magnesium oxide was formed on the surface of the molten metal during melting. In addition, since magnesium vaporized on the inner wall of the closed chamber after the dissolution was completed, deposits were observed. The index of the state of steam generation is the test No. of the comparative example described later. When the base number 3 is 1.0, the value is 0.4, and the test No. Although the generation of steam was less than that of Test No. 3, Test No. It was more than one. Further, the operating cost index is the test number of the comparative example described later. When 3 was set to 1.0 of the base, the operating cost was low at 0.2. However, the test No. It was higher than the operating cost of 1.

Test No. of the comparative example. In No. 3, the material of the crucible was tested No. 3. The same as in the case of 2, except that the lid of the closed chamber was opened and the crucible was heated by burning the CH ₄ fuel gas under an air atmosphere. When the temperature of the melting material reached just above the melting point of the magnesium alloy, the melting material completely melted. At that time, 72 g of the flux was added to the surface of the molten metal in the crucible using a flux addition device arranged above the crucible.

Test No. In No. 3, magnesium oxide was generated on the surface of the molten metal during melting, and the oxide generation rate was 0.5%. Further, a large amount of magnesium vapor adhered to the inner wall of the closed chamber after the dissolution was completed, and the vapor generation rate was 0.15%. By using a large amount of flux of 72 g, it was possible to suppress the oxide production rate and vapor generation rate to this extent. In addition, the operating costs are
Due to the large amount of oxidative combustion and evaporation of magnesium, the test No. 1 and No. The operation cost was 5 to 10 times higher than that of 2.

[0043]

EFFECTS OF THE INVENTION By applying the melting method and the casting method of the present invention, it is possible to prevent oxidative combustion of the molten metal without using an expensive protective gas when melting magnesium and a magnesium alloy, and therefore a high melting yield Can be dissolved in. Further, even when the flux is used, the amount used can be minimized. Further, when casting the molten magnesium alloy in the mold, without adding sulfur powder to prevent the molten surface immediately after casting from oxidative combustion, it can be cast in a good working environment, It is possible to obtain a magnesium alloy ingot having a small amount of non-metallic inclusions and good internal quality.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of an apparatus used when simultaneously carrying out a melting method and a casting method of the present invention.

FIG. 2 is a view showing an example of an apparatus of a conventional closed crucible furnace.

[Explanation of symbols]

1: Crucible 2: Protective crucible 3: Lid 4: Fireproof insulation 5: Furnace 6: Burner 7: Flame of combustion gas 8: Flux 9: Molten metal 10: Exhaust pipe 11: Induction heating device 12: Mold 13: Closed chamber body 14: Cover of closed chamber 15: Stand 16: Mold surface plate 17: Bed

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 3K059 AB15 AC76 AD03 AD07 AD08                       CD52                 4K001 AA38 FA14                 4K046 AA01 BA02 CD02

Claims (4)

[Claims] 1. A magnesium or magnesium alloy,
A method for melting magnesium and a magnesium alloy, which comprises melting magnesium or a magnesium alloy by heat generated by induction heating the crucible when melting using an iron crucible or an iron-based alloy crucible. 2. The inside of the crucible is provided by arranging the crucible and an induction heating device in the same closed chamber, and by using the induction heating device to induction-heat the crucible with an inert gas atmosphere in the chamber. 2. The method for melting magnesium and magnesium alloy according to claim 1, wherein the magnesium or magnesium alloy is melted. 3. A method for dissolving magnesium and a magnesium alloy according to claim 1, wherein a flux containing potassium chloride, magnesium chloride and calcium chloride is added and dissolved in the crucible. 4. The crucible, the induction heating device and the mold are arranged in the same closed chamber, and the inside of the chamber is filled with an inert gas atmosphere to induction-heat the crucible using the induction heating device. A method of casting magnesium and a magnesium alloy, which comprises melting magnesium or a magnesium alloy in a crucible and casting a molten metal of the melted magnesium or a magnesium alloy in a mold.