KR20200076105A - Manufacturing method for casted magnesium alloy - Google Patents

Abstract

According to one aspect of the present invention, a manufacturing method of a casted magnesium alloy comprises: a molten metal manufacturing step of inserting a magnesium alloy ingot or a scrap into a dissolution furnace with the temperature range of 650-750 °C to manufacture a magnesium alloy molten metal containing 0.2-1.0 wt% of Ca; 0.1-0.5 wt% of Y; and residual Mg and other impurities; and a casting step of supplying the magnesium alloy molten metal to the mold to manufacture a casted magnesium alloy. The molten metal manufacturing step supplies protective gas including SO_2 gas into the magnesium alloy molten metal only when the temperature of the magnesium alloy molten metal is 300 °C or higher, and is able to selectively control the concentration of the SO_2 gas contained in the protective gas in accordance with whether the insertion hole of the dissolution furnace is opened or closed. According to the present invention, it is possible to effectively secure properties and surface quality of the final magnesium alloy product.

Description

Manufacturing method for magnesium-based alloy casting material {Manufacturing method for casted magnesium alloy}

The present invention relates to a method of manufacturing a magnesium-based alloy casting material, and more particularly, to a method of manufacturing a magnesium-based alloy casting material capable of effectively securing the surface quality of a final product.

Magnesium-based alloy is a material that is in the spotlight as a lightweight material for transportation equipment as well as the electronic and IT industries due to its light weight, excellent specific strength, non-rigidity, and excellent vibration absorption. However, the magnesium-based alloy has such excellent physical properties, but technical limitations exist in applications in various fields due to ignition problems, low corrosion resistance, and poor formability during the manufacturing process. In particular, ignition occurring during the manufacturing process of the magnesium-based alloy may cause serious problems in safety, and it is urgent to develop a technology capable of effectively controlling it.

As a method for suppressing the ignition phenomenon of the molten magnesium-based alloy, a method using a flux and a method using a shield gas are widely used.

Representative materials used as solvents are chlorides such as MgCl ₂ and KCl, and these solvents block the reaction of magnesium and oxygen contained in the magnesium-based alloy molten metal to suppress the occurrence of ignition during the process. The solvent is advantageous in terms of suppressing ignition of the magnesium-based alloy, but the reaction product formed by reflecting the solvent and the magnesium-based alloy molten metal remains in the magnesium-based alloy and is not preferable in terms of securing corrosion resistance of the final product.

SF ₆ gas is a representative material used as a protective gas. SF ₆ gas is a toxic substance that is not only harmful to the human body, but is also a substance that causes damage to equipment by corrosion. In addition, SF ₆ gas is a representative greenhouse gas, and it is also expected to be strictly limited in its use in the future in terms of environmental protection.

In particular, when components such as calcium (Ca) and yttrium (Y) are added to the magnesium alloy molten metal to secure corrosion resistance and processability, these components react with fluorine (F) contained in the protective gas to cause CaF ₂ , YF, Intermetallic compounds such as MgCaF are formed, and these intermetallic compounds may remain in the magnesium-based alloy cast material to cause surface defects in the final product. Therefore, it is urgently required to introduce a method for manufacturing a magnesium-based alloy cast material capable of effectively securing physical properties and process safety while effectively securing the surface quality of the final product.

Republic of Korea Patent Publication No. 10-2010-0071512 (2010.06.29. public)

According to one aspect of the present invention, a method of manufacturing a magnesium-based alloy cast material may be provided.

The subject of this invention is not limited to the above-mentioned content. Those skilled in the art will have no difficulty in understanding the additional subject matter of the present invention from the general contents of this specification.

Method of manufacturing a magnesium-based alloy cast material according to an aspect of the present invention, after charging the magnesium-based alloy ingot or scrap to the melting furnace, heated to a temperature range of 650 ~ 750 ℃, by weight, calcium (Ca): 0.2 ~ A molten metal preparation step of manufacturing a magnesium-based alloy molten metal containing 1.0%, remaining magnesium (Mg) and other impurities; And a casting step of supplying the magnesium alloy molten metal to a mold to produce a magnesium alloy casting material, wherein the molten metal manufacturing step is performed only when the temperature of the magnesium alloy molten metal is 300°C or higher. A protective gas containing sulfur dioxide (SO ₂ ) gas is supplied, and the concentration of the anti-oxidation (SO ₂ ) gas contained in the protective gas can be selectively adjusted according to whether the furnace opening is opened or closed.

When the melting furnace charging port is closed, the first protective gas in which 0.1 to 1.0 vol% of sulfur dioxide (SO ₂ ) gas is mixed with any one selected from nitrogen (N ₂ ) gas or dry air is the magnesium alloy. When supplied to the molten metal, and the opening of the furnace is opened, the second protection in which any one selected from nitrogen (N ₂ ) gas or dry air and 1.5 to 5.0% by volume of sulfur dioxide (SO ₂ ) gas are mixed Gas can be supplied to the magnesium alloy molten metal.

In the casting step, nitrogen (N ₂ ) gas or any one selected from dry air (dry air) and 1.5 to 5.0% by volume of sulfur dioxide (SO ₂ ) gas mixed protective gas may be supplied to the magnesium alloy molten metal being coagulated. have.

The magnesium alloy molten metal, by weight, aluminum (Al): 2.5 to 3.5%, zinc (Zn): 0.5 to 1.5%, yttrium (Y): 0.1 to 0.5% and manganese (Mn): 0.3% or less It may further include one or more.

The thickness of the magnesium oxide (MgO) protective film formed on the surface layer portion of the magnesium alloy casting material may be 3 μm or less.

The solving means of the above problem does not list all the features of the present invention, and various features of the present invention and the advantages and effects thereof may be understood in more detail with reference to specific embodiments below.

According to an aspect of the present invention, it is possible to provide a method of manufacturing a magnesium-based alloy cast material that effectively secures process stability when manufacturing a magnesium-based alloy cast material, and can effectively secure physical properties and surface quality of a final magnesium-based alloy product.

FIG. 1 is a photograph of the surface side cross-section of a solidified specimen observed with a scanning electron microscope after supplying a protective gas mixed with 0.5% by volume of SO ₂ gas to N ₂ gas and heating for 120 minutes.
FIG. 2 is a photograph of the surface side cross-section of the solidified specimen observed with a scanning electron microscope after supplying a protective gas containing 0.5% by volume of SF ₆ gas to N ₂ gas and heating for 120 minutes.

The present invention relates to a method for manufacturing a magnesium-based alloy cast material, and the following will describe preferred embodiments of the present invention. The embodiments of the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The present embodiments are provided to those skilled in the art to further detail the present invention.

The magnesium-based alloy cast material of the present invention contains magnesium (Mg) as a main component, and may essentially include 0.2 to 1.0% by weight of calcium (Ca) in order to secure properties such as processability. In addition, the magnesium-based alloy cast material of the present invention is 2.5 to 3.5% by weight of aluminum (Al), 0.5 to 1.5% by weight of zinc (Zn), 0.1 to 0.5% by weight of yttrium (Y) to secure physical properties such as strength and corrosion resistance ) And 0.3% by weight or less of manganese (Mn) may be selectively included, and may include impurities inevitably included in the manufacturing process. Here, the weight percent representing the content of each component element is based on the total weight of the magnesium-based alloy cast material.

Hereinafter, the manufacturing method of the present invention will be described in more detail.

According to an aspect of the present invention, a molten metal manufacturing step for manufacturing a magnesium-based alloy molten metal; And a casting step of injecting the magnesium-based alloy molten metal into a mold to produce a magnesium-based alloy casting material.

Molten metal manufacturing

Magnesium-based alloy ingots or scraps are prepared for the production of magnesium-based alloy molten metal. As described above, the magnesium-based alloy cast material of the present invention essentially contains 0.2 to 1.0% by weight of calcium (Ca), 2.5 to 3.5% by weight of aluminum (Al), and 0.5 to 1.5% by weight of zinc (Zn). , 0.1 to 0.5% by weight of yttrium (Y) and 0.3% by weight or less of manganese (Mn) may further include one or more, thus preparing a magnesium-based alloy ingot or scrap to match these component contents.

The prepared magnesium-based alloy ingot or scrap may be preheated at a temperature of about 200° C. to remove moisture that may be present on the surface of the ingot and scrap, and these magnesium-based alloy ingots or scraps may be charged and heated in a melting furnace. If necessary for the adjustment of the components of the magnesium alloy molten metal, etc., other additives may be charged together. The magnesium-based alloy ingot or scrap charged in the melting furnace is heated to a temperature range of 650 to 750°C by an electric resistance heating method, and may be provided as a magnesium-based alloy molten metal.

When heating the magnesium-based alloy ingot or scrap, a protective gas including sulfur dioxide (SO ₂ ) gas may be supplied. The protective gas of the present invention may be a mixed gas in which sulfur dioxide (SO ₂ ) gas is mixed with any one selected from nitrogen (N ₂ ) gas or dry air. Here, dry air may mean air that does not contain moisture. In addition, the protective gas of the present invention may include impurities that are inevitably introduced during the process conditions, but it is possible to entirely exclude that the fluorinated gas is contained in the protective gas.

While the present invention excludes the use of fluorinated gas, since the mixed gas in which sulfur dioxide (SO ₂ ) gas is mixed at a certain content is used as a protective gas, the protective film containing magnesium oxide (MgO) as a main component is a magnesium-based alloy. It is possible to effectively suppress the formation of thick on the surface side of the molten metal and the casting material. When supplying a protective gas containing a fluorinated (SF ₆ ) gas, MgF ₂ and CaF ₂ are formed in the protective film to form a relatively loose protective film structure, whereas protection comprising sulfur dioxide (SO ₂ ) gas This is because when the gas is supplied, the magnesium oxide (MgO) protective film structure is densely formed by MgS formed together with the magnesium oxide (MgO).

In addition, since the magnesium alloy molten metal of the present invention contains calcium (Ca), when a protective gas containing a fluorinated component is supplied to the magnesium alloy molten metal, CaF ₂ , MgCaF and YF are formed on the surface side of the magnesium alloy casting material. Intermetallic compounds such as may be formed. Since these intermetallic compounds remain in the final product and cause surface defects, it is desirable to actively suppress the formation of these intermetallic compounds. While the present invention excludes the use of fluorinated gas, since the mixed gas in which sulfur dioxide (SO ₂ ) gas is mixed at a certain content is used as a protective gas, the formation of intermetallic compounds such as CaF ₂ , MgCaF and YF is actively suppressed. And can effectively secure the surface quality in the final product.

The first protective gas of the present invention can supply a protective gas containing sulfur dioxide (SO ₂ ) gas only when the magnesium-based alloy molten metal is heated to a temperature range of 300° C. or higher. This is because when the temperature of the magnesium-based alloy molten metal is 300° C. or lower, the risk of ignition of magnesium is low, so that the working stability can be sufficiently secured without supply of a protective gas.

In addition, the present invention can be supplied by adjusting the fraction of sulfur dioxide (SO ₂ ) gas contained in the protective gas depending on whether the inlet of the melting furnace is opened.

When the inlet of the melting furnace is closed, since the inside of the melting furnace is made of a thermodynamically closed system, oxygen inflow from the outside into the inside of the melting furnace is blocked. Therefore, even if the protective gas contains a relatively small amount of sulfur dioxide (SO ₂ ) gas, it is possible to effectively suppress the ignition of magnesium, so the present invention provides a nitrogen (N ₂ ) gas or dry air ( dry air) and a first protective gas in which 0.1 to 1.0% by volume of sulfur dioxide (SO ₂ ) gas is mixed may be supplied to the melting furnace.

When the fraction of the sulfur dioxide (SO ₂ ) gas contained in the first protective gas is less than a certain level, the effect of preventing the ignition of magnesium by the sulfur dioxide (SO ₂ ) gas is insufficient, so the present invention is included in the first protective gas. The fraction of sulfur dioxide (SO ₂ ) gas may be limited to 0.1% by volume or more. On the other hand, when the fraction of the sulfur dioxide (SO ₂ ) gas contained in the first protective gas exceeds a certain level, the effect of suppressing the formation of magnesium oxide (MgO) is saturated, while excessive sulfur dioxide (SO ₂ ) gas is used. Since problems such as safety hazards of workers and environmental pollution may occur, the present invention can limit the fraction of sulfur dioxide (SO ₂ ) gas contained in the first protective gas to 1.0% by volume or less.

On the other hand, when the charging port of the melting furnace is opened, since the inside of the melting furnace is made of a thermodynamically open system, oxygen can be introduced into the melting furnace from the outside. Therefore, in order to prevent ignition of magnesium, a relatively large amount of sulfur dioxide (SO ₂ ) may be required compared to the case where the charging port of the melting furnace is opened. Accordingly, the present invention provides a second protection in which 1.5 to 5.0% by volume of sulfur dioxide (SO ₂ ) gas is mixed with any one selected from nitrogen (N ₂ ) gas or dry air when the inlet of the melting furnace is opened. Gas can be supplied into the melting furnace.

If the fraction of sulfur dioxide (SO2) gas contained in the second protective gas is less than 1.5% by volume, it is not sufficient to prevent ignition of magnesium, and the fraction of sulfur dioxide (SO ₂ ) gas contained in the second protective gas is 5.0% by volume. If exceeded, the effect of suppressing the formation of magnesium oxide (MgO) is saturated, while the use of excessive sulfur dioxide (SO ₂ ) gas is undesirable in terms of worker safety and environmental pollution.

casting

The magnesium-based alloy molten metal manufactured under the above conditions can be supplied to the mold through a tundish and a nozzle after being maintained at a constant temperature range in a heat insulating furnace.

The magnesium-based alloy molten metal supplied to the insulating furnace may be insulated in a temperature range of 650 to 750° C. Since the inside of the insulating furnace is a closed space, protective gas having the same conditions as the first protective gas described above may be supplied. In addition, since the magnesium-based alloy molten metal moving through the tundish and the nozzle is in contact with the atmosphere, a protective gas having the same conditions as the above-described second protective gas may be supplied.

The magnesium alloy molten metal supplied through the nozzle may be supplied to a mold and provided as a casting material having a constant shape. The magnesium-based alloy cast material is generally manufactured to have a plate shape, but the shape of the magnesium-based alloy cast material of the present invention is not necessarily limited thereto.

After passing through the mold, the magnesium alloy casting material that is solidifying is still in a high temperature condition, and since it is in direct contact with the atmosphere, a protection gas having the same conditions as the second protective gas described above may be supplied to provide the magnesium alloy casting material.

The magnesium alloy cast material manufactured by the above-described manufacturing method can actively limit the thickness of the protective film mainly containing magnesium oxide (MgO) formed on the surface layer side, and the thickness of the protective film mainly containing magnesium oxide (MgO) is 3 μm or less. Can. In addition, the magnesium alloy cast material manufactured by the above-described manufacturing method may not contain a fluorinated intermetallic compound.

Hereinafter, the present invention will be described in more detail through examples.

(Example 1)

A magnesium-based alloy containing 0.5 wt% of calcium (Ca) was charged to an experimental melting furnace, and then heated at a temperature of about 700° C. to prepare a magnesium-based alloy molten metal under the conditions described in Table 1 below. In Table 1 below, Condition 1 is a case where molten metal heating is performed by supplying a protective gas in which 0.5% by volume of SO ₂ gas is mixed with N ₂ gas, and Condition 2 is 0.5% by volume of SF ₆ gas mixed with N2 gas. This is the case when molten metal is heated by supplying the protected gas. In each condition, the protective gas was continuously supplied into the melting furnace during the heating of the molten metal. 10 minutes, 60 minutes, and 120 minutes under each protective gas supply condition, the magnesium-based alloy molten metal was discharged to the outside of the melting furnace, and the results of observing the surface layers of the specimens in which these magnesium-based alloy molten metals were solidified are shown in Table 1 together. . After the magnesium-based alloy molten metal solidified specimen was processed with a FIB (Focused Ion Beam), the thickness of the oxide protective film formed on the surface of each specimen was measured using a scanning electron microscope (SEM).

division MgO protective film thickness (㎛) 30 minutes heating 60 minutes heating 120 minutes heating Condition 1 0.1 0.3 1.2 Condition 2 2.2 3.8 9.7

As shown in Table 1, in the case of condition 2 using a protective gas containing SF ₆ gas, it was confirmed that a magnesium oxide (MgO) protective film was formed to be significantly thicker than condition 1 using a protective gas containing SO ₂ gas. Can.

FIG. 1 is a photograph of a surface-side cross section of a specimen solidified after heating for 120 minutes under condition 1, and FIG. 2 is a scanning electron microscope of a surface-side cross section of the specimen solidified after heating for 120 minutes under condition 2. It is one picture. In addition to the magnesium oxide (MgO) film being thickly formed on the surface layer portion of the specimen under condition 2, a fluorinated compound (MgF ₂ ) is formed directly under the protective film of the magnesium oxide (MgO), while magnesium oxide (MgO) is formed on the surface layer portion of the specimen under condition 1 ) Not only is the protective film thinly formed. It can be seen that no intermetallic compound was formed near the magnesium oxide (MgO) protective film.

(Example 2)

After charging the magnesium-based alloy containing 0.5 wt% of calcium (Ca) into an experimental melting furnace, heating at a temperature of about 700° C. and supplying a protective gas under the conditions shown in Table 2 below to prepare a magnesium-based alloy molten metal. When the magnesium-based alloy was dissolved, the furnace conditions were controlled by simulating the opening and closing environment of the melting furnace, and under each condition, ignition in the magnesium-based alloy melt was visually observed. In the middle of the total heating time of 2 hours and 30 minutes, a 30 minute charging opening time was introduced, and the protective gas was supplied by adjusting the fraction of sulfur dioxide (SO ₂ ) gas contained in the protective gas in each time period.

Condition Closed (1 hour) Open (30 minutes) Closed (1 hour) Ignition occurred A 0.5% by volume SO2-N2 0.5% by volume SO2-N2 0.5% by volume SO2-N2 O B 0.5% by volume SO2-N2 2.0% by volume SO2-N2 0.5% by volume SO2-N2 X c 0.5% by volume SO2-N2 2.0% by volume SO2-N2 0.05% by volume SO2-N2 O

As shown in Table 2, in the case of condition B that satisfies the protective gas supply condition of the present invention, when the ignition of the magnesium-based alloy molten metal does not occur, conditions A and C that do not satisfy the protective gas supply condition of the present invention In this case, it can be confirmed that ignition of the magnesium-based alloy melt occurred.

Therefore, according to an aspect of the present invention, it is possible to provide a method of manufacturing a magnesium-based alloy cast material that effectively secures process stability when manufacturing a magnesium-based alloy cast material, and can effectively secure physical properties and surface quality of a final magnesium-based alloy product. .

Although the present invention has been described in detail through the above embodiments, other types of embodiments are possible. Therefore, the technical spirit and scope of the claims set forth below are not limited to the embodiments.

Claims (5)

After charging the magnesium-based alloy ingot or scrap to the melting furnace, heating it to a temperature range of 650 to 750°C, and by weight, calcium (Ca): 0.2 to 1.0%, magnesium containing magnesium (Mg) and other impurities A molten metal manufacturing step for manufacturing an alloy molten metal; And
Including the casting step of manufacturing the magnesium alloy casting material by supplying the magnesium alloy molten metal to the mold,
The molten metal production step,
A protective gas containing sulfur dioxide (SO ₂ ) gas is supplied to the magnesium alloy molten metal only when the temperature of the magnesium alloy molten metal is 300° C. or higher,
Method for manufacturing a magnesium-based alloy casting material to selectively adjust the concentration of the gas (SO ₂ ) gas contained in the protective gas depending on whether the melting furnace opening and closing. According to claim 1,
The molten metal production step,
When the melting furnace charging port is closed, the first protective gas in which 0.1 to 1.0 vol% of sulfur dioxide (SO ₂ ) gas is mixed with any one selected from nitrogen (N ₂ ) gas or dry air is the magnesium alloy. Supply to the molten metal,
When the melting furnace charging port is opened, the magnesium alloy is used as a second protective gas in which 1.5 to 5.0% by volume of sulfur dioxide (SO ₂ ) gas is mixed with any one selected from nitrogen (N ₂ ) gas or dry air. Method for manufacturing magnesium alloy casting material supplied to molten metal. According to claim 1,
The casting step,
Supplying a protective gas mixed with nitrogen (N ₂ ) gas or any one selected from dry air and 1.5 to 5.0% by volume of sulfur dioxide (SO ₂ ) gas to the molten magnesium alloy, which is a magnet? Method for manufacturing an alloy casting material. According to claim 1,
The magnesium alloy molten metal, by weight, aluminum (Al): 2.5 to 3.5%, zinc (Zn): 0.5 to 1.5%, yttrium (Y): 0.1 to 0.5%, and manganese (Mn): 0.3% or less Method of manufacturing a magnesium-based alloy cast material further comprising one or more of. According to claim 1,
Method of manufacturing a magnesium-based alloy cast material, the thickness of the magnesium oxide (MgO) protective film formed on the surface layer portion of the magnesium-based alloy cast material is 3 μm or less.

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