KR101858856B1 - High strength magnesium alloy having excellent fire-retardant, and method for manufacturing the same - Google Patents

Abstract

One aspect of the present invention relates to a high-strength magnesium alloy having excellent flame retardancy, comprising 2.0 to 13.0 wt% of Al, 0.1 to 0.5 wt% of Mn, 0.0015 to 0.02 wt% of B, 0.1 to 1.0 wt% of Y, and the remainder consisting of Mg and inevitable impurities. The volume fraction of a Mg-Al intermetallic compound includes greater than or equal to 10%. The average particle diameter of the Mg-Al intermetallic compound is in the range of 20 to 500 nm.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a high-strength magnesium alloy having excellent flame retardancy and a method of manufacturing the same.

The present invention relates to a high strength magnesium alloy excellent in flame retardancy and a method of manufacturing the same.

Because magnesium is the lightest metal in practical metals, it can be applied to portable electronic products such as smart phones, tablet PCs and notebooks, as a structural material for vehicles such as automobiles, trains, and aircrafts. Magnesium alloys with various elements added to magnesium Is attracting attention as an eco-friendly lightweight metal material.

Since the magnesium alloy has excellent castability, the casting products manufactured through the mold casting methods such as high-pressure casting, low-pressure casting and gravity casting have mainly been applied to practical products, and recently, they are manufactured through processing such as rolling or extrusion It is also promoting the development of products for all new products and expanding the market.

In general, alloying elements added to magnesium alloys for casting or magnesium alloys are similar, and the most commonly used magnesium alloys are AZ-based alloys containing Al and Zn or AM alloys containing Al and Mn Based alloy. The two types of alloys commonly contain Al to improve the castability and tensile strength of magnesium.

The AZ and AM magnesium alloys, which account for most of the commercial magnesium alloys, are suitable for manufacturing various casting products by improving the flowability of molten metal by Al addition, and are also suitable for billet casting and plate casting. However, the yield strength and the tensile strength are considerably lower than those of the competitive aluminum alloy, so that it is necessary to increase the thickness of the product or to modify the product shape.

In addition, the magnesium alloy has a high possibility of ignition due to its high oxygen affinity, which limits the use conditions.

Therefore, there is a demand for developing a high strength magnesium alloy having excellent flame retardancy and a manufacturing method thereof.

Korean Patent Publication No. 10-2015-0077494

One aspect of the present invention is to provide a high strength magnesium alloy having excellent flame retardancy and a method of manufacturing the same.

On the other hand, the object of the present invention is not limited to the above description. It will be understood by those of ordinary skill in the art that there is no difficulty in understanding the additional problems of the present invention.

An aspect of the present invention is a method for manufacturing a semiconductor device, comprising: 2.0 to 13.0% of Al, 0.1 to 0.5% of Mn, 0.0015 to 0.02% of B, 0.1 to 1.0% of Y, the balance of Mg and unavoidable impurities, Resistant magnesium alloy containing 10% or more of an intermetallic compound in a volume fraction and having an average particle size of 20 to 500 nm as the Mg-Al intermetallic compound.

In another aspect of the present invention, there is provided a method of manufacturing a honeycomb structure including, in weight percent, 2.0 to 13.0% of Al, 0.1 to 0.5% of Mn, 0.0015 to 0.02% of B, 0.1 to 1.0% of Y, ;

Casting the molten metal to obtain a magnesium alloy casting material;

Subjecting the magnesium alloy cast material to a solution treatment at a temperature of 370 to 490 캜 for 2 to 20 hours to obtain a magnesium alloy;

Cooling the magnesium alloy to 100 DEG C or less; And

And aging the cooled magnesium alloy at 150 to 250 DEG C for 2 to 48 hours. BACKGROUND OF THE INVENTION

In addition, the solution of the above-mentioned problems does not list all the features of the present invention. The various features of the present invention and the advantages and effects thereof can be understood in more detail with reference to the following specific embodiments.

According to the present invention, it is possible to provide a high-strength magnesium alloy having excellent flame retardancy and a method for producing the same.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a photograph of the microstructure of the magnesium alloy cast material of comparative material 1 (a) and inventive material 7 (b).
2 is a photograph of the microstructure after the solution treatment of the comparative material 1 is completed.
3 is a photograph of a microstructure after the solution treatment of the invention material 7 is completed.
FIG. 4 is a graph showing the results of measuring the hardness values of the comparative material 1 (a) and the inventive material 7 (b) according to the aging time at 200.degree.
5 is a photograph showing the microstructure of the magnesium alloy after the aging treatment of the comparative members 1 (a), 7 (b) and 5 (c).
6 is a graph showing a change in hardness value versus the aging time of Inventive material 7 and a change in Mg-Al intermetallic compound size within the crystal grain.
7 is a graph showing the volume fraction of Mg-Al intermetallic compound according to the aging time of Inventive Material 7. FIG.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art.

As a result of deep research to solve the problems of ignition characteristics and low strength of magnesium alloys, the present inventors have found that a large amount of intermetallic compounds can be finely distributed by additionally adding B and Y and aging treatment, Flame retardancy and high strength can be secured, and the present invention has been accomplished.

High strength magnesium alloy with excellent flame retardancy

Hereinafter, a high strength magnesium alloy having excellent flame retardancy according to one aspect of the present invention will be described in detail.

According to an aspect of the present invention, there is provided a high strength magnesium alloy excellent in flame retardancy, comprising 2.0 to 13.0% of Al, 0.1 to 0.5% of Mn, 0.0015 to 0.02% of B, 0.1 to 1.0% of Y, And an Mg-Al intermetallic compound in a volume fraction of 10% or more, and an average particle diameter of the Mg-Al intermetallic compound is 20 to 500 nm.

First, the alloy composition of the present invention will be described in detail. Hereinafter, the unit of each element content means weight% unless otherwise specified.

Al: 2.0 to 13.0%

Al increases the tensile strength and yield strength, and improves the castability by improving the fluidity of the alloy melt.

When the Al content is less than 2.0%, the above-mentioned effect is insufficient. On the other hand, when the Al content exceeds 13.0%, the brittleness can be increased and the workability and ductility can be reduced. Therefore, the Al content is preferably 2.0 to 13.0%, and more preferably 6.5 to 11.0%.

Mn: 0.1 to 0.5%

Mn is an element contributing to an increase in tensile strength by making fine grains by forming an intermetallic compound with Al. In addition, it plays a role of lowering the corrosion rate of magnesium by lowering Fe, which is a typical impurity element, unnecessary for the magnesium alloy through intermetallic compound formation.

When the Mn content is less than 0.1%, the above-mentioned effect is insufficient. On the other hand, when the Mn content exceeds 0.5%, brittleness due to excessive formation of the needle-shaped intermetallic compound may be caused.

B: 0.0015 to 0.02%

B (boron) has a very high melting point and its solubility in a magnesium phase or liquid phase is close to zero, so it is known as an element not commonly used in general magnesium alloys.

However, in the present invention, it is added to ensure flame retardancy and high strength. In particular, by adding B and Y to a magnesium alloy and aging treatment, it contributes to formation of a large amount of Mg-Al intermetallic compound, Flame retardancy and strength can be further improved as compared with the case where B is added alone. In addition, it can contribute to the reduction of the production cost and the environmental protection because it can reduce the use of the expensive SF ₆ gas which is used for prevention of the oxidation of the molten metal and the oxidation of the molten metal, and the SO ₂ gas which can cause environmental pollution.

When the B content is less than 0.0015%, the above-mentioned effect is insufficient. On the other hand, when the B content is more than 0.02%, the Al-B compound is formed in the grain boundaries and the ductility is reduced.

Therefore, the B content is preferably 0.0015 to 0.02%, more preferably 0.003 to 0.02%.

Y: 0.1 to 1.0%

Y is a element that binds to Al to form precipitates, contributes to strength improvement, and has a high oxygen affinity to firmly protect the surface of the molten metal to inhibit oxidation of the molten metal, and to improve flame retardancy even after solidification.

In addition, as described above, the addition of B and the aging treatment contributes to the formation of a large amount of Mg-Al intermetallic compounds, thereby improving not only the tensile strength but also the flame retardancy.

When the Y content is less than 0.1%, the above-mentioned effect is insufficient. On the other hand, if the Y content exceeds 1.0%, ductility may be reduced due to formation of a coarse Al-Y compound.

The remainder of the present invention is magnesium (Mg). However, in the ordinary manufacturing process, impurities which are not intended from the raw material or the surrounding environment may be inevitably incorporated, so that it can not be excluded. These impurities are not specifically mentioned in this specification, as they are known to any person skilled in the art of manufacturing. For example, there may be Fe, Cu, Ni, Ca, Na, Ba, F, S,

In this case, in addition to the above alloy composition, it may further include 0.3 to 3.0% by weight of Zn.

Zn: 0.3 to 3.0%

Zn is a solid solution strengthening element, which promotes the formation of Mg ₁₇ Al ₁₂ phase or improves the tensile strength by forming a separate intermetallic compound containing Zn such as Mg ₂ Zn.

When the Zn content is less than 0.3%, the above-mentioned effect is insufficient. On the other hand, when the Zn content exceeds 3.0%, a large amount of a separate intermetallic compound including Zn such as Mg ₂ Zn is formed to increase the brittleness, which may lead to a decrease in ductility and toughness.

Therefore, the Zn content is preferably 0.3 to 3.0%. Considering the improvement of the strength and the reduction of the brittleness, the more preferable range is from 0.5 to 1.5% by weight.

The Mg-Al intermetallic compounds according to one aspect of the present invention not only satisfy the above-mentioned alloy composition, but also contain Mg-Al intermetallic compounds in a volume fraction of 7.0% or more, and the average particle diameter of the Mg- To 500 nm.

When the main alloy element added to magnesium is Al, an Mg-Al intermetallic compound can be formed, and a typical Mg-Al intermetallic compound is Mg ₁₇ Al ₁₂ phase. Mg-Al intermetallic compounds play a role in ensuring high strength.

Since the maximum amount of Al or other alloying elements to be added to the magnesium alloy is smaller than the maximum amount of each of the alloying elements to Mg, most of the Al is contained in the Mg matrix rather than inducing the formation of intermetallic compounds, It is not a general phenomenon that an intermetallic compound is formed, and it is difficult to form a large amount of Mg-Al intermetallic compound. In the present invention, Mg and Al intermetallic compounds can be ensured to not less than 7.0% by additionally adding B and Y and aging treatment.

When the Mg-Al intermetallic compound is less than 7.0%, it is difficult to ensure high strength. The upper limit is not particularly limited, but if it exceeds 30%, the particle size of the Mg-Al intermetallic compound may become large and the brittleness may increase.

When the average particle diameter of the Mg-Al intermetallic compound is less than 20 nm, the fraction of the Mg-Al intermetallic compound is low and it is difficult to secure high strength. When the average particle diameter is more than 500 nm, the brittleness increases.

At this time, at least one of the Al-Mn intermetallic compound and the Al-Y intermetallic compound is further included, and the total amount thereof may be 5% or less in a volume fraction. If it exceeds 5%, the Mn and Y contents are excessive and the brittleness may increase.

At this time, The alloy may have an ignition temperature of 700 ° C or higher.

In addition, The alloy may have a hardness of 70 Hv or more.

In addition, The alloy may have a tensile strength of 130 MPa or more and an elongation of 3% or more.

Manufacturing method of high-strength magnesium alloy excellent in flame retardancy

Hereinafter, a method for producing a high strength magnesium alloy having excellent flame retardancy, which is another aspect of the present invention, will be described in detail.

According to another aspect of the present invention, there is provided a method of manufacturing a high strength magnesium alloy having excellent flame retardancy, comprising the steps of: preparing a molten metal satisfying the alloy composition; Casting the molten metal to obtain a magnesium alloy casting material; Subjecting the magnesium alloy cast material to a solution treatment at a temperature of 370 to 490 캜 for 2 to 20 hours to obtain a magnesium alloy; Cooling the magnesium alloy to 100 DEG C or less; And aging the cooled magnesium alloy at 150-250 < 0 > C for 2-48 hours.

Melt  Preparation phase

A molten metal satisfying the above alloy composition is prepared. It is not particularly limited, and it is possible to prepare a general magnesium alloy molten metal preparation.

For example, the above-described alloying elements are prepared in accordance with the indicated composition range, and then charged into a crucible for melting and then subjected to a melting operation. Since the melting point of the magnesium alloy is relatively low, any method such as gas, electric furnace, induction melting furnace, etc. may be applied.

In preparing the alloying elements, each alloy element may be prepared in a pure form, but it may be charged into the crucible in the form of a parent alloy in which Mn, B and Y are mixed with Mg or Al. B, Y, and Mn have high melting points, it is advantageous to melt them in the crucible in the form of parent alloy mixed with Mg or Al.

In addition, when the prepared dissolving material is charged into the crucible, it is advantageous to perform the dissolving work by charging the crucible in order from the element having a low melting point.

Casting step

The molten metal is cast to obtain a magnesium alloy cast material. The casting step is not particularly limited as in the case of the molten metal preparing step.

For example, a method using a movable mold and a method using a fixed mold can be used. Representative examples of the method using the movable mold include twin roll casting and belt casting using a movable mold such as twin roll or twin belt. Also, typical examples of the method using the fixed mold include continuous casting such as a billet casting or semi-continuous casting, and also casting such as high-pressure casting, low-pressure casting and gravity casting.

As the casting process, various methods as described above can be used. However, since boron or yttrium having a low solubility with respect to magnesium is added together with aluminum, it is advantageous to apply a casting method capable of increasing the cooling rate. In order to do this, the mold should be cooled with cooling water. When cooling water is applied, the mold surface should be maintained at room temperature or lower after the condensed water is removed, so that the condensed water on the surface of the mold is removed before casting.

Solution  Processing step

The magnesium alloy cast material is subjected to solution treatment at a temperature of 370 to 490 캜 for 2 to 20 hours to obtain a magnesium alloy. Since the Mg-Al intermetallic compound is formed in the magnesium alloy casting material, it is formed of a coarse Mg-Al or a mixed form with the Mg matrix (Lamellar Mg-Al) In order to employ the compound.

If the solution temperature is less than 370 ° C or the retention time is less than 2 hours, the entire Mg-Al intermetallic compound is difficult to be solved. If the solution temperature exceeds 490 ° C or the retention time exceeds 20 hours, the production cost increases Productivity may be deteriorated, and an oxidation phenomenon may occur before B and Y are added. Therefore, it is more preferable to carry out the reaction at a temperature of 400 to 460 DEG C for 2 to 20 hours.

Cooling step

The magnesium alloy is cooled to 100 DEG C or lower. So as to minimize the natural aging phenomenon that may appear before aging treatment.

At this time, the cooling rate may be 1 to 100 ° C / sec. So that the natural aging phenomenon that may occur during cooling is minimized and the dissolved Al element is not precipitated at random. For example, it is preferable to perform rapid cooling by forced blowing, water cooling, oil cooling, or the like.

Aging treatment step

The cooled magnesium alloy is subjected to aging treatment at 150 to 250 DEG C for 2 to 48 hours. In the microstructure of the cooled magnesium alloy after the solution treatment, most of the Al element added as the alloying element does not form a separate intermetallic compound by solid solution in the Mg matrix, so that the strength of the material can not be efficiently increased, In the present invention, a large amount of Mg-Al intermetallic compound is precipitated through aging to increase the strength and to secure excellent flame retardancy. However, when B and Y are combined in the range suggested in the present invention, a large amount of Mg-Al intermetallic compounds can be precipitated through the aging treatment described above.

Since the precipitation by the aging treatment is a solid-state reaction proceeding in the solid phase, it is possible to form an Mg-Al intermetallic compound having a particle shape, an average particle diameter, a volume fraction, etc. favorable to the improvement of strength and flame retardancy.

When the aging temperature is less than 150 ° C or the holding time is less than 2 hours, it is difficult to sufficiently secure the Mg-Al intermetallic compound. On the other hand, Mg-Al intermetallic compounds may be employed when the aging temperature exceeds 250 DEG C or the retention time exceeds 48 hours, resulting in an increase in production cost and a decrease in productivity. Therefore, it is preferable to perform the aging treatment at 150 to 250 DEG C for 2 to 48 hours. More preferably, the temperature and the holding time can be increased within the above temperature and holding time depending on the amount of Al added.

Hereinafter, the present invention will be described more specifically by way of examples. It should be noted, however, that the following examples are intended to illustrate the invention in more detail and not to limit the scope of the invention. The scope of the present invention is determined by the matters set forth in the claims and the matters reasonably inferred therefrom.

( Example  One)

A magnesium alloy casting having a thickness of 10 mm was cast by casting a molten metal having the composition shown in Table 1 below. The magnesium alloy cast material was solution-treated at 420 ° C for 4 hours, cooled to 20 ° C, and aged at 200 ° C for 12 hours to produce a magnesium alloy.

The Mg-Al intermetallic compound and the mechanical properties of the magnesium alloy were measured and are shown in Table 1 below. The size of the Mg-Al intermetallic compound was measured by the circle-equivalent diameter.

Except for the alloying element shown in Table 1, it was magnesium, and Mg-Al means Mg-Al intermetallic compound.

The ignition temperature was measured at a temperature at which the ignition occurred while raising the temperature inside the furnace while leaving a sample of 10 g in the form of a chip in the furnace in the atmosphere.

division Alloy composition (% by weight) Mg-Al Mechanical properties Ignition temperature
( ^o C) Al Mn B Y size
(nm) Fraction
(vol%) TS
(MPa) Hand
(%) Hardness
(Hv) Comparison 1 9 0.34 - - 193 2.6 113 5.2 59 530 Comparative material 2 3 0.05 0.013 1.23 178 1.7 113 5.2 48 624 Comparative material 3 6 0.21 0.001 0.41 205 2.1 121 4.2 53 590 Comparison 4 9 0.45 0.412 0.05 232 3.8 124 3.1 63 647 Comparative material 5 3 0.74 - 0.72 184 1.4 114 4.3 50 634 Comparative material 6 6 0.12 0.003 1.21 212 2.4 123 3.4 56 660 Comparison 7 9 0.33 - 0.21 228 3.1 125 3.2 61 612 Inventory 1 2.8 0.12 0.018 0.92 134 7.5 135 5.8 71 721 Inventory 2 2.7 0.32 0.012 0.63 128 8.1 138 6.2 72 712 Inventory 3 3.1 0.44 0.006 0.31 133 8.7 142 6.1 74 718 Invention 4 3.4 0.42 0.003 0.13 129 9.8 144 5.7 78 715 Invention Article 5 5.6 0.12 0.017 0.12 153 13.3 151 4.6 84 747 Inventions 6 6.2 0.3 0.012 0.54 161 14.4 155 5.8 87 733 Invention 7 6.2 0.4 0.006 0.81 154 14.7 158 4.7 88 742 Invention 8 5.8 0.42 0.002 0.88 139 13.8 152 4.4 85 739 Invention 9 8.5 0.12 0.013 0.14 176 19.1 164 3.5 103 783 Inventions 10 10.6 0.3 0.003 0.51 184 21.6 167 4.6 107 776 Invention invention 11 9.8 0.4 0.009 0.94 179 20.3 172 4.2 106 782 Invention 12 8.7 0.42 0.019 0.45 172 19.4 168 3.7 104 785

The inventive materials satisfying the alloy composition and the manufacturing conditions proposed in the present invention include those having an Mg-Al intermetallic compound in a volume fraction of 7.0% or more and an average particle diameter of the Mg-Al intermetallic compound of 20 to 500 nm Can be confirmed. Further, it can be confirmed that the flame retardancy is excellent at an ignition temperature of 700 ° C or higher, and the mechanical properties are also superior to the comparative materials.

On the other hand, the comparative materials satisfied the manufacturing conditions proposed in the present invention, but did not satisfy the alloy composition, so that it was confirmed that Mg-Al intermetallic compounds were not sufficiently secured. In addition, it can be confirmed that the flame retardancy is poor and the mechanical properties are also higher than those of the inventive materials.

( Example  2)

The changes in the manufacturing process of the comparative material 1 and the inventive material 7 shown in Table 1 were observed more closely.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a photograph of the microstructure of the magnesium alloy cast material of comparative material 1 (a) and inventive material 7 (b). The casting structure of the comparative member 1 is composed of a Mg-Al intermetallic compound (Coarse Mg-Al), Mg base structure + Mg-Al intermetallic compound mixed structure (Lamellar Mg-Al), Al- The Al-Y intermetallic compound (Al-Y) was observed in addition to the above-mentioned structure, and the boron-containing intermetallic compound was observed separately in the casting structure of invention material 7 in which yttrium and boron were added It was not.

When the comparative material having the cast structure and the inventive material are subjected to the solution treatment, most of the Mg-Al intermetallic compounds except for Al-Mn and Al-Y intermetallic compounds are solidified as the base structure as shown in FIGS. 2 and 3 It is not observed. The optical structures of the casting structure and the solution treatment material are almost similar except for the presence or absence of the Al-Y intermetallic compound, but show a large difference in the aging treatment material.

These differences can be confirmed first in the hardness measurement results according to aging time. As shown in FIG. 4, the hardness values of the comparative material 1 (a) and the inventive material 7 (b) were measured at 200 ° C. according to the aging time. As a result, it can be seen that the hardness of the inventive material was remarkably high. The value shows little change with aging time, but it can be seen that the hardness value of the inventive material greatly increases when the aging time exceeds 1 hour. Particularly, after 3 hours, the maximum hardness value corresponding to peak aging is shown, and the hardness value at this time is less than 1 hour, which shows a value of 97 ~ 107Hv which is 60% higher than the average hardness of the aged cast material have. In addition, the maximum hardness value of invention material 7 is about two times the maximum hardness value of the comparative material.

5 is a photograph showing the microstructure of the magnesium alloy after the aging treatment of the comparative members 1 (a), 7 (b) and 5 (c). It can be confirmed that a large amount of Mg-Al intermetallic compound having a size of several tens of nanometers is precipitated in Inventive Material 7, which shows that the hardness value of the inventive material is greatly increased.

FIG. 6 shows changes in the hardness value (rhombus) and the size of the Mg-Al intermetallic compound (square) in the crystal grains with respect to the aging time of the inventive material 7, The volume fraction of the compound is shown. As shown in FIGS. 6 and 7, when the inventive material 7 is aged for 3 hours or more, it can be seen that the average size and the volume fraction of the Mg-Al intermetallic compounds have grown to 20 nm or more and 10 vol% or more, respectively.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. It will be possible.

Claims (11)

Wherein the alloy contains 2.0 to 13.0% of Al, 0.1 to 0.5% of Mn, 0.0015 to 0.02% of B, 0.1 to 1.0% of Y, the balance of Mg and unavoidable impurities,
Mg-Al intermetallic compound in a volume fraction of not less than 7.0%
Wherein the Mg-Al intermetallic compound has an average particle diameter of 20 to 500 nm and is excellent in flame retardancy.
The method according to claim 1,
Wherein the magnesium alloy further contains 0.5 to 1.5% of Zn by weight, and the magnesium alloy has a high flame retardancy.
The method according to claim 1,
Wherein the magnesium alloy further comprises at least one of an Al-Mn intermetallic compound and an Al-Y intermetallic compound, and the total content thereof is 5% or less by volume in a high-strength magnesium alloy excellent in flame retardancy.
The method according to claim 1,
The magnesium alloy is a high-strength magnesium alloy having an ignition temperature of 700 ° C or more and excellent flame retardancy.
The method according to claim 1,
The magnesium alloy is a high strength magnesium alloy having a hardness of 70 Hv or more and excellent flame retardancy.
The method according to claim 1,
The magnesium alloy has a high tensile strength of at least 130 MPa and an elongation of at least 3%.
Preparing a melt containing 2.0 to 13.0% of Al, 0.1 to 0.5% of Mn, 0.0015 to 0.02% of B, 0.1 to 1.0% of Y, and the balance of Mg and unavoidable impurities in terms of% by weight;
Casting the molten metal to obtain a magnesium alloy casting material;
Subjecting the magnesium alloy cast material to a solution treatment at a temperature of 370 to 490 캜 for 2 to 20 hours to obtain a magnesium alloy;
Cooling the magnesium alloy to 100 DEG C or less; And
And aging the cooled magnesium alloy at 150 to 250 DEG C for 2 to 48 hours.
8. The method of claim 7,
Wherein the molten metal further contains 0.5 to 1.5% of Zn in terms of% by weight, and the flame retardancy is excellent.
8. The method of claim 7,
Wherein the step of preparing the molten metal is carried out by charging the crucible in the form of a parent alloy in which Mn, B and Y are mixed with Mg or Al.
8. The method of claim 7,
Wherein the step of preparing the molten metal is carried out by charging the crucible sequentially from an element having a low melting point.
8. The method of claim 7,
Wherein the cooling step is performed at a cooling rate of 1 to 100 캜 / second.

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