KR101223045B1 - Magnesium inactivating materal and method for manufacturing magnesium alloy using the magnesium inactivating materal - Google Patents

Abstract

PURPOSE: A magnesium inactivating agent and a magnesium alloy production method using the magnesium inactivating agent are provided to reduce the spontaneous ignition of chips by forming a dense composite oxide layer on the surface of a molten metal to improve flame retardancy. CONSTITUTION: A magnesium alloy production method using a magnesium inactivating agent comprises the steps of: forming the magnesium inactivating agent dissolvable under 750°C, forming molten magnesium alloy including at least magnesium, putting the magnesium inactivating agent in the molten magnesium alloy, and processing the molten metal including the magnesium inactivating agent through a casting to produce a magnesium alloy cast material. The magnesium inactivating agent comprises 6-41.6 wt% of Ca, 6-45 wt% of Y, and the remaining amount of Mg and inevitable impurities, where the contents of Ca and Y satisfy YΔ64.3-1.4 Ca.

Description

Magnesium inactivating materal and method for manufacturing magnesium alloy using the magnesium inactivating materal}

The present invention relates to a magnesium deactivator, more specifically, a magnesium deactivator input to suppress an activation reaction of magnesium when preparing a magnesium alloy, and a method of producing magnesium using the magnesium deactivator.

Magnesium alloy is the lightest alloy with high specific strength, and can be applied to various casting and processing processes. It is applicable to almost all fields requiring weight reduction such as automobile parts and electromagnetic parts and has a wide range of applications. Magnesium alloys, however, are electrochemically low-potential, highly active metals, and have a strong active reaction upon contact with oxygen or water. In commercial alloys, the ignition temperature does not exceed 550 ° C, which sometimes causes fire. There is still a limit in terms of reliability. Because of this, its application range is still limited compared to its potential, and it cannot be used especially for applications requiring safety.

Due to this active reaction of magnesium alloy, inert atmosphere should be created by using inert gas such as flux or CO ₂ + SF ₆ during melting. Since the flux used for dissolving and refining is chloride-based, there is a problem that residual chlorine remains inside the material and greatly degrades corrosion resistance when the melt treatment conditions are not met. Instead of using flux to solve this disadvantage, a method of dissolving and casting in a mixed atmosphere of SF ₆ , CO ₂ and Air is effective. However, SF ₆ is classified as a global greenhouse-induced substance with a global warming effect of 23,900 times that of CO ₂ , and is expected to be regulated in the future.

In order to solve this problem more fundamentally, researches to improve oxidation resistance of magnesium alloy itself have been conducted to improve the ignition temperature of magnesium alloy, especially by adding Ca, Be and rare earth metals. Conventionally, Ca is mainly used among the alloying elements added to the magnesium oxide alloy, because the price of the Ca element is cheaper than the rare earth metal, it is not toxic, and the ignition temperature is increased relative to the amount added. However, in order to dissolve Ca in a molten alloy, Ca must be maintained at a high temperature of 800 ° C. or higher. At this time, magnesium having a low melting point may cause an activation reaction such as ignition. In addition, it is very expensive to keep the temperature of the molten metal at a high temperature, so it is very difficult to manufacture a magnesium alloy for a small-scale producer that cannot increase the temperature of the molten metal. This will cause the economy to fall.

Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a method capable of maximally inhibiting the activation reaction of magnesium when producing an alloy containing magnesium as an active metal as a main component.

In addition, an object of the present invention is to provide a method for producing a magnesium alloy that enables an environmentally friendly manufacturing process that does not use a protective gas that is an environmental pollutant such as SF ₆ .

In addition, an object of the present invention is to provide a method for producing a magnesium alloy that can provide economical and safety by lowering the temperature of the molten metal as much as possible when producing an alloy containing magnesium as an active metal.

In order to achieve the above object, the present invention provides a configuration of adding a magnesium deactivator to suppress the activation reaction of magnesium in the manufacturing step of the magnesium alloy.

The magnesium deactivator according to the present invention is added to suppress the activation reaction of magnesium in the manufacturing step of the magnesium alloy, 6% to 41.6% by weight of Ca, 6% to 45% by weight of Y, the balance Mg And other unavoidable impurities, and the content of Ca and Y is characterized by the following equation.

Equation: Y ≤ 64.3-1.4Ca (wt%)

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In addition, the magnesium deactivator comprises 6% to 33.8% by weight of Ca, 6% to 42.2% by weight of Y, the balance of Mg and other unavoidable impurities, the content of Ca and Y is It is preferable to follow.

Equation: Y ≤ 50.0-1.3Ca (wt%)

In addition, the present invention provides a method for producing a magnesium alloy using a magnesium deactivator:

Forming a magnesium deactivator soluble at 750 ° C. or lower;

Forming a magnesium alloy melt containing at least magnesium;

Injecting a magnesium deactivator soluble in the magnesium alloy melt at 750 ° C. or lower;

Manufacturing a molten magnesium alloy casting material by using a predetermined casting method for the molten metal including the magnesium deactivator,

The magnesium deactivator comprises 6% to 41.6% by weight of Ca, 6% to 45% by weight of Y, the balance of Mg and other unavoidable impurities, the content of Ca and Y according to the following equation It is characterized by.

Equation: Y ≤ 64.3-1.4Ca (wt%)
In addition, the magnesium deactivator comprises 6% to 33.8% by weight of Ca, 6% to 42.2% by weight of Y, the balance of Mg and other unavoidable impurities, the content of Ca and Y is It is preferable to follow.

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Equation: Y ≤ 50.0-1.3Ca (wt%)

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The reason for limiting the content of each component in the magnesium alloy according to the present invention is as follows.

Calcium (Ca)

When the content of Ca is small, the amount of magnesium deactivator added to obtain a magnesium alloy of a desired composition is increased and the alloy to be added is diluted, so that Ca is preferably contained by 6% by weight or more. In addition, when the content of Ca is too high, the melting temperature of the magnesium deactivator is high, which makes it difficult to achieve the purpose of lowering the temperature of the molten metal in the manufacture of the magnesium alloy. Therefore, Ca of the magnesium deactivator is preferably contained at 41.6% by weight, preferably 33.8% by weight or less.

Yttrium (Y)

When the content of Y is small, the amount of magnesium deactivator added to obtain a magnesium alloy of a desired composition is increased and the alloy to be added is diluted, so that Y is preferably contained by 6% by weight or more. In addition, when the content of Y is too high, the melting temperature of the magnesium deactivator is high, which makes it difficult to achieve the purpose of lowering the temperature of the molten metal in the manufacture of the magnesium alloy. Therefore, the Y of the magnesium deactivator is preferably included at 45% by weight, preferably 42.2% by weight or less.

Total content of Ca-Y

When calcium and yttrium are added in combination, flame retardancy and corrosion resistance are significantly improved compared to alloys in which calcium and yttrium are separately added. This is because calcium oxide and yttrium oxide form a dense protective film on the surface of the solid and liquid magnesium alloy to effectively suppress the reaction with external oxygen. In addition, when a small amount of calcium and yttrium is added in combination with an alloy added with calcium alone, corrosion resistance may also be improved. On the other hand, the melting point of calcium and yttrium in Figures 1 and 2 is 840 ℃ and 1522 ℃, respectively, relatively high compared to magnesium, so in order to add calcium and yttrium to the magnesium alloy should be raised to about 840 ℃ or more. In the case of general melting and casting companies, heating a large amount of molten metal to 840 ° C. or higher means a large increase in manufacturing cost. Therefore, a method of directly injecting calcium and yttrium into the molten metal is not preferable. Therefore, the present invention prepared magnesium inactivation to effectively alloy calcium and yttrium in the magnesium alloy melt while maintaining the existing equipment and process conditions in the general melting and casting site.

In addition, as shown in Figure 3, at 700 ° C Mg-Al-Ca state diagram (Fig. 3) to add a calcium and yttrium in the region shown in gray to prepare a magnesium deactivator, and the magnesium deactivator to the magnesium alloy When added, alloying can be easily performed at a dissolution temperature of about 700 ° C. In FIG. 3, the equation obtained from the straight line 1 is as follows, and the amount of yttrium is preferably controlled within the range in which the equation 1 is satisfied according to the amount of calcium added. For example, when 30% by weight of calcium is added, yttrium should be controlled to within 22% by weight.

Equation 1

Y (wt.%) ≤ 64.3-1.4 Ca (wt.%)

More preferably, it is preferable to control the content of calcium and yttrium according to equation (2) obtained from straight line 2 corresponding to the liquid single phase region.

Equation 2

Y (wt.%) ≤ 50.0-1.3 Ca (wt.%)

On the other hand, when aluminum is added to a magnesium deactivator having a composition of Mg-Ca-Y, coarse Al ₂ Y (melting point: 1490 ° C.) may be formed in a large amount, and therefore, aluminum is not preferably added to the magnesium deactivator.

Other unavoidable impurities

The magnesium deactivator according to the present invention may include impurities that are inevitably incorporated in the raw material or manufacturing process of the alloy, and among the impurities that may be included in the magnesium deactivator according to the present invention, in particular iron (Fe), silicon (Si) and Nickel (Ni) is a component that serves to deteriorate the corrosion resistance of the final magnesium alloy product. Therefore, the Fe content is preferably 0.004% by weight or less, the Si content is 0.04% by weight, and the Ni content is preferably maintained at 0.001% by weight or less.

The magnesium deactivator according to the present invention forms a dense complex oxide layer acting as a protective film on the surface of the molten metal by simply adding it to all kinds of magnesium alloy molten metal, thereby greatly improving the flame retardancy of the magnesium alloy, thereby increasing the flame resistance of the magnesium alloy in the atmosphere or general inert atmosphere (Ar, N ₂ ) can be melted, cast and processed, and can suppress spontaneous ignition of chips accumulated in the machining process.

In addition, the magnesium deactivator according to the present invention does not need to use a gas such as SF ₆ when added to the existing commercial magnesium alloy, it is suitable for reducing manufacturing costs, worker health protection, environmental pollution prevention.

In addition, the magnesium deactivator according to the present invention can greatly improve the corrosion resistance of the magnesium alloy when added to the magnesium alloy.

In addition, the magnesium deactivator according to the present invention can improve the flame retardancy and corrosion resistance at the same time simply by adding to the molten metal without changing the additional equipment or process conditions.

In addition, the magnesium alloy to which the magnesium deactivator according to the present invention is added is to be made of extruded materials, plates, forgings, castings, etc. that can be practically applied to next-generation automobiles, high-speed railways, urban railways that require excellent safety and corrosion resistance Can be.

1 is a view showing a state diagram of the Mg-Ca binary alloy.
2 is a view showing a state diagram of the Mg-Y binary alloy.
Figure 3 is a view showing the Mg-Ca-Y state diagram at 700 ℃.
Figure 4 is a photograph showing the actual appearance of the Mg-30Ca-15Y (% by weight) deactivator prepared according to a preferred embodiment of the present invention.
5 is a diagram showing the results of EPMA analysis of the molten metal oxide surface layer after maintaining the Mg-6Zn-1Ca-1Y (wt%) alloy prepared in accordance with a preferred embodiment of the present invention at 670 ℃ for 10 minutes.
Figure 6 is a photograph showing the surface change after immersion test for 8 hours in the AZ31 alloy, AZ31-0.7Ca alloy and AZ31-0.5Ca-0.25Y alloy prepared in accordance with a preferred embodiment of the present invention in a 3.5% NaCl solution.

A magnesium deactivator and a method of preparing a magnesium alloy using a magnesium deactivator according to a preferred embodiment of the present invention will be described in detail below. The following examples are illustrative only and do not limit the invention.

The inventors of the present invention prepared a magnesium deactivator having various compositions in order to solve the problems of the prior art described above and to achieve the object of the present invention, a method of preparing a magnesium deactivator according to a preferred embodiment of the present invention is as follows.

First, Comparative Examples 1 to 3 of Table 1 are commercially available magnesium mother alloys, which are used in this experiment as the mother alloys having the chemical compositions shown in Table 1. Examples 1 to 3 of Table 1, after preparing a raw material of Mg (99.9%), Ca (99.5% or more), Y (99.5% or more), and then dissolving the raw material and using a gravity casting method A magnesium deactivator having the composition described in Examples 1 to 3 of Example 1 was prepared. In particular, in order to alloy Ca and Y having a relatively high melting point into the magnesium molten alloy, the molten metal is completely dissolved by raising the temperature of the molten metal from 850 ° C to 900 ° C in an induction furnace, and then gradually cooled to the casting temperature, followed by casting. To prepare a magnesium deactivator.

Magnesium deactivator according to a preferred embodiment of the present invention having the above composition contains a large amount of Ca and Y is brittle enough to be broken even with a small impact. In general, the smaller the size of the additive, the better the dissolution and the shorter the time for alloying. As shown in FIG. 4, when the small amount of the magnesium deactivator is added to the magnesium alloy molten metal to be added, the alloying can proceed quickly. have.

Magnesium mother alloy having the composition of Comparative Examples 1 to 3 of Table 1, CaO powder of Comparative Example 4 and magnesium deactivator having the composition of Examples 1 to 3 were added to pure magnesium or magnesium alloy having various compositions After the alloy was prepared, the effect of addition was compared, and the composition of the final product after addition is shown in Table 2. In addition, the addition temperature of the CaO powder, magnesium master alloy and magnesium deactivator according to the Examples and Comparative Examples is 700 ℃, it was maintained for 5 to 20 minutes for alloying after addition to the molten magnesium. Until the alloying was finished, SF ₆ and CO ₂ mixed gas was applied to the upper portion of the molten metal to prevent oxidation of the molten metal to prevent contact between the molten metal and the atmosphere. In addition, after the dissolution is completed, the mold was cast without using a protective gas using an iron-based mold (steel mould), a cylindrical billet having a diameter of 55mm, length 100mm for the ignition test of the alloy casting material was prepared.

In Table 2, Sample 6 Mg-2Sr alloy was prepared by adding 6.7% by weight of Mg-30Sr master alloy of Comparative Example 2 to pure magnesium, and Sample 9 Mg-3Al-0.8Zn-0.22Mn-0.7Ca alloy was AZ31 alloy. It is prepared by adding 2.4% by weight of the Mg-30Ca master alloy of Comparative Example 3 to (Sample 3). Similarly, the sample 10 Mg-6Al-0.7Ca alloy was obtained by adding 2.4% by weight of the Mg-30Ca master alloy of Comparative Example 3 to the Mg-6Al alloy (Sample 2), and the sample 11 Mg-6Al-0.7Ca alloy contained Mg- It is prepared by adding 1.0 wt% of CaO powder of Comparative Example 4 to the 6Al alloy. In addition, the sample 11 is distinguished from the sample 10 in that some of the added CaO powder is not dissolved in the casting material.

On the other hand, Sample 14 Mg-1Ca-1Y alloy is prepared by adding 5% by weight of XW-B deactivator of Example 2 to pure magnesium, Sample 15 Mg-6Al-1Ca-1Y alloy is carried out on Mg-6Al alloy It was prepared by adding 5% by weight of an XW-B deactivator of Example 2. Similarly, sample 18, Mg-8Sn-1Al-1Zn-0.3Ca-1.0Y alloy, was prepared by adding 3.4% by weight of the XW-C deactivator of Example 3 to Mg-8Sn-1Al-1Zn alloy (Sample 5). .

Ignition temperature measurement of magnesium alloy

In order to measure the firing temperature of the magnesium alloy, the outer shell of the cylindrical billet manufactured above was chip-processed at a constant speed of 0.5 mm in depth, 0.1 mm in pitch, and 350 rpm to obtain chips of a constant size. 0.1 g of the chip obtained by the above method was put into a heating furnace maintained at 1000 ° C. to raise the temperature. The temperature at which the rapid temperature rise starts due to the ignition of the sample in the temperature rising process was measured as the ignition temperature, and the results are shown in Table 3.

In Table 3, the ignition temperature of Sample 13 to which the Mg-30Zr mother alloy of Comparative Example 1 was added was 577 ° C, and the ignition temperature increased by only 31 ° C compared to Sample 4 to which Comparative Example 1 was not added. Therefore, it can be seen that the Mg-30Zr mother alloy of Comparative Example 1 is not effective in improving the ignition resistance of the magnesium alloy. On the other hand, when 2 wt% of Mg-30Sr and Mg-30Ca master alloys of Comparative Example 2 and Comparative Example 3 containing Ca and Sr mainly added to high-temperature heat-resistant magnesium alloy were added to magnesium, Sample 6 of Table 3 As can be seen from the ignition temperatures of and sample 7, there was an increase in the ignition temperatures of 146 ° C and 266 ° C, compared with 1 pure magnesium without the master alloy. From this, it can be judged that Ca is more effective than Sr in improving the ignition resistance of magnesium for the same amount added. In addition, when comparing the ignition temperature of sample No. 11, in which CaO powder of Comparative Example 4 having a similar effect to Ca and 0.7% by weight of Ca added to Mg-6Al alloy, was added to Mg-6Al alloy in Table 3, Even when 0.7 wt% of Ca is contained in the same amount, it can be confirmed that adding the Mg-30Ca master alloy of Comparative Example 3 is more effective in improving the ignition resistance than adding CaO powder of Comparative Example 4.

In addition, in Table 3, when the firing temperatures of the samples 6 to 13 and the firing temperatures of the samples 14 to 18 are compared, the case where the deactivator of Examples 1 to 3 is added to the pure magnesium or magnesium alloy is Comparative Examples 1 to 4 It can be seen that the ignition temperature is further increased compared to the case of adding the substance. In Table 3, the ignition temperature of Sample No. 17, in which 5.0 wt. It can be seen that the ignition temperature of Sample 16 in which Example 1 was added to the same alloy was 11 ° C. higher than Sample 9 in which 2.4 wt% of 3 was added. In addition, it can be seen that the firing temperature of Sample 14, in which 5.0 wt% of Example 2 was added to pure magnesium, was 42 ° C higher than that of Sample 6, in which 6.7 wt% of Comparative Example 2 was added to pure magnesium.

In particular, in the case of Mg-8Sn-1Al-1Zn alloy No. 5 in Table 3, the ignition temperature is very low as 373 ℃, by adding the deactivator of Example 3 the ignition temperature increased to 583 ℃. The reason why this is important is that the homogenization treatment is usually performed at a temperature of about 500 ° C for the extrusion or rolling of the Mg-8Sn-1Al-1Zn alloy, which is a processing alloy. There was a big problem with the risk of ignition in the process. Therefore, by adding Example 3 to the Mg-8Sn-1Al-1Zn alloy to increase the ignition temperature to 583 ℃ can eliminate the risk of ignition in the heat treatment process.

On the other hand, the reason for the increase in the ignition temperature of the magnesium alloy through the addition of a magnesium deactivator is shown in the electro-probe micro-analyzer (EPMA) results for the surface oxide layer of the Mg-6Zn-1Ca-1Y alloy in Figure 5 This is because a dense oxide layer composed of CaO and Y ₂ O ₃ is formed on the surface of Y in contact with the molten metal, and this oxide layer effectively suppresses the continuous infiltration of oxygen in the atmosphere into the molten metal.

Corrosion Characteristics of Magnesium Alloys

FIG. 6 shows the surface condition of the AZ31 alloy, the AZ31-0.7Ca alloy, and the AZ31-0.5Ca-0.25Y alloy after immersion test in 3.5% NaCl solution for 8 hours. It can be seen that the corrosion resistance of the AZ31-0.7Ca alloy to which Comparative Example 3 was added was improved compared to the AZ31 alloy having a high degree of corrosion on the surface. In general, it is known that corrosion resistance is improved when calcium is added in an amount of 1 wt% or less, and the same result can be obtained in this immersion test. On the other hand, in the case of the AZ31-0.5Ca-0.25Y alloy to which the XW-C deactivator of Example 3 is added, it was confirmed that almost no corrosion occurred on the surface, which is only 0.7 wt. Compared with the AZ31-0.7Ca alloy containing%, as shown in Example 3, the addition of the deactivator means that the corrosion resistance of the magnesium alloy can be further improved.

Meanwhile, the magnesium inactivator should be selected differently according to the magnesium alloy composition, and in particular, the optimum inactivator should be selected in consideration of the reactivity between the main elements and Ca and Y in the magnesium alloy. In the case of Mg-Al-based alloy, it is preferable to limit the Y content because the Al ₂ Y phase is generated in the molten metal by the reaction of Al and Y as the content of Y increases, in which case Ca / Y is large. Or it is preferable to select an inactivating agent as in Example 2. On the other hand, in the case of the Mg-Sn-based alloy, since Ca ₂ Sn phase is generated in the molten metal by the reaction of Sn and Ca, it is necessary to limit the amount of Ca added, so selecting an inactivator such as Example 3 with small Ca / Y is required. desirable.

According to the results of evaluating the ignition temperature and corrosion characteristics, when using the deactivator according to Examples 1 to 3 compared to Comparative Examples 1 to 4, by adding to the magnesium or magnesium alloy it can be further improved the fire resistance of the magnesium alloy At the same time, the corrosion resistance can be greatly improved. Therefore, only a small amount of the magnesium deactivator according to the present invention to the existing magnesium or magnesium alloy can be confirmed that it is very effective to greatly improve the safety and reliability of the magnesium alloy. This makes it possible to operate in the air without using expensive SF ₆ gas, which causes environmental problems, thereby establishing an eco-friendly process and at the same time reducing manufacturing and environmental costs. Furthermore, magnesium alloys can be applied in a wider range of fields where safety is required by greatly improving the reliability of magnesium alloy products.

As described above with reference to the accompanying drawings, a magnesium alloy manufacturing method using a magnesium deactivator and a magnesium deactivator according to a preferred embodiment of the present invention. However, one of ordinary skill in the art will appreciate that the above embodiments are merely illustrative of one example of the present invention and that various other modifications and variations are possible. Accordingly, the scope of the present invention is limited only by the claims that follow.

Claims (10)

As a magnesium deactivator added to suppress the activation reaction of magnesium in the manufacturing step of the magnesium alloy,
Magnesium comprising from 6% to 41.6% by weight of Ca, from 6% to 45% by weight of Y, the balance of Mg and other unavoidable impurities, the content of Ca and Y according to the following formula Deactivator.
Y ≤ 64.3-1.4 Ca (% by weight) delete delete The method of claim 1, wherein the magnesium deactivator comprises 6% to 33.8% by weight of Ca, 6% to 42.2% by weight of Y, the balance Mg and other unavoidable impurities, the content of Ca and Y is Magnesium deactivator, characterized in that following the equation.
Y ≤ 50.0-1.3 Ca (% by weight) The magnesium deactivator according to claim 1 or 4, wherein the magnesium alloy is an Mg-Al-Zn alloy. Forming a magnesium deactivator soluble at 750 ° C. or lower;
Forming a molten magnesium alloy containing at least Mg;
Injecting a magnesium deactivator soluble in the magnesium alloy melt at 750 ° C. or lower;
Manufacturing a molten magnesium alloy casting material by using a predetermined casting method for the molten metal including the magnesium deactivator,
The magnesium deactivator comprises 6% to 41.6% by weight of Ca, 6% to 45% by weight of Y, the balance of Mg and other unavoidable impurities, the content of Ca and Y according to the following equation Method for producing a magnesium alloy using a magnesium deactivator, characterized in that.
Y ≤ 64.3-1.4 Ca (% by weight) delete delete The method according to claim 6, wherein the magnesium deactivator comprises 6% to 33.8% by weight of Ca, 6% to 42.2% by weight of Y, the balance Mg and other unavoidable impurities, the content of Ca and Y is Method of producing a magnesium alloy using a magnesium deactivator, characterized in that following the equation.
Y ≤ 50.0-1.3 Ca (% by weight) The method for producing a magnesium alloy using a magnesium deactivator according to claim 6 or 9, wherein the molten magnesium alloy containing at least magnesium is an Mg-Al-Zn alloy.

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