KR101147650B1 - Magnesium alloy for high temperature and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a high-temperature magnesium-based alloy and a method for manufacturing the same, wherein after CaO is added to a molten magnesium or magnesium alloy of 0.5 to 4.0 wt%, a surface reaction between the molten metal and the added CaO is generated and the CaO As a result of the exhaustion of some or all of, the magnesium-based alloy is characterized in that the compound formed by combining Mg or other elements constituting the alloy and Ca.

Description

MAGNESIUM ALLOY FOR HIGH TEMPERATURE AND MANUFACTURING METHOD THEREOF

The present invention relates to a high temperature magnesium alloy and a method of manufacturing the same.

Magnesium has a specific gravity of 1.7, which is the lightest among commercial metals and is superior to iron and aluminum. In addition, the die casting casting method shows excellent mechanical properties and is currently used in various fields such as portable electronic components, aircraft, and sporting goods, mainly in the automotive parts field. Magnesium alloy can be applied to automobile parts to achieve 30% weight reduction.

Representative among commercially available die casting magnesium alloys are Mg-Al-based alloys such as AZ91D, AM50, and AM60. They are inexpensive and have good castability compared to other die casting alloys, and show high strength by producing β-Mg17Al12 phase when solidifying at room temperature. However, automotive and aircraft parts are used in high temperature environments of 150-200 ° C. The poor thermal stability of the β phase degrades the creep resistance of the alloy. The result is a disadvantage that it is not suitable for application to these products used in high temperature environments.

Since the 1990s, efforts have been made to develop and optimize high-temperature magnesium alloys. Magnesium alloys for high temperature can be classified into magnesium alloys for die casting and magnesium alloys for sand casting. This is due to the difference in alloy composition and manufacturing method due to the difference in use temperature of the target parts. The properties required to be suitable for high temperature magnesium alloys are castability suitable for die casting and also require corrosion and oxidation resistance. In addition, considering the competitiveness with steel and aluminum, it is required to develop an alloy that excludes expensive additive elements in terms of cost.

In view of the existing high temperature magnesium alloys developed based on this requirement, the alloys with a high ratio of rare earth element (RE) have disadvantages in terms of cost, and when the alkaline earth metals (Ca, Sr) are added, There is a problem that castability such as degradation, hot cracking, mold adhesion, etc. is significantly worsened.

In the present invention, Ca is widely known as a magnesium alloy element, that is, CaO is added to the magnesium molten metal to reduce CaO, and Ca reduced in CaO reacts with Mg or Al to form a phase, and thermally unstable β It is possible to suppress the formation of the -Mg17Al12 phase to provide a high-temperature magnesium-based alloy having improved strength and deformation resistance at high temperatures and a method of manufacturing the same.

The present invention provides a high-temperature magnesium-based alloy and a method for producing the same, which improves the ductility and strength by adding an alkaline earth metal oxide, ie, CaO, to the magnesium alloy to improve the internal integrity of the casting, such as oxides, inclusions, and pore reduction. It is to. Magnesium alloys are generally used for each alloy depending on the environmental temperature at which the product is used. Commonly use temperature is divided into 90 ℃, 120 ℃ and 150 ℃. The high temperature magnesium alloy according to the present invention is to provide a high temperature magnesium alloy that can be used at a high temperature of 120 ℃ and 150 ℃ including a temperature of more than 90 ℃.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the particular embodiments that are described. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, There will be.

In the high temperature magnesium alloy of the present invention for achieving the above object, after CaO is added to the molten magnesium or magnesium alloy 0.5 to 4.0 wt%, the surface reaction between the molten metal and the added CaO is generated, the CaO As a result of the exhaustion of some or all of them, a compound formed by combining Mg or other elements constituting Ca and Ca in the magnesium-based alloy is present.

Another high-temperature magnesium-based alloy of the present invention for achieving the above object, after CaO is added to the molten magnesium or magnesium alloy of 0.5 to 4.0 wt%, generates a surface reaction of the molten metal and the added CaO, As a result of the exhaustion of some or all of the CaO, a compound (intermetallic compound) formed by combining Ca with Mg or another element constituting the alloy in the magnesium-based alloy is present at room temperature, thereby increasing strength and elongation in high temperature mechanical properties. It is characterized by increasing at the same time.

Another high-temperature magnesium-based alloy of the present invention for achieving the above object, after CaO is added to the molten magnesium or magnesium alloy 0.5 to 4.0 wt%, to generate a surface reaction of the molten metal and the added CaO, As a result of the exhaustion of some or all of the CaO, there is a compound formed by combining Ca with Mg or other elements constituting the alloy in the magnesium-based alloy, so that the high temperature yield strength yields the magnesium or magnesium alloy before CaO addition. It is characterized by an increase in strength.

Another high-temperature magnesium-based alloy of the present invention for achieving the above object, after CaO is added to the molten magnesium or magnesium alloy 0.5 to 4.0 wt%, to generate a surface reaction of the molten metal and the added CaO, As a result of the exhaustion of some or all of the CaO, there is a compound formed by combining Ca with Mg or other elements constituting the alloy in the magnesium-based alloy, so that the tensile strength of the magnesium or magnesium alloy before the CaO addition is increased. It is characterized by an increase in strength.

Another high-temperature magnesium-based alloy of the present invention for achieving the above object, after CaO is added to the molten magnesium or magnesium alloy 0.5 to 4.0 wt%, to generate a surface reaction of the molten metal and the added CaO, As a result of the exhaustion of some or all of the CaO, there is a compound formed by combining Ca with Mg or other elements constituting the alloy in the magnesium-based alloy, so that the high temperature elongation is higher than the elongation of the magnesium or magnesium alloy before CaO addition. Characterized in that it is reduced.

Specifically, the magnesium alloy used to prepare a magnesium alloy for high temperature products is an Mg-Al alloy, and the compound formed is at least one of Mg ₂ Ca, Al ₂ Ca, or (Mg, Al) ₂ Ca. It is characterized in that, the added CaO is characterized in that 1.0 ~ 2.5 wt%.

High temperature magnesium-based alloy production method of the present invention for achieving the above object, the step of dissolving magnesium or magnesium alloy in the liquid phase; Adding 0.5 to 4.0 wt% of CaO to the molten metal in which the magnesium or magnesium alloy is dissolved; Generating a surface reaction of the molten metal and the added CaO to exhaust at least part of CaO in magnesium or magnesium alloy; And exhausting at least a portion of Ca from which the oxygen component is removed in the magnesium or magnesium alloy.

High temperature magnesium-based alloy production method of the present invention for achieving the above object, the step of dissolving magnesium or magnesium alloy in the liquid phase; Adding 0.5 to 4.0 wt% of CaO to the molten metal in which the magnesium or magnesium alloy is dissolved; Generating sufficient surface reaction of the molten metal with the added CaO to exhaust CaO from remaining in the magnesium or magnesium alloy; And exhausting Ca from which the oxygen component has been removed so as not to remain in the magnesium or magnesium alloy.

As described above, in the present invention, when CaO is added to a commercial magnesium alloy, the structure of the magnesium alloy is refined and an Al 2 Ca phase is formed. In addition, formation of the thermally unstable β-Mg17Al12 phase is suppressed, and casting defects are greatly reduced. As a result, the yield strength and tensile strength of the magnesium alloy increases at high temperatures, and in the case of the elongation, the elongation is abruptly increased at high temperatures unlike the existing magnesium alloy.

1 is a flowchart illustrating a method of manufacturing a magnesium-based alloy according to the present invention.
Figure 2 is a flow chart of the dissociation of alkaline earth metal oxide added to the molten magnesium in the present invention.
Figure 3 is an illustration of the alkaline earth metal oxide dissociation through the stirring of the magnesium molten metal upper layer in the present invention.
4a to 4d are optical micrographs taken of the structure of the magnesium alloy prepared in the present invention.
5A to 5D are TEM photographs of magnesium alloys prepared by the method of manufacturing magnesium-based alloys according to the present invention.
Figure 6 is a graph measuring the yield strength of the magnesium alloy prepared while varying the CaO content in the present invention at 150 ℃.
Figure 7 is a graph measuring the tensile strength of the prepared magnesium alloy at 150 ℃ while varying the CaO content in the present invention.
Figure 8 is a graph measuring the elongation of the magnesium alloy prepared while varying the CaO content in the present invention at 150 ℃.
Figure 9 is a graph of the comparison of room temperature mechanical properties of magnesium alloys prepared with different CaO contents in the present invention and high temperature magnesium alloys in general.
Figure 10 is a graph of the mechanical properties of the high temperature 150 ℃ of the magnesium alloy prepared with different CaO content in the present invention and a high temperature magnesium alloy in general.
FIG. 11 is a comparative graph of elongation characteristics at room temperature and high temperature of 150 ° C. of a magnesium alloy prepared with different CaO contents and a general high temperature magnesium alloy.
12A and 12B are photographs of oil pans and test specimens, which are automotive components, manufactured by the die casting method of the magnesium alloy prepared in the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention. Like elements in the figures are denoted by the same reference numerals wherever possible. In addition, detailed descriptions of well-known functions and configurations that may unnecessarily obscure the subject matter of the present invention will be omitted.

In the present invention, a method for producing a new alloy by adding alkaline earth metal oxide to the molten magnesium, and an alloy thereof, to solve the problem of adding the alkaline earth metal to magnesium and to overcome physical limitations.

1 is a flow chart showing a method for producing a magnesium-based alloy according to the present invention. As shown in FIG. 1, a method of manufacturing a magnesium-based alloy according to the present invention includes forming a magnesium-based molten metal (S1), adding an alkaline earth metal oxide (S2), stirring (S3), and exhausting an alkaline earth metal oxide (S4). ), Alkaline earth metal reaction step (S5), casting step (S6), and solidification step (S7). The alkaline earth metal oxide exhausting step (S4) and the alkaline earth metal reaction step (S5) are separated into separate steps for convenience of description, but the two processes (S4, S5) occur almost simultaneously.

In the magnesium-based molten metal forming step (S1), magnesium or a magnesium alloy (hereinafter, in the detailed description and claims, collectively referred to as magnesium or magnesium alloy) is placed in a crucible and the temperature of 400 to 800 ° C. in a protective gas atmosphere. To provide. Then, the magnesium alloy in the crucible is melted to form a magnesium-based molten metal.

Melting temperature of magnesium or magnesium alloy

In the present invention, the temperature for dissolving the magnesium or magnesium alloy means the temperature at which the pure magnesium metal melts and the temperature at which the magnesium alloy melts. Depending on the type of alloy, the melting temperature may be different. For sufficient reaction, alkaline earth metal oxide is added while magnesium or magnesium alloy is completely dissolved. The melting temperature of the magnesium or magnesium alloy is sufficient if the solid phase is sufficiently melted and exists in a complete liquid phase. However, in view of the point that the temperature of the molten metal falls due to the addition of the alkaline earth metal oxide in the present invention, it is necessary to maintain the molten metal in a sufficient temperature range.

Here, when the temperature is less than 400 ° C, the magnesium alloy melt is difficult to form, and when the temperature exceeds 800 ° C, the magnesium melt is liable to ignite. In the case of the magnesium, the molten metal is generally formed at a temperature of 600 ° C. or higher. In the case of the magnesium alloy, however, the molten metal may be formed even at a temperature of 600 ° C. or lower and 400 ° C. or higher. Generally, in metallurgy, the melting point is often lowered by alloying.

When the melting temperature is raised too high, sublimation of the liquid metal occurs, and due to the nature of magnesium, it may easily ignite to cause loss of the amount of molten metal and may adversely affect the final properties.

The magnesium used in the magnesium-based molten metal forming step may be any one selected from the group consisting of pure magnesium, a magnesium alloy, and equivalents thereof. In addition, the magnesium alloy is AZ91D, AM20, AM30, AM50, AM60, AZ31, AS41, AS31, AS21X, AE42, AE44, AX51, AX52, AJ50X, AJ52X, AJ62X, MRI153, MRI230, AM-HP2, Magnesium-Al, Magnesium-Al-Re, magnesium-Al-Sn, magnesium-Zn-Sn, magnesium-Si, magnesium-Zn-Y and the equivalent may be any one selected from, but the magnesium alloy is not limited to the present invention. Any magnesium alloy normally used in the industry can be used.

In the alkaline earth metal oxide addition step (S2), the alkaline earth metal oxide in powder form is added to the magnesium molten metal. Here, the alkaline earth metal oxide is preferably in a powder state in order to promote the reaction with the magnesium alloy.

Powder state of alkaline earth metal oxide

The alkaline earth metal oxide added for the reaction may be added in any form. Preferably, the addition of a powdered state is desirable in order to increase the reaction surface area for an efficient reaction. However, if it is too fine, less than 0.1 ㎛ is difficult to be introduced into the furnace is scattered by the sublimated magnesium or hot air. Then, they coagulate with each other and become agglomerated without easily mixing with the molten metal in the liquid phase. If it is too thick, it is not preferable from the viewpoint of increasing the surface area as mentioned above. It is preferable that the particle size of an ideal powder shall be 500 micrometers or less. More preferably not more than 200 mu m.

In order to prevent the scattering of the powder phases, it is also possible to add a pallet-type alkaline earth metal oxide.

Alkaline Earth Metal Oxide committed

CaO may be typically used as the alkaline earth metal oxide added to the molten metal. In addition, it may be at least one selected from SrO, BeO or MgO and equivalents thereof.

The alkaline earth metal oxide used in the alkaline earth metal oxide addition step may be added in an amount of 0.001 to 30 wt%. Preferably it may be 0.1 to 15% by weight. When the alkaline earth metal oxide is less than 0.001% by weight, the effect of the alkaline earth metal oxide is small.

The input amount of alkaline earth metal oxide is determined according to the final target alloy composition. In other words, the amount of CaO can be determined by inverse calculation according to the desired amount of Ca in the magnesium alloy. When the amount of Ca indirectly alloyed from CaO in the magnesium alloy exceeds 21.4 wt% (30 wt% in the case of CaO), the magnesium alloy is deviated from its original physical properties, so that the above amount is adjusted to 30.0 wt% or less . More preferably, 10.7 wt% Ca is used as the final target alloy composition and 15.0 wt% CaO is added.

The amount of the alkaline earth metal oxide for the high temperature magnesium alloy of the present invention and the method for producing the same is 0.5 to 4.0 wt%. The amount of alkaline earth metal oxides obtained was high mechanical properties at 4.0 wt% or less. If it is less than 0.5wt%, the effect of improving the physical properties was not relatively large. The composition is more preferably 1.0 to 2.5 wt%.

In the stirring step (S3) is stirred for 1 second to 60 minutes per 0.1wt% of the alkaline earth metal oxide to which the magnesium molten metal is added.

Here, if the stirring time is less than 1 second per 0.1 wt%, the alkaline earth metal oxide is not sufficiently mixed in the magnesium molten metal. If the stirring time exceeds 60 minutes per 0.1 wt%, the stirring time of the magnesium molten metal may be unnecessarily longer. In general, the time of stirring depends on the size of the melt and the amount of alkaline earth metal oxide introduced.

In order to accelerate the reaction and reduce the possibility of coagulation of the powder, it is also preferable to sequentially inject the oxide powder again with a time difference after the first injection and dividing it into an appropriate amount.

Stirring Method and Conditions

Stirring is preferred for efficient reaction of the magnesium or magnesium alloy of the present application with alkaline earth metal oxides. The shape of the stirring is provided with a device capable of applying an electromagnetic field around the furnace containing the molten metal to generate an electromagnetic field field to induce the convection of the molten metal. It is also possible to perform artificial stirring (mechanical stirring) on the molten metal from the outside. In the case of mechanical agitation, the alkaline earth metal oxide powder introduced may be appropriately stirred so as not to agglomerate. The ultimate goal of stirring is to properly induce the reaction of the molten metal with the incoming powder.

The time for stirring may vary depending on the temperature of the molten metal and the state of the powder to be charged (preheating state, etc.). Preferably, stirring is carried out until the powder is not visible on the surface of the molten metal. The reason is that the powder can be indirectly determined that the specific gravity is lower than that of the molten metal and flows on the molten metal in the steady state and when the powder is not visible on the molten metal, a sufficient reaction has occurred. Sufficient reaction herein means a state in which the alkaline earth metal oxide is exhausted by substantially reacting with the molten metal.

Even if the powder is not found on the molten metal, the possibility of existence in the molten metal cannot be excluded. Therefore, the holding time after confirming the presence of the non-injured powder with the holding time after the stirring time and giving the time to finish the reaction of the unreacted powder This is necessary.

Stirring  Time

The timing of stirring is effective at the same time as the addition of the oxide powder. In addition, after the oxide receives heat from the molten metal and reaches a predetermined temperature or more, the reaction may be accelerated by starting stirring. Stirring is continued until the powder of oxide introduced from the surface of the molten metal is not detected. After the alkaline earth metal oxides have been exhausted by the reaction, the stirring is completed.

Surface reaction

In general, when Ca and Sr of alkaline earth metals are added to the molten metal, the reaction occurs while sinking into the molten magnesium having a low specific gravity due to the specific gravity difference. Therefore, in order to assist the dissolution of Ca by simply stirring the molten alloy is made.

On the other hand, when the alkali metal oxide is added to the molten metal, it is suspended on the surface of the molten metal without sinking due to the specific gravity difference.

In the general case of alloying a metal, it is common to induce an active reaction by convection or stirring the molten metal and the alloying element metal so that the reaction occurs inside the molten metal. However, in the case of the present application, when an active reaction was induced, the oxide introduced into the molten metal failed to react, remaining in the final material, thereby lowering physical properties or causing defects. That is, when the reaction of the molten metal is induced not on the surface of the molten metal, the oxide of alkaline earth metal remains in the final molten metal more than the reaction on the surface of the molten metal.

 Therefore, in the present invention, it is important to create a reaction environment so that the oxide reacts on the surface of the molten metal rather than reacting in the molten metal. To do so, it is important not to force the oxide floating on the surface of the molten metal into the molten metal. It is important to simply spread the alkaline earth metal oxides that spread on the surface to the surface of the exposed molten metal.

It was better to do the reaction rather than to agitate, and it was better to stir on the outer surface (upper surface) than on the inside of the molten metal. That is, the outer surface (upper surface) was more responsive to the atmosphere and to the exposed powder. One side of CaO was better in contact with the atmosphere. The results were not good under vacuum or atmospheric gas. For sufficient reaction, it is necessary to stir the upper layer to induce the surface reaction.

Table 1 below was added to 5, 10, 15wt% calcium oxide having a particle size of 70㎛ to the molten metal of AM60B magnesium alloy, respectively, and the residual amount of calcium oxide in the magnesium alloy was measured according to the stirring method. As the stirring method, the upper portion of the molten metal was stirred, the molten metal was stirred inside, and the other was not stirred. As the residual amount of calcium oxide was 5, 10, 15 wt%, the final residual amount was 0.001 and 0.002, respectively, as compared with the case of stirring only the upper part of the stirring and the case of not stirring, , And 0.005 wt%, respectively. That is, it can be seen that when CaO is stirred on the surface of Mg molten metal, most of CaO added is separated into Ca.

5 wt% CaO addition 10wt% CaO addition 15wt% CaO addition In alloy
CaO balance No agitation 4.5wt% CaO 8.7 wt% CaO 13.5 wt% CaO Stirring in the molten metal 1.2wt% CaO 3.1 wt% CaO 5.8 wt% CaO Molten metal upper layer
Stirring (present invention) 0.001wt% CaO 0.002wt% CaO 0.005wt% CaO

Oxygen components of the alkaline earth metal oxides are substantially removed over the surface of the melt through agitation of the melt top layer. It is preferable that the agitation is performed at the upper layer portion of the depth of the molten metal from the surface of the molten metal to about 20% of the entire depth of the molten metal. At a depth of 20% or more, it is difficult to cause the surface reaction suggested by the present invention as a preferable example. More preferably, the stirring is performed at the upper layer part of about 10% of the total depth of the molten metal from the molten surface. This could minimize the disturbance of the molten metal by actually inducing the floating alkaline earth metal oxide in the 10% upper layer in the depth of the molten metal.

In the exhausting step (S4) of the alkaline earth metal oxide, the alkaline earth metal oxide is exhausted so as not to remain at least partially or substantially in the magnesium alloy through the reaction of the molten metal and the added alkaline earth metal oxide. Alkaline earth metal oxide introduced in the present invention is preferably exhausted by a sufficient reaction. However, it is also effective when the material remains unreacted and remains in the alloy and does not greatly affect the physical properties.

Here, exhausting alkaline earth metal oxides removes oxygen components from the alkaline earth metal oxides. The oxygen component may be removed in the form of oxygen (O ₂ ) gas, or may be removed in the form of dross or sludge through association with magnesium or its alloying elements in the molten metal. Then, the oxygen component is substantially removed over the surface of the molten metal through agitation of the molten upper layer. Figure 3 is an illustration of the alkaline earth metal oxide dissociation through the stirring of the magnesium molten metal upper layer in the present invention.

In the alkaline earth metal reaction step (S5), the alkaline earth metal produced as a result of the exhaustion of the alkaline earth metal oxide is reacted so as not to remain at least partially or substantially in the magnesium alloy. Here, the alkaline earth metal produced as a result of exhaustion is compounded with at least one of magnesium, aluminum in the magnesium alloy, and other alloying elements (components) in the molten metal so as not to remain substantially. Herein, the term " compound " refers to an intermetallic compound formed by bonding a metal and a metal.

Eventually, the added alkaline earth metal oxide is removed at least partly or substantially by removing oxygen component through reaction with magnesium alloy, which is a molten metal, and the alkaline earth metal from which oxygen component is removed is removed from the magnesium, aluminum and magnesium in the magnesium alloy. It is compounded with at least one of the other alloying elements so that it does not remain at least partially or substantially in the magnesium alloy. The processes described so far are shown in Figs. 1 and 2. Fig. Figure 2 is a flowchart of dissociation of alkaline earth metal oxides used in addition to the molten magnesium in the present invention.

On the other hand, in the casting step (S6), the magnesium molten metal is cast in a mold at room temperature or preheated state. Herein, the mold may use any one selected from a mold, a ceramic mold, a graphite mold, and an equivalent thereof. In addition, the casting method can be gravity casting, continuous casting and the equivalent method.

As the temperature of the magnesium-based molten metal falls, at least one of magnesium, aluminum, and other alloying elements in the molten metal and the compound is formed in the magnesium-based alloy.

In the solidifying step S7, the mold is cooled to room temperature and a magnesium alloy (eg, magnesium alloy ingot) is taken out from the mold. The magnesium alloy prepared by the above method will be described below, but will have a form including at least one of magnesium, aluminum, and other alloy elements in the molten metal in the magnesium-based alloy.

The intermetallic compound is mostly present at the interface that is outside of the magnesium grains, but may also be present inside the magnesium grains. The magnesium crystal grains may be any one selected from pure magnesium grains, magnesium alloy grains, and equivalents thereof. The intermetallic compound may be any one selected from compounds of magnesium and alkaline earth metals, compounds other than magnesium in magnesium alloys, and compounds of alkaline earth metals, or complex compounds thereof. Mainly intermetallic compounds may be magnesium-based intermetallic compounds and Al-based intermetallic compounds.

The magnesium-based alloy formed by the above-described production method may have a hardness (HRF) of 40 to 80. [ However, since the hardness value varies variously depending on the processing method and the heat treatment, the hardness value does not limit the magnesium-based alloy according to the present invention.

In the case of pure magnesium molten metal, the magnesium component in the molten metal reacts with alkaline earth metal to form a magnesium (alkaline metal) compound. For example, when the alkaline earth metal oxide is CaO, Mg ₂ Ca is formed. Oxygen, which forms CaO, becomes O _{2 and} is discharged out of the molten metal or combined with Mg to form MgO and discharged in the form of dross (see Scheme 1 below).

Scheme 1

Pure Mg + CaO -> Mg (Matrix) + Mg ₂ Ca

... [O ₂ occurrence + MgO dross occurrence]

In the case of magnesium alloy molten metal, the magnesium component in the molten metal reacts with alkaline earth metal to form a magnesium (alkaline earth metal) compound or an aluminum (alkaline earth metal) compound. Also, magnesium and aluminum together with magnesium form compounds with alkaline earth metals. For example, when the alkaline earth metal oxide is CaO, Mg ₂ Ca, Al ₂ Ca, or (Mg, Al, other alloying elements) ₂ Ca is formed. Oxygen, which is composed of CaO, becomes O _{2 and} is discharged out of the molten metal as in the case of pure magnesium, or it is combined with Mg to be MgO and discharged in the form of dross (see Scheme 2 below).

Scheme 2

Mg Alloy + CaO-> Mg Alloy (Matrix) +

(Mg ₂ Ca + Al ₂ Ca + (Mg, Al, other alloying elements) ₂ Ca}

... [O ₂ occurrence + MgO dross occurrence]

As described above, the present invention is a manufacturing method of magnesium alloy more economically than the conventional production method of magnesium alloy. Alkaline earth metals (eg Ca) are relatively expensive alloying elements compared to alkaline earth metal oxides (eg CaO), which acts as a factor to increase the price of magnesium alloy. In addition, it is relatively easy to alloy by adding alkaline earth metal oxide to magnesium or magnesium alloy in place of alkaline earth metal. On the other hand, the addition of chemically stable alkaline earth metal oxides (eg, CaO) without the addition of alkaline earth metals (eg, Ca) may result in the same or more alloying effects.

In addition, when the alkaline earth metal is directly added to magnesium or magnesium alloy, the solid solution of the alkaline earth metal occurs in the magnesium alloy, while in the case of utilizing the technique of the present invention, the alkaline earth metal oxide (CaO) is dissolved when added. The degree is less or very low compared to the case of the direct addition of alkaline earth metal (Ca). Therefore, in order to increase the properties of magnesium alloy, it is necessary to add more than a certain portion of alkaline earth metal, whereas when manufacturing magnesium alloy by adding alkaline earth metal oxide, a considerable amount of alkaline earth metal is directly intermetallic compound of magnesium or Al (eg, By forming Mg ₂ Ca or Al ₂ Ca), physical properties can be seen to be improved than when Ca is directly added.

Hereinafter, examples and various experimental results of the present invention will be described.

4a to 4d are photographs taken by optical microscope of the structure of the magnesium alloy prepared in the present invention according to the CaO addition ratio in the present invention.

As the addition ratio of CaO (Fig. 4a is added 0wt% CaO, Fig. 4b is added 1.2wt% CaO, Fig. 4c is added 2.2wt% CaO, Fig. 4d is added 3.2wt% CaO), the structure of the magnesium alloy becomes finer It can be seen that.

5a to 5d show the component analysis of the TEM image of the magnesium alloy prepared by adding 1.8wt% CaO to the AZ61 magnesium alloy by the method of manufacturing a magnesium-based alloy according to the present invention. FIG. 5A shows magnesium, FIG. 5B shows aluminum, and FIG. 5C shows the components of calcium are detected. As can be seen from the figure, aluminum and calcium are detected in the same phase. This means that Ca was separated from CaO added to the magnesium molten metal and combined with aluminum in the molten metal to form a compound.

Table 2 below is a quantitative amount for the composition of the phase. The compound was formed by Al and Ca, and it can be seen that the Al2Ca phase was formed by quantitative analysis of the phase. The high temperature properties of the magnesium alloy are improved due to the inhibition of grain boundary enhancement due to the formation of the Al2Ca phase and the formation of the thermally unstable β-Mg17Al12 phase.

wt% at% Al 68.73 76.55 Ca 31.27 23.45 Total 100 100

6 is a graph showing yield strength (TYS) when calcium oxide is added to magnesium alloy.

In the examples, the experiment was performed by adding 0.5 wt% to 3.8 wt% of calcium oxide to the AM60B magnesium alloy.

As shown in FIG. 6, the yield strength was found to be about 140 to 145 [MPa] when 0.9 wt% of calcium oxide was added to the magnesium alloy, and the yield strength was about 150 [when the wt% of calcium oxide was added to the magnesium alloy. MPa], yield strength of about 150 [MPa] when added 3.5% by weight of calcium oxide to the magnesium alloy.

Yield strength according to the weight percentage of such calcium oxide is shown in Table 3 below.

alloy Calcium oxide addition amount Yield strength [MPa] Magnesium alloy
(AM60B) 0.5 to 0.9 wt% 141 to 143 1.0 to 1.4 wt% 146-151 1.5 to 1.9 wt% 147-152 2.0 to 2.5 wt% 150 to 155 2.6-3.2 wt% 150 3.3 to 3.8 wt% 150 to 152

Therefore, it can be seen that the yield strength is most excellent when adding 1.2 to 2.0% by weight of calcium oxide to the magnesium alloy as shown in Table 3. In other words, 0.5 ~ 0.9% by weight shows the yield strength of the degree of use at a high temperature of 90 ℃ and at a higher content than 150 ℃ exhibits a suitable high temperature characteristics.

7 is a graph showing the tensile strength (UTS) when calcium oxide is added to the magnesium alloy.

In the examples, the experiment was performed by adding 0.5 wt% to 3.8 wt% of calcium oxide to the AM60B magnesium alloy.

As shown in FIG. 7, when 0.9 wt% of calcium oxide was added to the magnesium alloy, the tensile strength was about 225 [MPa], and when 1.4 wt% of calcium oxide was added to the magnesium alloy, the tensile strength was about 239 [MPa]. When 3.5 wt% of calcium oxide was added to the magnesium alloy, the tensile strength was about 232 [MPa].

The tensile strength according to the weight percentage of such calcium oxide is shown in Table 4 below.

alloy Calcium oxide addition amount Tensile Strength [MPa] Magnesium alloy
(AM60B) 0.5 to 0.9 wt% 222-224 1.0 to 1.4 wt% 225 to 230 1.5 to 1.9 wt% 232 to 238 2.0 to 2.5 wt% 234-239 2.6-3.2 wt% 232 3.3 ~ 3.8 wt% 230-232

Therefore, it can be seen that the tensile strength is most excellent when adding 1.1 to 2.0 wt% calcium oxide to the magnesium alloy as shown in Table 4. In other words, 0.5 ~ 0.9% by weight shows the tensile strength to be used at a high temperature of 90 ℃ and at a higher content than 150 ℃ exhibits a suitable high temperature characteristics.

8 is a graph showing elongation when calcium oxide is added to a magnesium alloy.

In the examples, the experiment was performed by adding 0.5 wt% to 3.8 wt% of calcium oxide to the AM60B magnesium alloy.

As shown in FIG. 8, when 0.9 wt% of calcium oxide is added to the magnesium alloy, the elongation is about 13-14 [%], and when the 1.4 wt% of calcium oxide is added to the magnesium alloy, the elongation is about 14-15 [. %], And elongation was about 14 [%] when 3.5 wt% of calcium oxide was added to the magnesium alloy.

Elongation according to the weight percentage of such calcium oxide is shown in Table 5 below.

alloy Calcium oxide addition amount Elongation [%] Magnesium alloy
(AM60B) 0.5 to 0.9 wt% 13 to 14 1.0 to 1.4 wt% 14-15 1.5 to 1.9 wt% 15 2.0 to 2.5 wt% 14-15 2.6-3.2 wt% 15 3.3 ~ 3.8 wt% 14-15

Therefore, as shown in Table 5, the elongation was most excellent when 1.2 to 2.5% by weight of calcium oxide was added to the magnesium alloy. However, elongation is somewhat different from yield strength and tensile strength in all ranges (0.5% to 3.0% by weight) shows excellent properties.

9a and 9b are graphs showing the mechanical properties of the magnesium-based alloy prepared by the present invention and the conventional alloy at room temperature and high temperature.

As shown in Figure 9a, the magnesium-based alloy (Eco-Mg) according to the present invention at room temperature was superior to the tensile strength (UTS) and elongation of MRI153 and AE44, MRI230 and AM60B alloy. The magnesium alloy according to the present invention (the magnesium alloy of the present invention is called "Eco-Mg") has a yield strength of about 160 MPa, a tensile strength of 260 MPa, and an elongation of about 12.3% at room temperature. For example, MRI153 alloy has a yield strength of about 165 MPa, a tensile strength of 248 MPa, and an elongation of about 5% at room temperature.

As shown in Figure 9b, the magnesium-based alloy (Eco-Mg) according to the present invention was shown to have a yield strength, tensile strength and elongation similar to room temperature even at high temperatures. That is, the magnesium-based alloy (Eco-Mg) according to the present invention has a yield strength of about 150 MPa, a tensile strength of 225 MPa, and an elongation of about 12.5% at high temperature. This means that the magnesium-based alloy (Eco-Mg) according to the present invention has similar mechanical properties at both room temperature and high temperature.

However, MRI153 alloy has yield strength of 125MPa, tensile strength of 180MPa and elongation of approximately 17.5% at high temperature, which is the mechanical properties (yield strength and tensile strength and elongation) at room temperature and high temperature. This means that it will vary a lot.

Therefore, it can be seen that the magnesium-based alloy (Eco-Mg) according to the present invention has a small amount of change in mechanical strength at room temperature and high temperature, and thus has stable mechanical properties according to temperature.

In addition, the CaO composition of 0.5 ~ 0.9wt% tends to have a somewhat low mechanical properties at 150 ℃, but it can be seen that the high temperature characteristics that can be applied to products used in the environment of about 90 ℃.

10 and 11 are graphs showing elongation comparison at room temperature and high temperature (150 ° C.) for each alloy.

As shown, the magnesium-based alloy (Eco-Mg) according to the present invention shows an elongation of about 12 to 13% at room temperature and high temperature, respectively, and shows similar elongation at both room temperature and high temperature.

However, MRI153 alloy showed elongation of about 5% at room temperature, but elongation of about 17% at high temperature. The remaining alloys (AE44, MRI230, and AM60B) also have a significant change in elongation with temperature.

Therefore, the magnesium-based alloy (Eco-Mg) according to the present invention has a small change in mechanical properties with temperature, and thus may be usefully used in an environment with severe temperature changes.

Figure 12a shows the appearance of the oil pan for automobile parts manufactured by the actual magnesium alloy die casting (cold chamber method) according to the present invention. In the figure, the end of the product is shown with a tension specimen to test the properties of the magnesium alloy. Although the end of the product is generally of poor quality due to the characteristics of die casting, the magnesium alloy of the present invention has been found to have excellent casting quality such as high temperature mechanical properties and casting defects as described above.

Figure 12b is a test specimen separated from the oil pan prepared by the die casting of various CaO content (0.5 ~ 3.8wt%).

The present invention has been described with reference to the preferred embodiments, and those skilled in the art to which the present invention pertains to the detailed description of the present invention and other forms of embodiments within the essential technical scope of the present invention. Could be. The scope of the present invention is defined by the appended claims, and all differences within the scope of the claims are to be construed as being included in the present invention.

Claims (12)

In magnesium alloy for high temperature products,
After adding 0.5 to 4.0 wt% of CaO to the surface of the molten magnesium or magnesium alloy, the added CaO generates a surface reaction with the molten metal, and as a result of the exhaustion of part or all of the CaO, the magnesium-based alloy High-temperature magnesium-based alloy in which a compound formed by combining Mg or another element constituting an alloy with Ca is present.
The method of claim 1,
When the magnesium alloy used to manufacture a magnesium alloy for high temperature products is an Mg-Al alloy, the compound formed is at least one of Mg ₂ Ca, Al ₂ Ca, or (Mg, Al) ₂ Ca. High temperature magnesium alloy.
The method according to claim 1 or 2,
The added CaO is a high temperature magnesium-based alloy, characterized in that 1.0 ~ 2.5 wt%.
In the method of manufacturing a magnesium-based alloy for high temperature products,
Dissolving magnesium or magnesium alloy in a liquid phase;
Adding 0.5 to 4.0 wt% of CaO to the surface of the molten metal in which the magnesium or magnesium alloy is dissolved;
Generating a surface reaction with the molten CaO, thereby at least partially exhausting CaO in magnesium or magnesium alloy; And
Reacting at least some of the Ca from which the oxygen component is removed in the magnesium or magnesium alloy;
High temperature magnesium-based alloy manufacturing method comprising a.
In the method of manufacturing a magnesium-based alloy for high temperature products,
Dissolving magnesium or magnesium alloy in a liquid phase;
Adding 0.5 to 4.0 wt% of CaO to the surface of the molten metal in which the magnesium or magnesium alloy is dissolved;
Causing the added CaO to generate sufficient surface reaction with the molten metal to exhaust CaO from remaining in the magnesium or magnesium alloy; And
Reacting Ca from which the oxygen component is removed so as not to remain in the magnesium or magnesium alloy;
High temperature magnesium-based alloy manufacturing method comprising a.
The method according to claim 4 or 5,
The added CaO is a method for producing a high temperature magnesium-based alloy, characterized in that 1.0 ~ 2.5 wt%.
In magnesium alloy for high temperature products,
After adding 0.5 to 4.0 wt% of CaO to the surface of the molten magnesium or magnesium alloy, the added CaO generates a surface reaction with the molten metal, and as a result of the exhaustion of part or all of the CaO, the magnesium-based alloy A magnesium alloy for high temperature, characterized by the presence of an intermetallic compound formed by combining Ca with other elements constituting Mg or an alloy, thereby simultaneously increasing strength and elongation among high temperature mechanical properties.
The method of claim 7, wherein
When the magnesium alloy used to manufacture a magnesium alloy for high temperature products is an Mg-Al alloy, the compound formed is at least one of Mg ₂ Ca, Al ₂ Ca, or (Mg, Al) ₂ Ca. High temperature magnesium alloy.
9. The method according to claim 7 or 8,
The added CaO is a high temperature magnesium-based alloy, characterized in that 1.0 ~ 2.5 wt%.
In magnesium alloy for high temperature products,
After adding 0.5 to 4.0 wt% of CaO to the surface of the molten magnesium or magnesium alloy, the added CaO generates a surface reaction with the molten metal, and as a result of the exhaustion of part or all of the CaO, the magnesium-based alloy A high-temperature magnesium-based alloy having a characteristic that the high temperature yield strength is increased than the yield strength of magnesium or the alloy of magnesium before CaO addition by the presence of an intermetallic compound formed by combining Ca with other elements constituting Mg or alloy.
In magnesium alloy for high temperature products,
After adding 0.5 to 4.0 wt% of CaO to the surface of the molten magnesium or magnesium alloy, the added CaO generates a surface reaction with the molten metal, and as a result of the exhaustion of part or all of the CaO, the magnesium-based alloy A high-temperature magnesium-based alloy having a characteristic that the high temperature tensile strength is increased than that of magnesium or an alloy of magnesium before adding CaO by the presence of an intermetallic compound formed by combining Ca with other elements constituting Mg or alloy.
In magnesium alloy for high temperature products,
After adding 0.5 to 4.0 wt% of CaO to the surface of the molten magnesium or magnesium alloy, the added CaO generates a surface reaction with the molten metal, and as a result of the exhaustion of part or all of the CaO, the magnesium-based alloy A high-temperature magnesium-based alloy having a characteristic that the high-temperature elongation is reduced than that of magnesium or an alloy of magnesium before adding CaO by the presence of an intermetallic compound formed by combining Ca with other elements constituting Mg or alloy.

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