WO2019123537A1

WO2019123537A1 - Magnesium alloy powder and sintered component thereof

Info

Publication number: WO2019123537A1
Application number: PCT/JP2017/045538
Authority: WO
Inventors: 伊達　賢治; 拓岩岡
Original assignee: 日立化成株式会社; 地方独立行政法人東京都立産業技術研究センター
Priority date: 2017-12-19
Filing date: 2017-12-19
Publication date: 2019-06-27
Also published as: JPWO2019123537A1

Abstract

The present invention provides: a Mg alloy powder which can be produced at low cost and which is capable of bringing about improved sintering properties; and a sintered component using same. This Mg alloy powder is produced by an air atomization method, and contains Mg as a main component and contains 3.5-12 mass% of Al as a first accessory component, with respect to a total mass of the Mg alloy powder.

Description

Magnesium alloy powder and sintered parts thereof

The present disclosure relates to magnesium alloy powder and sintered parts thereof.

Magnesium (Mg) is a resource abundantly present on the earth, and is excellent in recyclability like aluminum (Al). Therefore, development of materials using Mg is in progress in various fields.
For example, recently, in the medical field, biosafety of WE43 (Mg-4Y-3RE) alloy has been confirmed by Western organizations, and the development of biostructural materials such as bioabsorbable stent materials or biohard tissue implant materials Is expected.

In addition, in the field of transportation equipment such as automobiles, railway vehicles and aircrafts, it is essential to cope with the weight reduction of vehicles for energy saving by improving fuel efficiency and environmental measures by reducing CO ₂ gas emission. Therefore, the demand for conversion from conventional steel-based materials to lightweight metallic materials such as Mg alloy and Al alloy is increasing. In response to these requirements, Mg alloys are attracting attention as materials suitable for reducing the weight of transport equipment because they have the lowest specific gravity and high specific strength among typical metals used as structural materials. . Moreover, Mg alloy has high damping property and electromagnetic wave shielding property. Therefore, it is considered that the material can be an effective material also from the viewpoint of measures against vibration that are specific to transportation equipment or measures against noise accompanying electronic control such as a drive system.

Structural materials including Mg alloys are roughly classified into ingot materials and powder metallurgy materials, depending on the method of forming the structure (formed body). The molten material is used in a method of casting molten Mg alloy into a mold and casting it to a shape close to the final product or a method of hot or cold plastic working of a cast material of Mg alloy having a simple shape such as billet Be On the other hand, powder metallurgy materials are used in a method of filling and pressure forming Mg alloy powder in a mold or the like and then sintering.

In general, a compact obtained by sintering a metal powder (hereinafter referred to as a sintered part) has a finer and more uniform structure than a compact (hereinafter referred to as a cast) obtained by casting. Because of the presence, it is easy to obtain strong toughness. In a sintered part, a structure in which ceramic particles or intermetallic compound particles are uniformly finely dispersed in the above-mentioned base material by mixing ceramic particles or intermetallic compound particles with Mg alloy powder as a base material. Design is possible. In addition, for example, it is also possible to design a structure having dispersion density, such as setting the dispersion concentration near the surface layer of each particle higher than that inside. Thus, in the sintered part, in the tissue design, not only the strength but also various functions such as the improvement of the wear resistance and the impartation of the affinity with bone cells can be easily added depending on the application. It has the advantage of being able to

The atomizing method or the plasma rotating electrode method is known as a typical production method of metal powder used as a powder metallurgy material. In these methods, metal powder is obtained by refining and quenching molten metal. However, the molten Mg alloy is active and easily burnt in the atmosphere. Therefore, pulverization of the Mg alloy by the above method is usually carried out under an atmosphere of an expensive inert gas such as argon or helium.
The atomization method is a method of pulverizing a metal melt by refining a molten metal of metal using gas or water and quenching it, and is excellent in mass productivity. However, in the case of pulverizing the Mg alloy by gas atomization, it is necessary to use a large amount of expensive inert gas, which increases the operation cost and makes the Mg alloy powder very expensive. Therefore, a Mg alloy powder that can be suitably used as a powder metallurgy and is inexpensive is desired.

On the other hand, there has been proposed a method of producing Mg alloy powder by a water atomizing method, in which a molten metal in which calcium (Ca) is added to a Mg alloy is sprayed and powdered using a high-speed rotational water flow. ~ 3).

JP, 2014-162991, A JP, 2014-167136, A JP, 2017-61753, A

In the production of a sintered part, shear stress is applied to the contact interface between powders by pressing in a forming step of a metal powder or in a sintering step after forming, or by hot working after sintering. Therefore, even if a thin oxide film is present on the powder surface, the oxide film is broken in the normal processing step, and a strong metal bond can be obtained. However, when the oxide film has a thickness on the order of several microns, it becomes difficult to sufficiently destroy the oxide film in a normal treatment process, and the sinterability tends to be reduced.

According to the method of manufacturing Mg alloy powder by the above-described water atomization method, since water is used instead of expensive inert gas, the manufacturing cost can be reduced. However, in the above-mentioned production method, water is used to pulverize the Mg alloy and the powder is recovered in water. Therefore, a thick oxide film of several microns is formed on the surface of the powder, and it is considered difficult to obtain excellent sinterability. From such a thing, the further improvement is desired towards realization of Mg alloy powder which can be obtained cheap and excellent sinterability.
Therefore, in view of the above-described situation, an object of the present disclosure relates to providing a Mg alloy powder that is inexpensive and capable of improving sinterability.

In order to reduce the production cost of the metal powder by the gas atomizing method, it is conceivable to apply an air atomizing method using air in place of expensive inert gas at the time of spraying the molten metal. However, it is usually difficult to apply the air atomization method because the molten Mg alloy is active.
On the other hand, the present inventors variously study powderization of the Mg alloy, and when the Mg alloy contains a specific element, the flame retardance of the molten Mg alloy can be enhanced, and the air atomizing method We found that it would be possible to apply. Moreover, when the air atomization method is applied to manufacture of Mg alloy powder, it discovers that formation of the oxide film in a pulverization process can be controlled favorably, and came to complete this invention.

That is, the present invention relates to the embodiments described below. However, the present invention is not limited to the embodiments described below, but includes various embodiments.

One embodiment is a Mg alloy powder manufactured by an air atomizing method, containing Mg as a main component, and 3.5 to 12 mass% based on the total mass of the Mg alloy powder as a first auxiliary component The present invention relates to an Mg alloy powder containing Al.

In the said embodiment, it is preferable that the said Mg alloy powder has an oxide film on the surface, and the said oxide film contains Al of a said 1st subcomponent.

One embodiment is a Mg alloy powder containing Mg as a main component and containing 3.5 to 12% by mass of Al based on the total mass of the Mg alloy powder as a first accessory component,
The present invention relates to a Mg alloy powder having an oxide film having a thickness of less than 1 μm on the surface, and the oxide film containing Al as the first subcomponent.

In the above embodiment, the Mg alloy powder further contains one or more elements selected from the group consisting of Zn, Ca, Mn, Si, Ni, Cu, Zr and Sn as a second accessory component. It is preferable to contain.

The content of the second accessory component is preferably 0.01 to 12% by mass based on the total mass of the Mg alloy powder.

In the above embodiment, the Mg alloy powder preferably has an irregular shape.

In the above embodiment, the Mg alloy powder preferably has a composition of Mg-Al alloy, Mg-Al-Zn alloy, Mg-Al-Ca alloy, or Mg-Al-Zn-Ca alloy. .

One embodiment relates to a sintered part using the Mg alloy powder of the above embodiment.

According to the present invention, it is possible to provide an Mg alloy powder which is inexpensive and easy to obtain excellent sinterability.

FIG. 1 is a schematic cross-sectional view showing a structural example of an air atomizing device. FIG. 2 is a SEM photograph showing the shape of the Mg alloy powder produced in Example 1. FIG. 3 is a SEM photograph showing the shape of the Mg alloy powder produced in Example 2. FIG. 4 is a STEM photograph showing a state (cross section) near the surface of the Mg alloy powder produced in Example 1. FIG. 5A shows an image of elemental mapping (O) by EDX analysis (STEM / EDX) of a region corresponding to the STEM photograph shown in FIG. FIG. 5B shows an image of elemental mapping (Ca) by EDX analysis (STEM / EDX) of a region corresponding to the STEM photograph shown in FIG. FIG. 5C shows an image of elemental mapping (Al) by EDX analysis (STEM / EDX) of a region corresponding to the STEM photograph shown in FIG. FIG. 6 is a STEM photograph showing a state (cross section) near the surface of the Mg alloy powder produced in Example 2. 7A shows an image of elemental mapping (O) by EDX analysis (STEM / EDX) of a region corresponding to the STEM photograph shown in FIG. FIG. 7B shows an image of elemental mapping (Al) by EDX analysis (STEM / EDX) of a region corresponding to the STEM photograph shown in FIG. FIG. 8 is a graph showing the results of line analysis of Al distribution in the Mg alloy powder produced in Example 1. FIG. 9 is a graph showing the results of line analysis of Al distribution in the Mg alloy powder produced in Example 2.

Hereinafter, the present invention will be specifically described along the embodiments. However, the present invention is not limited to the embodiments described below.
In one embodiment, the Mg alloy powder is manufactured by an air atomizing method and contains Mg as a main component, and 3.5 mass% to 12 mass% based on the total mass of the Mg alloy powder as a first auxiliary component Contains Al. The Mg alloy powder preferably has an oxide film on the surface, and the oxide film preferably contains Al as the first subcomponent.

In powderization by the air atomization method, it is considered that a molten Mg of pure Mg forms a MgO film on its surface as soon as it becomes a droplet. However, since MgO is porous, the surface film of MgO can not shield the liquid phase Mg inside the droplet from the air, and the Mg droplet burns violently. Therefore, it is generally difficult to apply the air atomization method as a method of pulverizing pure Mg or a Mg alloy, and it is considered that the use of an inert gas is essential for the pulverization. On the other hand, the Mg alloy powder of the above embodiment has an alloy composition containing at least a specific amount of Al as a first subcomponent in addition to Mg as the main component, whereby Mg alloy powder in the air atomization method is obtained. Production of

More specifically, in order to suppress the combustion of Mg droplets, formation of a dense film such as an oxide film capable of sufficiently shielding oxygen in the atmosphere and the liquid phase inside the droplets, and Mg in the liquid phase It is necessary to enhance the flame retardancy in pulverization by lowering the vapor pressure and the like. On the other hand, according to the above-described embodiment, it is considered that the flame retardancy can be easily enhanced by the presence of a specific amount of Al in the Mg alloy when the molten metal of the Mg alloy is sprayed. Further, since the manufactured Mg alloy powder has a dense oxide film on the surface, it is considered that oxidation, which contributes to the deterioration of characteristics, does not proceed easily even when stored for a long time. Furthermore, from the viewpoint of production of the sintered part, it is considered that the fine oxide containing Al as the first subcomponent finely disperses in the structure, which is also effective for improving the strength of the sintered part. .

For example, when powdering is performed by gas atomization using argon gas, it is generally said that the cost of argon gas accounts for 90% of the operation cost of powdering. Therefore, according to the above embodiment, since air is used instead of expensive argon gas, the operation cost can be significantly reduced, and the Mg alloy powder can be provided at low cost.

In another embodiment, the Mg alloy powder contains Mg as a main component and Al as a first subcomponent, and has an oxide film with a film thickness of less than 1 μm on the surface, and the above-mentioned oxide film is the above-mentioned first 1 contains a minor component of Al. In one embodiment, the Mg alloy powder preferably contains more than 76% by mass of Mg as a main component. The Mg alloy powder preferably contains more than 80% by mass of Mg, more than 85% by mass It is more preferable to contain Mg.

Generally, in the production of sintered parts using Mg alloy powder, shear stress is applied to the contact interface between the powders at the time of pressure treatment at the time of forming or sintering, or at the time of hot working after sintering Is added. Even when the oxide film is present on the surface of the Mg alloy powder, the oxide film on the surface of the Mg alloy powder is broken during the above treatment to form a strong metal bond, which makes it easy to obtain a sintered part with high strength. Conceivable. However, if the film thickness of the oxide film is on the order of several microns, it becomes difficult to break the oxide film by ordinary processing, which is likely to affect the strength of the sintered part. On the other hand, in the Mg alloy powder of the above-described embodiment, the thickness of the oxide film on the powder surface is less than 1 μm, and it is thought that it is easy to obtain a high strength sintered part because it is thin.

The Mg alloy powder of the above embodiment may be manufactured by any method, but from the viewpoint of cost reduction, it is preferable to be manufactured by a method to which the air atomization method is applied. As described above, it is generally considered difficult to apply air atomization as a method of pulverizing pure Mg or Mg alloy, but Mg alloy powder has a specific composition containing at least Al. This makes it possible to safely carry out the production of Mg alloy powder by air atomization without using expensive inert gas.

Also, without being bound by theory, it is believed that the concentration of the first subcomponent Al in the oxide film makes the film growth rate slower and the thickness of the oxide film after solidification becomes thinner. As a matter of fact, in comparison with the Mg alloy powder manufactured by the water atomization method in the study of the present inventors, according to the manufacturing method to which the air atomization method is applied, the thickness of the oxide film formed on the surface of the Mg alloy powder It has been confirmed that the height can be reduced to less than 1 .mu.m.

In one embodiment, the thickness of the oxide film on the surface of the Mg alloy powder is preferably 800 nm or less, more preferably 500 nm or less, and still more preferably 200 nm or less, from the viewpoint of facilitating obtaining a high-strength sintered part. . In the Mg alloy powder of the above embodiment, the formation of the oxide film is suitably controlled by containing at least Al, and it becomes easy to adjust the thickness of the oxide film within the above range.

Furthermore, in one embodiment, the Mg alloy powder is preferably in an irregular shape (indeterminate non-spherical shape). The irregularly shaped powder increases the strength of the green compact after molding due to the anchor effect between the powder particles. In addition, there is an advantage that the binder is decomposed after the degreasing step, and the molded body is hardly deformed even after being dissipated. When air atomization is applied in the production of Mg alloy powder, it is easy to obtain a desired irregularly shaped powder.

In one embodiment, the Mg alloy powder contains 3.5 to 12 mass% of Al as a first minor component based on the total mass of the Mg alloy powder, and the balance of the alloy composition is Mg and a unavoidable component. It is preferable to have In the above embodiment, the content of the first subcomponent is more preferably 4.5 to 11% by mass, and still more preferably 5.5 to 10% by mass.

In another embodiment, the Mg alloy powder may further include a second subcomponent in addition to Mg and the first subcomponent from the viewpoint of further improving the functionality of the Mg alloy powder. The second accessory component preferably contains one or more selected from the group consisting of Zn, Ca, Mn, Si, Ni, Cu, Zr, and Sn.

The content is preferably 0.01% by mass or more based on the total mass of the Mg alloy powder from the viewpoint of expressing the effect of improving the functionality of the second additive in the Mg alloy powder, and the mass is 0.05% The above is more preferable, and 0.1 mass% or more is more preferable. On the other hand, the content of the second subcomponent is preferably 12% by mass or less, more preferably 11% by mass or less, and still more preferably 10% by mass or less, based on the total mass of the Mg alloy powder.

When Mg alloy powder has an alloy composition including the second subcomponent in the above proportion in addition to Mg and the above-mentioned first subcomponent Al, desirable characteristics by Mg, flame retardancy, and other functions It becomes easy to obtain a good balance with the sex. In one embodiment, the Mg alloy powder contains 3.5 to 12% by mass of the first subcomponent Al, 0.01 to 12% by mass of the second subcomponent, based on the total mass, and the balance thereof It is preferable to contain Mg and an unavoidable component.

The above-mentioned "unavoidable component" means a component which is originally contained in the Mg raw material or is inevitably mixed in the production process. Usually, it means an element that does not affect the properties of the Mg alloy, and the amount is a slight amount. In the present specification, the "unavoidable component" refers to an element component contained in an alloy raw material such as a molten raw material except Mg, the first accessory component, and the second accessory component. In one embodiment, the content of each of the unavoidable components is preferably less than 0.01% by mass based on the total mass of the alloy material.

Hereinafter, the composition of the Mg alloy powder will be specifically described.
In one embodiment, the Mg alloy powder contains Al as at least a first accessory component. The presence of Al in the Mg alloy powder is preferable in that it is easy to improve the strength of the sintered body, in addition to being advantageous for the improvement of the flame retardancy in the pulverization.

The content of Al is preferably 3.5 to 12% by mass, more preferably 4.5 to 11% by mass, and still more preferably 5.5 to 10% by mass, based on the total mass of the Mg alloy powder. When the content of Al in the Mg alloy powder is adjusted to 3.5% by mass or more, Al is easily concentrated to the oxide film and the liquid phase immediately inside the oxide film. Since the molar volume of Al ₂ O ₃ is larger than that of MgO, densification of the oxide film can be expected. Further, also in the liquid phase immediately inside the oxide film, effects such as a decrease in Mg vapor pressure accompanying the concentration of Al can be expected. From these facts, it is considered that Al can avoid the danger due to the burning of droplets. On the other hand, when the content of Al in the Mg alloy powder is adjusted to 12% by mass or less, the embrittlement of the sintered part due to the increase of the precipitation amount of the Mg-Al intermetallic compound is suppressed, and excellent workability is obtained. Becomes easy.

The Mg alloy powder of the above embodiment preferably contains at least Zn as a second accessory component. Mg alloy powder containing Al and Zn as minor components is easy to obtain a good balance of mechanical properties and processability. The content of Zn in the Mg alloy powder is preferably 0.1 to 8 mass%, more preferably 0.2 to 6 mass%, based on the total mass of the Mg alloy powder, from the viewpoint of improving the mechanical properties. 0.3 to 4% by mass is more preferable.
In a more specific embodiment, the Mg alloy powder comprises 3.5 to 12 wt% of the first accessory component Al, at least 0.1 to 8 wt% of Zn as the second accessory component, and the balance thereof. It is preferable to contain Mg and an unavoidable component as

The Mg alloy powder of the above embodiment may be manufactured using a mixture obtained by combining each metal material to achieve a desired composition, or using an Mg alloy material (billet or ingot) having a desired composition. it can.
For example, an example of a usable Mg alloy material is a Mg-Al based alloy material. Specific examples thereof include AM100A (containing 10% by mass Al), AM60A (containing 6% by mass Al), and AM50A (containing 5% by mass Al).

Other examples include Mg-Zn-Al based alloy materials. As specific examples, AZ91D (containing 9% by mass Al and 1% by mass Zn), AZ61A (containing 6% by mass Al and 1% by mass Zn), AZ63 (containing 6% by mass Al and 3% by mass Zn), AZ81A (Containing 8% by mass Al, 1% by mass Zn).
Among them, AZ91D can be suitably used. In addition, in the above-mentioned Mg alloy material mentioned as a specific example, content (mass%) of each element indicated in the parenthesis has described a typical value, and there is width actually. The same applies to the Mg alloy materials described below.

In another embodiment, the Mg alloy powder preferably contains at least Ca as a second accessory component. In addition to the fact that the presence of Ca in the Mg alloy is advantageous in the formation of the oxide film, it is possible to finely precipitate and disperse Mg-Al-Ca-based intermetallic compounds, Al ₂ Ca, etc. It is preferable also in the point which can improve the intensity | strength of a connection part.

The content of Ca in the Mg alloy powder is preferably 0.5 to 10% by mass, more preferably 1 to 8% by mass, and still more preferably 2 to 5% by mass, based on the total mass of the Mg alloy powder. By adjusting the content of Ca to 0.5% by mass or more, it becomes easy to form a fine oxide film containing Ca on the droplet surface during atomization by air atomization, and the danger due to the combustion of the molten metal It becomes easier to avoid. On the other hand, by adjusting the content of Ca to 10% by mass or less, the embrittlement of the sintered part due to the increase of the precipitation amount of the intermetallic compound is suppressed, and it becomes easy to obtain excellent processability. 20 mass% or less is preferable, as for the sum total of content of Al and Ca in Mg alloy powder from a viewpoint of suppressing the increase in the precipitation amount of an intermetallic compound, 15 mass% or less is more preferable, and 10 mass% or less is more preferable .
In a more specific embodiment, the Mg alloy powder comprises 3.5 to 12% by mass of the first accessory component Al, at least 0.5 to 8% by mass of Ca as the second accessory component, and the balance thereof. It is preferable to contain Mg and an unavoidable component as

The Mg alloy powder of the above embodiment may be manufactured using a mixture obtained by combining each metal material to achieve a desired composition, or using an Mg alloy material (billet or ingot) having a desired composition. it can. For example, an example of a usable Mg alloy material is a Mg-Al-Ca based alloy material. As a specific example, (containing 6 wt% Al, 2 wt% _Ca) AMX602, the _{Mg 85} Al 10 _Ca 5 (10 atomic% (10.7 mass%) Al, 5 atomic% (7.9 wt%) Ca Contained).

In yet another embodiment, the Mg alloy powder preferably contains Zn and Ca as second additives. When Zn and Ca are contained as the second accessory component, the total content thereof is preferably 0.6 to 12% by mass, more preferably 1 to 11% by mass, based on the total mass of the Mg alloy powder. And 2 to 10% by mass is more preferable. However, in view of suppressing an increase in the precipitation amount of the intermetallic compound in the Mg alloy powder, the total content of Al and Ca in the Mg alloy powder is preferably 20 mass% or less, more preferably 15 mass% or less, 10 mass% or less is further more preferable.
In a more specific embodiment, the Mg alloy powder contains 3.5 to 12% by mass of Al as the first accessory component, 0.1 to 6% by mass of Zn as the second accessory component, and 0.2% of Ca. It is preferable to contain 5 to 6% by mass, and Mg and the unavoidable components as the balance thereof.

The Mg alloy powder of the above embodiment may be manufactured using a mixture obtained by combining each metal material to achieve a desired composition, or using an Mg alloy material (billet or ingot) having a desired composition. it can. For example, as an example of the usable Mg alloy material, a Mg-Al-Zn-Ca based alloy material can be mentioned. As a specific example, AZX 912 (containing 9 mass% Al, 1 mass% Zn, 2 mass% Ca), AZX 311 (containing 3 mass% Al, 1 mass% Zn, 1 mass% Ca), and AZX 611 (6 mass%) Al, containing 1% by mass Zn, containing 1% by mass Ca). Among them, AZX 912 can be suitably used.

The Mg alloy powder of the above embodiment can be manufactured by applying a typical technique used in a gas atomization method. In one embodiment, the method of manufacturing the Mg alloy powder comprises (a) melting the molten material to obtain a molten Mg alloy, and (b) spraying the molten magnesium alloy using air. And obtaining the Mg alloy powder. The above step (b) can be carried out by applying a typical technique used in the air atomization method. Production of metal powder by gas atomization is generally carried out using a pulverizing apparatus having divisions such as dissolution, atomization, classification and accumulation. The manufacturing method of the above embodiment can be carried out using at least an apparatus for constituting a melting section and an atomizing section, in which at least air is used to spray the molten metal in the atomizing section.
More specifically, in the above manufacturing method, the step of (a) melting the molten material to obtain the molten metal of Mg alloy can be carried out using a melting furnace equipped with a graphite crucible or the like. In the step (a), the molten metal of the Mg alloy can be obtained by using the mixture or alloy material having the composition of the Mg alloy described above as the raw material for melting and putting the raw material for melting in a melting furnace and heating it. .

The melting temperature can be adjusted according to the raw material to be used, the characteristics of the apparatus, and the target powder particle size. The melting temperature should be set in consideration of the temperature drop while the molten metal moves from the melting furnace to the position where it is sprayed from the viewpoint of melting the molten material of the Mg alloy and obtaining a preferable liquid phase state when spraying the molten metal. Is preferred. In general, it is preferable to set the melting temperature so that a temperature higher than the liquidus temperature can be secured at the position where the molten metal is sprayed. In general, the dissolution temperature is preferably set to a temperature 50 to 300 ° C. higher than the liquidus temperature of the dissolution raw material.

When a nozzle with a stopper is attached to the bottom of the melting furnace, the temperature drop in the movement of the molten metal from the melting furnace to the nozzle can be suppressed, the temperature of the molten metal at the atomizing position can be controlled, and the oxidation of the molten metal can be suppressed. Becomes easy. In addition, when the atmosphere in the melting furnace is pressurized, it is easy to control the flow rate of the molten metal from the molten metal nozzle, and the formation of oxides in the molten metal and on the surface of the molten metal can be suppressed. In addition, the operability is easily improved, for example, the nozzles are less likely to be clogged, and the quality of the obtained powder is also stabilized.

In the manufacturing method, the step of spraying the molten metal of the Mg alloy using (b) air to obtain the Mg alloy powder can be performed using a general atomizing device. The type of injection of air during atomization may be either a free fall type or a confined type. Whichever method is used, air can be efficiently injected from the periphery of the melt flow, so it is possible to produce finer Mg alloy powder. Moreover, although the pouring direction from a dan dish is generally downward, it can also be sideways or upward. In the case where the pouring direction is horizontal or upward, it is possible to prevent combustion due to dripping of the molten metal to the deposited powder, and atomization can be performed more safely.
In one embodiment, it is preferable to use only air to spray the molten metal from the viewpoint of suppressing the manufacturing cost, but an inert gas may be mixed into the air if necessary. When an inert gas is mixed, it is considered that it becomes easy to control the film thickness and the like of the oxide film. As an inert gas, although argon gas or helium gas can be used typically, nitrogen gas can also be used.

FIG. 1 is a schematic cross-sectional view showing a structural example of an air atomizing device. In the atomizing apparatus shown in FIG. 1, in order to simplify the structure, a molten material is obtained by heating the molten material in a melting furnace, and then the molten metal is manually transferred to a tundish of the atomizing apparatus. In addition, an air nozzle is provided so that air can be jetted laterally to the flow of the molten metal falling from the molten metal nozzle under the tundish.

Hereinafter, the step (b) will be more specifically described by taking the case of using the atomizing apparatus 9 shown in FIG. 1 as an example.
First, the molten metal 1 obtained in the step (a) is transferred to the tundish 2, and the molten metal 1 is made to flow from the nozzle 3 provided below the tundish 2. On the other hand, the molten metal 1 is sprayed by injecting the air 5 from the air nozzle 4 to the flow of the molten metal to form a droplet (sprayed molten metal) 6. A powder is obtained by solidification of the droplets 6. The molten metal dropped without being atomized is recovered by the molten metal receiving plate 7. Also, the powder (not shown) formed by atomization is collected by the powder receiver 8.

When the molten metal is transferred to the tundish, that is, the temperature at the time of pouring is preferably set in consideration of the temperature drop while the molten metal moves from the tundish to the position where it is sprayed. It is preferable to adjust the temperature at the time of pouring so that the temperature higher than the liquidus temperature can be secured at the position where the molten metal is sprayed.

The injection of air can be carried out applying a conventional injection method. For example, air pressurized by a compressor is injected from an air nozzle. The flow velocity of air at the time of injection is adjusted by the injection pressure. The method of performing atomization using air can suppress oxidation because it uses air as a medium in contrast to the water atomization method, and there is no need to worry about the generation of hydrogen due to the reaction between powder and water. . In addition, since a large pump for pressurizing water and a water recovery and purification device are unnecessary, and a drying process of the recovered powder is also unnecessary, significant simplification of the device and process is possible.

The shape and size of the Mg alloy powder can be adjusted by the shape of the melt nozzle, the temperature of the melt, the injection pressure of air, and the like. In one embodiment, the Mg alloy powder obtained by the above-mentioned production method preferably has an irregular shape (amorphous non-spherical shape). The irregularly shaped powder increases the strength of the green compact after molding due to the anchor effect between the powder particles. In addition, there is an advantage that the binder is decomposed after the degreasing step, and the molded body is hardly deformed even after being dissipated.

In the production of metal powder by gas atomization, the droplets immediately after atomization have an irregular shape, but usually, spherical particles are obtained by being spherical due to surface tension before the droplets solidify. On the other hand, in the method of manufacturing the Mg alloy powder of the above embodiment, since air is used, an oxide film is formed on the surface of the droplet immediately after atomization, and it is easy to obtain a powder having an irregular shape.
In the atomizing method using argon gas, a spherical Mg alloy powder is usually obtained, which is considered to be because the formation of an oxide film on the droplet surface is suppressed by the argon gas. From such a point of view, the air atomization method can be said to be a method suitable for producing irregularly shaped Mg alloy powder because the droplet surface is rapidly oxidized by air.

Mg alloy powder manufactured by the manufacturing method of the above-mentioned embodiment has a composition corresponding to a dissolution raw material used at the time of manufacture. The Mg alloy powder can be used in various applications. Usually, in the Mg alloy powder produced by the water atomization method, the oxide film on the powder surface exceeds 1 μm, whereas according to the manufacturing method of the above embodiment, the film thickness of the oxide film is controlled to a thickness less than 1 μm. It is easy to do. The thickness of the oxide film can be observed by a scanning transmission electron microscope (STEM) of a cross section near the surface of the powder.

In one embodiment, from the viewpoint of obtaining excellent sinterability, the thickness of the oxide film on the surface of the Mg alloy powder is preferably 800 nm or less, more preferably 500 nm or less, and still more preferably 200 nm or less. According to the above manufacturing method, it is easy to control the thickness of the oxide film within the above range. Therefore, in one embodiment, the Mg alloy powder of the above embodiment has excellent sinterability and can be suitably used as a powder metallurgy material. By using the Mg alloy powder of the above embodiment, sintered parts excellent in various characteristics can be easily manufactured.

A sintered part can be manufactured by the method of filling and press forming Mg alloy powder in a metal mold etc., and then sintering. Since the thickness of the oxide film on the surface of the Mg alloy powder of the above embodiment is thin, a strong bond between metals is formed during sintering, and it is easy to obtain a sintered part with high strength. The sintering temperature is preferably adjusted appropriately according to the composition of the Mg alloy powder. For example, in the case of Mg alloy powder having a composition of Mg—Al—Zn based alloy material, it is preferable to carry out sintering at a temperature of 450 to 550 ° C. By appropriately adjusting the sintering temperature, it becomes easier to obtain a sintered part with high strength. Further, by adding a step of hot working after that, it is further densified, and the strength of the sintered body is further improved by the introduction of strain. Sintering by hot pressing or pulse current pressure sintering is also effective for densification and high strength.
The sintered parts are not particularly limited, and can be used in various applications. Sintered parts are, for example, parts for transportation equipment such as automobiles, railway vehicles, and aircrafts, parts for electronic equipment such as personal computers and mobile phones, and materials for living bodies such as artificial bones and implants because of characteristics of Mg alloy. It can be suitably used in applications such as

EXAMPLES Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples.

(Examples 1 to 3 and Comparative Examples 1 and 2)
1. Production of Mg Alloy Powder The Mg alloy material shown in Table 1 was used as a raw material for dissolution, and air atomization was performed according to the procedure shown below.
First, commercially available billets or ingots of Mg alloy materials shown in Table 1 were cut into appropriate sizes as melting materials. About 80 g of the cut billet or ingot was weighed and placed in a graphite crucible, placed in a heating furnace, and heated to 650 ° C. in an argon gas atmosphere to melt the billet or ingot.

Next, the graphite crucible was promptly taken out from the heating furnace, and the molten metal was poured into a tundish of an internally-made air atomizing device (see FIG. 1). With respect to the flow of the molten metal falling from the molten metal nozzle set to the downward direction of the tundish, air was injected from the air nozzle installed sideways, the molten metal was sprayed and atomized (powdering). The bore diameter of the molten metal nozzle was φ10 mm, the injection pressure of air was 10 kgf / cm ² , and the bore diameter of the air nozzle was φ1.8 mm.

In Examples 1 to 3, combustion was not confirmed at the time of atomization, and the Mg alloy powder obtained after atomization could be recovered. However, in Example 3, a part of the admixing was insufficient and the molten metal scattered around the molten metal saucer turned blackish, but the fine powder sprayed far showed silver white. The yields of the Mg alloy powder in Examples 1, 2 and 3 were approximately 40 g, 40 g and 20 g in order.

On the other hand, in Comparative Example 1, the molten metal burned violently at the time of taking out the graphite crucible from the heating furnace and pouring it into a tundish. The experiment was stopped because it was judged that the combustion became more intense by the injection of air. Moreover, about the comparative example 2, the droplet immediately after being sprayed by injection of air turns black, and it collides with the wall of the atomizing apparatus, or after falling to a powder receiving tray, it burned with intense flash and white smoke. The molten metal that did not atomize and dropped to the molten metal pan also burned violently as well.
From the above, it can be seen that when the dissolution raw material contains a specific amount of Al, the flame retardancy of Mg is improved, and the production of Mg alloy powder by the air atomization method becomes possible.

2. Analysis of Mg Alloy Powder (1) Observation of Powder Shape by Scanning Electron Microscope (SEM) The powder shape of each of Mg alloy powders by the air atomization method manufactured in Examples 1 and 2 was observed using SEM. The observation was performed by irradiating an electron beam under conditions of an acceleration voltage of 15 kV using Quanta 200 3D FEG manufactured by FEI. Each SEM photograph is shown in FIG. 2 (Example 1) and FIG. 3 (Example 2). As apparent from the SEM photographs, it was found that any of the Mg alloy powders produced in Examples 1 and 2 had irregular shapes.

(2) Analysis of Cross Section of Mg Alloy Powder In order to analyze the state (cross section) in the vicinity of the surface of the Mg alloy powder manufactured in Examples 1 and 2, focused ion beam (FIB) processing is performed on each Mg alloy powder. And foil-like test pieces (about 100 nm thick) were respectively collected. FIB processing was performed under conditions of ion beam: Ga ion, acceleration voltage: 30 kV, protective film: carbon, using a composite beam processing and observation apparatus “JIB4501” manufactured by Nippon Denshi Co., Ltd.

Using the scanning transmission electron microscope (STEM) “JEM-2100F” manufactured by JEOL Ltd. for each of the test pieces of Examples 1 and 2 collected as described above, under the conditions of an accelerating voltage of 200 kV, Each cross section was observed. Further, analysis of element mapping was performed using an energy dispersive X-ray detector “JED-2300” manufactured by Nippon Denshi Co., corresponding to the measurement region of the STEM photograph, and the distribution state of the elements was observed.

The STEM photograph which shows the state (cross section) of the surface vicinity of Mg alloy powder manufactured in Example 1 is shown in FIG. Further, images of elemental mapping by STEM / EDX corresponding to the STEM photograph shown in FIG. 4 are shown in FIGS. 5A to 5C. FIG. 5A is an image showing elemental mapping of O, FIG. 5B is an elemental mapping of Ca, and FIG. 5C is an image showing elemental mapping of Al.
The STEM photograph which shows the state (cross section) of the surface vicinity of Mg alloy powder manufactured in Example 2 is shown in FIG. Moreover, the image of the element mapping by STEM / EDX corresponding to the STEM photograph shown in FIG. 6 is shown to FIG. 7A and 7B. FIG. 7A is an image showing elemental mapping of O, and FIG. 7B is an image showing elemental mapping of Al.

In the test piece of the Mg alloy manufactured in Example 1, as can be seen from the STEM photograph shown in FIG. 4, a black layer and a thin gray layer under the black layer were present on the surface side (above the image) of the test piece. . In the element mapping (O) shown in FIG. 5A, the concentration of oxygen (O) can be confirmed across the above-mentioned layers, and thus it was found to be an oxide film having a thickness of about 130 nm. Further, as can be seen from the element mapping (Ca) shown in FIG. 5B and the element mapping (Al) shown in FIG. 5C, concentration of Ca and Al was also confirmed in the oxide film.

In the test piece of the Mg alloy manufactured in Example 2, as can be seen from the STEM image shown in FIG. 6, a black layer was present on the surface side of the test piece (above the image). From the element mapping (O) shown in FIG. 7A, the concentration of oxygen (O) can be confirmed, which indicates that the layer is an oxide film having a thickness of about 70 nm. As can be seen from the element mapping (Al) shown in FIG. 7B, in the test piece of the Mg alloy manufactured in Example 2, the clear Al as seen in the test piece of the Mg alloy manufactured in Example 1 No thickening to the oxide film (see FIG. 5C) was observed.

(3) Line Analysis of Al Distribution For the Mg alloy powders of Example 1 and Example 2, line analysis was performed to compare the distribution of Al. The line analysis result of each test piece of Example 1 and Example 2 is shown in FIG. 8 and FIG. Since the oxide film on the powder surface is not a plane perpendicular to the observation surface and the analysis line, the boundary of the oxide film is not sharpened by picking up the information on the outermost surface and the matrix interface. Here, the area of the oxygen (O) peak is defined as the area of the oxide film. In line analysis, the elemental mapping data by EDX was used for the range of 200 nm in width centered on the dotted line (a in the figure) shown in the STEM photographs of Example 1 and Example 2 shown in FIG. 4 and FIG. It is used to convert line analysis results.

Although the absolute value of strength can not be compared between FIG. 8 and FIG. 9 due to the influence of the thickness of the sample, the alloy composition, etc., in either case, the rise of the Al strength (concentration) from the surface to the inside starts It was found that the position or peak position was shifted to the inner side (inside) of the powder compared to other elements. In the Mg alloy powder of Example 1, a peak of Al was observed in the region of the oxide film (see FIG. 8), and it was found that Al was enriched. On the other hand, in the Mg alloy powder of Example 2, a broad Al peak is observed in the vicinity of the inner side boundary of the oxide film (see FIG. 9), and Al is concentrated from the oxide film to the inner base material. I understand.

From the above results, as represented by Examples 1 and 2, it was found that the presence of a specific amount of Al in the Mg alloy is effective for improving the flame retardancy of the molten metal. Without being bound by theory, the Mg alloy powder contains a specific amount of Al, so that the molten metal of the melting material is refined by the injection of air, and is quenched to become droplets, and at the same time Al is deposited on the droplet surface. A thick, thin and dense oxide film was formed, and the film blocked the contact between the liquid phase inside the droplet and oxygen in the air atmosphere, so that the molten metal could form powder particles without burning at the time of atomization. Conceivable. In addition, when Ca is contained simultaneously with Al, the concentration of Al into the oxide film is promoted, so the oxide film is further densified and it is considered that the flame retardancy is improved. Also, from the results of line analysis of the Mg alloy powder of Example 2, Al concentrated in the oxide film contributes to the densification of the oxide film, and Al concentrated in the base material from the oxide film has a vapor pressure of Mg It is inferred that it contributes to the improvement of the flame retardance by contributing to the descent of the

On the other hand, it is understood from the condition at the time of atomization in Example 3 that the effect of the flame retardancy in the molten metal decreases with the decrease in the Al concentration. Therefore, it is clear that in order to apply the air atomization method, a specific amount of Al is required in the Mg alloy, and therefore, in the pure Mg of Comparative Example 1 containing no Al, combustion occurs and the atomization is not possible. It is thought that it became possible.

As typified by Examples 1 to 3, according to the embodiment of the present invention, irregular shaped Mg alloy powder can be obtained, and the thickness of the oxide film on the powder surface is as thin as about 70 to 130 nm. Therefore, it is considered easy to obtain excellent sinterability. Therefore, in one embodiment, the Mg alloy powder produced by the production method of the above embodiment is considered to be effective as a powder sintered material for producing a sintered part.

1: Molten metal 2: Tundish 3: Molten metal nozzle 4: Air nozzle 5: Air 6: Droplet 7: Molten metal pan, 8: Powder pan, 9: Atomizing device

Claims

Mg alloy powder manufactured by air atomizing method, containing Mg as a main component and containing 3.5 to 12 mass% of Al as a first subcomponent based on the total mass of the Mg alloy powder , Mg alloy powder.
The Mg alloy powder according to claim 1, having an oxide film on the surface, wherein the oxide film contains Al as the first subcomponent.
An Mg alloy powder containing Mg as a main component and containing 3.5 to 12% by mass of Al based on the total mass of the Mg alloy powder as a first accessory component,
Mg alloy powder which has an oxide film with a film thickness of less than 1 micrometer on the surface, and the oxide film contains Al of the 1st subcomponent.
The method according to any one of claims 1 to 3, further comprising one or more elements selected from the group consisting of Zn, Ca, Mn, Si, Ni, Cu, Zr and Sn as a second accessory component. Mg alloy powder according to item 1.
The Mg alloy powder according to claim 4, wherein the content of the second accessory component is 0.01 to 12% by mass based on the total mass of the Mg alloy powder.
The Mg alloy powder according to any one of claims 1 to 5, which has an irregular shape.
The composition according to any one of claims 1 to 3, which has a composition of Mg-Al alloy, Mg-Al-Zn alloy, Mg-Al-Ca alloy, or Mg-Al-Zn-Ca alloy. Mg alloy powder.
A sintered part using the Mg alloy powder according to any one of claims 1 to 7.