JP2002256307A - Method for manufacturing magnesium-alloy powder using rapid solidification, and method for forming from the powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a high strength article of complicated shape requiring no inert gas in the powder metallurgy of magnesium alloy and extrusion thereof. SOLUTION: In the method for manufacturing the magnesium-alloy member of complicated shape, a rapidly solidified magnesium-alloy nonequilibrium material is prepared, pulverized into ultrafine grain size and then formed into a preformed material at room temperature or at room temperature in vacuum or at a temperature right under the solidus by means of a press, etc., and the preformed material is extruded using an extruding machine. By this method, the magnesium-alloy member of complicated shape combining high formability with high strength of >300 MPa class tensile strength can be manufactured by utilizing the high-temperature softening of the material at high temperature and resultant small amounts of liquid phase of metal while obviating the necessity of inert gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a magnesium alloy powder utilizing rapid solidification and a method of manufacturing a compact thereof, and more particularly to a powder metallurgy method generally used for an aluminum alloy or the like. This method is applied to magnesium alloy materials to eliminate the danger of ignition associated with the melting process during casting of magnesium alloys, and is a method of forming homogeneous, high-strength, high-hardness complex shapes using magnesium alloy powder. Also, it relates to pre-processing and the like necessary for performing the process.

[0002]

2. Description of the Related Art In general, a powder metallurgy method of a magnesium alloy is reported only at a laboratory level, and is limited to a report of extrusion of a bar. In addition, the complex-shaped product is manufactured by a casting method, and an alloy that is frequently used at present is AZ91 which exhibits excellent properties in castability and corrosion resistance.
(ASTM standard) alloy. The technique used for this casting is a die casting method or a thixo molding method. In the molding by casting of a magnesium alloy, there is a problem that the risk of ignition is high because the material is in a molten state at the time of molding. Therefore, oxygen that always touches the molten metal must be shut off by an inert gas for fire prevention. On the other hand, there is no industrial example relating to powder metallurgy of magnesium alloy, and molding by a conventional casting method will be exemplified below.

[0003] In the die casting method of magnesium alloy,
Casting is performed at a temperature of about 700 ° C. in order to ensure the ability of the mold to run. The feature of this method is that the molten metal temperature is high,
The advantage is that a part having a good shape, a thin wall and a complicated shape can be produced. Once the molten metal is exposed to air at this temperature and once ignited, the temperature reaches nearly 2200 ° C. For this reason, in die casting, molding is performed by a cold chamber or hot chamber machine, and sulfur hexafluoride gas having a large flame-retardant effect is generally used as a nonflammable gas.
This sulfur hexafluoride gas is a gas whose use has been suppressed and is in a direction of being prohibited from being used. The tensile strength of the cast product obtained by this die casting is about 200 MPa (JIS standard-MC2E).

[0004] Another method of obtaining a high-strength cast material is an American DOWCHEMICAL which has rapidly spread in recent years.
There is a thixomolding method developed by the company. In this case, an injection molding machine used for molding plastics is used to mold a complicated shaped product or a thin-walled product utilizing a semi-molten state of metal. The melting temperature is about 600 ° C. or lower because the shaping is performed at a temperature between the solidus temperature and the liquidus temperature in order to utilize the semi-molten state of the metal. The liquid phase ratio is quite high because the liquid phase gives more fluidity,
In addition, an inert gas is always used because it is necessary to avoid ignition. The tensile strength of the casting obtained by this method is 230M
Pa (Reference 1: Proceeding of the Second In)
ternational Conference on the proceeding of Semi-S
olid Alloys and Composites, (1992) pp159-169).

[0005] In addition, there is an example of a research report in which, although not a powder, a coarse chip during machining is hot-extruded at about 300 ° C to produce a material having a fine crystal grain size, and the material is investigated ( Reference 2: Light metal (1995) vol. 45, No. 10, pp560-5
65).

Further, a gas atomizing method is used as a method for producing a quenched powder. In this case, a large amount of inert gas is required for cooling. Also, the shape of the powder to be produced is
It has been reported that the rods are spherical particles or scale-like (flakes), and are sintered as they are to extrude rods (Reference 3: Scripta METALLURGICA (1989) vol. 23, pp1079-10)
84).

As described above, the forming of a magnesium alloy is mainly limited to the production of a rod by extrusion or the casting utilizing a molten state, and there is no example of producing a complex-shaped product by a powder metallurgy method. Until now, powder metallurgy of magnesium alloys has not been performed because the reactivity with oxygen in the molten state is severe, so a large amount of inert gas is required at the time of powder production, and ordinary bulk materials are not used. This is because extrusion cannot form complicated shapes, and furthermore, it is said that pulverization leads to an explosion immediately. Magnesium alloys have few slip surfaces at room temperature due to their crystal structure, and have poor plastic workability at high temperatures compared to aluminum. Therefore, only a simple-shaped low-strength member using a low-alloy material could be formed.

[0008]

SUMMARY OF THE INVENTION In view of the above prior art, the present inventors have conducted intensive studies with the aim of developing a method of manufacturing a magnesium alloy having a complicated shape, and as a result, have utilized rapid solidification. It was found that the intended purpose could be achieved by producing a magnesium alloy powder, thereby completing the present invention. An object of the present invention is to provide a method for obtaining a complex shaped member of a magnesium alloy by applying powder metallurgy and a subsequent extrusion process to the magnesium alloy. Another object of the present invention is to manufacture and provide a magnesium alloy material having a tensile strength of more than 300 MPa, instead of a conventional cast material having a tensile strength of about 230 MPa.

[0009]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) A method for producing a magnesium alloy powder using rapid solidification, which comprises the following steps: 1) A magnesium alloy is introduced into a roll device and rapidly cooled under vacuum or an inert gas to obtain a non-equilibrium state (supersaturation) (Solid solution) and foil material (ribbon material) with fine crystal grain size
2) A method for producing a magnesium alloy powder, characterized in that a ribbon material is pulverized into powder to obtain a quenched powder. (2) Introduce the molten magnesium alloy into the roll device and
The method according to the above (1), wherein a quenched material of 0 to 50 microns is produced. (3) The method according to (1), wherein the quenched powder is pulverized by a high-energy-input mill in an inert gas or a vacuum at or below atmospheric pressure. (4) A method for forming a quenched powder produced by the method described in the above (1) to produce a molded body, comprising the following steps: 1) Sintering the powder, preforming and extruding And 2) extruding and molding the material with an extruder to produce a molded body of magnesium alloy powder. (5) A method for storing a sample of a ribbon material or a quenched powder according to the above (1), wherein 1) winding the ribbon material and storing it with a reduced bulk density.
Or 2) Fill the mold with the quenched powder, and apply a pressure of 50 to 50
The method for storing a sample described above, wherein the sample is stored after being densified while holding at about 180 MPa.

[0010]

Next, the present invention will be described in more detail. In the present invention, a non-equilibrium state (supersaturated solid solution) is produced by rapidly cooling the structure of a metal-based material by a single roll made of metal having a high thermal conductivity, and a ribbon material having a fine crystal grain size is produced. Next, the ribbon material is crushed. At this time, when the ribbon material is sheared into powder, a processing strain is applied, so that powder having a finer crystal grain size can be obtained. Further, this powder is preformed for the purpose of degassing to obtain a material for extrusion. Since this material has extremely good fluidity in a wide temperature range from just below the solidus temperature to the temperature at which a liquid phase is formed on the equilibrium diagram, a member having a complicated shape can be formed.
In addition, the obtained member has excellent properties such as a tensile strength exceeding 300 MPa and a Vickers hardness of 80.

In the present invention, it is necessary to prepare a rapidly solidified powder. For example, a method of blowing a molten magnesium alloy onto a copper single roll or twin rolls having good heat conductivity is exemplified. This melting operation is performed in a chamber filled with a vacuum or an inert gas such as argon in order to suppress ignition due to oxidation. The quenched material is a quenched foil material (ribbon) having a thickness of about 100 microns, preferably about 30 to 50 microns for effective subsequent pulverization. The obtained ribbon material can be stored with reduced bulk density by winding.

Next, grinding is carried out by a ball mill. Since the strength of the quenched ribbon material is higher than that of the cast material and is close to 300 MPa, the crushing effect of the rolling mill is small, and efficient grinding cannot be performed. The use of a high-energy-input mill such as a mold enables more rapid pulverization. As for the atmosphere during the pulverization, the oxidation in the powder can be more suppressed when the pulverization is performed in an inert gas or a vacuum at or below atmospheric pressure. Table 1 shows the results of grinding at 170 rotations per minute for up to 25 hours.

In the present invention, the pulverization time was increased to 50 hours, and it was confirmed whether or not the particles became finer. However, there was no change. This is because the crushed powder is already in an agglomerated state when crushed for 25 hours and sticks to the bottom of the crushing container.
This coagulated state is hard enough to be broken by picking by hand, and no special pulverization for re-dispersion is required. In addition, ordinary magnesium alloy chips lose their metallic luster in a few hours when the humidity is high, and the surface oxidation progresses. It was shown.

The quenched powder obtained has a ribbon material thickness of 4
Some of the powders were pulverized to about 10 μm compared to 0 μm, and the surface area was significantly increased. If such a fine metal powder is stored at room temperature as it is, there is a risk of ignition.

Therefore, the method of storing the powder was also tested. At room temperature, 14 g of powder was filled into a superhard cylindrical mold having a diameter of 20 mm, and a pressure of 60 MPa was applied from above and below and held for 1 minute, and then a sample was taken out. The apparent density of this sample is 1.5 g / cm ^3, which is more porous than the true density of 1.8 g / cm ³ , but the surface shows a mirror-like metallic luster, and no dust Since the surface area is significantly reduced as compared with the case where the powder is stored, the oxidation can be suppressed. By cutting and observing the cross section, it was confirmed that the surface was a dense pellet. Next, the powder is sintered in vacuum at about 20 ° C. just below the solidus temperature to produce a preform material having a true density of about 99%. Next, the above-mentioned material is extruded to produce a molded body. It is preferable that the extruder can control the temperature within ± 5 ° C as much as possible, and in order to avoid ignition, it is preferable to extrude at a liquidus ratio of 10% or more at a temperature higher than the solidus temperature.

[0016]

According to the present invention, a powder having high fluidity which can be extruded in a wide temperature range from immediately below the solidus to immediately above the solidus can be produced. In particular, directly above the liquidus line, a member having a complicated shape can be manufactured. This fluidity guarantees a high fluidity that does not cause solid-liquid separation even in a state of a higher liquid phase ratio, but it is preferable that the liquid phase ratio be as low as possible in order not to use a gas for fire prevention. This fluidity is ensured by the fact that the liquid phase appears at the grain boundaries during the temperature rise.
It is coarse, 0 micron, and has already been separated into two phases, an α phase and a β phase, at room temperature, resulting in solid-liquid separation. However, in this non-equilibrium powder, a liquid phase is gradually generated at a fine grain boundary of about 5 μm due to diffusion of atoms from a supersaturated solid solution state. A liquid phase exists around the crystal particles, and the fluidity can be improved.

[0017]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to the examples. Example 1 In the following Examples 1 and 2, as a single roll device,
A quenched ribbon manufacturing device (manufactured by Nissin Giken) was used. A planetary ball mill (manufactured by Ito Seisakusho) was used for pulverization. An electric current sintering apparatus (manufactured by Sumitomo Coal Mining (currently Izumitec)) was used for preforming the powder. For the extrusion, a press equipped with an image furnace was used. Chemical composition Mg-9m
Cut out magnesium alloy (AZ91D alloy manufactured by Ube Industries, Ltd.) of ass% Al-1mass% Zn,
It was set in a single roll ribbon production apparatus and heated and maintained at 700 ° C. for 1 minute. Then, at 0.15MPa, diameter 200
mm single copper roll at 3000 revolutions, width 2mm
A ribbon material having a thickness of about 40 microns was obtained. In a planetary ball mill, 40 g of the ribbon material was put into a steel container together with steel balls, and the material was placed in a steel container at 65 KPa in an argon atmosphere.
Grinding was performed at 0 rotation for 25 hours.

[0018]

[Table 1]

The powder is taken out and placed in a vacuum at 400 ° C.
To obtain a preform material of almost true density. This was inserted into a container in an extruder, heated to 450 ° C. where a small amount of a liquid phase was formed in the atmosphere, held for 10 minutes, and extruded at an extrusion ratio of 4: 1 to produce a round bar. This material had a strength of 320 MPa, a hardness of Hv80, and exhibited high strength properties. For comparison, when a normal cast material is directly extruded under these conditions, separation of solid and liquid occurs at the initial stage of extrusion, the liquid phase is extruded first, and only the solid phase component is involved. Extrusion occurs only in the state, and cannot be easily extruded. Table 2 shows these results.
Shown in

[0020]

[Table 2]

Example 2 Further, in order to produce a complicated shaped product, a preform material was prepared by sintering this powder at 400 ° C. in a vacuum in the same manner as in Example 1. This was inserted into a container in the extruder, and the same die having the same diameter as that of Example 1 having a diameter of 7 mm was extruded in the atmosphere using a gear-shaped mold having a diameter of 35 mm below the die. The temperature was raised to 470 ° C. where a liquid phase of about 5% was present and maintained for 10 minutes in order to ensure fluidity, but the complex gear-shaped mold could be completely filled.

Example 3 This pulverized powder was converted into a cylindrical form of carbide having a diameter of 20 mm.
g, and a pressure of 60 MPa was applied from above and below and held for 1 minute. Then, the sample was taken out and the diameter was 4 m without preliminary sintering.
m on a die. A press pressure of 100 MPa was applied and the temperature was raised at 15 ° C. for 1 minute. The sample is 3 below the liquidus
Extrusion began at 50 ° C., and the speed gradually increased with increasing temperature. At 450 ° C., which was above the liquidus temperature, sufficient pressure could not be applied with a small hydraulic press. The obtained round bar was free from cracks due to liquid phase generation, and a high-quality bar could be produced without preforming.

[0023]

As described above in detail, the present invention relates to a method for producing a magnesium alloy powder using rapid solidification, a method for molding the same, and the like.
1) It is possible to produce a powder having high fluidity that can be extruded in a wide temperature range from immediately below to just above the solidus line. 2) It is possible to eliminate the danger of ignition accompanying the melting process during casting of a magnesium alloy. 3) A homogeneous, high-strength and high-hardness complex-shaped product can be molded using magnesium alloy powder. 4) A member with a complex shape can be manufactured with high precision. 5) A magnesium alloy material of a grade exceeding 300 MPa. And 6) a method of storing the magnesium alloy ribbon material or the quenched powder produced by the above method safely and with suppressed oxidation can be provided. Is done.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Akira Sugiyama 1-70 Heiwagaoka, Meito-ku, Nagoya City, Aichi Prefecture Inokoishi Housing Building No. 302 (72) Inventor Akihiro Matsumoto Heiwagaoka, Meito-ku, Nagoya City, Aichi Prefecture 1-chome No. 1 Inokoishi House 6 Building 401 F-term (reference) 4E004 DB02 NC09 TA02 TA07 TB04 4K017 AA04 BA10 BB01 EA03 FA03 4K018 AA13 BA07 EA32

Claims (5)

[Claims] 1. A method for producing a magnesium alloy powder using rapid solidification, comprising the following steps: 1) introducing a magnesium alloy into a roll device and rapidly cooling it under a vacuum or an inert gas to obtain a non-equilibrium state; (Supersaturated solid solution) and foil material (ribbon material) with fine crystal grain size
2) A method for producing a magnesium alloy powder, characterized in that a ribbon material is pulverized into powder to obtain a quenched powder. 2. The method according to claim 1, wherein the molten magnesium alloy is introduced into a roll device to produce a quenched material of 30 to 50 microns. 3. The method according to claim 1, wherein the quenched powder is pulverized by a high-energy-input mill in an inert gas or a vacuum at or below atmospheric pressure. 4. A method for molding a quenched powder produced by the method according to claim 1 to produce a molded article,
The following steps; 1) sintering the powder, preforming to obtain a material for extrusion, 2) extruding and molding the material with an extruder to form a magnesium alloy powder. A method for producing a molded article. 5. A method for storing a sample of a ribbon material or a quenched powder according to claim 1, wherein: 1) winding the ribbon material and storing it with a reduced bulk density;
Or 2) Fill the mold with the quenched powder, and apply a pressure of 50 to 50
The method for storing a sample described above, wherein the sample is stored after being densified while holding at about 180 MPa.