JP3776069B2 - Method for producing magnesium rapidly solidified alloy products - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a magnesium alloy product that is excellent in strength and elongation and can be used in various industrial fields.
[0002]
[Prior art]
It is known that amorphous alloys or alloys having very fine crystals can be obtained in various compositions by rapidly cooling a molten alloy. These alloys are called rapidly solidified alloys, and particularly alloys made of fine crystals of nanometer size are often manufactured by a single roll method that can easily realize a high cooling rate, and are Fe-based, Al-based, or A number of rapidly solidified alloy materials have been obtained for Mg-based alloys. Among these, Mg-based rapidly solidified alloys have a lower specific gravity and lighter weight than other rapidly solidified alloys, and are expected to be applied in various fields. As such an Mg-based rapidly solidified alloy, there is an Mg-Al-M (M is at least one selected from Ga, Sr, and Ba) -based rapidly solidified alloy (Patent Document 1).
[0003]
However, the shape of Mg-based rapid solidification alloys that can be produced by the single roll method is limited to ribbons, and the range of application is limited if the ribbons are in the shape of ribbons, so various shapes such as rods can be rapidly solidified. There is a need to develop alloy materials. Therefore, a rapidly solidified alloy having a powder shape is prepared by using an atomizing method, and an alloy that is easily solidified and formed into a target shape by hot pressing, extrusion molding, or the like has been developed (Patent Documents 2 and 3).
In addition, a closed system for powder metallurgy that is possible from atomization to hot pressing in a completely sealed state has been reported (Non-Patent Document 1).
On the other hand, a method for producing an amorphous magnesium alloy has been developed as a technique for producing a large rapidly solidified cast material by a casting technique regardless of the powder metallurgy technique (Patent Document 4).
The inventors of the present invention have found that an Mg-based alloy having both high strength and high ductility can be obtained by limiting the composition of the Mg-based alloy and its crystal structure and causing a long-period hexagonal structure to appear. -60978 was filed and reported as a paper (Non-Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-171331 [Patent Document 2]
Japanese Patent Laid-Open No. 7-3375 [Patent Document 3]
JP 7-90462 A [Patent Document 4]
Japanese Patent No. 2963225 [0005]
[Non-Patent Document 1]
Journal of the Japan Institute of Metals, “Materia”, 27 (1998) p.412
[Non-Patent Document 2]
Akihisa Inoue et al., `` Novel hexagonal structure and ultrahigh strength of magnesium solid solution in the Mg-Zn-Y system '', J. Mater. Res., Materials Research Society, July 2001, Vol. 16, No. 7, p. .1894-1900
[0006]
[Problems to be solved by the invention]
The Mg-based rapidly solidified alloy disclosed in JP-A-7-3375 and JP-A-7-90462 produces a fine Mg alloy powder having a powder particle size of 100 μm or less by a method such as an atomizing method, and then Manufactured by a solidification molding process. Highly active magnesium alloys are ignitable by themselves, and there is a risk of dust explosion and the like when the powder particle size becomes small. In addition, since the magnesium-based alloy is highly active, the powder easily oxidizes, and the oxide generated in the powder state is present even after being molded into the target shape, which causes a problem that the strength is reduced.
[0007]
As a method for preventing such danger and the formation of an oxide film, a closed system for powder metallurgy that is possible from atomization to hot pressing in a completely sealed state has been reported (Non-Patent Document 1). Such manufacturing processes can produce samples for testing and research, but considering productivity, the manufacturing equipment itself is expensive and large parts cannot be produced. There was a problem with the conversion. From the viewpoint of practical use, there has been a demand for a method of producing a rapidly solidified alloy having high strength and high ductility by a casting method regardless of the method of powder metallurgy.
[0008]
The method for producing an amorphous magnesium alloy (Patent Document 4) is a production method that can provide a magnesium alloy having excellent strength by limiting the alloy composition and casting conditions. High crystallizing ability, that is, the supercooled state when cooling from the molten metal is very stable, and it is an alloy composition that can be cast without crystallization to room temperature, so it can produce large products. is there.
[0009]
However, the amorphous magnesium alloy has a phenomenon of embrittlement at room temperature and has no plastic elongation at all, so it cannot be put into practical use due to a problem of reliability. Even when trying to apply the above manufacturing method to a conventional crystalline magnesium-based alloy, unlike an amorphous magnesium alloy, the supercooled state is very small, so that precipitation of compounds causing embrittlement occurs. There was a problem that it was difficult to cast in a suppressed state.
[0010]
[Means for Solving the Problems]
In view of these problems, the present inventors have intensively studied for the purpose of providing a method for producing a high-strength magnesium alloy that can withstand practical use regardless of the method of powder metallurgy. As a result, in a specific magnesium alloy, the molten metal is inserted into a mold that rotates at a high speed, and the molten metal rapidly solidifies while obtaining centrifugal force in the mold to produce a rapidly solidified magnesium alloy. The inventors have found that a highly ductile magnesium alloy can be produced, and have completed the present invention.
[0011]
That is, the present invention relates to a composition formula Mg _100-ab Ln _a Zn _{b in which} the average composition of the entire alloy is atomic% (where Ln is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, One or more rare earth elements selected from Tb, Dy, Ho, Er, Tm, Yb, Lu, or Misch metal, 0.5 ≦ a ≦ 5, 0.2 ≦ b ≦ 4, and 1.5 ≦ a + b ≦ 7) is melted into a molten metal, and a mold made of a material selected from steel, stainless steel, copper, or copper alloy is kept in the mold with the mold temperature kept at 50 ° C. or lower. The mold is rotated at a speed at which the rotational peripheral speed of the part closest to the center of rotation of the product forming part is 20 m / s or more, the molten metal is inserted into the mold, and the molten metal is held by the centrifugal force received from the mold. A magnet characterized by rapidly solidifying in a mold while producing a magnesium alloy casting with a maximum thickness of 10 mm or less This is a method for producing a cesium rapidly solidified alloy product.
[0012]
The magnesium alloy according to the present invention has a composition formula by atomic% Mg _100-ab Ln _a Zn _b (where Ln is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, One or more rare earth elements selected from Ho, Er, Tm, Yb, Lu, or Misch metal, 0.5 ≦ a ≦ 5
0.2 ≦ b ≦ 4 and 1.5 ≦ a + b ≦ 7, preferably 1.5 ≦ a ≦ 4.5, 0.5 ≦ b ≦ 2, and 2 ≦ a + b ≦ 6 . When this alloy is rapidly cooled in the mold, it has a feature that a supercooled liquid state is generated during cooling below the melting temperature and the mold can be filled with the molten metal.
[0013]
The content of one or more rare earth elements selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or Misch metal is 0. If it is less than 5 atomic%, the increase in strength is not remarkable, and the supercooled liquid is not stable, so that it easily solidifies and makes it difficult to fill the mold. If it exceeds 5 atomic%, it becomes brittle and cannot be put to practical use. If the Zn content is less than 0.2 atomic%, the increase in strength is not remarkable, and the supercooled liquid is not stable, so that it easily solidifies and makes it difficult to fill the mold. If Zn exceeds 4 atomic%, it becomes brittle and cannot be put to practical use.
[0014]
Sum of one or more rare earth elements selected from Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or Misch metal and Zn 1.5 atomic% or more and 7 atomic% or less. If it is less than 1.5 atomic%, the increase in strength is not remarkable, and the supercooled liquid is not stable, so that it is easy to solidify and it is difficult to fill the mold. If it exceeds 7 atomic%, it becomes brittle and cannot be put to practical use.
[0015]
The mold used in the present invention is a mold made of a material selected from steel, stainless steel, copper and copper alloy. Because the molten metal needs to be cooled rapidly in the mold, a sand mold or the like cannot be used. Any material can be used as long as the mold material is a material selected from steel, stainless steel, copper and copper alloys, depending on the product to be manufactured. Alternatively, it is desirable to use a copper alloy. Further, if the mold temperature may rise, such as when casting a large product, it is desirable to use a mold that can be cooled with water. When manufacturing products with complex shapes, use steel or stainless steel that has high hardness and a relatively low cooling rate on the mold surface in order to maintain high mold accuracy and maintain a normal hot water flow during casting. It is desirable.
[0016]
The temperature of the mold is 50 ° C. or less. Although the minimum of temperature is not limited, Usually, it is 0 degreeC or more for prevention of dew condensation. When the temperature is higher than 50 ° C., it cannot be rapidly solidified, the compound is precipitated, and the product becomes brittle.
[0017]
The rotational peripheral speed of the mold needs to be 20 m / s or more at the portion closest to the rotation center of the product forming portion in the mold. When it is less than 20 m / s, when the molten metal is inserted into the mold, the centrifugal force does not act greatly on the molten metal, the cooling rate does not increase, blow holes are generated, and a normal cast product cannot be obtained. . The upper limit of the speed is not particularly specified, but is usually 80 m / s or less. If the rotational peripheral speed exceeds 80 m / s, the mold may be destroyed, and when the molten metal collides with the innermost part of the product forming part of the mold, there is a tendency that the impact is strong and a hot water defect is likely to occur.
[0018]
The shape of the mold is not particularly defined, but it must be designed so that a rotational balance can be obtained before and after casting so that vibration does not occur even if it rotates within the scope of the manufacturing method of the present invention. In addition, it is necessary to design the mold shape so that the pouring gate part from the part reflecting the jet made of molten metal to the product forming part and the hot water flow in the product forming part are good.
[0019]
The shape of the magnesium rapidly solidified alloy material produced by the production method of the present invention needs to have a maximum thickness of 10 mm or less, preferably 5 mm or less. If it exceeds 10 mm, the cooling rate inside the product tends to be low and the product tends to become brittle. Further, the maximum width of the product shape is desirably 200 mm or less, and more preferably 100 mm or less in order to allow the molten metal to flow through the entire product forming portion. If the maximum width of the product shape exceeds 200 mm, it tends to be difficult to uniformly insert the molten metal into the mold.
[0020]
In addition, when it is difficult to fill the mold with molten metal, the temperature of the molten metal is improved in the normal casting method to improve the flow of molten metal, but in the method of the present invention, increasing the temperature of the molten metal is a mold. However, since the amount of heat taken away from the molten metal increases, the cooling rate is lowered, causing precipitation of the compound and reducing the elongation, which is not preferable. Therefore, as for the temperature of the molten metal at the time of charging to a metal mold | die, melting temperature + (20-100 degreeC) is desirable.
[0021]
In the present invention, the cooling rate in rapid solidification is not limited, but normally, the manufacturing method of the present invention can realize a cooling rate of 10 ³ K / sec or more.
[0022]
Furthermore, according to the method of the present invention, since the cooling rate is fast and the hot water of the product is likely to be produced, the method of inserting the molten metal into the mold is selected with a fast insertion rate, and the rate faster than the solidification rate of the product forming part. Need to be inserted. As a desirable insertion method, use a mold with a part that reflects the jet of molten metal at the center of the rotating mold, and jet the molten magnesium alloy from the place where the rotation axis of the mold is extended toward the mold center. There is a method in which a jet of molten metal is reflected by the reflecting portion in a direction perpendicular to the product forming portion of the mold, and the molten metal is inserted into the product forming portion of the mold.
[0023]
According to this insertion method, the molten metal can be rapidly filled in the product forming portion by the speed of the molten metal jet and the acceleration received from the mold. Furthermore, according to this insertion method, the molten metal can be transported to the vicinity of the product forming portion, and the insertion speed is controlled by controlling the speed of the jet by pressing the molten metal in the container that supplies the molten metal into the mold. Is easy.
[0024]
In the production method of the present invention, the magnesium alloy cast material has a portion where a component element other than Mg is concentrated in a part of each crystal, and further, a part of the crystal of the magnesium alloy cast material or It is desirable to have a long-period hexagonal structure over the entire area. The state having a portion where elements other than Mg are concentrated in a part of the crystal and the state having a long-period hexagonal structure in a part or the whole of the crystal adopt the manufacturing method of the present invention, It can be easily obtained by keeping the insertion temperature within the above temperature range. The strength of magnesium rapid solidification alloys is increased by having a part where the elements other than Mg are concentrated in a part of the crystal or having a long-period hexagonal structure in part or all of the part of the crystal. Tend to.
[0025]
The ratio in the crystal of the region where the constituent elements other than Mg are concentrated, and the ratio in the crystal of the region having the long-period hexagonal structure differ depending on the manufacturing conditions. When it has a long period hexagonal structure, it is 20%-100% area | region in a crystal | crystallization by volume ratio.
[0026]
A state in which a part other than Mg is concentrated in a part of the crystal can be easily determined by measuring the concentration distribution inside the crystal of the magnesium alloy cast material using an energy dispersive X-ray fluorescence analyzer. be able to. Moreover, the state which has a long-period hexagonal structure in a part or the whole in a crystal | crystallization can be easily judged by obtaining a limited visual field diffraction pattern for a magnesium alloy cast material with a transmission electron microscope.
[0027]
The manufacturing method will be described below based on examples of apparatuses suitable for the manufacturing method of the present invention.
FIG. 1 conceptually shows an example of a casting apparatus used in the present invention. According to the apparatus of FIG. 1, at the upper part of the copper rotating mold 15 where the rotational peripheral speed of the portion closest to the rotation center of the product forming portion 17 is rotating at a peripheral speed of 20 m / s to 50 m / s, The alloy 19 is filled in the mild steel nozzle 13 and heated with the coil 14 of the high-frequency induction heating device in a state where the mild steel nozzle 13 is moved upward to melt the mother alloy 19. When the mother alloy 19 is sufficiently dissolved, the mild steel nozzle 13 is lowered by the operation of the air cylinder 12, an inert gas such as argon is introduced from the gas supply tube 11, the inside of the mild steel nozzle 13 is pressurized, and the nozzle Extrude the molten magnesium alloy through the orifice at the tip.
[0028]
After the molten metal flow 16, which is pushed out toward the center of the rotary mold from the orifice located at the place where the rotary shaft of the rotary mold is extended and jetted in a jet shape, falls from the orifice at the lower end of the mild steel nozzle 13 to the molten metal receiving portion 18. The jet made of the molten metal is reflected by the molten metal receiving portion 18, passes through the runner 20 in the rotating mold 15, and is inserted into the product forming portion 17. In the product forming unit 17, the molten metal is rapidly cooled and solidified by contact with the rotating mold 15 while receiving centrifugal force from the rotating mold 15. Thereafter, the rotation of the rotary mold 15 is stopped, and the upper part of the rotary mold 15 is removed from the lower part, and then the magnesium rapid solidification alloy material as a product is taken out from the product forming portion 17.
[0029]
Thus, the manufacturing method of the present invention improves the thermal contact between the molten metal and the rotating mold due to the centrifugal force, so that a product solidified at a high cooling rate can be produced. Therefore, supersaturated solute atoms can be prevented and unnecessary precipitates can be prevented from being deposited, and a magnesium alloy product having high strength and high ductility can be provided. Furthermore, since the supercooled state of the alloy used in the present invention is stable, when the molten metal is held by centrifugal force and cooled, the product forming portion in the supercooled liquid state can be densely filled. For this reason, the generation of pores and the like can be made minute, and a magnesium alloy product having high strength and high ductility can be produced.
[0030]
【Example】
The present invention will be specifically described below with reference to examples and comparative examples.
(Example 1)
The Mg ₉₇ Zn ₁ Y ₂ (at%) alloy material was cast under the following conditions using the apparatus shown in FIG. Melting temperature: 700 ° C., orifice diameter: 1.5 mm, ejection pressure: 3 kg / cm ² , rotating mold: copper 200 mmφ (radius from rotating center to product part: 100 mm), product shape: 30 mm × 50 mm × 3 mm, mold Rotational speed: 5000 rpm, master alloy weight: 30 g, atmosphere: 5 × 10 ⁻² Pa, and then argon gas is replaced with 0.9 Pa.
[0031]
The product was cut, and the cross section was observed at 10 points with a 200 × field of view by an optical microscope, but no pores were observed in the cross section. A tensile test was performed with an Instron tensile tester. The tensile rupture stress was 240 MPa and the elongation was 17%, and a material having an elongation much higher than that of the conventional die-cast alloy could be obtained.
[0032]
When the cast material was analyzed for concentration and structure inside the crystal using a transmission electron microscope and the attached energy dispersive X-ray fluorescence spectrometer, elements other than Mg were found in 7at% Y and 7at% Zn in part of the crystal. Concentrated sites were observed with a width of about 50 nm, and some of them were found to have a long-period structure having a periodic structure three times that of normal Mg.
[0033]
(Example 2)
A mother alloy having a composition of Mg ₉₇ Zn ₁ Mm ₁ (Mm is a misch metal) was cast under the same conditions as in Example 1. The cross section of the product was observed in the same manner as in Example 1, but no pores were observed in the cross section. The tensile strength was 240 MPa, and the elongation was 8%, and a product having elongation compared to the conventional die casting method could be obtained.
[0034]
(Example 3)
A mother alloy having a composition of Mg ₉₅ Y ₄ Zn ₁ (at%) was cast under the same conditions as in Example 1. The cross section of the product was observed in the same manner as in Example 1, but no pores were observed in the cross section. The tensile strength was 300 MPa, and the elongation was 6%. A product having higher strength than that of the conventional die-cast material and the same elongation could be obtained. The cast material was analyzed for concentration and structure inside the crystal using a transmission electron microscope and the attached energy dispersive X-ray fluorescence spectrometer. As a result, 7at% Y and 7at% Zn other than Mg were partially contained inside the crystal. The site where the element is concentrated was observed to have a width of about 50 nm, and a part of it was found to have a long-period structure having a periodic structure three times that of normal Mg.
[0035]
(Comparative Example 1)
Mold casting was performed using the same Mg ₉₅ Y ₄ Zn ₁ (at%) alloy as in Example 2 in a configuration in which the rotating mold portion of the manufacturing apparatus in FIG. 1 was replaced with the stationary mold shown in FIG. The casting conditions are as follows.
Melting temperature: 700 ° C., orifice diameter: 1.5 mm, ejection pressure: 3 kg / cm ² , stationary mold: copper mold, product shape: 30 mm × 50 mm × 3 mm, master alloy weight: 30 g, atmosphere: 5 × 10 ⁻² After deaeration to Pa, argon gas is replaced to 0.9 Pa.
[0036]
When the cross section of the product was observed in the same manner as in Example 1, pores having a diameter of 1 to 3 μm were observed in each field of view. The tensile strength was 250 MPa, and the elongation was 6%. Both the tensile strength and the elongation were lower than those produced using the method for producing a high-strength magnesium alloy material of the present invention.
[0037]
(Comparative Example 2)
A mother alloy having an AZ91C (JIS standard MC2) composition was cast under the same conditions as in Example 1. When the cross section of the product was observed in the same manner as in Example 1, pores having a diameter of 1 to 2 μm were observed in each field of view. The tensile strength was 220 MPa, and the elongation was 5%. Only products that were equivalent in strength and elongation to those obtained by the conventional die casting method were obtained.
[0038]
【The invention's effect】
As described above, a magnesium alloy product with high strength and elongation can be provided by using the method for producing a rapidly solidified magnesium alloy material of the present invention.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an example of an apparatus for carrying out the method for producing a magnesium rapidly solidified alloy product of the present invention.
FIG. 2 is a conceptual diagram showing an example of an apparatus for producing a magnesium rapid solidification alloy material by a conventional method as a comparative example.
[Explanation of symbols]
11 Gas supply tube 12 Air cylinder 13 Mild steel nozzle 14 High frequency coil 15 Rotating die (copper)
16 Molten metal flow 17 Product formation part 18 Molten metal receiving part 19 Master alloy 20 Runway 21 Stationary mold (made of copper)

Claims (4)

A composition formula in which the average composition of the whole alloy is atomic% Mg _100-ab Ln _a Zn _b (where Ln is Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, One or more rare earth elements selected from Er, Tm, Yb, Lu, or Misch metal, 0.5 ≦ a ≦ 5, 0.2 ≦ b ≦ 4, and 1.5 ≦ a + b ≦ 7) The magnesium alloy is melted to form a molten metal, and the mold made of a material selected from steel, stainless steel, copper, or copper alloy is rotated at a product forming portion in the mold while the mold temperature is 50 ° C. or lower. The mold is rotated at a speed at which the rotational peripheral speed of the part closest to the center is 20 m / s or more, and the molten metal is inserted into the mold, and the molten metal is rapidly retained in the mold by the centrifugal force received from the mold. Magnesium rapid solidification alloy, characterized by solidifying and producing a magnesium alloy cast material having a maximum thickness of 10 mm or less Product manufacturing method. Using a mold with a part that reflects the jet of molten metal at the center of the rotating mold, the molten magnesium alloy is jetted from the place where the rotation axis of the mold is extended toward the mold center. The magnesium rapid solidification alloy product manufacturing method according to claim 1, wherein the reflective portion reflects the molten jet to the product forming portion in the mold and inserts the molten metal into the product forming portion in the mold. Method. 3. The method for producing a magnesium rapidly solidified alloy product according to claim 1, wherein the magnesium alloy cast material has a portion where a component element other than Mg is concentrated in a part of each crystal. The method for producing a rapidly solidified magnesium alloy product according to any one of claims 1 to 3, wherein the magnesium alloy cast material has a long-period hexagonal structure in part or all of the crystal.

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