JP2003239033A - Magnesium alloy cast and its casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnesium alloy cast and its casting method with which a plastic formability can be improved when a primary working such as extrusion and rolling is performed to sheets or when a secondary working such as forging is performed to a processed sheet. <P>SOLUTION: The magnesium alloy material is melted under state of shutting off from oxygen and the magnesium alloy cast 1, in which a precipitation range 3 dispersed in the magnesium alloy crystal grain exists with little casting defect, is obtained by cooling and solidifying the molten-state magnesium alloy at 1-20 K/sec cooling speed in the casting time. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesium alloy base material cast for plastic working in order to manufacture a magnesium alloy part from a magnesium alloy material, and a casting method thereof.

[0002]

2. Description of the Related Art Recently, for mass-produced home electric appliances, one of the measures for recycling processing and environmental problems is
Attention has been focused on manufacturing exterior parts of home electric appliances from metal materials instead of conventional resin materials. The recycling rate of the resin material is 20%, while 90% of the metal material is recyclable.

Among metal materials, magnesium alloys are lighter and stronger than other metal alloys, and have excellent vibration damping properties. Therefore, magnesium alloys are practically used in portable electronic devices and automobile parts. ing. Further, the magnesium alloy has a characteristic that it requires less recycling energy because it has a relatively low melting point.

FIG. 8 is a schematic view showing a process of manufacturing a magnesium alloy part from a magnesium alloy material. First, in order to obtain a magnesium alloy molded product from a magnesium alloy material, it is generally roughly classified into casting such as die casting and thixomolding and plastic working such as pressing, bending and forging. Casting has a high degree of freedom in molding, but has a problem that the yield is poor and the cost is high due to problems such as surface defects of the cast product and entrapment of bubbles inside. Therefore, in the case of a household electric appliance, etc., which has a relatively simple shape, after directly casting a raw material that approximates the final shape of the component, directly plastically work the raw material.
Alternatively, a method in which primary processing such as extrusion / rolling is performed to make a thin plate, which is then subjected to secondary processing to make a magnesium alloy molded product, and then a magnesium alloy part is manufactured through a coating / drying process is also put into practical use. Has been done. As described above, the method of combining casting and plastic working is considered to be superior to the method of casting alone in terms of shortening tact time during processing, reducing surface defects, and suppressing capital investment.

FIG. 10 schematically shows the state of the metallographic structure of a general shaped material for plastic working used in this manufacturing method. This template 4 is a magnesium alloy of AZ31 containing aluminum, zinc, and manganese as main alloy elements in addition to magnesium. Since the AZ-based magnesium alloy has higher strength and higher corrosion resistance than other magnesium alloys, it is an alloy suitable for the housing of home electric appliances that is easily exposed to sweat and water. Further, in addition to magnesium, an AM-based magnesium alloy containing aluminum and manganese as main alloy elements has high ductility and high impact resistance, and is therefore an alloy suitable for internal mechanical parts and the like.

Magnesium alloy has a hexagonal crystal structure and a small slip surface, and is inferior in plastic workability as compared with other metals. Therefore, conventionally, in order to improve plastic workability, a method of refining the crystal grain size by controlling the cooling rate of a magnesium alloy or adding a crystal refining agent has been proposed. However, it has been found that the refinement of the crystal grain size can be controlled to some extent by controlling the processing strain amount and the processing temperature during the primary processing such as extrusion and rolling.

[0007]

However, if there are many casting defects and segregation of inclusions at the stage of forming, it is not easy to improve these defects during the primary working. That is, this is the magnesium alloy cast material shown in FIG. 10, and in this cast material 4, the precipitate regions 6 are segregated at the crystal grain boundaries of the magnesium alloy crystal phase 5 and the internal voids 7 generated during casting are present. Precipitated at grain boundaries.

Generally, when a molten AZ type magnesium alloy is solidified, components (metals and oxides) which are difficult to form a solid solution in magnesium segregate at the grain boundaries as the magnesium seed crystal grows. It often precipitates in the form of intermetallic compounds in the vicinity of grain boundaries. Further, the gas component which is hard to form a solid solution with magnesium accumulates at the magnesium crystal grain boundaries during solidification, and remains in the matrix 4 as voids 7.

The points where casting defects and inclusions are segregated are
Such a raw material 4 is poor in workability because it easily becomes a starting point of cracks when plastically working from the raw material 4 to a thin plate and from the thin plate to a molded product. Especially for magnesium alloys with few slip systems and poor ductility, the workability is greatly influenced by the quality of the material. In order to improve the workability of such a magnesium alloy, it is desirable to reduce casting defects and inclusions in the base material that is the base material of the thin plate, and prevent segregation thereof.

In view of the above situation, the present invention is intended to reduce the casting defects of metal structures, the inclusions and the prevention of segregation during the primary processing such as extrusion and rolling into a thin plate, or the forging of the processed thin plate. An object of the present invention is to provide a magnesium alloy matrix material capable of improving plastic workability during secondary processing.

[0011]

The magnesium alloy matrix material of the present invention developed to achieve the above object is a magnesium alloy matrix material to be cast for plastic working, wherein In addition, a plurality of precipitate regions containing any one or more of aluminum, zinc, and manganese are present.

Further, the plurality of precipitate regions are characterized in that the distance between the end faces is larger than 0 and smaller than 400 μm.

Inside the alloy, metals other than magnesium, aluminum, zinc, manganese, and other inclusions such as oxides and carbides of these metals are also contained. Most of these inclusions are hard to form a solid solution in the magnesium region, and are present in association with or included in the precipitate region. A state in which multiple precipitate regions are separated from each other in the crystal grain is a state in which the dendrite phase of the magnesium alloy is ghosted and crystal grain boundaries are generated, and multiple precipitate regions are scattered. , Magnesium alloys are present in positions separated from each other by the crystalline phase.

As described above, since the plurality of precipitate regions are separated from each other within the crystal grains, inclusions are also scattered, and segregation of large inclusions, which are the starting points of cracks, is small and the shape material itself. Is highly ductile. When the material has a high ductility, a thin plate obtained by subjecting the material to a primary process such as extrusion or rolling also has a high ductility and good plastic workability. In addition, in general, when subjecting a raw material to primary processing such as extrusion or rolling,
The crystal grains around the inclusions tend to be finer than other crystal grains. Therefore, when the plurality of precipitate regions are separated from each other as in the cast material of the present invention, the crystal grains are fine and uniform throughout the cast material when the primary processing such as extrusion or rolling is performed. The grain size is adjusted to a certain size, the number of large crystal grains that deteriorate the workability is reduced, and the plastic workability is improved.

The practical magnesium alloy is ASTM
The standard defines the composition ratio of alloy components to be contained. Strictly speaking, the precipitate region can be defined as a region in which the concentration of alloy components other than magnesium defined in the ASTM standard exceeds the standard upper limit value of the component defined in the ASTM standard. .

However, in the present invention, the area of one precipitate region is 25 × 10 ⁻¹² πm ² or more and 2500 × 10.
^-12 πm ² or less. A method of deriving the area of the precipitate region will be described. First, a cross-sectional photograph is enlarged and printed, and the weight of the entire paper is measured (this is referred to as M). Next, the paper corresponding to the deposit area is cut out, and the weight of each paper piece is measured (this is defined as m). Letting S be the area of the actual cross section of the raw material taken as a cross-sectional photograph, the area σ of each precipitate area is expressed by the formula σ = S × m / M. Further, the area-equivalent circular diameter of the precipitate region indicates the diameter when the area of one precipitate region observed in the cross-sectional photograph is converted into a circle having the same area. The average diameter of the deposit regions means the average of the area-equivalent circular diameters of the plurality of deposit regions. The precipitate shows a three-dimensional region inside the raw material. When the above-mentioned base material is cut at any cross section, the size of the above-mentioned three-dimensional area can be approximated by averaging a sufficient number of two-dimensional precipitate areas observed at that cross section. In the present embodiment, the sufficient number is 20 or more.

The ratio of the magnesium alloy cast material (sometimes abbreviated as cast material) is 98 to 100% of the theoretical density calculated from the composition of the alloy elements. That is, since there are few voids and gas entrainment in the metal structure of the raw material, it is rich in ductility, and when the raw material is subjected to primary processing such as extrusion and rolling to form a thin plate, and this thin plate is subjected to forging and the like. When performing secondary processing, it is possible to prevent the voids (voids and cavities) from becoming the starting points for cracks during processing and to prevent rupture. Also, when coating and drying the molded product after processing, rupture of internal bubbles It is possible to prevent the problem of surface defects due to.

The shaped material produced in the present invention may be one characterized by containing aluminum in a content ratio of 1.8 to 9.1 wt.%. In the present invention,
The target is an AZ-based magnesium alloy containing a large amount of zinc next to magnesium and aluminum, and an AM-based magnesium alloy containing a large amount of manganese next to magnesium and aluminum. The zinc content in the AZ-based magnesium alloy is lower than the aluminum content, and is substantially less than 2 wt.%, Preferably 1.5 wt.
% To 0.5 wt.%, The manganese content in the AM-based magnesium alloy is less than the aluminum content, and is substantially less than 1 wt.%, Preferably 0.6 wt.%.
The target is ~ 0.3 wt.%. As mentioned above, AZ
The magnesium-based magnesium alloy is excellent in strength and corrosion resistance, and the AM-based magnesium alloy has excellent ductility and impact resistance, and is widely put into practical use as a structural material and a housing.

The present invention is characterized in that a plurality of precipitate regions are separated from each other within the crystal grain, but when the aluminum content ratio is less than 1.8 wt.%, The precipitate region occupied in the crystal grain becomes small. Therefore, it is considered that the effect of inclusion dispersion due to the dispersion of the precipitate region is reduced, and therefore the plastic workability of the blank is deteriorated. On the contrary, if the aluminum content ratio is more than 9.1 wt.%, The volume of the precipitate region itself becomes large, and the precipitate region is connected in a mesh shape and spreads over a wide area. Therefore, there is a possibility that inclusions having a relatively large volume may exist, and thus plastic workability may deteriorate. However, in the matrix material of the present invention, aluminum is 1.8 to 9.1.
Since it is a magnesium alloy raw material contained in a wt.% ratio, the effect of dispersing inclusions in the crystal grains can be expected, and the raw material has excellent plastic workability.

A cylindrical billet, which is a general cast material, is processed into a plate shape through an extrusion process or a forging process, and is then rolled into a magnesium alloy casing plate material that is subjected to plastic working. On the other hand, when the shape of the raw material according to the present invention is a plate shape, it is subjected to only rolling several times without undergoing an extrusion step or a forging step to adjust the wall thickness and to be used for plastic working for a magnesium alloy housing. Since the plate material can be obtained, the process can be simplified and the cost can be reduced.

When the plate thickness of the above-mentioned base material is set to 10 mm or less, only a few rolling steps are carried out without passing through an extrusion process or a forging process, so that a desirable value of 0.
Since a thin plate having a plate thickness of about 3 to 1.5 mm can be obtained, the process can be further simplified and the cost can be reduced.

Since the (0002) plane appears preferentially in the crystal orientation of the surface in the X-ray diffraction pattern, the above-mentioned shaped material is characterized by the crystal growth direction when the material surface is solidified. . Generally, in a magnesium alloy, the (0002) plane becomes prominent in the surface subjected to the pressure, but in the product of the present invention, it is shown that the pressure is applied during the casting.

Further, in order to achieve the above object, the method for casting a magnesium alloy base material of the present invention is to put a magnesium alloy material into a crucible which is a melting device, and to keep the oxygen shut off, the magnesium alloy material inside the crucible. After being melted and supplied to a cooling mold, the molten magnesium alloy is cooled at a cooling rate of 1 to 20 K / sec to be solidified, and the solidified magnesium alloy is drawn out from the cooling mold so that the ingot is continuous. Thus, the magnesium alloy matrix material is cast.

When the molten magnesium alloy is solidified in the cooling mold, the solidified magnesium alloy portion is alternately pulled out and stopped for a time to intermittently pull out the molten magnesium alloy, thereby causing inertial force and vibration. The gas components and inclusions present at the solid-liquid interface where solidification proceeds will be pushed out to the liquid portion, and the gas components and inclusions contained inside the raw material can be reduced.

In this casting method, a method in which the cooling rate in the cooling mold is 3 to 8 K / sec can be adopted. This 3-8K
The cooling rate of / sec is a desirable cooling rate so that the dendrite phase of magnesium solidifies while growing, but is partially annealed by the heat conduction inside the raw material and the dendrite phase becomes a ghost. . As described above, when the precipitate region is left behind in the framework of the ghosted dendrite phase and the precipitate region exists in the crystal grains in a dispersed state, inclusions are dispersed, so plastic workability is superior. It is possible to obtain a raw material.

In this casting method, the magnesium alloy material is prevented from being melted in a state where oxygen is blocked and coming into contact with oxygen to burn. However, in order to block oxygen, the crucible is placed under an inert gas atmosphere. A method can be adopted in which flux is added to a molten magnesium alloy to prevent oxygen from coming into contact with the liquid surface. As the inert gas, air mixed with argon gas, helium gas, SF6 or the like is used.
As the flux, a flameproof flux mainly composed of potassium chloride or magnesium chloride can be used. When the flux is added to the material, it also has the effect of preventing evaporation of the metal from the surface of the molten magnesium alloy.

In the above method, the magnesium alloy material to be charged into the melting apparatus is made into a particulate solid, and the material is charged with the atmosphere around the melting apparatus kept in an inert atmosphere, whereby the crucible for melting the magnesium alloy is obtained. Even if the holding furnace is not provided in the above, by continuously or intermittently feeding the solid particulate material, continuous casting can be performed without interruption of the material feeding. In particular, when a protective atmosphere is created on the surface of the magnesium alloy in the crucible to block oxygen, if the inert atmosphere is opened to feed the material, tact is consumed to create the inert atmosphere again. However, according to this method, the material can be charged without opening, so that the tact can be shortened.

In the above method, the inner wall of the cooling mold has a rectangular cross section, and at least a part of the inner wall is tapered so that the length of its short side is different between the crucible side and the drawing means side. By doing so, it is possible to increase or decrease the stress applied to the magnesium alloy at the time of drawing, improve the material properties, and prevent the ingot from breaking by reducing the friction between the ingot and the mold. it can.

In the above method, if the material of the alloy receiving portion of the crucible which is the melting device and / or the cooling mold is graphite, the thermal conductivity is excellent and the heating / cooling of the material can be carried out smoothly. However, any other material that does not easily react with the magnesium alloy may be used, and a material that does not contain copper, nickel, or iron that significantly impairs corrosion resistance when mixed in the raw material is desirable. It has also been reported that crystal grains become finer when graphite is mixed in a magnesium alloy.

In the above method, a structure capable of blocking oxygen on the surface of the molten magnesium alloy in the melting apparatus or the peripheral portion of the melting apparatus, for example, a chamber outside the melting apparatus, for example, so that evacuation or inert gas replacement can be performed. It is desirable to have a structure that can control the atmosphere in which the melting device is placed. Further, since vaporization frequently occurs from the molten magnesium alloy, it is preferable to provide a chamber also in order to prevent the metal vapor from being released into the atmosphere.

In the above method, if the melting device is provided with an openable / closable lid, diffusion of the metal vapor to the outside of the melting device is suppressed, and the diffused metal vapor adheres to the inner wall of the chamber or the like to solidify the powder metal. It is possible to reduce the generation, reduce the material yield due to the accumulation of powder metal, and prevent the risk of spontaneous combustion. As mentioned in the above method,
It is possible to mix flux with the magnesium alloy material in the crucible as a means of blocking oxygen from the material to control evaporation from the surface of the magnesium alloy in the molten state, but in that case, flux components may mix into the raw material. Therefore, it is desirable to improve the device by attaching a lid to the melting device.

In the above method, if a horizontal cooling mold is connected to the side of the melting apparatus and the magnesium alloy is drawn horizontally, impurities that float on the liquid surface of the molten magnesium alloy and the bottom of the crucible are accumulated. It is possible to prevent the inclusion of impurities, and to manufacture a magnesium alloy matrix material having a good structure and rich ductility.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to FIGS. The embodiment described below is an example embodying the present invention and does not limit the technical scope of the present invention.

FIG. 1 is a sectional view schematically showing the state of the metal structure of the magnesium alloy matrix material 1 according to this embodiment. This magnesium alloy raw material 1 is a magnesium alloy AZ31 having an aluminum content of about 3% and a zinc content of about 1%, which is formed into a plate shape by a casting method described later. The magnesium alloy crystal phase 2 and a plurality of precipitate regions (including one or more of aluminum, zinc, and manganese other than magnesium) 3 are present apart from each other. In this state, the components of the precipitate region 3 divided by the framework of the dendrite phase of magnesium remain dispersed in the crystal grains even when the dendrite phase is ghosted and the grain boundaries appear. It is considered to be in a state of sagging.

Table 1 below shows the ASTM (American Society fo) of AZ31 magnesium alloy.
r Testing and Materials (American Society for Testing and Materials) standards and component ratios of the magnesium alloy matrix 1 according to the present embodiment. The unit is% by weight. In addition, in this embodiment, component measurement was performed by ICP emission spectroscopy.

[0036]

[Table 1] Further, FIG. 2 shows a cross-sectional photograph of the metal structure of the magnesium alloy base material 1 according to this embodiment by a scanning electron microscope (SEM). In the figure, 31 to 34 are a scanning electron microscope-energy dispersive specific X-ray detector (SEM-ED).
S) shows the measurement points, and Table 2 below shows the elemental composition ratio (% by weight) at each measurement point.

[0037]

[Table 2] As shown in Table 1, the component ratio of the entire cast material of this embodiment is within the ASTM standard. However, the “precipitate region” of this embodiment, that is, the “region containing at least one of aluminum, zinc, and manganese other than magnesium” is a point as shown by the measurement points 32 to 34 in FIG. , As shown in Table 2, Mg such as Al and Zn
The ratio of at least one of the other elements is A
It is larger than the upper limit of the STM standard. In addition,
At measurement point 32, C which is not specified in the ASTM standard
The proportion of O and O is high, which indicates that carbides and oxides may be contained in this precipitate region.

Next, how the above-mentioned precipitate regions are distributed with respect to the crystal grains is shown in FIGS. 3 (a), (b),
This is shown by (c). FIG. 3A is related to the above embodiment,
Plate-shaped magnesium alloy base material molded to a plate thickness of 10 mm
The optical microscope sectional photograph in a part of 1a is shown. Grain boundary 8 is seen, average grain size is about 200 μm
Although it is before and after, a plurality of precipitate regions 3 having a diameter of several μm to 30 μm, which is converted into an area-equivalent circular diameter, are present inside the crystal grains at a distance. In this cross-sectional structure, the area of the precipitate region 3 is usually 25 × 10 ⁻¹² πm ² or more and 2500 × 10.
^-12 πm ² or less, and in the cross-sectional photograph of FIG. 3A, about 30 to 40 precipitate regions 3 are found inside one crystal grain. The individual precipitate regions 3 are approximately 2 to 30 at the shortest.
They are scattered in the state of being separated by about μm, and are separated by a maximum of about 200 μm in the grain of one magnesium alloy.
There are individual precipitate regions 3.

Further, FIG. 3B shows an optical microscope cross-sectional photograph of a part of a plate-shaped magnesium alloy matrix 1b molded to a plate thickness of 5 mm. Grain boundaries 8 are seen, and the average grain size is about 80 μm. In this cross-sectional structure, the area is 25 × 10 ^-12 πm ² or more and 2500 × 10 ^-12
About 3 to 20 precipitate regions 3 having a size of πm ² or less are found in one crystal grain. The individual precipitate regions 3 are scattered at a distance of about 1 to 40 μm at the shortest, and a maximum of about 180 μ in the crystal grains of one magnesium alloy.
There are two precipitate regions 3 separated by m.

Further, FIG. 3 (c) shows an optical microscope cross-sectional photograph of a part of a plate-shaped magnesium alloy matrix 1c molded to a plate thickness of 3 mm. Grain boundaries 8 are seen, and the average grain size is about 250 μm. In this cross-sectional structure, the area is 25 × 10 ⁻¹² πm ² or more and 2500 × 10
About 60 to 160 precipitate regions 3 of ^-12 πm ² or less are found in one crystal grain. The individual precipitate regions 3 are scattered at a distance of approximately 1 to 30 μm at the shortest,
Maximum of about 4 in the crystal grain of one magnesium alloy
There are two precipitate regions 3 separated by 00 μm.

As described above, the magnesium alloy matrix 1 of this embodiment is the conventional general matrix 4 shown in FIG.
As described above, the precipitate regions 6 are not segregated at the crystal grain boundaries of the magnesium alloy crystal phase 5, and the voids 7 generated during casting are not precipitated at the crystal grain boundaries. Since about 3 to 160 pieces are dispersed in the crystal grains in a relatively small size, inclusions are also present in a dispersed manner, and at the time of extrusion / rolling for extruding the magnesium alloy raw material 1 into a thin plate. It is hard to break and has excellent ductility. Even when processed into a thin plate, the thin plate has excellent ductility, and when subjected to secondary processing such as pressing and forging, the workability becomes excellent. It should be noted that the precipitate region 3 is 3 in one crystal grain.
If the number is less than the number, the effect of dispersing inclusions due to the dispersion of precipitate regions cannot be obtained, and the plastic workability of this raw material and the thin plate obtained by primary processing of this raw material deteriorates. . On the other hand, when the number is more than 160, the distance between the individual precipitate regions becomes short, the precipitate regions are connected, and relatively large inclusions may be unevenly present, resulting in poor plastic workability.

Table 3 shows the results of measuring the ratio of the test pieces randomly cut out from the magnesium alloy matrix 1 of the present embodiment to the theoretical density. The volume of the test piece is calculated by measuring the dimension after machining the outer shape.

[0043]

[Table 3] In addition to the above test pieces, the ratio of the magnesium alloy matrix 1 in the present embodiment to the theoretical density of 1.78 g / cm ³ calculated from the alloy composition is 98 to 1.
It is within the range of 00%. On the other hand, in the raw material 4 shown in FIG. 10 having the same composition as the magnesium alloy raw material 1, since there are many voids 7 inside, the theoretical density of 1.7 is obtained.
Ratio of less than 98% to 8 g / cm ³ (density 1.74
4g / cm ³ or less). The magnesium alloy cast material 1 of the present embodiment has a dense structure and a small number of internal voids, and as a result, is unlikely to break during extrusion and rolling in the subsequent steps and subsequent secondary processing, and the coating / drying step (FIG. 8). Also in (), the problem of surface defects due to bursting of internal bubbles can be avoided.

In this embodiment, the plate thickness is 3 mm, 5 mm, 1
Magnesium alloy matrix 1 was molded by a casting method described later so that the thickness became 0 mm. Due to the difference in the plate thickness among these three types, no remarkable difference was observed in the above-mentioned characteristics and ratio of the cross-sectional structure.

Although the AZ31 magnesium alloy is used in this embodiment, it is possible to use other AZ type magnesium alloys. However, in order to realize the above-mentioned characteristic cross-sectional structure, aluminum is 1.8 to 9.1 wt.%.
The AZ type magnesium alloy contained is desirable.

An X-ray diffraction analysis of the surface of the template 1 of this embodiment revealed that the crystal orientation of the (0002) plane was preferentially shown as shown in FIG. this is,
It is considered that pressure was applied vertically from the surface of the material when the material solidified.

FIG. 5 shows the structure of a casting apparatus 21 for producing the magnesium alloy base material 1 of this embodiment.

This casting apparatus 21 contains a magnesium alloy material 13 and a crucible 1 as a melting apparatus for melting the magnesium alloy material 13 by a heater (heating means) 12.
1, a cooling mold 15 which is connected to the crucible 11 and cools the molten magnesium alloy 13a by a water cooling pipe (cooling means) 20 to solidify it into a desired shape, and a solidified magnesium alloy 13b from inside the cooling mold 15. The ingot is composed of a dummy bar 16 and a pinch roll 17, which are pulling means for pulling the ingot continuously.

In this casting apparatus 21, the magnesium alloy material 13 charged in the crucible 11 is heated by the heater 12 to become the molten magnesium alloy 13a. Since magnesium alloy burns violently when it comes into contact with oxygen in a molten state, it is desirable to shut off oxygen during melting. In this embodiment, as a method for blocking oxygen, the crucible 11 is installed in the chamber 14, and although not shown in the drawing, a vacuum can be drawn and an inert gas can be introduced.

Although the molten magnesium alloy 13a is stored in the crucible 11, it also flows into the cooling mold 15 directly connected to the crucible 11, so that the dummy bar 16 is inserted into the cooling mold 1.
5 inside the chamber 14 from the lower side of the pinch roll 17
This makes it possible to take in and out. In the middle of the casting process, instead of the dummy bar 16, the magnesium alloy 13b that has been previously drawn out and solidified suppresses the outflow of the molten magnesium alloy 13a.

The cooling mold 15 absorbs the heat from the molten magnesium alloy 13a and releases it to the peripheral portion. In the present embodiment, cooling means such as a water cooling pipe 20 is arranged around the cooling mold 15 to release the heat. It is designed to take away the heat. At that time, the configuration is such that the flow rate and temperature of water can be adjusted. As such a cooling means, it is possible to use air cooling instead of water cooling.

The cross-sectional shape of the inner wall of the cooling mold 15 is the cross-sectional shape of the magnesium alloy 13b solidified in the inner wall, that is, the magnesium alloy matrix 1, but in the present embodiment, this magnesium alloy matrix 1 has The cross-sectional shape of the inner wall of the cooling mold 15 is determined so that the cross-sectional shape is a rectangular shape having a width of 50 mm and a thickness of 3 or 5 or 10 mm.
The length of the cooling portion of the cooling mold 15 is 170 mm, but it can be set to another length in consideration of the shape of the magnesium alloy raw material cast in the cooling mold 15 and the amount of cooling water. Is.

When the solidified magnesium alloy 13b (ingot) is easy to break when casting the magnesium alloy base material 1 using the casting apparatus configured as described above, as shown in FIG. By tapering the inner wall of the cooling mold 15 with a taper 15a so that the pinch roll 17 side becomes gradually wider with respect to the crucible 11 and reducing the friction with the cooling mold 15, it is possible to prevent the ingot from breaking. is there. On the contrary, as shown in FIG. 7, when the taper 15b is attached to the connecting portion of the cooling mold 15 with the crucible 11 so that the pinch roll 17 side becomes narrower than the crucible 11 side, the molten magnesium alloy Appropriate stress is applied to the portion of 13a where solidification progresses in the direction perpendicular to the drawing direction, and the amount of inclusions and gas caught in the raw material can be reduced.

The crucible 11 for accommodating and melting the magnesium alloy material 13 has an internal depth of 220 mm, and a cooling mold 15 is connected vertically upward by about 10 mm from the bottom surface to cool the molten magnesium alloy 13a. Impurities 19 that accumulate on the bottom surface of the crucible 11 when pulled out into the mold 15 are difficult to be caught in the magnesium alloy 13b.

A material charging shooter (material supplying means) 18 shown in FIG. 5 does not open / close the chamber 14 but is in the crucible 11
It is installed in the upper part of the chamber 14 so that the magnesium alloy material 13 can be continuously charged therein. The shape of the magnesium alloy material 13 charged in the initial stage is the crucible 1
There is no particular problem as long as the size fits within 1. However, in the case of charging through the material charging shooter 18, in order to prevent damage to the crucible 11 and scattering of the molten magnesium alloy 13a to the outside of the crucible 11, a diameter of 1 mm to Particles or chips having a size of about 10 mm are desirable.

The casting apparatus 21 according to the present embodiment has the crucible 1
1 is a horizontal type in which the cooling mold 15 is connected to the side surface, but it is also possible to use a vertical type in which the cooling mold 15 is connected to the bottom surface of the crucible 11.

Further, the heater 12 as a heating means has 1
A high-frequency heater capable of realizing an output of about 0 kW is used, but any heating means having a capacity capable of heating a material to 780 ° C. or higher may be used, and is not limited to the high-frequency heater.

Further, the crucible 11 and the cooling mold 15 in this embodiment are made of graphite, and are made of a material having excellent thermal conductivity and being hard to react with the molten magnesium alloy 13a. Further, a material containing copper, nickel and iron, which significantly impairs the corrosion resistance of the material when mixed in the magnesium alloy, is not desirable as the material of the crucible 11 and the cooling mold 15.

The magnesium alloy 13a in a molten state
From this, evaporation always occurs, and when the metal vapor touches the inner wall of the chamber 14 and the like, it solidifies and becomes powder. This not only lowers the material yield but is also dangerous because it may cause spontaneous combustion, so it is desirable to provide the crucible 11 with an openable / closable lid (not shown). Further, it is preferable that the lid is opened only when the material is charged to prevent the metal vapor from flowing out of the crucible 11.

It is desirable that the dummy bar 16 be made of a material that can withstand the high temperature (about 650 to 800 ° C.) when melting the magnesium alloy material 13 and has strength, but in the present embodiment, it is made of stainless steel. Is used.

Next, the casting apparatus 2 configured as described above
The continuous casting method for magnesium alloy blanks using No. 1 will be specifically described.

First, the magnesium alloy material 13 is put in the crucible 1
1, and the chamber 14 is closed to make a closed state.

Next, after evacuating the inside of the chamber 14,
An inert gas, preferably argon gas, is introduced to fill the inside with the inert gas. The pressure in the chamber 14 at this time is, for example, 0.1 to 0.2 Torr (1
3.3-26.6 Pa), 14-1 when an inert gas is introduced
The pressure may be 8 Torr (1870 to 2400 Pa), but is not limited thereto. If a gas discharge port is provided in the chamber 14 at the time of introducing the inert gas, and the air layer initially contained therein is discharged from the gas discharge port, vacuuming can be omitted.

Next, water is flowed through a water cooling pipe 20 which is a cooling means arranged around the cooling mold 15 to cool the cooling mold 15 and the dummy bar 16. The amount of water at this time is 0.5-
2.0 l / min, the water temperature was controlled at 20 to 35 ° C,
It is not limited to this condition.

Next, the crucible 11 is heated by the heater 12 to melt the magnesium alloy material 13. The AZ31 magnesium alloy melts when heated to a melting point of 630 ° C. or higher, but in the present embodiment, it is kept at 750 to 780 ° C. in consideration of the fluidity of the molten metal and the temperature gradient inside the metal. This is because of the experimental results that the ingot (solidified magnesium alloy 13b) is likely to be broken when the temperature of the molten metal is low. It is considered that this is because when the temperature of the molten metal is low, unevenness occurs in the way the metal is cooled, solid-liquid interfaces occur at a plurality of locations during casting, and continuous solidification is hindered.

When the molten metal is controlled to the above temperature, the fluidity is increased, the surface tension is reduced, and the gas contained inside is easily released, resulting in voids (voids, cavities) remaining inside the molded product. It is considered that casting defects such as the above are reduced. On the other hand, increasing the temperature of the molten metal more than necessary not only wastes energy but also increases the amount of powdered metal adhered to the crucible 11 and the chamber 14 due to the increase in the vapor pressure of the molten metal. Not preferable.

Next, the pinch roll 17 is rotated to pull out the dummy bar 16. In this embodiment, the drawing speed at this time is controlled to 45 to 125 mm / min. In addition, in this embodiment, since the drawing is performed intermittently, for example, when the drawing speed is 100 mm / min, 10
Pull out 5 mm at a speed of mm / sec, then 2.
Casting was performed under the condition of intermittent withdrawal in time, such as stopping for 5 seconds, so that the total withdrawal speed was 100 mm / min. In addition, by controlling the rotation of the pinch roll 17 in combination with forward rotation and reverse rotation, the magnesium alloy 1 is repeatedly pulled and pushed.
It is also possible to pull out 3b.

It should be noted that, as compared with the case where the magnesium alloy 13b is continuously withdrawn at a constant speed without giving a stop time, as in this embodiment, the extraction time and the stop time are mixed and the time is intermittent. In the case where the molten magnesium alloy 13a is solidified, inertial force and vibration are applied to the solid-liquid interface where solidification of the molten magnesium alloy 13a progresses, and inclusions and bubbles are extruded into the liquid portion, so that there are few inclusions and voids (voids) and more plasticity is achieved. It can be expected to form a material with excellent workability.

When the dummy bar 16 is sufficiently pulled out and the solidified magnesium alloy 13b reaches the position of the pinch roll 17, the magnesium alloy 13b in this state plays the role of the dummy bar 16.

The magnesium alloy 13b immediately after being pulled out from the cooling mold 15 has a temperature of about 100 ° C. or lower. In this casting device 21, a cooling mold 15 having a cooling portion of 170 mm was used. Therefore 1
When the magnesium alloy 13b was pulled out at a speed of 00 mm / min, the magnesium alloy that had been 780 ° C in the crucible was cooled to 100 ° C while passing 170 mm, that is, in 1.7 minutes (102 seconds). Therefore, the cooling rate of about 6.7K / sec is realized.
Similarly, when the magnesium alloy 13b is pulled out at a rate of 45 mm / min, the cooling rate becomes 3.0 K / sec and 1
When the magnesium alloy 13b is pulled out at a rate of 25 mm / min, the cooling rate is 8.3 K / sec.

When the magnesium alloy material 13a in the crucible 11 is reduced by casting, the pressure applied to the solid-liquid interface where the material is solidified is reduced and the ingot (magnesium alloy 13
b) is likely to be interrupted. Therefore, in the present embodiment, when the amount of the material in the crucible 11 decreases to about half the initial amount, the material input shooter 18 additionally supplies the material. At that time, it is not necessary to leak the atmosphere in the chamber 14, and in some cases, it is possible to supply the material while casting. This material supply method can be either an intermittent supply method in which a certain amount of material is reduced and then collectively supplied, or a continuous supply method in which material is reduced by casting and sequentially supplied simultaneously.

Next, a simple casting experiment was conducted to confirm the cooling rate of the molten metal and the characteristics of the base material. The basic structure of the device used in this Experimental Example 1 is the same as that of the above-mentioned embodiment, but for simplification of the device, the chamber 14 and the shooter 18 are omitted and a lid is attached to the crucible 11 to add material. It cannot be used, but it has a small structure.

In this experiment, the same A as in the above embodiment was used.
Z31 alloy material is used, cooling rate is 0.5K / sec,
1.0K / sec, 3.0K / sec, 8.0K / sec, 16K / sec,
Casting experiments were carried out by controlling so as to be 20 K / sec and 24 K / sec. The results are described below.

When the cooling rate is 0.5 K / sec, the crystal grain boundaries form thick and clear lines, and the area within the crystal grains is 25 × 10 ^-12 πm ² or more and 2500 × 10 ^-12 π.
It became a matrix material in which no precipitate area of m ² or less was found.
It is considered that this material has poor plastic workability because the precipitate region is segregated at the grain boundaries.

When the cooling rate was 1.0 K / sec, the crystal grain boundaries were clear, but the precipitate regions with an area of 25 × 10 ^-12 πm ² or more and 2500 × 10 ^-12 πm ² or less were formed in the crystal grains. 1
About 2 to 10 pieces could be confirmed for each piece. Cooling rate is 3.0
K / sec, 8.0K / sec, and 16K / sec, the area within the crystal grains is 25 × 10 ^-12 πm ² or more 2500
The number of precipitate regions of x10 ^-12 πm ² or less increased, and the number of crystal grains was about 5 to 160 per grain.

On the other hand, when the cooling rate was 20 K / sec, traces of the dendrite phase of the crystal did not disappear, and although crystal grain boundaries could be confirmed, the cross-sectional structure was difficult to confirm.

When the cooling rate was 24 K / sec, the dendrite phase of the crystal remained, and the crystal grain could not be confirmed. It is considered that the cast material in this state is in a state in which a dendrite phase having poor workability is formed in the entire cast material and plastic workability is deteriorated.

Table 4 below summarizes the characteristics of the sectional structure of the AZ31 alloy for each cooling rate.

[0079]

[Table 4] From the above results, the cooling rate is in the range of 1 to 20 K / sec in order to prepare the magnesium alloy matrix material having the sectional structure in which the precipitate regions are dispersed in the crystal grains. It can be said that it is desirable to be within. However, in order to realize a state in which the precipitate region containing inclusions is sufficiently dispersed while the dendrite phase having poor workability disappears, 3
A cooling rate of about 8 K / sec is considered to be the most desirable.

Next, as Experimental Example 2, pure magnesium,
A casting experiment similar to that of Experimental Example 1 was performed using each material of AZ21, AZ61, AZ91, and AM60 and a material containing about 11% of aluminum. Here, casting is performed at cooling rates of 3 K / sec and 8 K / sec,
It was confirmed whether or not each material had the above-mentioned "cross-sectional structure in which precipitate regions were dispersed in the crystal grains".

Table 5 below shows the measurement results of the component ratios of pure magnesium, AZ21, AZ61, AZ91, AM60 and various alloys containing about 11% aluminum according to the present experimental example after casting. The unit of the component ratio in this table is% by weight.

[0082]

[Table 5] In this experimental example, the cross-sectional structure of the above material produced by casting at a cooling rate of 3 K / sec and 8 K / sec was observed. As a result, almost the same cross-sectional structure was observed with the same metal regardless of the cooling rate of 3 K / sec or 8 K / sec.

In the cast material of pure magnesium, relatively clear crystal grain boundaries could be confirmed, but no precipitate region could be confirmed inside the crystal grains.

On the other hand, AZ21, AZ61, AZ91, A
In each alloy of M60, similar to the cross-sectional structure of AZ31 described in the embodiment, precipitate regions having an area of 25 × 10 ⁻¹² πm ² or more and 2500 × 10 ⁻¹² πm ² or less are present inside the crystal grains. I was able to confirm that

In the high aluminum content alloy cast material containing 11% aluminum, the precipitate regions were connected to each other in a mesh shape and spread over a wide area, and no clear crystal grain boundaries could be confirmed. It was

Table 6 below shows the cross-sectional structure of each material when these alloys were cast at cooling rates of 3 K / sec and 8 K / sec.

[0087]

[Table 6] From the above results, in producing an AZ-based or AM-based magnesium alloy matrix by the method of the present invention,
In order to obtain a magnesium alloy raw material having a characteristic that precipitate regions are dispersed inside the crystal grains, it is considered preferable that the aluminum content is about 1.8 to 9.1 wt.%. . In addition, even when it contains an elemental component other than magnesium and aluminum, if the elemental content ratio is lower than the content ratio of aluminum and the aluminum content is 1.8 to 9.1 wt. It is considered that the magnesium alloy matrix material has a characteristic that precipitate regions are dispersedly present inside the crystal grains.

Regarding the cooling rate, if the cooling rate is within the range of 1 to 20 K / sec confirmed for the AZ31 alloy, the AZ system containing about 1.8 to 9.1 wt.% Of the above aluminum. Alternatively, it can be predicted that, in the AM-based magnesium alloy, it is possible to produce the above-mentioned "magnesium alloy matrix material having a plurality of precipitate regions separated from each other inside the crystal grain".

Further, when the cooling rate is higher than 20 K / sec, the dendrite phase remains and the magnesium grain boundaries do not appear, and when it is lower than 1 K / sec, the dendrite phase completely disappears to cause precipitation. The material region 3 becomes a solid solution in the crystal phase 2 of the magnesium alloy or has a structure in which it migrates and segregates.

As described above, according to the present invention, it is possible to fabricate a characteristic cast material in which a plurality of precipitate regions in which crystal grain boundaries appear and which are separated from each other are present in the crystal grain without performing solution treatment. .

Next, an experimental example of superiority of plastic workability of the magnesium alloy matrix material 1 according to the present invention will be described.

In the AZ31 magnesium alloy base material 1 according to the present embodiment, one molded into a plate thickness of 3.0 mm, one molded into a plate thickness of 5.0 mm, and a plate thickness of 10.0 m.
Rolled to a thickness of 0.5 m
m thin plates (test plates 1, 2, and 3 in order) were obtained. The rolling is performed multiple times by cold rolling with a reduction rate of about 10 to 30% so that the raw material is not cracked.
Annealing was performed at 10 ° C. for 10 minutes. After final cold rolling to a plate thickness of 0.5 mm, strain relief annealing was performed at about 200 ° C. for 1 hour. The actual number of rolling was 6 for the test plate 1, 7 for the test plate 2 and 12 for the test plate 3.

Further, a magnesium alloy thin plate (test plate 4) having a plate thickness of 0.5 mm, which was produced by a commercially available extrusion process and rolling, which is not the present embodiment, was prepared. In addition, these 4
The average crystal grain size of each test plate was about 7 to 12 μm.

These test plates were cut into an octagonal blank shape (about 40 mm × 40 mm and the corner portion was cut by 6 mm) as shown in FIG. 9, and the punch shoulder R2.0 mm, punch outer shape 25 mm × 25 mm, four corners R2.0 mm. The square tube drawing test was performed. Clearance is 0.1mm on one side,
The experiment was conducted while controlling the die lowering speed and changing the drawing speed. Strictly 100 mm / sec, 70 mm / sec, 50 m
m / sec, 20 mm / sec, 10 mm / sec, 5 mm / sec, 2
mm / sec, 1 mm / sec, 0.75 mm / sec, 0.5 mm
The experiment was performed by changing the aperture speed to / sec and 0.1 mm / sec.

When the drawing speed is high, cracks are formed in the four corners of the molded product, but when the molding is performed at a low speed, a molded product can be obtained without cracks. The maximum speed at the drawing speed at which no cracks were formed was defined as the "limit drawing speed", and the limiting drawing speed of each test plate was obtained. The mold temperature is 250
C., 200.degree. C. and 150.degree. C. were set, and a molybdenum disulfide-based spray agent was used as a lubricant. In addition, a plurality of blanks were prepared for the test, and each condition was performed three times or more to visually confirm how cracks were formed, and the limiting drawing speed was determined from the average state.

Table 7 below shows the limiting drawing speeds of the above four test plates. The unit of the limiting aperture speed is mm / sec.

[0097]

[Table 7] From this experiment, each of the test plates 1, 2, and 3 made by rolling the magnesium alloy raw material 1 according to the present embodiment has a drawing speed of about 10 times that of a commercially available plate (test plate 4). It can be said that cracking does not easily occur even at a high speed, that is, plastic workability is excellent. The above experimental result is one experimental example confirming the superiority in the plastic working of the magnesium alloy base material 1 according to the present embodiment, but not only for the drawing work but also for another plastic working such as forging and bending deformation. However, the same effect can be expected.

[0098]

As described above, according to the present invention,
Since casting defects such as voids and cavities in the metal structure and segregation of inclusions can be prevented, a cast material with high ductility can be obtained. Therefore, when a plurality of precipitate regions exist apart from each other in the crystal grains as in the cast material of the present invention, the crystal grains are processed into a cast material when subjected to primary processing such as extrusion or rolling. The grain size is finely and uniformly sized throughout, the number of large crystal grains that deteriorate the workability is reduced, and the plastic workability is improved. When the raw material is subjected to primary processing such as extrusion or rolling to make it into a thin plate, and when this thin plate is subjected to secondary processing such as forging, the defective portion becomes the starting point of cracks during processing and breaks. It is possible to prevent this, and when the raw material is directly rolled and used as a thin plate for plastic working, the process can be simplified and the cost can be reduced. Further, even when the molded product after processing is coated and dried, it is possible to prevent the problem of surface defects due to rupture of internal bubbles.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing the metallographic structure of an AZ-based magnesium alloy matrix material according to an embodiment of the present invention.

FIG. 2 is a cross-sectional photograph of a AZ-based magnesium alloy base material of the same embodiment, taken by a scanning electron microscope (SEM).

FIG. 3 is a cross-sectional photograph of three plate-shaped AZ-based magnesium alloy base materials having different plate thicknesses according to the same embodiment, taken by an optical microscope, where (a) is a plate thickness of 10 mm and (b) is a plate thickness. 5m
In the case of m, (c) is a cross-sectional photograph when the plate thickness is 3 mm.

FIG. 4 is a graph showing an X-ray diffraction pattern in a surface state of the magnesium alloy base material in the same embodiment.

FIG. 5 is a vertical cross-sectional view schematically showing the casting apparatus in the same embodiment.

FIG. 6 is a vertical cross-sectional view showing a main part of a casting device that is tapered so that the pinch roll side becomes wider in the same embodiment.

FIG. 7 is a vertical cross-sectional view showing a main part of a casting apparatus that is tapered so that the pinch roll side becomes narrower in the same embodiment.

FIG. 8 is a general schematic view showing a process of manufacturing a magnesium alloy part from a magnesium alloy material.

FIG. 9 is a schematic view showing a magnesium alloy thin plate blank for evaluation of square tube drawing forming.

FIG. 10 is a sectional view schematically showing the metallographic structure of an AZ-based magnesium alloy matrix produced by a conventional casting method and casting apparatus.

[Explanation of symbols]

1 Magnesium alloy cast material 2 according to the present embodiment 2 Magnesium alloy crystal phase 3 Precipitate region (a region where the average concentration of aluminum, zinc, and manganese is higher than the alloy composition ratio) 4 Conventional magnesium cast alloy cast material 5 Magnesium alloy crystal phase 6 Precipitate region (region where the average concentration of aluminum, zinc, and manganese is higher than the alloy composition ratio) 7 Voids (voids / cavities) 8 Crystal grain boundaries 9 Blank 11 made from a magnesium alloy thin plate Crucible ( Melting device) 12 Heater (heating means) 13 Magnesium alloy material 13a Molten magnesium alloy 13b Solidified magnesium alloy 14 Chamber 15 Cooling molds 15a, 15b Taper 16 Dummy bar (pulling-out means) 17 Pinch roll (pulling-out means) 18 Material charging shooter (Material supply means) 19 Object 20 water cooling pipe (cooling means) 21 casting apparatus 31 to 34 scanning electron microscope - energy dispersive particular X-ray detection device (SEM-EDS) measured at the measurement point

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) B22D 11/059 120 B22D 11/059 120A 11/106 11/106 Z 11/124 11/124 L 11/20 11/20 A 11/22 11/22 A 23/00 23/00 C (72) Inventor Takaaki Akira 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F term (reference) 4E004 AA07 AB01 AC00 AD00 BA00 KA12 MA01 NA03 NB02 NC09 SE07 TB04

Claims (12)

[Claims] 1. Within a crystal grain of a magnesium alloy,
A magnesium alloy material having a plurality of precipitate regions containing one or more of aluminum, zinc and manganese. 2. The magnesium alloy casting material according to claim 1, wherein the plurality of precipitate regions are separated by more than 0 and less than 400 μm in distance between the end faces. 3. The area of one precipitate region is 25 × 10.
⁻¹² πm ² or more and 2500 × 10 ⁻¹² πm ² or less, The magnesium alloy matrix material according to claim 1, wherein 4. The magnesium alloy casting material according to any one of claims 1 to 3, which contains aluminum in a content ratio of 1.8 to 9.1 wt.%. 5. The magnesium alloy matrix material according to claim 1, which has a plate shape. 6. A magnesium alloy material is put into a melting device, and the magnesium alloy material in the melting device is melted in a state where oxygen is blocked and then supplied to a cooling mold. A method for casting a magnesium alloy cast material, comprising: a step of cooling and solidifying at a cooling rate of s; and a step of drawing with a drawing means so that solidified ingots of metal are continuous. 7. The method for casting a magnesium alloy raw material according to claim 6, wherein the solidified ingot of metal is withdrawn intermittently with time by repeatedly withdrawing and stopping. 8. The method for casting a magnesium alloy cast material according to claim 6, wherein the molten magnesium alloy is cooled and solidified at a cooling rate of 3 to 8 K / sec. 9. The magnesium alloy material to be charged into the melting device is in the form of a particulate solid, and the molten magnesium alloy is supplied to the cooling mold while keeping the atmosphere around the melting device inactive. The method for casting a magnesium alloy base material according to any one of claims 6 to 8. 10. The cooling mold has a rectangular inner wall cross-sectional shape, and at least a part of the inner wall is tapered so that the length of the short side of the cooling mold is different between the melting device side and the drawing means side. The method for casting a magnesium alloy raw material according to any one of claims 6 to 9, wherein the casting is performed in the state of being cast. 11. The alloy containing portion of the melting apparatus and / or the material of the cooling mold is graphite.
10. The method for casting a magnesium alloy base material according to any one of items 10 to 10. 12. The method for casting a magnesium alloy base material according to claim 6, wherein a cooling mold is connected to a side surface of the melting device to draw out the magnesium alloy in a horizontal direction.